This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.
The selection of wound types has resulted in a wide range of wound dressings with new products often begun to target different aspects of the wound healing process. The perfect dressing has to accomplish fast healing at acceptably price with minimal annoyance to the patient. Also important is the use of biological polymers as tissue engineered scaffolds and skin grafts. Direct delivery of these agents to the wound site is preferable, mainly when systemic delivery could cause organ injury because of toxicological concerns combined with the preferred agents (Boateng, Matthews, Stevens, & Eccleston, 2008).
Figure 1. Structure of the Human skin
They used crude drug extracts (mostly of plant origin), animal fat and honey to heal wounds. For example in Senegal, the people used the leaves of Guiera senegalensis to put on wound. In Ghana the people used extracts of Commelina diffusa herb and Spathodea campanulata bark to put on wound and heal it. The interesting point is that the researches have shown that some of these extracts and herbs have indeed antibacterial and antioxidant effect (Boateng et al., 2008).
In order to specify optimal features of ideal wound dressing, dressings must contain a fine balance of characteristics; they should facilitate the quick and successful healing of wounds, be safe and biocompatible, and, if possible, contain a curative to enhance the healing process.
An ideal material to be applied to wound should be nontoxic and biocompatible, enhance cellular interaction and tissue development (Huang and Fu, 2010). done
Some of wound dressings can cause allergic reactions when applied to the defected
area. There are three kind of allergic reactions that can appear via wound dressings:
Irritant reactions that originally have mechanical reasons. These reactions can
happen because of occlusion or strong adhesion of dressing to the wound
Immediate allergic reaction (contact urticaria)
Delayed allergic reactions (contact eczema) (Goossens and Cleenewerck,
1.1.1Classification of dressings
Dressings can be classified in a number of ways. They can be classified based on
their function in the wound (antibacterial, absorbent), type of material employed to
produce the dressing (collagen, hydrocolloid), physical form of the dressing
(ointment, film and gel), traditional and modern dressings. Some dressings can be
placed in several classifications because they fit criteria in several groups. The
simplest classification is as traditional and modern dressings and particular focus will
be given to hydrogels, one of the most common modern dressings (Boateng et al,
To meet this need, we have created a novel wound dressing from a complex of collagen and Polyhema which are biocompatible, bioabsorbable, biodegradable, and has therapeutic efficacy. Here, we present the methods by which this dressing was fabricated, and we describe the results of an investigation of the dressing's physiological properties.
1.2 Materials used for wound dressings (properties / main types of materials:
Many natural polymers and their synthetic analogues are applied as biomaterials, however the characteristics of collagen as a biomaterial are clear from those of synthetic polymers mostly in its mode of interaction in the body (Lee, et al., 2001). Done
Naturally occurring materials such as purified collagen and hyaluronic acid have been considered as alternatives to synthetic scaffolds (Bao et al, 2008).
This type of dressing is produced from calcium and sodium salts of alginic acid, a polysaccharide comprising mannuronic and guluronic acid units. When alginate dressings are applied to the wound, ions present in the alginate fibers are exchanged with those present in exudates and blood. This makes it possible to maintain an optimal moist environment and an optimal temperature for the wound during healing process. They can be used for moderate to heavily exuding wounds (Boateng et al., 2008). Alginates can hold water up to 20 times of their weight. Alginates contain
calcium and sodium salts of alginic acid. An ion exchange occurs between calcium from alginate and sodium from wound fluid, forming sodium-calcium alginate which gives a gelatinous mass and can keep the moist environment (Fonder et al., 2008). done
Figure 7: A classical hydrocolloid dressing
Hydrocolloid dressings: unwichtig
This group of dressings is a combination of hydrocolloid materials (gel forming agents) and other materials such as elastomers and adhesives. They are widely clinically used because they can adhere to both dry and moist surface. They are used mostly in light to moderately exuding wounds (Boateng et al., 2008).
