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Title: Surface chemical modification of PCL films for peripheral nerve repair
Author: De Luca, Alba Carla
ISNI:       0000 0004 2733 9397
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2012
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Nerve injury is a very common trauma affecting 300,000 people in Europe every year. Although autografts are currently the gold standard in surgery, they can cause loss of sensation and scar tissue formation. Artificial nerve conduits are a valid alternative for peripheral nerve repair. They can provide a confined environment during the regeneration process, enabling axons sprouting from the proximal to the distal nerve segments as well as reducing scar tissue formation. Poly-e-caprolactone (PCL) is a biocompatible and biodegradable polymer suitable for the fabrication of nerve guidances. In particular, previous works demonstrated that neural cells are able to adhere and proliferate on micropitted PCL films obtained through solvent casting. Also, short term studies showed that axons were able to bridge 1cm injury gap. In this work a 18 weeks long term in vivo experiment using a rat model was performed to investigate the reinnervation of end organ skin and muscle. PCL conduits were compared to autografts, with no significant differences in terms of regeneration and reinnervation. However, Schwann cells (SCs), the most important glial cells in the peripheral nervous system, showed poor attachment in vitro on PCL scaffolds; hence, surface modification was carried out in order to improve the material biocompatibility. The effect of both hydrophilicity and functional groups on SCs was first investigated. PCL films were then hydrolysed and aminolysed to modify the surface with carboxylic and amino groups respectively. Hydrolysed films increased remarkably the surface hydrophilicity, although topography and mechanical properties were not affected. Conversely, the tensile modulus and strength were significantly reduced by aminolysis, but still suitable for the desired application. The two treatments influenced also the morphology of SCs. It was demonstrated that cell elongation was induced by hydrophilic surfaces, whilst cells preferred cell-cell interaction when cultured on aminolysed films. However, cell proliferation was remarkably increased on the latter surfaces, confirming previous results obtained on substrates characterised by amino groups. These results confirmed that a good balance between hydophilicity and surface chemistry is necessary to guarantee the best cell response. In order to enhance both proliferation and morphology of SCs, arg-gly-asp (RGD) sequences were immobilised on the PCL film surface using two different reaction mechanisms. Carbodiimide chemistry was compared to a new mechanism developed in the present study based on the Thiol chemistry. Biological tests performed on these modified films demonstrated the improvement of SC response after the peptide immobilisation using the novel approach. Cell attachment and proliferation were three times higher compared to untreated PCL films. It was also observed that the presence of peptides on the film surface induced the formation of focal adhesion plaques by SCs, important for the perception of cellular signals when in contact with a particular substrate. Hence, a good balance between focal adhesion and adhesion forces was achieved after peptide immobilisation. Overall the results of this study showed that material functionalisation is very important for SC response and it will be fundamental for the production of artificial nerve conduits.
Supervisor: Terenghi, Giorgio; Downes, Sandra Sponsor: Newby Trust Ltd
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Polycaprolactone ; Peripheral nerve repair ; Surface modification ; Peptide functionalisation