Who will reign as the best, worst and most surprising baseball teams for the upcoming 2019 season? Read our predictions here and see if you agree.
If major league teams, with all that money amassed, aren't going to make the effort to better their chances by picking up a Bryce Harper or Dallas Keuchel or Craig Kimbrel, then why should I make the effort to pick winners and losers when, frankly, the balance of power has hardly been shifted about? It certainly would make my job easy—just copy and paste and go with the Red Sox over the Dodgers again in October.
Okay, so I exaggerate. It is funny, though, that this great game seems to have become captive to front office paralysis in regards to strengthening rosters. Fans of the Brooklyn Dodgers used to yell out, "Wait 'til next year." But they usually said that at the end of the season, when their Bums managed to fail them again. Now teams are basically saying that before Opening Day. Some even suggest something along the lines of, "Wait 'til the year after the year after next year." Nobody seems to be in a hurry to win a World Series; many would rather tank than challenge.
In a day and age when teams are keeping payrolls down, using relievers in place of starters, and rewarding younger players under their control with advance payments instead of dishing out nine-figure contracts to established stars entering their 30s, the status quo is left unshaken. But amid all the patience being preached by tight-fisted franchises operating on massive profits, there are a few teams who are bucking the trend. Their high-spending ways may be scoffed at by the majority of teams, but that will just make it easier for those few with win-now mentalities to do just that—win now. And they will be rewarded, in the short term and in my annual predictions to follow.
Of course, seven months from now, we'll see just how righteous—or stupid—myself and those teams were to take this tact.
Let's start right off the bat by talking about the one team, more than anyone else, that has made the great leap forward while most everyone else sits on their hands: The Philadelphia Phillies. The Phillies hooked onto the Catch of the Offseason by reeling in Bryce Harper, giving the team a potentially devastating 1-2 power punch in the lineup with evolving boomer Rhys Hoskins—who, like Harper, is a spry 26 years of age. They made a big offseason trade by snagging catcher J.T. Realmuto, who desperately wanted out of Miami. They added speed with infielder Jean Segura, from Seattle. They brought in sage with outfielder Andrew McCutchen. And they solidified their bullpen with the addition of closer David Robertson. This influx of star talent is bound to upgrade a lineup that hit a major league-worst .234 in 2018 and take the pressure off returnees like outfielder Odubel Herrera and second baseman Cesar Hernandez, who no longer won't have to shoulder the burden of being team leaders. Meanwhile, the rotation looks stable (if not dominant), led by ace Aaron Nola and could-be-again ace Jake Arrieta. The future is now in Philadelphia, in part because they're sick of the recent past, having not had a winning season in seven years. Expect that to finally change.
Losing Harper is not the end of the world for the Washington Nationals. On the contrary, their new world may very possibility be a better one. This is a team that still has Max Scherzer and Stephen Strasburg topping its rotation, and now is backed by former Diamondback Patrick Corbin; has a better catcher in Yan Gomes, from Cleveland; and has a whole list of potential reclamation projects, from second baseman Brian Dozier to pitcher Anibal Sanchez to relievers Trevor Rosenthal and Kyle Barraclough. But what will make or break the Nationals in 2019 is a young, heady heart of the batting order, brimming with impressionable youth (Juan Soto), blazing speed (Trea Turner), high promise (top prospect Victor Robles) and salivating incentive (free agent-to-be Anthony Rendon). If that core can produce, the Nationals can look back on the Harper-to-Philly saga and shrug with laughter into the postseason.
If the NL East is a game of tag, then the Atlanta Braves are it. That's good—and well, not so good. The Braves took advantage of an otherwise fractured division and grabbed their first postseason spot (and winning season) since 2013; they won't encounter that same luck this year with the improvement of most everyone else in the field. This is a solid, young team that's expected to continue its evolution, principally through reigning NL Rookie of the Year Ronald Acuna Jr., infielders Ozzie Albies and Dansby Swanson, and potential aces Mike Foltynewicz and Sean Newcomb. The Braves did make one noteworthy acquisition by bringing on veteran third baseman Josh Donaldson—but he's a calculated risk given his age (33) and recent injury history. Atlanta fans are upset that the team didn't do more to upgrade, and continually pinged the Braves that available closer Craig Kimbrel was having a meal near the team's spring training complex. After their recent period spent in the doldrums, the Braves are at least relevant again. Whether that's good enough to make a return to the postseason remains to be seen.
The New York Mets are the one team that always seem to mess with my expectations of them. I expect them to be good, they go bad. And vice versa. This must mean I have some sort of distant kinship with Mets fans who've grown tried and true—or is fried and blue? So now comes 2019, and here we go again; the Mets are one of those few teams mentioned above that are trying this year to win, and I said I'd give those teams love. But not the Mets. I don't trust them after all this time, and neither do their fans. Somehow, someway, they'll blow it—because that's what the Mets do best. Yes, the roster is better; the additions include second baseman Robinson Cano, catcher Wilson Ramos, infielder Jed Lowrie and once-and-current Mets reliever Jeurys Familia. Should an upstart outfield (anchored by Michael Conforto) break out, should aces Jacob deGrom and Noah Syndegaard not break down, should 2018 surprise Jeff McNeill be given an everyday spot to make good as a sophomore, then the Mets might have something here. But I'm in sync with the Citi Field faithful; I'll believe it when I see it.
Miami Marlins franchise face Derek Jeter recently said this: Don't come to Marlins Park for the wins, but for the entertainment. If a no-name roster that doesn't hit, doesn't score, and doesn't particularly pitch well merits as entertainment, well hell—no wonder the Marlins can't draw a million fans. As bad as it seems for the Marlins, it's actually worse; they're in what many believe is baseball's most improved division, they let go of their one true star (catcher J.T. Realmuto) to a divisional opponent, and changed up their roster with once-talented players (Curtis Granderson, Neil Walker, Sergio Romo) with one foot in the baseball grave. There can be growth from within through outfielder Lewis Brinson, third baseman Brian Anderson and upcoming prospects in pitcher Sixto Sanchez and young Cuban Victor Victor Mesa (because two Victors are better than one)—but all that is too little, too early for this edition of the Fish. Whether the sum total of all of the above adds up to entertainment is up to the fans. The question is, will they even show up?
It seems like a lot of folks have forgotten that the Chicago Cubs actually won 95 games last year. "What have you done for us lately?", those folks ask. Well there you have it. The Cubs won all those games but tripped up in the stretch, laying eggs against Milwaukee in a NL Central tiebreaker and a wild card playoff against Colorado—both at Wrigley Field. The end-of-year slump has soured a lot of people's feelings about the 2019 Cubs; even the good 'ol PECOTA computer has them finishing last this season—yes, even behind the Reds. Think about it, though; the Cubs got as far as they did last season despite off-years for three of their biggest hitting stars (Kris Bryant, Willson Contreras and Addison Russell) and first-year busts out of rotation members Yu Darvish and Tyler Chatwood. If just some of those guys can rebound and get their 2016 mojo back behind a solid bullpen, almost-MVP Javier Baez and late 2018 arrival Cole Hamels, the Cubs will turn the PECOTA report into incoherent gobbledygook. Yes, this is an increasingly salt-and-pepper roster and the farm system represents a barren food cabinet, but the Cubs as we know them should have one good swing left in them to make it to October.
Among the more interesting stats I stumbled upon was this one about the St. Louis Cardinals; in their first four innings last season, they had a +105 run differential—but from the fifth on, it was -37. This runs counter to the Cardinals' season in general, which started slow and with such great frustration that manager Mike Matheny was canned, before rebounding under interim (now permanent) replacement Mike Shildt (41-28). There's added momentum in St. Louis with the surprise offseason acquisition of Arizona star Paul Goldschmidt, who definitely should represent that big bat that the Redbirds have ached for since Albert Pujols' departure. But back to those late-inning issues, and what will keep the Cardinals from conquering the division: A defense that committed an MLB-worst 133 errors, and a pitching staff that's got issues outside of Miles Mikolas (assuming he continues to pitch at the same level as 2018) and supersonic reliever Jordan Hicks, who settles into the closer role. A good team still, but flawed.
Yes, I have the Milwaukee Brewers, who finished just one game shy of a NL pennant last year, finishing third. This is a good, fun team with a bit of chutzpah to it, but it's essentially the same cast from last year. That's good, right? No, it's not. So many players performed above their heads last year—from MVP Christian Yelich to slugger Jesus Aguilar to starter Jhoulys Chacin to all those dynamite relievers—that it's hard to believe they can maintain that same level. And since the Brewers pretty much stood pat during the offseason except for the addition of catcher Yasmani Grandal—whose awful NLCS defense for Dodgers nearly gift-wrapped the pennant for Milwaukee—don't expect much of a lift from everyone else. People will say the Cubs didn't do much to improve either—but as I mentioned, the Cubs didn't overachieve last season, while the Cardinals, well, Paul Goldschmidt. Maybe I'm wrong and the Brewers will evolve even further; perhaps the six guys capable of hitting 30+ homers will do just that, Yelich will hit .400, Josh Hader will strike out an average of three guys per inning, and maybe one or two of their starters will throw into the seventh inning on occasion. But the roster's status quo is likely to lead to an October no-show in Milwaukee.
