Biomedical Engineering Reference
In-Depth Information
However, the alkaline treatment altered the perichardial tissue stress relaxation behaviour
(Mendoza-Novelo et al., 2011).
3.2 Pre-treatments (pre-crosslinking) methods to reduce tissue calcification
Bovine perichardium undergoes several treatments prior to crosslinking with the aim to
improve its biocompatibility, to reduce immunogenicity, to decrease its tendency to
calcification, to promote neo-vascularization and infiltration, and to increase cell adhesion
and proliferation. Some of the pre-treatments proposed in the literature to reduce
calcification of cardiovascular bioprostheses are showed in the table 2. It has been reported
that with the treatment of bioprostheses with sodium dodecyl sulphate and Triton™X-100
most of the acidic phospholipids are extracted resulting in the initial suppression of
calcification in the cell membrane (Schmidt & Baier, 2000).
Pre-
treatment
Anti-calcification action mode
Reference
Surfactants
Removal of acidic phospholipids
Schmidt & Baier, 2000; Chang et al.,
2004
Alcohols
Removal of phospholipids and
cholesterol
Alteration in the collagen
conformation
Cellular death
Removal of Cardiolipin
Vyavahare et al. 1997; Pfau et al. 2000;
Pathak et al., 2002
Table 2. Tissue pretreatment in order to reduce the bioprostheses calcification
The pretreatment of collagen-rich biomaterials with different concentrations of ethanol may
prevent calcification through the extraction of phospholipids and cholesterol but causes a
permanent alteration in the collagen conformation (Schmidt & Baier, 2000). Additionally,
this treatment affected the interaction of the tissue with water and lipids and increased the
resistance of the tissue to the action of collagenase. Several high molecular weight alcohols
have been used in order to remove cellular components that contain elements responsible
for the calcification (Pathak et al., 2002). The pretreatment with 50% ethanol for 5 min
reduces fibrosis of bovine perichardium implanted in the aorta of sheep as a result of cell
death and cardiolipin removal more than the phospholipids extraction (Vyavahare et al.,
1997). Mixtures of chloroform/methanol have also been effective in reducing tissue
calcification (Jorge-Herrero et al., 1994).
4. Stabilization of tissues
The stability of tissues is increased by physical or chemical crosslinking. The fixation
enhances tissue stability, inhibits autolysis, allows a prolonged shelf-life, and allows a
surgeon to have medical devices of various sizes readily available for implantation (Schoen
& Levy, 1999). The chemical treatments also mitigate immunogenicity while maintaining
both thromboresistance and antimicrobial sterility but greatly influence their degradation
and calcification. However, tissue calcification is multifactorial phenomenum where
chemical crosslinking is considered just one of these factors. In fact, the alteration in the
electrical charge that exists in the perichardial tissue surface has been associated to the
