Fully Printed, Wireless, Stretchable Implantable Biosystem toward Batteryless, Real-Time Monitoring of Cerebral Aneurysm Hemodynamics

Polyimide as a biomedical material: advantages and applications

Polyimides (PIs) are a class of polymers characterized by strong covalent bonds, which offer the advantages of high thermal weight, low weight, good electronic properties and superior mechanical properties. They have been successfully used in the fields of microelectronics, aerospace engineering, nanomaterials, lasers, energy storage and painting. Their biomedical applications have attracted extensive attention, and they have been explored for use as an implantable, detectable, and antibacterial material in recent years. This article summarizes the progress of PI in terms of three aspects: synthesis, properties, and application. First, the synthetic strategies of PI are summarized. Next, the properties of PI as a biological or medical material are analyzed. Finally, the applications of PI in electrodes, biosensors, drug delivery systems, bone tissue replacements, face masks or respirators, and antibacterial materials are discussed. This review provides a comprehensive understanding of the latest progress in PI, thereby providing a basis for developing new potentially promising materials for medical applications.

A Human-Computer Interaction Strategy for An FPGA Platform Boosted Integrated "Perception-Memory" System Based on Electronic Tattoos and Memristors

The integrated "perception-memory" system is receiving increasing attention due to its crucial applications in humanoid robots, as well as in the simulation of the human retina and brain. Here, a Field Programmable Gate Array (FPGA) platform-boosted system that enables the sensing, recognition, and memory for human-computer interaction is reported by the combination of ultra-thin Ag/Al/Paster-based electronic tattoos (AAP) and Tantalum Oxide/Indium Gallium Zinc Oxide (Ta2O5/IGZO)-based memristors. Notably, the AAP demonstrates exceptional capabilities in accommodating the strain caused by skin deformation, thanks to its unique structural design, which ensures a secure fit to the skin and enables the prolonged monitoring of physiological signals. By utilizing Ta2O5/IGZO as the functional layer, a high switching ratio is conferred to the memristor, and an integrated system for sensing, distinguishing, storing, and controlling the machine hand of multiple human physiological signals is constructed together with the AAP. Further, the proposed system implements emergency calls and smart homes using facial electromyogram signals and utilizing logical entailment to realize the control of the music interface. This innovative "perception-memory" integrated system not only serves the disabled, enhancing human-computer interaction but also provides an alternative avenue to enhance the quality of life and autonomy of individuals with disabilities.

Printable and flexible integrated sensing systems for wireless healthcare

The rapid development of wearable sensing devices and artificial intelligence has enabled portable and wireless tracking of human health, fulfilling the promise of digitalized healthcare applications. To achieve versatile design and integration of multi-functional modules including sensors and data transmission units onto various flexible platforms, printable technologies emerged as some of the most promising strategies. This review first introduces the commonly utilized printing technologies, followed by discussion of the printable ink formulations and flexible substrates to ensure reliable device fabrication and system integration. The advances of printable sensors for body status monitoring are then discussed. Moreover, the integration of wireless data transmission via printable approaches is also presented. Finally, the challenges in achieving printable sensing devices and wireless integrated systems with competitive performances are considered, so as to realize their practical applications for personalized healthcare.

Implantable Self-Reporting Stents for Detecting In-Stent Restenosis and Cardiac Functional Dynamics

Despite the increasing number of stents implanted each year worldwide, patients remain at high risk for developing in-stent restenosis. Various self-reporting stents have been developed to address this challenge, but their practical utility has been limited by low sensitivity and limited data collection. Herein, we propose a next-generation self-reporting stent that can monitor blood pressure and blood flow inside the blood arteries. This proposed self-reporting stent utilizes a larger inductor coil encapsulated on the entire surface of the stent strut, resulting in a 2-fold increase in the sensing resolution and coupling distance between the sensor and external antenna. The dual-pressure sensors enable the detection of blood flow in situ. The feasibility of the proposed self-reporting stent is successfully demonstrated through in vivo analysis in rats, verifying its biocompatibility and multifunctional utilities. This multifunctional self-reporting stent has the potential to greatly improve cardiovascular care by providing real-time monitoring and unprecedented insight into the functional dynamics of the heart.