The Cincinnati Reds aren't ready to contend yet, but by God, they're trying. Instead of sinking further into anonymity, the Reds got frisky this offseason and bulked up their roster with some eye-raising pick-ups—most notably with a blockbuster trade that brought outfielders Yasiel Puig, Matt Kemp and starting pitcher Alex Wood to Cincinnati. (Best part of that deal for the Reds: Convincing the Dodgers to eat the rest of Homer Bailey's salary.) But perhaps the more crucial maneuvering done by the Reds was to juice up a rotation so hopelessly stuck in neutral over recent times—their starters had a 5.02 ERA last season—with the addition of Wood, Sonny Gray and Tanner Roark. It could be argued that these three are borderline reclamation projects given their shaky health history and success rate, but at least they're names. Further key to a Cincinnati uptick this year will be a rebound from Joey Votto, anticipated growth from young outfielder Jesse Winker and a bullpen that finally might put its head on straight. Let's go back to the top of this column and recall that I'm rewarding teams who are in it for now. The Reds are pretty much one of those teams, so while they pretty much won't win the division, they'll pretty much give it a good shot.
It's interesting to note that the Pittsburgh Pirates have, among others, their top two pitchers (Jameson Taillon, Trevor Williams) and three-quarters of their starting infield (Josh Bell, Erik Gonzalez and Adam Frazier) all having made their major league debuts in 2016. Maybe the Bucs' brass thinks it's onto something, that a team that finished strongly and surprisingly placed above .500 in 2018 has momentum from these kids who are starting to feel it. It's something of a gamble given that the team made no substantial moves via trade or free agency during the offseason while losing a few vets (pitcher Ivan Nova, infielder Josh Harrison). Maybe the fourth year will be the charm for these guys—but to be honest, someone needs to break through this no-name malaise and make a name for himself and, by extension, the Pirates. It may be too much to ask.
Spring camp for the Los Angeles Dodgers didn't get off to a great start when ace of aces Clayton Kershaw found it difficult making simple throws, a circumstance that more often than not leads to an appointment for Tommy John surgery. As of this typing, Kershaw appears to have dodged the worst-case scenario—but even without him, the Dodgers should be okay enough to at least win the West. Yes, they lost vibe with the departures of Yasiel Puig and Manny Machado, but they remain a team not only loaded with exceptional depth, but also amazing versatility that manager Dave Roberts constantly takes advantage of; last year, an average of seven players performed at each field position, and that wasn't because of an influx of late-season scrubs. To win their seventh straight NL West crown and third straight NL pennant, the Dodgers will need Kershaw to stay in one piece, emerging sidekick ace Walker Buehler to further evolve, 2018 breakout slugger Max Muncy to keep munching the ball, and rebounds from Cody Bellinger, Chris Taylor and Tommy John survivor Corey Seager. So while there's potential downside, the Dodgers are just too flush with able talent not to fall apart over a speed bump.
Fans of the Arizona Diamondbacks absorbed one of the offseason's biggest gut punches when their beloved Paul Goldschmidt was given a one-way ticket to St. Louis. In his absence, what's left behind is a cast of supporting players looking for someone from within to take the lead. Here's the bigger question for the Diamondbacks: Which direction will the front office be taking them? Is the team looking to fine-tune itself quick back toward prominence, or will it give it up for the short-term, as it has given up on Goldschmidt, as it has given up on the grass at Chase Field (it's now an artificial surface), and perhaps how it might give up on ace Zack Greinke and his massive salary if things go sour to start. The Diamondbacks do appear to have the horses to consider October participation a reality, but it's going to take an alignment of the planets and stars that sees David Peralta, Jake Lamb and/or Ketel Marte take over as the new Goldschmidt—and an improved rotation should Robbie Ray return to full strength and Miles Mikolas-wannabe Merrill Kelly thrives out of nowhere after three stable campaigns in Korea. Until then, the D-Backs' middle name will likely be mediocrity.
Many people believed the San Diego Padres were bluffing in trying to hook onto Bryce Harper and/or Manny Machado, and were stunned when they actually committed to the latter. Machado's debut is bound to provide the Padres with long-overdue spark, and while he's long since proven that he's ready for prime time, the rest of his team badly needs to catch up. San Diego's farm system is considered tops at the moment, with as many as 10 players among the majors' top 100 prospects—and that's great news for say, 2022. But this is 2019, and the current reality is that the Padres' rotation is woefully green and, beyond Machado, Eric Hosmer, Wil Myers and what's left of Ian Kinsler, there's not much to get excited about in the lineup. As a result, we may have a Petco Park first in that most games will finish in favor of the over, and hey—Machado will give the fans something to get excited about, good or bad. But the Padres just aren't there yet. by October.
No team has perhaps suffered a more dismal time of late than the San Francisco Giants. They finished second in the Bryce Harper lottery; their lead investor (Charles Johnson) was slammed for giving political donations to right-wing interests; and smooth-as-silk CEO Larry Baer violently lost it with his wife in a public square. Even the über-popular Willie McCovey passed away. Meanwhile on the field, the Giants have done next to nothing to bring in fresh talent and help prop up their aging World Series core of yesteryear. More glaringly, the Giants' failed pursuit of Harper leaves their contingent of outfielders as, easily, baseball's worst. For the sake of avoiding the rare display of endless empty seats at renamed Oracle Park, the glue better be working on likeable but fragile guys like catcher Buster Posey, first baseman Brandon Belt and second baseman Joe Panik—while Madison Bumgarner and Jeff Samardzija must reclaim the workload that they've failed to provide of late. The Giants begin their season already at a fail-safe point; with a few roster slips, the whole thing could fall apart. And what a way that would be to send retiring manager Bruce Bochy out.
Continuing on the trend of rewarding teams that don't shy away from bulking up, I say congrats to the New York Yankees, who improved their status while everyone else in the AL East sat on their hands—and thus they should surpass Boston as divisional champs. The Yankees brought in James Paxton from Seattle as a crucial add-on to a high-end but fragile rotation, strengthened an already exceptional bullpen by signing on ex-Rockie Adam Ottavino, and brought on a few other guys (infielders DJ LeMahieu and Troy Tulowitzki) who used to call Colorado home. But what should really pump the Yankees up is a crop of Yankee sluggers that produced a record 268 homers in 2018—and are confident they can up that to 300. That's not out of the question, considering that the team suffered less-than-peak years from Aaron Judge (50 games missed), Gary Sanchez (.186 average) and Giancarlo Stanton (a rather mundane 38 homers). Plus, between first basemen Luke Voit and Greg Bird, someone's going to rake. Major injuries and the apocalypse are the only obstacles getting in the Yankees' way this season.
If it works, don't fix it. That seems to be the Boston Red Sox' credo for 2019, but be careful what you feel confident about. The same group that won a franchise-record 108 games and its fourth world title in 15 years is back, less its closer (Craig Kimbrel), top reliever (Joe Kelly) and late-arriving but contributory second baseman Ian Kinsler—leaving the Sox, at the very least, with no one whose last name starts with 'K.' To press the repeat button, the Red Sox need Mookie Betts and J.D. Martinez to play at the same super-elite level, Dustin Pedroia to return to form after an injurious year off, no breakdowns from china-grade starters Chris Sale and Nathan Eovaldi, and continued improvement from outfielder Andrew Benintendi and third baseman Rafael Devers. Should any of these needs not be met, the fine line between a triumphant encore and disappointment will become quite thin. Sure, it's easy to fix what's not broken. Just don't say that to any of the past 19 World Series champs who've all failed to repeat.
The Tampa Bay Rays pulled off a great magic trick last year by using a substandard roster on a shoestring budget to win 90 games thanks to the introduction of the bullpenning technique. The Rays have three main aversions that could keep them from impressing anew. One is the team's continued aversion to a traditional rotation, indicated by the fact that the Rays' depth chart shows only three "traditional" starting pitchers including reigning Cy Young winner Blake Snell. Then there's the aversion to cash; fans won't be able to use it at Tropicana Field this year, and only two players on the 2019 roster will make over $5 million—with Snell himself being given a raise of relative peanuts ($15,000, to $573,000) that he'll surely remember when he hits free agency. (That is, if the Rays haven't traded him by then.) The third aversion is to home runs, as the Rays seem to have to made a recent habit of trading their top sluggers; of the team's returnees, only Willie Adames reached double-figures in homers (he belted exactly 10). This all adds up to one big, fourth aversion: That of being competitive. The Rays will certainly try to conjure up more low-budget magic, but there can't be too many rabbits left to pull out of the hat.
On a radio program at the start of spring training, Toronto Blue Jays general manager Ross Atkins actually said this: "Vladimir Guerrero Jr. is not a major league player." If that's true, neither are the other 25 Blue Jays who get to occupy the Opening Day roster while Guerrero, the majors' top prospect—and very possibly the organization's best player, right now—is held back in Triple-A for the sake of forging one more full year of service out of him. One might think that keeping Guerrero off the roster for the first three weeks or so might handicap Toronto out of the gate and hurt its chances of making the postseason when all is said and done. But to be honest, the Blue Jays don't have a prayer to match up with the Yankees and Red Sox, with or without Guerrero. The heady days of Juan Bautista, Edwin Encarnacion and Josh Donaldson are gone; now the Jays have Randal Grichuk, Brandon Drury and whoever the heck Danny Jansen is. The Blue Jays' rotation does have familiar names (Marcus Stroman, Aaron Sanchez and newcomers Matt Shoemaker, Clayton Richard and Clay Buchholz), but they lack the reliability of good health. Toronto's theme for 2019 might as well be: Thank God for Baltimore.
