Advances in Collagen-based Tissue Engineering - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 212

has been demonstrated that chemically activated or radiation modified monometh-
oxy poly(ethylene glycol) (MPEGs), derivatives conjugated to collagen decreased its
biodegradability, immunogenicity and antigenicity while maintaining its biological
activity. These biomaterials have been used as templates for tissue ingrowth assisting
wound healing. The results obtained show unambiguously that some of the collagen-
polymers compositions give rise to the appearance of formation of an ether link and
modification of the protein secondary structure as determined by the analysis of the
amide I and amide II infrared bands. Furthermore, using irradiation, it is possible to
offer both a biodegradable implant with stable structure and a well-suitable implant for
surgery in a sterile and ready-to-use state. Additional advance in this manner is that
the collagen structure can be stabilized without any impurities in catalysts or chemical
initiators.
The other type of collagen-based material is a new family of tri--component hy-
drogel consisting of water-soluble, substantially biocompatible synthetics, and bioac-
tive collagen (Pietrucha and Banas, 2009; Pietrucha and Verne, 2010). The concept
in the preparation of a copolymeric hydrogel is to incorporate in the system a slowly
degradable, bio-inert poly(vinyl alcohol) (PVA) of high glass transition temperature,
T g , a highly biocompatible and hydrophilic MPEG of low T g , and biodegradable, bio-
active natural macromolecule collagen. These hydrogels were synthesized by using
a two-stage process: multiple freeze-thaws followed by irradiation with an electron
beam.
It has been shown that repetitive freeze-thawing of PVA solutions containing colla-
gen and MPEG results in formation of physically cross-linked hydrogels. The mecha-
nism by which these physical cross-links are formed may involve hydrogen bonding,
formation of crystallites or a liquid-liquid phase separation process and chains entan-
glements. The immediate effect of irradiation of above polymer systems, in water and
under oxygen-free atmosphere, is radiolysis of water and formation of polymers free
radicals. The structure of these free radicals is shown in Figure 6.
Figure 6. Schematic description of products radiolysis of H 2 O, PVA, MPEG, and collagen.