Nonpatterned Soft Piezoresistive Films with Filamentous Conduction Paths for Mimicking Multiple-Resolution Receptors of Human Skin

Abstract

Soft pressure sensors play key roles as input devices of electronic skin (E-skin) to imitate real human skin. For efficient data acquisition according to stimulus types such as detailed pressure images or macroscopic strength of stimuli, soft pressure sensors can have variable spatial resolution, just like the uneven spatial distribution of pressure-sensing receptors on the human body. However, previous methods on soft pressure sensors cannot achieve such tunability of spatial resolution because their sensor materials and read-out electrodes need to be elaborately patterned for a specific sensor density. Here, we report a universal soft pressure-sensitive platform based on anisotropically self-assembled ferromagnetic particles embedded in elastomer matrices whose spatial resolution can be facilely tuned. Various spatial densities of pressure-sensing receptors of human body parts can be implemented by simply sandwiching the film between soft electrodes with different pitches. Since the anisotropically aligned nickel particles form independent filamentous conductive paths, the pressure sensors show spatial sensing ability without crosstalk, whose spatial resolution up to 100 dpi can be achieved from a single platform. The sensor array shows a wide dynamic range capable of detecting various pressure levels, such as liquid drops (∼30 Pa) and plantar (∼300 kPa) pressures. Our universal soft pressure-sensing platform would be a key enabling technology for actually imitating the receptor systems of human skin in robot and biomedical applications.

E-Tattoos: Toward Functional but Imperceptible Interfacing with Human Skin

“…Pressure-sensing e-tattoos allow for long-term monitoring of diverse physiological parameters, including blood pressure, respiration and heart rate, and physical activities. These e-tattoos can be categorized into eight types based on working principle: piezoresistive, − capacitive, − piezoelectric, − triboelectric, ,− active matrix, − iontronic, ,, hybrid-response, − and ultrasonic devices. ,, Figure provides an overview of some representative pressure-sensing e-tattoos.…”

“…Piezoresistive pressure-sensing e-tattoos utilize materials whose resistance changes with pressure-induced deformation. − These e-tattoos can outperform other pressure sensors owing to their high sensitivity and easy readout. For instance, Luo et al developed a flexible piezoresistive sensor comprising carbon-black-decorated fabric as the piezoresistive material and gold interdigital electrodes for cuffless blood pressure measurement (Figure a-i, left) .…”

Recent Advances in Flexible Piezoresistive Arrays: Materials, Design, and Applications

“…For the sensor array, the spatial distribution of measurement points can be characterized by spatial resolution, which is represented in the form of N × N [ 24 ], the spatial period of the arrangement (center-to-center distance between adjacent pixels) [ 25 ], or the number of measuring points per unit area (in dots per inch or pixels per inch) [ 26 ]. A detailed discussion about array design and spatial resolution is presented in Section 3.1.2 .…”

“…Conductive components usually include (1) carbon-based materials, e.g., carbon black (CB) [ 35 , 38 ], carbon nanotubes (CNTs) [ 39 , 40 ], graphene [ 41 , 42 ], hybrid carbon fillers [ 43 ], etc. ; (2) metal materials, e.g., metal nanowires [ 34 , 44 ] and metal particles [ 26 ]; (3) others include MXene [ 45 , 46 ], conductive polymers, e.g., polypyrrole (PPy) [ 16 , 47 ], polyaniline (PANI) [ 48 ], poly(3,4-ethylene dioxythiophene) (PEDOT) [ 49 ], etc. For the electrode material connecting each measurement point of the array, metal materials are usually selected, e.g., Au-based serpentine connections [ 50 ] and spay-coated Ag nanowire electrode strips [ 26 ].…”

Bio-Inspired Homogeneous Conductive Hydrogel with Flexibility and Adhesiveness for Information Transmission and Sign Language Recognition

“…In this work, a bio-inspired strategy to prepare adhesive hydrogels driven by quaternized adenine is proposed. The hydrogel provided a Young’s modulus and toughness similar to that of skin, thus assuring no tightness while the self-adhesive hydrogel adhered to the human. Moreover, the copolymerized adenine moieties in the polyacrylamide (PAM) matrix can also break the intra- and intermolecular hydrogen bonds of the chitosan- graft -PANI (chi- g -PANI) to enhance their dissolution.…”