Biomedical Engineering Reference
In-Depth Information
linked to the tissue crosslinking to increase durability. However, due to some complications
in the stabilized tissue, several post-crosslinking protocols have been proposed to address
these complications. More recently, biological scaffolds derived from acellular tissue has
been used in tissue engineering and regenerative medicine.
Therefore, this chapter deals with the processing of collagenous tissue for the preparation of
cardiovascular biomaterials. The processing techniques include the extraction of cellular and
nuclear material by various decellularization methods, the preservation of tissue through of
crosslinking reactions, hydrogen-bond interactions or interstitial space filling, and the
functionalization or the blocking of free groups with various low molecular and
macromolecular substances.
2. The biomaterial choice
The replacement of damaged organs or tissues is one of the objectives of the biomaterials
science. For this, natural or synthetic materials can be used for example in the
cardiovascular field in the manufacture of heart valves and vascular grafts. The success of a
device depends not only on the type of biomaterials but also on a set of acceptable
characteristics
such
as
biocompatibility,
biostability,
haemocompatibility,
anti-
trombogenecity, resistance to degradation and calcification.
Among those biomaterials that can fulfil these requirements, natural tissues are good
candidates and that is why they have been under investigation in the past fifty years.
2.1 Composition and sources of natural tissue
Natural tissue biomaterial can be obtained from either animal-derived tissue (xenograft) or
human-derived tissue (homograft). However, due to the limited availability of autografts,
animal-derived tissues are, in many cases, the first choice for cardiovascular biomaterials.
Animal derived tissues widely used as biological biomaterials include perichardial tissue
from various sources such as cows, calves and ostrich in addition to pig aortas.
Tissue-derived biomaterials are mainly comprised of collagen in addition to the tissue
extracellular matrix (ECM) which is a complex mixture of structural and functional proteins
such as collagen, proteoglycans, glycoproteins, elastin, metalloproteins, etc. Collagen, being
the main structural protein, is a polypeptide that contain amino (-NH
2
), carboxylic acid (-
COOH) and hydroxyl (-OH) functional groups as substituents, and together with the amide
bonds in the polymer backbone form the reactive centers. The repetitive unit in the polymer
backbone of collagen and the amino acid residues as side group are depicted in figure 1.
Fig. 1. Representation of the repetitive unit of collagen and some side group R of amino acid
residue
