New technique to extend the useful life of a biodegradable cartilage implant

Biodegradable implants made of alpha-hydroxypolyesters, such as polylactic acid, polyglycolic acid, or their copolymers, undergo bulk degradation with a concomitant mass loss. Although biocompatibility or toxicity problems, which have occasionally been reported in response to these materials' in vivo behavior, have not been conclusively linked to rapid mass loss, we hypothesized that such implants should degrade and lose mass in a more uniform rate. To this end, we designed a new implant, intended to be used in articular cartilage repair, consisting of a blend of three copolymers of 50:50 poly(d,l)-lactide coglycolide with inherent viscosities of 0.23, 0.58, and 1.37 dL/g. The objective of the blend implant design was to achieve a slower rate of degradation and mass loss in comparison to a previous design, which used a single copolymer of inherent viscosity of 0.58 dL/g. The blend's in vitro degradation characteristics were obtained and compared to those of the control design in terms of mass, molecular weight, pH, mechanical properties, gross morphology, and porosity. Another objective of our study was to design and employ a novel test for assessing the permeability of porous scaffolds, using a custom apparatus under direct permeation conditions. Significant differences in the temporal behavior of the two groups were found. The blend implants maintained their overall structural integrity longer than control specimens (6 weeks versus 3 weeks). This was a surprising finding in light of the fact that losses in molecular weight were similar in the two groups. Extension of structural usefulness to 6 weeks, achieved by the method described in the study, can be expected to enhance the viability of this scaffold in an in vivo application such as cartilage repair. Thus, the blended copolymer implants may be more suitable in orthopedic applications, where a decreased degradation rate would be preferable.