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Chitin is second most abundant polysaccharide in nature after cellulose. Chitin is a high molecular weight linear polymer. It is a copolymer of N-acetyl-glucosamine and N-glucosamine units linked by Î²-D (1ïƒ 4) bonds. If the number of N-acetyl-glucosamine is higher than 50%, it is known as Chitin. On the other hand if N-glucosamine units are higher than they are known as Chitosan (Figure 1).
Figure1. Schematic representation of the chitin and Chitosan depicting the co-polymer character of the biopolymers
It resembles cellulose in solubility, as it is highly insoluble material with low chemical reactivity. It functions as a structural polysaccharide naturally. Chitin is a white, hard, inelastic material and it causes lot of trouble in coastal areas because it leads to surface pollution. Nitrogen content in Chitosan is high .i.e. 6.89% as compared to synthetically substituted cellulose (1.25%) which makes due to this it is of great interest commercially. Figure 2 shows the structure of cellulose, chitin and Chitosan.
Figure 2 Structures of cellulose, chitin, and Chitosan
Wound healing is a complicated process. In cases of distortion of tissue structure, tissues may not be healed as it was before. Furthermore, it can lead to fibrous appearance lowering mechanical strength and which leads to scar formation. To overcome this issue, biomaterials which provides better healing of tissues and avoiding scar tissue formation plays vital role. Chitin, Chitosan have been found to promote wound healing particularly in phase of proliferation and matrix formation.
Problems faced in wound dressing:
Major problem faced in wound healing includes antibiotic resistance of microorganisms which causes infection and delayed wound healing. In this article, researchers have developed novel chitin /nanosilver composite scaffolds for wound healing applications.
Why silver is used:
Due to its polycationic nature silver acts as an effective antibacterial agent. It can be used in wound dressings as it is very effective when used in forms of nanoparticles as the surface area to volume ratio of silver nanoparticles is high which leads to better contact with bacteria.
Antibacterial activity studies:
Bacterial efficiency of Chitin/ nanosilver composite scaffolds against gram positive S.aureus is shown in figure 6a while gram negative E. coli is shown in figure 6b. There is limitation to the movement of silver nanoparticles in gram positive bacteria as these are protected by a thick peptidoglycan wall which provides inhibition zone in E.coli than S.aureus. As there is increase in nanosilver particles zone of inhibition also increases. Thereby, we can conclude that antibacterial activity is due to presence of nanosilver in chitin scaffolds.
Due to presence of silver nanoparticles these scaffolds were found to be toxic. Though it is ambiguous that this will effect on wound healing as previous studies have shown that wound dressing having nanoparticles are cytotoxic in vitro, while they give satisfactorily results in vivo.
Chitosan which is prepared from natural biopolymers was casted into membrane which was furthermore tested for wound dressing at the skin graft donor site in patients.
Bactigras which is commonly used as impregnated tulle grass bandage, acted as a control. Shrimp Chitosan which are having 75% degree of deacetylation and thickness of 10 Âµm was used in nonmesh and mesh form. After the measurement of thickness, moisture content and swelling index, Chitosan membranes were sterilized and kept at room temperature in dry and clean place until used.
For testing purposes patients were admitted who needed split skin grafts. After the removal of skin layer .i.e. 0.010-0.105 inch thickness Chitosan membranes were applied to cover the fresh wound. Half of the wound was dressed with Chitosan membrane and other half with control Bactigras. It was random and about 20-25 pieces of gauze were used wrapping with elastic bondage. From day 0 to day 10 digital images were taken. After the removal of dressing healed and unhealed areas were compared.
Chitosan served as a successful wound dressing material as it adhere uniformly to wound surface there by reducing bacterial growth, hence reducing pain.
