Cell Adhesion to Biomaterials: Concept of Biocompatibility - Advances in Biomaterials Science and Biomedical Applications - page 220

3.2.2.1. Extracellular matrix
The extracellular matrix (ECM) represents an important element in the processes of cell ad‐
hesion. Indeed, at this level, cell adhesion is under the control of a well defined zone in the
cytoplasmic membrane called focal contact. At this zone, filaments of actin are linked to fi‐
bronectin through an intracellular complex of proteins, the adherence complex. The extracel‐
lular matrix (ECM) is made of different proteins such as fibronectins, collagen, laminin,
vitronectin [41] and represents the mediator of cell adhesion thanks to its integrins.
Although the extracellular matrix generally provides mechanical support to tissues, it serves
several other functions as well. Different combinations of ECM components tailor the extrac‐
ellular matrix for specific purposes: strength in a tendon, tooth, or bone; cushioning in carti‐
lage; and adhesion in most tissues. In addition, the composition of the matrix, which can
vary, depending on the anatomical site and physiological status of a tissue, can let a cell
know where it is and what it should do (environmental cues). Changes in ECM components,
which are constantly being remodeled, degraded, and resynthesized locally, can modulate
the interactions of a cell with its environment. The matrix also serves as a reservoir for many
extracellular signalling molecules that control cell growth and differentiation. In addition,
the matrix provides a lattice through or on which cells can move, particularly in the early
stages of tissue assembly [42].
Many functions of the matrix require transmembrane adhesion receptors that bind directly
to ECM components and that also interact, through adapter proteins, with the cytoskeleton.
The principal class of adhesion receptors that mediate cell-matrix adhesion are integrins, a
large family of αβ heterodimeric cell surface proteins that mediate both cell-cell and cell-
matrix adhesions and inside-out and outside-in signalling in numerous tissues.
3.2.2.2. Adhesion proteins and receptors in fibroblast cells
Different proteins and their receptors are involved in fibroblast cells adhesion process. The
most important and known are fibronectins and their receptors; integrins:
• Fibronectins
Fibronectins are dimers of two similar polypeptides linked at their C-termini by two di‐
sulfide bonds; each chain is about 60-70 nm long and 2-3 nm thick. The combination of
different repeats composing the regions, another example of combinatorial diversity, con‐
fers on fibronectin its ability to bind multiple ligands [40].
Fibronectins help attach cells to the extracellular matrix by binding to other ECM compo‐
nents, particularly fibrous collagens and heparan sulfate proteoglycans, and to cell sur‐
face adhesion receptors such as integrins. Through their interactions with adhesion
receptors (e.g., α5β1 integrin), fibronectins influence the shape and movement of cells and
the organization of the cytoskeleton. Conversely, by regulating their receptor-mediated
attachments to fibronectin and other ECM components, cells can sculpt the immediate
ECM environment to suit their needs.
• Integrins