Piezoelectric nanogenerators for personalized healthcare.

The development of flexible piezoelectric nanogenerators has experienced rapid progress in the past decade and is serving as the technological foundation of future state-of-the-art personalized healthcare. Due to their highly efficient mechanical-to-electrical energy conversion, easy implementation, and self-powering nature, these devices permit a plethora of innovative healthcare applications in the space of active sensing, electrical stimulation therapy, as well as passive human biomechanical energy harvesting to third party power on-body devices. This article gives a comprehensive review of the piezoelectric nanogenerators for personalized healthcare. After a brief introduction to the fundamental physical science of the piezoelectric effect, material engineering strategies, device structural designs, and human-body centered energy harvesting, sensing, and therapeutics applications are also systematically discussed. In addition, the challenges and opportunities of utilizing piezoelectric nanogenerators for self-powered bioelectronics and personalized healthcare are outlined in detail.

Nickel/Cobalt Molybdate Hollow Rods Induced by Structure and Defect Engineering as Exceptional Electrode Materials for Hybrid Supercapacitor.

Oxygen defects and hollow structures positively impact pseudocapacitive properties of diffusion/surface-controlled processes, a component of critical importance when building high-performance supercapacitors. Hence, we fabricated hollow nickel/cobalt molybdate rods with O-defects (D-H-NiMoO4 @CoMoO4 ) through a soft-template and partial reduction method, enhancing D-H-NiMoO4 @CoMoO4 's electrochemical performance, yielding a specific capacitance of 1329 F g-1 , and demonstrating excellent durability with 95.8 % capacity retention after 3000 cycles. D-H-NiMoO4 @CoMoO4 was used as the positive electrode to construct an asymmetric supercapacitor, displaying an energy density of up to 34.13 Wh kg-1 and demonstrating good predisposition towards practical applications. This work presents an effective approach to fabricate and use hollow nickel/cobalt molybdate rods with O-defects as pseudocapacitor material for high-performance capacitive energy storage devices.

Anti-bacterial and wound healing-promoting effects of zinc ferrite nanoparticles.

BACKGROUND: Increasing antibiotic resistance continues to focus on research into the discovery of novel antimicrobial agents. Due to its antimicrobial and wound healing-promoting activity, metal nanoparticles have attracted attention for dermatological applications. This study is designed to investigate the scope and bactericidal potential of zinc ferrite nanoparticles (ZnFe2O4 NPs), and the mechanism of anti-bacterial action along with cytocompatibility, hemocompatibility, and wound healing properties. RESULTS: ZnFe2O4 NPs were synthesized via a modified co-precipitation method. Structure, size, morphology, and elemental compositions of ZnFe2O4 NPs were analyzed using X-ray diffraction pattern, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. In PrestoBlue and live/dead assays, ZnFe2O4 NPs exhibited dose-dependent cytotoxic effects on human dermal fibroblasts. In addition, the hemocompatibility assay revealed that the NPs do not significantly rupture red blood cells up to a dose of 1000 µg/mL. Bacterial live/dead imaging and zone of inhibition analysis demonstrated that ZnFe2O4 NPs showed dose-dependent bactericidal activities in various strains of Gram-negative and Gram-positive bacteria. Interestingly, NPs showed antimicrobial activity through multiple mechanisms, such as cell membrane damage, protein leakage, and reactive oxygen species generation, and were more effective against gram-positive bacteria. Furthermore, in vitro scratch assay revealed that ZnFe2O4 NPs improved cell migration and proliferation of cells, with noticeable shrinkage of the artificial wound model. CONCLUSIONS: This study indicated that ZnFe2O4 NPs have the potential to be used as a future antimicrobial and wound healing drug.

Self-Powered Programming of Fibroblasts into Neurons via a Scalable Magnetoelastic Generator Array.

Developing scalable electrical stimulating platforms for cell and tissue engineering applications is limited by external power source dependency, wetting resistance, microscale size requirements, and suitable flexibility. Here, a versatile and scalable platform is developed to enable tunable electrical stimulation for biological applications by harnessing the giant magnetoelastic effect in soft systems, converting gentle air pressure (100-400 kPa) to yield a current of up to 10.5 mA and a voltage of 9.5 mV. The platform can be easily manufactured and scaled up for integration in multiwell magnetoelastic plates via 3D printing. The authors demonstrate that the electrical stimulation generated by this platform enhances the conversion of fibroblasts into neurons up to 2-fold (104%) and subsequent neuronal maturation up to 3-fold (251%). This easily configurable electrical stimulation device has broad applications in high throughput organ-on-a-chip systems, and paves the way for future development of neural engineering, including cellular therapy via implantable self-powered electrical stimulation devices.

