Dynamic Pore Modulation of Stretchable Electrospun Nanofiber Filter for Adaptive Machine Learned Respiratory Protection

Human Circulatory/Respiratory-Inspired Comprehensive Air Purification System

The circulatory and respiratory systems in humans are marvels of biological engineering that exhibit competence in maintaining homeostasis. These systems not only shield the organism from external contaminants but also orchestrate the vital gases via the bloodstream to sustain cellular respiration and metabolic processes across diverse tissues. It is noticed that spaces inhabited encounter challenges akin to those of the human body: protecting the indoor air from external pollutants while removing anthropogenic byproducts like carbon dioxide (CO2), particulate matters (PM), and volatile organic compounds (VOCs) tooutside. A biomimetic approach, composed of a microbubble-based gas exchanger and circulating liquid inspired by alveoli, capillary beds, and bloodstream of the human circulatory/respiratory system, offer an innovative solution for comprehensive air purification of hermetic spaces. Circulatory/respiratory-inspired air purification system (CAPS) ensure both continuous removal of PM and exchange of gas species between indoor and outdoor environments to maintain homeostasis. The effectiveness of this system is also supported by animal behavior experiments with and without CAPS, showing an effect of reducing CO2 concentration by 30% and increasing mice locomotor activity by 53%. CAPS is expected to evolve into robust and comprehensive air purification schemes through the networked integration of plural internal and external environments.

Hyperbranched Polymer Induced Antibacterial Tree-Like Nanofibrous Membrane for High Effective Air Filtration

The air filtration materials with high efficiency, low resistance, and extra antibacterial property are crucial for personal health protection. Herein, a tree-like polyvinylidene fluoride (PVDF) nanofibrous membrane with hierarchical structure (trunk fiber of 447 nm, branched fiber of 24.7 nm) and high filtration capacity is demonstrated. Specifically, 2-hydroxypropyl trimethyl ammonium chloride terminated hyperbranched polymer (HBP-HTC) with near-spherical three-dimensional molecular structure and adjustable terminal positive groups is synthesized as an additive for PVDF electrospinning to enhance the jet splitting and promote the formation of branched ultrafine nanofibers, achieving a coverage rate of branched nanofibers over 90% that is superior than small molecular quaternary ammonium salts. The branched nanofibers network enhances mechanical properties and filtration efficiency (99.995% for 0.26 µm sodium chloride particles) of the PVDF/HBP-HTC membrane, which demonstrates reduced pressure drop (122.4 Pa) and a quality factor up to 0.083 Pa-1 on a 40 µm-thick sample. More importantly, the numerous quaternary ammonium salt groups of HBP-HTC deliver excellent antibacterial properties to the PVDF membranes. Bacterial inhibitive rate of 99.9% against both S. aureus and E. coli is demonstrated in a membrane with 3.0 wt% HBP-HTC. This work provides a new strategy for development of high-efficiency and antibacterial protection products.

Actuation for flexible and stretchable microdevices

Flexible and stretchable microdevices incorporate highly deformable structures, facilitating precise functionality at the micro- and millimetre scale. Flexible microdevices have showcased extensive utility in the fields of biomedicine, microfluidics, and soft robotics. Actuation plays a critical role in transforming energy between different forms, ensuring the effective operation of devices. However, when it comes to actuating flexible microdevices at the small millimetre or even microscale, translating actuation mechanisms from conventional rigid large-scale devices is not straightforward. The recent development of actuation mechanisms leverages the benefits of device flexibility, particularly in transforming conventional actuation concepts into more efficient approaches for flexible devices. Despite many reviews on soft robotics, flexible electronics, and flexible microfluidics, a specific and systematic review of the actuation mechanisms for flexible and stretchable microdevices is still lacking. Therefore, the present review aims to address this gap by providing a comprehensive overview of state-of-the-art actuation mechanisms for flexible and stretchable microdevices. We elaborate on the different actuation mechanisms based on fluid pressure, electric, magnetic, mechanical, and chemical sources, thoroughly examining and comparing the structure designs, characteristics, performance, advantages, and drawbacks of these diverse actuation mechanisms. Furthermore, the review explores the pivotal role of materials and fabrication techniques in the development of flexible and stretchable microdevices. Finally, we summarise the applications of these devices in biomedicine and soft robotics and provide perspectives on current and future research.

