Year

2013

Degree Name

Doctor of Philosophy

Department

School of Chemistry

Abstract

Fabrication and characterisation of conducting biomaterials in 3-dimensional configuration for biomedical applications have been studied and is presented in this thesis. Different fibre spinning techniques (wet-spinning and electrospinning) were utilised to create multifunctional fibres to be employed for controlled drug delivery and cellular growth supports. Two different classes of organic conductors, namely conducting polymers and graphene, were utilised to induce and develop electrical and electrochemical features in the fibres for their potential applications in drug delivery and cell growth enhancement via electrical stimulation. Physical, mechanical, electrical, electrochemical and biological characterisations of the fibres were investigated.

In chapter two, Poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) and polypyrrole (Ppy) were utilised in conjugation with chitosan for fabrication of conducting biocompatible fibres using wet-spinning. Then, a layer of Ppy with an antibiotic drug Ciprofloxacin hydrochloride (Cipro) as a dopant for Ppy was produced on the PEDOT:PSS-CHI fibres. The wet-spinning of PEDOT:PSS in a chitosan coagulation bath was successfully carried out and the fibres were shown to have an electrical conductivity of 56 ± 7 S/cm with a modulus and strength of 2.0 ± 0.3 GPa and 99 ± 7 MPa, respectively. The PEDOT:PSS-CHI fibres were subsequently employed as an electrode for the electropolymerisation of Ppy.Cipro on their surfaces. Scanning electron microscopy (SEM) of the fibres showed the morphological differences between PEDOT:PSS and Ppy.Cipro layers, confirming the deposition of the Ppy.Cipro. Cyclic voltammograms of fibres exhibited that the Ppy.Cipro was electroactive and showed an oxidation and reduction peak at +0.2 V and -0.1 V, respectively. The conducting and electroactive fibres were utilised for controlling the release of Cipro using an electrochemical stimulation protocol. The results of electrical stimulation of fibres revealed that Cipro release could be tuned by utilizing the different redox states of PEDOT:PSS-CHI and Ppy.Cipro conducting polymers. The in vitro antibacterial studies on the fibres and released Cipro demonstrated that the drug did not lose its antibacterial property during electropolymerisation and electrochemically stimulated release processes. In vitro fluorescent staining images revealed that the fibres were not cytotoxic to B35 neuroblastoma cells, however, the cells tended to cluster together rather than attach to the fibres. Moreover, the results of a lactate dehydrogenase (LDH) test revealed that the Cipro concentrations released in this study did not have an adverse effect on B35 neural cell.

In chapter three, the development of a novel and facile system of wet-electrospinning (combined electrospinning and wet-spinning) is presented. This new method was developed in order to improve the attachment behaviour of B35 neuroblastoma cells on wet-spun fibres containing conducting polymers. The process of fibre fabrication consists of simultaneously wet-spinning and electrospinning to form a structure composing of micro-size wet-spun fibres coated in nano-sized electrospun fibres. The new fibre configuration demonstrated increased B35 neuroblastoma cell attachment as well as promising electrochemical property. Extended electrospinning times resulted in a thick coating of poly(D,L-lactic-co-glycolic acid) (PLGA) around the PEDOT:PSS-CHIT fibres which hindered the electroactivity of this conducting inner core. This was attributed to the thick PLGA coating blocking any ions from solution interacting with the PEDOT:PSS. This result had implications on the ability to use these particular fibres in electrical stimulation experiments, and therefore shorter electrospinning times were investigated. Additionally, the release of Cipro from PLGA electrospun fibres has shown the potential of the fibres in drug delivery applications.

In chapter four, fabrication and characterisation of graphene as an organic conductor in a wet-spun composite fibres structure was studied to induce and develop electrical conductivity and electrochemical activity in the fibres. The graphene dispersion exfoliated in N-Cyclohexyl-2-pyrrolidone (CHP) exhibited dispersion stability over an extended period of time. The free-standing graphene paper fabricated from the dispersion (thickness between 5.0 to 100 μm) demonstrated well-defined layered morphology of graphene. The TEM characterisations of CHP-exfoliated graphene showed that the graphene dispersion consisted of monolayer and few layers of graphene. Additionally, the blend of PLGA with graphene was fabricated using a wet-spinning system. The rheological characterisation of wet-spinning solutions showed that a concentration of 1.5 wt. % PLGA and above, dissolved in 5 mg/ml graphene dispersion in CHP, can provide viscosity of ≥ 0.023 Pa s which was found to be spinnable. The wet-spinning of graphene with the biocompatible PLGA was carried out successfully with the fibres demonstrating an electrical conductivity of 1.5 S/cm. The PLGA-graphene fibre showed electroactivity in phosphate buffered saline (PBS) when tested by cyclic voltammetry. The electrical conductivity measurements showed that, once the graphene content was greater than 11.1 wt. % (with respect to PLGA), electrical conductivity increased above the percolation threshold (~30 S/m) and increased to 150 S/m when the graphene content was 24.3 wt. %. The cytocompatibility tests and cryo-SEM images showed that C2C12 myoblast cells were metabolically active on the fibres and attached along the length of the fibres. Furthermore, the proliferation assessment over 72 hr on the fibres revealed that C2C12 cells proliferated along the fibres.

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