Southern Medical University, Lu Feng teams, etc. \”AFM\”: egg white hydrogel phase transition – toward transparent, without delay wearable electronics product development
Soft wearable electronic devices has recently become a new research field, which extends the functionality of conventional rigid electronic devices in medical records, human-machine interface and the energy collection of; at the same time, will contribute to the similarity of human tissue on the machine stimulation to a minimum, and be able to monitor the ongoing health care. A conductive polymer, carbon, or a metal nano-materials with superior performance at a conductor, the display, aspects of the wearable electronic device is widely used and green energy. But its transparency, lack of ductility (<90％），制造成本、潜在毒性限制进一步应用；聚合物-弹性体杂化体渗流网络具有明显的滞后、连接损耗和疲劳失效。液态金属（LM）的模量比弹性体低几个数量级，所以流体LM对弹性体的载荷微不足道。水凝胶与弹性体复合材料具有响应延迟、恢复时间长、磁滞高的缺点。因此，具有高成本效率、透明性、无滞后性及多功能的柔性导体-弹性体混合物导电材料仍是个严峻的挑战。
Southern Medical Lu Feng team and the University of Manitoba in Canada Malcolm Xing teamwork on the \”Advanced Functional Materials\” published Protein gel\’s Phase Transition:.. Toward superiorly transparent and Hysteresis-Free wearable Electronics hydrogel of egg white from liquefaction development wearable electronic devices, HMI and clean energy transparent egg white hydrogel (EWH) [ 123] is generated in a basic environment by a physical crosslinking; EWH shear thinning and self-healing properties, for which direct printing ink for a writing 3D structure is essential to achieve a complex system induced alkaline hydrolysis EWH. unique phase change process, and can spontaneously liquefied into a liquid protein electrophoresis from a solid hydrogel phase change during a sharp decline in the mechanical modulus (reduced from 1 Pa to 770Pa), obtained egg white (EW) liquid ( EWL) was significantly higher than the transmittance of EW original solution, and exhibits excellent ion conductivity at room temperature can be directly EWH 3D printing, a complicated circuit can be designed by adjusting the extrusion rate; based EWH bis stretching / compression sensitive detection sensor strenuous exercise (finger and wrist movements) and Microsoft\’s motion (e.g., pulse rate, facial expression, and vasodilatation) and other practical life scene (acoustic vibration, shearing forces and roughness) . EWL to an electrode, the authors also developed the nano triboelectric generator (TENG is) having a high compression resistance and transparency. [results and discussion] 
1. mechanical properties of EWH EWL and, transmittance and electrical properties
EWH hydrogel fromEW original solution to form the aqueous gel system secondary crosslinking between the carboxyl group and polyvalent cations through. Two stained green and red fluorescent dye EWH cylindrical blocks vertically stacked and sealed stacked hydrogel will fuse together under gravity (Figure 1a). EWH occurrence \”of liquidation\” phenomenon in the alkali hydrolysis, i.e. form a synchronized phase transition occurs EWH EWH trigger, and during a phase change, the smaller peptide or amino acid fragments dispersed in the EWL instead of the full protein chain (FIG. 1b). After gelation of EWH modulus EW two orders of magnitude (FIG. 1c). Since the time required for settlement decreases with increasing temperature (Fig. 1d). Mechanical modulus EWH made different basic solution (LiOH and KOH) almost unchanged (FIG. 1e). After 4 ° C refrigerator for 2 months, a thin liquid EWH, which mold measured out aging higher than the original EW solution (FIG. 1f). Compared to EW, the hydrogel has a modulus of time is relatively dynamic behavior.
FIG. 1 after a phase change physical and mechanical properties of EWH and EWL.
FIG 2 EWH light transmittance and electrical properties and the EWL.2.2 EWL of 3D printing configuration
In EWH OF shear thinning as Direct 3D printing ink at room temperature, the UV curing technique without the rheology modifier. EWH has a typical shear thinning behavior, can be printed (FIG. 3a) by a printing ink as a direct extrusion nozzle. In three commercial products Sylgard 184 silicone rubber series and Ecoflex (00-35 and 00-50) as EWL soft substrate. The contact angle tests show all of the inherent hydrophobic elastomer or EW of EWL, even after full settlement remains clear boundaries (FIG. 3b). In printing, the line resolution can be varied by varying the extrusion speed. Shown in Figure 3c, the extrusion rate of the extruder increases lead to a reduction in the hydrogel is deposited on the substrate, which greatly reduces the resolution of the line. OF then creates a hierarchical structure having an array of interconnected flow, only by changing the extrusion rate can be obtained with high fidelity and linearly gradually decreasing width (FIG. 3D), the device has excellent stretchability (FIG. 3e ). In addition, injection can EWL patterned by microfluidic casting and needle, an electronic circuit for the strain sensor and the ambient temperature (FIG 3f- h).