In Situ Grown Silver-Polymer Framework with Coordination Complexes for Functional Artificial Tissues.

Self-sensing actuators are critical to artificial robots with biomimetic proprio-/exteroception properties of biological neuromuscular systems. Existing add-on approaches, which physically blend heterogeneous sensor/actuator components, fall short of yielding satisfactory solutions, considering their suboptimal interfaces, poor adhesion, and electronic/mechanical property mismatches. Here, a single homogeneous material platform is reported by creating a silver-polymer framework (SPF), thus realizing the seamless sensing-actuation unification. The SPF-enabled elastomer is highly stretchable (1200%), conductive (0.076 S m-1 ), and strong (0.76 MPa in-strength), where the stretchable polymer matrix synthesis and in situ silver nanoparticles reduction are accomplished simultaneously. Benefiting from the multimodal sensing capability from its architecture itself (mechanical and thermal cues), self-sensing actuation (proprio-deformations and external stimuli perceptions) is achieved for the SPF-based pneumatic actuator, alongside an excellent load-lifting attribute (up to 3700 times its own weight), substantiating its advantage of the unified sensing-actuation feature in a single homogenous material. In view of its human somatosensitive muscular systems imitative functionality, the reported SPF bodes well for use with next-generation functional tissues, including artificial skins, human-machine interfaces, self-sensing robots, and otherwise dynamic materials.

Giant Magnetoelastic Effect Enabled Stretchable Sensor for Self-Powered Biomonitoring.

Interfacing with the human body, wearable and implantable bioelectronics are a compelling platform technology for healthcare monitoring and medical therapeutics. However, clinical adoption of these devices is largely shadowed by their weakness in humidity resistance, stretchability, durability, and biocompatibility. In this work, we report a self-powered waterproof biomechanical sensor with stretchability up to 440% using the giant magnetoelastic effect in a soft polymer system. By manipulating the magnetic dipole alignment, the sensor achieved a particularly broad sensing range from 3.5 Pa to 2000 kPa, with a response time of ∼3 ms. To validate the excellent performance of the magnetoelastic sensor in biomonitoring, both ex vivo porcine heart testing and in vivo rat model testing were performed for cardiovascular monitoring and heart disease diagnosis. With the obtained sensing data, we have successfully detected ventricular arrhythmia and ventricular fibrillation in the Sprague-Dawley rat model. Holding a collection of compelling features, including minimal hysteresis, ultrawide sensing range, waterproofness, and biocompatibility, the magnetoelastic sensor represents a unique platform technology for self-powered biomonitoring in both wearable and implantable manners.

A Soft Magnetoelastic Generator for Wind-Energy Harvesting.

The current energy crises and imminent danger of global warming severely limit the ability to scale societal development sustainably. As such, there is a pressing need for utilizing renewable, green energy sources, such as wind energy, which is ubiquitously available on Earth. In this work, a fundamentally new wind-energy-harvesting technology is reported, which is based on the giant magnetoelastic effect in a soft composite system, namely, magnetoelastic generators. Its working principle is based on wind-induced mechanical deformation, which alters the magnetic field in a soft system converting the wind energy into electricity via electromagnetic induction from arbitrary directions. The wind-energy-harvesting system features a low internal impedance of 68 Ω, a high current density of 1.17 mA cm-2 , and a power density of 0.82 mW cm-2 under ambient natural wind. The system is capable of sustainably driving small electronics and electrolytically splitting water. The system can generate hydrogen at a rate of 7.5 × 10-2 mL h-1 with a wind speed of 20 m s-1 . Additionally, since magnetic fields can penetrate water molecules, the magnetoelastic generators are intrinsically waterproof and work stably in harsh environments. This work paves a new way for wind-energy harvesting with compelling features, which can contribute largely to the hydrogen economy and the sustainability of human civilization.

Brain-on-a-chip: Recent advances in design and techniques for microfluidic models of the brain in health and disease.