Advances in Wireless, Batteryless, Implantable Electronics for Real-Time, Continuous Physiological Monitoring

This review summarizes recent progress in developing wireless, batteryless, fully implantable biomedical devices for real-time continuous physiological signal monitoring, focusing on advancing human health care. Design considerations, such as biological constraints, energy sourcing, and wireless communication, are discussed in achieving the desired performance of the devices and enhanced interface with human tissues. In addition, we review the recent achievements in materials used for developing implantable systems, emphasizing their importance in achieving multi-functionalities, biocompatibility, and hemocompatibility. The wireless, batteryless devices offer minimally invasive device insertion to the body, enabling portable health monitoring and advanced disease diagnosis. Lastly, we summarize the most recent practical applications of advanced implantable devices for human health care, highlighting their potential for immediate commercialization and clinical uses.

3D Printed Integrated Sensors: From Fabrication to Applications-A Review

The integration of 3D printed sensors into hosting structures has become a growing area of research due to simplified assembly procedures, reduced system complexity, and lower fabrication cost. Embedding 3D printed sensors into structures or bonding the sensors on surfaces are the two techniques for the integration of sensors. This review extensively discusses the fabrication of sensors through different additive manufacturing techniques. Various additive manufacturing techniques dedicated to manufacture sensors as well as their integration techniques during the manufacturing process will be discussed. This review will also discuss the basic sensing mechanisms of integrated sensors and their applications. It has been proven that integrating 3D printed sensors into infrastructures can open new possibilities for research and development in additive manufacturing and sensor materials for smart goods and the Internet of Things.

Advancements in Passive Wireless Sensors, Materials, Devices, and Applications

In recent years, passive wireless sensors have been studied for various infrastructure sectors, making them a research and development focus. While substantial evidence already supports their viability, further effort is needed to understand their dependability and applicability. As a result, issues related to the theory and implementation of wireless sensors still need to be resolved. This paper aims to review and summarize the progress of the different materials used in different passive sensors, the current status of the passive wireless sensor readout devices, and the latest peripheral devices. It will also cover other related aspects such as the system equipment of passive wireless sensors and the nanogenerators for the energy harvesting for self-powered sensors for applications in contemporary life scenarios. At the same time, the challenges for future developments and applications of passive wireless are discussed.

3D printed electronics with nanomaterials

A large variety of printing, deposition and writing techniques have been incorporated to fabricate electronic devices in the last decades. This approach, printed electronics, has gained great interest in research and practical applications and is successfully fuelling the growth in materials science and technology. On the other hand, a new player is emerging, additive manufacturing, called 3D printing, introducing a new capability to create geometrically complex constructs with low cost and minimal material waste. Having such tremendous technology in our hands, it was just a matter of time to combine advances of printed electronics technology for the fabrication of unique 3D structural electronics. Nanomaterial patterning with additive manufacturing techniques can enable harnessing their nanoscale properties and the fabrication of active structures with unique electrical, mechanical, optical, thermal, magnetic and biological properties. In this paper, we will briefly review the properties of selected nanomaterials suitable for electronic applications and look closer at the current achievements in the synergistic integration of nanomaterials with additive manufacturing technologies to fabricate 3D printed structural electronics. The focus is fixed strictly on techniques allowing as much as possible fabrication of spatial 3D objects, or at least conformal ones on 3D printed substrates, while only selected techniques are adaptable for 3D printing of electronics. Advances in the fabrication of conductive paths and circuits, passive components, antennas, active and photonic components, energy devices, microelectromechanical systems and sensors are presented. Finally, perspectives for development with new nanomaterials, multimaterial and hybrid techniques, bioelectronics, integration with discrete components and 4D-printing are briefly discussed.

