Stretchable helical gold conductor on silicone rubber microwire

Compliant and stretchable three-dimensional golden tracks are produced by metallization of silicone wires maintained under twisting and stretching constraints. Upon release, the metallic track deforms to a helix presenting a wavy and cracked surface. Wavelet and crack orientations are function of three parameters: the wire radius, the number of imposed rotations divided by the length of the cylinder, and the stretching in its axis direction. Electrical conductivity at rest and under stretching can be optimized by finding the prestraining conditions that provide the best trade off between the maximum amount of surface buckling and a limited amount of cracks. (C) 2007 American Institute of Physics

Stretchable gold tracks on flat polydimethylsiloxane (PDMS) rubber substrate

A process to fabricate stretchable gold tracks on silicone rubber substrates is studied by XPS, static water contact angle measurement, AFM, and SEM. The process involves several steps: removing uncured oligomers by hexane Soxhlet extraction; pre-stretching the substrate; activating the strained silicone surface by an oxygen plasma treatment; coating the strained substrate with 5nm titanium and 80nm gold layers; and finally releasing the sample. The plasma treatment creates a thin brittle silica-like layer that temporarily increases the substrate's surface energy. Indeed, the plasma treatment is followed by a hydrophobic recovery. As a consequence, the delay between plasma treatment and metal deposition has to be reduced as much as possible. The silica-like layer can be nicely observed after release. The entire process allows us to obtain stretchable metallized samples that remain conductive even after an excessive deformation leading to electrical failure

Thickness and Elastic Modulus of Plasma Treated PDMS Silica-like Surface Layer.

The adhesion of poly(dimethylsiloxane) (PDMS) rubber is largely improved by oxygen plasma surface treatment. The thickness of the silica-like surface layer is characterized by performing transmission electron microscopy imagery on microtome slices of welded plasma treated surfaces. The specific double layer contrast can be considered as equal to twice the thickness of the silica-like layer. The thickness measurements combined with strain-induced elastic buckling instability analysis gives an estimate of the elastic modulus of the silica-like layer equal to 1.5 GPa

Fracture-based fabrication of normally closed, adjustable, and fully reversible microscale fluidic channels

Adjustable fluidic structures play an important role in microfluidic systems. Fracture of multilayered materials under applied tension has been previously demonstrated as a convenient, simple, and inexpensive approach to fabricate nanoscale adjustable structures; here, it is demonstrated how to extend this concept to the microscale. This is achieved by a novel pairing of materials that leverages fracture mechanics to limit crack formation to a specified region, allowing to create size-controllable and adjustable microfluidic structures. This technique can be used to fabricate "normally closed" microfluidic channels that are completely reversible, a feature that is challenging to achieve in conventional systems without careful engineering controls. The adjustable microfluidic channels are then applied to mechanically lyse single cells, and subsequently manipulate the released nuclear chromatin, creating new possibilities for epigenetic analysis of single cells. This simple, versatile, and robust technology provides an easily accessible pathway to construct adjustable microfluidic structures, which will be useful in developing complex assays and experiments even in resource-limited settingsclose1

Substrates with Patterned Extracellular Matrix and Subcellular Stiffness Gradients Reveal Local Biomechanical Responses

A substrate fabrication process is developed to pattern both the extracellular matrix (ECM) and rigidity at sub-cellular spatial resolution. When growing cells on these substrates, it is found that cells respond locally in their cytoskeleton assembly. The presented method allows unique insight into the biological interpretation of mechanical signals, whereas photolithography-based fabrication is amenable to integration with complex microfabricated substructures