Biomedical Engineering Reference
In-Depth Information
Among others, the main benefits of using chitin based materials for wound
healing are that they initiate fibroblast proliferation, help in ordered collagen
deposition, and stimulate an increased level of natural hyaluronic acid synthesis
at the wound site, leading to faster wound healing and scar prevention. Chitosan
possesses ionic charges, which leads to the ability to chemically bind with negatively
charged fats, lipids, cholesterol, metal ions, proteins and macromolecules. Chitosan
based materials also proved to exhibit radical scavenging activity towards a number
of radicals, being this activity directly related to the degree of deacetylation of
the macromolecule [
26
]. This property is important to regulate the inflammatory
process of the wound by reducing the reactive oxygen and reactive nitrogen species
that are overproduced by inflammatory cells, especially in chronic wounds [
27
].
N
-Carboxybutylchitosan, a modified and more water-soluble chitosan derivative,
presents inhibitory and bactericidal/fungal activities and is able to prevent secondary
infections leading to limited scar formation [
28
]. This biomaterial also presents
relatively good mechanical properties for several biomedical applications and can
be processed by different methods, originating materials in different forms and
shapes such as particles, thin films and porous monolith structures [
29
]. This is
an important issue when developing wound dressing materials as it will permit
to control the membranes permeation to water vapor and oxygen, their swelling
capacity, as well as the sustained rate-controlling release of drugs or bioactive
species, by varying the thickness and the porosity of the processed layers. Besides
its biocompatibility, it may also neutralize the wound alkalinity (pH
8) and restore
the natural pH of the wound or the skin. This happens due to its chemical inherent
acidity (presence of an acidic carboxylic group in their chemical structure) or to
the formation of acidic compounds during their hydrolysis by the action of skin
enzymes [
5
]. Agarose is a non-charged neutral polysaccharide that is soluble in hot
water and capable of forming thermoreversible physical or non-covalent hydrogels
when cooled down below its gelation temperature [
30
]. Because of its non-toxicity,
biocompatibility, favorable interactions with living cells and fast degradation into
non-toxic metabolites, agarose-based physical hydrogels are widely implemented in
many biological and medical fields [
31
-
33
] and, more recently, as natural polymer-
based scaffolds [
34
,
35
].
Based on intensive research, modern wound dressings are developed by taking
into consideration two essential factors: that the dressing is able to provide a moist
wound environment and able to stimulate the granulating process or protecting
against the damage of a new formed tissue. This later can be enhanced by the
impregnation of the dressing based materials with active substances like antibiotics
and antimicrobial and antiseptic agents such as calcium, zinc or silver ions,
framycetin, chlorhexidine acetate and povidone iodine. Zinc and copper ions in par-
ticular, besides being non-toxic, can be easily attached to wound dressings through
chelation with fibres containing amine groups. In this respect, chitosan fibres treated
with zinc and copper compounds have the combined antimicrobial properties of
the chitosan as well as the metal ions. Commercially available examples of these
impregnated materials include Acticoat, Aquacell Ag, Arglaes, Inadine, Iodoflex,
Silverlon, Sofra-Tulle, Bactigras and Inadine [
13
,
36
]. Recent studies have also
