Bio-integrated wearable systems can measure a broad range of biophysical, biochemical, and environmental signals to provide critical insights into overall health status and to quantify human performance. Recent advances in material science, chemical analysis techniques, device designs, and assembly methods form the foundations for a uniquely differentiated type of wearable technology, characterized by noninvasive, intimate integration with the soft, curved, time-dynamic surfaces of the body. This review summarizes the latest advances in this emerging field of “bio-integrated” technologies in a comprehensive manner that connects fundamental developments in chemistry, material science, and engineering with sensing technologies that have the potential for widespread deployment and societal benefit in human health care. An introduction to the chemistries and materials for the active components of these systems contextualizes essential design considerations for sensors and associated platforms that appear in f...

Bio-Integrated Wearable Systems: A Comprehensive Review

Recent advances in material innovation and structural design provide routes to flexible hybrid electronics that can combine the high-performance electrical properties of conventional wafer-based electronics with the ability to be stretched, bent, and twisted to arbitrary shapes, revolutionizing the transformation of traditional healthcare to digital healthcare. Here, material innovation and structural design for the preparation of flexible hybrid electronics are reviewed, a brief chronology of these advances is given, and biomedical applications in bioelectrical monitoring and stimulation, optical monitoring and treatment, acoustic imitation and monitoring, bionic touch, and body-fluid testing are described. In conclusion, some remarks on the challenges for future research of flexible hybrid electronics are presented.

Flexible Hybrid Electronics for Digital Healthcare.

Wearable human-machine interfaces (HMIs) are an important class of devices that enable human and machine interaction and teaming. Recent advances in electronics, materials, and mechanical designs have offered avenues toward wearable HMI devices. However, existing wearable HMI devices are uncomfortable to use and restrict the human body’s motion, show slow response times, or are challenging to realize with multiple functions. Here, we report sol-gel-on-polymer–processed indium zinc oxide semiconductor nanomembrane–based ultrathin stretchable electronics with advantages of multifunctionality, simple manufacturing, imperceptible wearing, and robust interfacing. Multifunctional wearable HMI devices range from resistive random-access memory for data storage to field-effect transistors for interfacing and switching circuits, to various sensors for health and body motion sensing, and to microheaters for temperature delivery. The HMI devices can be not only seamlessly worn by humans but also implemented as prosthetic skin for robotics, which offer intelligent feedback, resulting in a closed-loop HMI system.

Metal oxide semiconductor nanomembrane-based soft unnoticeable multifunctional electronics for wearable human-machine interfaces.

Nanomaterial-enabled flexible and stretchable electronics have seen tremendous progress in recent years, evolving from single sensors to integrated sensing systems. Compared with nanomaterial-enabled sensors with a single function, integration of multiple sensors is conducive to comprehensive monitoring of personal health and environment, intelligent human-machine interfaces, and realistic imitation of human skin in robotics and prosthetics. Integration of sensors with other functional components promotes real-world applications of the sensing systems. Here, an overview of the design and integration strategies and manufacturing techniques for such sensing systems is given. Then, representative nanomaterial-enabled flexible and stretchable sensing systems are presented. Following that, representative applications in personal health, fitness tracking, electronic skins, artificial nervous systems, and human-machine interactions are provided. To conclude, perspectives on the challenges and opportunities in this burgeoning field are considered.

Nanomaterial-Enabled Flexible and Stretchable Sensing Systems: Processing, Integration, and Applications

The Internet of Things (IoT) is a megatrend that cuts across all scientific and engineering disciplines and establishes an integrating technical evolution to improve production efficiencies and daily human life. Linked machines and sensors use decision-making routines to work toward a common product or solution. Expanding this technical revolution into the value chain of complex areas such as agriculture, food production, and healthcare requires the implementation and connection of sophisticated (bio)analytical methods. Today, wearable sensors, monitors, and point-of-care diagnostic tests are part of our daily lives and improve patients' medical progression or athletes' monitoring capabilities that are already beyond imagination. Also, early contributions toward sensor networks and finally the IT revolution with wireless data collection and transmission via Bluetooth or smartphones have set the foundation to connect remote sensors and distributed analytical chemical services with centralized laboratories, cloud storage, and cloud computing. Here, we critically review those biosensor and chemosensor technologies and concepts used in an IoT setting or considered IoT-ready that were published in the period 2013-2018, while also pointing to those foundational concepts and ideas that arose over the last two decades. We focus on these sensors due to their unique ability to be remotely stationed and that easily function in networks and have made the greatest progress toward IoT integration. Finally, we highlight requirements and existing and future challenges and provide possible solutions important toward the vision of a seamless integration into a global analytical concept, which includes many more analytical techniques than sensors and includes foremost next-generation sequencing and separation principles coupled with MS detection.

