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Crohn's disease (CD) is associated with chronic inflammation in regions throughout the gastrointestinal (GI) tract but is most likely to develop at the end of the small intestine and the first part of the colon. A single massive resection or multiple repeated resections in CD leads to short bowel syndrome (SBS). Therefore, a novel treatment to cure SBS is needed. Poly (vinyl pyrrolidone-methyl methacrylate) hydrogel is chosen as a self-inflating expander device to address the issue of inadequate functional intestinal length in SBS. The hydrogel employs mechanotransduction, wherein mechanical force elongates the intestine and activates cellular mechanisms regulating growth. In this study, the VP/MMA hydrogel was designed by varying the composition ratio of each monomer and size. The ratios of VP to MMA were 95:5wt%, 90:10wt%, and 85:15wt%. The shape of hydrogel was cylindrical with the sizes of 12mmD & 3mmL (A), 6mmD & 3mmL (B), 6mmD & 6mmL (C), 6mmD & 9mmL (D), 3mmD & 3mmL (E). These variables influenced the pore size structure, swelling capacity, swelling force, and mechanical property. Finally, the hydrogel with a composition ratio of 85:15 wt% VP/MMA (VP85) was chosen for ex vivo and in vivo studies. The reason is due to the pressure generated during swelling (77.9 kPa) close to the required stress value to stretch the small intestine (78.9 kPa). Due to the small size of the rat intestine, the 2mmD & 2mmL hydrogel was chosen. A stretched segment of the intestine was found to lengthen 2.5-folds from the original length on days 1 and 7. Histological intestine sample after being stretched using hydrogel showed a significantly greater muscularis thickness, crypt depth and villous height.

An ideal scaffold for the regeneration of valvular tissue should replicate the natural heart valve extracellular matrix (ECM) in terms of microstructure and properties. Tissue engineers have achieved limited success so far in designing an ideal scaffold; scaffolds lack in mechanical compatibility, appropriate degradation rate, and microstructural similarity. This thesis, therefore, is the first attempt to develop interlaced scaffolds from collagen type I and hyaluronic acid (HA), polymers found in the natural valve, via a modified carbodiimide based crosslinking technique. Scanning electron micrographs (SEM) and images of Alcian blue - Periodic acid Schiff (PAS) stained samples suggested that our crosslinking technique yielded an ECM mimicking microstructure with interlaced bands of collagen and HA in the hybrid scaffolds. Hybrid scaffolds also offered a wide range of pore size (66 - 126 μm) which fulfilled the criteria for valvular tissue regeneration. Swelling studies revealed that crosslinking densities of parent networks increased with increasing the concentration of the crosslinking agents whereas crosslinking densities of hybrid scaffolds averaged from those of parent collagen and HA networks. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) showed that this technique could crosslink collagen type I and HA without denaturation. Also, no intermediate phase formation between collagen and HA could be detected. Elastic moduli increased with increasing crosslinking densities, in the dry and wet state, for parent networks whereas those of interlaced scaffolds were higher than either network alone. Compressive, bending, and storage moduli ranged from 35 ± 5 kPa to 95 ± 5 kPa, 154 ± 12 kPa to 1660 ± 7 kPa, and 16 ± 2 kPa to 113 ± 6 kPa respectively in the dry state. Corresponding wet mechanical moduli ranged from 1 ± 0.3 kPa to 5 ± 0.1 kPa, 7 ± 2 kPa to 55 ± 4 kPa, and 2 ± 0.4 to 9 ± 2 respectively. Bending and storage moduli, in the dry state, matched and exceeded those of human aortic valve leaflets (HAVL). Similarly, degradation resistance increased with increasing the crosslinking densities for collagen only and HA only scaffolds. Interlaced scaffolds showed partial degradation in the presence of either collagenase or hyaluronidase as compared to when exposed to both enzymes together. These results agreed with FTIR and SEM that interlaced scaffolds were composed of independent collagen and HA networks without crosslinking between them. Cardiosphere derived cells (CDCs) attached and proliferated on all scaffolds in cell culture experiments as confirmed by AlamarBlue® assay and SEM images. The increase in crosslinking density, however, affected the cell affinity because of the engagement of the cell-attachment sites in the crosslinking process. CDCs seeded scaffolds also showed 50 % increase in bending modulus after 28 days of culture. While evaluated against the criterion for tissue engineered heart valve (TEHV), S-3 and S-4 among interlaced scaffolds/compositions not only matched mechanically but also showed high degradation resistance which potentially made them as 'close-fit' candidates. Findings from this thesis indicated that collagen/HA interlaced scaffolds have the potential to fill in the niche for designing an ideal TEHV. Furthermore, the properties of the interlaced scaffolds, fabricated by our crosslinking technique, can be tailored by controlling the crosslinking density which can also widen the scope of these scaffolds for other tissue engineering applications such as bone, cartilage etc.

Artificial tissue expansion is required to generate new skin prior to reconstructive surgery, in order to compensate for a deficit of healthy tissue. Hydrogel tissue expanders, which expand anisotropically, show great promise in overcoming clinical limitations in the field, thus allowing the technique to be used in a wider range of surgeries. These devices consist of pellets of dry poly(methyl methacrylate-co-vinylpyrrolidone), compressed into discs through a hot compression moulding process. However, a number of significant problems still exist in these devices, and this thesis aims to address these issues. To date, there has been a lack of investigation of the factors governing the behaviour of anisotropic swelling. For this reason, a range of different compression ratios have been investigated, with particular focus on the relationship between the material flow during compression and the swelling behaviour of the resulting device. It was found that samples of the same initial size expand to the same reference swelling dimensions, regardless of compression ratio. During hot pressing, the material flow was found to be governed by slip-stick behaviour at the interface between the hot press and the device, affecting the properties and swelling behaviour of the devices. Based on these findings, devices were developed which could expand from a disc into a non-prismatic shape (dome or wedge). Such devices could reduce complication rates and allow the growth of new tissue with anisotropic resting tension. The devices were tested in a small in vivo trial, where it was shown that there were no adverse effects on the tissue produced, and that the shape of the expander (dome) was retained. As devices are being produced for medical use, understanding the effect of sterilization by γ-irradiation is essential, but to date this has been overlooked in the literature. It was found that γ-irradiation caused an increase in cross-linking in the P(MMA-co-NVP). Whilst this produced little change in swelling behaviour for isotropic devices, in the case of anisotropic devices it caused a change in the shape of expansion, reducing the area of new skin which could be generated by the device. It was found that by reducing the concentration of impurities (residual molecules from the polymer synthesis) the impact of γ-irradiation could be greatly reduced. Finally, controlling the rate of expansion is essential in order to avoid clinical complications. In order to control the rate of expansion, particularly during the initial period of swelling, semi-permeable PDMS coatings were applied to the compressed devices. Coatings of thickness greater than 0.375mm were found to effectively control the rate of swelling, for both cylindrical and non-prismatic shapes. As the coating thickness increased, the maximum swelling size decreased. However, it has been shown that change in height (the parameter which governs the area of skin produced) is affected less than the change in mass or diameter.

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.