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).
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
Synthetic materials such as poly (Image )-(lactic acid) and poly(glycolic acid) have received considerable attention for tissue engineering applications and have shown promise in preclinical animal studies and some early human clinical trials. Synthetic materials have predictable and reproducible mechanical and physical properties (e.g., tensile strength and pore size) and can be manufactured with great precision. 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.
http://www.biomedcentral.com/content/figures/1471-2334-5-45-1.jpg
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.
1.4 PolyHEMA (general properties and applic, in detail)
http://www.chemicalregister.com/upload/cr/1991.png(Paulo et al., 2010)
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, styrene± butadiene±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).
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).
