The ability to monitor subtle changes in vital and arterial signals using flexible devices attached to the human skin can be valuable for the detection of various health conditions such as cardiovascular disease. Conventional Si device technologies are being utilised in traditional clinical systems; however, its fabrication is not easy owing to the difficulties in adapting to conventional processes. Here, we present the development of a fully printed, wearable, ferroelectric-polymer vital sensor for monitoring the human pulse wave/rate on the skin. This vital sensor is compact, thin, sufficiently flexible, and conforms to the skin while providing high pressure sensitivity, fast response time, superior operational stability, and excellent mechanical fatigue properties. Moreover, the vital sensor is connected to a communication amplifier circuit for monitoring the pulse waves with a wireless sensing system. This sensor system can realise the development of new healthcare devices for wearable sensor applications.

Flexible printed analogic amplifier circuits are required in wearable sensors to enhance their sensitivity for application in various fields such as healthcare, artificial skins, and soft robotics. Various technologies have been proposed to develop wearable sensors for healthcare. However, the development of piezopolymer-based printed healthcare devices for monitoring human vital signs that simultaneously achieve high sensitivity and low operating voltage remains a challenging task. Here, a highly pressure-sensitive printed sensor with low operating voltage is demonstrated and applied to monitor human pulse wave velocity (PWV). The printed sensor consists of a 2 μm thick pressure detector and an organic analogic amplification circuit that are simultaneously formed on flexible substrates. The printed organic analogic circuit can amplify the generated signal by a gain factor of 10. This configuration makes it possible to combine good pressure sensitivity (∼10 kPa) with a low operating voltage of −3 V. We attached the sensor on the skin to efficiently monitor human vital signs using PWV to estimate health conditions.

By using additives to change the higher-order structure of a poly(L-lactide) (PLLA) film, an improvement in its piezoelectricity was realized. The additive used was a triblock copolymer, which is a pure acrylic symmetric block copolymer consisting of a center block of poly(butyl acrylate) (PBA), corresponding to its soft part, and two side blocks of poly(methyl methacrylate) (PMMA), corresponding to its hard part. The triblock copolymer is hereafter denoted as PMMA-b-PBA-b-PMMA. The piezoelectric e-constant of the PLLA film with added PMMA-b-PBA-b-PMMA (PLLA/PMMA-PBA-PMMA film) was over two times higher than that of the PLLA film without adding PMMA-b-PBA-b-PMMA (reference PLLA film). Also, we found that the glass transition temperature increases with increasing PMMA-b-PBA-b-PMMA content. From atomic force microscopy (AFM) images, it was found that a new higher-order structure was formed in the PLLA/PMMA-PBA-PMMA film with high piezoelectricity. The method of using PMMA-b-PBA-b-PMMA has high productivity and its promising for industrial use.

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Tactile sensing is considered essential for effective object handling by robots. To this end, flexible smart materials are being extensively researched for application as soft pressure sensors. This paper proposes a soft pressure sensor featuring a ferroelectric-polymer sensing layer for dynamic pressure detection during robotic grasping operations. The solution-processed sensing layer is optimized in terms of the molecular weight of the ferroelectric polymer and the processing solvent. The proposed sensor exhibits high sensitivity to pressure with minimal response delay. Furthermore, these sensors successfully sensitize a robotic hand, enabling the real-time detection of pressure signals during object handling, thus demonstrating the potential of the proposed sensor for novel robotic interface applications such as biomimetic electronic skin.