The clinical use of biologics for acute disease management is constrained by rapid clearance and systemic accumulation, which may compromise therapeutic outcomes. While sustained release nanoparticles are well-established for chronic conditions, analogous strategies for acute indications─particularly those requiring controlled release within 48 h─remain insufficiently developed. This study explores polysuccinimide-oleylamine (PSI-OA), a polymer with a tunable dissolution profile, for protein delivery. Using inverse flash nanoprecipitation and a herringbone T-shaped microfluidic mixer, PSI-OA nanoparticles encapsulating bovine serum albumin and lipase were fabricated. Optimized synthesis parameters yielded nanoparticles with less than 200 nm, with encapsulation efficiencies of roughly 75 and 98%, respectively, while retaining enzymatic activity. Both systems demonstrated ∼50% release at 24 h and full release by 48 h. These findings underscore the potential of PSI-OA nanoparticles for short-term sustained delivery of protein therapeutics in acute care settings.