Fully Screen-Printed PI/PEG Blends Enabled Patternable Electrodes for Scalable Manufacturing of Skin-Conformal, Stretchable, Wearable Electronics

Recent advances in soft materials and nano-microfabrication have enabled the development of flexible wearable electronics. At the same time, printing technologies have been demonstrated to be efficient and compatible with polymeric materials for manufacturing wearable electronics. However, wearable device manufacturing still counts on a costly, complex, multistep, and error-prone cleanroom process. Here, we present fully screen-printable, skin-conformal electrodes for low-cost and scalable manufacturing of wearable electronics. The screen printing of the polyimide (PI) layer enables facile, low-cost, scalable, high-throughput manufacturing. PI mixed with poly(ethylene glycol) exhibits a shear-thinning behavior, significantly improving the printability of PI. The premixed Ag/AgCl ink is then used for conductive layer printing. The serpentine pattern of the screen-printed electrode accommodates natural deformation under stretching (30%) and bending conditions (180°), which are verified by computational and experimental studies. Real-time wireless electrocardiogram monitoring is also successfully demonstrated using the printed electrodes with a flexible printed circuit. The algorithm developed in this study can calculate accurate heart rates, respiratory rates, and heart rate variability metrics for arrhythmia detection.

Ultrasoft and Biocompatible Magnetic-Hydrogel-Based Strain Sensors for Wireless Passive Biomechanical Monitoring

Implantable flexible mechanical sensors have exhibited great potential in health monitoring and disease diagnosis due to continuous and real-time monitoring capability. However, the wires and power supply required in current devices cause inconvenience and potential risks. Magnetic-based devices have demonstrated advantages in wireless and passive sensing, but the mismatched mechanical properties, poor biocompatibility, and insufficient sensitivity have limited their applications in biomechanical monitoring. Here, a wireless and passive flexible magnetic-based strain sensor based on a gelatin methacrylate/Fe₃O₄ magnetic hydrogel has been fabricated. The sensor exhibits ultrasoft mechanical properties, strong magnetic properties, and long-term stability in saline solution and can monitor strains down to 50 μm. A model of the sensing process is established to identify the optimal detection location and the relation between the relative magnetic permeability and the sensitivity of the sensors. Moreover, an in vitro tissue model is developed to investigate the potential of the sensor in detecting subtle biomechanical signals and avoiding interference with bioactivities. Furthermore, a real-time and high-throughput biomonitoring platform is built and implements passive wireless monitoring of the drug response and cultural status of the cardiomyocytes. This work demonstrates the potential of applying magnetic sensing for biomechanical monitoring and provides ideas for the design of wireless and passive implantable devices.

Fully implantable batteryless soft platforms with printed nanomaterial-based arterial stiffness sensors for wireless continuous monitoring of restenosis in real time

Atherosclerosis is a common cause of coronary artery disease and a significant factor in broader cardiovascular diseases, the leading cause of death. While implantation of a stent is a prevalent treatment of coronary artery disease, a frequent complication is restenosis, where the stented artery narrows and stiffens. Although early detection of restenosis can be achieved by continuous monitoring, no available device offers such capability without surgeries. Here, we report a fully implantable soft electronic system without batteries and circuits, which still enables continuous wireless monitoring of restenosis in real-time with a set of nanomembrane strain sensors in an electronic stent. The low-profile system requires minimal invasive implantation to deploy the sensors into a blood vessel through catheterization. The entirely printed, nanomaterial-based set of soft membrane strain sensors utilizes a sliding mechanism to offer enhanced sensitivity and detection of low strain while unobtrusively integrating with an inductive stent for passive wireless sensing. The performance of the soft sensor platform is demonstrated by wireless monitoring of restenosis in an artery model and an ex-vivo study in a coronary artery of ovine hearts. The capacitive sensor-based artery implantation system offers unique advantages in wireless, real-time monitoring of stent treatments and arterial health for cardiovascular disease.

