Functionalised self-assembled peptide hydrogel for cell transplantation

Abstract

Cell transplantation has provided a novel approach for the treatment of brain disorders due to its inherent ability to introduce replacement cells for tissue regeneration. The direct injection of the grafted cells via syringe administration represents the current administration strategy for deployment within the central nervous system (CNS). Successful cell transplantation is dependent on two phases: the initial survival of grafted cells, and the integration of the transplanted cells with the host neural circuitry. However, to date, the efficacy of cell transplantation for CNS repair is inadequate due to poor cell survival, not only initially caused by high shear forces acting on the suspension, but also compounded in the long term by the presence of a protracted immune/inflammatory response. These limitations highlight the need for alternative strategies to improve cell survival during administration, whilst also attenuating the immune/inflammatory response post administration. Here, we present novel bioactive functionalised self-assembly peptides (SAPs), demonstrating their inherent ability to form a shear-thinning and protective scaffold during administration. Post-injection, our biomaterials have been functionalised to provide relevant biologically active motifs. These motifs can replicate features of the native cellular microenvironment of the brain and present a mechanistic understanding for the increased cell survival of transplanted cells administered within our hydrogel. With further functionalisation, we have developed a multifaceted anti-inflammatory hydrogel delivery system by the co-assembly of the anti-inflammatory macromolecule, fucoidan, into SAPs. Using this system, we have demonstrated the attenuation of the size of primary glial scar to half that of a stab injury(control), with increased organisation of astrocytes with fewer hypertrophic and intertwined processes within the scar, and a change of morphology to a cytotrophilic phenotype. This is essential to successful cell transplantation to promote the long-term survival and integration of transplanted cells, and to attenuate confounding issues associated with iatrogenic injury. To further improve the survival, differentiation, and maturation of transplanted cells post administration, we have developed a composite scaffold, incorporating electrospun short fires (SFs) with our novel SAP hydrogel matrix, demonstrating its potential for the temporally and spatially controlled drug delivery. Both SFs and SAPs were loaded with growth factors, providing distinct growth factor delivery profiles essential for the initial protection of vulnerable transplanted cells and subsequently promoting their long-term survival and integration. These materials resulted in the stabilisation of the growth factor in vivo and promote the cell integration in both animal models of Parkinson's disease (PD) and ischemic stroke. This thesis reports the rational design and functionalisation of fluorenylmethyloxycarbonyl-self-assembled peptide (Fmoc‐SAP) scaffolds for cell transplantation, demonstrating their ability to significantly improve cell survival, whilst concomitantly providing a growth-permissive environment. Added to this, when the spatial and temporally controlled growth factor delivery was engineered into our novel materials, we have demonstrated the efficacy of our strategy in both PD and stroke models.