A laser-customizable insole for selective topical oxygen delivery to diabetic foot ulcers
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A laser-customizable insole for selective topical oxygen delivery to diabetic foot ulcers H. Jiang, and M. Ochoa, School of Electrical and Computer Engineering, Electrical Engineering Building, 465 Northwestern Ave, West Lafayette, IN 47907-2035, USA; Birck Nanotechnology Center, 1205 W State Street, West Lafayette, IN 47907-2057, USA V. Jain, Birck Nanotechnology Center, 1205 W State Street, West Lafayette, IN 47907-2057, USA; School of Mechanical Engineering, 585 Purdue Mall, West Lafayette, IN 47907, USA B. Ziaie, School of Electrical and Computer Engineering, Electrical Engineering Building, 465 Northwestern Ave, West Lafayette, IN 47907-2035, USA; Birck Nanotechnology Center, 1205 W State Street, West Lafayette, IN 47907-2057, USA Address all correspondence to B. Ziaie at [email protected] (Received 29 May 2018; accepted 15 August 2018)
Abstract In this work, we present an oxygen-releasing insole to treat diabetic foot ulcers. The insole consists of two layers of polydimethylsiloxane: the top layer has selective laser-machined areas (to tune oxygen permeability) targeting the ulcerated foot region, while the bottom layer provides structural support and incorporates a chamber for oxygen storage. When loaded with a pressure of 150 kPa (average value for standing/walking), the insole is able to release oxygen at a rate of 1.8 mmHg/min/cm2. At lower sitting pressures, the delivery rate persists at 0.092 mmHg/ min/cm2, raising the oxygen level to an optimal healing value (50 mmHg) for a 2 × 2 cm2 wound within 150 min.
Introduction In the USA, 15% of diabetics develop chronic wounds in their foot, of which 14–43% result in amputations due to their nonhealing status.[1] The main treatments for chronic diabetic foot ulcers include hydrogel/polymer-based wound dressings, negative pressure therapy, and skin grafts.[2,3] Adequate issue oxygenation plays an important role in all stages of wound healing (inflammation to tissue remodeling). Many chronic wounds, including diabetic foot ulcers, have hypoxic regions that prevent, impede, and delay the healing process. Several oxygenbased therapies have been proposed and deployed for chronic wound treatment. These include hyperbaric oxygen (HBO) therapy, topical oxygen (TO) therapy, and continuous diffusion of oxygen (CDO).[4–8] In HBO therapy, the patient is placed in a HBO chamber (1.4–3.0 atm) for 90 min per day, 4 or 5 days per week. In addition to reducing wound hypoxia, HBO has been reported to promote fibroblast proliferation, increase collagen production, enhance immune function, and stimulate angiogenesis. This technique, however, is cumbersome, requiring sophisticated/bulky equipment (hyperbaric chamber and a large oxygen source) and trained personnel. In addition, it can result in systemic side effects such as myopia, pneumothorax, and hyperoxia-induced toxicity. An alternative but similar approach is TO therapy; this technique creates a sealed and localized oxygen-rich environment around the limb or affected area with barometric pressure slightly above
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