APT001 is a medical device that generates nitric oxide (NO) from ambient room air within a defined plasma stream. This study is a randomized, prospective, multi-center feasibility study that will assess the effect of Nitric Oxide treatment time (minutes) and frequency (days/week) on wound healing in adults with diabetic foot ulcers (DFUs) and to provide information that will be used to develop final safety and effectiveness hypotheses for a pivotal trial of the APT001 device.