Periodontal membranes from composites of hydroxyapatite and bioresorbable block copolymers

Biomembranes are frequently proposed as devices for "guided bone regenerati on." Such membranes consist generally of a thin sheet of polymeric material , mostly textured from polymeric yarns or clots, which all have a diffuse v ery fine winding porosity. The cross-section size of the holes of such poro sity is nanometric (diameter < 0.1 mu m); thus these holes can be indicated as nanoholes. Whatever the method of production, the surface density of na noholes (number per square centimeter) has to be as high as possible. It is important also that no variation of this density occurs. The fine dimensio n of these microholes allows the crossing of small molecules (O-2, CO2, H2O , sugars, many nutritional organic compounds and even some simple proteins) but not other larger molecules and particulates, including cells of any ki nd. These biomembranes have, consequently, a semipermeable behavior, provid ing the functional role which is the interposition of a barrier for the cel ls, separating the bone from the surrounding soft tissues. The kinetic of p roliferation of osteoblasts is lower than that of fibroblasts. Most membran es of this kind are not resorbable. The main problem for the resorbable one s is the speed of size increase of the holes during the time. Their diamete r must not exceed a threshold value until the reconstruction of bone is com plete, otherwise soft tissue cells will invade the growing bone tissue with formation of undesirable mixed tissue. The present paper deals with a resorbable membrane made with a composite po lymer/ceramic. A poly(epsilon-caprolactone)-block-poly(oxyethylene)-block-p oly(epsilon-caprolactone) copolymer is the polymeric matrix which contains dispersed ceramic hydroxyapatite microgranules, a stiff filling additive. T he main possible use is that of periodontal membranes. The copolymer, obtai ned by thermal polymerization of epsilon-caprolactone onto poly(ethylene-gl ycol), presents good biological tolerance, is resorbable under physiologica l conditions and can promote cell growth. Histological tests, performed 6 m onths after implantation, showed that the polymeric matrix is almost totall y resorbed. New-formed bone colonizes even the innermost parts of the membr ane, with bone trabeculae closely surrounding the hydroxyapatite granules. (C) 1999 Kluwer Academic Publishers.