A Megatrend Challenging Analytical Chemistry: Biosensor and Chemosensor Concepts Ready for the Internet of Things.

Excessive ultraviolet (UV) radiation induces acute and chronic effects on the skin, eye and immune system. Personalized monitoring of UV radiation is thus paramount to measure the extent of personal sun exposure, which could vary with environment, lifestyle, and sunscreen use. Here, we demonstrate an ultralow modulus, stretchable, skin-mounted UV patch that measures personal UV doses. The patch contains functional layers of ultrathin stretchable electronics and a photosensitive patterned dye that reacts to UV radiation. Color changes in the photosensitive dyes correspond to UV radiation intensity and are analyzed with a smartphone camera. A software application has feature recognition, lighting condition correction, and quantification algorithms that detect and quantify changes in color. These color changes are then correlated with corresponding shifts in UV dose, and compared to existing UV dose risk levels. The soft mechanics of the UV patch allow for multi-day wear in the presence of sunscreen and water. Two evaluation studies serve to demonstrate the utility of the UV patch during daily activities with and without sunscreen application.

/pdf/soft-stretchable-epidermal-sensor-with-integrated-255kocwbx1.pdf

Soft, stretchable, epidermal sensor with integrated electronics and photochemistry for measuring personal UV exposures.

Medical deployment of electronics is often hampered by boxy and rigid packaging. Biological tissues are soft and curved, while electronic components are hard and angular. The mechanical mismatch can be improved by re-packaging electronics in radical new form factors. We present a technology platform using ultra-thin components linked with conformal interconnects and embedded in low modulus polymers to provide an excellent match to biological tissues. This technology platform builds on the pioneering work by Prof. John Rogers @ UIUC. [1, 2] Rather than developing novel semiconducting, conducting and insulating materials, the platform exploits the concept that only the top 5-15 μm of a silicon IC contributes to functional behavior. Similar considerations apply to other high performance components such as LEDs and photodiodes. The thin active layer can be removed and transferred to polymer by various processes, which we discuss below. The resulting thin and flexible silicon islands can be interconnected using metallization patterned to permit substantial macro-scale deformation while experiencing minimal micro-scale deformation, just as a coiled spring can stretch several times its own length while keeping the local metal strain within the elastic limit. On-body and in-body applications are both well suited to the technology platform. Epidermal electronics are skin-mounted systems that resemble electronic tattoos, and can be worn for extended periods without discomfort while providing continuous monitoring. In this paper, we discuss in detail, the following technologies and concepts that enable epidermal electronics: (1) Advanced die preparation methodologies that allow for thinning, placement, and attachment of sub-50μm commercial IC devices (COTS); (2) die embedding methods in flexible polymer substrates; (3) use of conformal metal interconnects to connect components; and (4) elastomer stacking optimized for application strain and compatibility with biological tissue. We present data of thinned COTS ICs embedded in flex test circuits to demonstrate the technology.

Epidermal electronics for seamless monitoring of biopotential signals

In this investigation, the “archipelago” design is presented as a platform for skin-mounted wearable and stretchable electronics. The electronic components of the design were distributed between islands connected by stretchable serpentine structures. The analytical results show that at 20% overall elongation, the serpentines stretch 60% due to the rigidity of the islands. This 20% elongation is defined as the system stretchability. The 60% elongation on the serpentines is defined as the effective stretchability. At 60% effective stretch, the calculated equivalent plastic strain in a serpentine interconnect is 0.67%, which is well below the fracture limit of copper. Elongation experiments show that the archipelago structure has the system stretchability up to 76% for one-time-stretching, translating to 228% of the effective stretchability on the serpentines. Fatigue-tension experiments show that at 20% system stretch, the archipelago structure can withstand on average 71,950 cycles without electrical or mechanical degradation.

Gil Huppert

Papers

Soft, stretchable, epidermal sensor with integrated electronics and photochemistry for measuring personal UV exposures.

Epidermal electronics for seamless monitoring of biopotential signals

Archipelago platform for skin-mounted wearable and stretchable electronics