Self-folding particle chains

The synthesis of materials in biological systems is different from the way human engineered materials are produced. Biological materials are predominantly soft materials which exhibit multiple encoded functionalities and can respond to external stimuli. We propose a biomimetic experimental route to the creation of 3D-structured nano- and micromaterials through directed self-folding of colloid strings. Such a general approach to design and construction of 3-D, man-made, functional materials based on self-organization is practically experimentally unexplored. A ubiquitous material structure in nature is found in peptide chains, which form structurally and functionally diverse materials out of a limited set of monomers through self-folding of the pol-ymer chain. The folding is guided by the sequence of the differently interacting peptides. Designing strings of different colloidal sub-units that can self-fold - in the spirit of proteins and amino acids - is a tantalizing prospect that holds the promise to create materials that explore structure-function relationships in three dimensions. Such materials would have interesting new properties such as encoded structural and functional sensitivity to environmental conditions and the ability to self-repair their structures by refolding. Recently we showed, using simulations that by linking particles that have directional interactions as well as isotropic interactions into a string, i.e. into a “patchy polymer”, it is possible to create chains that spontaneously fold into given target structures. This work suggests that directed self-folding can be realized using a wide variety of interaction potentials, patch interactions and numbers of patches. We are therefore confident that we can experimentally realize a toolbox of colloids with well-characterized interaction potentials that match the reductionist criteria in the model. The particles comprise new systems in their own right but are based on existing synthetic concepts. The particles will be linked into linear chains and used to explore design principles to encode 3D structures into folding chains. Our focus is on establishing suitable characterization techniques and protocols to fabricate and measure the properties of colloid monomers, colloid chain sequence and the folding into secondary and tertiary structures. The new methodology to characterize folding in real time will be developed by application of advanced microscopy techniques, primarily digital holographic microscopy, which is applicable to the size and time-scale of movement of the colloids under investigation, combined with confocal fluorescence microscopy. Together with the synthesis of the new colloidal system, these developments will enable experimentally testing the theoretical prediction of designable, self-folding, 3D colloidal materials, based on patchy colloid monomers.