Non mesh membrane versus mesh membrane:
Blood clots were formed between the non mesh Chitosan membrane and regenerating epithelial tissue of the wound. Cleaning of clot was painful and there was damage of new epithelial tissue when clot was removed which leads to scar formation in the healing area. Whereas wounds which were dressed with Chitosan mesh membrane did not show any blood clotting. Mesh membrane was easy to clean off and there was no pain upon removal (Figures 3&4)
Figure 3 Wound site treated with Bactigras (B) and nonmesh Chitosan membrane (C). (a) Dressing on Day 0, (b) covering gauze showing soaked blood at Day 1, (c) blood clotting at Day 1 and (d) scar formation at 2 months.
Figure 4 Wound site treated with Bactigras (B) and Chitosan mesh membrane (CM). (a) Meshed
Chitosan membrane, (b) covering gauze showing soaked blood at Day 1, (c) healed wound at Day 10, and (d) scar formation at 1 month
Healing time is defined as the time which is needed for removal of dressing without any need of soaking and bleeding. In case of mesh Chitosan membrane healing rate was faster and better as compared to non mesh membranes.
Table1: Histological Findings of Masson's Trichrome Stain
Studying of wound healing in human body was followed by animal model using rats. Clinical data shows that mesh Chitosan membranes give more efficient adherence, hemostasis, healing and re-epitheliazation of wound as compared to non mesh Chitosan membrane. In case of mesh membrane itching and pain is also less and use of no mesh membrane is not advised.
Synthesis of PEG
Hydrogels are large polymeric compounds which can retain huge amount of water within their structure without dissolving in them which gives them resemblance to living tissue.
Use of Î²- Chitosan as hydrogels:
Î²- Chitosan has much higher reactivity and versatility than Î±- chitin because Î²- chitin has very weak hydrogen bonding. There is a solubility issue in Î²- chitin as formic acid is used to prepare solution which irritates human skin but this issue can be resolved by preparing hydrogels under milder conditions.
Synthesis of PEG/ Î²- Chitosan:
PEG was dried by azeotrophic distillation with benzene and then acryloyl choride was added to it which yields acrylate terminated PEGM. This acrylate terminated PEGM was synthesized by UV- irridation in presence of aqueous acetic acid which gives PEGM/ Î²- Chitosan semi- IPN. For detailed synthesis refer schematic Figure 4
Figure5 Synthesis scheme of PEGM/ Î²- Chitosan semi- IPN
Synthesis of PET
Poly (ethylene terephthalate) PET was treated with oxygen plasma to produce peroxides on its surface. Further it was treated with Acrylic acid involving graft polymerization to yield PET-A.
PET-A-C and PET-Q-C were obtained using Chitosan and quaternized Chitosan (QC) respectively by treatment of PET-A with carboxyl groups.
Poly (ethylene terephthalate) PET, Chitosan, Quaternized Chitosan (QC) and acrylic acid
PET - A was obtained by treating PET with oxygen plasma. It was then immersed in 10% acrylic acid, and sodium pyrosulfite was used as reducing agent which gives (PET-A) which is shown in scheme1.
Scheme 1 Oxygen plasma treatment of PET and graft polymerization of acrylic acid (AA) on PET.
This PET-A obtained was further used to obtain PET-A-C and PET-A-QC which is explained below:
Chitosan grafting to obtain (PET-A-C)
Firstly, PET-A was dipped in Chitosan solution for 8 h which leads to immobilization of Chitosan on the surfaces and then it was oven dried for 5 min at 120oc. This leads to production of PET-A-C+ sample. PET-A was dipped in a 0.1% (w/v) 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide(wsc) aqueous solution for 3hr at 4oc to activate the carboxyl groups on the surfaces and it was transferred into Chitosan solution which gives (PET-A-C) which is Chitosan grafted PET (refer scheme2)
Scheme 2 Schematic diagram showing the formation of Chitosan-grafted poly (ethylene
Quaternization of Chitosan was carried by adding a 5gm of Chitosan to 250 ml of N-methyl-2-pyrrolidinone followed by stirring at room temperature for 12 hrs. Ice water was used to lower the temperature of suspension to 4oc. 43 ml of 1.4NNaOH aqueous solution, 6g of sodium iodide, and 64g methyl iodide were added to this solution. Excess of acetone was removed using filter paper. This procedure was repeated five times. For the activation of carboxyl groups PET-A was dipped into a sodium citrate buffer solution containing 0.1% water soluble carbodiimide. QC grafted PET which is (PET-A-QC) was obtained by dipping QC solution at 4oc for 24 hrs to activated PET-A (Scheme 3)
Scheme 3 Schematic diagram showing the Quaternization of Chitosan and their
Immobilization on PET-A
Strengths and weaknesses:
Chitin and Chitosan are natural polymers due to this; they have excellent properties such as biocompatibility, biodegradability, non-toxicity and adsorption.
