Development of novel hydrogel composites for bioprinting and engineering of thick tissues
Date of Issue2018-01-22
School of Mechanical and Aerospace Engineering
Nanyang Technological University
Tissue engineering (TE) is a technology that combines life sciences and engineering knowledge to restore and replace the functionality of impaired tissues and organs. However, the research work for tissue engineering has achieved limited success in engineering thick tissues. The goal of this work is to address two issues encountered in current technologies when creating 3D thick tissue structures. The major issue is vascularization or creating a 3D complex perfusable vasculature structure. Recently, an emerging solution is 3D bioprinting, a technology that integrates cells and bioinks (biomaterials) with an automated fabrication system such as a bioprinter. In 3D bioprinting, hydrogel, which is biocompatible with cells, is usually used as a cell carrier or bioink. However, most of hydrogels that have good biocompatibility have low printability or low mechanical strength. To solve this problem, a novel hydrogel composite has been developed which is both biocompatible and bioprintable. Separately, another issue in engineering thick tissues is the convenience in transfer and assembly of individual high cell density constructs such as cell laden hydrogels or cell sheets. In this research, another hydrogel composite, a biodegradable membrane modified with collagen gel has been developed to address this issue. A large part of this thesis focuses on the synthesis, characterization, 3D printing and modelling of a novel hydrogel composite - Pluronic-Gelatin methacrylate (Plu-GelMA). Pluronic needs to be modified into pluronic monocarboxylate (Plu-MP) before it can physically interact with GelMA. After synthesis, the Plu-GelMA hydrogel composites at different mass ratio are studied. A series of characterization have been performed, including chemical tests (NMR and FTIR), mechanical tests (compression and tensile test), rheological test, physical tests (morphology and microstructure analysis, water swelling properties, perfusion test and diffusion test), printability test and biological test (live/dead staining, Prestoblue and immunohistology). The results show that at the mass ratio 2:1 of PluMP:GelMA, the composite has the best printability and biocompatibility. Moreover, based on immunohistology results, this hydrogel composite is able to support HUVECs differentiation, evidenced by the expression of two endothelial cell markers. Thus, this hydrogel composite can serve as a new bioink to create 3D complex structures that can mimic vascular branches and could be a potential solution to the vascularization problem. A second part of this thesis investigates solvent-free membrane fabrication and membrane surface modification for application of an intermediate cell carrier for transfer and assembly of cell-laden hydrogels and cell sheets. Briefly, a layer of polymer particles is directly spread on top of water to form surface suspension. After that, with the use of heat, a solid powder layer transforms into a melted layer and a porous thin membrane can be obtained after cooling. Membrane characterization is separated into two parts. The first part focuses on the physical characteristics of membrane such as thickness, surface roughness, mechanical strength, pore size and porosity. The second part of the experiment investigates chemical properties and surface modification. The L929 in vitro cell compatibility study on the modified membrane shows good cell attachment and proliferation.