Biodegradable, open porous scaffolds for the prevention of alveolar bone loss after tooth extraction: CO₂-processing and in vitro-behavior (2001)

The loss of a tooth may lead to the atrophy of alveolar bone, which may cause problems for later surgical reconstruction or esthetic disagreement.However, the immediate implantation of a defect analogous, biodegradable, open porous scaffold in the empty dental alveolus might prevent the resorption of alveolar bone.This work presents a novel processing method to create such scaffolds and the characterization of their behavior in vitro.Pressurized CO 2 in the gaseous state was investigated as a solvent for biodegradable polymers such as poly(D,L-lactide) (PDLLA) and poly(D,L-lactide-co-glycolide) (PLGA).Sorbed CO 2 reduced the glass transition temperature ofPDLLA and PLGA of typically from about 55C to 5-10C for weight fraction of CO 2 of 0.063-0.069.The plasticization influence could be also observed on polymer-gas mixtures by the means of tensile tests.Interaction between CO 2 and PLGA, revealed by negative Flory-Huggins coefficients, could be seen in sorption isotherrns experiments.The diffusion coefficient ofC0 2 in PLGA copolymers should allow fast processing ofPLGA scaffolds.Open porous scaffolds were then manufactured within a few minutes by filling PLGA granules or -tricalcium phosphate (-TCP) granules coated with a PLGA thin film in a mould and subsequent consolidation using gaseous CO 2 .The obtained scaffolds had a porosity of about 55-60% and an average pore diameter of about 100 um for PLGA and more than 200 um for -TCP-PLGA scaffolds.The in vitro behavior ofthese scaffolds were then investigated in phosphate buffer saline (PBS, pR 7.4).Degradation experiments perforrned at 37C and 55C demonstrated that it was possible to accelerate the degradation kinetics by increasing the temperature.However, degradation at 55C led to a fast collapse of the microstructure of PLGA scaffolds.Thus, extrapolation of results obtained at 55C to 37C should not be used to predict behavior at 37C.PLGA50:50, PLGA75:25 and PLGA85:15 scaffolds revealed the same morphology changes during degradation, but different degradation kinetics were found.These degradation kinetics seemed to agree with models describing autocatalytic hydrolysis mechanism.Depending on the scaffolds composition, the first changes in the structure were observed after a few days to 2 months after the beginning of the degradation experiments.During the last stages of degradation, the release of acidic degradation products resulted in a pR of 3 in the PBS solution -TCP-PLGA (l5wt% PLGA50:50) scaffolds showed a different behavior in vitro as compared to PLGA scaffolds.The degradation of the implant led to a detachment of granules after an immersion period in PBS of about 17 days and to the progressive dissolution ofthe -TCP ceramic.During the degradation ofthe polymer film, the pR ofthe medium decreased, but stayed above pR 6.After about 40 days, the PLGA film completely degraded leaving pure -TCP.The use of -TCP combined with low amounts of PLGA could be effective for the development of plI-neutral degrading scaffolds.This promising, in vitro, result permitted to start an in vivo study in order to assess the efficiency of -TCP-PLGA50:50 scaffolds for the prevention of alveolar bone loss after the extraction of a tooth.