Extracellular matrix mimetic multi-functional scaffolds for tissue engineering and biomedical applications

Sammanfattning: Regeneration of functional tissues or complex organs via the combination of viable cells, biomimetic scaffolds, morphogenic factors, and external biophysical cues are the principle aims of Tissue Engineering (TE). TE relies on the use of artificial 3D scaffolds that can mimic the microenvironment of native tissue to harness the regenerative potential of cells. The 3D scaffold provides an appropriate structural and functional support to foster the dynamic interplay of cells and signalling molecules to facilitate the formation of functional tissue. Taking inspiration from the multi-component and multi-functional role of native extracellular matrices (ECM), scaffold engineering provides a platform to understand and integrate the critical features from micro to macro scale necessary for repair and regeneration of tissues. Scaffold engineering also enables the interconnection of TE with its sub-disciplines such as drug delivery, in vitro disease modelling, biosensors or surgical science etc., by designing appropriate multi-functional scaffolds suitable for target specific applications.This thesis, addresses existing challenges to manipulate and customise ECM mimicking scaffolds and approaches to overcome these problems, by emphasising the importance of biomaterial design that can emulate the native ECM and potentially be tuned for tissue specific applications. Type I Collagen was functionalised with reactive methacrylate groups without altering its native triple helical structure. Methacrylated collagen (MAC) was further used as a functional building block to fabricate tuneable multifunctional scaffolds using bio-orthogonal thiol-Michael addition click chemistry by optimising several biophysical and biochemical parameters. This method provides the flexibility needed to fabricate injectable and implantable scaffolds based on the same functional components by tuning the modulus from Pa to kPa, thus rendering scaffolds suitable for use for either soft or hard tissues. The versatility of the scaffolds was evaluated by using it as pre-fabricated substrate for human corneal epithelial cells and as an injectable scaffold encapsulated with cardiac progenitor cells.The potential of MAC serving as a building block for engineering tailored made ECM mimetic scaffolds was further demonstrated by fabricating smart multi-functional stimuliresponsive scaffolds and conductive scaffolds using a free-radical co-polymerisation technique by choosing appropriate counterparts (polymers). The co-polymerisation of MAC and N-isopropyl acrylamide (NIPAm) formed an in situ, fast gellable, dual responsive (temp and pH) hydrogel comprising covalently linked networks of collagen and thermoresponsive NIPAm polymer. The multi-functionality of these hydrogels was demonstrated as an in-situ depot-forming tunable delivery platform for proteins and small drugs and as a structural support for human skeletal muscle cells. Pyrrole as a monomer was co-polymerised with MAC resulting in MAC-polypyrrole conductive hydrogel scaffold. The utility of ECM mimetic injectable conductive hydrogel scaffold was explored as a long-term continuous glucose-monitoring sensor under physiological conditions.Further, to overcome several challenges of Collagen such as inconsistent batch-tobatch reproducibility, risk of disease transmission, stability etc., a collagen-like-peptide (CLP) scaffold was designed as an alternative to collagen. This thesis demonstrates the use of Flexible Template Assisted Self-Assembly (TASS) of CLPs to mimic higher order collagen triple helical assembly by conjugating 38 amino acid length CLP with a multi-arm PEG maleimide template. 8-armPEG conjugated CLP (PEG-CLP) was used to fabricate robust hydrogel scaffolds using carbodiimide chemistry. The biocompatibility and potential of CLP scaffolds as an alternative to collagen was demonstrated by implanting it in mini pigs using corneal transplantation as a test bed. The bottom up-approach to assemble ECM mimetic functional peptides also allows us to design or manipulate CLPs with other bioactive motifs such as RGD or IKVAV to promote specific cell activities suitable for specific tissue regeneration.Overall, this thesis provides a modular platform to engineer multi-functional tunable ECM scaffolds based on type I Collagen and collagen-like peptides that combines multiple structural and bio-functional features for wide range of tissue engineering applications.