Piezostimulation using ultrasound-active poly-L-lactide films: the effects of a ZnO filler and cold atmospheric plasma surface treatment

Piezostimulation has the potential to promote human cell growth while inhibiting bacterial growth. Antimicrobial action physically destroys the bacterial cell wall without providing bacteria with too many options for developing resistance. However, the mechanism is typically not fast enough to follow the rapid kinetics of microbial growth, and improvement of the efficacy is needed. Here, we show that the synergy of bulk modification with a ZnO filler and surface modification with cold atmospheric plasma leads to a highly functional organic piezoelectric biomaterial. Specifically, the ZnO filler strengthens the piezoelectric response of piezoelectric poly-L-lactide (piezo-PLLA) after its integration into the polymer bulk, whereas the plasma surface treatment changes the surface chemistry and partially reveals integrated ZnO particles on the surface. Both effects significantly affected piezostimulation and improved the interactions with two types of cells. Specifically, the increased content of ZnO NPs in the piezo-PLLA films increased the contact of both bacteria (E. coli) and human keratinocytes (HaCaT) with the film surface. Consequently, after activation with ultrasound (1 MHz), the surface very effectively transferred the signal to the adhered cells, which resulted in fast and effective antimicrobial activity. Moreover, for adhered HaCaT cells, stimulation promoted proliferation, cell mobility, intercellular connections and cytoskeleton formation. In combination, these two types of interactions are very important for promoting skin regeneration and wound healing.