Resorbable matrices

Williams, R.J., Gamradt, S.C., 2008. Articular cartilage repair using a resorbable matrix scaffold. Instructional Course Lectures 57, 563-571. 

Nesbitt SA, Horton MA. 1997. Trafficking of matrix collagens through bone-resorbing osteoclasts. Science 27 266-9. 

Abstract Compact bone is a well-organised, multi-level porous structure. Strain-derived fluid flow likely steers the activity of cells within the bone matrix, which in turn orchestrate the concerted activity of bone resorbing and bone forming cells at the surface. We present a model of the strain-driven bone remodelling proces, which could explain the mechanically optimised structure of compact bone. 

Polymeric carriers are biodegradable or water-soluble polymer matrices, typically in the form of colloidal-sized particles (microspheres or nanospheres), rods, or films. The active agent is entrapped within but not chemically bonded to the matrix. The drug is released in a sustained fashion as the polymer is dissolved or degraded, eroded, and finally resorbed [24,30,58-62]. 

Bone is synthesized by osteoblasts which transport calcium ions from blood into a secreted, uncalcified osteoid matrix composed mostly of type I collagen. During calcification, monocyte-like cells are attracted out of the adjacent blood capillaries and adhere to irregularities in the calcifying bone surface and eventually become osteoclasts. These cells, which resorb the bone, develop according to genetic and environmental stimuli that determine bone shape and response to stress. 

FIG. 23 A schematic of the processes involved in osteoclastic resorption of bone. Two SECM tips, a potentiometric Ca2+ sensor, and an amperometric superoxide anion sensor are shown. The osteoclast resorbs bone through secretion of protons and hydrolytic enzymes, enz, which break down the bone matrix. The disposal of Ca2+ released in this process may, in principle, occur via intracellular (i) or extracellular (ii) pathways. 

Several criteria define the ideal material for a cell transplantation matrix, (i) The material should be biocompatible, in the sense that it does not provoke a connective tissue response which will impair the function of the new tissue (ii) it should be resorbable, to leave a completely natural tissue replacement (this is important, because it could avoid some of the problems that occur in long-lasting polymers such as those used in breast implants) (iii) it should be processable into a variety of shapes and structures which retain their shape once implanted and (iv) the surface should interact with transplanted cells in a way which allows retention of differentiated cell function and which promotes cell growth if such growth is desired. 

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