Development and Reliability Evaluation of Additively Printed Biosensing Device for Wearable Applications in Harsh Environment
Authors: Lall Pradeep , Jang Hyesoo , Narangaparambil Jinesh , Hill Curtis 
Published: November 2023

Abstract
Using additive technologies for the production of printed circuit boards avoids the need for costly tooling, such as photomasks or etching containers for removing photoresist and metallization. Design and manufacturing based on software enables production flexibility, as well as speedier tool adjustments and design development. In addition, unlike traditional methods that remove unwanted material from a copper-clad board additive printing methods may be used to several fabrics, vehicles, and polymers with a variety of surfaces and forms. This allows for more flexibility and creativity in designing PCBs that can fit on different shapes and surfaces. This versatility to a broad variety of applications allows engineers to create diverse applications, such as wearable bio sensing device (biosensor) with an electrocardiography (ECG) sensor, an electrodermal activity (EDA) sensor, a pulse-oximetric sensor, a body temperature sensor, and a humidity sensor, and so on. devices that can measure and monitor various aspects of the human body’s health and status. The wearable biosensors can track parameters such as heart rate, blood oxygen level, skin conductance, body temperature, and humidity. This data can provide useful information and feedback for medical diagnosis, fitness tracking, or stress management. Due to its potential for adaptability and integration, the development of additively printed wearable biosensors has been the subject of several prior investigations. However, there are some challenges in terms of the reliability and durability of current wearable biosensor technology when flexing force is coupled with it. They need to withstand different environmental conditions and mechanical stresses that can affect their performance and quality. For the avoidance of stability issues, it is required to develop a better printing technique, process recipe, and sensing material encapsulation. In this research paper, the direct write (D-write) printing approach was employed with a nScrypt printer to print integrated wearable biosensor patch with the circuits, encapsulations, body temperature sensor, humidity sensor, pulse-oximetric (pulse-Ox) sensor and electrodermal activity (EDA) sensor on the integrated wearable biosensor. We also print electrically conductive adhesive (ECA) pads to attach the components such as a flexible battery, microcontroller, and wireless module. Additionally, we developed firmware and data acquisition software for the biosensor to collect and transmit the biosignals to mobile devices. We tested the biosensor under various conditions such as different temperatures, humidities, and body statuses (resting, walking, and running). We evaluated the accuracy, repeatability, stability, sensitivity, linearity, response time, and hysteresis effect of each sensor by comparing them with reference devices. The biosensor has been characterized by analyzing the biosignals with respect to the various conditions (temperature, humidity, and status of the human body). In addition, the assessment of the sensor accuracy and reliability in harsh conditions such as humidity and temperature fluctuation, has been measured. In conclusion, we have developed an integrated wearable biosensor using additive technologies for printed circuit boards. Our biosensor can monitor multiple vital signs of the human body with high reliability and flexibility. Our work contributes to advancing sustainable additive manufacturing of electronic devices for health care applications.