Articular joints are comprised of different tissues, including cartilage and bone, with distinctive structural and mechanical properties. Joint homeostasis depends on mechanical and biological integrity of these components and signaling exchanges between them. Chondrocytes and osteocytes actively sense, integrate, and convert mechanical forces into biochemical signals in cartilage and bone, respectively. The osteochondral interface between the bone and cartilage allows these tissues to communicate with each other and exchange signaling and nutritional molecules, and by that ensure an integrated response to mechanical stimuli. It is currently not well known how molecules are transported between these tissues. Measuring molecular transport in vivo is highly desirable for tracking cartilage degeneration and osteoarthritis progression. Since transport of contrast agents, which are used for joint imaging, also depend on diffusion through the cartilage extracellular matrix, contrast agent enhanced imaging may provide a high resolution, non-invasive method for investigating molecular transport in the osteochondral unit. Only a few techniques have been developed to track molecular transport at the osteochondral interface, and there appear opportunities for development in this field. This review will describe current knowledge of the molecular interactions and transport in the osteochondral interface and discuss the potential of using contrast agents for investigating molecular transport and structural changes of the joint.
Osteoarthritis (OA) is a chronic joint disease that causes disability and pain. The osteochondral interface is a gradient tissue region that plays a significant role in maintaining joint health. It has been shown that during OA, increased neoangiogenesis creates porous channels at the osteochondral interface allowing the transport of molecules related to OA. Importantly, the connection between these porous channels and the early stages of OA development is still not fully understood. Microcomputed tomography (microCT) offers the ability to image the porous channels at the osteochondral interface, however, a contrast agent is necessary to delineate the different X‐ray attenuations of the tissues. In this study BaYbF5‐SiO2 nanoparticles are synthesized and optimized as a microCT contrast agent to obtain an appropriate contrast attenuation for subsequent segmentation of structures of interest, that is, porous channels, and mouse subchondral bone. For this purpose, BaYbF5 nanoparticles were synthesized and coated with a biocompatible silica shell (SiO2). The optimized BaYbF5‐SiO2 27 nm nanoparticles exhibited the highest average microCT attenuation among the biocompatible nanoparticles tested. The BaYbF5‐SiO2 27 nm nanoparticles increased the mean X‐ray attenuation of structures of interest, for example, porous channel models and mouse subchondral bone. The BaYbF5‐SiO2 contrast attenuation was steady after diffusion into mouse subchondral bone. In this study, we obtained for the first time, the average microCT attenuation of the BaYbF5‐SiO2 nanoparticles into porous channel models and mouse subchondral bone. In conclusion, BaYbF5‐SiO2 nanoparticles are a potential contrast agent for imaging porous channels at the osteochondral interface using microCT.
ABSTRACT. Structural optimization has received increasing attention in several different areas of engineering and has been identified as the most challenging and economically rewarding task in the field of structural design. In this context, the current paper proposes a methodology based on Evolutionary Structural Optimization (ESO) that corresponds to an evolutionary procedure applied for topological optimization in which the finite elements with the lowest stress levels are progressively removed from a structure. The optimization studies are applied for structures subjected to a transient dynamic response where different damping ratios are applied in the physical models, since its determination is extremely hard and can even change the structural stiffness in case of elastoplastic regime. Thus, a nonlinear behavior is considered to evaluate the effects for each damping ratio, and elastoplasticity theory for small strains is extended for a von Mises material with linear, isotropic work-hardening. For this purpose it is possible to evaluate a combination of different optimal topologies for the different damping ratios through an algorithm developed in the Python programming language. The stress levels present such a difference for each linear and nonlinear response, which characterizes a marked change in the structural stiffness of each analyzed model. Keywords: evolutionary structural optimization, dynamic response, damping, finite element method.Influência da taxa de amortecimento no projeto de otimização estrutural considerando análise dinâmica no domínio do tempo RESUMO. A otimização estrutural vem recebendo cada vez mais atenção em diversas áreas da engenharia e tem sido identificada como um dos maiores desafios em projeto estrutural. Neste contexto, o presente trabalho propõe uma metodologia baseada na Otimização Estrutural Evolucionária (ESO) que corresponde a um procedimento evolutivo aplicado em otimização topológica em que os elementos finitos com os mais baixos níveis de tensão são progressivamente removidos da estrutura. Os estudos de otimização são aplicados em estruturas sujeitas a uma resposta dinâmica transitória, e diferentes taxas de amortecimento são aplicadas nos modelos físicos, pois a sua determinação é extremamente difícil, podendo inclusive, alterar a rigidez da estrutura em casos de regime elastoplástico. Assim, o comportamento não linear é considerado a fim de se avaliar os seus efeitos para cada taxa de amortecimento, e a teoria da elastoplasticidade para pequenas deformações é estendida a um material de von Mises com encruamento isotrópico linear. Com este propósito é possível avaliar uma combinação das topologias ótimas distintas para as diferentes taxas de amortecimento através de um algoritmo desenvolvido em linguagem de programação Python. Os níveis de tensões apresentaram diferenças significativas para respostas linear e não linear, caracterizando acentuada alteração na rigidez estrutural dos modelos analisados.Palavras chave: otimização estrutural evolucionária, resposta dinâmic...
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