Biophysical Considerations in the Rational Design and Cellular Targeting of Flexible Polymeric Nanoparticles

Abstract

gene therapy [1][2][3] and their application as biomarkers for imaging and detection. [4][5][6] Functional nanoparticles are finding applications in genome editing, immune modulation, cell therapies, and molecular diagnostics to stratify patients based on biomarkers. However, the functional NPs' design, optimization, and deployment are hampered by our lack of understanding of their biological barriers and pharmacokinetics. [7] While such barriers have contributions that are systemic and span multiple scales, the specificity for a given application has essential contributions from the cellular scale. Cellular targeting is governed by avidity (adhesion) and uptake (internalization), which depend on the properties of the NPs and the cellular microenvironment.Adhesion between an NP and a cell surface typically involves the simultaneous binding [8,9] of many hundreds of ligands on the NP's surface to a similar number of receptors on the cell surface. [9][10][11][12][13] The physiological outcome of such multivalent adhesion, which can mediate diverse phenomena, including cell crowding and cell uptake, [14] depends on the strength of ligandreceptor binding interactions. Other factors that can modulate multivalent adhesion strength include physiochemical properties of both the NPs and the cell surfaces. [15] Previous How nanoparticle (NP) mechanical properties impact multivalent ligandreceptor-mediated binding to cell surfaces, the avidity, propensity for internalization, and effects due to crowding remains unknown or unquantified. Through computational analyses, the effects of NP composition from soft, deformable NPs to rigid spheres, effect of tethers, the crowding of NPs at the membrane surface, and the cell membrane properties such as cytoskeletal interactions are addressed. Analyses of binding mechanisms of three distinct NPs that differ in type and rigidity (core-corona flexible NP, rigid NP, and rigid-tethered NP) but are otherwise similar in size and ligand surface density are reported; moreover, for the case of flexible NP, NP stiffness is tuned by varying the internal crosslinking density. Biophysical modeling of NP binding to membranes together with thermodynamic analysis powered by free energy calculations is employed, and it is shown that efficient cellular targeting and uptake of NP functionalized with targeting ligand molecules can be shaped by factors including NP flexibility and crowding, receptor-ligand binding avidity, state of the membrane cytoskeleton, and curvature inducing proteins. Rational design principles that confer tension, membrane excess area, and cytoskeletal sensing properties to the NP which can be exploited for cellspecific targeting of NP are uncovered.