ReviewBiomaterials and bone mechanotransduction
Introduction
“Every change in the form and function of bone or of its function alone is followed by certain definite changes in the bone internal architecture, and equally definite alteration in its external conformation, in accordance with mathematical laws [1].” This statement is known as Wolff's law and has provided the foundation for a large number of clinical applications concerning skeletal disorders. New developments in the fields of bone biology, physiology and orthopedic research have led to a wealth of information on the mechanisms involved in the transduction of mechanical stimulation to bone cells. These mechanisms are implicated in the continuous bone remodeling process that involves bone cells (osteoblasts, osteoclasts and osteocytes) in order to transduce the external mechanical signals. A large number of non-mechanical factors are also involved in bone mechanotransduction. Bone deformations result in fluid flow inside the lacunar–canalicular bone porosity, which is associated with the osteocytes (mature osteoblasts, buried in the bone matrix).
A major challenge in the area of biomaterials is the synthesis of polymer scaffolds suitable for a certain cell type that in the presence of the appropriate media and reactor conditions will secrete extracellular matrix and form tissue [2]. In this review an attempt is made to link the new developments in bone biology, bone mechanotransduction and biomaterials in order to provide new insights in the field of orthopedic tissue engineering.
Section snippets
Bone biology
Bone performs several integral functions in the maintenance of body systems, such as: (1) protection of vital organs, (2) providing support and site of muscle attachment for locomotion, (3) generation of red and white blood cells for immunoprotection and oxygenation of other tissues and (4) retaining reserve stores of calcium, phosphate, and other important ions [3], [4]. Therefore, pathologies of bone can be very serious, affecting a wide range of body functions. Bone deficiencies can result
Bone mechanotransduction
Since bone remodeling is dependent on cellular processes (bone formation by osteoblasts and bone resorption by osteoclasts) it is expected that the detection of the applied mechanical forces is done either by each individual cell, and the sensation is restricted to the cellular level, or by certain sensor cells which generate biochemical signals in order to transduce the obtained mechanical signal and modulate bone formation and resorption. In the latter case the sensation is at the tissue
Mechanotransduction and the solid-state environment
The interaction of bone cells with the solid microenvironment influences their attachment, viability, proliferation, and differentiation [62]. The extracellular matrix on which bone cells are attached not only assists in the maintenance of tissue structure but it also transmits information to the attached cells using structural ligands for bone cell surface receptors, signaling peptides, proteinases and their inhibitors [63]. When bone cells are attached on a solid substrate (biomaterial) their
Conclusion
The potentially variable effects of mechanical stimuli on cells of different maturity levels together with the effect of the microenvironment and the adhesive forces exerted on the cells from the surface that they are attached create a very challenging engineering problem. The use of three-dimensional scaffolds seeded with osteoblastic cells that can generate a 3-D bone matrix, which can be transplanted to bridge large bone defects, is of great clinical significance [84]. The use of scaffolds
Acknowledgements
This work was funded by the National Institutes for Health (R29-AR42639) and the National Aeronautics and Space Administration (NAGW-5007, NAG5-4072). J.S. Temenoff also acknowledges financial support by a Whitaker Foundation Graduate Fellowship.
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