(6aj) Soft, Flexible Tissue-Integrated Chemical Sensors: From Wearable to Implantable Neural Systems

Postdoctoral Experience.

PI: John Rogers, Northwestern University.

Project: Wireless, battery-free, bio-integrated chemical sensors for wearable and implantable applications.

The rich composition of solutes and metabolites in sweat and the relative ease with which it can be noninvasively collected make this class of biofluid highly attractive for diverse applications in ambulatory health diagnostics and sports performance. Advances in biotechnology, nanoscience, materials science and electrical engineering lay the foundations for recent demonstrations of skin-interfaced devices that continuously monitor biochemicals in human perspiration. However, majority of the reported systems require complex electronics and batteries resulting in bulky, large footprint devices that are cumbersome to the users. I address this issue by developing first examples of wireless, battery-free, skin-integrated sweat analyses and capturing systems that are nearly 20 times lighter and 4 times smaller than the most sophisticated sweat sensors reported to date. Such devices result from an unusual combination of enzymatic biofuel cell-based electrochemical sensors, colorimetric assays, advanced microfluidics with passive capillary burst valves, and near field communication (NFC) protocols.

A widespread route to understanding neural circuitry relies on optical/electrical stimulation at precise regions of the brain, followed by subsequent neurochemical measurements. Unfortunately, at present, stimulation and sensing functions each involve completely distinct platforms and components. The need for inserting multiple separate, wired components, and inability to precisely control the spatial orientation of these components during insertion significantly compromises animal behavior and impedes correct interpretation of the data. I am addressing this important issue by developing a new class of integrated wireless, battery-free neural implants for simultaneous optical stimulation and neurochemical sensing. The microneedle comprises of a µLED for precise optical stimulation of dopaminergic neurons and an electrochemical microsensor for dopamine detection. An unconventional amalgamation of disparate technologies, such as, lithography, laser patterning, electrochemical nano-structuring, polymer science and wireless electronics results in seamless fabrication of the dopamine sensor adjacent to the optical stimulation components. Separately, developed mathematical models help predict the device’s sensing characteristics and obtain 3D maps of dopamine release from the neurons. Studies with freely moving mice are presently underway.

PhD Experience.

PI: Joseph Wang, UC San Diego

Project: Novel ink formulations for all-printed stretchable and self-healing electrochemical devices for wearable sensing and energy applications.

Conventional electrochemical systems are rigid and hence cannot be easily conformed to the soft, curvilinear structures of the human skin. I addressed this major issue by pioneering the development of novel printable inks for realizing first examples of highly stretchable and self-healing electrochemical devices. The all-printed carbon nanotube and conducting polymer based stretchable devices developed by me exhibit electrochemical properties similar to conventional, rigid electrodes. However, unlike the traditional electrodes, my devices can easily accommodate strains upto 500% with negligible impact on their electrochemical properties. I leveraged such systems to obtain stretchable glucose and ammonia sensors for real-time sweat sensing. Similarly, I also developed a high power density lactate-based biofuel cell for scavenging energy from the human sweat to power wearable devices. The biofuel generated ~1mW/cm² which represents nearly 10 times higher power density compared to previous examples and enabled me to power a Bluetooth radio using the wearable biofuel cell. Separately, I developed a new class of printable inks that result in devices with self-healing properties similar to the human skin. Such smart systems are attractive for wearable applications since they can recover their function autonomously if damaged during the ambulatory functions performed by the body. The self-healing agent encapsulated microcapsules and magnetic microparticles-based systems self-restored their electrochemical properties within seconds of complete mechanical damage. I demonstrated the practical viability of such intelligent systems by developing self-healing sodium sensor and zinc-silver oxide battery for wearable applications.

