This SBIR Phase I project will develop and test a minimally invasive method and device that blocks pain. The device will offer patients and physicians a new non-addictive way of controlling severe pain with the ultimate goal of reducing or eliminating society's need for opioids and other narcotics. More than 350,000 Americans died from opioid overdose during 1999-2016, and the societal cost of opioid misuse exceeds $75 billion per year. The number one risk factor of opiate addiction is receiving a prescription for opiates. The technology developed in this project uses gentle warm and cool temperatures to block the transmission of nerve signals without drugs or electric stimulation. Uniquely, this method appears to block pain signals across all mammalian and amphibian nerves. The device developed in this project will reduce human suffering and risk of addiction by giving patients the ability to rapidly adjust how much of a nerve's firing is felt. The device will also provide researchers studying neurological mechanisms with precise control over nerve conduction. Thermal nerve blocks represent a powerful new way of blocking pain and has broad applicability following surgery and across a number of disorders and diseases. Gently warming a short section of nerve tissue to 45C and then cooling it to 15C can quickly initiate complete nerve block that can be maintained by cycling between these temperatures while avoiding nerve damage from exposure to higher or lower temperatures. Thermal nerve block will be delivered by the minimally invasive device developed in this project, which includes an inserted thermal probe and an external microfluidic controller. The drug-free, non-addictive, device will provide continuous block of severe pain initially for peri- and post-operative pain management. This project will build prototype thermal tips that can be inserted via 5mm introducer sheath, refine the device implantation technique and optimize thermal performance in vitro before demonstrating the utility of the system for thermal block of intercostal pain in C-fiber evoked potential experiments in anesthetized felines. The thermal tips will be held in place with non-permanent anchoring silicone tynes, while the external wearable controller will have battery-powered micro-piezo pump, thermoelectric heater/cooler, and microcontroller. This minimally invasive design offers an effective alternative for controlling severe pain that does not attenuate over time and brings no risk of addiction. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.