Biomedical Engineering Reference
In-Depth Information
4.5 Tissue crosslinking with naturally-derived compounds
Crosslinking agents of natural origin have also been explored in the tissue crosslinking.
Such is the case of genipin, an aglycone or an iridoid glycoside, which can be obtained by
enzymatic hydrolysis of the glucoside previously isolated from gardenia fruit. The
stabilization of porcine perichardium (Sung et al., 1999) and acellular bovine perichardium
(Sung et al., 2000) with genipin probably was achieved through cyclic structures. The
crosslinking density for genipin-fixed tissue was similar to glutaraldehyde and ethylene
glycol diglycidyl ether -crosslinked tissues. Moreover, the genipin-crosslinked porcine
perichardium was less cytotoxic (fibroblasts) than glutaraldehyde-crosslinked tissue,
whereas exhibiting the same tensile strength and resistance to enzymatic degradation
(Chang et al., 2002). Furthermore, acellular bovine perichardium fixed with genipin showed
capacity of angiogenesis (microvessel infiltration) after implantation in rats (Liang et al.,
2004). Moreover, cell extraction with solutions of Triton™X-100 and the crosslinking with
different concentrations of genipin were used to establish a relationship between the
crosslinking degree and the degradation rate or the model of acellular tissue regeneration
(Chang et al., 2004).
Polyphenolic compounds have also been investigated as natural agents of tissue
stabilization, such as the proanthocyanidins from the family known as condensed tannins,
which are essentially oligomers of flavonoids available in several fruits and vegetables. The
stabilization of collagen with proanthocyanidins may involve the formation of hydrogen
bond type interactions between the phenolic hydroxyl and amide carbonyls of the
polypeptide chains.
The proanthocyanidin has a high affinity for proline-rich proteins, because this amino acid
is a good hydrogen bond acceptor (Zhai et al., 2006). The proanthocyanidins can be used to
crosslink collagen sponges with similar density and efficiency to glutaraldehyde but with
reduced calcification after 6 weeks implantation in rats and it was reported to be 120 times
less toxic to fibroblasts direct contact (Han et al., 2003). The proanthocyanidin crosslinking
procedure was repeated in decellularized porcine aortic valves resulting in low toxicity to
bovine aortic valve interstitial cells and in the stimulation of cell proliferation to low
concentrations of this stabilization agent in the culture media (Zhai et al., 2009).
The stabilization of elastin in porcine aortas has been achieved by treatment with
polyphenolic tannins, which is composed of a central molecule of glucose (hydrophobic
core) and one or more galoil residues (hydrophilic shell) (Isenburg et al., 2006). Polyphenolic
compounds were acetylated tannic acid, pentagaloil glucose, gallic acid and glucose. In this
study, pentagaloil glucose treatment was the least toxic to fibroblasts (Isenburg et al., 2004).
Also, the study revealed that polyphenolic hydroxyl groups are essential for the interaction
between the tannic acid and elastin. The combination of tannic acid and glutaraldehyde
rendered a biostable tissue with high resistance toward elastase and collagenase and low
tendency to calcify (Isenburg et al., 2006).
The reuterin (-hydroxypropionic acid) produced by
Lactobacillus reuteri
has been used in
the fixation of porcine perichardium (Sung et al., 2002). The reuterin is soluble in water, with
antimicrobial and antifungal activity. The properties of reuterin-fixed tissue are comparable
to glutaraldehyde-fixed tissue in terms of amino group content, denaturation temperature,
tensile strength and collagenase digestion resistance (Sung et al, 2003).
Microbial (mTG;
Streptoverticillium mobaraense
) and tissue (TG2; tTG) transglutaminases
(protein-glutamine -glutamyltransferase, EC 2.3.2.13) have been explored in the
