© 2003 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003

15.5.1.3 Epithelial Pressure Ulcers

Pressure ulcers (e.g., decubitus ulcers or bedsores) are normally caused by a prolonged mechanical pressure against epidermal tissues (e.g., in persons bedridden for prolonged time periods), typically at sites over bony or cartilaginous prominences including sacrum, hips, elbows, heels and ankles. The combination of pressure, shearing forces, friction and moisture [3704, 3705] leads to tissue death due to a lack of adequate blood supply. If untreated, the ulcer progresses from a simple erosion to complete involvement of the dermal deep layers, eventually spreading to the underlying muscle and bone tissue [2004]. In at least one rare case [3706], mechanical frictional stimulation of the skin apparently precipitated systemic cutaneous necrosis and calciphylaxis, a state of induced tissue sensitivity characterized by calcification of tissues.

Nanomedical applications which envision prolonged periods of dermal contact with tight-fitting articles of nanorobotic apparel (Chapter 28), haptic or VR controllers (Chapter 12), exoprostheses (Chapter 30), or defensive armor (Chapter 31) must incorporate active components on the skin-contacting interior surface that can forestall the development of pressure ulcers. Molecular sorting rotors can remove water [3707, 3708], waste gases, secreted salts and other organic materials from the skin-device interface volume. A sensor-guided metamorphic interior surface can allow the garment to dynamically mirror epidermal tissue micromovements and perhaps actively undulate to mechanically encourage blood flow in the underlying tissues [3709, 3710]. A thin layer of slightly pressurized dry nitrogen gas could be maintained in the interface volume, greatly reducing shearing forces and friction [3711]. For example, fluid mattresses can greatly reduce pressure ulcers in long-duration surgeries [3712]. Pressure-relieving surfaces have been investigated for surgical patients [3713, 3714], wheelchair users [3715-3718], and for other circumstances [3719-3721]. The interior surface should employ materials having roughly the same mechanical properties as the enclosed tissue [3207-3210], and the applied interfacial pressures should be reduced to below 1 psi [3716] or ~ 50 mmHg. Mechanical pinch-induced pain [5449] should also be avoided.

Stercoral ulcers [3722-3724] are caused by the necrosis of intestinal epithelium due to the pressure of impacted feces. Macroscale colonic nanorobot aggregates (Chapter 26) must avoid applying such harmful luminal pressures during lengthy missions.

Last updated on 30 April 2004