have porosity levels higher than about 90 often reaching 95 or even higher if desired layer 110 can also be covered with an outermost semi permeable membrane as described in u s patent application ser no 09 690 897 on its opposed side flexible implant 100 will have a bone ingrowth pad 130 with an anchoring surface 132 that will be pressed against a bone surface after implantation in order to promote solid and stable anchoring bone ingrowth pad preferably should promote and induce ingrowth by bony osseous calcified tissue biocompatible materials that promote bony tissue ingrowth have been developed over the past two decades and are known to those skilled in the art examples include meshes made of biocompatible metallic alloys which can be u201c sputter coated u201d if desired with calcium phosphate blends that emulate hydroxyapatite the crystalline structure that gives bones their hardness in a preferred embodiment a u201c multi perforated non planar interface u201d component 120 also referred to herein as a u201c perforated waffle u201d layer can be provided between the relatively soft material of the hydrogel bearing component 110 and the substantially harder material of the bone ingrowth pad 120 this type of interface layer 120 is described in more detail in provisional application ser no 60 250 091 cited above and incorporated by reference herein a small segment from such a layer shown in a perspective cutaway view is provided in fig2 this cutaway drawing depicts.