Composites

The development of mineral-organic composite materials offers the possibility of combining the favorable properties of bioceramics such as the HAP, alumina or titanium dioxide with the molding capacity of biocompatible polymers (polymethylmethacrylate): PMMA [KHO 92], poly(L-lactic) acid: PLLA [ROD 95], poly(ethylene): PE [DOW 91]). It is also conceivable to attain a value of the modulus of elasticity near to that of the bone.
We can differentiate composites as bioresorbable or non-bioresorbable. The non- bioresorbable composites are the result of the combination of a non-bioresorbable calcium phosphate (HAP) with a non-bioresorbable polymer (PMMA, PE). In this case, we have to avoid the covering of ceramic grains of the surface, so as to preserve their biological activity.

Bioresorbable composites combine a bioresorbable polymer (PLLA, poly(glycolic) acids and poly(butyric) acids) with HAP particles or of resorptive calcium phosphate. In order to guarantee a successful combination of calcium
phosphates with a bioresorbable polymer, it is important to adapt the resorption of the two constituents to avoid inflammatory reactions due to the release of ceramic particles.
These materials should grow in the future on account of the great many combination possibilities and their aptitude at combining a biological activity with mechanical properties similar to those of the bone.
Besides, various combinations of calcium phosphates – with chitosan [VIA 98], with cellulosic composites [OKA 97], with collagen [NIS 95] – have also been well studied, but these combinations cannot be considered as real composite materials. It
refers most often to sintered ceramic particles, quite coarse (in order to avoid an inflammatory reaction) and poorly bonded by the macromolecule. Some inject able formulations have been developed.
Certain ceramic-ceramic composites have also been studied, particularly in the fluorohydroxyapatite-alumina and hydroxyapatite-alumina systems