In contrast to hydrogels, hydrocolloids have the absorbent ability. They absorb wound exudate and form a hydrophilic gel that helps to maintain a moist environment. These types of dressings are adhesive, occlusive and comfortable dressings. They have less moisture vapour transmission compared to films and manage absorb exudate well (Fonder et al., 2008). done
Chitosan has been helpful for many biomedical applications, including wound dressing, tissue engineering applications, and drug delivery, because it has good biocompatibility, low toxicity, and degradation by enzymes such as chitosanase. Chitosan is readily soluble in the presence of acid and is insoluble in neutral conditions and most organic solvents. Many chitosan derivatives have been enhancing solubility and processing. Moreover, chitosan was found to wound healing and it is also an ideal wound dressing. (Huang & Fu, 2010) done
Chitin/Chitosan from victory
Chitin is the second abudant natural polymer in the world after cellulose
Chitin occurs as a component of crustacean shells, insect exoskeletons, fungal cell walls, micro fauna and plankton
Chemically chitin is a polymer formed primarily of repeating units of N-acetylglucosamine
Most commercial applications use of deacetylated derivative, chitosan
Chitosan is a polysaccharide formed primarily of repeating units of D-glucosamine
Synthetic materials such as poly (Image )-(lactic acid) and poly(glycolic acid) have received considerable attention for tissue engineering applications. Synthetic materials have predictable and reproducible mechanical and physical properties, for example tensile strength and pore size and can be manufactured with great accuracy. On the other hand, synthetic materials tend to extract a foreign material type of response in the host, in particular, a fibrous connective tissue deposition leading to formation of dense scars and fibrosis. Naturally occurring materials such as purified collagen and hyaluronic acid have been considered as alternatives to synthetic scaffolds (Bao, et al., 2008).
Biodegradable synthetic polymers provide a number of benefits over other materials for developing scaffolds in tissue engineering. The main advantages include the ability to tailor mechanical characteristics, degradation kinetics to match diverse applications and in addition they are attractive since they can be fabricated into diverse shapes with favoured pore morphologic performances conducive to tissue in-growth. Moreover, polymers can be designed with chemical functional groups that can commence tissue in-growth.
Biodegradable synthetic polymers such as poly (lactic acid), poly (glycolic acid) and their copolymers, poly(p-dioxanone), and copolymers of trimethylene carbonate have been applied in a number of clinical applications. The chief applications include resorbable sutures, drug delivery systems and orthopaedic fixation devices such as pins, rods and screws. And also the polyesters have been attractive for these applications because of their ease of degradation by hydrolysis of ester linkage, degradation products being resorbed through the metabolic pathways in some cases and the potential to tailor the structure to alter degradation rates. Polyesters have been considered for development of tissue engineering applications( Pathiraja A.Gunatillake and Raju Adhikari) done
Properties of Collagen
Collagen is the major fibrous protein of extracellular connective tissues, and it is also the most ubiquitous and plentiful protein in the animal kingdom. Collagen is synthesized by fibroblasts and degenerated by metalloproteinases (e.g. collagenases). They are the most abundant type of protein in the human body comprising more than 30% of the total body protein. The word collagen is derived from Greek word kola (glue) plus gene. The function of nearly all systems and organs of the body is dependent on collagenous structures. About 70 percent of the dry weight of the skin is collagen. Use of collagen for wound healing has drawn tremendous interest from the scientist in recent years. (endarbeit) .done
In addition collagen has been joined with other materials for application, for instance collagen microsponges can be simply impregnated into earlier prepared synthetic polymer scaffolds to improve mechanical performance. Collagen has good biocompatibility, weak antigenicity and degradation and water uptake properties. In spite of its biocompatibility property, collagen is mechanically weak and goes through fast integration upon implantation (Huang & Fu, 2010).
The efficacy of collagen in biomedical application is that collagen can form fibers with more strength and stability through its self-aggregation and cross-linking. Mostly drug delivery systems prepared of collagen, in vivo absorption of collagen is checked by the use of crosslinking agents, such as glutaraldehyde. (Lee, et al., 2001). Done
Applications of collagen
The application of collagen as a drug delivery system is very comprehensive.
