Application of Chitosan-Based Biomaterials in Tissue Engineering - Chitosan Based Hydrogels: Functions and Applications - page 423

overcome these disadvantages. Tissue-engineered skin needs to (a) provide a barrier layer
of renewable keratinocytes (the cells that form the upper barrier layer of our skin), which
is (b) securely attached to the underlying dermis, (c) well vascularized, and (d) provides
an elastic structural support for skin [91], which can mimic the structure of normal skin.
Chitosan can influence the behaviors of keratinocytes and fibroblasts and can
modulate human skin cell mitogenesis [41]. It has the functions of hemostasis and steriliza-
tion. Moreover, the structure of the chitosan molecule is similar to GAG and can stimulate
fibroblast synthesis of collagen. These characters endow chitosan-based biomaterials with
the ability to construct epidermal, dermal, or even epidermal-dermal replacement.
9.5.2.1 Epidermal Cover
Research into epidermal tissue engineering has revealed three periods: epidermal cell
suspension, epidermal sheet, and epidermal cell-biomaterials composites [92]. Keratinocytes
did not proliferate on the chitosan matrix. Chitosan seemed to be cytostatic toward human
keratinocytes: it is not cytotoxic, but inhibits cell proliferation due to extremely high adhe-
sion behaviors [93]. That is to say, pure chitosan is very difficult to construct the epidermal
substitute. Some peptides, proteins, or polysaccharides are conjugated into the chitosan
network to modulate the proliferation and migration behaviors of keratinocytes. However,
it is important to note that the keratinocyte-chitosan-based biomaterials allogenic graft
acts only as temporary coverage, helping to reduce inflammation and decrease the severity
of hypertrophic scarring. The graft was eventually replaced by autologous keratinocytes
migrating from the basement film or periphery [94].
Compared with pure chitosan, chitosan-gelatin film can improve the proliferation of
keratinocytes. Moreover, increasing the contents of gelatin in chitosan-gelatin film could
promote keratinocyte migration. The migration distance of cultured keratinocytes on
pure chitosan film was 61.47 ± 2.70 μm, while this value increases to 66.22 ± 9.39 μm,
120.31 ± 15.82 μm, and 225.38 ± 10.48 μm when the ratio of chitosan to gelatin is 7:3, 5:5, and
3:7, respectively [95]. That is to say, keratinocytes migrated out of the film into the wound
where they aggregated to form stratified structures resembling the epidermis [96]. Human
tissue-engineered epidermis can be constructed by culturing human keratinocytes onto
chitosan-gelatin film ( cf . Figure 9.18) [97]. The keratinocyte-chitosan-gelatin epidermal
film can successfully promote the healing of the skin graft donor sites compared with the
classic treatment method (petroleum jelly gauze). On postoperative day 7, the average healed
surface area was 91% for the keratinocyte-chitosan gelatin group and 31% for the classic
treatment method. At 3 months, the epidermis was well differentiated ( cf. Figure 9.19) [98].
The development of nanotechnology provides another effective method for constructing
the chitosan-based epidermal coverage. Some nanoparticles, such as silver nanocrystalline
[99], nano-titanium oxide [100], and nanosized gold colloid [101], were combined into a
chitosan network to modulate the behavior of keratinocytes and promote the formation of
new epidermis. The viability of keratinocytes attached or proliferated on the chitosan
nanofibrous scaffolds was greater than that on the chitosan film counterparts owing to the
larger surface area of the fibrous scaffolds that is available for the cells to attach.
9.5.2.2 Dermal Equivalent
The dermis can increase elasticity, softness, and mechanical wear and decrease scar prolif-
eration. The dermis is composed of various amounts of glycoproteins (e.g., collagen, elas-
tin, fibronectin, laminin, and chondronectin) and GAGs (including HA, chondroitin