Natural and synthetic polymers for wounds and burns dressing

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Abstract

In the last years, health care professionals faced with an increasing number of patients suffering from wounds and burns difficult to treat and heal. During the wound healing process, the dressing protects the injury and contributes to the recovery of dermal and epidermal tissues. Because their biocompatibility, biodegradability and similarity to macromolecules recognized by the human body, some natural polymers such as polysaccharides (alginates, chitin, chitosan, heparin, chondroitin), proteoglycans and proteins (collagen, gelatin, fibrin, keratin, silk fibroin, eggshell membrane) are extensively used in wounds and burns management. Obtained by electrospinning technique, some synthetic polymers like biomimetic extracellular matrix micro/nanoscale fibers based on polyglycolic acid, polylactic acid, polyacrylic acid, poly-ɛ-caprolactone, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, exhibit in vivo and in vitro wound healing properties and enhance re-epithelialization. They provide an optimal microenvironment for cell proliferation, migration and differentiation, due to their biocompatibility, biodegradability, peculiar structure and good mechanical properties. Thus, synthetic polymers are used also in regenerative medicine for cartilage, bone, vascular, nerve and ligament repair and restoration. Biocompatible with fibroblasts and keratinocytes, tissue engineered skin is indicated for regeneration and remodeling of human epidermis and wound healing improving the treatment of severe skin defects or partial-thickness burn injuries.

Introduction

During the wound healing process, dressings are used for the regeneration and repairing of dermal and epidermal tissues. Wound dressing materials, as physical barriers permeable for moisture and oxygen, protect the wound mainly against microorganisms (Adamian et al., 2004).

For the stimulation of wound healing, a passive dressing is essential for maintaining an optimally moisture. Several products such as gauzes, hydrogels, foams, hydrocolloids (carboxymethylcellulose), alginate, collagen, cellulose, cotton/rayon, transparent films (polyurethane) are recommended as passive dressings for wounds and burns, because of their influence on local cellular response (Livshits, 1988, Cornelius et al., 2007). Thus, they are distinguished by some useful properties: protect peri-wound skin, maintain a suitable moisture at the wound level, prevent and keep under control microbial biofilms, cleanse the injured tissues, eliminate/minimize pain, remove dead spaces and nonviable tissues, control the odors (Seaman, 2002, Boateng et al., 2008, Sawant et al., 2012).

Some natural products having emollient, demulcent, epithelializing, astringent, antimicrobial, anti-inflammatory and antioxidant properties can improve the wound healing process (Mogoşanu et al., 2012).

Active wound dressings are impregnated with antimicrobials (topical antibiotic and antifungal products), collagen or enzyme debriding agents. Silver sulfadiazine, methylene blue, crystal violet, honey, polyhexamethylene biguanide (PHMB) and cadexomer iodine are commonly used as antimicrobials, for the prevention of local infection, especially in chronic wounds (Zilberman and Elsner, 2008).

For the peri-wound skin protection, skin sealants, moisture barriers or pastes, solid skin barriers and skin barrier powders are the most used (Yudanova and Reshetov, 2006a).

Certain factors such as the presence of infection, the accumulation of fluid and debris, the cleanliness and integrity of bandage influence the frequency of dressing change (Stojadinovic et al., 2008).

Acting as molecular absorptive filters or traps, odor-controlling dressings are recommended for the management of wounds and burns odor. For this purpose, activated charcoal is the most used deodorizing agent because its large surface absorption area. In a recent randomized clinical trial, silver-impregnated activated charcoal dressing was better tolerated than the control, for the management of chronic venous leg ulcers, even at the debridement stage. Thus, this dressing may be used to remove fluids and toxins which delay the wound healing process (Kerihuel, 2010). Honey dressings are used for healing and reducing odor of abscesses, diabetic foot ulcers, leg ulcers because of their in vitro and in vivo antibacterial activity against anaerobic Bacteroides spp., Peptostreptococcus spp., Prevotella spp. (Moura et al., 2013).

By means of growth factors and natural or synthetic polymers (e.g., alginate, collagen, acrylates, polyvinyl alcohol derivatives), the modern concept of interactive dressing envisages the changes in the wound environment for a better healing (Atiyeh et al., 2005). Consequently, the influence on local cellular response is revalued by improving the retention of moisture and wound collagen matrix, inhibiting microbial biofilm, decreasing of exudates and stimulating the epithelialization process (Singh et al., 2013).

Local delivery of growth factors and the application of tissue engineered skin (biosynthetic dressings) are up-to-date wound healing therapies. By using the so-called “artificial dermal layer”, in which natural or synthetic polymers are used as three-dimensional scaffolds for the adhesion and integration of dermal fibroblasts, the re-epithelialization process is enhanced especially for full thickness wounds (Sefton and Woodhouse, 1998). Sustained by a biocompatible polymer layer, skin substitutes are made mainly of collagen and seeded cells or reconstituted collagen and chondroitin sulfate (Bala and Thangeswaran, 2005, Nair and Laurencin, 2006).