FIG. 3 EWH for 3D printing and stretchable electronics manufacturing.2.3 high sensitivity and hysteresis-free EWL-Eco mixture as double the strain / compression sensors
On the EWL automatic packaging in Ecoflex then embedded in 3D printing EWH line Ecoflex by to produce a self-liquidating EWL-Eco sensor. Resistance change value (ΔR%) will increase as the tensile deformation sensor during stretching from 0% to 200% have a reproducible response. ΔR% size is closely related to the internal dimensions, the smaller the diameter, the greater the resistance variation (FIG. 4a-c), the inside width of the associated conductor EWL sensitivity, and have high sensitivity variations (FIG. 4d) in the board-level range. Sensor having a \”speed insulation\” feature, which means that the sensor can withstand stretching very fast, and without significant change remains reliable sensitivity (FIG. 4e). EWL-Eco response time of the sensor and the skin faster recovery time than 10ms, and long-term durability of the electron lifetime (FIG. 4g, h). Due to the flow characteristics and high elasticity EWL of Ecoflex, the sensor exhibits excellent compression rate, up to 90% (Fig. 4i). Resistance of the sensor increases as the load pressure increases (Fig. 4j), stability and durability and no significant deviations (FIG. 4k) to 300 k in the cycle of 12 kPa.
FIG 4 EWL-Eco sensor electromechanical properties of the tensile and compressive forces.2.4 Application of wearable sensor EWL-Eco and curves on a plane surface
In view of its high flexibility and flexibility, as well as negligible hysteresis and tensile stress double electromechanical sensitivity, EWL-Eco sensing apparatus is used for identification and verification on a screen and a non-planar (FIG 5a- e), include intense / weak exercise (FIG. 5a- b), such as a finger and wrist bending (FIG. 5c), analog vasoconstriction and vasodilation, Morse code identification (FIG. 5E); sedentary monitor and pulse (FIG. 5f) in the situation after exercise; forehead wrinkles detecting subtle contraction (FIG. 5g); non-contact mode detecting sound ( Figure 5h). EWL-Eco sensor also stimulated dynamic capability (FIG. 5i), a texture recognition (FIG. 5J) and programmable manufacturing capabilities (e.g., 3D visual pressure sensor (FIG. 5k)). EWL-Eco apparatus can recognize subtle differences in health status, and to accommodate a large dynamic stimulation of non-planar surfaces, which indicates high sensitivity and accuracy as the wearable sensor having a wide potential.
FIG. 5. EWL-Eco sensor for detecting a variety of real-world behavior subtle and dramatic.2.5 EWL fluidity gesture based console
human-machine interface devices (i.e. touching, pressing or gripping) by physical interaction between people to perform the operation, and based on touch electronic devices (such as keyboard, mouse, smart phones) for the life and development of science and paved the way. By sealing OF EWL with LED indicator 3D printing plastic mold manufacturing a novel and simplified gesture console that allows the electronic device is an on / off / standby state. Briefly, the conductive contacts as stream EWL delamination integrated circuit to alternately open / close signal; gesture chamber changes according to the design liquid intoAnd connected electrically to the current branch, and then open the respective adjacent electronic controller to achieve the function. The programming console software based gesture recognition and control device, can be used in the future IOT art (FIG. 6).
FIG. 6 EWL gesture made by the control console.2.6 EWL as a friction nano-generators (TENG is) energy harvesting conductor
TENG to efficiently convert mechanical energy to various coupling contact charging only by electrostatic induction and electric energy, having low-cost, convenient material advantages. On a simple casting process to manufacture a bulk TENG shape, EWH is sandwiched between two layers of Ecoflex to achieve self-liquidating. From when the skin friction (positive charge) Ecoflex film surface electrical contact, and induced the same amount of negative charge on the elastomer but does not generate an electric potential. EWL ion motion in the elastic body due to the negative charge excess of positive charge is generated, away from the skin surface can be driven Ecoflex free electrons flow from the ground through an external circuit EWL, once again approaching the elastomeric skin, the entire electron flow will reverse motion; EWL -TENG can be stably and quickly in response to external movement, the current output capacity increases with increasing pressure, thereby producing a further feature of electrical array-based skin.
FIG generator 7 EWL-TENG processing, structural design, and mechanical sensing characteristics can be collected.