Cells are able to sense and react to their physical environment by translating a mechanical cue into an intracellular biochemical signal that triggers biological and mechanical responses. This process, called mechanotransduction, controls essential cellular functions such as proliferation and migration. The cellular response to an external mechanical stimulation has been investigated with various static and dynamic systems, so far limited to global deformations or to local stimulation through discrete substrates. To apply local and dynamic mechanical constraints at the single cell scale through a continuous surface, we have developed and modelled magneto-active substrates made of magnetic micro-pillars embedded in an elastomer. Constrained and unconstrained substrates are analysed to map surface stress resulting from the magnetic actuation of the micro-pillars and the adherent cells. These substrates have a rigidity in the range of cell matrices, and the magnetic micro-pillars generate local forces in the range of cellular forces, both in traction and compression. As an application, we followed the protrusive activity of cells subjected to dynamic stimulations. Our magneto-active substrates thus represent a new tool to study mechanotransduction in single cells, and complement existing techniques by exerting a local and dynamic stimulation, traction and compression, through a continuous soft substrate.

This article presents a magnetically actuated two-way, three-position (+, 0, −), paper-based microfluidic valve that includes a neutral position (0)—the first of its kind. The system is highly robust, customizable, and fully automated. The advent of a neutral position and the ability to precisely control switching frequencies establish a new platform for highly controlled fluid flows in paper-based wicking microfluidic devices. The potential utility of these valves is demonstrated in automated, programmed, patterning of dyed liquids in a wicking device akin to a colorimetric assay but with a programmed fluid/reagent delivery. These valves are fabricated using facile methods and thus remain cost-effective for adoption into affordable point-of-care/bioanalytical devices.