Simple Approach to High-Performance Stretchable Heaters Based on Kirigami Patterning of Conductive Paper for Wearable Thermotherapy Applications

Abstract

Recent efforts to develop stretchable resistive heaters open up the possibility for their use in wearable thermotherapy applications. Such heaters should have high electrothermal performance and stability to be used practically, and the fabrication must be simple, economic, reproducible, and scalable. Here we present a simple yet highly efficient way of producing high-performance stretchable heaters, which is based on a facile kirigami pattering (the art of cutting and folding paper) of a highly conductive paper for practical wearable thermotherapy. The resulting kirigami heater exhibits high heating performance at low voltage (>40 °C at 1.2 V) and fast thermal response (<60 s). The simple kirigami patterning approach enables the heater to be extremely stretchable (>400%) while stably retaining its excellent performance. Furthermore, the heater shows the uniform spatial distribution of heat over the whole heating area and is highly durable (1000 cycles at 300% strain). The heater attached to curvilinear body parts shows stable heating performance even under large motions while maintaining intimate conformal contact with the skin thanks to the high stretchability and sufficient restoring force. The usability of the heater as a wearable thermotherapy device is demonstrated by increased blood flow at the wrist during operation.

Functional Fibers, Composites and Textiles Utilizing Photothermal and Joule Heating

“…Because of the highly conductive LM, its sinusoidal patterns, and 3D network in the PDMS matrix, the resulting composite film showed a high stretchability of over 100%, good conductivity of 1.81 × 10 3 Scm −1 , and excellent dynamic stability with only a slight change in electrical resistance and heating temperature of 4.23% and 7.56% upon 100% stretching. In a similar methodology, a kirigami pattern of a highly conductive Al paper was embedded in a highly elastic silicone elastomer (Ecoflex) ( Figure 11) [111]. The pristine paper was immersed in an Al precursor solution, and the subsequent decomposition of the Al precursor led to Al coating on all fiber surfaces in the paper.…”

Conformal Printing of Graphene for Single‐ and Multilayered Devices onto Arbitrarily Shaped 3D Surfaces

“…Joule heating, also known as ohmic heating is the process by which the passage of an electric current through a conductor produces heat and is currently the primary method by which many thin‐film heaters function. Printed graphene heaters have huge potential for disposable devices such as wearable heaters for therapeutic purposes . Demonstrations to date on flat surfaces has seen screen printing emerge as an attractive method for the large‐scale fabrication of joule heaters.…”

Design of Rigidity and Breaking Strain for a Kirigami Structure with Non-Uniform Deformed Regions

“…In recent years, many researchers have conducted investigations using sheets with incised periodic cuts, or so-called kirigami structures. Such structures show interesting mechanical characteristics [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]. For example, a kirigami structure can tune the rigidity and breaking strain of the overall device by virtue of changes in its length or the density of cuts in the structure [1,2,3,4,5,6,7,8,9].…”

“…Dias et al designed linear actuators that can perform four fundamental forms of linear actuation, that is, roll, pitch, yaw, and lift, by tuning the locations and arrangements of the cuts [10]. Various practical applications have been suggested by changing the mechanical characteristics of kirigami structures, such as increasing the breaking strain of the material and testing steric out-of-plane deformations by stretching the structure [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]. Such applications include strain sensors [11,12,13,14], stretchable heaters [15], solar cells with solar tracking systems [16], bioprobes [17], crawling robots [18], artificial muscles [19], soft deployable reflectors [20], self-folding hinges [21,22], metamaterial bricks [23], and adhesives with tunable anisotropic adhesive strength [24].…”

“…Various practical applications have been suggested by changing the mechanical characteristics of kirigami structures, such as increasing the breaking strain of the material and testing steric out-of-plane deformations by stretching the structure [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]. Such applications include strain sensors [11,12,13,14], stretchable heaters [15], solar cells with solar tracking systems [16], bioprobes [17], crawling robots [18], artificial muscles [19], soft deployable reflectors [20], self-folding hinges [21,22], metamaterial bricks [23], and adhesives with tunable anisotropic adhesive strength [24]. It has been confirmed that a kirigami structure becomes non-uniformly deformed when it is stretched, because the deformation is inhibited at regions close to both ends connected to the uncut region in the longitudinal direction [1,2,3,4,5,11,12,13,14,15,16,17].…”