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With the rise in diabetes mellitus cases worldwide and lack of patient adherence to glycemia management using injectable insulin, there is an urgent need for the development of efficient oral insulin formulations. However, the gastrointestinal tract presents a formidable barrier to oral delivery of biologics. Here we report the development of a highly effective oral insulin formulation using choline and geranate (CAGE) ionic liquid. CAGE significantly enhanced paracellular transport of insulin, while protecting it from enzymatic degradation and by interacting with the mucus layer resulting in its thinning. In vivo, insulin-CAGE demonstrated exceptional pharmacokinetic and pharmacodynamic outcome after jejunal administration in rats. Low insulin doses (3-10 U/kg) brought about a significant decrease in blood glucose levels, which were sustained for longer periods (up to 12 hours), unlike s.c. injected insulin. When 10 U/kg insulin-CAGE was orally delivered in enterically coated capsules using an oral gavage, a sustained decrease in blood glucose of up to 45% was observed. The formulation exhibited high biocompatibility and was stable for 2 months at room temperature and for at least 4 months under refrigeration. Taken together, the results indicate that CAGE is a promising oral delivery vehicle and should be further explored for oral delivery of insulin and other biologics that are currently marketed as injectables.

Nanoparticle-based therapeutic formulations are being increasingly explored for the treatment of various ailments. Despite numerous advances, the success of nanoparticle-based technologies in treating brain diseases has been limited. Translational hurdles of nanoparticle therapies are attributed primarily to their limited ability to cross the blood-brain barrier (BBB), which is one of the body's most exclusive barriers. Several efforts have been focused on developing affinity-based agents and using them to increase nanoparticle accumulation at the brain endothelium. Very little is known about the role of fundamental physical parameters of nanoparticles such as size, shape, and flexibility in determining their interactions with and penetration across the BBB. Using a three-dimensional human BBB microfluidic model (μHuB), we investigate the impact of these physical parameters on nanoparticle penetration across the BBB. To gain insights into the dependence of transport on nanoparticle properties, two separate parameters were measured: the number of nanoparticles that fully cross the BBB and the number that remain associated with the endothelium. Association of nanoparticles with the brain endothelium was substantially impacted by their physical characteristics. Hard particles associate more with the endothelium compared to soft particles, as do small particles compared to large particles, and spherical particles compared to rod-shaped particles. Transport across the BBB also exhibited a dependence on nanoparticle properties. A nonmonotonic dependence on size was observed, where 200 nm particles exhibited higher BBB transport compared to 100 and 500 nm spheres. Rod-shaped particles exhibited higher BBB transport when normalized by endothelial association and soft particles exhibited comparable transport to hard particles when normalized by endothelial association. Tuning nanoparticles' physical parameters could potentially enhance their ability to cross the BBB for therapeutic applications. K E Y W O R D S

The delivery of therapeutics to the brain in an efficient, noninvasive manner continues to be a major unmet need in the field of drug delivery. One significant impediment to brain delivery results from the existence of the physical yet dynamic blood–brain barrier (BBB). Despite the many, often complex strategies that currently exist to breach the BBB, adequate delivery of effective therapeutics from the bloodstream continues to remain quite low. Nanotechnology has emerged as a promising tool for brain delivery, but little is known about the important particle parameters that influence delivery. Here, we synthesized and characterized a library of nanoparticles with distinct properties ranging from size, shape, stiffness, and composition to investigate and identify the key attributes influencing particle uptake and transport for brain delivery. To accomplish this task, an in vitro human BBB model was developed and validated using human cerebral microvascular endothelial cells (hCMEC/D3). Particle uptake and apparent permeability coefficients (P app) were then determined for each particle group. To elucidate the roles of different parameters on particle uptake and transport across the BBB, the predominant mechanisms of endocytosis were also investigated. Our results show that particle composition yielded the greatest impact on penetration across the BBB model. This work lays the foundation and provides new insights into the role of particle parameters on penetration across the BBB.