Biomedical Engineering Reference
In-Depth Information
9.1 Introduction
Tissue engineering is an emerging interdisciplinary field that combines the knowledge
and technology of cells, engineering materials, and suitable biochemical factors to create
artificial organs and tissues, or to regenerate damaged tissues. The common concepts
associated with tissue engineering research are based on the construction of hybrid mate-
rials obtained from the incorporation of cells into three-dimensional (3D) porous scaffolds
or hydrogels. The scaffold material, which can mimic the extracellular matrix (ECM), has
an essential function concerning cell anchorage, proliferation, and tissue formation in
three dimensions [1]. To perform these varied functions in tissue engineering, an ideal
scaffold should have the following characteristics: (1) an extensive network of intercon-
necting pores and spread porosity (usually exceeding 90%) so that cells can migrate, mul-
tiply, and attach deep within the scaffolds (this would allow
in vitro
cell adhesion, ingrowth,
and reorganization and would provide the necessary space for neo-vascularization
in vivo
);
(2) channels through which oxygen and nutrients are provided to cells deep inside the
scaffold, and waste products can be easily carried away; (3) biocompatibility with a high
affinity for cells to attach and proliferate; (4) the right shape, however complex as desired
by the surgeon; and (5) appropriate mechanical strength and biodegradation profile. The
decomposition products should be free from immunogenicity or any toxicity [2].
Recently, chitosan-based biomaterials have been reported as attractive candidates for
scaffolding materials due to the inherent properties of chitosan. First, chitosans have excel-
lent biodegradation, cytocompatibility, blood compatibility, and antimicrobial activity, and
are without inflammatory reactions. Chitosan-based implants evoke minimal foreign
body reaction, with little or no fibrous encapsulation. Second, they have environment-
stimuli response. Third, the mechanical properties of chitosan-based biomaterials could
be modulated via physical or chemical cross-linking. In addition, the degradation behav-
iors can also be adjusted. Fourth, chitosan can be molded in various forms with a fairly
well-designed porous structure by means of different techniques, such as freeze-drying,
rapid prototyping (RP), and the internal bubbling process. Seed cells may be encapsu-
lated in gels or seeded in porous scaffolds including sponge-like or fibrous structures.
Combinations of chitosan with other biocompatible materials are applied to modify bio-
mechanical and cell-matrix interaction properties. Different adaptations of chitosan may
help in optimizing cell and tissue differentiation and tailoring the transplant to different
clinical cell delivery situations (
cf.
Figure 9.1)
[3]. Here, the preparation of a chitosan-based
scaffold and the interactions between cell/growth factor and chitosan-based biomaterial
are introduced. Moreover, we focus on various types of chitosan-based biomaterials and
their use in various tissue engineering applications, namely, blood vessel, skin, cartilage,
bone, nerve, and liver.
9.2 Preparation of Chitosan-Based Scaffolds
9.2.1 Chitosan-based Porous Scaffolds
The freeze-drying method is usually used to prepare chitosan-based porous scaffolds.
Briefly, chitosan-based solutions or chitosan-based gels are frozen at certain temperatures
for 12 h followed by lyophilization for 24 h. Chitosan scaffolds have high porosity >85%,
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