Matthijs de Geus

Polymers from functional macrolactones as potential biomaterials: enzymatic ring opening polymerization, biodegradation, and biocompatibility.

We systematically investigated a series of polymers derived from macrolactones, namely, pentadecalactone, hexadecalactone, and their unsaturated analogues ambrettolide and globalide as potential biomaterials. By enzymatic ring-opening polymerization these monomers can conveniently be polymerized to high molecular weight. The polymers are highly crystalline with melting points around 95 degrees C for the saturated polymers and lower melting points for the unsaturated polymers (46-55 degrees C). All polymers are nontoxic as measured by an MTT assay for metabolic cell activity of a 3T3 mouse fibroblast cell line. Degradation studies showed no hydrolytic or enzymatic degradability of the polymers, which was ascribed to the high crystallinity and hydrophobicity of the materials. The unsaturated polymers were cross-linked in the melt, yielding fully amorphous transparent materials with a gel content of 97%.

Autocatalytic Equation Describing the Change in Molecular Weight during Hydrolytic Degradation of Aliphatic Polyesters

The autocatalytic equation derived in this study describes and even predicts the evolution of the number average molecular weight of aliphatic polyesters upon hydrolytic degradation. The main reaction in the degradation of aliphatic polyesters is autocatalytic hydrolysis of ester bonds, which causes the molecular weight to decrease. During hydrolysis of the ester bonds in the main chain of the polyester, the chains are cleaved and the end group concentrations will rise. The fundamentals of this equation are based on that principle. To validate the derived equation, the hydrolytic degradation of poly(4-methylcaprolactone), poly(epsilon-caprolactone), poly(d,l-lactide), and two different poly(d,l-lactide-co-glycolide) copolymers was monitored after immersion in a PBS buffer (pH = 7.4) at 37 degrees C. The number average molecular weight, mass loss, and crystallinity were determined after different time intervals. The experimental results confirm that hydrolytic degradation of aliphatic polyesters is a bulk erosion process. When comparing the M(n), calculated with the new autocatalytic equation, with the experimental results, it was found that the new model can predict the decrease of the M(n) upon hydrolytic degradation for semicrystalline and amorphous polymers, as well as for copolymers, without the need for complicated mathematics and excessive input parameters. This is a major improvement with respect to earlier proposed models in literature.