Biomedical Engineering Reference
In-Depth Information
tissue, which is then remodeled by osteoclast-mediated resorption and new matrix forma-
tion by osteoblasts in response to changes in diet, exercise, and age (Baron 2003).
One of the most important functions of the ECM is to mediate cellular adhesion and con-
sequent differentiation (Ruoslahti, Hayman, and Pierschbacher 1985). Most cell types need to
be attached to a matrix in order to survive, grow, and differentiate. Cell adhesion occurs via
heterodimeric receptors found in the plasma membrane, known as integrins, which recog-
nize and bind to specific domains found in adhesive ECM proteins. The specific type of inte-
grin receptor involved depends on the cell type and the composition of the ECM. A single cell
usually expresses several types of integrin receptors during its lifetime, depending on the
type of signals it receives from its environment. These integrins form a part of focal adhesion
complexes, linking the ECM molecules to the cell cytoskeleton thus controlling cell adhesion.
Furthermore, integrins are also capable of triggering specific cell signaling pathways and
thus effectively modulating a variety of cellular functions including cell growth and migra-
tion, and differentiation and suppression of apoptosis (Plopper 2007; Ruoslahti, Hayman,
and Pierschbacher 1985; Lebaron and Athanasiou 2000; Ruoslahti 1996). Once adhered, cells
proliferate and differentiate into a specific lineage with the aid of growth factors and other
signaling molecules that are sequestered by the ECM and released during the various stages
of cellular activity. Hence, the cell-matrix system is dynamic and complex in nature.
Disruption of cell-cell and/or cell-matrix connections causing either lack of commu-
nication or the wrong type of communication to occur between the cells and their sur-
roundings results in abnormal cell activity, manifested in the form of diseased tissues/
organs. The fields of tissue engineering and biomimetics employ concepts from biological
sciences and engineering to regenerate healthy tissues to replace diseased or damaged
ones. Biomimetic materials derive inspiration from naturally occurring systems by imitat-
ing aspects of their structural and functional complexity. The main goals of these mimetic
biomaterials are to facilitate cellular adhesion and production of ECM by replicating nor-
mally occurring cell-matrix interactions in order to control tissue formation.
Biomaterials to be used in bone tissue engineering applications should meet both physi-
cal requirements such as mechanical support, surface and bulk material properties and
architecture, and biological requirements such as supporting cellular differentiation into
osteoblasts. Biomimetic precipitation of calcium phosphate mineral onto biomaterial sur-
faces facilitates integration of the surface into host bone as well as allows for the incorpora-
tion of bioactive moieties under physiological conditions. This chapter focuses on the use of
biomimetic apatite coatings to bond to native bone and recreate cell-matrix interactions in
vitro and in vivo. The cellular and ECM components present in bone are briefly presented
first, followed by a summary of the important material requirements needed to recreate
cellular microenvironments in prosthetic and tissue engineering systems. The concept of
biomimetic apatite formation and the use of these coatings on metals, ceramics, and poly-
mers are then explored. Finally, a discussion of the use of biomineralization techniques to
synthesize organic/inorganic hybrid (bone-like mineral (BLM) integrated with biologically
active molecules) coatings that allow for mimicry of cell-matrix interactions is presented.
EngineeringCellularMicroenvironments
Before designing any material system to be placed in vivo, it is important to understand the
biology of the targeted tissue. Knowledge of the type of cells present, their surrounding
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