Biomedical Engineering Reference
In-Depth Information
Chitosan, a deacetylation product of chitin, is a linear polysaccharide composed of
randomly distributed b-(1-4)-linked D-glucosamine (the deacetylated unit) and N-acetyl-D-
glucosamine (the acetylated unit), it is hydrophilic and exhibits good cell adhesion and
proliferation characteristics (Suh JKF & Matthew, HWT 2000)
Moreover, the N acetylglucosamine present in chitosan is a structural feature that is also
found in glycosaminoglycan, which is involved in many specific interactions with growth
factors, receptors and adhesion proteins. Chitosan as a glycosaminoglycan analogue might
therefore also exhibit similar bio-functionality. Furthermore, chitosan can create highly
porous structures that make it especially suitable for a scaffolding material used in tendon
tissue engineering (Kumar MNVR et al. 2004)
The bio-functionality of chitosan, such as supporting of cellular attachment and
proliferation, and the ability to induce cells to produce ECM has been demonstrated. In a
study conducted by Bagnaninchi et al. (Bagnaninchi et al. 2007), porous chitosan scaffolds
with microchannels were designed to engineer tendon tissues.
Hyaluronan (HA) is a uniformly repetitive linear GAG composed of disaccharides of
glucuronic acid and N-acetylglucosamine: [-b (1,4)- GlcUA- b (1,3)-GlcNAc-]n (Toole BP
2001) It is an essential component of ECM. Anionic hyaluronan interacts with other
macromolecules, such as link proteins and proteoglycans, to facilitate tissue morphogenesis,
cell migration, differentiation and adhesion (Toole BP 2001), whereas cationic chitosan can
elicit electrostatic interactions with anionic glycosaminoglycans and other negatively
charged species. (Kumar MNVR et al. 2004)
Hybridization of hyaluronan and chitosan is expected to augment the mechanical properties
and bioactivities of tendon tissue engineering scaffolds. Funakoshi et al. (Funakoshi et al.
2005a) demonstrated that scaffolds composed of hybridized chitosan-hyaluronan exhibited
enhanced mechanical competence. In another study, Funakoshi et al. (Funakoshi et al.
2005b) reported that the chitosan-hyaluronan scaffold improved the biomechanical
properties of the regenerated tendon tissue in the rotator cuff and bolstered production of
collagen type I.
Alginate, another type of polysaccharide that can be used for hybridization with chitosan, is
an anionic polysaccharide composed of homopolymeric regions of glucuronic acid and
mannuronic acid interspersed with mixed sequences (M-G blocks). Because it contains D-
glucuronic acid as the main sugar residue in the repeat unit, alginate is often considered to
have similar biological activity to glycosaminoglycans. However, owing to its anionic
nature, cell adhesion to alginate is often unsatisfactory (Rowley JA et al. 1999) (Genes NG et
al. 2004)
Adding cationic chitosan to alginate would augment the bio-functionality of the scaffold
because the ionic interactions between alginate and chitosan are expected to facilitate
retaining and recruiting of cells and growth factors, as well as cytokines (Madihally SV &
Matthew HWT 1999) (Hsu SH et al. 2004)
It was reported that an alginate-chitosan hybrid scaffold showed significantly enhanced cell
adhesion to tenocytes. (Majima et al. 2005)
2.4 Decellularized scaffolds
In order to be utilized successfully as a biomaterial, native extracellular matrix must first be
decellularized to remove any allogenic cells and to prevent adverse immunological
reactions. Native scaffolds are bioactive and promotes cellular proliferation and tissue
ingrowth.