Fully implantable wireless batteryless vascular electronics with printed soft sensors for multiplex sensing of hemodynamics

The continuous monitoring of hemodynamics attainable with wireless implantable devices would improve the treatment of vascular diseases. However, demanding requirements of size, wireless operation, and compatibility with endovascular procedures have limited the development of vascular electronics. Here, we report an implantable, wireless vascular electronic system, consisting of a multimaterial inductive stent and printed soft sensors capable of real-time monitoring of arterial pressure, pulse rate, and flow without batteries or circuits. Developments in stent design achieve an enhanced wireless platform while matching conventional stent mechanics. The fully printed pressure sensors demonstrate fast response times, high durability, and sensing at small bending radii. The device is monitored via inductive coupling at communication distances notably larger than prior vascular sensors. The wireless electronic system is validated in artery models, while minimally invasive catheter implantation is demonstrated in an in vivo rabbit study. Overall, the vascular system offers an adaptable framework for comprehensive monitoring of hemodynamics.

Combining printing and nanoparticle assembly: Methodology and application of nanoparticle patterning

Functional nanoparticles (NPs) with unique photoelectric, mechanical, magnetic, and chemical properties have attracted considerable attention. Aggregated NPs rather than individual NPs are generally required for sensing, electronics, and catalysis. However, the transformation of functional NP aggregates into scalable, controllable, and affordable functional devices remains challenging. Printing is a promising additive manufacturing technology for fabricating devices from NP building blocks because of its capabilities for rapid prototyping and versatile multifunctional manufacturing. This paper reviews recent advances in NP patterning based on the combination of self-assembly and printing technologies (including two-, three-, and four-dimensional printing), introduces the basic characteristics of these methods, and discusses various fields of NP patterning applications.

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Nanoparticles (NPs) printing assembly is a good solution for patterned devices

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NPs assembly can be combined with 2D, 3D, and 4D printing technologies

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A variety of ink-dispersed NPs are available for printing assembly

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NPs printing assembly technology is applied for nanosensing, energy storage, photodetector

Recent Advances in 3D Printing of Biomedical Sensing Devices

Additive manufacturing, also called 3D printing, is a rapidly evolving technique that allows for the fabrication of functional materials with complex architectures, controlled microstructures, and material combinations. This capability has influenced the field of biomedical sensing devices by enabling the trends of device miniaturization, customization, and elasticity (i.e., having mechanical properties that match with the biological tissue). In this paper, the current state-of-the-art knowledge of biomedical sensors with the unique and unusual properties enabled by 3D printing is reviewed. The review encompasses clinically important areas involving the quantification of biomarkers (neurotransmitters, metabolites, and proteins), soft and implantable sensors, microfluidic biosensors, and wearable haptic sensors. In addition, the rapid sensing of pathogens and pathogen biomarkers enabled by 3D printing, an area of significant interest considering the recent worldwide pandemic caused by the novel coronavirus, is also discussed. It is also described how 3D printing enables critical sensor advantages including lower limit-of-detection, sensitivity, greater sensing range, and the ability for point-of-care diagnostics. Further, manufacturing itself benefits from 3D printing via rapid prototyping, improved resolution, and lower cost. This review provides researchers in academia and industry a comprehensive summary of the novel possibilities opened by the progress in 3D printing technology for a variety of biomedical applications.

Recent Advances in Printing Technologies of Nanomaterials for Implantable Wireless Systems in Health Monitoring and Diagnosis

The development of wireless implantable sensors and integrated systems, enabled by advances in flexible and stretchable electronics technologies, is emerging to advance human health monitoring, diagnosis, and treatment. Progress in material and fabrication strategies allows for implantable electronics for unobtrusive monitoring via seamlessly interfacing with tissues and wirelessly communicating. Combining new nanomaterials and customizable printing processes offers unique possibilities for high-performance implantable electronics. Here, this report summarizes the recent progress and advances in nanomaterials and printing technologies to develop wireless implantable sensors and electronics. Advances in materials and printing processes are reviewed with a focus on challenges in implantable applications. Demonstrations of wireless implantable electronics and advantages based on these technologies are discussed. Lastly, existing challenges and future directions of nanomaterials and printing are described.

