Coarse-grained molecular dynamics simulations of nanopatterning with multivalent inks.

A coarse-grained molecular dynamics (MD) model is developed to study the multivalent, or multisite, binding of small functionalized dendrimer molecules to beta-cyclodextrin-terminated self-assembled monolayers, the so-called "molecular printboards" used to print "ink" molecules on surfaces with a high degree of positional control and specificity. Some current and future bionanotechnology applications are in the creation of nanoparticle assemblies, directed protein assembly, platforms for biosensing, and cell:surface attachment. The coarse-grained model allows us to probe up to microsecond timescales and model ink diffusion, crucial for the application of the printboard in, for example, medical diagnostics. Recent all-atom MD simulations identified and quantified the molecular strain limiting the stability of nanopatterns created with small dendrimer inks, and explained the different patterns obtained experimentally with different dendrimer inks. In the present work, the all-atom simulations are "scaled up" to longer timescales via coarse graining, without incurring significant additional computational expense, and, crucially, without significant loss in atom-scale detail, the coarse-grained MD simulations yielding properties similar to those obtained from the all-atom simulations. The anchoring of the ink molecules to the monolayer is of multivalent nature and the degree of multivalency shows a sharp dependence on temperature, control of temperature thus providing a further operational "switch" for directed molecular assembly. The computational protocol developed can, in principle, be extended to model any multivalent assembly, for example, virus-cell complexation.