Supercritical-Assisted Chain Engineering of Biodegradable Polyhydroxyalkanoates for Simultaneous Mechanical, Optical and Dielectric Enhancement
Biodegradable polymers are promising for bioelectronic materials, yet simultaneously improving their mechanical, electrical, and optical performance remains a major challenge. Poly(3-hydroxybutyrate-co-4-hydroxyvalerate) (P34HB), a microbially synthesized polyhydroxyalkanoate (PHA), exhibits excellent biocompatibility and degradability but suffers from poor chain length control, limiting its functional performance. Here, we report a low-temperature, non-destructive supercritical ethyl alcohol-assisted polymerization (SEAP) strategy to enhance P34HB at the molecular level. Operating at 40 °C and 1500 psi, SEAP combines the permeability of supercritical CO2 with ethanol-mediated catalysis to promote in situ dehydration polymerization and efficiently remove impurities. Post-treatment, P34HB exhibits a 16% increase in number-average molecular weight, along with a record-high Young's modulus of 51.08 GPa and a 144% increase in elongation at break, overcoming the conventional trade-off between stiffness and ductility. Optical performance is also improved, with transmittance rising by 44% and refractive index increasing to 1.2. Material analyses confirm a higher ester group density and reduction of residual impurities. Electrical insulation is notably enhanced, with leakage current reduced by 50% to below 1 pA and reduced dielectric loss to 0.06. Cytotoxicity assays further verify excellent biocompatibility. This work establishes SEAP as a sustainable strategy for functionalizing P34HB, enabling its deployment in next-generation bioelectronics and flexible electronics.