Biomedical Engineering Reference
In-Depth Information
or polymerization can be achieved by photopolymerization, changes in temperature, radiation, self-
assembly, or cross-linking enzymes. Hydrogels undergo responsive swelling by absorbing solvent
when placed in an aqueous solution (solvation). Swollen hydrogels can absorb many times their own
weight in water and can switch between swollen and collapsed forms. The key properties of hydro-
gels for biomedical applications are high biocompatibility, biodegradability, and ability to incorporate
biomolecular cues (due to high permeability for oxygen, nutrients, and water-soluble metabolites).
These key characteristics along with the ease of in-situ fabrication have made hydrogels a biomate-
rial of choice in
in-vitro
studies for analyzing cell-biomaterial interactions and in biomedical applica-
tions
[80]
. Hydrogels are extensively used in cosmetic and reconstructive surgery
[81]
, as a matrix
for the fabrication of artificial organs in tissue engineering
[82]
and as “intelligent” stimuli sensitive
drug delivery systems
[83]
. Hydrogels have also been extensively used to fabricate contact lenses
[84]
,
breast implants
[85]
, tissue engineering scaffolds
[86]
, delivery vehicles for bioactive drug molecules
[87]
, coatings for biosensors
[88]
, dressings for wound healing and burn injuries
[89]
, and as carrier
scaffolds for guided bone regeneration (GBR) using osteogenic growth factors
[90]
. Although many
polymer hydrogels have been studied, poly(ethylene glycol) hydrogel (PEG) is one of the most widely
investigated systems. PEG hydrogel can be fabricated into three-dimensional microstructures to study
the response of cells for their applications in tissue engineering. PEG hydrogel offers the simplicity
and advantage of incorporating bioactive molecules into the hydrogel matrix passively or by covalent
linking with the PEG monomers. Time-dependent release of these biomolecular cues from the PEG
hydrogel micropatterns serves as an excellent platform for studying cell response in tissue culture.
PEG hydrogel micropatterns have been fabricated by photopolymerization through a micropatterned
photomask (photolithography)
[91]
.
PEG hydrogel has also been used as a carrier matrix for the delivery of cell-adhesive peptides
[92,93]
and growth factors due to its biocompatibility, biodegradability, and tissue-like conformational
properties
[94,95]
. PEG hydrogel has also been used to fabricate “nonfouling” or “antifouling” sur-
faces (surfaces resistant to protein adsorption) on titanium. Many techniques like molecular assembly
[96]
and formation of interpenetrating networks (IPNs)
[97]
have been used to immobilize PEG onto
titanium surface as they are compatible with titanium surface chemistry. Photolithography combined
with silanization technique has been utilized to produce cell-adhesive and antiadhesive PEG hydrogel
micropatterns on a silicon substrate
[98]
. In this study, vascular endothelial growth factor (VEGF) was
tested for its osteoinductive property. Silanization of titanium and its alloys has already been reported
for KRG peptide grafting onto Ti-6Al-4V surface
[99]
and RGD-containing peptides delivered from
PEG hydrogel-coated titanium surface
[100]
. Such biomimetic surface modifications to gain con-
trol over nonspecific protein adsorption and introducing specific ligands like cell-adhesive peptides
(RGD) linked covalently to the PEG layer
[101]
would give control over surface chemistry of titanium
implants made for commercial applications.
6.2.3.5 Antibacterial Titanium Surfaces
As an alternative to the previous biochemical modification methods of titanium and its alloys, recent
approaches have focused on delivering antibacterial drugs to prevent biofilm formation. Biofilm
(plaque) formation on titanium dental implants hinders early bone formation and subsequently leads
to peri-implantitis and implant failure. Peri-implantitis is the inflammatory process affecting the
tissues around an osseointegrated implant in function, thereby resulting in loss of supporting bone.