As Chitosan is naturally abundant material which exhibits limitation on its reactivity and processability
Chemically modified chitin and Chitosan provides great increase in their solubility in general organic solvents.
In coastal areas it acts as major source of pollution
These are highly basic polysaccharides, which provides them properties such as polyoxysalt formation, optical structural characteristics and they can easily form chelate metal ions and films
It is highly hydrophobic, is insoluble in water and most organic solvents
When fibers of chitin and Chitosan are made these are very useful in field of absorbable suture and wound dressing materials
Due to poor solubility, there is limitation on chitin utilization which makes it difficult to investigate its properties and structure.
When wound dressing is made of chitin and Chitosan, these play vital role in removal of heavy metal ions (waste water treatment)
It is the only natural cationic gum that becomes viscous on being neutralized with acid.
Chitin Derivatives and Their Proposed Uses
Formyl, acetyl, propionyl, butyryl, hexanoyl, Textiles, membranes, and
acetanoyl, decanoyl, dodecanoyl, tetradecanoyl, medical aids
lauroyl, myristoyl, palmitoyl, stearoyl, benzoyl,
trifluoroacetyl, carbamoyl, succinyl
Textiles, membranes, and
, medical aids
N-Carboxyalkyl (aryl) chitosans
N-Carboxybenzyl, glycine-glucan, N-carboxy- methyl Chitosan, alanine glucan, phenylalanine glucan, tyrosine glucan, serine glucan,
glutamicacid glucan, methionine glucan,
Chromatographic media and metal ion collection
o-Carboxymethyl, cross-linked o-Carboxymethyl
Molecular sieves, viscosity
builders, and metal ion
Metal ion chelates
Palladium, copper, silver, iodine
Catalyst, photography, health
products, and insecticides
Application of Chitosan
Chitosan and its derivatives have a wide range of applications. Hydroxyl methyl chitin and water soluble Chitosan derivatives can be used to solve environmental and biomedical problems, such as anionic waste streams. For controlled drug release applications Chitosan derivatives can be employed as a carrier. It can be useful to be bio-scaffold for tissue engineering particularly in case of skin and bones. Chitosan possesses all the desired features for an ideal contact lens like optical clarity, optical clarity, optical correction, mechanical stability, gas permeability, wettability and immunological compatibility.
Future directions for further research and development
In case of in vivo toxicity studies comparison with experimental animals is very useful for attaining in vitro biocompatibility models. As biocompatibility of biomedical grade Chitosan is tedious phenomenon compromising other immune reactions with various inflammatory cells, therefore we cannot completely replace toxicity studies in experimental animals. By comparing the biocompatibility results both from both in vitro and in vivo we can be little secured but for full assurance we need to try clinical trials of newly developed synthesized biomedical grade Chitosan on the humans .For the study of single cell proliferation and invasion pattern within a porous structured biomedical grade Chitosan gives better results as compared to in vivo model.
There are recent advancements in understanding of biology, chemistry and related fields which will give more development of present in vitro biocompatibility model. To minimize risk to humans and animals we should focus detailed evaluation of not only cellular but also molecular responses that we can do in vivo tests.