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Nano-sized Organization in Nature
Published in Paula V. Messina, Luciano A. Benedini, Damián Placente, Tomorrow’s Healthcare by Nano-sized Approaches, 2020
Paula V. Messina, Luciano A. Benedini, Damián Placente
This means that the final result is rather obtained by an algorithm than by the replication of a design. This approach presents three main advantages. First, it allows flexibility at all levels, enabling a functional adaptation through the growth. For example, the bone in a healthy person or an animal will adapt to the loads under which it is placed; that is the statement of “Wolff’s law”, developed by the German anatomist and surgeon Julius Wolff (1836–1902) in the 19th century. If the load on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading. The internal architecture of the trabeculae undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone, perhaps becoming thicker as a result. The inverse is true as well: if the loading on a bone decreases, the bone will become less dense and weaker due to the lack of the stimulus required for continued remodeling (Frost 1990).
Structure and Function of Cartilage
Published in Kyriacos A. Athanasiou, Eric M. Darling, Grayson D. DuRaine, Jerry C. Hu, A. Hari Reddi, Articular Cartilage, 2017
Kyriacos A. Athanasiou, Eric M. Darling, Grayson D. DuRaine, Jerry C. Hu, A. Hari Reddi
Mechanotransduction is the process by which cells convert physical forces into biochemical signals. Classically, one of the earliest descriptions of mechanotransduction is the work of Julius Wolff during the nineteenth century, in which he proposed the eponymous law, which states that bone remodeling results from the physical forces applied to the bone. Specifically, sites of increased loading will have more bone deposited, while sites of disuse will resorb bone during remodeling. This would later be refined as the mechanostat by Frost in the 1960s, reviewed elsewhere (Frost 2000). Articular cartilage may also follow Wolff’s law, with anatomical regions of increased loading exhibiting thicker cartilage (Shepherd and Seedhom 1999).
Biocomposites as Implantable Biomaterials
Published in Yaser Dahman, Biomaterials Science and Technology, 2019
Living tissue continuously regenerates. Aging of cells causes tissue to die, decompose, and be replaced by new cells. A similar process applied to bone tissue, which is comprised of osteoblasts and osteoclasts. Osteoblasts build up extracellular matrices and osteoclasts resorb them. The formation of bone by osteoblasts and resorption of bone by osteoclasts is balanced by hormones. The orientation, rearrangement, or density of trabecular architecture orientation of a bone if rearranged or density varies impacts the bone structural load-bearing capacity. Wolff’s law of bone remodelling explains the influence of trabecular architecture on the main stress and the minimization of shear stress of composites. Placement of an orthopaedic implant inside the bone changes the local stress level. Loads on the bone may be same, but the mechanical stress of the bone adjacent to the implant will be impacted. As per Wolff’s law, the insertion of a composite implant changes the bone density and architecture by remodelling. Thus, local stress on the bone becomes the dominant factor for bone material retention. When a high stress area of a bone observes a lack of stress, it creates a problem for the composite implants. The section of the bone where the implant is placed may atrophy due to reduction of mass in the bone and the decrease in mechanical strength known as “stress shielding”. A biocomposite implant that minimizes this bone atrophy is structurally biocompatible. Structural bioincompatibility occurs due to composite implants that are stiffer than the original bone and implants. Again, composite implants which are very stiff and isotropic can cause a high extent of strain mismatch in the bone interface, resulting in the hindrance of implant bonding to the bone (Ramakrishna, 2004).
The application of nanogenerators and piezoelectricity in osteogenesis
Published in Science and Technology of Advanced Materials, 2019
Fu-Cheng Kao, Ping-Yeh Chiu, Tsung-Ting Tsai, Zong-Hong Lin
According to Wolff’s Law, bone can respond to mechanical loading and is subsequently reinforced in the areas of stress [7]. In the view of a biophysical concept, bone remodeling is the interaction between osteoblasts and osteoclasts, which serves to regulate the process of bone formation and resorption. Fracture healing is a proliferative physiological process in which osteoblasts are activated to facilitate the repair of the fracture site. However, it remains undetermined exactly how a bone is capable of responding to mechanical signals and specifically how osteoclasts and osteoblasts can perceive such forces. Importantly, bone was first determined to be a piezoelectric material in the 1960s [8], with demonstrable electrical polarization when it is mechanically deformed. The occurrence of piezoelectricity, therefore, is one theory that could potentially explain how electrical signals and mechanical loads are involved in the adaptation of bone.
Tibial implant fixation in TKA worth a revision?—how to avoid stress-shielding even for stiff metallic implants
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
B. Eidel, A. Gote, C.-P. Fritzen, A. Ohrndorf, H.-J. Christ
Stress shielding refers to the reduction in bone density caused by a reduction of physiological stress from the bone by a stiff, metallic implant. This is because of bone’s adaptivity to remodel in response to the loads referred to as Wolff’s law. As a consequence, a decrease of loading on bone decreases bone density and stiffness because of the lowered stimulus for maintaining the existing bone density.