Tailoring the topography, crystalline structure, and piezoelectric response of electrospun biodegradable poly(3-hydroxybutyrate) scaffolds by glycine loading

Abstract

Tissue engineering (TE) represents an interdisciplinary field introduced for the recovery, preservation, and improvement of tissue function. Piezopolymers make it possible to generate exogenous potentials close to endogenous ones to promote tissue regeneration. Biodegradable poly(3-hydroxybutyrate) (PHB) has gained particular attention; however, the piezoelectric (PE) response of PHB is poor, and there is a need to improve it without compromising the biocompatibility of the scaffold. Herein, a drastic increase in the PE response of electrospun PHB scaffolds was achieved by incorporation of homogeneously distributed crystals of piezoactive β-glycine (Gly). We successfully optimized the electrospinning parameters to prepare composite PHB fibers with Gly content (5, 15, 20, and 30 wt%) and tailored topography, crystalline structure, and PE response. Gly incorporation creates a nanoporous textured surface of polymer fibers, which improves surface area, surface wettability, and the free surface energy of intrinsically hydrophobic scaffolds. In addition, Gly crystals act as nucleators for PHB crystallization, diminishing the polymer crystallite size and increasing its crystallinity degree from (39.9 ± 0.8) % for pure PHB to (45.8 ± 1.6) % for PHB-Gly-30. Using piezoelectric force microscopy, we obtained distributions of PE response along the fibers, uncovering a considerable increase in the lateral PE response for PHB scaffolds with 30 wt% Gly (from 0.28 ± 0.13 to 3.9 ± 1.0 pm/V) due to (i) the presence of PE β-Gly phase and (ii) higher PHB crystallinity. First-principles calculations revealed that the interaction of the Gly molecule with PHB surfaces occurred predominantly through hydrogen bonding and demonstrated a mechanism ranging from strong physisorption to weak chemisorption. This study opens new fundamental insights into straightforward one-stage engineering of biodegradable piezopolymer properties and offers a prospective scaffold for a wide range of TE applications.