BIOMATERIALS FOR BIOPRINTING - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 137

FIGURE 6.4
Neutrally charged PHEMA monomer.
6.4.2.2 Poly(vinyl alcohol)
Poly(vinyl alcohol) (PVA) ( Figure 6.5 ) is prepared from the partial hydrolysis of poly(vinyl acetate). It
can be cross-linked into a gel through chemical or physical methods (e.g. via treatment with monoalde-
hydes). PVA can also be photocured to fabricate hydrogels as an alternative to chemical cross-linking.
It is similar to PHEMA in terms of having available pendant alcohol groups that function as attachment
sites for biological molecules. PVA is an elastic material, which means it can induce matrix synthesis
or cell orientation by enhancing the transmission of mechanical stimuli to seeded cells ( Schmedlen
et al., 2002 ). PVA hydrogels are neutral and nonadhesive to proteins and cells. They have a low fric-
tion coefficient and their structural properties are similar to natural cartilage. More importantly, they
are generally stronger than most other synthetic gels, making them successful for avascular tissue.
Furthermore, PVA can be copolymerized with Poly(ethylene glycol) (PEG) to produce a biodegrad-
able hydrogel that has a degradation rate faster than that of PEG hydrogels but slower than that of PVA
homopolymer hydrogels.
6.4.2.3 Poly(ethylene glycol)
PEG ( Figure 6.6 ) is a biocompatible and hydrophilic material, with properties that limit antigenicity,
immunogenicity, cell adhesion, and protein binding (Alcantar et al., 2000 ). PEG homopolymer is a
polyether that can be polymerized from ethylene oxide by condensation. It is nonadsorptive due to the
lack of protein binding sites on the polymer chain. Compared to PHEMA and PVA, PEG does not have
hydrogen bond donating groups, a feature that is critical in reducing protein binding.
PEG hydrogels have been considered as one of the most successful synthetic hydrogels for tis-
sue engineering applications. The ends of a PEG polymer can be modified with either acrylates or
methacrylate to form photo-cross-linkable polyethylene glycol dimethacrylate (PEGDA) ( Drury and
Mooney, 2003 ). PEGDA is extensively used to encapsulate cells into scaffolds. Furthermore, PEG can
act as a mediator for immobilizing the RGD sequence.
FIGURE 6.5
Neutrally charged PVA monomer.