Biomaterials 22 (2001) 165}173 Fabrication and characterization of a sponge-like asymmetric chitosan membrane as a wound dressing Fwu-Long Mi, Shin-Shing Shyu*, Yu-Bey Wu, Sung-Tao Lee, Jen-Yeu Shyong, Rong-Nan Huang Department of Mathematics, Physics and Chemistry, Division of Chemistry, Chinese Naval Academy, 669 Jiun Shiaw Road, Kaohsiung, Taiwan 813, Republic of China Laboratory of Polymer Materials Research, Department of Chemical Engineering, National Central University, Chung-Li, Taiwan 32054, Republic of China Department of Surgery and Plastic Surgery, Naval 806 Hospital, Kaohsiung, Taiwan 813, Republic of China Institute of Life Science, National Central University, Chung-Li, Taiwan 320, Republic of China Received 6 December 1999; accepted 28 April 2000 Abstract A novel asymmetric chitosan membrane has been prepared by immersion}precipitation phase-inversion method and evaluated as wound covering. This new type of chitosan wound dressing which consists of skin surface on top-layer supported by a macroporous sponge-like sublayer was designed. The thickness of the dense skin surface and porosity of sponge-like sublayer could be controlled by the modi"cation of phase-separation process using per-evaporation method. The asymmetric chitosan membrane showed controlled evaporative water loss, excellent oxygen permeability and promoted #uid drainage ability but could inhibit exogenous microorgan- isms invasion due to the dense skin layer and inherent antimicrobial property of chitosan. Wound covered with the asymmetric chitosan membrane was hemostatic and healed quickly. Histological examination con"rmed that epithelialization rate was increased and the deposition of collagen in the dermis was well organized by covering the wound with this asymmetric chitosan membrane. The results in this study indicate that the asymmetric chitosan membrane thus prepared could be adequately employed in the future as a wound dressing.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Chitosan; Asymmetric membrane; Wound dressing; Immersion}precipitation phase inversion 1. Introduction Serious burns are usually caused from the explosive chemicals in industrial accidents or the weapons of mod- ern warfare in armed con#ict. In a third-degree burn, the full thickness of the skin has been destroyed. One treat- ment is to remove a thin sheet of healthy skin from the patient's own body and graft it on the burned area. To protect the skin defect from infections and dehydration in the intervening period between hospitalization and graft- ing, wound has to be protected from its environment. Protection can be accomplished by covering the wound with wound dressing [1}3]. The wound surface should be kept just damp enough to obtain the bene"ts of acceler- ated healing, but there should be no accumulation of * Corresponding author. Tel.: #886-3-422-7151 Ext. 4204; fax: #886-3-425-2296. E-mail address: s3154006@cc.ncu.edu.tw (S.-S. Shyu). #uid between the wound and the dressing because of the risk of infection [4]. Bacterial invasion may make the wound unsuitable for skin grafting due to the growth of bacteria population. Wound dressing has a skin top- layer supported with a sponge-like sublayer can meet the requirements such as higher gas permeation and protec- tion of wound from infection and dehydration [5]. Chitosan, a bio-copolymer comprising glucosamine and N-acetylglucosamine, is the alkaline deacetylated products of chitin, derived from the exoskeletons of insects and shells of crustaceans. Chitosan could also be found in the cell walls of some fungi such as Mucor rouxii. Chitin and chitosan have been examined to be used in a wide variety of biomedical application, such as drug delivery carriers, surgical thread, bone healing materials, especially wound dressing [6}9]. Chitin and certain derivatives could accelerate tensile strength of wounds by speeding the "broblastic synthesis of collagen in the "rst few days of wound healing [10]. Chitosan 0142-9612/01/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 6 1 2 ( 0 0 ) 0 0 1 6 7 - 8