(197e) Aggregation Kinetics in Biological Environments as a Determinant of Nanoparticle Behavior in the Brain

Aims: Develop an assay to assess colloidal stability of nanotherapeutic platforms in biologically relevant environments. Investigate the impact of key physiological variables on nanoparticle diffusion within the brain microenvironment.

Methods: Use dynamic light scattering and confocal microscopy to measure aggregation dynamics of nanoparticles in biologically complex milieu. Use high-speed multi-particle tracking and fluorescence microscopy to measure diffusion coefficients of nanoparticles in an agarose gel model of the brain.

Results: The presence of divalent cations, including Mg²⁺ and Ca²⁺ can cause aggregation of electrocratically stabilized particles. Even particles coated with PEG, a common agent used to provide both steric stabilization and stealth properties, experience aggregation under certain conditions. Additional factors that can vary in biological environments, including temperature, CO₂ partial pressure, and pH, have a significant impact on nanoparticle aggregation kinetics. Diffusion studies in agarose gels demonstrate that PEGylated and non-PEGylated polystrene nanoparticles have similar diffusive behavior at short time scales in the absence of proteins and divalent cations. However, when divalent cations are introduced, PEGylated particles maintain similar diffusion coefficients, while non-PEGylated nanoparticles exhibit significantly hindered behavior.

Conclusions: Reduced diffusive capabilities of non-PEGylated paticles has been largely attributed to interactions with proteins. This study demonstrates that an additional mechanism, decreased colloidal stability due to interactions with divalent cations, also plays a role. Even in protein-poor environments, such as cerebrospinal fluid, nanoparticles can become hindered and lose their ability to provide improved delivery to target sites. Using the assays demonstrated in this poster, engineers can design nanoparticle platforms and predict their behavior in the brain and other organs before performing in vivo and ex vivo studies.