THE BONE-BONDING POLYMER POLYACTIVE(R)-80 20 INDUCES HYDROXYCARBONATEAPATITE FORMATION IN-VITRO/

The bone-bonding polymer known as Polyactive(R) is a block copolymer c omposed of a polyethylene oxide (PEO) soft segment and a polybutylene terephthalate (PBT) hard segment. This study focuses on the in vitro i nduction of hydroxyapatite by Polyactive(R). Our results show that Pol yactive(R) is capable of inducing hydroxycarbonate apatite (HCAp) form ation from a metastable calcium phosphate solution analogous to a phys iological solution. In a 4-day incubation, the HCAp formation extended approximately 100 mu m deep from the surface. A great number of globu les about 1 mu m large were found in the calcified Polyactive(R). Thes e globules were composed of HCAp crystals embedded in the polymer matr ix. There were so many globules in the surface that they connected wit h each other and formed a calcified layer. Next to the calcified layer was a zone where the globules were scattered. The calcified surface m ay have acted to promote HCAp growth from the solution, bringing about the formation of a HCAp layer on top of the calcified layer. The tran sition of solid Polyactive(R) into a Polyactive(R) hydrogel in calcium phosphate solution permitted HCAp formation within the polymer. It is proposed that the COOH groups produced during hydrolysis of Polyactiv e(R) play an important role in nucleating hydroxyapatite. A remarkable affinity of the PEO segment of the polymer for calcium ions may facil itate moving calcium and phosphate from the solution into the polymer for the growth of HCAp. (C) 1997 John Wiley & Sons, Inc.