Oh yes, the Baltimore Orioles. How low is this team? If they improved by 22 wins—matching the most by any team (Oakland) in 2018 over the previous year—they'd still finish 69-93. There was change with a new GM (Mike Elias) and manager (Brandon Hyde), but they don't play the game; they build the team that plays it. So far, they haven't built anything. This is essentially the same bad ol' Orioles of 2018, with a roster that some could confuse for a Triple-A outfit; the only names that stick out, unfortunately, include slugger Chris Davis—arguably coming off the worst year by any major leaguer, ever—Mark Trumbo, increasingly a shell of his former 47-homer self of a few years ago, and pitcher Dylan Bundy, who led the league in home runs…allowed, with 41. Fellow rotation mates/vets Andrew Cashner and Alex Cobb (a combined 9-30 record and 5.10 ERA in 2018) are also still around, probably wondering how they ever signed on to this mess. If the Orioles are looking for youth to replenish team spirit, it may be a difficult search; their minor league system is regarded as one of baseball's least promising. Look at it this way; it can't be much worse than last year—right? Bottom line is, they're beneath the bottom; if the light at the top can be seen from that far down, that in itself will be a moral victory.
As a baseball fan who also diligently follows soccer, I fancy the Cleveland Indians as kind of like the powerhouse of a lower European league; they dominate against the other clubs, but when they take on the Colossuses of the bigger circuits in a Champions League-type setup, they don't stand a chance. The AL Central is no problem for the Indians; it's the bigger boys in the AL's more competitive divisions—baseball's Liverpools and Real Madrids—that continually keep them from reaching World Series glory. But the Indians may not even be masters of their divisional domain after letting go of or losing key players over the winter, with Band-Aid solutions to fix the bleeding. The Indians have one of baseball's strongest rotations and two MVP-level stars (shortstop Francisco Lindor and third baseman Jose Ramirez), but after that it's pot luck, with an underwhelming outfield and overwhelmed bullpen that posted a terrible 4.60 ERA last season despite throwing fewer innings than any other team. If any of the starters or stars break down—Lindor is already struggling through spring camp pains—then the Indians aren't so automatic to return to the postseason for a fourth straight year. The days of phoning in first place, like an Ajax Amsterdam, are likely over.
So if the Indians falter, who takes over? The Minnesota Twins have been hovering close to the precipice of good times—everyone thought they crossed through into that promised land after 2017—but a rough backslide in 2018 cost, among other things, Paul Molitor's managerial job. Much has been done to upgrade the offense, with super-utility guy Marwin Gonzalez, power hitter C.J. Cron and ageless boomer Nelson Cruz joining the fold. But the Twins are really hoping for a spirited bounce off the canvas from third baseman Miguel Sano and outfielder Byron Buxton, both of whom were badly KO'd in 2018. Even if all of the above works out, the Twins and new skipper Rocco Baldelli will need to depend on a pitching staff that hardly scares anyone and includes no proven closer. (You know, Twins—as this is being typed, Dallas Keuchel and Craig Kimbrel are still available.) The Twins are a work in progress, and they could luck into first place if the Indians create an embarrassing void at the top—but it's tough to tell if the positives outweigh the negatives.
The Chicago White Sox made a lot of offseason noise about making that one big splash, but kept coming up empty. No Bryce Harper. No Manny Machado. No Amazon headquarters. Yet it was the little splashes that could turn this team into a surprise. Wearing White Sox jerseys for the first time this year is ex-Indian Yonder Alonso, veteran starting pitcher Ivan Nova (from Pittsburgh), and two upper-crust relievers in Alex Colome and Kelvin Herrera. Beyond that, whether the Sox can mount an unexpected challenge will depend on how fast the highly praised young ones evolve, including infielder Yoan Moncada, pitcher Lucas Giolito and latest top prospect Eloy Jiminez (who's likely to get the delayed debut treatment a la Vladimir Guerrero Jr.) A year ago I sensed that the White Sox could be candidates as surprise contenders; I was premature on that assessment. Let's find out if I was off by a year…or more.
It's a stone-cold lock: The Kansas City Royals will lead the majors in steals this season. Infielder Whit Merrifield led the majors last year with 45; Aldaberto Mondesi swiped 32 in just 75 games; Billy Hamilton, exiled from Cincinnati, has averaged over 50 in his last five years; and there's pinch-runner extraordinaire Terrance Gore, with 27 career steals spread over 16 career at-bats. So the Royals will be fast—but that doesn't mean they'll be good. They'll be running for their lives as they try to escape a second straight 100-loss season, a job made tougher with the season-long loss of All-Star catcher Salvador Perez (Tommy John surgery). A pitching staff that waffles between inexperience and just plain meh only adds to the woes. There is potential power production from Mondesi (who beyond all those steals also punched out 14 homers) and TGG 2018 Teaser Ryan O'Hearn, who conked out 12 long balls in limited action late last season. But the Royals are kind of like MLB's DeLorean: Fast as hell, but ultimately out of business.
Unlike the Royals, the Detroit Tigers haven't lost 100 games recently—but they keep trying. If suffering 98 defeats in each of the last two seasons has tried the patience of the Comerica Park fan base, wait to you see what this season has in store. The big problem in Detroit is that the roster is full of names whose best years have long since taken place (Miguel Cabrera, Josh Harrison, Jordan Zimmermann, Tyson Ross, Matt Moore), and it's unlikely that most or all of them will be Comeback Player of the Year candidates. The one guy who keeps getting better every year—outfielder Nick Castellanos—is a free agent at the end of the year and will likely get traded before the end of July for prospects the Tigers badly need. And there's a weak bullpen anchored by closer Shane Greene, who saved 32 games last year—but also posted a 5.12 ERA. This division remains so bad that somebody's bound to lose 100 games—and the Tigers look to be the ones drawing the short straw.
In ideal, healthy form, the Houston Astros are easily the team to beat in the AL West. But…do you remember last summer when the team's three big hitters—Jose Altuve, George Springer and Carlos Correa—were all out with injuries? While they sat, the Astros—who won a franchise-record 103 games last season—played sub-.500 ball. Let that be a warning to this year's edition. The projected everyday lineup lacks no holes, given the addition of ex-Cleveland outfielder Michael Brantley and ex-Texas catcher Robinson Chirinos; even DH Tyler White, the relative no-namer in this group, looks like he can go in the .280-20-80-ish range based on his past (albeit part-time) results. But there's a big drop in talent, even by big-league standards, once you look at the Astros' bench. And the rotation? Beyond an age-defying (for now) Justin Verlander and Gerrit Cole, the ranks have thinned with the loss of Dallas Keuchel, Charlie Morton and Lance McCullers Jr. (Tommy John surgery). So here's to durability in Houston—because if the cracks begin to show up, the glue to repair them may not be strong enough.
Should the Astros fall apart, the Oakland A's could be next in line to assume the divisional throne. This, a year after the A's—MLB's Bizarro World team of 2018—defied all odds, microscopic payrolls and waves of rotation injuries to, somehow, win 97 games. Convention does not apply to this fearless, cocky group of underachievers who seem to enjoy the anonymity. It hardly bothers the A's that they've lost a few key players (infielder Jed Lowrie among them) from last year's unit, or that they've lost players they never had (NFL-bound Kyler Murray); it hardly bothers Khris Davis that he keeps hitting .247, because it comes with 40+ home run power; and it hardly bothers third baseman Matt Chapman that he's considered the game's best defensive player when few have ever heard of him. I've always found it dangerous to bet against the A's, and that's now true more than ever; it's tough to imagine them winning close to 100 games again, but with a young, hungry roster and a beast of a bullpen, you can't just say that 2018 was but a mirage. Hard to believe, but the Coliseum may actually be a more fun place to enjoy baseball this season than that evolving morgue across the bay, Oracle nee AT&T Park (see San Francisco Giants, above).
Everything seems to be in the short-term interest of the Los Angeles Angels. Their four top free agent additions—pitcher Matt Harvey, reliver Cody Allen, catcher Jonathan Lucroy and first baseman/DH Justin Bour—all signed one-year contracts. They technically could leave Angels Stadium after 2020. So could megastar Mike Trout, who hits free agency at the same time. But for now, the Angels will be fun to watch in 2019, with Trout's usual excellence, Shohei Ohtani's slugging theatrics (he's on hold as a pitcher as he recovers from Tommy John), Albert Pujols' milestone watch and party animal Harvey's possible reincarnation into once-upon-a-time Angel Bo Belinsky. Bun fun does not equal success. The pitching staff, in particular, could remain the fractured mess that it's been, and that's the primary reason the Angels will be unable to seriously contend. But maybe sometime in the mid-2020s, when the Angels are toiling at their new Tustin ballpark, Trout is buddy-buddy with Bryce Harper in Philadelphia and all those one-year wonders of 2019 are long gone, the fans will be able to laugh back on what a wonderful time it was.
For a time this past offseason, it seemed a day didn't go by without the Seattle Mariners getting rid of another player. Before you knew it, the Mariners were without slugger Nelson Cruz, speedster Jean Segura, 57-save guy Edwin Diaz, veteran Robinson Cano and long-time catcher Mike Zunino. But it wasn't a blatant fire sale; from all of those transactions and losses, the Mariners did gain a worthy Cruz replacement in Edwin Encarnacion, speed-for-Segura-speed swap in outfielder Mallex Smith, and leftover power in veteran outfielder Jay Bruce. Seattle also has a potential wild card in pitcher Yusei Kikuchi, who could be the next in a line of successful ex-Japanese standouts at Safeco, er, T-Mobile Park. But when it's all said and done, the net from all of the above is a loss, with less overall talent and no closer (former Giants hothead Hunter Strickland has the inside track as Diaz's replacement). The highlight of the Mariners' season could very well be Opening Day in Japan, when 45-year-old Ichiro Suzuki gets a ceremonial send-off against the A's; the season will likely go downhill from there.
