The Cell–Surface Interaction - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 8

3.1.2 Protein Adsorption
The importance of surface chemistry is demonstrated with greatest efficacy when
considering protein adsorption. Cells bind to titanium and its alloys through a
series of adhesive molecules such as vitronectin and fibronectin [ 36 ]; thus, alter-
ations in surface chemistry will effectively influence protein adsorption and con-
formation, and ultimately initial cell attachment. Yang et al. [ 37 ] found that
increased cell attachment was directly proportional to the amount of preadsorbed
protein; however, this mechanism was also protein-type dependent. In this study,
both fibronectin and albumin were assessed and it was reported that the concen-
tration of fibronectin adsorbed onto the titanium surfaces was higher than the
concentration albumin adsorbed. Considering the hydrophilic nature of commer-
cially pure titanium, and the fact that albumin is known to display improved
binding to hydrophobic surfaces, this finding seems coherent. Time also appeared
to be a factor as the positive effect of preadsorbed fibronectin was observed to be
highest after 15 min; however, after 180 min this effect on cell attachment was
negated [ 37 ]. This outcome seems logical since the rapid adsorption of proteins
onto devices is considered to be one of the first events to occur upon implantation
[ 38 ], an effect that is suggested to then diminish as the effect of topography comes
to the fore. However, this system works in synergy rather than exclusively.
More recently, Rapuano and McDonald [ 39 ] showed that negatively charged
surface oxide functional groups in TAV can modulate fibronectin integrin receptor
activity by altering the adsorbed protein's conformation.
Interestingly Howlett et al. [ 40 ] found that vitronectin was essential for osteoblast
cell attachment onto titanium, stainless steel, alumina, and poly(ethlyene tere-
phthalate). However, this outcome was fibronectin-independent, a result which
contradicts others identifying fibronectin as the principal component [ 41 ]. One must
keep in mind, however, that this effect may also be cell-type-dependent and/or
species-dependent (Howlett et al. [ 40 ] used cells derived from human bone, whereas
Horbett and Schway [ 41 ] used a mouse cell line). Furthermore, it was suggested by
Howlett et al. [ 40 ] that perhaps fibronectin (in this model) plays a role in cell adhesion
rather than initial attachment and that vitronectin is a more effective competitor
compared with other serum proteins for surface binding. Nevertheless, the 90-min
time point included by the authors may have clouded the outcome slightly. For
instance, Meyer et al. [ 38 ] showed that protein and lipid adsorption was already
detectable after 5 min implantation, the earliest time point studied.
3.1.3 Surface Chemical Modifications
To induce cell adhesion and spreading, the surface chemistry of a material can be
altered. This can be achieved by different treatments involving chemical and
biochemical surface modifications. Biological coatings, such as immobilized ECM
proteins of implant surfaces, give more promising results than chemical modifi-
cations with calcium phosphate (CaP), for instance. Although CaP modifications