Degenerative disorders of the rotator cuff tendons account for nearly 75% of all shoulder pain, causing considerable pain and morbidity. Given the strong correlation between age and tendinopathy, and unprecedented population aging, these disorders will become increasingly prevalent. Improved understanding of tendon degeneration will guide the development of future diagnostic and treatments, and is therefore urgently needed. However, the aetiology and pathology of rotator cuff tendinopathy remain unclear. The complicated mechanical environment of the rotator cuff is hypothesised to influence the susceptibility of the tendons to degeneration and tearing. Studies have reported biological adaptations in torn cuff tendons indicative of increased compressive loading within the tendon. The material adaptations of healthy and degenerative cuff tendons are largely unreported but will provide further insight into the role of the mechanical environment in rotator cuff aetiology and pathology. This thesis examined the material adaptations of healthy and diseased tendons to explore the role of mechanical loading in rotator cuff pathology. The material adaptations of healthy animal tendons, and healthy and delaminated human cadaveric rotator cuff tendons, in response to different loading environments were characterised. The effects of age, tears, steroid injection and subacromial decompression surgery on the structural adaptations of human cuff tendons were also studied, as was the effect of tendon cell proliferation on the mechanical properties and degradation behaviour of collagen scaffolds. Loading environment significantly affected the structural adaptations of healthy tendons. Regions exposed to compressive and shear strains exhibited thinner fibres, shorter crimp lengths and thinner, less aligned fibrils compared with regions exposed to tensile strains alone. In healthy rotator cuff tendons, the inhomogeneous loading environment produced topographically inhomogeneous structural adaptations. The tendons of a delaminated rotator cuff exhibited less topographical variation in properties and thinner, less aligned fibrils compared with healthy cuff tendons. Torn cuff tendons exhibited thinner fibrils and shorter crimp lengths compared with control samples. These adaptations were identifiable early in the disease progression, and neither steroid injection nor subacromial decompression surgery significantly influenced these adaptations at seven weeks post‐treatment. Significant correlations between decreasing dimensions and increasing tear size were found when age was included as a confounding factor, reflecting the importance of age and tear size in determining the material properties of tendons. Tendon cell proliferation influenced the mechanical properties and degradation behaviour of the collagen scaffolds, emphasising the integral role of cells in the functional adaptation of biological materials. These results demonstrate the effect of mechanical environment on the material adaptations of tendons. They also indicate the importance of the complicated mechanical environment experienced by the rotator cuff tendons in predisposing the tendons to degeneration and tearing. The observed material adaptations of degenerative and torn tendons suggest that rotator cuff pathology is associated with increased levels of compressive and/or shear strains within the tendon. These changes begin early in the disease progression and neither steroid injection nor sub‐acromial decompression surgery are capable of reversing the changes in the timeframe investigated. These findings highlight the urgent clinical need for pre‐rupture diagnostic techniques for the detection of early pathological changes in the rotator cuff. They also emphasize the requirement for new intervention strategies that restore the healthy mechanical environment and reverse early pathological adaptations in order to prevent catastrophic failure of the tendons.

Since current prosthetic heart valve replacements are costly, cause medical complications, and lack the ability to regenerate, tissue-engineered heart valves are an attractive alternative. These could provide an unlimited supply of immunological-tolerated biological substitutes, which respond to patients' physiological condition and grow with them. Since collagen is a major extra cellular matrix component of the heart valve, it is ideal material for constructing scaffolds. Collagen sources have been shown to influence the manufacturing of collagen scaffolds, and two commercial sources of collagen were obtained from Sigma Aldrich and Devro PLC for comparison. Consistencies between the collagens were shown in the primary and secondary structures of the collagen, while inconsistencies were shown at the tertiary level, when a higher level of natural crosslinking in the Sigma collagen and longer polymer chains in the Devro collagen were observed. These variations were reduced and the consistency increased by introducing crosslinking via dehydrothermal treatment (DHT). Collagen scaffolds produced via freeze-drying (FD) and critical point-drying with cross-linking via DHT or 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide /N-hydroxysuccinimide (EDC/NHS) were investigated. All the scaffolds were compatible with mesenchymal stem cells (MSCs) according to the proliferation of the cells and their ability to produce ECM, without differentiating between osteogenic, chondrogenic or endothelial lineages. The FD EDC/NHS scaffold demonstrated the most suitable physical property of all. This result illustrates that FD EDC/NHS crosslinking is the most suitable scaffold investigated as a start for heart valve tissue engineering. To prepare a scaffold with a controlled local, spatial and temporal delivery of growth factor, a composite scaffold comprising poly (lactic-co-glycolic acid) (PLGA) microspheres was developed. This composite scaffold demonstrated the same compatibility to the MSCs as untreated scaffold. However, the PLGA microspheres showed an increase in the deterioration rate of Young's modulus because of the detachment of the microspheres from the scaffold via cellular degradation.

Tissue engineers – in order to develop therapies for the treatment of complex neurological injuries and diseases – attempt to recreate elaborate developmental mechanisms in vitro. Neuronal precursor cells are excellent candidates for the study of developmental operations such as cell adhesion, differentiation, and axonal pathfinding. Hyaluronan (HA) is a common polysaccharide that is found extensively throughout the neuronal extracellular matrix (ECM), and can be functionalised and crosslinked to form stable hydrogels that support growing neuronal cells. Hyaluronan hydrogels can be modified chemically and mechanically to mimic the ECM of the developing brain, awarding control over mechanisms such as differentiation and axonal pathfinding. This thesis is concerned with the functionalisation and characterisation of HA hydrogels, ultimately in order to simulate vital properties of the developing brain. Here we show that HA hydrogels can be finely tuned mechanically (by modulating stiffness and viscosity), and chemically, by the conjugation of peptides that mimic the neural cell adhesion molecule (NCAM). NCAM mimics and novel mimics of sialylated NCAM significantly influence the differentiation of NSPCs in 2D and 3D. HA hydrogels successfully support long term culture of neural cells in 3D, and encourage the formation and extension of neurites of several cell types including human, mouse and rat neuronal precursor and stem cells. These results demonstrate for the first time that novel NCAM mimicking peptides can be conjugated to well defined hydrogel matrices that influence intricate developmental behaviours in 3D. Understanding how neural cells form functional networks is essential for the development of clinical approaches that attempt to address the injuries and diseases that affect these systems.