Doctor of Philosophy
Intelligent Polymer Research Institute
Mirabedini, Azadeh, Developing novel spinning methods to fabricate continuous multifunctional fibres for bioapplications, Doctor of Philosophy thesis, Intelligent Polymer Research Institute, University of Wollongong, 2017. http://ro.uow.edu.au/theses1/6
Developmental work in the field of multifunctional hybrid fibres has revealed a number of characteristics that promise great benefits to their possible use in a broad range of devices and applications including tissue scaffolds and implantable electrodes as well as the accessory energy storage devices necessary to provide power to implantable devices and smart garments. There has, therefore, been much interest and many attempts to produce lightweight, foldable and electroactive multiaxial fibres. The main aim of this thesis is to establish a wet-spinning process to develop three-dimensional coaxial and triaxial electroactive fibres. Using a coaxial wet-spinning method that takes advantage of the electroactivity inherent in a conductive core, we also aim to improve the fibres’ mechanical, biocompatibility and cell adhesion properties by using an appropriate biomaterial for the surrounding sheath, opening up the possibility for its use in many biomedical applications. Although some success has been achieved via the use of either electrospinning or coating approaches, only a few studies have reported the successful fabrication of either coaxial or triaxial fibres via novel application of wet-spinning methodology to the best knowledge of the author. This poor rate of success may be due to the complexity of this method in terms of the number of concurrent solution and processing parameters that need to be optimised and controlled in order to achieve the successful (and consistent) formation of a core-sheath structure in a coagulation bath. Wet-spinning has the advantage that it produces individual, collectable fibres that can be drawn out and tested for their mechanical properties. Electrospinning can produce extremely fine fibres in the form of a non-woven mat; however, the mechanical testing of individual fibres is not feasible. There have been also reported on difficulties involved with preparation of fibres using already charged polymer backbones via electrospinning wherein a stable jet cannot be achieved and no nanofibres will form, although single droplets may be achieved (electrospray). In addition to this, there is a limitation in choosing the maximum concentration for a given solution by which it could flow. Consequently, the molecular weight and the concentration as long as a solvent with the necessary volatility which can be spun this way, are within a certain range. Thus, although this method shows a lot of promise, these restrictions are placed on the spinnability of certain polymers by solution parameters like viscosity and surface charging.
As a result of this research, the production of continuous core sheath fibres has been achieved using a variety of materials. Hydrogels have been used as the sheath components since they provide mechanical and structural properties that mimic many tissues and their extracellular matrix. Organic conductors such as graphene and intrinsically conducting polymers have been useful in the creation of electrical pathways within the inner core where they are able to provide safe electrical stimulation of the surrounding tissue – enhancing the electro-cellular communication process - whilst also avoiding undesirable chemical reactions and cell damage.