Model for assembly and gelation of four-armed DNA dendrimers.

We introduce and numerically study a model designed to mimic the bulk behaviour of a system composed of single-stranded DNA dendrimers. Complementarity of the base sequences of different strands results in the formation of strong cooperative intermolecular links. We find that in an extremely narrow temperature range the system forms a large-scale, low-density disordered network via a thermo-reversible gel transition. By controlling the strand length, the gel transition temperature can be made arbitrarily close to the percolation transition, in contrast with recent model systems of physical gelation. This study helps the understanding of self-assembly in this class of new biomaterials and provides a bridge between physical and chemical gels.