The most important applications of collagen as drug delivery systems are collagen shields in ophthalmology, sponges for wounds, and tablets for protein delivery, as controlling material for transdermal delivery, and tissue engineering including basic matrices for cell culture systems (Lee, et al., 2001). Done
The Structure of Collagen
The collagen molecule is a triple helix assembled from three individual protein chains
The collagen molecules contribute a structural framework to other issues, such as blood vessels and most organs. Six types of collagen have been isolated. (I-VI)
Collagen is the principal protein component of skin tendons, bone and blood vessels.
Figure 1: Triple Helical Structure of Collagen
Types of Collagen
The collagens represent a large family of proteins and at least 19 different collagen types have been described so far (Prockop and Kivirikko 1995; van der Rest and Garrone 1991). These are divided roughly into three groups, based on their abilities to form fibrils.
The most easily recognized forms of collagens are those that form banded fibrils, and these are called fibril-forming collagens. Type I, II, III, V, and XI collagens belong to this group. In these molecules, the triple helical domain contains an uninterrupted stretch of 338 to 343 GIy-X-Y triplets in each alpha chain, and the molecule measures 15 x 3000 A (Ramachandran and Ramakrishna; Peiz 1976).
The second group of collagens consists of proteins in which collagenous domains are interrupted by noncollagenous sequences (Fibril associated collagens with the interrupted triple helices - FACIT), and includes collagen types IX, XII, XIV, and perhaps XVI. The type IX, XII, and XIV collagens are unique as they contain glycosaminoglyscan components covalently linked to the protein. All other nonfibrillar collagens form the third group, including network forming collagens (types IV, VII and X) those forming beaded (type VI) and anchoring fibrils (type VII) and invertebrate cuticle collagens. These collagens form
sheets of proteins incorporating short triple helical collagen domains. This group of collagen includes the Clq component of Cl complement, lung surfactant protein, acetycholinesterase, and mannose binding protein.
(Paulo et al., 2010) http://www.chemicalregister.com/upload/cr/1991.png
Poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels were first studied and prepared for biological use by Wichterle and Lim. They have then been commonly explored and applied in biomedical applications. PolyHEMA hydrogel is flexible, biocompatible, non-toxic and has no antigenic properties (Hsiue, Guu, & Cheng, 2001).
It is used to manufacture skin coatings, immune isolation membranes, polyHEMA hydrogel presents light weight. Although polymers are considered prosperous as biomaterials, it may bring hazard along due to its degradation and interaction with the tissue.(Paulo et al., 2010). done
Poly(2-hydroxyethylmethacrylate) [poly(HEMA)] is a widely used biomaterial which does not allow cell adhesion and growth on its surface, limiting its use in biomedical applications in which cell cohesion is detrimental (Santin et al., 1996).
Applications of polyHEMA hydrogel are versatile and it has been used in the post-surgical reconstruction of nasal cartilages, artifcial corneas and wound dressings in the control of wound infection. The main disadvantage of the polyHEMA hydrogels in application is its bad
mechanical property after swelling. Methods for advancement have been well documented, for example bulk copolymerization, grafting onto cotton cellulose or polymers, for instance, styreneÂ± butadieneÂ±styrene; and forming interpenetrating composite network with natural biopolymers like collagen. Done
These modified composites showed better strength than the pure ones, their poor mechanical properties still remained. We have previously observed that the extent of water in the gels from different batches of the newly synthesized pure polyHEMA fail to exhibit proper mechanical properties. This observation prompted us to hypothesize that the amount of water initially added to the monomer mixture may later determine the tensile strength of the membranes of the newly synthesized polymers. In this study, the effect of initial water content in the monomer mixture and the equilibrium water content in the polymer on the physical properties of the polyHEMA products such as polymerization degree, wettability by water, dimensional change during swelling and the tensile strength are discussed. (Young, Wu, & Tsou, 1998).
An Overview of PolyHEMA
2-Hydroxyethylmethacrylate (HEMA) is an important functional monomer, which was first used in biomedical applications and now widely used in the manufacture of soft contact lenses ( Montheard et al, 2002)(Dumitriu et,al 1994).