I think of the Texas Rangers kind of like that Monty Python skit in which a track race is held for runners with no sense of direction; when the starter's gun goes off, everyone takes off in different directions. The Rangers have become not so much a team but a collection, a reflection of an aimless course. If this team has a plan, it's hard to spot it; yes, they have a new manager in former Dodgers bench coach Chris Woodard, but unfortunately he couldn't bring the Dodgers with him. Instead, he's stuck with a rotation mostly full of reclamation projects, a weak bullpen, and a powerful but undisciplined lineup—though we should give Joey Gallo plaudits for finally trying to bunt against the shift in spring games. Maybe with Adrian Beltre retired and a new ballpark figuratively and literally around the corner, the Rangers are content to just lame-duck it this season. But hopefully it doesn't get so bad that the fans start fleeing to wherever they could…as if they had no sense of direction.
I teased at the top that the Red Sox and Dodgers would meet again at the World Series, but I'm only half-messing with you, as the Yankees appear to have better momentum coming into 2019 based on how they've improved—while the Red Sox have regressed. Meanwhile, my TGG partner in crime Ed Attanasio joins me here to give his thoughts on the playoffs/awards picture—and he's going with the same two pennant winners and World Series champs he picked last year. Let's see if the second time is the charm for Ed.
Baseball's Best, Worst and Most Surprising: The 2018 Season in Review A look back at who thrived, survived and professionally died among the 30 major league teams in 2018 as surprises and disappointments reigned.
Can the Teasers of 2018 Prove They Belong in 2019? A look at 10 ballplayers who got their first taste of the major league life late in 2018—and their chances of sticking around in 2019.


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View ORCID ProfileYusen Zhao1,
Chen Xuan2,*,
View ORCID ProfileXiaoshi Qian1,
Yousif Alsaid1,
View ORCID ProfileMutian Hua1,
View ORCID ProfileLihua Jin2 and
View ORCID ProfileXimin He1,3,†
1Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA.
2Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA.
3California NanoSystems Institute, Los Angeles, CA 90095, USA.
↵†Corresponding author. Email: ximinhe{at}ucla.edu
↵* Present address: Department of Mathematical Sciences, Xi'an Jiaotong-Liverpool University, 111 Ren'ai Rd, 215123, Suzhou, China.
Science Robotics 21 Aug 2019:
Vol. 4, Issue 33, eaax7112
DOI: 10.1126/scirobotics.aax7112
Yusen Zhao
ORCID record for Yusen Zhao
Chen Xuan
ORCID record for Xiaoshi Qian
Yousif Alsaid
Mutian Hua
ORCID record for Mutian Hua
Lihua Jin
ORCID record for Lihua Jin
Ximin He
ORCID record for Ximin He
For correspondence: ximinhe@ucla.edu
Oscillations are widely found in living organisms to generate propulsion-based locomotion often driven by constant ambient conditions, such as phototactic movements. Such environment-powered and environment-directed locomotions may advance fully autonomous remotely steered robots. However, most man-made oscillations require nonconstant energy input and cannot perform environment-dictated movement. Here, we report a self-sustained soft oscillator that exhibits perpetual and untethered locomotion as a phototactic soft swimming robot, remotely fueled and steered by constant visible light. This particular out-of-equilibrium actuation arises from a self-shadowing–enabled negative feedback loop inherent in the dynamic light–material interactions, promoted by the fast and substantial volume change of the photoresponsive hydrogel. Our analytical model and governing equation unveil the oscillation mechanism and design principle with key parameters identified to tune the dynamics. On this autonomous oscillator platform, we establish a broadly applicable principle for converting a continuous input into a discontinuous output. The modular design can be customized to accommodate various forms of input energy and to generate diverse oscillatory behaviors. The hydrogel oscillator showcases agile life-like omnidirectional motion in the entire three-dimensional space with near-infinite degrees of freedom. The large force generated by the powerful and long-lasting oscillation can sufficiently overcome water damping and effectively self-propel away from a light source. Such a hydrogel oscillator–based all-soft swimming robot, named OsciBot, demonstrated high-speed and controllable phototactic locomotion. This autonomous robot is battery free, deployable, scalable, and integratable. Artificial phototaxis opens broad opportunities in maneuverable marine automated systems, miniaturized transportation, and solar sails.
Phototaxis, spontaneous and directional movement toward or away from light (1), has been observed in many living organisms—such as Platynereis dumerilii (2), jellyfish (3), and insects (4)—for navigation and photosynthesis. Such stimuli-dictated and environment-powered directional locomotions, if realized with human-made robots, would open new avenues for fully autonomous remotely steered robots. However, artificial phototaxis, the locomotion following illumination direction, has not been realized, despite considerable efforts on photoactuation that have typically been nondirectional (nastic movement) (5). Biological phototaxis has typically been realized by helical swimming (2) or oscillatory propulsion (3). Oscillation is a classic mechanical motion used to generate kinetic energy in propulsion and directional locomotion for various applications, such as robots (6), wind-powered drones (7), sensing (8), and energy coupling (9). Current human-made oscillations are typically generated by stimuli variation or intermittent power transmission, such as using AC signals on a piezoelectric transducer. Thus, these systems require a tethered or battery-connected power source and complicated mechanisms. By contrast, living organisms can directly harness energy from a constant ambient environment and produce autonomous oscillations like heartbeats, neuron impulses, circadian clocks, and cell division (10). Biological oscillations are mainly out-of-equilibrium phenomena arising from built-in negative feedback loops, which are able to interconvert between two or more kinetically stable states (10). If human-made oscillations could be generated using life-like mechanisms and powered by constant environmental sources, it would be extremely advantageous for robotics, especially untethered autonomous robots; however, it remains another great challenge. Hence, the above two challenges in realizing environment-dictated movement directionality and generating oscillatory motion from non-oscillatory ambient input make realizing artificial phototaxis prohibitively difficult.
In recent years, several new materials and mechanisms of oscillation have emerged from attempts to create synthetic active systems that can autonomously oscillate under respective constant stimuli. Examples include chemo-mechanical oscillation based on the Belousov-Zhabotinsky reaction (11, 12) and nonredox reaction (13), chemo-mechano-chemical self-regulation (14), thermo-mechanical oscillation (15), humidity-driven mechanical oscillation (16), and pressure-induced mechanical oscillation (17). Nevertheless, few of these materials and mechanisms could be applied to create autonomous soft robots, due to constraints on their ability to realize remotely and precisely controlled locomotion of high degrees of freedom (DOFs).
Among several attempts to address these issues, photonic energy has been used because of the synergetic capabilities of wireless signaling, remote powering, and directional control (18). Currently, most of the reported work on photoactuation under unsteady state is focused on liquid crystalline networks (LCNs), using preoriented mesogens to induce substantial configuration change associated with the photon-induced phase transition (19–24). However, limited by the mesogen alignment prerequisite, the LCN-based oscillators are predominantly shaped into thin films, which suffer from single-direction actuation, low available thickness (20 to 50 μm) for generating sufficient forces, complicated fabrication with strict requirements, and limited capabilities to operate with a load or in an ambient environment with a high damping coefficient, i.e., in fluids. Moreover, relying on an anisotropic-isotropic phase transition to power macroscopic motion, the current material systems are quite selective in the input photonic energy, which usually bears high requirements in polarization (19–21), wavelength (20), and narrow operation windows (25).
Here, we report a visible light–triggered self-sustained oscillation effect of a hydrogel system showing arbitrary directional motion in fluids with high damping coefficients. The hydrogel oscillator exhibited high scalability (0.36 to 1.1 mm in thickness) and broad operational window (120 to 1125 mW of light) without the need of a polarized light source. Typically, we used a facile one-step synthesis strategy to incorporate the thermally responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel, which undergoes volumetric change as high as 70% at elevated temperatures (~32°C or other tunable transition temperatures), with gold nanoparticles (AuNPs) embedded as visible light absorbers (fig. S1). To demonstrate the design generality and broad operation condition, we have also achieved hydrogel oscillation under ambient, diffusive light using broadband white light as input and polyaniline (PANi) as absorbers. We achieved oscillatory behavior by establishing a built-in negative feedback loop through self-shadowing and efficient diffusion/mass transfer. The symmetric cylindrical hydrogel pillar design allows for omnidirectional oscillation covering the entire three-dimensional (3D) space at a wide range of deflection angles (the angle between the deflected direction and the initial direction; Fig. 1B) from ±90° to nearly 0° (zenith angles) and 0° to 360° wide azimuthal angles. Through computational analytical modeling, a quantitative model with the governing equation of dynamics was established. It not only has precisely depicted the complex physics and identified the key parameters as a robotic design tool but also enables accurate prediction of oscillation frequency with >90% agreement with the experimental results.
Fig. 1 Light-driven hydrogel oscillator.
