Biodegradable Elastomeric Scaffolds for Tissue Engineering
Ana Paula P
In the past years the search for suitable materials for use in tissue engineering represents a major area of study. Most attention has been given to polymers based on lactic acid and glycolic acid, however these materials have the disadvantage of being rather stiff and brittle. In addition, the rate of hydrolysis of these polymers can be quite high, with high degrees of swelling at late stages of the degradation. We have recently reported on the properties of poly(ester carbonate)s based on the slowly degrading poly(trimethylene carbonate) (poly(TMC)). TMC is copolymerized with ?-caprolactone (CL) or with D,L-lactide (DLLA) to prepare processable, hydrophobic elastomers with suitable mechanical properties and little or no crystallinity. By copolymerization, the degradation rate of poly(TMC) can also be tuned. In vitro degradation studies conducted on these polymers show that the nature of the comonomer and the composition are of influence on the degradation rate. DLLA copolymers with 50 or 80 mol% of DLLA lose their tensile strength in less than 5 months and undergo total degradation in 11 months. For CL copolymers a slow and gradual decrease of molecular weight was observed during the same time period. This is accompanied by a small deterioration of the mechanical performance. In both cases the higher the comonomer content the higher the observed hydrolysis rate. Presently we are investigating the use of scaffolds based on TMC elastomers for long- and short-term applications. Poly(TMC-CL) (10:90 mol%) is processed into porous two-ply tubes by means of salt leaching (inner layer) and fiber winding (outer layer) techniques. These grafts seeded with Schwann cells will be used as nerve guides for the bridging of large peripheral nerve defects. Such a graft is designed to maintain its shape and mechanical performance for 1 year. Poly(TMC) and poly(TMC-DLLA) (50:50 mol%) are totally amorphous and very flexible, they are excellent candidates for scaffolds for tissue engineering of blood vessels, heart tissue and skin substitutes. Porous structures are being prepared by the combination of phase separation techniques and porosifying agents.