Stress shielding represents a significant problem with current devices used in osteosynthesis and occurs whenever a high stiffness fixation device is affixed securely to bone. In order to minimize disuse atrophy from stress shielding during osteosynthesis a novel biodegradable interpenetrating phase composite (IPC) material has been developed as a potential material for fabrication of internal fixation devices.

Presently, we report on the effect of ceramic porosity on the initial mechanical properties of a novel biodegradable ceramic-polymer composite produced from porous calcium polyphosphate (CPP) infiltrated with a specially designed polyvinyl acid-carbonate copolymer (PVA-C) that forms ionic bonds with CPP. The resin is polymerized in situ to yield the final IPC. IPCs formed from CPP having volume percentage porosities ranging from 18 – 35 % were studied and showed as much as a six-fold increase over that of porous CPP samples. IPC samples had three-point bending strength of 60 – 80 MPa, elastic constant of 15.4 – 39.8 GPa, and fracture toughness, K_IC, of approximately 1 MPa·m^˝, all very similar to the corresponding properties of cortical bone. Polymer resin infiltration also significantly enhanced material machining characteristics.

Initial in vitro testing revealed that the current PVA-C polymer system is sensitive to swelling in a simulated body solution environment resulting in unacceptable degradation characteristics (i.e. too rapid strength loss). However, the initial mechanical properties of the IPCs formed in this study support the rationale of IPC composite design utilizing appropriate ceramic/polymer combinations for fabricating biodegradable fracture fixation systems suitable for use in high load-bearing applications.