Bioresorbable composites made from degradable polymers and bioactive calcium phosphates are clinically desirable for bone fixation and repair, because they do not have to be removed by second surgery after bone heals. However, a critical barrier to wider and more successful use of current bioresorbable polylactide/calcium phosphate (PLA/CaP) composites to bone fixation is their weak mechanical properties. The goal of this project is to develop a new technology to improve the mechanical strength of PLA/CaP composites to match that of natural bone, so that they can have wider application in load-bearing locations. Due to the critical importance of the interfacial adhesion between the PLA matrix and CaP filler within the composites, the strategy is to develop a technology that effectively combines a core-shell organic-inorganic hybrid structure with a special phosphonic chelating agent and surface initiated polymerization to establish direct chemical bonds between the PLA matrix and CaP filler. Based on the improved interface, we target to improve the mechanical strengths of the bioresorbable composites to the average value of natural bone (e.g. 100 MPa as the target value of the tensile strength). Moreover, by additional optimizing a number of critical variables (e.g. CaP phase, particle size, PLA molecular weight (MW) and CaP/PLA mass ratio), we seek to adjust the mechanical strength of PLA/CaP composites into a wide range (e.g. tensile strength 50 - 100 MPa), so that they can best match those of natural bones from varied locations. Both of the initial mechanical strength and the degradation dependent mechanical strength as well as biological interaction of the composites will be studied in the proposed research. Success of the proposed research will produce bioresorbable composites with improved biocompatibility and high and adjustable mechanical strength which can well match new bone growth. This will allow such bioresorbable materials to be more widely and successfully applied to bone fixation and repair, particularly for the load-bearing areas, by maintaining sufficient strength during bone healing, eliminating stress-shielding, and avoiding the clinical adverse inflammatory effects. Clinically, using such bioresorbable materials instead of current non-resorbable metallic devices would be of great benefit to patients, by avoiding the interference with diagnostic instruments (e.g. computed tomography (CT)), eliminating the possible second surgery to remove the device after bone heals, and reducing the total treatment cost.
A technology that effectively combines a core-shell organic-inorganic hybrid structure with modern surface initiated polymerization will be developed to improve the mechanical strength of bioresorbable composites to well match bone. This will allow such materials to be successfully used for bone fixation in load-bearing locations, and eliminate second surgery to remove them after bone heals as that for current non-resorbable metallic implants.
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