(A) Schematic representation of the gel oscillator and the setup. Initially, the gel-made pillar is placed vertically on the ground in water. As the light is switched on, the gel pillar bends toward the light (step i) and then starts the oscillation (step ii). (B) Superimposed frames indicating the tracking followed with oscillation. The gel dimensions are 14 mm (L) by 0.9 mm (d). (C) Mechanism of the oscillation: The out-of-equilibrium actuation is controlled by a self-shadowing–enabled negative feedback loop inherent in the dynamic stimuli-material interactions. Photothermal effect of AuNP induces the temperature increase over the LCST of the PNIPAAm gel, leading to the local shrinkage of the gel and pillar tracking toward the light. Among the oscillation cycles, the tip displacement, temperature, and specific volume of the gel experience periodically change over time. (D) Time-resolved tip displacement and local temperature of the hinge for the system with the LCST of 32°C. There is a 90° phase shift of two curves. Dark columns represent the upstroke of the tip, where the temperature is lower than LCST and gel locally recovers. Bright columns, however, represent the downstroke of the tip, where the temperature is higher than LCST and gel locally deswells.
Ultimately, we have demonstrated that this soft agile hydrogel oscillator is capable of producing significant work, specifically propulsion-enabled locomotion. As a soft swimming robot, termed "OsciBot," its efficient self-propulsion mimicked biological negative phototaxis, the behavior of moving away from a light stimulus. This hydrogel oscillator was able to generate remarkably large forces, which were enough to overcome the damping load in an aqueous environment. The OsciBot performed a highly controllable oscillating motion with outstanding output work and hence a fast and controllable swimming speed, >1.15 body lengths/min, which outperforms state-of-the-art soft swimmers. A series of quantitative analyses provided a deeper understanding of the correlation between oscillation parameters and swimming performance. Moreover, the OsciBot could shrink to 5% of its original size in its dry state and reswell in water, making it encapsulatable and deployable on demand. The hydrogel oscillator provides potential in automated systems, soft robotics, miniaturized transport, solar sails, drug delivery, and surgical applications.
For the typical oscillation, an AuNP-embedded PNIPAAm (AuNP/PNIPAAm) hydrogel pillar was mounted vertically on the ground of a water bath, as shown in Fig. 1 (A and B) and movie S1. Upon exposure to a horizontal green laser (532 nm; input power, 175 to 900 mW; beam diameter, 1 mm), the photonic energy was absorbed and converted into thermal energy. With an appropriate pillar diameter, photoabsorber concentration, and light power, the illuminated site of the pillar (referred to as the "hinge" hereafter) reached a local temperature (T) above the lower critical solution temperature (LCST) of PNIPAAm (~32°C), whereas the back side of the hinge remained at a temperature lower than the LCST. The illuminated side with T > LCST therefore shrank as a result of the expulsion of water through diffusing out of hydrogel network, whereas the nonilluminated side remained swollen. Such a photo-triggered asymmetric stretching field induced the pillar to bend toward the light source, followed by continuous and stable oscillation.
The mechanism of self-sustained oscillation is rooted in the photothermally induced self-shadowing effect coupled with the high speed of hydrogel actuation, regulated by a built-in negative feedback loop shown in Fig. 1C. At state 1, an arbitrary spot of the pillar is illuminated and heated above the LCST. The front side of the pillar rapidly shrinks because of fast water diffusion, leading to the overbending (past the equilibrium position determined by the incidence angle) (state 1 − state2) and thus an initial speed caused by inertia. Then, the overbent tip blocks the light source from illuminating the hinge (in the shade), resulting in a decrease of the hinge temperature. At state 2, the tip is at the lowest position with the largest elastic energy, and the temperature is at the LCST, as shown in Fig. 1D. The shadowing by the tip then allows for a continuous cooling of the hinge below the LCST, leading to the rapid reswelling of the gel and pillar unbending (recovery) back to state 3, where the hinge is exposed to light again. Because the hinge temperature is still below LCST and there is an upward velocity, the gel keeps recovering until the temperature reaches the LCST (state 4). At state 4, the tip is at the highest position, also re-storing the largest elastic energy. With the light exposure on the hinge, the temperature keeps increasing to above the LCST, which bends the tip back down to state 1 to start the next cycle. The mechanical oscillation of the tip corresponds to the temperature fluctuation of the hinge (Fig. 1D), exhibiting a 90° phase shift between the two oscillations, which forms a photo-thermo-mechanical negative feedback loop inherent to the light-material interactions. Overall, the mechanism of out-of-equilibrium actuation has two folds: During the dynamic light–material interactions, a self-shadowing–enabled negative feedback loop makes the bending pillar inclined to stay aligned with the light source (equilibrium state photo-tracking, fig. S6A); however, meanwhile, the fast and substantial volume change of the photoresponsive hydrogel generates the (un)bending driving force that is large enough to overcome the water damping, breaking the equilibrium and thus presenting an out-of-equilibrium behavior, oscillatory actuation (fig. S6B).
To identify the material requirements for oscillation to occur, we fabricated hydrogels with a series of cross-linking densities [N,N′-methylenebis(acrylamide) (BIS) as cross-linker]. The relatively densely cross-linked hydrogel pillars [2.0 weight % (wt %) and 3.0 wt % BIS] reached an equilibrium state, steadily pointing to and tracking the light source, instead of oscillating (fig. S7). By contrast, the loosely cross-linked hydrogel (1.5 wt % BIS) had relatively larger pores (fig. S4), which facilitated fast water diffusion in and out of the hydrogel network, resulting in higher diffusivity (D) and thus rapid volume change (fig. S3). In addition, larger pores also led to a larger degree of volume change than the dense gel under an identical illumination condition (fig. S3). Hence, given the same deflection angle (90°) of the pillar (Fig. 1B), the loosely cross-linked hydrogel deforms a smaller amount across its thickness compared with the relatively dense hydrogels. Smaller deformation depth (t) and the higher diffusivity (D) enable a smaller diffusion time scale (t2/D) required for reaching a certain deflection angle. This ultrafast deswelling and swelling generates large driving forces for deflection and recovery, respectively, which are sufficient to overcome water damping (i.e., the frictional force from the surroundings) and to produce the overshoot of the pillar. This driving force breaks through the equilibrium for the light-tracking state exhibited by the slower-responding gel, facilitates an out-of-equilibrium motion, and also maintains the oscillation (movie S2 and fig. S7).
To further explore the geometrical and spatial requirement of the oscillation, we demonstrated the oscillation of a fishhook pillar (fig. S9A and movie S3), where only the hinge and tip were alternatively exposed to the light. However, the front and back sidewalls of its arm (or cantilever) were not exposed to light and thus did not contribute to the oscillation. The oscillation of fishhook pillar had a similar frequency and amplitude as those of the straight pillar. Also, the oscillation was found to be independent of the original orientation of the pillar, as shown in fig. S9 (B and C) and movie S4 for an example 90° deflection angle. Therefore, the only key requisite for realizing oscillation is rapid and reversible deformation of the exposed hinge, which does not impose constraints on the cantilever geometry or the initial pillar position. Note that the hinge here is not preprogrammed or predesigned in the pillar, which is chemically and structurally homogenous; instead, the hinge is redefinable, because it is instantly formed by the variable light incident on any arbitrary location on the pillar.
To date, most soft actuators and oscillators can achieve only single-directional motion, limiting the DOFs in robotic motion (19–22). To realize an omnidirectional response to stimuli coming from arbitrary zenith angles (Fig. 2A) and azimuthal angles (Fig. 2B), we designed a chemically homogeneous and geometrically symmetric hydrogel pillar (see movie S5). For an originally upright pillar (d = 0.9 mm), the 500-mW light approached from different oblique angles. We found that an oscillation could be generated with any deflection angle in the range of 59° to 90° (Fig. 2C) with about the same frequency (Fig. 2G). At this particular light power and pillar diameter, an angle smaller than 59° resulted in light tracking (movie S5). To achieve the oscillation at a smaller deflection angle, one approach was to increase the power density of incident light, which increased the driving force as a result. Alternatively, when the pillar diameter was reduced to 0.36 mm, oscillation was realized for deflection angles as small as 8° (Fig. 2D). When the pillar was initially placed horizontally, we realized an oscillation at 0° deflection angle, which has proven hard to achieve in previous reports. Realization of this 0° oscillation perhaps is facilitated by the contribution of the weight of the pillar in the horizontal position in partially providing the driving force downward (Fig. 2E). For this 0° oscillation, by slightly tuning the height of the light with respect to the initially horizontal pillar, a unique asymmetric flapping was achieved (upper-biased flapping and lower-biased flapping, respectively) in addition to the symmetric flapping (fig. S10). Therefore, the wide operation window of deflection angles allows for sophisticated, versatile actuation.
Fig. 2 Realization of omnidirectional oscillation.
(A) Schematic of zenith scenario, where the pillar is originally placed upright at the bottom with light approaching at different zenith angles. (B) Schematic of azimuthal scenario, where the pillar responds to the light approaching at different azimuthal angles. (C) Zenith angle test for a pillar with a diameter of 0.9 mm. Under light exposure of 500 mW, the oscillation could be initialized ranging from 90° to 59°. Deflection angle ≤56° resulted in tracking. (D) As the diameter was reduced to 0.36 mm, oscillations with 90° to 0° deflection angles and a large oscillation amplitude were observed. Each frame represents 1.3 s for all four different angles. (E) Symmetric, upper-biased, and lower-biased oscillations at 0° deflection angle. (F) Superimposed snapshots of a pillar in response to different azimuthal angles of light. The frequency dependence of oscillation at (G) different zenith angles and (H) different azimuthal angles. Error bars indicate SD. (To show the relative positions, all images are superimposed photos of pillars of different configurations at different time points during oscillation.)
