Application deadline: 3rd March
Interviews to be held: 31 March 2021
The first semester of this project will be based at the University of Manchester and the remaining duration will be based at the University Sheffield as this CDT is a partnership between the two universities.
Injury to peripheral nerves through trauma, and sometimes surgery, results in over 300,000 cases each year in the EU. In contrast to the central nervous system, proximal motor and sensory axons have some ability to repair. Individuals who sustain injury with no loss of tissue can be treated by directly suturing proximal and distal ends together, as end-end anastomosis. A fundamental understanding of the molecular and cellular responses to injury is essential when designing approaches for repair, especially for implantable nerve guide conduits (NGCs). We have reviewed NGC performance in detail1, with conclusions supporting biomaterials improvements in NGCs a realistic approach (e.g. versus cell therapy). NGCs are typically made from inert biomaterials (e.g. polyesters, collagen), and do not stimulate neuronal or Schwann cell adhesion, migration or differentiation for nerve repair. Consequently, existing devices are poor at supporting regeneration. A major challenge is to increase regeneration distance from a few millimetres to critical gap distances of 10-20 mm. For clinically practical improvement, simple innovations in the biomaterial chemistry, in combination with fabrication methods for making porous and flexible materials to reflect the mechanical properties of nerve are proposed and will be investigated in this project. In this project we also will address the problems of inflammation and scarring associated with nerve repair. Devices will therefore delivery key anti-inflammatories (a-MSH, IL-10) and/or an anti-scarring compound (M6P) known to improve functional repair. Devices will be evaluated in vitro, and in vivo in this PhD project, with a route to following on a clinical study of lingual nerve reconstruction.
Main question to be answered
1. Synthesise PGS blends with controlled degradation rates and mechanical properties as candidate materials for NGCs. The main questions are: a) suitability of PGS as a nerve implant biomaterial and b) value in exploiting soft mechanical properties of PGS for this purpose. PGS has been explored for cardiac patches and for retinal transplantation regeneration, but little to date on nerve repair. We recently published on PGS for supporting neuronal and Schwann cell growth in vitro and nerve repair in vivo, using a 1:1 ratio of glycerol:sebacic acid. This created a flexible polymer with favourable mechanical properties for soft nerve repair (3.2 MPa). PGS will be formulated as a low molecular weight prepolymer, which cross-links to produce a fully cross-linked elastomer (using in house methods2). A range of blend ratios with varying modulus to support the growth of neuronal and Schwann cells will then be investigated. Primary neuronal and Schwann cells will be cultured on surfaces for 4 days to facilitate neurite sprouting, using methods developed in-house (e.g.3) for selection of optimal blends.
2. Fabricate PGS blends to form NGCs by microSL. The main question is on identifying an optimal PGS blend suitable for making NGCs by 3D printing. Optimal blends will be investigated in detail for NGC manufacture. Templates will be built by micro-sterolithography (microSL), which enables accurate and rapid construction of 3D scaffolds to make NGCs. We have published on core methods for PGS NGC manufacture4, and will extend these to investigation of porosity. Dimensions will be fabricated suitable for a critical mouse sciatic nerve 6 mm injury gap (8 mm length x 0.9 mm internal diameter x 250 µm wall thickness).
3. Investigate the problems of inflammation and scarring associated with nerve repair. The main question is whether an increase in inflammation will impede regeneration, and whether local delivery key anti-inflammatories (a-MSH, IL-10) and/or an anti-scarring compound (M6P) will improve functional repair. Acute injury triggers an inflammatory response necessary for early repair, however chronic inflammation is known to be damaging, and can also lead to scar formation. We will therefore combine the scaffold properties of nerve guides, with the therapeutic delivery of a-MSH (a potent anti-inflammatory peptide), IL-10 (an anti-inflammatory cytokine) and/or mannose-6-phosphate (an anti-scarring compound). We have separately published on the roles of a-MSH, IL-10 and M6P as potential therapeutic agents.
4. Evaluate prototype NGCs using a dorsal root ganglion 3D in vitro chick model. The main question is whether the chick dorsal root ganglion model will allow quantitative evaluation of porous constructs and identify optimal devices according to PGS blend and degree of connected porosity. Analysis will be undertaken for devices using an in vitro 3D chick dorsal root ganglion model established in our group (Behbehani et al, 2018). The model uses chick DRGs isolated at embryonic day development 12 (EDD12), and allows axon and Schwann cell migration distance to be determined. Variables in PGS blend and porosity (using a fixed number of optimally aligned fibres) by light sheet microscopy will be undertaken.
5. Evaluate selected NGCs using thy-1 YFP mouse and rat in vivo models. The main question is to identify if an optimal PGS blend and porous density from in vitro selection (above) supports axon regeneration in vivo. In vivo evaluation will be conducted on NGCs using genetically modified mice with a subpopulation of axons that express yellow fluorescent protein (YFP). Studies in our lab using this model allow quantification of axon regeneration across injury sites.3,4 A critical 6 mm sciatic nerve gap injury will be created using a subset of optimally performing devices will be evaluated at 12 weeks following implantation.
EPSRC Centre for Doctoral Training in Advanced Biomedical Materials
This project is part of the EPSRC Centre for Doctoral Training in Advanced Biomedical Materials. All available projects are listed here.
Find out how to apply, with full details on eligibility and funding here.
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