Effect of Particle Rigidity on Transport across a Blood-Brain Barrier Model

<b>Introduction:</b> Despite numerous advances in application of nanotechnology in medicine, the success of these nanocarriers in addressing brain diseases remains limited, primarily due to their poor transport across the BBB, one of the most exclusive barriers in the body. Prior studies have revealed that particle physicochemical properties such as size, shape, and surface chemistry are detrimental for their ability to cross BBB. However, the effect of particles’ rigidity on their transport across BBB has not been studied independent of other particle characteristics. This study aims to unravel the role of particle rigidity, without changing other particle properties, in their BBB transport using an <i>in vitro</i> BBB model. Towards this goal, we utilize nanoliposomes and encapsulate hydrogels of various concentrations in their core. The resultant nanoliposomes are characterized and examined for their transport across a transwell BBB model.<br/><b>Methods:</b> Hydrogel-core nanoliposomes were prepared by encapsulating poly(ethylene glycol) diacrylate (PEDGA) in the lumen of liposomes using a previously reported technique [1]. In brief, a thin film of lipid was prepared and hydrated with a solution of PEGDA. The mixture was extruded through a porous membrane to produce small unilamellar liposomes. Next, a photoinitiator was incorporated into liposomes followed by UV exposure to crosslink PEGDA within liposomes. The size and zeta potential of liposomes were assessed using dynamic light scattering and laser Doppler electrophoresis techniques, respectively. The Young's moduli of bulk PEGDA at concentration of 10 and 30 v/v% were evaluated using uniaxial compression testing. The BBB model was prepared by co-culture of brain endothelial and astrocyte cells in a transwell system. The integrity of the BBB model was evaluated by measuring the trans-endothelial electrical resistance (TEER). The resultant nanoliposomes were introduced onto the BBB model where their transport was assessed by monitoring the particle concentration across the barrier using nanoparticle tracking analysis.<br/><b>Results:</b> Three groups of nanoliposomes containing no hydrogel core, 10%v/v PEGDA core, and 30%v/v PEGDA core were prepared and utilized as soft, intermediate, and hard particles, respectively. Increasing the PEGDA gel volume ratio from 10 to 30% led to an increase in its Young’s modulus from 0.1 to 4 MPa. Notably, all three liposome groups showed similar size distribution (~117 nm) and zeta potential (~2.3 mV), indicating similar surface properties. The measured value of TEER for the BBB model was ~162 Ω.cm², indicating proper formation of tight junctions within the endothelial cell layer. Introducing the three groups of nanoparticles to the BBB model, they all were able to cross the BBB, however the difference in transport was not substantial. This finding suggests that the rigidity changes within the range examined here had no significant impact on the ability of liposomes to cross the BBB.<br/><b>Conclusions: </b>In this work, inclusion of PEGDA within liposomes was used to vary the rigidity of particles independent of other physical properties. All three groups of liposomes were able to cross the BBB model and their rigidity differences did not have a significant effect on their transport. Future studies will focus on widening the range of elasticity of liposomes to further explore the role of particle rigidity in their transport across BBB.<br/><b>Acknowledgments: </b>This Research was supported by National Science Foundation (DMR-1753328) and University of Houston GEAR (Grants to Enhance and Advance Research).<br/><b>References: </b>[1] F. Mirab, et al., <i>2019 41st Annual International Conference of the IEEE (EMBC)</i>, 2019, pp. 3935-3938