Evaluation of biocatalytic pathways in the synthesis of polyesters: Towards a greener production of surgical sutures

This review presents an updated and alternative perspective on enzymatic synthesis to obtain polyesters, with a focus on the precursor materials for absorbable sutures: poly-lactic, poly-glycolic, and poly-lactic-co-glycolic acids. Currently, the profitable path towards the industrial synthesis of polyesters is ring-opening polymerization (ROP) of lactones, which is an experimentally complex process and implies a hazardous environmental impact due to the need for energy consumption, use of large volumes of toxic organic solvents and of non-biocompatible metal-based catalysts. On the contrary, enzymatically driven reactions may be performed under mild conditions in simple reactors. Mechanistic and experimental issues of the two major biocatalyzed strategies -direct condensation and ROP- were analyzed from a green chemistry perspective. These enzyme-catalyzed poly-esterifications often return low yield and/or low final molecular weight (M_w). Considering all the analyzed published data available, possible strategies to overcome these limitations were postulated: implementation of aqueous biphasic reaction systems, use of ultrasound agitation and sequential addition of reactants or co-solvents. To promote M_w increment, post-reaction treatments can be carried out such as thermally induced short-chain polymerization under vacuum and incorporation of glycols as chain extenders.