Applications of PolyHEMA
Applications are due to high mechanical stability, high refractive index and oxygen permeability. It forms non-ionic hydrogels and exhibits no pH dependent swelling. The monomer is water-soluble while the polymer has limited solubility. This phase behaviour allows the formation of a macroporous sponge structure when reacted in dilute monomer solutions. The water content can be regulated by copolymerization with hydrophobic or hydrophilic comonomers . Mizuno et al. have investigated the structure of water sorbed into HEMA copolymers by attenuated total reflection infrared spectroscopy (ATR-IR). Their results indicate that the interaction between the primary hydration water around the polymer chains and the water surrounding the primary hydration water is very weak. This confirms the formation of cold crystallisable water generated by caging water molecules in a small space by the polymer chains. Although high molecular weight HEMA homopolymer is hydrophilic and has relatively high degree of hydration, it is usually known as water swellable, rather than water-soluble . This insolubility may be linked to the presence of low level of ethylene glycol dimethacrylate found in HEMA monomer, which could lead to some crosslinking reaction during polymerization. HEMA cannot be polymerized by anionic polymerization due to the presence of labile proton on the hydroxyl group. Moreover in radical polymerization, the key difference between acrylate and methacrylate polymerization, which can be pronounced in ATRP processes, is that, like methyl methacrylate (MMA), the propagating radicals of HEMA are more stable and propagate more slowly. Unlike MMA, solvents required to dissolve HEMA polymer are very polar, which may dramatically affect the polymerization process. Beers et al.  and Weaver et al.  have reported efficient and controlled polymerization of
HEMA using atom transfer radical polymerization in mixed solvents at lower temperatures.
1.5 Bioadhesive properties of wound dressings (generalities on adhesion / theories of adhesion / importance for wound dressings)
The term bioadhesion is specified as adhesion between two materials where at least one of the materials is of biological origin. In the case of bioadhesive drug delivery systems, bioadhesion regularly relates to the adhesion between the excipients of the formulation and the biological tissue. The aspect of applying bioadhesive materials in the progress of pharmaceutical formulations emerged in scientific articles in the early 1980s (Edsman & Hagerstrom, 2005).
Bioadhesives are used for tissue adhesion and hemostasis in surgery. The most commonly used surgical adhesive is fibrin glue. However, it is readily separated from the adhered tissue since its poor bonding strength (Edsmann). Done
Bioadhesives are used for tissue adhesion and hemostasis in surgery. The most commonly used surgical adhesive is fibrin glue. However, it is readily separated from the adhered tissue since its poor bonding strength (Sung, Huang, Chang, Huang, & Hsu, 1999).
L. Maggi New 19.12. done
Bioadhesion occurs under various degree of hydration and nearly in every application has to be reversible. The materials used should not change tissue activity and functionality. Bioadhesion is fairly a complex occurrence since a lot of physiochemical variables are involved in the procedure. Consequently, a new standardized method is required to screen the bioadhesive properties of various materials. It must be versatile enough to be modified to various experimental conditions, especially to simulate the biological environment and at the same time, able to produce similar results.
The method most widely used for this purpose is the fracture test.
The five theories that are most commonly presented in conjunction with bioadhesion are the absorption, diffusion, electronic, fracture and wetting theories.