Review of 3D-printing technologies for wearable and implantable bio-integrated sensors

Thin-film microfabrication-based bio-integrated sensors are widely used for a broad range of applications that require continuous measurements of biophysical and biochemical signals from the human body. Typically, they are fabricated using standard photolithography and etching techniques. This traditional method is capable of producing a precise, thin, and flexible bio-integrated sensor system. However, it has several drawbacks, such as the fact that it can only be used to fabricate sensors on a planar surface, it is highly complex requiring specialized high-end facilities and equipment, and it mostly allows only 2D features to be fabricated. Therefore, developing bio-integrated sensors via 3D-printing technology has attracted particular interest. 3D-printing technology offers the possibility to develop sensors on nonplanar substrates, which is beneficial for noninvasive bio-signal sensing, and to directly print on complex 3D nonplanar organ structures. Moreover, this technology introduces a highly flexible and precisely controlled printing process to realize patient-specific sensor systems for ultimate personalized medicine, with the potential of rapid prototyping and mass customization. This review summarizes the latest advancements in 3D-printed bio-integrated systems, including 3D-printing methods and employed printing materials. Furthermore, two widely used 3D-printing techniques are discussed, namely, ex-situ and in-situ fabrication techniques, which can be utilized in different types of applications, including wearable and smart-implantable biosensor systems.

Noninvasive Flow Monitoring in Simple Flow Phantom Using Resistive Strain Sensors

In this paper, we introduce a monitoring method for flow expansion and contraction in a simple flow phantom based on electrical resistance changes in an epidermal strain sensor attached to the phantom. The flow phantom was fabricated to have a nonflat surface and small modulus that are analogous to human skin. The epidermal sensors made of polydopamine and polyvinyl alcohol show sufficient linearity (R = 0.9969), reproducibility, and self-adhesion properties, as well as high sensitivity to small modulus measurements (<1% tensile strain). Pulsatile flow monitoring experiments were performed by placing the epidermal sensor on the flow phantom and measuring the relative changes in resistance by the heartbeat. Experiments were conducted for three types of vessel diameters (1.5, 2, and 3 mm). In each of the experiments, the vessels were divided into Top, Middle, and Bottom positions. Experiments for each position show that the relative changes in resistance increase proportionally with the diameter of the vessel. The vessels located close to the epidermal layer have greater relative electrical changes. The results were analyzed using the Bernoulli equation and hoop stress formula. This study demonstrates the feasibility of a noninvasive flow monitoring method using a novel resistive strain sensor.

Flexible/Stretchable Supercapacitors with Novel Functionality for Wearable Electronics

With the miniaturization of personal wearable electronics, considerable effort has been expended to develop high-performance flexible/stretchable energy storage devices for powering integrated active devices. Supercapacitors can fulfill this role owing to their simple structures, high power density, and cyclic stability. Moreover, a high electrochemical performance can be achieved with flexible/stretchable supercapacitors, whose applications can be expanded through the introduction of additional novel functionalities. Here, recent advances in and future prospects for flexible/stretchable supercapacitors with innate functionalities are covered, including biodegradability, self-healing, shape memory, energy harvesting, and electrochromic and temperature tolerance, which can contribute to reducing e-waste, ensuring device integrity and performance, enabling device self-charging following exposure to surrounding stimuli, displaying the charge status, and maintaining the performance under a wide range of temperatures. Finally, the challenges and perspectives of high-performance all-in-one wearable systems with integrated functional supercapacitors for future practical application are discussed.

