Differentially photo-crosslinked polymers enable self-assembling microfluidics.

An important feature of naturally self-assembled systems such as leaves and tissues is that they are curved and have embedded fluidic channels that enable the transport of nutrients to, or removal of waste from, specific three-dimensional regions. Here we report the self-assembly of photopatterned polymers, and consequently microfluidic devices, into curved geometries. We discover that differentially photo-crosslinked SU-8 films spontaneously and reversibly curve on film de-solvation and re-solvation. Photolithographic patterning of the SU-8 films enables the self-assembly of cylinders, cubes and bidirectionally folded sheets. We integrate polydimethylsiloxane microfluidic channels with these SU-8 films to self-assemble curved microfluidic networks.

Enzymatically triggered actuation of miniaturized tools.

We demonstrate a methodology that utilizes the specificity of enzyme-substrate biomolecular interactions to trigger miniaturized tools under biocompatible conditions. Miniaturized grippers were constructed using multilayer hinges that employed intrinsic strain energy and biopolymer triggers, as well as ferromagnetic elements. This composition obviated the need for external energy sources and allowed for remote manipulation of the tools. Selective enzymatic degradation of biopolymer hinge components triggered closing of the grippers; subsequent reopening was achieved with an orthogonal enzyme. We highlight the utility of these enzymatically triggered tools by demonstrating the biopsy of liver tissue from a model organ system and gripping and releasing an alginate bead. This strategy suggests an approach for the development of smart materials and devices that autonomously reconfigure in response to extremely specific biological environments.

Three-dimensional fabrication at small size scales.

Despite the fact that we live in a 3D world and macroscale engineering is 3D, conventional submillimeter-scale engineering is inherently 2D. New fabrication and patterning strategies are needed to enable truly 3D-engineered structures at small size scales. Here, strategies that have been developed over the past two decades that seek to enable such millimeter to nanoscale 3D fabrication and patterning are reviewed. A focus is the strategy of self-assembly, specifically in a biologically inspired, more deterministic form, known as self-folding. Self-folding methods can leverage the strengths of lithography to enable the construction of precisely patterned 3D structures and "smart" components. This self-assembly approach is compared with other 3D fabrication paradigms, and its advantages and disadvantages are discussed.

Compactness determines the success of cube and octahedron self-assembly.

Nature utilizes self-assembly to fabricate structures on length scales ranging from the atomic to the macro scale. Self-assembly has emerged as a paradigm in engineering that enables the highly parallel fabrication of complex, and often three-dimensional, structures from basic building blocks. Although there have been several demonstrations of this self-assembly fabrication process, rules that govern a priori design, yield and defect tolerance remain unknown. In this paper, we have designed the first model experimental system for systematically analyzing the influence of geometry on the self-assembly of 200 and 500 microm cubes and octahedra from tethered, multi-component, two-dimensional (2D) nets. We examined the self-assembly of all eleven 2D nets that can fold into cubes and octahedra, and we observed striking correlations between the compactness of the nets and the success of the assembly. Two measures of compactness were used for the nets: the number of vertex or topological connections and the radius of gyration. The success of the self-assembly process was determined by measuring the yield and classifying the defects. Our observation of increased self-assembly success with decreased radius of gyration and increased topological connectivity resembles theoretical models that describe the role of compactness in protein folding. Because of the differences in size and scale between our system and the protein folding system, we postulate that this hypothesis may be more universal to self-assembling systems in general. Apart from being intellectually intriguing, the findings could enable the assembly of more complicated polyhedral structures (e.g. dodecahedra) by allowing a priori selection of a net that might self-assemble with high yields.

Self-loading lithographically structured microcontainers: 3D patterned, mobile microwells.

We demonstrate mass-producible, mobile, self-loading microcontainers that can be used to encapsulate both non-living and living objects, thus forming three-dimensionally patterned, mobile microwells.