Steering the self-assembly of deformable nanoscale building blocks

Most coarse-grained models of the nanoscale self-assembly process employ rigid building blocks that do not exhibit shape adaptation, limiting our understanding of the role of elasticity in altering self-assembly pathways. We study how bending rigidity of nanoscale building blocks affects their self-assembly using microsecond-long Langevin dynamics simulations of a coarse-grained model of deformable building blocks. Our model is inspired by the protein subunits, also known as capsomers, of a typical small icosahedral virus system. Transitions in assembly products from dispersed capsomers to symmetric cages to malformed aggregates are observed with increasing bending modulus of the capsomer. Simulations find a mechanical "goldilocks zone" in the space of capsomer bending modulus and capsomer-capsomer steric attraction for successful protein cage formation, where capsomers are sufficiently rigid to suppress strong shape fluctuations and promote capsid assembly nucleation, and also sufficiently soft to correct errors during the capsid growth pathway. The pronounced effects of changing capsomer bending rigidity on the steady-state assembly products are linked to the changes in the assembly kinetics, and explained by the variations in the angular fluctuations characterizing the capsomer and associated "shape entropy" costs. We apply the deformable capsomer model to probe the encapsulation of charged nanoparticles and show that encapsulation behavior depends on capsomer elasticity. Our results highlight how block elasticity can guide nanoscale assembly and provide a computational framework for designing deformable particles and reconfigurable materials.