Printed, Wireless, Soft Bioelectronics and Deep Learning Algorithm for Smart Human-Machine Interfaces

Recent advances in flexible materials and wearable electronics offer a noninvasive, high-fidelity recording of biopotentials for portable healthcare, disease diagnosis, and machine interfaces. Current device-manufacturing methods, however, still heavily rely on the conventional cleanroom microfabrication that requires expensive, time-consuming, and complicated processes. Here, we introduce an additive nanomanufacturing technology that explores a contactless direct printing of aerosol nanomaterials and polymers to fabricate stretchable sensors and multilayered wearable electronics. Computational and experimental studies prove the mechanical flexibility and reliability of soft electronics, considering direct mounting to the deformable human skin with a curvilinear surface. The dry, skin-conformal graphene biosensor, without the use of conductive gels and aggressive tapes, offers an enhanced biopotential recording on the skin and multiple uses (over ten times) with consistent measurement of electromyograms. The combination of soft bioelectronics and deep learning algorithm allows classifying six classes of muscle activities with an accuracy of over 97%, which enables wireless, real-time, continuous control of external machines such as a robotic hand and a robotic arm. Collectively, the comprehensive study of nanomaterials, flexible mechanics, system integration, and machine learning shows the potential of the printed bioelectronics for portable, smart, and persistent human-machine interfaces.

Breathable, large-area epidermal electronic systems for recording electromyographic activity during operant conditioning of H-reflex

Operant conditioning of Hoffmann's reflex (H-reflex) is a non-invasive and targeted therapeutic intervention for patients with movement disorders following spinal cord injury. The reflex-conditioning protocol uses electromyography (EMG) to measure reflexes from specific muscles elicited using transcutaneous electrical stimulation. Despite recent advances in wearable electronics, existing EMG systems that measure muscle activity for operant conditioning of spinal reflexes still use rigid metal electrodes with conductive gels and aggressive adhesives, while requiring precise positioning to ensure reliability of data across experimental sessions. Here, we present the first large-area epidermal electronic system (L-EES) and demonstrate its use in every step of the reflex-conditioning protocol. The L-EES is a stretchable and breathable composite of nanomembrane electrodes (16 electrodes in a four by four array), elastomer, and fabric. The nanomembrane electrode array enables EMG recording from a large surface area on the skin and the breathable elastomer with fabric is biocompatible and comfortable for patients. We show that L-EES can record direct muscle responses (M-waves) and H-reflexes, both of which are comparable to those recorded using conventional EMG recording systems. In addition, L-EES may improve the reflex-conditioning protocol; it has potential to automatically optimize EMG electrode positioning, which may reduce setup time and error across experimental sessions.

Advanced Nanomaterials, Printing Processes, and Applications for Flexible Hybrid Electronics

Recent advances in nanomaterial preparation and printing technologies provide unique opportunities to develop flexible hybrid electronics (FHE) for various healthcare applications. Unlike the costly, multi-step, and error-prone cleanroom-based nano-microfabrication, the printing of nanomaterials offers advantages, including cost-effectiveness, high-throughput, reliability, and scalability. Here, this review summarizes the most up-to-date nanomaterials, methods of nanomaterial printing, and system integrations to fabricate advanced FHE in wearable and implantable applications. Detailed strategies to enhance the resolution, uniformity, flexibility, and durability of nanomaterial printing are summarized. We discuss the sensitivity, functionality, and performance of recently reported printed electronics with application areas in wearable sensors, prosthetics, and health monitoring implantable systems. Collectively, the main contribution of this paper is in the summary of the essential requirements of material properties, mechanisms for printed sensors, and electronics.

Bioresorbable, Wireless, Passive Sensors as Temporary Implants for Monitoring Regional Body Temperature

Measurements of regional internal body temperatures can yield important information in the diagnosis of immune response-related anomalies, for precisely managing the effects of hyperthermia and hypothermia therapies and monitoring other transient body processes such as those associated with wound healing. Current approaches rely on permanent implants that require extraction surgeries after the measurements are no longer needed. Emerging classes of bioresorbable sensors eliminate the requirements for extraction, but their use of percutaneous wires for data acquisition leads to risks for infection at the suture site. As an alternative, a battery-free, wireless implantable device is reported here, which is constructed entirely with bioresorbable materials for monitoring regional internal body temperatures over clinically relevant timeframes. Ultimately, these devices disappear completely in the body through natural processes. In vivo demonstrations indicate stable operation as subcutaneous and intracranial implants in rat models for up to 4 days. Potential applications include monitoring of healing cascades associated with surgical wounds, recovery processes following internal injuries, and the progression of thermal therapies for various conditions.

