#### Integration of printed sensors to flexible hybrid electronics for wearable health monitoring

Overview of a wearable sensor platform, where flexible sensors are utilized for real-time health monitoring.


A skin-like flexible and wearable sensor patch, seamlessly measuring body’s vital signs - realizing this device is a major goal of my doctoral work. My research focuses mainly on the system-level implementation of wearable medical devices, with an emphasis on flexible and printed bioelectronic and biophotonic sensors.

Wearable and flexible sensors are promising for medical sensing because they provide an improved signal-to-noise ratio (SNR) by establishing a conformal skin-sensor interface [1]. Moreover, in my work, printing techniques are used to fabricate the sensors, which ensures large-area scaling of the devices. Additionally with the rapid prototyping capability of printing, the sensors can be designed in different sizes and shapes, accommodating the needs of a diverse population.

An overview and system design of the wearable sensor patch (WSP) enabled by flexible hybrid electronics. The sensor side faces down toward the skin, and the component side faces up. The printed gold ECG electrodes and the thermistor are shown.


A flexible power source integrating a lithium-ion battery and amorphous silicon solar module for powering wearable health monitoring devices.


Flexible hybrid electronics (FHE) are a fundamental enabling technology for system-level implementation of novel printed and flexible devices. FHE bring together soft and hard electronics into a single platform, where the soft devices are used for conformal sensor interfaces, and the hard silicon-based devices provide the computational backbone and compatibility with existing electronic systems and standards. The interfacing of soft and hard electronics is a key challenge for flexible hybrid electronics.

For a project in collaboration with Binghamton University, i3 Electronics, Lockheed Martin, and American Semiconductor, we demonstrated a single substrate interfacing approach, where soft devices, i.e., sensors, are directly printed on Kapton polyimide substrates that are widely used for fabricating flexible printed circuit boards (FPCBs). Utilizing a process flow compatible with the FPCB assembly process, a wearable sensor patch was fabricated composed of inkjet-printed gold ECG electrodes and a stencil-printed nickel oxide thermistor [2]. In another project, for powering wearable health monitoring devices, we demonstrated a flexible power source by integrating a lithium-ion battery and amorphous silicon solar module [3].

Relevant publications:

1. Monitoring of vital signs with flexible and wearable medical devices Advanced Materials, 2016 28, 22.

Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

@article{khan2016monitoring, title = {Monitoring of vital signs with flexible and wearable medical devices}, author = {Khan, Yasser and Ostfeld, Aminy E and Lochner, Claire M and Pierre, Adrien and Arias, Ana C}, journal = {Advanced Materials}, volume = {28}, number = {22}, pages = {4373--4395}, year = {2016}, publisher = {Wiley Online Library}, url = {http://dx.doi.org/10.1002/adma.201504366}, doi = {10.1002/adma.201504366}, thumbnail = {khan2016monitoring.png}, pdf = {khan2016monitoring.pdf} }

1. Flexible hybrid electronics: Direct interfacing of soft and hard electronics for wearable health monitoring Advanced Functional Materials, 2016 26, 47.

The interfacing of soft and hard electronics is a key challenge for flexible hybrid electronics. Currently, a multisubstrate approach is employed, where soft and hard devices are fabricated or assembled on separate substrates, and bonded or interfaced using connectors; this hinders the flexibility of the device and is prone to interconnect issues. Here, a single substrate interfacing approach is reported, where soft devices, i.e., sensors, are directly printed on Kapton polyimide substrates that are widely used for fabricating flexible printed circuit boards (FPCBs). Utilizing a process flow compatible with the FPCB assembly process, a wearable sensor patch is fabricated composed of inkjet-printed gold electrocardiography (ECG) electrodes and a stencil-printed nickel oxide thermistor. The ECG electrodes provide 1 mVp–p ECG signal at 4.7 cm electrode spacing and the thermistor is highly sensitive at normal body temperatures, and demonstrates temperature coefficient, α ≈ –5.84% K–1 and material constant, β ≈ 4330 K. This sensor platform can be extended to a more sophisticated multisensor platform where sensors fabricated using solution processable functional inks can be interfaced to hard electronics for health and performance monitoring, as well as internet of things applications.

@article{khan2016flexible, title = {Flexible hybrid electronics: Direct interfacing of soft and hard electronics for wearable health monitoring}, author = {Khan, Yasser and Garg, Mohit and Gui, Qiong and Schadt, Mark and Gaikwad, Abhinav and Han, Donggeon and Yamamoto, Natasha AD and Hart, Paul and Welte, Robert and Wilson, William and Czarnecki, Steve and Poliks, Mark and Jin, Zhanpeng and Ghose, Kanad and Egitto, Frank and Turner, James and Arias, Ana C}, journal = {Advanced Functional Materials}, volume = {26}, number = {47}, pages = {8764--8775}, year = {2016}, publisher = {Wiley Online Library}, url = {http://dx.doi.org/10.1002/adfm.201603763}, doi = {10.1002/adfm.201603763}, thumbnail = {khan2016flexible.png}, pdf = {khan2016flexible.pdf} }

1. High-performance flexible energy storage and harvesting system for wearable electronics Scientific reports, 2016 6,

This paper reports on the design and operation of a flexible power source integrating a lithium ion battery and amorphous silicon solar module, optimized to supply power to a wearable health monitoring device. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide, respectively, on thin flexible current collectors. It displays energy density of 6.98 mWh/cm2 and demonstrates capacity retention of 90% at 3C discharge rate and  99% under 100 charge/discharge cycles and 600 cycles of mechanical flexing. A solar module with appropriate voltage and dimensions is used to charge the battery under both full sun and indoor illumination conditions, and the addition of the solar module is shown to extend the battery lifetime between charging cycles while powering a load. Furthermore, we show that by selecting the appropriate load duty cycle, the average load current can be matched to the solar module current and the battery can be maintained at a constant state of charge. Finally, the battery is used to power a pulse oximeter, demonstrating its effectiveness as a power source for wearable medical devices.

@article{ostfeld2016high, title = {High-performance flexible energy storage and harvesting system for wearable electronics}, author = {Ostfeld, Aminy E and Gaikwad, Abhinav M and Khan, Yasser and Arias, Ana C}, journal = {Scientific reports}, volume = {6}, pages = {26122}, year = {2016}, publisher = {Nature Publishing Group}, url = {http://dx.doi.org/10.1038/srep26122}, doi = {10.1038/srep26122}, thumbnail = {ostfeld2016high.png}, pdf = {ostfeld2016high.pdf} }