Nanofibrous matrices, microspheres or hydrogels solid foams obtained from biodegradable and biocompatible polymeric scaffolds, containing cellular and molecular modulators that stimulates wound healing are used for tissue engineering. Because of their open porous structure and good mechanical strength, they provide an optimal microenvironment for cell proliferation, migration, and differentiation. In addition, for the complete regeneration of damaged tissues, natural or synthetic polymeric scaffolds can be surface engineered to provide a biocompatible extracellular matrix (ECM) (Chung and Park, 2007, Ma, 2008, Garg et al., 2012).

For the regeneration of full-thickness wounds, polysaccharides and proteins are the most common natural polymers used in the field of tissue engineering, because of their biocompatibility, biodegradability and similarity with ECM (Malafaya et al., 2007, Wiegand and Hipler, 2010).

Natural polymers such as collagen, chitosan, elastin, fibrinogen are biocompatible substrates similar to macromolecules recognized by the human body. They are also used in regenerative medicine for human epithelial stem cells culture or in vitro reconstituted epithelia, respectively (Guerra et al., 2009, Natesan et al., 2012).

In the last years, starting from natural or synthetic polymers, the production of biomimetic ECM micro/nanoscale fibers (80 nm–1.5 μm) through electrospinning process was found to be effective for tissue engineering. Thus, for wound healing or cartilage, bone, vascular, nerve and ligament repair and also for regeneration different non-woven structures of natural (e.g., collagen, fibrinogen, elastin) or synthetic (e.g., polyglycolic acid, polylactic acid, polydioxanone, poly-ɛ-caprolactone, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol) origin are used (Sell et al., 2007, Sell et al., 2010, Naghibzadeh, 2012).

Natural macromolecules show a relatively low mechanical strength compared to synthetic polymers. By cross-linking or blending with synthetic polymers, the mechanical properties of natural polymers are improved; however, their biocompatibility is somewhat affected. Modern bandage materials, such as electrospun nanofibrous polymeric bandages are also used for active wound dressings. In addition, nanofibrous membranes may be used as carriers for local active principles (antimicrobial and anti-inflammatory drugs) and wound dressing materials that speed up the wound healing process (Zahedi et al., 2010, Zhong et al., 2010).

Section snippets

Natural polymers for wounds and burns healing

Natural polymers are widely used in the regenerative medicine field, for wounds and burns dressing because of their biocompatibility, biodegradability and similarity to the ECM. Inducing and stimulating the wound healing process, natural polymers are involved in the repair of damaged tissues and consequently in skin regeneration (Huang and Fu, 2010). Due to their three dimensional cross-linked polymeric networks that are soaked with water or biological fluids, biomaterial hydrogels are employed

Synthetic polymers

Synthetic polymers (composite nanobiomaterials with small pores and very high specific surface area) used for wounds and burns dressing are made by various techniques but mainly by electrospinning (Khang et al., 2010, Supaphol et al., 2012, Goh et al., 2013): wound-dressing materials with antibacterial activity from electrospun polyurethane-dextran nanofiber mats containing ciprofloxacin hydrochloride (Unnithan et al., 2012), water soluble polymer–carrageenan hydrogels (Abad et al., 2003),

Skin substitutes and tissue engineered skin

Skin substitutes are developed starting from biocompatible and bioresorbable polymeric dermal scaffolds such as chitosan–gelatin composite films, poly(d,l-lactic acid), poly(d,l-lactic acid)–polyethylene glycol–poly(d,l-lactic acid), poly(lactic-co-glycolic acid) membranes containing (1→3),(1→6)-β-d-glucans (Garric et al., 2008, Kim et al., 2012, Parvez et al., 2012), porous scaffolds composed of gelatin, hyaluronic acid and (1→3),(1→6)-β-d-glucans cross-linked with

Conclusion and future perspectives

Dressings play an important role in the management of wounds and burns. The use of three-dimensional polymeric scaffolds for cell targeting is already a common strategy for tissue engineering. Recent studies of biocompatible and biodegradable natural/synthetic polymers will lead to a substantial development of novel types of wound dressings and to outstanding applications in the biomedical area and especially for regenerative medicine. In this respect, the most promising materials for wounds

Conflict of interest

The authors confirm that the content of this article has no conflict of interest.

Acknowledgments

This paper is partially supported by the Sectoral Operational Programme Human Resources Development, financed from the European Social Fund and by the Romanian Government under the contract number POSDRU/89/1.5/S/64153.

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