A new injectable bone substitute combining poly(epsilon-caprolactone) microparticles with biphasic calcium phosphate granules.

Previous studies have shown the effectiveness of an injectable bone substitute (IBS) composed of biphasic calcium phosphate in 2% hydroxypropyl methylcellulose gel (50/50 w/w). A therapeutic agent in the form of a drug can be added to the biomaterial by encapsulation into microparticles to protect the active agent, control its release and preserve the material rheological properties. Poly(epsilon-caprolactone) was used in this study because of its biocompatibility and resorbability, as tested in orthopaedic implants and surgical sutures. Particles (80-200 microm) were manufactured by a solvent evaporation-extraction process (1 g of polymer, 11-15 ml methylene chloride, with a stirring speed of 400-600 rpm) and introduced into the IBS in a 5-50% (V/V) range. Injectability was evaluated by texture analysis. With less than 45% of particles, the material had rheological properties similar to those of the reference IBS, whereas injectability decreased markedly with more than 45% of particles. A preliminary in vitro release study showed that this type of triphasic IBS could be efficient for drug delivery systems with osteoconduction properties.