ch5_skin_case

ch5_skin_case - III. Design case study: device for partial...

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III. Design case study: device for partial regeneration of skin. (outline of topics) 1. The clinical problem. 2. Design at the patient scale. 3. … at the organ scale. 4. … at the cell scale. Text: TOR, Chs. 6, 7, 10.
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1. The clinical problem. Brief review of skin anatomy and physiology . Epidermis, the moisture seal and bacteria seal. Dermis, the mechanical barrier and vital supporter of the epidermis. Skin receives from and sends signals to the environment. Pathology (mortality and morbidity) . Loss of skin due to injury or chronic disease. Burns. Abrasion. Ulcers. Threats to life: Dehydration, sepsis. Threats to quality of life: Scarring and contracture.
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1. The clinical problem. (cont.) Patient population (narrow down to burn patients for better clinical focus; omit plastic surgery patients and ulcers patients). Categories: First-, second- and third-degree burns. The epidermis regenerates spontaneously provided there is a dermal substrate. The dermis does not regenerate spontaneously. Narrow down to third-degree burns.
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1. The clinical problem. (cont.) Approaches to solving problem . Allograft : Cadaver skin. Must immunosuppress patient, thereby complicating problem of survival. Epidermis is much more immunogenic than dermis. Use acellular dermis with some success. Xenograft : pig skin. Problem of bacterial and viral “load” of graft. Temporary dressings: synthetic polymeric scaffold seeded with keratinocytes and fibroblasts. Must be removed after a few days. No permanent cover. Gold standard: Autograft . Problems: not enough when burned area is >50%; patient traumatized (“donor site”).
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Clinical scale: bottom line ¶ The device will be directed toward patients with third degree burns. ¶ The gold standard is the autograft.
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2. Design at the patient scale. a. The burn patient population : Large areas , scale about 1 cm 2 , of missing skin. b. Short-term care problem (<20 days): Survival inside clinic. • Massive bacterial invasion. Risk: lethal sepsis. • Massive dehydration. Risk: lethal shock. • Loss of thermoregulation. Risk: acute discomfort.
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2. Design at the patient scale. (cont.) c. Long-term care problem (>20 days): Quality of life outside clinic. • Contraction. Prevents movement if occurring near joints. • Scar. Mechanically weak cover, reduced tactility, cosmetically objectionable. No thermoregulation. ¶ Therefore, the device must provide both temporary and lifelong physiological cover to patient.
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3. Design at the organ scale a. Anatomy of the missing skin. Epidermis, dermal-epidermal junction (DEJ), dermis, accessory organs. b. The epidermis keeps water in, bacteria out. c. The epidermis bonds to the dermis (DEJ). d. The dermis protects the epidermis mechanically and metabolically. Nerve endings inside the dermis provide sense of touch (tactility).
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The epidermis is spontaneously regenerative Diagram removed due to copyright restrictions.
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3. Design at the organ scale (cont.) e. Accessory organs located inside the dermis
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This note was uploaded on 11/11/2011 for the course BIO 2.797j taught by Professor Matthewlang during the Fall '06 term at MIT.

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ch5_skin_case - III. Design case study: device for partial...

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