Rapid advances in sensing technologies are leading to the development of integrated wearable electronics for biomedical applications. Piezoelectric materials have great potential for implantable devices because of their self-powered sensing capacities. The soft and highly deformable surfaces of most tissues in the human body, however, restrict the wide use of piezoelectric materials, which feature low stretchability. Flexible piezoelectric polyvinylidene fluoride films that could conformably integrate with human bodies would have advantages in health monitoring. Here, a Kirigami technique with linear cut patterns has been employed to design a stretchable piezoelectric sensor with enhanced piezoelectricity. A parametric Finite Element Analysis study is first performed to investigate its mechanical behaviour, followed by experiments. An inter-segment electrode connection approach is proposed to further enhance the piezoelectric performance of the sensor. The voltage output shows superior performance with 2.6 times improvement compared to conventionally continuous electrodes. Dynamic tests with a range of frequencies and strains are performed to validate the sensor design. With its high performance in large strain measurements, the Kirigami-based sensing system shows promise in stretchable electronics for biomedical devices.

A novel hierarchical metamaterial with tunable negative Poisson’s ratio is designed by a re-entrant representative unit cell (RUC), which consists of star-shaped subordinate cells. The in-plane mechanical behaviors of star-re-entrant hierarchical metamaterial are studied thoroughly by finite element method, non-dimensional effective moduli and effective Poisson’s ratios (PR) are obtained, then parameters of cell length, inclined angle, thickness for star subordinate cell as well as the amount of subordinate cell along x, y directions for re-entrant RUC are applied as adjustable design variables to explore structure-property relations. Finally, the effects of the design parameters on mechanical behavior and relative density are systematically investigated, which indicate that high specific stiffness and large auxetic deformation can be remarkably enhanced and manipulated through combining parameters of both subordinate cell and parent RUC. It is believed that the new hierarchical metamaterial reported here will provide more opportunities to design multifunctional lightweight materials that are promising for various engineering applications.