Moreover, we showcased the hydrogel oscillation in response to multiple azimuthal angles (Fig. 2, B and F). Light coming from four different angles covering the entire horizontal plane could all initiate oscillation with the same frequency (Fig. 2H). The oscillation frequency under various zenith angles (Fig. 2G) and azimuthal angles (Fig. 2H) is governed by the frequency formula (Eq. 1) shown below. At this stage, we have achieved omnidirectional oscillation at arbitrary zenith and azimuthal angle, exhibiting photo-induced kinetic energy generation in the entire 3D space.
To describe the fundamental physics of the oscillation, we performed analytical modeling to establish a governing equation. First, to characterize the oscillation frequency, we considered the oscillating pillar as a cantilever beam. Because the hydrogel is submerged in water, the damping due to the water cannot be neglected. The angular frequency of the first bending mode of the damped cantilever beam can be calculated as (26)ωd=ω11−c2L44ρAEI(1)where ω1≈3.5EI/ρAL4 is the angular frequency of the first bending mode without damping, c is the damping coefficient per unit cantilever length, E is Young's modulus, I is the area moment of inertia, ρ is the hydrogel density, A is the cross-sectional area of the cantilever, and L is the cantilever length (see details in section S5.2). The oscillation frequency (fd = ωd/2π) for a pillar with a circular cross section of diameter d is then written as (see details in section S5.2)fd=3.58πdL2Eρ1−64c2L4ρEπ2d6(2)
According to our experimental data, E = 6.3 kPa (see fig. S5), ρ = 103 kg/m3, L ≈ 10 mm, d ≈ 1 mm, and the natural period of the cantilever vibration without damping is t1 = 2π/ω1 ≈ 0.29 s. Solvent diffusion in the hydrogel has a different time scale of tdiff = d2/D, where D is the diffusivity. On the basis of our measurement D ≈ 10−7 m2/s, the diffusion time scale tdiff can be estimated as around 10 s, which is larger than the inertia time scale. Thus, this model has revealed that the oscillation frequency is dominated by inertia and less influenced by diffusion.
With this model, we further investigated the contributions of inertia and diffusion in the oscillation. Figure 3 and movie S6 illustrate the theoretically and experimentally measured frequency as a function of arm length and diameter. As the arm length increased, the frequency for an undamped cantilever dropped in a scaling of f1 = ω1/2π ≈ L−2, as shown by the black dashed curve of Fig. 3A. Considering the water damping of the system, the fitting curve of experimental results will be modified to the red solid curve (see details in section S5.1). To explore the diameter effect, we fabricated pillars with different diameters but the same arm length. The frequency-diameter profile was linear when the diameter was relatively large, consistent with the frequency formula in Eq. 2. However, the water damping term became dominant as the diameter decreased, leading to a deviation from the black line. By fitting the experimental results of the frequency versus diameter plot (Fig. 3C) and the frequency versus arm length plot (Fig. 3A), we obtained the damping coefficients per unit length c to be 3.265 × 10−4 and 1.272 × 10−4, respectively, which validates the formula of the vibration frequency, Eq. 2 (see details in section S5.1). Furthermore, Fig. 3 (A and C) shows that the experimentally observed oscillation frequency agreed well with the theoretical prediction, verifying the domination of frequency by inertia rather than diffusion. On the other hand, for the pillar to bend to a large angle such as 90°, the water does not need to diffuse through the entire thickness of the hydrogel, but only through a thin layer on the surface. This is sufficient for the hydrogel to bend to a relatively large angle in an oscillation period. Generally, during the oscillation, the diffusivity and speed of bending determines whether there is oscillation or tracking, while the inertia determines the frequency of the oscillation (see details in section S5.4).
Fig. 3 The frequency of the oscillator dependent on the geometry.
(A) Frequency as a function of arm length. The fitting curve with water damping consideration matches better with the experimental data (red curve, R2 = 0.987) compared with no water damping (black dashed curve, R2 = 0.983). (B) Comparison of the experimental (upper) and computer simulation (lower) result of the time-resolved tip displacement. The dimensions of pillars are as follows: d = 0.56 mm; L = 13 mm (blue), 17 mm (red), and 22 mm (gray). (C) Frequency as a function of diameter. (D) Comparison of the experimental and theoretical results. The dimensions of pillars are as follows: d = 0.56 mm (purple), 0.78 mm (green), and 1.03 mm (brown); L = 17 mm. Input power, 300 mW. Scale bars (in A and C insets), 1 cm. Error bars indicate SD.
In addition, we numerically solved the dynamic oscillation equation for the damped cantilever beam under constant light illumination (section S5.2). The tip displacements for different values of arm length and diameter are shown in Fig. 3 (B and D). The simulated and experimental results for variations in both diameter and arm length show very good agreement, with only ~10% mismatch.
The oscillation performance could also be affected by light intensity. As movie S7 shows, for a hydrogel pillar of certain response rate/ratio and dimension (L = 17 mm, d = 0.36 to 0.9 mm, 1.5 wt % BIS), an input power lower than a certain threshold (150 to 225 mW) yielded only light tracking. As the input power increased above the threshold, the vibration was amplified cycle by cycle and eventually reached a stable oscillation (fig. S8). A higher light intensity allowed for a broader temperature fluctuation and thus a larger pillar overbending angle, leading to a higher oscillation amplitude (Fig. 4A). Increasing the input power initially induced a slight frequency drop (Fig. 4B), which may arise from the longer traveling distance required to overcome the water damping and slow down the bending/recovering speed. As the light intensity was increased further, the frequency drop was then compensated by the higher bending speed at a higher light intensity (Fig. 4B). Therefore, the oscillation frequency of the current system solely depends on the geometry and the mechanical properties of the pillar. Moreover, our study indicates that a lower pillar diameter can initiate a higher oscillation amplitude at a given input power (Fig. 4C). The higher amplitude for thinner pillars is due to the smaller tdiff for a thin pillar, which results in considerable bending kinetics and magnitudes.
Fig. 4 Input energy dependency and long-term stability of oscillation.
(A and B) Amplitude and frequency as a function of input power. When the input power was higher than the threshold energy, the amplitude increased as input power increased. The frequency, however, maintained a relatively similar value. The thinner pillar could also oscillate with larger amplitude at the same power input. (C) Given the same power input of 300 mW, a thinner pillar oscillated at larger amplitude because of a smaller diffusion time scale t2/D. Tip displacement (D) and frequency (E) upon irradiation of 200 mW over a long period. The dimensions of the pillar are as follows: L = 22 mm and d = 0.56 mm. Once reaching steady oscillation, the long-lasting oscillation could be maintained stably over a long period with little frequency and amplitude fluctuation. Error bars indicate SD.
The operation condition of input power was systematically investigated. We summarized the anticipated effects of parameters including the pillar diameter, the arm length, and the absorption (section S4.6). Optimal operation condition of oscillation (blue regime in fig. S11) is defined between the threshold intensity of oscillation (i.e., the minimum input power density required for realizing oscillation) and the unstable intensity, beyond which the oscillation will deviate significantly and be chaotic. First, with a higher arm length, the threshold intensity required to oscillate was gradually reduced, specifically 122 mW for an aspect ratio of 20. In the meantime, the upper limit for stable oscillation (unstable intensity) was also reduced. Second, with a smaller pillar diameter, both the threshold intensity and the unstable intensity were reduced because of the lower tdiff. Third, a higher concentration of photoabsorber could also help reduce the threshold intensity and unstable intensity, due to the stronger photothermal effect. Therefore, to reduce the required input power intensity for oscillation, a hydrogel pillar with a larger arm length, a lower diameter, and strong photothermal absorbers would be preferred.
Realizing oscillation using ambient light source is challenging but important for practical applications. On the basis of above analyses of operation condition, we optimized the material composition and geometry to lower the threshold intensity of oscillation to better adapt to the ambient environment with relatively lower light intensity and diffusive direction. Here, we have successfully demonstrated a hydrogel pillar oscillating under broadband white light, which has a spectrum close to that of sunlight and the intensity of 2.5 suns (section S4.7 and movie S11). To respond to this white light, we used PANi as absorbers for its high light absorption efficiency throughout broad wavelength spectra. We also made pillars slightly thinner and longer in arm length (section S2.5) to further lower the threshold intensity. The tip displacement was not as regular as under laser (fig. S12). The oscillation amplitude was slightly chaotic, which might be due to the diffusive light direction making the shadowing less regular. However, the frequency of oscillation stably maintained at ~0.085 Hz, indicating that the oscillation still obeyed the governing equation of frequency.
Figure 4 (D and E) and movie S8 demonstrate the long-term stability of the AuNP-PNIPAAm hydrogel oscillation under prolonged green light exposure. We monitored the motion of the hydrogel oscillator over 3600 s of continuous illumination. It displayed highly stable and relentless long-lasting motion with nearly no noticeable fluctuation. Being continuously fueled by light in a stable environment, the hydrogel pillar is anticipated to oscillate perpetually.