Recent advances in biomaterials, microfabrication, microfluidics, and cell biology have led to the development of organ-on-a-chip devices that can reproduce key functions of various organs. Such platforms promise to provide novel insights into various physiological events, including mechanisms of disease, and evaluate the effects of external interventions, such as drug administration. The neuroscience field is expected to benefit greatly from these innovative tools. Conventional ex vivo studies of the nervous system have been limited by the inability of cell culture to adequately mimic in vivo physiology. While animal models can be used, their relevance to human physiology is uncertain and their use is laborious and associated with ethical issues. To date, organ-on-a-chip systems have been developed to model different tissue components of the brain, including brain regions with specific functions and the blood brain barrier, both in normal and pathophysiological conditions. While the field is still in its infancy, it is expected to have major impact on studies of neurophysiology, pathology and neuropharmacology in future. Here, we review advances made and limitations faced in an effort to stimulate development of the next generation of brain-on-a-chip devices.

Improving Relative Permittivity and Suppressing Dielectric Loss of Triboelectric Layers for High-Performance Wearable Electricity Generation.

High relative permittivity and low dielectric loss are two desired parameters of a triboelectric layer to enhance its mechanical-to-electrical energy conversion efficiency in a triboelectric nanogenerator (TENG). However, the elevated permittivity of the triboelectric layer is always accompanied by increasing dielectric loss, limiting further improvement or even reducing the electrical output. Herein, we report a method for improving the relative permittivity and suppressing the dielectric loss of the triboelectric layer via nanoscale design at the particle-polymer interface. When incorporated with 2 wt % Ag@C, the triboelectric-layer-enhanced TENG (TLE-TENG) presents a 2.6-fold increment in relative permittivity and a 302% current enhancement. An instantaneous peak power density of 1.22 W m-2, an excellent pressure sensitivity of 90.95 V kPa-1, and an optimized sheet resistance (∼0.14 Ω/sq) are attributes of this greatly enhanced device. Such improvements bode well for the implementation of these enhancing strategies to help position TLE-TENGs as pervasive and sustainable power sources and active self-powered sensors in the era of the Internet of Things.

Laponite-Based Nanomaterials for Drug Delivery.

Laponite is a clay-based material composed of synthetic disk-shaped crystalline nanoparticles with highly ionic, large surface area. These characteristics enable the intercalation and dissolution of biomolecules in Laponite-based drug delivery systems. Furthermore, Laponite's innate physicochemical properties and architecture enable the development of tunable pH-responsive drug delivery systems. Laponite's coagulation capacity and cation exchangeability determine its exchange capabilities, drug encapsulation efficiency, and release profile. These parameters are exploited to design highly controlled and efficacious drug delivery platforms for sustained drug release. In this review, they provide an overview of how to design efficient delivery of therapeutics by leveraging the properties and specific interactions of various Laponite-polymer composites and drug moieties.

Simultaneous Biomechanical and Biochemical Monitoring for Self-Powered Breath Analysis.

The high moisture level of exhaled gases unavoidably limits the sensitivity of breath analysis via wearable bioelectronics. Inspired by pulmonary lobe expansion/contraction observed during respiration, a respiration-driven triboelectric sensor (RTS) was devised for simultaneous respiratory biomechanical monitoring and exhaled acetone concentration analysis. A tin oxide-doped polyethyleneimine membrane was devised to play a dual role as both a triboelectric layer and an acetone sensing material. The prepared RTS exhibited excellent ability in measuring respiratory flow rate (2-8 L/min) and breath frequency (0.33-0.8 Hz). Furthermore, the RTS presented good performance in biochemical acetone sensing (2-10 ppm range at high moisture levels), which was validated via finite element analysis. This work has led to the development of a novel real-time active respiratory monitoring system and strengthened triboelectric-chemisorption coupling sensing mechanism.

Flexible patch with printable and antibacterial conductive hydrogel electrodes for accelerated wound healing.

Electrical stimulation can facilitate wound healing with high efficiency and limited side effects. However, current electrical stimulation devices have poor conformability with wounds due to their bulky nature and the rigidity of electrodes utilized. Here, a flexible electrical patch (ePatch) made with conductive hydrogel as electrodes to improve wound management was reported. The conductive hydrogel was synthesized using silver nanowire (AgNW) and methacrylated alginate (MAA), with the former chosen as the electrode material considering its antibacterial properties, and the latter used due to its clinical suitability in wound healing. The composition of the hydrogel was optimized to enable printing on medical-grade patches for personalized wound treatment. The ePatch was shown to promote re-epithelization, enhance angiogenesis, mediate immune response, and prevent infection development in the wound microenvironment. In vitro studies indicated an elevated secretion of growth factors with enhanced cell proliferation and migration ability in response to electrical stimulation. An in vivo study in the Sprague-Dawley rat model revealed a rapid wound closure within 7 days compared to 20 days of usual healing process in rodents.

Engineering bandgap of CsPbI3 over 1.7 eV with enhanced stability and transport properties.

