As an effective way of power-to-electricity conversion, piezoelectric energy harvesters have received extensive attention in the past decade. However, the relationship between output performance and the topological structure of piezoelectric devices is still unknown. In this study, a simple and fast in-situ chemical foaming assisted fused deposited modeling (FDM) method was developed, and complex three-dimensional (3D) bioinspired bone structures of polyvinylidene fluoride (PVDF) were successfully fabricated. The hierarchical porous structure couples advantages of arbitrary shape design by 3D printing and abundant inner pores inside the printed piezoelectric parts that amplify the stress–strain effect and improve the output capacity. Moreover, with the assistance of ionic liquid, high β-phase content (86.72%) PVDF was achieved, producing an output of ∼13 V and a maximum current density of ∼0.27 μA/cm2, which outperforms most of the PVDF piezoelectric energy harvesters reported so far. Impressively, the as-prepared PVDF device can directly light up eight green LED bulbs and charge a 1 μF commercial capacitor to 3.65 V within 300 s. This work highlights a new 3D printing strategy integrated with a 3D biomimetic structural design for high-performance piezoelectric energy harvesting.

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With the advent of 5G and the Internet of Things era, sensitive and stable sensors have begun to develop rapidly, which are important substantial fundaments of smart medical care. In this study, based on the positive temperature coefficient (PTC) in conductive polymer composites (CPC), a novel polyolefin elastomer (POE)/carbon fiber (CF) composite was prepared. By regulating the rheological behavior of the polymer matrix, we realized its controllable thermal expansion in the temperature field and finally realized the reversible construction–destruction of the conductive CF network. Under optimal molecular weight conditions, the POE/CF PTC sensor showed a high sensitivity of 0.11 °C –1 and stability. It was also demonstrated that the heat transfer efficiency of the composite material played an essential role in the sensitivity of the as-prepared PTC sensor. Most impressively, we have assembled an invisible respiratory monitoring device based on the POE/CF composite to achieve real-time monitoring of human breathing, which displayed wide potential prospects in thermal monitoring and provided good prospects for micron-scale functional composites.