Biomedical Engineering Reference
In-Depth Information
4.2 Coating of the pericardium
Another possible post-decellularization treatment resides in the coating of the bioprosthesis.
This procedure should allow improvement of graft integration at the site of implantation as
well as decreasing degradation of the pericardial tissue.
Coating bovine pericardium with biopolymeric films, either chitosan or silk fibroin, has
been investigated by Nogueira
et al.
(Nogueira et al., 2010). These methods are interesting
approaches and both treatments appear to be non-cytotoxic. Nevertheless, chitosan does not
allow endothelialisation and silk fibroin-coated bovine pericardium calcifies
in vivo
. Further
investigation has to be performed to tackle these major concerns.
In their study, Dong
et al
. suggested treating bovine pericardium with acetic acid coupled
with RGD polypeptides (Dong et al., 2009). Acetic acid increases pericardial scaffold pore
size and porosity while RGD peptides is meant to improve cell adhesion and growth.
Hence, RGD polypeptides have been identified in fibronectin (Pierschbacher & Ruoslahti,
1984), collagen, vitronectin and membrane proteins (Ruoslahti & Pierschbacher, 1987). These
sequences have an impact on integrins, which display cell adhesion receptor roles
controlling cell signaling pathways.
4.3 Pericardium anti-calcification treatments
The mechanism of calcification on glutaraldehyde-treated pericardium is not well
understood because of its complexity. Nevertheless, there is evidence that pericardial tissue
residual antigens, free aldhehyde groups of glutaraldehyde and phospholipids are involved
in this mechanism.
Thus, circulating antibodies can contribute to pericardial calcification due to a possible
immune response. Free aldehyde groups of glutaraldehyde can attract host plasma calcium,
increasing tissue calcification. Phospholipids may bind calcium and play an important role
in the calcium phosphate crystal formation. Several strategies have been investigated to
tackle these major issues.
Suppression of residual antigenicity has been proposed to prevent calcification and it has
been shown to be effective. This was performed by fixation treatments using a broad range
of high concentrations of glutaraldehyde (Trantina-Yates et al., 2003; Zilla et al., 2000). To
remove free aldehyde groups, a large number of amino acids or amino compounds were
studied. Post-fixation treatments with amino acids displayed an improved spontaneous
endothelialisation
in vivo
of glutaraldehyde-fixed bovine pericardium (Moritz et al., 1991;
Jorge-Herrero et al., 1996). The use of L-glutamic acid did reduce residual and unbound
aldehyde groups, on glutaraldehyde-fixed bovine pericardium and significantly decreased
the risk of calcification (Grimm et al., 1991; Leukauf et al., 1993). Post-treatment with L-
arginine also resulted in decreased calcium deposition (Jee et al., 2003). Recently, Lee
et al.
proposed a post-fixation treatment with glycine (Lee et al., 2010). Early results are promising
but require further investigation on larger studies.
Alcohol solutions, including ethanol, have been investigated as a treatment to remove tissue
phospholipids, thus preventing calcification (Pathak et al., 2004; Vyavahare et al., 1998).
Besides, other techniques have been proposed to minimize the side effects of glutaraldehyde
residues on GA-treated pericardium. Lyophilization has been shown to decrease aldehyde
residues, decreasing the risk of calcification and cytotoxicity (Santibáñez-Salgado et al., 2010).
Moreover, treatments with heparin or sulphonated poly(ethylene oxide) following
glutaraldehyde pre-treatment have been proposed (Lee et al., 2000, 2001). Both methods block
side effects of GA residues and thus prevent calcification of the pericardium. Finally, a
