Nanoscale piezoelectric effect of biodegradable PLA-based composite fibers by piezoresponse force microscopy

The piezoelectricity of the biocompatible and biodegradable polymer polylactic acid (PLA) was investigated as a potential magnetoelectric (ME) nanocomposite for biomedical applications. A key focus was to quantify the piezoelectric properties of single PLA fibers while tuning their polymer degradability through the addition of faster degrading polymer, poly (DL-lactide-co-glycolide) (PLGA), which is not a piezoelectric polymer. Piezoresponse Force Microscopy (PFM) showed that electrospun PLA fibers gave a piezoelectric response of 186 ± 28 pm. For comparison both PLA/PLGA (75/25) and PLA/PLGA (50/50) fibers gave significantly lower piezoelectric responses of 89 ± 12 pm and 50 ± 9.1 pm, respectively. For the highest content PLGA fibers, PLA/PLGA (25/75), only very few fibers exhibited a low response of 28 pm while most showed no response. Overall, an increasing PLGA content caused a decrease in the piezoelectric response, thus an expected trade-off existed between the biodegradability (i.e. PLA to PLGA content ratio) versus piezoelectricity. The findings were considered significant due to the existence of piezoelectricity in a tuneable biodegradable material that has potential to impart piezoelectric induced effects on biointeractions with the surrounding biological environment or drug interactions with the polymer to control the rate of drug release. In such applications, there is an opportunity to magnetically control the piezoelectricity and henceforth PLA/CoFe₂O₄ ME nanocomposite fibers with 5% and 10% of CoFe₂O₄ nanoparticles were also investigated. Both 5% and 10% PLA/CoFe₂O₄ nanocomposites gave lower piezoelectric responses compared to the PLA presumably due to the disturbance of polymer chains and dipole moments by the magnetic nanoparticles, in addition to effects from the possible inhomogeneous distribution of CoFe₂O₄ nanoparticles.