Application of Chitosan-Based Biomaterials in Tissue Engineering - Chitosan Based Hydrogels: Functions and Applications - page 422

than endothelial growth. This result suggests that the scaffold material may have intrinsic
biological activity, which could contribute to retardation of SMC growth relative to ECs
[87]. Heparin will inhibit the proliferation of vascular SMCs, attract and protect many
heparin-binding growth factors, such as bFGF, vascular endothelial growth factor (VEGF),
and PDGF, and help control the release of these growth factors. Thus, chitosan-heparin com-
posites have potential applications in small-diameter blood vessel tissue engineering [88].

9 . 5 . 2 S k i n

On the surface of our body, the skin provides a protective barrier that keeps microbes
out and essential body fluids in. The skin is divided into two anatomically distinct
regions: the epidermis and the dermis ( cf. Figure 9.17). The epidermis prevents moisture
and heat loss from the skin and bacterial infiltration from the environment. A major
component of the epidermis is the keratinocyte, which forms overlapping structures
held together by desmosomes that provide cell-to-cell adhesion. The dermis is composed
of various amounts of glycoproteins and GAGs. The fibroblast is the cell type that is most
prevalent in the dermis and is responsible for synthesizing and depositing collagen
fibers in continuous networks that form the structural scaffold [89]. It can bear daily
assau lt s, i nclud i ng ha r m f u l u lt rav iolet rad iat ion f from t he su n, a nd sc ratc hes a nd wou nds
[90]. Its structure can be damaged under a stronger external force and it cannot finish the
self-repair. The healing of a skin wound involves complicated courses, including a wide
range of cellular, molecular, physiological, and biological processes. There are millions
of patients suffering from skin loss annually. The cost of skin recovery is about $36,000-
117,000 per patient. Full-thickness skin defects on large scale cannot be repaired sponta-
neously. In past decades, many skin substitutes such as xenografts, allografts, and
autografts have been employed for wound healing. However, due to the antigenicity or
the limitation of donor sites, these skin substitutes cannot accomplish the purpose of
skin recovery and hence are not used widely. The tissue-engineering skin strategy can

Hair shaft
Sweat
gland
pore
Capillary
Dermal
papilla
Basement
membrane
Touch
receptor
Sweat
gland
duct

Epidermis

Dermis

Subcutaneous
layer

Figure 9.17
Structure of human skin showing the upper epidermal barrier layer and the much thicker dermal layer with
hair follicles and sweat glands lined with epithelial cells. (From Shier, D., Butler, J., and Lewis, R. 1999. In Hole's
Human Anatomy and Physiology , 8th Edn. McGraw Hill, pp. 160-183. With permission.)