Biomedical Engineering Reference
In-Depth Information
are available in sheet, amorphous gel or sheet hydrogel impregnated dressings.
Hydrogels provide a moist environment for cell migration and absorb some
exudate. As absorption of exudate is poor, they can cause maceration. Examples
of these materials include Aquafoam, Intrasite, Nu-Gel, Purilon and Sterigel
Due to the complexity that characterizes the wound healing process, new
materials, usually known as multi-layered wound dressings, are being developed.
They are comprised by a combination of the different materials described above,
where each layer has a distinct property to enhance the wound-healing process,
maintains a proper moisture level, prevents adherence (consequently reducing the
pain associated with wound treatment and dressing changes) and at a relatively re-
duced cost [
15
-
17
]. These multi-layer products are usually constituted by a physical
bacterial barrier, an absorptive layer (alginate or other fiber-gelling dressing, foam,
hydrocolloid or hydrogel) and a semi-adherent or non-adherent layer over the wound
site. Examples of commercially available composite dressings include Stratasorb
(Medline), 3M Tegaderm (3M), Alldress (Molnlycke health Care), Covaderm Plus
(DeRoyal), Versiva (ConvaTech), Coversite plus (Smith & Nephew), Telfa Ventex
(Kendall), MPM (MPM), Viasorb (Sherwood-davis & Geck), Silon Dual-Dress (Bio
Med Sciences).
Recent research is centered on the use of biodegradable and biocompatible
materials to be used in each of the above discriminated layers. Healing of der-
mal wounds with natural polymers is attractive mostly because these polymers
(or their degradation products) are usually biocompatible and they present non-
irritant and non-toxic properties, thus being their dermis application easy and safe
[
18
]. Moreover, natural polymers are normally inexpensive, readily available from
renewable sources, potentially biodegradable and capable of a multitude of possible
chemical modifications [
19
]. These materials include alginates, collagens, chitosan,
chitin, derivatives from chitosan or chitin and their blends as is the case of chitosan
and alginate [
20
], alginate and water-soluble chitin [
21
] or collagen and chitosan
blends [
22
]. So far, research has focused on studies with alginate based materials
but the interest in chitin and its derivatives is growing due to the benefits that this
biomaterial presents to the wound healing process.
Chitin, a naturally abundant polysaccharide obtained from crustaceans (shrimps,
crabs and crawfish) and insects' shells is the second most abundant organic
compound in nature, after cellulose. Studies demonstrated that chitin represents
14-27% and 13-15% of the dry weight of shrimp and crab processing wastes,
respectively [
23
]. Chitin is highly hydrophobic and is insoluble in water and most
organic solvents, while chitosan, obtained from chitin by removing sufficient acetyl
groups (-COCH
3
) from the molecule, is soluble in dilute acids such as acetic
and formic acids. Several efforts have been reported in the literature to prepare
functional derivatives of chitosan in order to make them soluble in aqueous systems
[
24
]. The presence of the more or less bulky substituent weakens the hydrogen bonds
of chitosan inducing changes in the swelling capacity of the matrix, depending on
the hydrophobicity of the substituent, although retaining the film-forming property
of chitosan [
25
].
