A Sensing Method based on Elastic Instabilities of Swelllng Hydrogels

We present a biologically inspired sensing method which can be used to detect toxins or other chemical compounds. We engineer our hydrogels in such a way that an elastic instability is triggered by a designated stimulus. Two different bi-polymer strips are fixed together. When swelling is induced, the differential response of the two gels forming the composite strip causes the strip to bend. If the bending is constrained, an explosive elastic instability can occur if either the constraint is removed or the stored elastic energy is enough to induce fracture. A judicious choice of materials (e.g., degradable adhesive materials specific to certain enzymes or chemicals) and geometric constraints allow for the tuning of the instability. The rapid geometric changes associated with the elastic instability can be easily observed