In approximately 8% of fracture reductions treated with resorbable polymeric devices fabricated from poly(lactide), poly(gycolide) or copolymers of lactic and glycolic acids, sterile abscesses are a complication requiring drainage and debridement. These abscesses are not immediately evident, forming seven to twenty weeks after surgery. Evidence is accumulating that these complications are associated with the acidic degradation products formed by in vivo hydrolysis of the polymers. A primary goal of our degradable bone repair system is to control the microenvironment of the implant by incorporating some buffering capacity in to the polymer which will neutralize the acidic products. However, while these polymers are suitable in terms of biocompatibility, they are frequently either too brittle or weak for safe clinical use in bone surgical applications. Thus, the development of a buffered fixture must address two issues simultaneously: effective neutralization of the acidic degradation products and reinforcement to maintain strength. The problems are of course related in that incorporation of neutralizing agents will further weaken the device. We have shown that calcium sales such as calcium carbonate are effective in controlling pH during fixture degradation. However, some weakening occurs. In the proposed Phase I project, we will determine the feasibility of compensating for his loss of strength by introducing unbuffered fibers of the same polymer (self reinforcement). In this regard, we introduce a novel approach to self reinforcement by placing the fibers under tension while being embedded in the matrix of buffered polymer. This new technique should result in improved mechanical properties.
Of the more than 1.1 million fractures in the U.S. each year, greater than 470.000 require internal fixation devices to stabilize the fracture during the healing process. While there is significant clinical demand for resorbable devices, available products have not been widely adopted because of inflammatory responses to degradation. Our studies show that a buffered resorbable fixation device may ameliorate these responses. Development of the necessary strength will address the clinical demand for acceptable resorbable orthopedic materials.