All-printed nanomembrane wireless bioelectronics using a biocompatible solderable graphene for multimodal human-machine interfaces

Recent advances in nanomaterials and nano-microfabrication have enabled the development of flexible wearable electronics. However, existing manufacturing methods still rely on a multi-step, error-prone complex process that requires a costly cleanroom facility. Here, we report a new class of additive nanomanufacturing of functional materials that enables a wireless, multilayered, seamlessly interconnected, and flexible hybrid electronic system. All-printed electronics, incorporating machine learning, offers multi-class and versatile human-machine interfaces. One of the key technological advancements is the use of a functionalized conductive graphene with enhanced biocompatibility, anti-oxidation, and solderability, which allows a wireless flexible circuit. The high-aspect ratio graphene offers gel-free, high-fidelity recording of muscle activities. The performance of the printed electronics is demonstrated by using real-time control of external systems via electromyograms. Anatomical study with deep learning-embedded electrophysiology mapping allows for an optimal selection of three channels to capture all finger motions with an accuracy of about 99% for seven classes.

Though wearable electronics remain an attractive technology for bioelectronics, fabrication methods that precisely print biocompatible materials for electronics are needed. Here, the authors report an additive manufacturing process that yields all-printed nanomaterial-based wireless electronics.

Artificial Biosystems by Printing Biology

The continuous progress of printing technologies over the past 20 years has fueled the development of a plethora of applications in materials sciences, flexible electronics, and biotechnologies. More recently, printing methodologies have started up to explore the world of Artificial Biology, offering new paradigms in the direct assembly of Artificial Biosystems (small condensates, compartments, networks, tissues, and organs) by mimicking the result of the evolution of living systems and also by redesigning natural biological systems, taking inspiration from them. This recent progress is reported in terms of a new field here defined as Printing Biology, resulting from the intersection between the field of printing and the bottom up Synthetic Biology. Printing Biology explores new approaches for the reconfigurable assembly of designed life-like or life-inspired structures. This work presents this emerging field, highlighting its main features, i.e., printing methodologies (from 2D to 3D), molecular ink properties, deposition mechanisms, and finally the applications and future challenges. Printing Biology is expected to show a growing impact on the development of biotechnology and life-inspired fabrication.

Printed, Soft, Nanostructured Strain Sensors for Monitoring of Structural Health and Human Physiology

Soft strain sensors that are mechanically flexible or stretchable are of significant interest in the fields of structural health monitoring, human physiology, and human-machine interfaces. However, existing deformable strain sensors still suffer from complex fabrication processes, poor reusability, limited adhesion strength, or structural rigidity. In this work, we introduce a versatile, high-throughput fabrication method of nanostructured, soft material-enabled, miniaturized strain sensors for both structural health monitoring and human physiology detection. Aerosol jet printing of polyimide and silver nanowires enables multifunctional strain sensors with tunable resistance and gauge factor. Experimental study of soft material compositions and multilayered structures of the strain sensor demonstrates the capabilities of strong adhesion and conformal lamination on different surfaces without the use of conventional fixtures and/or tapes. A two-axis, printed strain gauge enables the detection of force-induced strain changes on a curved stem valve for structural health management while offering reusability over 10 times without losing the sensing performance. Direct comparison with a commercial film sensor captures the advantages of the printed soft sensor in enhanced gauge factor and sensitivity. Another type of a stretchable strain sensor in skin-wearable applications demonstrates a highly sensitive monitoring of a subject's motion, pulse, and breathing, validated by comparing it with a clinical-grade system. Overall, the presented comprehensive study of materials, mechanics, printing-based fabrication, and interfacial adhesion shows a great potential of the printed soft strain sensor for applications in continuous structural health monitoring, human health detection, machine-interfacing systems, and environmental condition monitoring.