Transparent Electronics for Wearable Electronics Application

Recent advancements in wearable electronics offer seamless integration with the human body for extracting various biophysical and biochemical information for real-time health monitoring, clinical diagnostics, and augmented reality. Enormous efforts have been dedicated to imparting stretchability/flexibility and softness to electronic devices through materials science and structural modifications that enable stable and comfortable integration of these devices with the curvilinear and soft human body. However, the optical properties of these devices are still in the early stages of consideration. By incorporating transparency, visual information from interfacing biological systems can be preserved and utilized for comprehensive clinical diagnosis with image analysis techniques. Additionally, transparency provides optical imperceptibility, alleviating reluctance to wear the device on exposed skin. This review discusses the recent advancement of transparent wearable electronics in a comprehensive way that includes materials, processing, devices, and applications. Materials for transparent wearable electronics are discussed regarding their characteristics, synthesis, and engineering strategies for property enhancements. We also examine bridging techniques for stable integration with the soft human body. Building blocks for wearable electronic systems, including sensors, energy devices, actuators, and displays, are discussed with their mechanisms and performances. Lastly, we summarize the potential applications and conclude with the remaining challenges and prospects.

Artificial Intelligence: A Next-Level Approach in Confronting the COVID-19 Pandemic

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which caused coronavirus diseases (COVID-19) in late 2019 in China created a devastating economical loss and loss of human lives. To date, 11 variants have been identified with minimum to maximum severity of infection and surges in cases. Bacterial co-infection/secondary infection is identified during viral respiratory infection, which is a vital reason for morbidity and mortality. The occurrence of secondary infections is an additional burden to the healthcare system; therefore, the quick diagnosis of both COVID-19 and secondary infections will reduce work pressure on healthcare workers. Therefore, well-established support from Artificial Intelligence (AI) could reduce the stress in healthcare and even help in creating novel products to defend against the coronavirus. AI is one of the rapidly growing fields with numerous applications for the healthcare sector. The present review aims to access the recent literature on the role of AI and how its subfamily machine learning (ML) and deep learning (DL) are used to curb the pandemic's effects. We discuss the role of AI in COVID-19 infections, the detection of secondary infections, technology-assisted protection from COVID-19, global laws and regulations on AI, and the impact of the pandemic on public life.

Scalable Fabrication of Electrospun True-Nanoscale Fiber Membranes for Effective Selective Separation

Electrospun fibers have received wide attention in various fields ranging from the environment and healthcare to energy. However, nearly all electrospun fibers suffer from a pseudonanoscale diameter, resulting in fabricated membranes with a large pore size and limited separation performance. Herein, we report a novel strategy based on manipulating the equilibrium of stretch deformation and phase separation of electrospun jets to develop true-nanoscale fibers for effective selective separation. The obtained fibers present true-nanoscale diameters (∼67 nm), 1 order of magnitude less than those of common electrospun fibers, which endows the resultant membranes with remarkable nanostructural characteristics and separation performances in areas of protective textiles (waterproofness of 113 kPa and breathability of 4.1 kg m^-2 d^-1), air filtration (efficiency of 99.3% and pressure drop of 127.4 Pa), and water purification (flux of 81.5 kg m^-2 h^-1 and salt rejection of 99.94%). This work may shed light on developing high-performance separation materials for various applications.

