Hydrophilicity Affecting the Enzyme-Driven Degradation of Piezoelectric Poly-l-Lactide Films

Abstract

Biocompatible and biodegradable poly-l-lactic acid (PLLA) processed into piezoelectric structures has good potential for use in medical applications, particularly for promoting cellular growth during electrostimulation. Significant advantages like closer contacts between cells and films are predicted when their surfaces are modified to make them more hydrophilic. However, there is an open question about whether the surface modification will affect the degradation process and how the films will be changed as a result. For the first time, we demonstrate that improving the polymer surface’s wettability affects the position of enzyme-driven degradation. Although it is generally considered that proteinase K degrades only the polymer surface, we observed the enzyme’s ability to induce both surface and bulk degradation. In hydrophilic films, degradation occurs at the surface, inducing surface erosion, while for hydrophobic films, it is located inside the films, inducing bulk erosion. Accordingly, changes in the structural, morphological, mechanical, thermal and wetting properties of the film resulting from degradation vary, depending on the film’s wettability. Most importantly, the degradation is gradual, so the mechanical and piezoelectric properties are retained during the degradation.

Structure and properties of new biodegradable elastomers composed of poly(ethylene succinate)‐based poly(ether ester)s and poly(lactic acid)

“…With degradation time extending to 21 days, the dense pits were observed. After 28‐day degradation, the wide and deep cavities were observed on the film, clearly suggesting the fast bulk degradation in the presence of lipase 47,48 . In contrast, although small holes were observed on the surface of PES 89 ‐PDES 11 and PLA as control, the whole surfaces looked intact after 28 days degradation.…”

“…After 28-day degradation, the wide and deep cavities were observed on the film, clearly suggesting the fast bulk degradation in the presence of lipase. 47,48 In contrast, although small holes were observed on the surface of F I G U R E 8 Scanning electron microscope (SEM) images of the copolymers degradation. The first six images for the copolymer (PES 92 -PDES 8 ) 83 -PLA 17 during 28-day degradation, and the six image was the regional magnification of the fifth image; the last three SEM images for PES 89 -PDES 11 , PLA and (PES 91 -PDES 9 ) 23 -PLA 77 after 28-day degradation [Color figure can be viewed at wileyonlinelibrary.com] PES 89 -PDES 11 and PLA as control, the whole surfaces looked intact after 28 days degradation.…”

Antimicrobial activity of piezoelectric polymer: piezoelectricity as the reason for damaging bacterial membrane

“…PLLA is a polyester which degrades through hydrolysis releasing acidic products consequently decreasing the pH, particularly in microenvironment close to the film surface. However this process is not fast and, as we observed earlier, degradation in presence of enzymes takes several days (44). This period is longer than the time needed for obtaining antibacterial effect, therefore contribution of the pH change due to the release of lactic acid is discarded.…”

“…However this process is not fast, and as we observed earlier, degradation in the presence of enzymes takes several days. 44 This period is longer than the time needed for obtaining an antibacterial effect, and therefore the contribution of pH changes due to the release of lactic acid was discarded. More importantly, with polymer degradation, the piezoelectric properties gradually decrease, 44 implying the prolonged availability of their surface for providing piezo-stimulation-induced antimicrobial activity.…”

Biodegradable Materials for Tissue Engineering: Development, Classification and Current Applications

“…Both kinds of the signals can be categorized into three groups: biological, chemical, and physical [ 133 ]. For instance, PLLA-based biomaterials processed into piezoelectric structures can be engineered as scaffolds for promoting cellular growth during electrostimulation [ 134 ]. The low piezoelectric effect of PLLA is similar in magnitude to that of natural biomacromolecules like collagen [ 135 ] giving it the ability to interact with biological systems without being rejected [ 136 ].…”