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Incorporation of Surfactants into Electrospun Scaffolds for Improved Bone Tissue Engineering Applications

Coverdale, Benjamin David Miles

[Thesis]. Manchester, UK: The University of Manchester; 2016.

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Abstract

Electrospinning is a process by which micro and nanofibrous scaffolds can be easily fabricated to mimic structures such as the extracellular matrix of bone. A number of materials have been used to fabricate such scaffolds making the process an extremely versatile tool in the field of bone tissue engineering. Many scaffolds however are hydrophobic, leading to poor cellular attachment and proliferation, whilst the actual process of electrospinning is highly variable, producing irregular scaffolds that can ultimately influence cell invasion and differentiation.The focus of this thesis was to address the issues of poor biocompatibility and irregular scaffold production in three commonly used polymers each with different mechanical properties and degradation profiles. Poly (ε-caprolactone) (PCL), polyethylene terephthalate (PET) and poly lactic-co-glycolic acid (PLGA) were functionalised with surfactants in order to improve the biocompatibility and osteoinductive properties of electrospun scaffolds, whilst electrospinning equipment was modified to improve uniformity of scaffold production.Reducing variables known to affect scaffold formation such as temperature and humidity through the use of an environmental stability cabinet improved the reproducibility of scaffolds. The introduction of a Faraday cage, a larger electrode and a negative mandrel potential also improved the quality and quantity of electrospun fibres collected.Lecithin was selected as an appropriate additive for both improving biocompatibility and uniformity of electrospun fibres as it is naturally occurring and induced dose dependent reductions in water contact angle, allowing tailored hydrophobicity. Through gravimetric determination of pore sizes coupled with mathematical modelling, the addition of lecithin was found to reduce both mean fibre diameter and pore size in all scaffolds, improving scaffold homogeneity.At low concentrations (i.e. 2 %) lecithin generally did not affect the mechanical properties of scaffolds, however significant improvements in tensile strength for PCL and nanoindentation for PET were evident, indicating these scaffolds remained suitably strong for bone regeneration purposes.Reduced hydrophobicity acted to improve cellular attachment of Saos-2 osteoblasts to polymers, whilst proliferation on all scaffolds was similar to TCP controls. Furthermore, lecithin incorporation induced osteoinduction, as bone marrow mesenchymal stem cells seeded on these hybrid scaffolds expressed upregulated gene expression for alkaline phosphatase, collagen 1, osteocalcin and osteopontin.In conclusion, these scaffolds, functionalised with lecithin, improve the homogeneity of fibrous mats allowing increased reproducibility and efficiency of the electrospinning process. Furthermore, the improved biocompatibility and osteoinductivity that lecithin presents, allows for the production of more suitable electrospun scaffolds in the field of bone tissue engineering.