Comb-like temperature-responsive polyhydroxyalkanoate-graft-poly(2-dimethylamino-ethylmethacrylate) for controllable protein adsorption

Polyhydroxyalkanoates (PHA) are a family of diverse biopolyesters produced by many bacteria grown on sustainable bio-resources such as glucose or fatty acids. A PHA copolymer P(3HDD-co-3H9D) consisting of 3-hydroxydodecanoate (3HDD) and 3-hydroxy-9-decenoate (3H9D) was synthesized by the engineered bacterium Pseudomonas entomophila. The PHA was used to generate a comb-like temperature-responsive graft polymer P(3HDD-co-3H9D)-g-poly(2-dimethylamino-ethylmethacrylate), abbreviated as (PHA-g-PDMAEMA), via a three-step reaction developed for this study. Uniform “side chain” PDMAEMA oligomers were first prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization. Each PDMAEMA oligomer was subsequently added with a thiol group at the end of the chain via aminolysis. Thiol PDMAEMA was then grafted onto unsaturated P(3HDD-co-3H9D), with a tunable grafting density from 2.5 to 10 mol%. Graft copolymer PHA-g-PDMAEMA showed enhanced thermal stability, biocompatibility and controllable hydrophilicity compared with non-grafted P(3HDD-co-3H9D). The grafted material presented an obvious tendency of increasing protein adsorptions over the lower critical solution temperature (LCST 47.5 °C) on PHA-g-PDMAEMA with an increasing percentage of DMAEMA in the copolymers. At a temperature below LCST, PHA-g-PDMAEMA presented poor protein absorption in contrast to P(3HDD-co-3H9D). The temperature-responsive properties of the comb-like graft polymer PHA-g-PDMAEMA can be manipulated toward controllable protein adsorption for biomedical usages.