DOI: 10.14457/tu.the.2023.527
title: Preparation and characterization of multifunctional composite scaffolds of polylactic acid/modified graphene for tissue engineering applications

description: Three-dimensional (3D) bioprinting has emerged as a promising tool for fabricating scaffolds with highly accurate detailing and complex geometry of the net structures for tissue-engineered products. This study developed polylactic acid (PLA)-based composites by introducing graphene modified with alkyl ketene dimer (AKD) for multifunctional materials with a controllable structure by extrusion-based 3D bio-printing. Multilayer graphene was successfully synthesized by electrolytic exfoliation technique in poly (sodium 4-styrene sulfonate) (PSS) and ammonium sulfate ((NH4)2SO4) electrolyte solutions. The structures, morphology, and size of the synthesized GP were characterized by Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) analyses. The results showed that GP prepared from PSS electrolyte solution attained the best performance in low defect content with average lateral flakes compared to those derived from the reaction with (NH4)2SO4 electrolyte. Therefore, the GP prepared from PSS electrolyte was selected and modified by ball milling with alkyl ketene dimer (AKD) to improve its compatibility and dispersibility in a bio-based PLA solution. Optimum dispersion conditions of materials in the PLA matrix were achieved with 20 wt.% of AKD (GPD20). The material was then incorporated with the PLA matrix as reinforcing filler by solution blending at varied contents from 0 – 30 wt.% to form biocomposite films. Incorporating GPD20 significantly improved elongation at break of the composites, with lower tensile strength compared to those integrated with unmodified GP. The maximum value was observed when the content was 20 wt.% of GPD20. All biocomposite samples exhibited high stiffness as their glass transition temperature (Tg) was above room temperature. GPD20/PLA composites showed higher electrical conductivity than GP/PLA counterparts because GPD20 can disperse more homogeneously in the PLA matrix, which is a positive effect of the presence of AKD. In contrast, GP’s structure might be in micron size and highly stacked, which causes poor dispersion in PLA/GP composites, leading to lower conductivity. A series of PLA/GPD20 composite scaffolds were used as bio-inks at different concentrations (0.0-5.0 wt.%) and further fabricated at different dispensing patterns. The results of mechanical properties indicate that the tensile strength and modulus value of the composite materials increased with increased GPD20 content and reached a maximum value at 5 wt.%. In terms of bioprinting performance, the printing patterns strongly affected the mechanical deformation of the printed specimens, as reflected by the lower tensile strength and modulus of those printed at 45 degrees compared to those from 90-degree patterns for all particle loading contents. In addition, the samples fabricated from printing patterns at 90 degrees showed higher stiffness and elongation than those from 45-degree counterparts, even when adding less GPD20. The presence of AKD may improve GP’s compatibility with PLA, leading to enhanced hydrophobicity on the sample surfaces. The composite materials have a high potential for multifunctional use, especially in tissue engineering applications.