The Cell–Surface Interaction - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 6

showed that a 3 and a 6 were not expressed. Additionally, in both cases a 5 was not
detected. Interestingly, a 5 b 1 integrin, the receptor for fibronectin and regulator of
differentiation, is expressed mainly on the polystyrene surface, whereas on tita-
nium surfaces a 2 b 1 integrin, binding to collagen and laminin, is primarily
expressed [ 22 ]. Moreover, Olivares-Navarette et al. [ 23 ] demonstrated that a 2 b 1
integrin regulates differentiation of cells cultured on titanium implants in long-
term culture. For the attachment of cells to the proteinaceous coating, heterodimers
a v b 1 , receptor for fibronectin and vitronectin, a 6 b 1 , interacting with laminin, and
multifunctional receptors a 3 b 1 and a v b 3 are essential [ 12 , 22 ]. Additionally,
Schneider and Burridge [ 24 ] indicated that fibronectin enhances formation of focal
contacts and stress fibres. Furthermore, they localized b 1 integrin subunits within
focal contacts on surfaces precoated with fibronectin, whereas b 3 was evident on
surfaces precoated with vitronectin. However, these contradictions may result
from the different cell models used in these studies.
3 Cell Meets Surface: Factors Involved
in the Surface-Dependent Response
In a presidential address to the American Biomaterials Society, Buddy Ratner [ 25 ]
meaningfully noted that current biomaterials have been developed as a result of
trial-and-error optimization rather than specific design. However, as acknowledged
by Brunette [ 26 ], to design materials that elicit specific responses from tissues is a
complex proposition. The main reason for this is that the vast majority of the
biological principles controlling the interaction of cells with implants remain
largely ambiguous. For instance, the early 1980s saw the introduction of the
inhibition of epithelial down growth onto implants via contact inhibition [ 27 ].
Even in a well-studied phenomenon such as contact guidance, elucidating the
controlling mechanisms of cell response remains challenging.
3.1 Surface Chemistry
It is no great stretch of the imagination to see why the chemical composition of an
implant surface has attracted interest. The excellent biopassivity, corrosion resis-
tance and repassivation ability of metal implant materials are a direct consequence
of the chemical stability and integrity of the oxide film. Further, importance has
been assigned to the oxide layer since essentially it is this that interacts with
proteins and cells upon implantation and persists at the interface for the life of the
fixation [ 28 ]. In fact, the sensitivity of cells to the chemical composition of a
device is to the extent that even different grades of titanium are detected at a cell
level [ 29 ]. Some studies suggest that by increasing the thickness of the oxide layer,