A strategy to optimize the strength and degradation rate of calcium polyphosphates biomaterials

髋关节和膝关节置换术越来越多地被用来替换因关节炎而软骨被破坏的关节。人工材料(金属、陶瓷或聚合物)替代人工关节的一种新方法是组织工程学，即在体外生长新的软骨组织。这种方法的主要问题之一是新形成的软骨组织锚定到骨中。我们的团队(Kandel，Pilliar和Grynpas博士)开发了一种方法来形成两相结构，该结构由固定在聚磷酸钙(CPP)多孔固体上的组织工程软骨组成。一个小的双相结构已经植入绵羊的膝盖长达9个月，在这一点上，该结构的软骨已经与周围的软骨整合。骨已经生长到CPP固体的毛孔中，这种固体被证明是生物相容的，并且降解缓慢。必须确保这种CPP材料具有足够的机械性能来支撑整个关节，或在目前仅使用金属保持架的承重应用中用作骨替代品。此外，CPP的降解率低于预期。CPP的多聚磷酸链水解成较短的链、多聚磷酸环和正磷酸盐的机理尚不清楚。本项目的目的是最大限度地提高CPP生物材料的力学性能，并了解其降解机理。

Hip and knee replacements are increasingly used to replace joints where the cartilage has been destroyed by arthritis. A novel alternative approach to total joint replacement by artificial materials (metals, ceramics or polymers) is tissue engineering where new cartilage tissue is grown in vitro. One of the main problems with this approach is the anchorage of the newly formed cartilage tissue into bone. Our group (Drs. Kandel, Pilliar and Grynpas) has developed a method to form biphasic constructs consisting of tissue engineered cartilage anchored on top of a calcium polyphosphate (CPP) porous solid. A small biphasic construct has been implanted in a sheep knee for up to 9 months at which point the cartilage of the construct has integrated with the surrounding cartilage. Bone has grown into the pores of the CPP solid, which has been shown to be biocompatible and to degrade slowly. It is essential to ensure that this CPP material has sufficient mechanical properties to support a whole joint or to be used as a bone substitute in load bearing applications where only metal cages are currently used. In addition the rate of degradation of the CPP is lower than desired. The mechanism by which the polyphosphate chains of CPP hydrolyze into shorter chains, polyphosphate rings and orthophosphates is still not well understood. The aim of this project is to maximize the mechanical properties of the CPP biomaterial and to understand its mechanisms of degradation.