Biopolymer toughening with chain extenders

Polylactic acid (PLA) is one of the most popular biodegradable polymers today. However, it has its drawbacks, such as poor melt strength and narrow processing window. In this study, PLA 2003D was compounded with chain extenders (CE) at weight percentages of 0.2%, 0.5%, 0.75% and 1.0%, using two co-rotating screws. Two types of multifunctional epoxy extenders were used, Joncryl® ADR-4300 and Joncryl® ADR-4370F. The thermal, mechanical, chemical and rheological properties of the PLA blends were investigated. The DSC results showed that there was a lower crystallinity with increasing concentrations of CE, suggesting that the blends increased in ductility. The results showed that the mechanical (i.e. impact resistance, ductility) and rheological (i.e. melt strength) properties improved with increasing concentrations of CE. The impact resistance and ductility of the blends increased with increasing concentrations of CE. When compared to pure PLA, the PLA blends exhibit enhanced melt strength and strain-hardening behaviour. These results are supported by results of the FTIR and GPC, which indicated that the PLA blends had an increase in molecular weight. The change in molecular weight and molecular architecture due to the chain extender plays an important role in the enhancement of the properties. Lastly, a blown film application was used to demonstrate the improvements in melt strength and processing window. This experiment allows for future research to explore other possible applications of PLA blends or other polymer blends.Bachelor of Engineering (Materials Engineering

Improving printability of hydrogel-based bio-inks for thermal inkjet bioprinting applications via saponification and heat treatment processes

Material jetting bioprinting is a highly promising three-dimensional (3D) bioprinting technique that facilitates drop-on-demand (DOD) deposition of biomaterials and cells at pre-defined positions with high precision and resolution. A major challenge that hinders the prevalent use of the material jetting bioprinting technique is due to its limited range of printable hydrogel-based bio-inks. As a proof-of-concept, further modifications were made to gelatin methacrylate (GelMA), a gold-standard bio-ink, to improve its printability in a thermal inkjet bioprinter (HP Inc. D300e Digital Dispenser). A two-step modification process comprising saponification and heat treatment was performed; the GelMA bio-ink was first modified via a saponification process under highly alkali conditions to obtain saponified GelMA (SP-GelMA), followed by heat treatment via an autoclaving process to obtain heat-treated SP-GelMA (HSP-GelMA). The bio-ink modification process was optimized by evaluating the material properties of the GelMA bio-inks via rheological characterization, the bio-ink crosslinking test, nuclear magnetic resonance (NMR) spectroscopy and the material swelling ratio after different numbers of heat treatment cycles (0, 1, 2 and 3 cycles). Lastly, size-exclusion chromatography with multi-angle light scattering (SEC-MALS) was performed to determine the effect of heat treatment on the molecular weight of the bio-inks. In this work, the 4% H2SP-GelMA bio-inks (after 2 heat treatment cycles) demonstrated good printability and biocompatibility (in terms of cell viability and proliferation profile). Furthermore, thermal inkjet bioprinting of the modified hydrogel-based bio-ink (a two-step modification process comprising saponification and heat treatment) via direct/indirect cell patterning is a facile approach for potential fundamental cell-cell and cell-material interaction studies.Submitted/Accepted versionThis study was supported by the RIE2020 Industry Alignment Fund – Industry Collaboration Projects (IAF-ICP) Funding Initiative, as well as cash and in-kind contribution from the industry partner, HP Inc., through the HP-NTU Digital Manufacturing Corporate Lab