The Effect of Nanomechanical\nStimulation Strategies\non the Shear Piezoelectric Response of Poly(l‑lactide)\n(PLLA)

Electrical stimulation has been shown to enhance tissue\nregeneration,\nwhich is why piezoelectric-polymer-based scaffolds are on the rise\nfor advanced tissue-engineering approaches. Recent studies have shown\nthat electrical cues can modulate cell function <i>in vitro</i> and <i>in vivo</i> and that these cues can be delivered\nthrough the application of an external noninvasive ultrasound (US)\nsource to actuate a piezoelectric polymer. However, poly(l-lactide) (PLLA) possesses a shear piezoelectric coefficient and\ntherefore requires different strategies of US stimulation relative\nto other well-established piezoelectric materials such as poly(vinylidene\nfluoride-trifluoroethylene) P(VDF-TrFE). Thus, this work compares\nthree different stimulation methods ranging from 1 to 500 kHz (a nanokicking\nbioreactor, an US transducer, and an US bath) to actuate a PLLA diaphragm\nwith the aim of creating a bioelectrical cell culture device. The\nUS bath stimulated PLLA films (37 kHz) generated an output voltage\nof 548 ± 16 mV, the highest of all tested systems. The nanokicker\nstimulated PLLA films (1.3 kHz) were associated with a voltage output\nof 4.8 ± 0.7 mV, and the US probe (500 kHz) actuated films generated\nan output voltage of 9.1 ± 0.8 mV, which is still high enough\nfor electrical cell stimulation. Moreover, the influence of the film\ntension on the voltage output was examined, and reduced tension was\nobserved to increase the piezoelectric response of the PLLA films\nby 118% and reduce the piezoelectric response of P(VDF-TrFE) films\nby 24%. This shows that piezoelectric PLLA-based scaffolds can be\ndesigned in a manner to take advantage of the shear piezoelectric\neffect of PLLA, when applying external US stimulation.