title: Multi-scale Structural and Mechanical Investigations on Diseased Mineralised Tissues
Creators: name: Bohns, Fabio
Publisher: name: University of Liverpool Repository
Year: 2024

description: Bone is a multi-functional material that protect our organs, sustain our body weight and produce skeletal cells. Osteoporosis and osteogenesis imperfecta are chronic and genetic bone diseases, respectively, that share a phenotype of bone fragility. Bone fracture is an important subject for discussion due to the economic burden that it causes across all ages, but especially in the elderly. In order to minimise the negative consequences of bone diseases, a series of medical recommendations should be followed; they involve the intake of anti-resorptive drugs (i.e., alendronate) and maintaining an active and healthy routine. Despite the advances in the understanding of osteoporosis and osteogenesis imperfecta, some underlying mechanisms of bone fragility and its relationship with bone morphometrics (e.g., mineral density and bone volume), remain unanswered. To further the knowledge on bone diseases, animal models have been proposed.
Zebrafish are small teleost fish that the bones have shown high conservation with those of human. These fish are able to regenerate parts of their body, like caudal fin, contributing to the 3Rs (Reduction, Replacement and Refinement) in animal research by, for example, reducing the number of rodents in research. Because of this, zebrafish have been used for the exacerbation of clinical bone conditions such as glucocorticoid-induced osteoporosis. Osteogenesis imperfecta murine is a spontaneous mutation of mild-to-severe cases of osteogenesis imperfecta. These mice show deformed skeleton and brittle bones. These mice have been used to evaluate effects of collagen defects in bone properties. In this study, a series of structural and mechanical analysis were used in zebrafish and murine models to establish a relationship between poor mechanical properties caused by bone diseases and parameters used to measure bone quality.
The potential of zebrafish to regenerate their amputated caudal fins was used to explore the effects of osteoporosis and alendronate on the mineralisation of the fin bony rays. Diseased fish displayed a slower bone formation than controls; fish treated with alendronate showed increased bone formation than both groups. Similarly, the reduced elastic modulus and hardness levels were decreased in osteoporotic bones (5.60 ± 5.04 GPa and 0.12 ± 0.17 GPa, respectively), whereas alendronate recovered them to the pre-amputation condition (8.68 ± 8.74 GPa and 0.34 ± 0.47 GPa, respectively). Prednisolone and alendronate effects on zebrafish vertebrae were exacerbated by the reduction of the bone-mineral density and recuperation of hardness to controls levels. In the osteogenesis imperfecta model, the misfolding of α2 chains (homozygous) produced bones with decreased biomechanics at early age.
Zebrafish showed that osteoporosis is exacerbated by hampered mineral formation (fin bony rays), reduced hardness (fin bony rays and vertebrae) and reduction of bone-mineral density (vertebrae). In murine models, the biomechanical properties increased with age, demonstrating that low elastic modulus and hardness, and high creep rates at young ages may play key role in osteogenesis imperfecta phenotype. The techniques applied in this thesis have potential, in the future, to be applied in humans to better understand osteoporosis and osteogenesis imperfecta.