membrane sheet 20 for example by grasping two opposing corners 23 25 of sheet 20 with forceps and pulling placental membrane sheet 20 outwardly the distance between the edges of the slits 22 moves apart to expand the width of sheet 20 as the sheet expands slits 22 of placental membrane sheet 20 widen due to lateral and or vertical movement of slit edges relative to one another thus expanding slits 22 created by the mesher into openings 25 in this manner the sizes of the openings can be increased preferably slits 22 are dispersed over the entire surface of sheet 20 in order to maximize expandability of the material however is anticipated that there may be applications where expandability or porosity of sheet 20 may be desired for only certain portions of the material in those instances slits 22 may be provided in only a fraction of the material or limited only to certain areas of the material such as around the perimeter of the material in a central portion of the material or within a top bottom left or right half of the material for posterolateral spinal fusion applications it is anticipated that slits 22 will be formed only at the ends of the placental membrane sheet 20 that will contact bone surfaces of the transverse processes while the central section of sheet 20 remains essentially impermeable or non porous as indicated above the osteoconductive implants of the invention can include a growth promoting protein the protein can be dispersed in the osteoconductive material or applied.