NC ACS Local Section Online Poster Session

Background: Capacitive stress sensors have attracted significant interest due to their high sensitivity and low energy consumption and have been used in a variety of applications, including healthcare monitoring[1], human-machine interfaces[2], and electronic textiles[3]. Capacitive stress sensors consist of a dielectric layer sandwiched between electrodes. The sensitivity and measurement range of capacitive sensors can be increased by decreasing or increasing the elastic modulus of the dielectric layer, which leads to a contradiction with each other. To solve this problem, a capacitive stress sensor based on dual-structure liquid metal elastomer foam (DSLMEF) is proposed. Inclusion of liquid metal in the elastomer is used to tune the dielectric constant of the mixed material[4], which was shown to give higher stress sensitivity[4].

Results: The DSLMEF is composed of a stiff elastomer slab (elastic modulus: ~655 kPa) and a soft liquid metal elastomer foam (LMEF, elastic modulus: ~7 kPa). Small stress (<10 kPa) only deforms the soft LMEF, and large stress (> 10 kPa) deforms the soft LMEF and the stiff elastomer slab at the same time. Using the DSLMEF as the dielectric layer, a capacitive stress sensor with high sensitivity (0.073 kPa-1), and a large stress measurement range (200 kPa) is demonstrated.

Conclusions: We report a bioinspired soft multi-scale capacitive stress sensor based on dual structure liquid metal elastomer foam. The fabrication process of the sensor is easy to implement, low cost, and environment friendly. Compared with other capacitive soft stress sensors, this work achieves a better combination of sensitivity and measurement range. In addition, the high elastic modulus and high energy loss coefficient of DSLMEF also mimic the dermis of human skin, which can cushion objects from stress and strain. The development of the bioinspired soft multi-scale capacitive stress sensor based on DSLMEF has important scientific value and practical significance.

References: 1. Gao, Y.; Yu, L.; Yeo, J. C.; Lim, C. T. Flexible Hybrid Sensors for Health Monitoring: Materials and Mechanisms to Render Wearability. Adv. Mater. 2020, 32 (15), e1902133, DOI: 10.1002/adma.201902133. 2. Hammock, M. L.; Chortos, A.; Tee, B. C.; Tok, J. B.; Bao, Z. 25th anniversary article: The evolution of electronic skin (e-skin): a brief history, design considerations, and recent progress. Adv. Mater. 2013, 25 (42), 5997-6038, DOI: 10.1002/adma.201302240. 3. Kim, D. C.; Shim, H. J.; Lee, W.; Koo, J. H.; Kim, D. H. Material-Based Approaches for the Fabrication of Stretchable Electronics. Adv. Mater. 2020, 32 (15), e1902743, DOI: 10.1002/adma.201902743. 4. Yang, J. Y.; Tang, D.; Ao, J. P.; Ghosh, T.; Neumann, T. V.; Zhang, D. G.; Piskarev, E.; Yu, T. T.; Truong, V. K.; Xie, K.; Lai, Y. C.; Li, Y.; Dickey, M. D. Ultrasoft Liquid Metal Elastomer Foams with Positive and Negative Piezopermittivity for Tactile Sensing. Adv. Funct. Mater. 2020, DOI: ARTN 2002611 10.1002/adfm.202002611.

Shreyas Sanjay Kanetkar <sskanetk@ncsu.edu>

North Carolina State University

Sweat is an important biofluid for monitoring individuals’ health as it contains a number of essential biomarkers. However, sampling sweat for analysis still remains challenging as most of the commercially available sweat sensing devices are either invasive in nature or work only under active perspiration. These devices may not function under low-sweating conditions and are incapable of deriving information in sweat from sedentary subjects. We demonstrate a new principle for the design of flexible and wearable devices, which are capable of extracting sweat under both sedentary and actively perspiring conditions using osmotic pressure difference for pumping, and evaporation for liquid disposal. The device is composed of silicone, polyacrylamide hydrogel patch, and paper microfluidic conduit with a site of evaporation at the end (evaporation pad). The hydrogel is equilibrated with glycerin, glucose, or NaCl solution to build up the desired osmotic strength. We investigate their operation using dye (a model biomarker). In-vitro testing with gelatin-based model skin platform revealed that both glucose and glycerin infused gels facilitate high accumulation on the evaporation pad, with glucose being having the highest driving pressure. Parameters including the dimensions of the paper channel, hydrogel area and paper porosity also affect the cumulative dye collection. Human trials using prototype devices containing gels infused with glucose show potential to extract sweat and analyze it for lactate under both resting and non-resting conditions within a period of two hours. This sweat sampling concept can be integrated with continuous sensing using enzymatic electrochemical sensors. We chose lactate as a concept demonstrator, as sweat appears to be much more informative medium for lactate quantification than blood. The ability to measure lactate is interesting for monitoring metabolism and oxidative stress levels in athletes and military personnel.

Tamoghna Saha

NCSU

#papermicrofluidics, #sweat, #sensing, #hydrogels, #osmoticpumping, #evaporation, #capillary, #wicking, #biochemical assay

Fluorinated organic compounds are gaining prominence in number of research fields such as drug modifications, biomedical imaging and material science. A concise approach to synthesize [6]-2,2-difluorogingerol compound 3 via mild release of trifluoroacetate is studied. The target potentially possesses antipyretic, cardiotonic, analgesic and gastroprotective and antihepatotoxic activities. The synthetic approach would demonstrate the flexibility of this methodology and its potential for synthesizing a variety of natural and unnatural compounds. Biological activities of both (R)- and (S)-isomers will be tested.

Bi Youan Eric Tra

Methodist University