PROJECT ABSTRACT Acute ischemic stroke care has been revolutionized in the past 3 years, with multiple trials showing the efficacy of mechanical thrombectomy retrieval devices. Because of this revolution, there are many clinical needs for improved adjunctive devices that have not kept up with the swift growth of the thrombectomy field. This Phase II SBIR grant will support Good Lab Practices animal models testing Marblehead Medical?s innovative balloon guide device, the Balloon Occlusion Sheath for Stroke (BOSS), as well as FDA submission. Thus, the BOSS will be tested in the best available preclinical models against the best existing balloon guide devices for acute ischemic stroke and bring this device, which has crucial usability innovations and a novel balloon material, to tens of thousands of stroke patients a year undergoing mechanical thrombectomy. Balloon devices like BOSS have proven improvements in patient outcomes?half the mortality and double the rate of good neurological outcome?but less than 25% of stroke interventionalists use them because of technical limitations that BOSS is specifically designed to overcome based on intensive interviews with 80 physicians. BOSS not only has a more durable, compliant, and usable balloon, but also increases the inner lumen size without a larger arteriotomy, thus allowing the largest and best retrieval devices to be used without introducing greater hemorrhage risks. BOSS achieves this through a more stable braid-and-coil combination device that can be used for both arterial access and flow arrest in the carotid artery, simplifying and speeding stroke procedures. We have also discovered two further unmet clinical needs in the stroke community: stability is the most important usability characteristic to device companies and interventionalists, and no current device provides maximized advancement into to the carotid artery (which contributes to stability). Furthermore, older patients tend to have tortuous carotid anatomies, preventing navigation by all but the most flexible catheters. Therefore, this grant would also support creating BOSS Slender, a novel iteration of BOSS that optimizes stability (through a stiff catheter along most of its length) while also maximizing advancement (through a flexible, narrowed distal tip). This will also make Marblehead Medical a portfolio company offering a suite of specialized devices to allow physiology-specific treatment to the growing population of stroke patients. Thus, Marblehead Medical has assembled an experienced team of neurovascular engineers, quality experts, and regulatory writers to work alongside Mayo Clinic?s specialized preclinical stroke laboratory to translate BOSS and its diverse follow-on devices to clinical use; we have also received interest from strategic device companies and established 8 early adopter key opinion leaders at major clinical sites. This grant will provide support for the key development, preclinical, and regulatory work to put BOSS devices on the market and drive adoption of the best-proven neurovascular accessory devices through usability innovations. This would bring us closer to our vision of improving patient outcomes and preventing mortality for patients afflicted by stroke.