Another important physical property of dressings meant for application to moist wound surfaces, is adhesive strength both in vivo (bioadhesivity, mucoadhesion) and in vitro (adhesivity). Adhesivity has been defined as the force required to detach a sample from the surface of excised porcine skin292 (using a Texture Analyser, a common type of mechanical testing equipment). The test is adopted from characterisation of bioadhesive polymeric formulations meant for application to other moist surfaces such as vagina, buccal and nasal cavities.271, 293-296 Sakchai et al.220 have determined the bioadhesive properties of Eudragit-chitosan film dressings by measuring the force required to detach the film from pig large intestine washed in physiological solution. Peppas and Buri297 have discussed the surface and interfacial phenomena that occur during bio-adhesion of polymeric molecules to soft tissue including wound surfaces. Adhesivity can also be determined by evaluating various tensile responses of different gels.296 Adhesivity is important in wound healing where dressings should be self adhesive with the wound, easily removed and painless (i.e. it must have reduced adhesiveness with time).296 The force of adhesion depends on factors such as hydrophobicity which is reported to improve bioadhesion,105 level of hydration and rate of polymer erosion in contact with the hydrating surface.298 A novel drug-loaded wound dressing with optimised adhesive drug releasing properties was developed by binding self-adhesive Eudragit E (cationic copolymer based on dimethylaminoethyl methacrylate and neutral methacrylic esters) film with antibacterial loaded poly(N-isopropyl-acrylamide) microgel beads to achieve adhesive, absorptive and easy to peel functions.299. (Boateng et al., 2008)
2. AIMS AND OBJECTIVES
The aim of the present study is to evaluate the bioadhesive properties of novel polymeric materials prepared from collagen poly(HEMA) which were designed for skin regeneration and drug delivery.
The main objectives of the present study:
were particularly to measure the adhesive properties such as total work of adhesion and force of detachment of a variety of materials in contact with artificial membranes by using an automated Texture Analyser.
Raman spectroscopy will possibly be applied in a try to gain an insight into the intimate structural aspects responsible for the adhesive behaviour of these materials.
Was obtained from Fisher Scientific (UK)
The collagen films used in this study were supplied by the Faculty of Biomaterials and Bioengineering, University of Iasi, Romania.
Preparing of Phosphate buffer (PB), pH 7.0
A litre of BP solution was prepared using the following solutes and their corresponding quantities: xxxxxxxxxxx
Distilled water ( ml) was added and the solutes were allowed to dissolve using a magnetic stirrer for 15 minutes. The solution was made up to a litre by adding distilled water.
The temperature of the water bath of the phosphate buffer was kept at 37 ËšC.
3.2.2. Preparation of collagen samples
A software controlled penetrometer, TA-XT2 Texture Analyzer (Stable Micro Systems, UK), with a 5 kg load cell, a force measurement accuracy of 0.0025% and a resolution of 0.0025 mm was applied in texture analysis (Tamburic & Craig, 1997).
This apparatus is able to determine the resistance that a probe comes across to penetrate into a semisolid material as a function of distance, however can also carry out tensile experiments. The main difference is that the Texture Analyzer can adjust and keep the preload applied to the viscoelastic settlement of the sample. The control unit, by continuous monitoring of the force used, drives the motor to move the sliding stand upwards or downwards to maintain the selected preload value (500g in this case) stable for all the preload time. The force required to detach the polymer from the substrate is recorded as a function of elongation. With the software equipped both maximum strength and work of adhesion can be obtained (Maggi et al., 1994).
Apparatus: A-XT2 Texture Analyzer (Stable Micro Systems, UK)
The pre-test speed was set up at 1 mm/s, the test speed at 2 mm/s a and the penetration depth at 5 mm, with an acquisition rate of 100 points/s. The probe used was a plastic cylinder with a diameter of 13 mm. The study was carried out at room temperature (37 C) with at least at three repeats obtained for each sample (Tamburic and Craig, 1997)
Text procedure: The sample to be examined is fixed to the sliding stand using a double side tape. The sliding stand is conveyed into contact with the collagen samples and a preload is used. A given time is left for the establishment of adhesion bonding called preload time. The sample holder is then lowered at constant speed (0.1 mm/s), the measurement ends when the two substrates are totally detached. The force calculated by the transducer, during the process, is plotted versus distance. A negative peak is obtained whose maximum value, normalized by the 1 cm2 is considered as bioadhesion strength. This procedure is validated and standardized for the in vitro determinations in a previous study in which the main variables, able to influence the phenomenon, were also discussed. Half done. Maggi
Fig. 1. Typical plot obtained from the Texture Analyser (with an applied
force of 12.5N and a contact time of 10 s).