Recent Developments in Printing Flexible and Wearable Sensing Electronics for Healthcare Applications

Abstract

Wearable biosensors attract significant interest for their capabilities in real-time monitoring of wearers’ health status, as well as the surrounding environment. Sensor patches are embedded onto the human epidermis accompanied by data readout and signal conditioning circuits with wireless communication modules for transmitting data to the computing devices. Wearable sensors designed for recognition of various biomarkers in human epidermis fluids, such as glucose, lactate, pH, cholesterol, etc., as well as physiological indicators, i.e., pulse rate, temperature, breath rate, respiration, alcohol, activity monitoring, etc., have potential applications both in medical diagnostics and fitness monitoring. The rapid developments in solution-based nanomaterials offered a promising perspective to the field of wearable sensors by enabling their cost-efficient manufacturing through printing on a wide range of flexible polymeric substrates. This review highlights the latest key developments made in the field of wearable sensors involving advanced nanomaterials, manufacturing processes, substrates, sensor type, sensing mechanism, and readout circuits, and ends with challenges in the future scope of the field. Sensors are categorized as biological and fluidic, mounted directly on the human body, or physiological, integrated onto wearable substrates/gadgets separately for monitoring of human-body-related analytes, as well as external stimuli. Special focus is given to printable materials and sensors, which are key enablers for wearable electronics.

Flexible potentiometric pH sensors for wearable systems

“…45 The substrate, which is oen a at, solid-state platform that facilitates the processing of sensitive materials, signicantly inuences the sensors' physical, mechanical, and electrical features. 45,101 Various substrates used for pH sensors fabrication are discussed in this section.…”

“…In this regards, biocompatible polymeric substrates such as polydimethylsiloxane (PDMS) have been explored for the fabrication of pH sensors. 101,103,111,112 Among the many available polymeric substrates, PI, which is commercially available as Apical, Kapton, and UPILEX lms, etc., presents impressive bendability, good mechanical strength, dimensional stability, low surface roughness, excellent electrical properties and low dielectric constant (Table 2). 45,102,113 It also displays good thermal and chemical stability resisting weak acids, alkalis and commonly used organic solvents.…”

Carbon Nanotube Yarn for Fiber‐Shaped Electrical Sensors, Actuators, and Energy Storage for Smart Systems

“…Temperature sensors can be classified into several types based on the material and their operation and include thermistors (temperature‐sensitive resistors) and thermocouples (voltage generating metal junctions) and silicon‐based sensors 2b,21c,31. Many types of temperature sensors are used to detect the temperature by sensing changes in electrical resistance of the thermosensitive materials such as ceramics, polymers, and metals 2b,21c,31. Importantly, new types of temperature sensor have attempted to monitor the body temperature in the real‐time through the wearable sensor 2b,21c,31…”

“…Many types of temperature sensors are used to detect the temperature by sensing changes in electrical resistance of the thermosensitive materials such as ceramics, polymers, and metals 2b,21c,31. Importantly, new types of temperature sensor have attempted to monitor the body temperature in the real‐time through the wearable sensor 2b,21c,31…”

Durability of Functionalized Carbon Structures with Optical Fiber Sensors in a Highly Alkaline Concrete Environment

“…Thus, it is evident from the current literature that the utilization of FOSs for SHM has not yet reached its full potential and requires further investigations paired with advances in chemical and materials engineering. In fact, the recent merging between textile and sensor engineering has seen rapid developments in wearable technology, especially in the biomedical engineering field [13][14][15], which provides much motivation for adopting advances in chemical/textile engineering in other areas of sensing, i.e., SHM.…”