Skin Structure：

Skin structure has epidermis, dermis, hypodermis.

Epidermis：

Composed with keratinocytes, has protective effects, could to prevent the excessive loss of water and to protect body from the invasion of harmful substance.

Dermis：

It is kind of irregular, compact connective tissue. It has growth factor to help epithelium to grow, also to help to repair the dermis. Besides, using artery and sweat gland in skin, dermis can control the loss of bodily heat and to counterpoise the body fluid. Structurally, dermis has fibrillar structure such as collagen fiber, reticular fiber and elastic fiber, these structure have tenacity and elasticity. It also has fibroblast, endothelial cell, muscle cell, mast cell and macrophages.

Subcutaneous：

Subcutaneous, including capillary, nerve, hair follicle tissue, sweat gland and sebaceous gland, is almost formed by fat. It has soft muscle to ease external stimulation. Sweat gland can regulate the temperature of the body. Hydrolipidic film which in sebaceous gland can protect body and suppress bacterial reproduction.

Skin Substitutes：

It can be fibrous, film, colloid or vesicular. Skin Substitutes have temporary type and permanency type. The temporary type only can protect wound from infection and body fluid lossing. The permanency type can be absorbed by human body, even can be used to be architectureas for reconstruction of epidermis and dermis.

Ideally skin Substitutes should have features as follows：

(1)Could to adhere to wound smoothly.
(2)To keep wound moistly.
(3)Allow the changing of gas, also can cut off the invasion from microbe and heat.
(4)Can avoid loss of heat and water vapor.
(5)Has same level of feature and exterior as autograft.
(6)Has biocompatibility, could not have immunological rejective reaction.
(7)Accelerate wound healing, forming new epidermis and dermis.
(8)Reduce the cost of treatment.
(9)Having physical strength：flexible and elastic.
(10)Sterile and non-toxic, also can secrete fat appropriately to moisten skin.