Biopolymers as Wound Healing Materials: Challenges and New Strategies

the dead layer of skin.Whereas dead cells are being pushed from the deeper portion of the epidermis toward the surface, they are replaced by proliferating cells by mitosis in the basal layer.This change is called cytomorphosis.Cytomorphosis takes an average of 15 to 30 days for a healthy individual.The basic cell type of epidermis is keratinocytes.The content of the keratin constantly changes in the epidermis because keratinocytes undergo changes in epidermis and consists of 85 % of total protein of the Stratum corneum (Gartner et al., 2001).Keratinocytes synthesize different keratins in different stages of cytomorphosis.Whereas basal layer cells include only low molecular weight keratins, cells with high molecular weight keratin begin to build the heap structure of the Stratum corneum as the cells move upward.Keratins in this layer are cross-connected by disulphide bonds at the same time.The epidermis consists of five layers.These are, respectively, from the inside to out (Junqueria et al., 1992). Stratum basale (germinativum):This layer consists of a single row of cylindrical cells sitting on the basal membrane, located on the dermis and basal lamina.This layer is responsible for continuous renewal of the epidermis due to the proliferation of cells.Cytoplasmic fibrillar protein is found in all cells that form the structure.As proliferating cells migrate towards the upper layer, the number of protein filaments increases.Stratum spinosum: This is a multi-storey layer composed of polygonal or squamous epithelial cells.The cytoplasm and cytoplasmic extensions are filled with bundles of fibrils and connected to each other with bridges on the cell surface.These cells are called spino-cellular cells, due to the spine-like structures around this layer of cells.All the layers of both Stratum basale and Stratum spinosum are called the Malpighian layer.Stratum granulosum: This layer consists of small, flat, polygonal-shaped cells.These cells contain keratohyalin granules.The number of lamellar structures emerging in the Stratum spinosum increases in the Stratum granulosum, their contents are secreted to intercellular spaces as accumulating in the periphery of the cell, providing intercellular lipids, which are essential for the barrier function of the epidermis. Stratum lucidum (Transparent layer):This layer is composed of flat, transparent, and tightly gathered cells ranging from 3 to 5 rows.It is a thin layer that is only found in regions where the epidermis is thick.The cytoplasm of the transparent layer is filled with a substance refracting light called eleidin and cell organelles decrease in this layer.As tonofibrils become more numerous and regular, they make the cell membrane thicker.Desmosomes are located between cells and the amount of intercellular materials increases.Stratum corneum: It is a dead cell layer having no nucleus.Keratin is found in the cytoplasm of these cells.Intercellular gaps are full of lipids which are secreted from the lamellar structures in the Stratum spinosum and Stratum granulosum.Superficial cells of the Stratum corneum shed continuously (desquamation) and new tissue is produced by mitosis of cells in the germinal layer.Keratinization occurs with the formation of disulfide groups from sulphydryl groups of protein fibrils during migration to the upper layer.These protein fibrils make reticulated bundles, forming a substantial long chain by disulfide bonds and also including a dense, amorphous matrix between them, composed of keratohyalin granules.At this stage, the cell membrane thickens.This layer, formed by the thickening of the cell membrane, takes the shape of cornified cells losing its core and other organelles after reaching of keratohyalin granules to maximum point and forming of keratin lipids (Gartner et al., 2001; Junqueria et al., 1992). www.intechopen.comBiopolymers as Wound Healing Materials: Challenges and New Strategies 385 DermisThe dermis is a type of elastic, flexible bond tissue locating under epidermis and is vascularised, enabling it to provide energy and nutrition to the epidermis.The dermis extends limitlessly by integrating to the subcutaneous layer and its thickness varies according to the region (Leeson & Leeson, 1981).Its surface contacting the epidermis is rough and composed of papillae.Papillae are named Stratum papillare by integrating deep surface of the epidermis.Some papillae also contain special nerve endings, called vascular papillae (Young & Heath, 2000).The deepest part of dermis is called as Stratum reticulare.This layer consists of irregular, dense connective tissue and has rather weak cells, primarily fibroblasts and macrophages.Hair follicles are concentrated around sebaceous and sweat glands in the dermis (Leeson & Leeson, 1981). HypodermisHypodermis, the subcutaneous layer, is a loose connective tissue located under the dermis and containing varying amounts of flat cells.Collagen and elastic fibrils within its structure continue into the dermis.Hair roots also are found in this layer (Junqueria et al., 1992; Leeson et al., 1988).The increase in the number of fibrils results in a rigid binding of dermis to hypodermis and thus affects the mobility of the skin. Wounds and burns Types of woundsA wound is the disruption of the integrity of anatomical tissues caused by exposure to any factor.Wounds are examined under two groups: Closed Wounds: This group includes contusion, hematoma and abrasion.Contusion-type injuries involve damage to soft tissues, small blood vessels and deep tissue layers, resulting in their separation, but the anatomy of the skin remains intact.Oedema, and in later periods, atrophy and defective pigmentation are observed in wound and the healing is delayed.Vessel rupture or hyperaemia due to vessel damage is called hematoma and wounds such as scrapes are termed abrasions.The healing process is very painful because this type of wound involves damage to sensory nerves and the wound can easily become infected (Mutsaers et al., 1997).Open Wounds: This group includes lacerations, cutting-pricking tool wounds, gunshot wounds, surgical wounds, insect bites and stings, radionecrosis, vascular neurological and metabolic wounds.Wounds except for lacerations cause serious damage to tissues beneath the skin.In laceration type wounds, skin and subcutaneous tissue have been destroyed, but deep tissues remain healthy.The anatomical integrity of tissues is damaged in cuttingpricking tool wounds without any tissue damage at the edges of the wound (Aydın, 2000;Kapoor & Appleton, 2005).Wounds are also classified according to tissue loss.Wounds with Tissue Loss: These types of wounds involve damage or loss in some or all of the skin layers.Healing occurs via filling of the wound area by granulation tissue typically growing from the base of a wound.Wounds that involve tissue loss are collected in two groups in proportion to the loss.In superficial wounds, the entire epidermis and the papillar layer of the dermis are damaged.The epidermis, all the layers of the dermis and even www.intechopen.com