Biomedical Engineering Reference
In-Depth Information
crosslinking of collagen type I due to their ability to crosslink proteins through the -amino
group of lysine and -carboxamide group of glutamine residue (Chen et al., 2005; Chau et
al., 2005). The results indicated the efficiency of this crosslinking agents in terms of
denaturation temperature, mechanical strength, low toxicity to fibroblasts (Chen et al., 2005)
and an increase in osteoblasts and fibroblasts adhesion and proliferation compared to native
collagen (Chau et al., 2005).
4.6 Other methods for the tissue stabilization
Others non-aldehydic crosslinking procedures have been proposed with the aims of prevent
or mitigate tissue calcification. The disuccinimidyl glutarate (DSG) is another non- aldehyde
alternative to tissue crosslinking. The process is carried out by the reaction between primary
amino groups of tissue and NHS ester groups of DSG forming amide bonds with a length of
five-carbon crosslinking and releasing NHS. The DSG crosslinked tissue was resistant to
enzymatic degradation, exhibited low tendency to calcify and high temperature of
denaturation. However, it was necessary to use dimethyl sulfoxide due to the insolubility of
crosslinking agent in water (Pathak et al., 2000). In response to this drawback, a water
soluble crosslinking agent has been used, i. e., the disuccinimidyl suberate. The presence of
sulfonyl groups at the ends of the molecule conferred water solubility while retaining
reactivity with amino groups by crosslinking chemistry similar to DSG, but with a length of
8 carbon intermediates. The tissue crosslinked under these conditions showed very low
levels of calcium (0.2 mg/g of tissue) after 90 days of implantation in rats (Pathak et al.,
2001). The crosslinking of collagen type I proposed for cartilage regeneration has also been
achieved by the diimidoesters—dimethyl suberimidate (DMS). In this procedure, collagen
amino groups react with DMS imidoester groups to form amidine groups and a length
crosslinking of 8 carbons (Charulatha & Rajaram, 2003).
The stabilization of bioprosthetic tissue by filling the tissue interstitial spaces with
polyacrylamide hydrogel resulted in the mitigation of tissue calcification in a rat study
(Oosthuysen et al., 2006). Physical methods such as photo-oxidation (Khorn et al., 1997) or
the use of ultraviolet radiation (Pfau et al., 2000) have also been proposed for the
crosslinking of collagen-rich biomaterials. However, despite the increase in tissue shrinkage
temperature, in some case the treated tissue did not show resistance to the proteins
extraction (Moore et al., 1996).
4.7 Masking reactions
At this point it is important to distinguish between the effective formation of crosslinking
sites, i. e., two reactive sites in collagen linked by a same molecule of crosslinking agent, and
the masking of crosslinking, i.e., the reaction between a single end of bifunctional
crosslinking agent and one reactive site of collagen. Table 6 shows the possible reactions of
crosslinking and masking between collagen and difunctional crosslinking agents.
4.8 Glycosaminoglycans stabilization
Glycosaminoglycans present in both aortic valves and perichardium have been fixed to
prevent the loss of these polysaccharides during the fixation of bioprosthetic valves. The
sodium metaperiodate has been used for the stabilization of glycosaminoglycans in porcine
aortic valves with the subsequent glutaraldehyde crosslinking (Vyavahare & Lovekamp,
2001). The stabilized porcine aortic valve showed compatibility and reduced calcification
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