Development of Low Frequency (20–100 kHz) Clinically Viable Ultrasound Applicator for Chronic Wound Treatment

This paper details the systematic approach used to develop a viable clinical prototype of a therapeutic ultrasound applicator and discusses the rationale and deliberations that led to the design strategy. The applicator was specifically devised to treat chronic wounds and - to the best of the author's knowledge - is the first truly wearable device with a proven record of reducing healing time, directly translating to a reduction of healthcare costs. The prototype operates in the kHz (20-100) range of frequencies and uses noncavitational and nonthermal levels of ultrasound energy. Hence, in the absence of inertial cavitation and temperature elevation, the tissue-ultrasound interaction is considered to be dependent on stable cavitation (if any) and radiation force. The peak acoustic output pressure amplitude is limited to 55 kPa, corresponding to a spatial peak-temporal peak intensity of 100 mW/cm
²
. This level of intensity is considered to be safe to apply for extended (up to 4 h) periods of time. The patch-like applicator design is suitable to be embedded in wound dressing. With its lightweight (<;20 g) and circular (40 mm dia) disk-shape architecture, the applicator is well suited for chronic wound treatment. A small (n = 8) pilot study on the effects of the applicator on diabetic ulcers (DUs) healing time is presented. The average time to wound closure was 4.7 weeks for subjects treated with the active ultrasound applicator, compared to 12 weeks for subjects treated with a sham applicator, suggesting that patients with DUs may benefit from the proposed treatment.