Potential multijunction application of CsPbI3 perovskite with silicon solar cells to reach efficiencies beyond the Shockley-Queisser limit motivates tremendous efforts to improve its phase stability and further enlarge its band gap between 1.7 and 1.8 eV. Current strategies to increase band gap via conventional mixed halide engineering are accompanied by detrimental phase segregation under illumination. Here, ethylammonium (EA) in a relatively small fraction (x < 0.15) is first investigated to fit into three-dimensional CsPbI3 framework to form pure-phase hybrid perovskites with enlarged band gap over 1.7 eV. The increase of band gap is closely associated with the distortion of Pb-I octahedra and the variation of the average Pb-I-Pb angle. Meanwhile, the introduction of EA can retard the crystallization of perovskite and tune the perovskite structure with enhanced phase stability and transport properties.

Triboelectric Nanogenerators for Therapeutic Electrical Stimulation.

Current solutions developed for the purpose of in and on body (IOB) electrical stimulation (ES) lack autonomous qualities necessary for comfortable, practical, and self-dependent use. Consequently, recent focus has been placed on developing self-powered IOB therapeutic devices capable of generating therapeutic ES for human use. With the recent invention of the triboelectric nanogenerator (TENG), harnessing passive human biomechanical energy to develop self-powered systems has allowed for the introduction of novel therapeutic ES solutions. TENGs are especially effective at providing ES for IOB therapeutic systems given their bioconformability, low cost, simple manufacturability, and self-powering capabilities. Due to the key role of naturally induced electrical signals in many physiological functions, TENG-induced ES holds promise to provide a novel paradigm in therapeutic interventions. The aim here is to detail research on IOB TENG devices applied for ES-based therapy in the fields of regenerative medicine, neurology, rehabilitation, and pharmaceutical engineering. Furthermore, considering TENG-produced ES can be measured for sensing applications, this technology is paving the way to provide a fully autonomous personalized healthcare system, capable of IOB energy generation, sensing, and therapeutic intervention. Considering these grounds, it seems highly relevant to review TENG-ES research and applications, as they could constitute the foundation and future of personalized healthcare.

Advances in triboelectric nanogenerators for biomedical sensing.

Biomedical sensors have been essential in improving healthcare outcomes over the past 30 years, though limited power source access and user wearability restraints have prevented them from taking a constant and active biomedical sensing role in our daily lives. Triboelectric nanogenerators (TENGs) have demonstrated exceptional capabilities and versatility in delivering self-powered and wear-optimized biomedical sensors, and are paving the way for a novel platform technology able to fully integrate into the developing 5G/Internet-of-Things ecosystem. This novel paradigm of TENG-based biomedical sensors aspires to provide ubiquitous and omnipresent real-time biomedical sensing for us all. In this review, we cover the remarkable developments in TENG-based biomedical sensing which have arisen in the last octennium, focusing on both in-body and on-body biomedical sensing solutions. We begin by covering TENG as biomedical sensors in the most relevant, mortality-associated clinical fields of pneumology and cardiology, as well as other organ-related biomedical sensing abilities including ambulation. We also include an overview of ambient biomedical sensing as a field of growing interest in occupational health monitoring. Finally, we explore TENGs as power sources for third party biomedical sensors in a number of fields, and conclude our review by focusing on the future perspectives of TENG biomedical sensors, highlighting key areas of attention to fully translate TENG-based biomedical sensors into clinically and commercially viable digital and wireless consumer and health products.

Triboelectric Nanogenerators for Self-Powered Wound Healing.

Wound healing, one of the most complex processes in the human body, involves the spatial and temporal synchronization of a variety of cell types with distinct roles. Slow or nonhealing skin wounds have potentially life-threatening consequences, ranging from infection to scar, clot, and hemorrhage. Recently, the advent of triboelectric nanogenerators (TENGs) has brought about a plethora of self-powered wound healing opportunities, owing to their pertinent features, including wide range choices of constitutive biocompatible materials, simple fabrication, portable size, high output power, and low cost. Herein, a comprehensive review of TENGs as an emerging biotechnology for wound healing applications is presented and covered from three unique aspects: electrical stimulation, antibacterial activity, and drug delivery. To provide a broader context of TENGs applicable to wound healing applications, state-of-the-art designs are presented and discussed in each section. Although some challenges remain, TENGs are proving to be a promising platform for human-centric therapeutics in the era of Internet of Things. Consequently, TENGs for wound healing are expected to provide a new solution in wound management and play an essential role in the future of point-of-care interventions.

