Biomedical Engineering Reference
In-Depth Information
inflammatory degradation, mechanical damage and pannus overgrowth (Zilla et al., 2008).
In general, the stabilization of collagen-rich tissue is achieved by direct binding of functional
groups to amino acid residues from collagen by coupling agents or by the linkage between
the functional groups on collagen and various chemical agents. Both processes are referred
in literature as the fixation or crosslinking processes. While the crosslinking agents make
durable, stable and resistant tissues, the crosslinking density and the chemical process seems
to have an effect on some of the major disadvantages of bioprostheses, such as calcification
(Zilla et al., 2008). For this reason, a large number of crosslinking agents have been
suggested with the aim of obtaining bioprosthesis that fulfill successfully its function. In
addition to this treatment, there are reports on the post-crosslinking and pre-crosslinking
treatments in order to reduce the calcification of biomaterial and in order to prepare porous
biomaterials as scaffolds for tissue engineering.
3. Decellularization of tissues
The concept of decellularization is referred as the extraction of cellular components from
natural tissues of human or animal origin. Different approaches have been reported as
effective procedures to remove cells from xenogeneic and allogeneic collagenous tissue with
the aim of removing cellular antigens and procalcifying remnants while the extracellular
matrix (ECM) integrity is preserved as much as possible (Schmidt & Baier, 2000). The
combination of chemical, physical and enzymatic methods destroys the cell membrane and
removes nuclear and cellular material (Gilbert et al., 2006). The remaining acellular ECM
will be a complex mixture of structural and functional proteins, glycoproteins and
glycosaminoglycans arranged in a three-dimensional architecture. However, some
mechanical and structural alterations on the ECM can be induced during the
decellularization process.
3.1 Effect of decellularization treatment on tissue properties
A biomaterial or scaffold for tissue engineering should provide not only mechanical support
for the cell proliferation but also they must be versatile to give the required anatomical
shape (Kidane et al., 2009). The decellularization of collagenous tissues has been explored as
the ECM may serve as appropriate biological scaffold for cell attachment and proliferation.
However, alterations both in the structural composition and in the mechanical properties of
the remaining ECM can be induced during the decellularization protocols. The mechanical
integrity can be affected and it may be associated either to the denaturation of the collagen
triple helix or to the loss of macromolecular substances such as glycoproteins.
The efficiency of a given decellularization method and their effects on the properties of
animal tissues must be studied in a specific manner due to compositional and structural
differences (Gilbert et al., 2006). For example, the decellularization of porcine heart valve
with sodium dodecyl sulphate, an anionic detergent, appeared to maintain the critical
mechanical and structural properties of the valves leaflets (Liao et al., 2008) while
decellularization of bovine perichardium with sodium dodecyl sulphate caused irreversible
swelling, resulted in a reduction of the denaturation temperature (Courtman et al., 1994;
García-Páez et al, 2000) and caused a reduction of almost 50% on tensile strength when
compared to native tissue and tissue treated with Triton X100, a non-ionic detergent
(Mendoza-Novelo & Cauich-Rodríguez, 2009).