Last, with the powerful oscillator, we successfully created an all-soft phototaxis swimming robot, the OsciBot, capable of propulsion-based high-speed locomotion (Fig. 5A). It is worth pointing out that although there are some propelling robots based on temperature-responsive hydrogels, they mainly rely on the alternating stimuli to achieve the motion (27, 28). However, we can convert the constant energy input into a periodically moving unit in the quest to generate energy-efficient and robust robotic materials. Our swimming robot is made entirely of the same hydrogel material; the design included a long hydrogel strip, serving as the paddle, attached perpendicular to a planar hydrogel sheet (fig. S13). As Fig. 5B shows, the robot could float on water because of surface tension on the hydrogel sheet, despite the slightly higher density of hydrogel than that of water. The strip of OsciBot serves as an active flipper to kick water backward and generate propulsion, providing the force to swim away from the light source. When shining light on an arbitrary position of the flipper, it immediately bent upward, followed by continuous oscillating that propelled the OsciBot to move away from light precisely following the illumination direction.
Fig. 5 Self-sustained oscillator-based soft swimming robot (OsciBot) powered and controlled by visible light.
(A) Scheme of the soft swimmer and (B) real oscillation in water. The green arrows denote the light direction. (C) Sequential snapshots of swimmer while shining constant light. Input power was 450 mW. (D) Velocity versus mass of swimmer in comparison with previous reports. A represents a PDMS-cardiomyocyte biohybrid swimmer (35); B represents a ciliate-inspired swimmer (29); C represents a flagellum-inspired swimmer (30); D represents a hydrogel swimmer under water (36); and E represents an eel-inspired microrobot (37). (E) Comparisons of the fully swollen, thoroughly dried, and reswollen soft swimmer, showing on-demand encapsulating and deployable abilities. Scale bars, 1 cm. (F) On/off control of soft swimmer. While the light was switched on, the swimmer kept moving forward. Once the light was switched off, the swimmer stopped in response. During every cycle of the oscillation, mainly the downward stroke (via deswelling) pushed the swimmer forward, resulting in the step-by-step movement over time.
Figure 5C depicts OsciBot's movement fueled and controlled by light. The maximum measured swimming speed was 18.3 mm/min, equivalent to 1.15 body lengths/min, which outperforms previous photoresponsive soft robots inspired by cilia (29) and flagella (30) with swimming speeds of 0.08 body lengths/min and 0.32 body lengths/min, respectively (Fig. 5D). We have further investigated the robotic performance quantitatively (sections S4.9 and 5.5) and found that the oscillating parameters—including the frequency, the amplitude, and the tip velocity or the thrust—all affect the swimming velocity. From the different oscillation amplitudes of the same OsciBot with a fixed thickness and aspect ratio of the arm, we observed that the OsciBot swam faster with a larger oscillation amplitude in a linear fashion (Fig. 6A), because the strip propelled more water backward during one cycle. The larger amplitude also indicates longer distance for the strip tip to travel, leading to a slight frequency drop, consistent with our experimental observation in Fig. 4B. Thus, the swimming velocity inversely correlates with the oscillation frequency. Furthermore, we established the correlation of swimming velocity of the OsciBot and the velocity of strip tip displacement. With the strip beating faster, the thrust of cantilever was calculated to increase in a quadratic law (section S5.5). Experimentally, such faster beating resulted in higher swimming velocity. Therefore, a larger thrust leads to higher swimming velocity of the OsciBot. By further increasing the light intensity, improving the light absorption efficiency, and rationally optimizing the geometry of the paddle as well as the substrate, the swimming performance can be further enhanced. In addition, potentially, the speed may also be tuned with the fluid properties and flow structure. For instance, a symmetric, reciprocal oscillation is likely to generate directional movement more efficiently in a non-Newtonian fluid of a low Reynolds number, where the net propulsion is caused by the differential apparent fluid viscosity under asymmetric shearing conditions (31).
Fig. 6 The effects of oscillation parameters on swimming performance of the OsciBot.
OsciBot velocity as the function of (A) the amplitude, (B) the frequency, and (C) the beam tip velocity of the oscillation.
To demonstrate the controllability and flexibility of the light-induced motion, we examined the swimming behavior by intermittently switching the light on and off (Fig. 5F). The swimming robot moved forward at constant speed while the light was on. In the absence of the light, it instantly slowed down and rapidly stopped. Another remarkable point is to determine the dependency of the OsciBot's motion on the upstroke and downstroke during a single cycle. As illustrated by the inset in Fig. 5F, the robot swam forward quickly during every upstroke (deswelling) and moved slowly during every downstroke (recovery and reswelling), exhibiting a stepwise motion. This suggests that the beating-flipper system features a small reciprocating motion effect. With the highly controllable steering directionality, the phototactic locomotion also has demonstrated the potential of maneuverability (section S4.10), owing to the nature of the oscillator precisely following the incident light.
The hydrogel swimmer can also be deployable on demand to perform tasks such as miniaturized packaging and transport. Benefitting from the nature of the hydrogel with a high water content (up to 95.1 ± 0.64% for our system), the soft swimmer could be dried and shrunk to 1/20th of its original fully swollen size and weight. Thus, as shown in Fig. 5E, the soft swimmer could be encapsulated and stored at a greatly reduced size and then swollen back to its original shape on demand, showing easy portability, good deployability, and robustness.
In summary, we have realized artificial phototaxis with an all-soft self-propelled swimmer actuated by the autonomous oscillation of a photosensitive hydrogel under illumination. The phototactic locomotion robot is propelled by autonomous oscillation, which is generated, powered, and controlled by constant visible light. This has advantages from using ambient environmental energy and alleviates an on-board battery or a tether in performing tasks in open water or limited space. With the intelligent material that can perform the lower-level control task using its built-in feedback loop, the overall load on the control system for a robotic system can be significantly reduced, allowing for more sophisticated autonomy and performing previously unachievable complex tasks.
Specifically, we created a conceptually new autonomous oscillator with a constant input. This fundamentally breaks through the conventional pulsed-input-relying oscillation systems. Here, this out-of-equilibrium actuation in particular arises from a self-shadowing–enabled negative feedback loop inherent in the dynamic light–material interactions, promoted by the fast and substantial volume change of the photoresponsive hydrogel. This mechanism is verified by the experimental observation of the periodic tip displacement rhythmically well matched with the time-dependent hydrogel hinge temperature changes. Combining experimental and theoretical modeling, we can expand from this photo-thermal-kinetic self-oscillation generation mechanism into a generic physical principle—how to convert a continuous input into a discontinuous output in different energy forms. One can use the input stimuli–induced responses (e.g., shape or property changes) as the feedback to, in turn, inform and modulate the input. This will form a built-in feedback loop to realize self-control of the material property or environmental condition and to generate periodic behaviors (e.g., mechanical, temperature, or chemical oscillations, such as in local pH or molecular concentration).
Furthermore, this soft oscillator is powerful and robust in generating a force large enough to overcome water damping. This allows it to perform as an all-soft autonomous swimming robot. The OsciBot exhibits negative phototactic movements with a high swimming speed and controllable motion in a high damping environment. The demonstrated phototactic locomotion precisely follows the incident light, showing highly controllable steering directionality and potential maneuverability (section S4.10). This broad-based platform of self-oscillator–based autonomous robots may be expanded from light-driven to be powered by many other input energy forms and switched from aquatic to aerial robots (e.g., flapping-wing flight), with following customizations on material and robotic design.
In terms of materials design, this particular photo-oscillation is achieved by combining photoabsorbers of high photothermal efficiency (fig. S1) with fast and reversible thermally responsive hydrogels. The modular design of responsive materials allows the oscillator platform to be customized and expanded by incorporating a variety of absorbers and stimuli-responsive soft materials that transduce many continuous input stimuli—such as light, pH, (electro)magnetic fields, electric fields, and microwaves—into kinetic energy, in the form of the oscillatory movements and resulting directional locomotion. In addition, the homogeneous featureless structure of the oscillator makes it convenient to fabricate by additive manufacturing. It may be easily scaled down as a micromachine or scaled up and integrated as an active element into large autonomic systems to meet the requirements for different environments. The untethered, environmental energy–powered robots may perform solar-powered water sampling for oceanographic application.
In terms of robotic motions, the oscillation frequency and amplitude can be tuned by the gel geometry and dimensions and light intensity, as well captured by our established governing equation. With our predictive analytical model, a broad range of oscillatory behaviors may be achieved by tuning or optimizing the oscillator design, oscillation mechanics, and ambient conditions to meet different users' demands (32). The self-sustained oscillation provides a versatile capability that may be used in autonomous soft robots, such as submerged swimmers with cilia-like motion (33) and transporting devices (34). It may also be scaled up or integrated in a large marine vehicle as the active component. Such a self-sustained, tightly controlled, synthetic oscillatory material system may lead to advances in developing robotic counterparts of natural systems. For example, this system may be potentially used for maintaining homeostatic control and generating autonomous oscillations for biomedicine and surgical applications.
Materials preparation
AuNPs were fabricated using the citrate reduction method (section S2.1). Pillar and swimmer polydimethylsiloxane (PDMS) molds were fabricated by curing PDMS (Sylgard 184) around hypodermic needles of varying gauge widths and 3D-printed swimmer models, respectively, at a 10:1 elastomer–to–curing agent weight ratio at 45°C for 4 hours. The AuNP/PNIPAAm precursor solution was prepared by mixing 40 wt % NIPAAm monomer, 1.5 wt % BIS, 0.5 volume % Darocur 1173, and 0.5 wt % AuNPs in dimethyl sulfoxide (DMSO).
