Year

2020

Degree Name

Master of Philosophy

Department

Intelligent Polymer Research Institute

Abstract

Melt electrowriting (MEW) is an additive manufacturing technique that combines the advantages of both, solution electrospinning and fused filament fabrication by allowing the deposition of ultra-fine fibres in a controlled way without the necessity for dispersion of the material being prepared in toxic solvents. This approach is promising for the research field of tissue engineering that requires not only different types of materials but also different manufacturing techniques for scaffolds that are supposed to provide robust but flexible support, which facilitates cell growth without causing damage to the surrounding tissue.

Recent advances in MEW technology (Mar 2018) that allow the processing through coaxial extrusion geometries are examined in the context of composite materials and their possible application as for example drug delivery systems. In this study, poly(ε-caprolactone) (PCL) containing different percentages of different fluorophores was prepared using a precipitation process. The resulting composites were printed uniaxially as a means to investigate the effects of the added salts and the emerging additional charges on the jet. It was shown that the acceleration of the jet was increased with an increasing fluorophore loading, which could be seen in the resulting critical translation speeds.

The uniaxial investigation was also important to validate the thermal stabilities for the dyes, which were used in the coaxial process. For the latter, DiOC18 and Rhodamine B were chosen because of their stability as well as their compatibility with PCL and each other. The feasibility of core-shell structures was examined by varying process and material parameters. Amongst other things, the green and red dyed polymers were processed through the inner and the outer syringe in order to get a clear distinction between the core and the shell. While these structures were observed occasionally using confocal laser scanning microscopy, they were found to be unstable due to diffusion and mixing at the Taylor cone during the MEW process. The in-process-mixing of the materials can be of interest for the application-specific compounding of heat- and strain-sensitive polymers while having control over their composition depending on the chosen flow rates. Janus fibres were also shown possible through adjustment of the axial location of the core syringe used, although mixing of the polymer prior to solidification affected this effect. Nevertheless, MEW is a technique with a vast amount of possible parameter combinations. Hence, the production of core-shell and Janus fibres is shown possible and offers a variety of applications such as in microelectromechanical and drug delivery systems as well as robotics. When applying air through the core syringe, the insertion of air into the melt leading to hollow channels in the fibres was shown feasible and reproducible. This technique offers the printing of fibres with outer diameters as big as 90 μm while containing a 25 μm cavity, as well as fibres with an outer and inner diameter of 10 and 2 μm, respectively. While the production of hollow fibres usually demands for a fabrication of core-shell structures first with a later dissolving of the core material, the coaxial MEW of hollow fibres is a one-step approach that works without toxic solvents. Furthermore, it enables the fabrication of structures that are known to be lighter while having improved mechanical properties compared to dense materials, hence offering a wide spectrum of applications such as in regenerative medicine and microfluidics.

FoR codes (2020)

400301 Biofabrication, 401401 Additive manufacturing

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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.