Non-deterministic self-assembly of two tile types on a lattice

TL;DR

This paper investigates the non-deterministic self-assembly of two types of tiles on a lattice, revealing diverse concentration-dependent behaviors and fractal structures, extending understanding of biological aggregation processes.

Contribution

It introduces a lattice model for non-deterministic self-assembly with two tile types, cataloging various behaviors and estimating critical concentrations for phase transitions.

Findings

Several tile sets show sharp transitions from bound to unbound structures.

Structures exhibit fractal dimensions, indicating complex self-similar patterns.

The model predicts critical concentrations for some phase transitions.

Abstract

Self-assembly is ubiquitous in nature, particularly in biology, where it underlies the formation of protein quaternary structure and protein aggregation. Quaternary structure assembles deterministically and performs a wide range of important functions in the cell, whereas protein aggregation is the hallmark of a number of diseases and represents a non-deterministic self-assembly process. Here we build on previous work on a lattice model of deterministic self-assembly to investigate non-deterministic self-assembly of single lattice tiles and mixtures of two tiles at varying relative concentrations. Despite limiting the simplicity of the model to two interface types, which results in 13 topologically distinct single tiles and 106 topologically distinct sets of two tiles, we observe a wide variety of concentration-dependent behaviours. Several two-tile sets display critical behaviours in form of a sharp transition from bound to unbound structures as the relative concentration of one tile to another increases. Other sets exhibit gradual monotonic changes in structural density, or non-monotonic changes, while again others show no concentration dependence at all. We catalogue this extensive range of behaviours and present a model that provides a reasonably good estimate of the critical concentrations for a subset of the critical transitions. In addition we show that the structures resulting from these tile sets are fractal, with one of two different fractal dimensions.