Year

2019

Degree Name

Master of Philosophy

Department

Intelligent Polymer Research Institute

Abstract

The ability to synthesise biomaterials of academic, clinical, and industrial significance remains a central goal of 3D-bioprinting. Substantial efforts by researchers have been made in the field of biofabrication to develop new bioinks capable of closely mimicking specific human tissue(s). The most common being the complex protein collagen, which undergoes spontaneous self-assembly into a fibrilar structure providing: the high tensile strength for bone, the basis for muscle contractions, and the high transparency of the stroma layer found within the cornea. Translating these natural architectural features into a biomimetic scaffold remains a significant challenge. Herein, the development of a microfluidic system capable of guiding the electrostatic complexation of methacrylated gellan gum (a polyanion), and chitosan (a polycation), through microfluidic channels to form highly aligned fibre bundles in a spatially controlled manner. Through the development of an ad hoc 3D-bioprinter, biomimetic fibre bundles that replicate the self-assembly and hierarchy of natural collagen fibres down at the microscale have been achieved. The topography and morphology of the fabricated fibre bundles were evaluated via scanning electron microscopy (SEM). Extruded polyelectrolyte fibre bundles were shown to have a diameter in the range of 10-1000 μm and each individual fibre has shown to be approximately 1-2 μm. These diameters are consistent with collagen fibres found within the human body. Moreover, the developed printable ‘ink’ can be customised in terms of its printability and mechanical properties to better achieve specific target tissue(s) by means of a microfluidic approach. The introduction of a UV light source (via LEDs) mounted in close proximity to the micro-channels and therefore to the photoinitiator (Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP)), was shown to stabilise the hydrogel via chemical crosslinking of the methacrylate groups. A wavelength of 395 nm for the LED light sources was selected and experimentally shown to penetrate through the microfluidic device walls and enable crosslinking of the material during extrusion. Moreover, the established results show that upon polyelectrolyte complexation, the resulting fibre diameter was significantly influenced by the flow rate. Considering the fundamental substance of the stroma, mechanical testing showed robust mechanical properties with a tensile strength range of ~1 MPa at a single fibre bundle level. Furthermore, this biomimetically-aligned fibrous hydrogel system has been shown as a viable substrate for scaffold creation and potential to access tissues of interest, such as nerves and muscles.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.