Biomedical Engineering Reference
In-Depth Information
radicals, ions, protons, electrons, gas atoms, and molecules of different energies.
These high-energy species are driven onto the material surface to result in
chemical and physical changes ranging in depths of several hundred angstroms
to 10 microns [36]. Introducing hydroxyl, carboxyl, amino, and sulfate groups
on substrate surfaces, not only increases hydrophilicity, but also prepares
these surfaces for the covalent immobilization of ECM-derived proteins
(section 5.1). The other common method to increase hydrophilicity on polymer
surfaces is to graft hydrophilic polymers such as poly(acrylamide) (PAM) or
poly(hydroxylethyl methacrylate) (PHEMA) onto hydrophobic polymers such as
PCL [56] and PLA [57]. The introduction of initiators can be achieved by argon
plasma treatment, ozone oxidation, γ-ray, electron irradiation, and laser treatment
[58-60]
Numerous studies have explored the role of hydrophilicity on protein
adsorption, integrin expression, focal adhesion formations, and whole cell
adhesion. Alves et al. [61] recently showed that oxygen radio frequency glow
discharge on poly (D, L, lactide) (PDLLA) affects protein adsorption and bone
cell behavior. Plasma treated films showed an increase in hydrophilicity and
surface energy, which lead to higher percentages of FN deposition and increased
MG63 osteoblast-like cell and fetal rat calvarial cell adhesion as compared to
untreated films. To explore the effects of hydrophobicity on integrin expression,
Liu et al. [62] compared
ŋ
2
,
ŋ
3
,
ŋ
4
,
ŋ
5
,
ŋ
v
,
Ȳ
1
, and
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3
integrin subunit expression
by human fetal osteoblastic (hFOB) cells cultured on hydrophilic and
hydrophobic surfaces for 3 and 6 days. They found that hFOB cells cultured
on hydrophillic surfaces initially expressed significantly higher levels of
ŋ
v
and
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3
subunits than on hydrophobic surfaces, but this difference decreased with
time in culture. In another study, researchers quantified downstream signaling
events associated with successful integrin-mediated adhesion of human alveolar
osteoblasts (AOBs) to Ti surfaces. They observed that within 3 hours, the
attachment rates of AOBs cultured on chemically modified hydrophilic SLA
(modSLA) surfaces were significantly higher than that on hydrophobic
sandblasted and acid-etched surfaces (SLA). Further, after 6 hours the AOBs
developed more defined actin stress fibers and expressed FAK at higher levels on
modSLA [63]. Cell proliferation is enhanced on plasma-treated surfaces as
well, as demonstrated by the two-fold increase in mouse 3T3 fibroblast cell
number on PDLLA plasma-modified surfaces as compared to untreated PLA
surfaces [54].
This general hydrophilicity rule varies with specific polymer surfaces and
cell types, as well as method used. For instance, Zhu et al. [56] demonstrated that
the best water contact angle for endothelial cell attachment and proliferation on
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