Biodegradable foam coating of cortical allografts

Clinical outcomes of bone allograft procedures may be improved by modifying the surface of the graft with an osteoconductive biopolymeric coating. In this comparative in vitro study, we evaluated the dimensional stability, me chanical strength, hydrophilicity, and water uptake of biodegradable foams of poly(propylene fumarate) (PPF) and poly(d,l-lactic-co glycolic acid) (PL GA) when applied as surface coatings to cortical bone. Cortical bone sample s were divided into four groups: Type I, untreated bone; Type II, laser-per forated bone; Type III, partially demineralized bone; and Type IV, laser-pe rforated and partially demineralized bone. Results show that PPF wets easil y, achieving 12.5% wt/wt in 30 min. Compressive tests on the PPF foam mater ial showed that the compressive strength was 6.8 MPa prior to in vitro incu bation but then gradually reduced to 1.9 MPa at 8 weeks. Push-out and pull- off strength tests showed that initially both PPF and PLGA foam coatings ha d comparable adherence strengths to the cortical bone samples (100-150 N). When additional geometrical surface alteration by perforation and demineral ization of the bony substrate was employed, in vitro adherence of the PPF f oam coating was further increased to 120 N, demonstrating a statistically s ignificant improvement of push-out strength throughout the entire 8-week ob servation period (p < 0.0002 for all four data points). The pore geometry o f PPF-foam coatings changed little over the 2-month evaluation period. In c omparison, PLGA foam coating around the cortical bone samples rapidly lost structure with a decrease of 67% in strength seen after 1-week in vitro inc ubation. These new types of bone allografts may be particularly useful wher e the use of other replacement materials is not feasible or practical.