Wearable strain sensors for human motion detection are being highlighted in various fields such as medical, entertainment and sports industry. In this paper, we propose a new type of stretchable strain sensor that can detect both tensile and compressive strains and can be fabricated by a very simple process. A silver nanoparticle (Ag NP) thin film patterned on the polydimethylsiloxane (PDMS) stamp by a single-step direct transfer process is used as the strain sensing material. The working principle is the change in the electrical resistance caused by the opening/closure of micro-cracks under mechanical deformation. The fabricated stretchable strain sensor shows highly sensitive and durable sensing performances in various tensile/compressive strains, long-term cyclic loading and relaxation tests. We demonstrate the applications of our stretchable strain sensors such as flexible pressure sensors and wearable human motion detection devices with high sensitivity, response speed and mechanical robustness.

Reliable integration of solution processed nanoparticle thin films for next generation low-cost flexible electronics is limited by mechanical damage in the form of delamination and cracking of the films, which has not been investigated quantitatively or systematically. Here, we directly measured the interfacial fracture energy of silver nanoparticle thin films by using double cantilever beam fracture mechanics testing. It was demonstrated that the thermal annealing temperature and period affect the interfacial fracture energy. Also it was found that the interfacial fracture resistance can be maximized with optimized annealing conditions by the formation of organic residual bridges during the annealing process.

We demonstrate the biopsy needle integrated with multi-pair electrode based impedance sensing device for biological tissue discrimination. The impedance sensing biopsy needle has several pairs of electrodes which enable the selective tissue analysis during biopsy process. In order to verify the usefulness of the device, we demonstrate the conductance measurement of various saline solutions and the real-time conductance monitoring of soft elastomeric materials during the needle insertion. Finally, the tissue discrimination of porcine meat tissues during the needle insertion was successfully carried out.