Future Directions:

As a faculty member I would like to establish a highly interdisciplinary research group that builds upon my expertise in biochemical sensing, biofuel cells, batteries, and printed electronics to address some of the key challenges in wearables, neuroscience, printed electronics and pollution sequestration. (i) Wearable chemical sensors: My group will develop next generation of wearable systems for metabolomic, proteomic and peptidomic analysis of sweat for deeper understanding of the sweat chemistry and its relation to the human physiology. (ii) Neural implants: We will aspire to develop new classes of brain implantable systems for simultaneous stimulation, sensing and targeted drug delivery at specific regions of the brain that will provide us deeper understanding of how the brain functions and help us test new drugs and develop new strategies to address scourge of neurodegenerative diseases such as Alzheimer’s and Parkinson’s. (iii) Self-assembly enhanced printing of high-performance devices: My group will leverage my expertise in developing nano/micro-particle ink formulations to realize new classes of inks and printing processes that, unlike present inks and printing techniques, will lead to precise orientation and self-assembly of particles within the printed devices for various energy storage and sensing applications. Such printed devices will exhibit superior performance to their counterparts developed using conventional printing methods since the highly ordered nano/micro-particles within the printed systems will play a key role in enhancing their energy storage and sensing characteristics. (iv) Pollution sequestration for fabricating printed electronics: We will develop new strategies that leverage my knowledge of printable inks, fuel cells, batteries, and sensors to sequester particulate matter pollutants from the environment and transform them into printable inks for various printed electronics applications.

Selected Publications

Total papers: 46

First/co-first author papers: 24

H-index: 29

Total citations > 3700

1. “Soft, skin-interfaced microfluidic systems with passive galvanic stopwatches for precise chronometric sampling of sweat”, A. J. Bandodkar et al, Adv. Mater. 2019 (DOI: https://doi.org/10.1002/adma.201902109)
2. “Battery-free, skin-interfaced microfluidic/electronic system for simultaneous electrochemical, colorimetric & volumetric sweat analysis”, A. J. Bandodkar et al, Sci. Adv. 2019, 5, eaav3294.
3. “Soft, skin-integrated multi-functional microfluidic systems for accurate colorimetric analysis of sweat biomarkers and temperature”, J. Choi, A. J. Bandodkar et al, ACS Sensors 2019, 4, 379.
4. “Soft, stretchable, high power density electronic skin-based biofuel cells for scavenging energy from human sweat” A. J. Bandodkar et al, Energy Environ. Sci., 2017,10, 1581.
5. “All-printed magnetically self-healing electrochemical devices”, A. J. Bandodkar et al, Sci. Adv. 2016, 2, e1601465.
6. “A wearable chemical–electrophysiological hybrid biosensing system for real-time health and fitness monitoring”, S. Imani, A. J. Bandodkar et al, Nat. Commun. 2016, 7, 11650.
7. “Highly Stretchable Fully-Printed CNT-based Electrochemical Sensors and Biofuel Cells: Combining Intrinsic and Design-induced Stretchability”, A. J. Bandodkar et al, Nano Lett. 2016, 16, 721.
8. “All-Printed Stretchable Electrochemical Devices”, A. J. Bandodkar et al, Adv. Mat. 2015, 27, 3060.

Teaching Interests:

Teachers are important pillars in one’s success and I owe my accomplishments to the teachers in my past and present who instilled scientific curiosity in me, taught me scientific skills, helped me overcome my weaknesses, and guided me in tackling challenging tasks. A major motivation for me to become a faculty member is to partake in the noble occupation of teaching and guide young minds towards a successful, fruitful and content life. During my PhD and now as a postdoc, I have mentored 23 undergraduate students of which 8 are currently PhD students in top tier schools; 5 work in industry and 10 are pursing undergraduate degrees. I have also been a Lecturer/TA for three graduate level courses (~50 students in each course). Apart from helping students understand the concepts during office hours, on occasions, I have also given lectures on behalf of the concerned professor. Considering my ability to explain complex scientific concepts in a simple manner to people without STEM background and my passion to motivate people towards research, I was invited as a guest lecturer for an undergraduate course (~150 students) on “Designing Information” at the UC San Diego’s Fine Arts Department. In this lecture, I illustrated various ways in which wearable devices offer an exciting avenue for achieving personalized Internet of Things and how these devices are having an impact in today’s day and age. I was surprised and overjoyed by the overwhelming interest shown by these Fine Art students, whom till then had given little thought to this technology. In fact, one of the students even collaborated with me on a project that combined chemical sensors with fine arts – a truly unique learning experience for both of us. In addition to these, I have also been invited as a speaker at the University’s undergraduate outreach events to motivate and encourage young minds to take up careers in the STEM fields. As a faculty member I would be thrilled to teach courses on mass and heat transfer, thermodynamics, electrochemistry, chemical sensors, nanobiotechnology and surface science. Additionally, I would be excited to get involved in committees focused on increasing student participation in STEM fields.