fig3 g demonstrated different nanoindentation forces upon both approaching and retracting phases of the afm scanning tip chondrogenic and osteogenic constructs showed significantly different young 39 s moduli fig3 h which are defined as the slope of the strain vs stress curve and represent the elastic mechanical properties of the material under study the average young 39 s modulus of osteogenic constructs was 582 u00b1 59 kilopascal kpa significantly higher than chondral constructs 329 u00b1 54 kpa which in turn were significantly higher than peg hydrogel alone 166 u00b1 23 kpa p lt 0 01 fig3 h these nanomechanical data suggest that msc derived osteogenic cells encapsulated in peg hydrogel have produced stiffer matrices than matrices synthesized by msc derived chondrogenic cells both of which are significantly stiffer than peg hydrogel alone fig3 h mscs induced to differentiate into chondrogenic cells after 4 week monolayer culture in tgf u03b21 containing chondrogenic medium showed intense reaction to safranin o fig4 a representing synthesis of cartilage specific glycosaminoglycans gag after photoencapsulation in peg based hydrogel msc derived chondrogenic cells continued to show intense safranin o reaction especially in their pericellular matrix fig4 b rt pcr data corroborated histological findings by showing the expression of aggrecan and type ii collagen genes after 6 week incubation in chondrogenic medium fig4 c peg hydrogel encapsulating msc derived.