Multi-Dimensional Printing for Bone Tissue Engineering.

The development of 3D printing has significantly advanced the field of bone tissue engineering by enabling the fabrication of scaffolds that faithfully recapitulate desired mechanical properties and architectures. In addition, computer-based manufacturing relying on patient-derived medical images permits the fabrication of customized modules in a patient-specific manner. In addition to conventional 3D fabrication, progress in materials engineering has led to the development of 4D printing, allowing time-sensitive interventions such as programed therapeutics delivery and modulable mechanical features. Therapeutic interventions established via multi-dimensional engineering are expected to enhance the development of personalized treatment in various fields, including bone tissue regeneration. Here, recent studies utilizing 3D printed systems for bone tissue regeneration are summarized and advances in 4D printed systems are highlighted. Challenges and perspectives for the future development of multi-dimensional printed systems toward personalized bone regeneration are also discussed.

Microneedle-based bioassays.

Disease diagnosis and therapeutic efficacy can be monitored via a number of established bioassays that sample body fluids to assess and monitor health conditions. Traditional bioassays generally include several steps and start with invasive body fluid extraction procedures. These steps are painful and often require specialized techniques and tailored equipment, as well as the supervision of professional medical personnel. Innovations in engineering alternative bioassays to address these shortcomings are thus desired. Microneedles (MNs) represent promising tools to sample body fluids, in view of their minimal invasiveness, painlessness, and uncomplicated implementation. Recent progress in microfabrication and materials engineering, including the development of hollow and solid MNs with uniquely optimized architectures and multi-functional materials, has positioned MN-based platforms as prime candidates for bioassay solutions. In this minireview, we summarize the studies of MN-based platforms for detection and diagnosis. We categorize the platforms based on three different mechanisms: MNs as body fluid reservoirs, MNs integrated with electrochemical assays, and MNs engineered with colorimetric analyses. A discussion of design principles for MN-based bioassay platforms is presented. We also discuss the challenges and opportunities associated with MN-based bioassays in future clinical applications.

Triboelectric Nanogenerator Enabled Smart Shoes for Wearable Electricity Generation.

The parallel evolution of wearable electronics, artificial intelligence, and fifth-generation wireless technology has created a technological paradigm with the potential to change our lives profoundly. Despite this, addressing limitations linked to continuous, sustainable, and pervasive powering of wearable electronics remains a bottleneck to overcome in order to maximize the exponential benefit that these technologies can bring once synergized. A recent groundbreaking discovery has demonstrated that by using the coupling effect of contact electrification and electrostatic induction, triboelectric nanogenerators (TENGs) can efficiently convert irregular and low-frequency passive biomechanical energy from body movements into electrical energy, providing an infinite and sustainable power source for wearable electronics. A number of human motions have been exploited to properly and efficiently harness this energy potential, including human ambulation. Shoes are an indispensable component of daily wearing and can be leveraged as an excellent platform to exploit such kinetic energy. In this article, the latest representative achievements of TENG-based smart electricity-generating shoes are comprehensively reviewed. We summarize ways in which not only can biomechanical energy be scavenged via ambulatory motion, but also biomonitoring of health parameters via tracking of rhythm and strength of pace can be implemented to aid in theranostic fields. This work provides a systematical review of the rational structural design, practical applications, scenario analysis, and performance evaluation of TENG-based smart shoes for wearable electricity generation. In addition, the perspective for future development of smart electricity-generation shoes as a sustainable and pervasive energy solution towards the upcoming era of the Internet of Things is discussed.

Smart Insole for Robust Wearable Biomechanical Energy Harvesting in Harsh Environments.

Footfall contains the highest harvestable biomechanical energy from the human body, which can attain 67 W, showing great potential as a pervasive and sustainable power source for wearable bioelectronics in the era of the Internet of Things. Developing an effective technology for robust and efficient energy harvesting from human walking remains highly desired. Here, we present a waterproof smart insole, based on a triboelectric nanogenerator, for highly efficient and robust human biomechanical energy harvesting. This insole was rationally designed as a composite structure to fully utilize the pressure distribution of a footfall for wearable electricity generation and to deliver a power output reaching 580 µW. The insole was additionally able to withstand use in harsh environments, including pluvial conditions, without affecting the power output consistency. A total of 260 light-emitting diodes were lit up with perspiring feet and water on the floor, and a capacitor of 88 µF was charged to 2.5 V in 900 s. This work represents a practical approach to developing a highly efficient and robust smart insole that can be used as a sustainable power source for wearable bioelectronics.