Design of three-dimensional, millimeter-scale models for molecular folding.

This communication describes the fabrication of three-dimensional structures of organic polymers using principles of design inspired by protein folding. The structures consist of rigid polyhedral components with dimensions of a few millimeters ("microdomains"), representing alpha-helical and beta-sheet secondary structures, connected with flexible linkers representing loops or turns. These structures were fabricated from polyurethane using photolithographic and soft lithographic techniques. The surfaces of the microdomains were patterned into hydrophobic and hydrophilic regions, and a hydrophobic photocurable liquid (serving both as lubricant and adhesive) was selectively precipitated onto the hydrophobic areas. The unfolded structures were suspended in water and agitated by tumbling. Self-assembly occurred through coalescence of the thin films of hydrophobic liquid, and was caused by minimization of the free energy of the interface between the liquid adhesive and the water. The self-assembled structures were locked in place by curing the adhesive with UV light. These results demonstrate the use of concepts abstracted from the study of proteins-including attractive hydrophobic interactions, shape complementarity, and conformational constraint-in the self-assembly of complex, three-dimensional structures on the millimeter scale.