The prepolymer solution was injected into the desired PDMS mold and covered with a 3-(trimethoxysilyl)propyl methacrylate (TMSPMA)–treated cover glass (section S2.3). The hydrogel pillar was cured in its respective PDMS mold under ultraviolet (UV) light for 80 s and then carefully removed and immersed in water to remove DMSO and excess monomer. The OsciBot was fabricated in its respective PDMS mold without the cover glass step and also polymerized under UV light for 80 s.
The tip displacement for all hydrogel was recorded with a digital camera equipped with a red filter. Temperature evolution of the hinge was measured with a thermocouple. The deswelling and swelling kinetics of the hydrogel was measured by heating and cooling a hydrogel cylinder in a water bath. The microstructure was observed with a Supra 40VP scanning electron microscope. The tensile test was measured with the dynamic mechanical analyzer (Q800, TA Instruments). All details of characterization are discussed in the Supplementary Materials.
We modeled the hydrogel pillar as a 1D damped cantilever beam. The dynamic vibration equation of the beam with small deflection was formulated. The actuation of the beam is induced by the surface illumination, which causes a temperature gradient and therefore solvent concentration gradient in the thickness direction of the hydrogel. The photo-thermally driven solvent migration was modeled as a 1D diffusion problem in the thickness direction. With the oscillation of the hydrogel, the light spot resides on its top or bottom surface, and the boundary condition of the diffusion equation is switched correspondingly. We solved the coupled diffusion equation and the dynamic vibration equation by the forward-time central-space finite difference method. The parameters that we used in the simulation are laser diameter dph = L/20, cross-link number per monomer volume NΩ = 10−3, polymer-solvent interaction constant χ = 0.3, photo-chemical potential μph/kBT = 5 × 10−4, diffusivity D = 10−7 m2/s, density ρ = 103 kg/m3, and Young's modulus E = 6.3 kPa, unless otherwise stated.
robotics.sciencemag.org/cgi/content/full/4/33/eaax7112/DC1
Section S1. General
Section S2. Fabrication of materials
Section S3. Characterization of materials
Section S4. Characterization of oscillation
Section S5. Theory and simulations
Fig. S1. UV-visible absorption spectrum of AuNPs.
Fig. S2. The schematic of the measurement of hydrogel deswelling/swelling ratio and rate.
Fig. S3. Deswelling/swelling kinetics of oscillating hydrogel and tracking hydrogel.
Fig. S4. Scanning electron microscope images of hydrogels.
Fig. S5. The stress-strain curves of hydrogels with different cross-linking densities.
Fig. S6. Photo-tracking versus photo-oscillation.
Fig. S7. Comparisons of the bending and unbending kinetics of oscillating pillar and tracking pillar.
Fig. S8. Switch from tracking to oscillation by tuning light power.
Fig. S9. Fishhook-shaped oscillator and position independency.
Fig. S10. Schematic of lower-biased (case I), upper-biased (case II), and symmetric flapping (case III).
Fig. S11. Range of operation input correlated to the dimension and the photothermal properties.
Fig. S12. Realization of oscillation under ambient white light.
Fig. S13. The hydrogel oscillator floating on the surface of water in the container.
Fig. S14. Maneuverability of the OsciBot.
Table S1. Summary of effect of cross-linking density on materials properties and oscillation performance.
Movie S1. Hydrogel-based light-driven oscillator.
Movie S2. Comparison of light-induced tracking and oscillation.
Movie S3. Fishhook-shaped hydrogel oscillator.
Movie S4. Position independency.
Movie S5. Realization of omnidirectional oscillation.
Movie S6. Oscillation frequency as a function of geometry.
Movie S7. Initialization: From tracking to oscillation.
Movie S8. Long-term stability of the oscillation.
Movie S9. OsciBot: Continuous swimming.
Movie S10. OsciBot: Controllable motion.
Movie S11. Oscillation under ambient white light.
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Acknowledgments: We thank Y. Qiu for help with dynamic mechanical analysis testing for the mechanical properties of the hydrogel. Funding: The research was supported by ONR awards N000141712117 and N00014-18-1-2314, AFOSR awards FA9550-17-1-0311 and FA9550-18-1-0449, the Hellman Fellows Funds, and the start-up funds from the University of California, Los Angeles. Author contributions: X.H. conceived the concept, planned the project, and supervised the research. X.H. and Y.Z. designed and conducted the experiments and data analysis. Y.Z. and Y.A. conducted the fabrication and characterization. C.X. and L.J. developed the model and numerical code for the analytic modeling. Y.Z., X.H., L.J., M.H., Y.A., C.X., and X.Q. wrote the manuscript. Competing interests: Y.Z. and X.H. are inventors on a provisional patent application on the photo-oscillation technology. The other authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate and support the conclusions in the manuscript are included in the main text or the Supplementary Materials. Contact Y.Z. for any questions.
You are going to email the following Soft phototactic swimmer based on self-sustained hydrogel oscillator
By Yusen Zhao, Chen Xuan, Xiaoshi Qian, Yousif Alsaid, Mutian Hua, Lihua Jin, Ximin He
Science Robotics 21 Aug 2019
A self-sustained hydrogel oscillator, fueled by constant light, exhibits omnidirectional oscillation and powerful phototactic locomotion.

redpajama_set_name: RedPajamaCommonCrawl


text:
Commentary: Senate Paves Road to Reopening the Economy with Coronavirus Relief Bill, But When Will States Reopen Schools?
March 27, 2020 March 26, 2020 Michigan Star Staff
by Robert Romano
By a vote of 96-0, the U.S. Senate has passed a $2.2 trillion legislative package, by far the largest in U.S. history, to keep tens of millions of Americans on payroll and expand unemployment benefits to those who are laid off while the country waits out the deadly Chinese coronavirus that poses additional risk to seniors and those with underlying conditions.
That way, when the virus passes, those businesses, particularly the 30 million small businesses that are struggling most of all right now, but also critical industries, will be able to rapidly reopen and we can get back to our lives.
President Donald Trump has offered April 12, Easter Sunday, as a national goal to begin reopening what he says are "sections" of the country where the outbreak is not so bad. Every state for the moment has effectively shut down their schools, creating a daycare problem for tens of millions of parents, many of whom are temporarily working from home or are furloughed.
To get the economy reopened, President Trump and his administration will have to work with governors in all 50 states, who have 50 different plans about how long everything should remain closed:
Wyoming Schools closed until April 6
Schools closed until May 1
Schools closed until April 17
Schools closed through May 15
Schools closed until March 31
Schools closed for school year
Schools closed until April 6
Schools closed through April 10
Schools closed through April 3
Schools closed indefinitely
Schools closed until May 15
Schools until April 3
Schools closed April 20
So, when it comes to reopening the economy, the first thing to do would be to reopen the schools in some capacity. Parents are likely to take that as a cue from local authorities that it is safe to return to work.
As it is, many states are mulling over cancelling the remainder of the school year, which Kansas, Oklahoma and Virginia have already done. The more that do, likely the longer the recession we are in will last, because it will be that much longer that people stay home. That is because, again, if schools are closed due to public health concerns, individual families in localities are going to listen to their local authorities.
Adding a layer of complexity, many localities are extending closures even beyond what the states are ordering. For example, Chicago public schools will be closed until mid-April, while the guidance currently says March 30 for Illinois. New York City schools are closed until April 20, although the state guidance is for April 1.
That's federalism.
Two decisions likely to weigh in favor of skipping the rest of the school year are President Trump's decision to waive standardized testing requirements for states. It opens the door for states to take the additional steps of cancelling the tests, as many have already done, and potentially to cancel school until September.
And the Senate bill financially incentivizes states and businesses to remain in stasis until the virus passes.
That said, not even New York Democratic Gov. Andrew Cuomo has cancelled school for the rest of the year, at least not yet, saying that there is a "smarter" way to respond to the coronavirus without shutting down the entire state's economy. New York far and away has the most coronavirus cases at the moment, but so far not so many that the hospitals are yet overwhelmed. He promised his state could be considered a template for other states to follow in terms of how to mitigate risk without shutting everything down.
At the end of the day, all the federal government can do is issue recommendations to the states to follow, and to ease travel restrictions when the President believes it is safe to do so. President Trump and his task force are setting the tone that many states will follow.
Real consideration should be given by the President and states to the potential lifelong consequences of cancelling education for the remainder of the school year for students, as well as the economic impacts of those closures. These must be weighed against the virus' trajectory, the rate of infection, hospitalization and fatality.
When we get to day 15 of the President's coronavirus guidelines, the task force has promised a better read on where the virus is and where it's going to be.
It will be up to the President to coordinate with state governors responsible for the closures, and to come up with reasonable recommendations to help our schools and economy to be reopened as soon as possible.
Recommendations for each state for reopening should be criteria-based and geared towards how to reopen while keeping the elderly and those with preexisting conditions safe.
Perhaps if we get to mid-April or the beginning of May and there are no new cases, maybe we can call that summer vacation and reopen the schools to finish their school years, with perhaps a two-week interlude between grades in September.
As it is, every state has closed their schools, and so long as that is the case, the country and the economy will largely remain on standby and the longer the recession we are in will last. Stay tuned.
Robert Romano is the Vice President of Public Policy at Americans for Limited Government.
Reprinted with permission from DailyTorch.com
Commentary, NewsCoronavirus Relief Bill, school closures, unemployment
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