Filler‐Enhanced Piezoelectricity of Poly‐L‐Lactide and Its Use as a Functional Ultrasound‐Activated Biomaterial

Abstract

Poly‐L‐lactide (PLLA) offers a unique possibility for processing into biocompatible, biodegradable, and implantable piezoelectric structures. With such properties, PLLA has potential to be used as an advanced tool for mimicking biophysical processes that naturally occur during the self‐repair of wounds and damaged tissues, including electrostimulated regeneration. The piezoelectricity of PLLA strongly depends on the possibility of controlling its crystallinity and molecular orientation. Here, it is shown that modifying PLLA with a small amount (1 wt%) of crystalline filler particles with a high aspect ratio, which act as nucleating agents during drawing‐induced crystallization, promotes the formation of highly crystalline and oriented PLLA structures. This increases their piezoelectricity, and the filler‐modified PLLA films provide a 20‐fold larger voltage output than nonmodified PLLA during ultrasound (US)‐assisted activation. With 99% PLLA content, the ability of the films to produce reactive oxygen species (ROS) and increase the local temperature during interactions with US is shown to be very low. US‐assisted piezostimulation of adherent cells directly attach to their surface (such as skin keratinocytes), stimulate cytoskeleton formation, and as a result cells elongate and orient themselves in a specific direction that align with the direction of PLLA film drawing and PLLA dipole orientation.

The Combined Effects of Optical Purity, Chain Orientation, Crystallinity, and Dynamic Mechanical Activation as Means to Obtain Highly Piezoelectric Polylactide Materials

“…Because of the strain rate dependency of the piezoelectric response of PLA, the amorphous PLA L99 as-drawn film with minor piezoelectric properties at 110 Hz but good mechanical properties (see Figure S12) was enhanced to a remarkably high d 14 of 13.2 ± 0.5 pC N – 1 , being a promising candidate for piezoelectric cell stimulation at high frequencies. ,,, The strong frequency dependence of the piezoelectric response of PLA represents a great advantage for energy harvesting purposes, going toward high frequency in the range of kHz and MHz for remote external ultrasound activation of implantable energy harvesting devices. , Using piezoelectric PLA for slow movement, such as implantable pressure sensors , or external wearable motion tracker, , would be a less convenient application because of an expected low activation frequency of 1–2 Hz, resulting in low strain rates that may be too little to obtain an efficient piezoelectric response for reliable force sensors or motion tracking.…”

Nanogallium-poly(L-lactide) Composites with Contact Antibacterial Action

“…It would be very interesting and meaningful to see how this material performs in other shapes, such as drawn films, coatings, or fibers. We have very recently shown how uniaxially drawn PLA-based nanocomposites can direct and polarize HaCaT keratinocytes through the ultrasonically triggered piezoelectric effect [ 103 ], while another recent investigation added 300 nm Ga particles onto different fibers (cellulose-polyester, cotton, nylon, and linen) and converted them to Ga/Cu particles with strong antimicrobial and antiviral properties, with the Ga part enabling good attachment to the fibers [ 104 ]. These are a few possible further directions in the investigation and development of Ga/PLA.…”

Flexible Piezoelectric Sensors Based on Ionic Liquid‐doped Poly(L‐Lactic Acid) for Human Coughing Recognition

“…Poly(L‐lactic acid) (PLLA) is one of the emerging biodegradable polymer materials that is prepared from renewable resources [ 31 ] and has broad applications. [ 32–34 ] In addition, PLLA also possesses excellent shear piezoelectric properties, [ 28 ] thermal stability, [ 35 ] and mechanical tensile properties, [ 36 ] as well as transparent, [ 37 ] nontoxic, [ 38 ] easy to process, [ 39 ] and good biocompatibility. [ 40–42 ] Compared with traditional non‐degradable materials, it eliminates unnecessary material retention and can minimize the risk of environmental pollution and adverse reactions to human application.…”