Novel Poly(l-lactide)/graphene oxide films with improved mechanical flexibility and antibacterial activity

Poly(l-lactic acid) (PLLA) is a biocompatible polyester derived from renewable sources. It is desirable to reduce its brittleness and introduce antibacterial activity for biomedical applications by using graphene oxide (GO) as a structural and antibacterial agent. However, commonly used polymer/GO composite synthesis methods, such as physical mixing and covalent functionalization, either cause phase segregation or compromise the intrinsic properties of GO. Here, a novel approach is demonstrated to synthesize PLLA/GO films. First, perylene bisimides-containing PLLA (PBI-PLLA) was synthesized via ring-opening polymerization of l-lactide using a hydroxyl-derivate of perylene bisimides (PBI-OH) as the initiator. Next, PBI-PLLA was conjugated with GO via π-π stacking to form PLLA-conjugated GO (PLLA-c-GO). Last, PLLA/GO films were fabricated by simple solution casting of commercial PLLA and PLLA-c-GO dissolved in chloroform. Detailed characterization shows that GO retains its morphology and functional groups in PLLA-c-GO, which enables unique properties in the PLLA/GO films. The starting thermal degradation temperature of PLLA/GO films in N₂ increases to 313°C comparing to commercial PLLA films at 293°C. Their surface is more hydrophilic with the water contact angle of 53°. Their elongation at break improves significantly from 3% to 30% compared to commercial PLLA films, demonstrating much better flexibility. Most importantly, the PLLA/GO films show good antibacterial activity towards Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Bacillus subtiliscells (B. subtilis) cells with the bacterial colony number reduction by 80%. At the same time, they show low toxicity towards mammalian cells, such asL929 and macrophage cells. Overall, the novel PLLA/GO films demonstrate various beneficial characteristics for potential biomedical applications.