Smart Mask as Wearable for Post-Pandemic Personal Healthcare

A mask serves as a simple external barrier that protects humans from infectious particles from poor air conditions in the surrounding environment. As an important personal protective equipment (PPE) to protect our respiratory system, masks are able not only to filter pathogens and dust particles but also to sense, reflect or even respond to environmental conditions. This smartness is of particular interest among academia and industries due to its potential in disease detection, health monitoring and caring aspects. In this review, we provide an overlook of the current air filtration strategies used in masks, from structural designs to integrated functional modules that empower the mask's ability to sense and transfer physiological or environmental information to become smart. Specifically, we discussed recent developments in masks designed to detect macroscopic physiological signals from the wearer and mask-based disease diagnoses, such as COVID-19. Further, we propose the concept of next-generation smart masks and the requirements from material selection and function design perspectives that enable masks to interact and play crucial roles in health-caring wearables.

Electrostatic Polydopamine-Interface-Mediated (e-PIM) filters with tuned surface topography and electrical properties for efficient particle capture and ozone removal

Ambient particulate matter (PM) poses severe environmental health risks to the public globally, and efficient filtration technologies are urgently needed for air ventilation. In this contribution, to overcome the efficiency-resistance trade-off for fibrous filtration, we introduced an electrostatic polydopamine-interface-mediated (e-PIM) filter utilizing a combined effect of particle pre-charging and filter polarizing. After delineating the PM-fiber interactions in electrostatic filtration, we designed a composite fiber structure and fabricated the filters by a two-step dip-coating. The surface topography and electrical potential of the polyester (PET) coarse substrates were regulated by successively coating polydopamine (PDA) layers and manganese oxide clusters. By this means, an 8-mm-thick Mn-P @ P-100 filter possessed improved efficiency of 96.05%, 97.60%, and 99.14% for 0.3-0.5 µm, 0.5-1 µm, and 1-3 µm particles, the ultralow air resistance of 10.4 Pa at a filtration velocity of 0.5 m/s, and steady ozone removal property. Compared with the pristine PET substrates, the efficiency for 0.3-0.5 µm particles expanded 12 times. Compared with the pristine PET substrates, the efficiency for 0.3-0.5 µm particles expanded 12 times. We expect e-PIM filters and the filtration prototype will be potential candidates as effective and low-cost air cleaning devices for a sustainable and healthy environment.

Portable Heating and Temperature-Monitoring System with a Textile Heater Embroidered on the Facemask

Personal heating systems are getting increasing interest because of the need to reduce the negative impact of cold weather on the health of people and animals. Heating the air before inhalation is of great importance as it can reduce the probability of various diseases. In this paper, we present a textile-based heater composed of commercial conductive threads, embroidered on an ordinary protective facemask. We also present the design and implementation details of the temperature monitoring and controlling circuit. Air temperature inside the facemask was monitored by a thermocouple placed in close proximity to the nose (nostrils). Preliminary testing revealed that the difference among temperatures in repeated heating cycles is in the range of ±1.5 °C. The response time for temperature increase from 29.9 to 40.5 °C was about 4 min, while the recovery time from 40.5 to 31.3 °C was about 4.3 min. Safety for human use and wireless data transmission to an application installed on a mobile phone are also demonstrated.

A Sensor-Integrated Face Mask Using Au@SnO2 Nanoparticle Modified Fibers and Augmented Reality Technology

In this work, we develop a wireless sensor-integrated face mask using Au@SnO₂ nanoparticle-modified conductive fibers based on augmented reality (AR) technology. AR technology enables the overlay of real objects and environments with virtual 3D objects and allows virtual interactions with real objects to create desired meanings. With the help of the AR system, the size of the mask could be precisely estimated and then manufactured using 3D printing technology. The body temperature sensor and respiratory sensor were integrated into the mask so that vital parameters of the human body could be continuously monitored without removing the personal protective equipment. Furthermore, the outer part of the mask consists of conductive fabric modified with Au@SnO₂ core-shell nanoparticle additives, which enhanced the filtration efficiency of airborne aerosols. A significant improvement in the filtration efficiency of particulate matter 2.5 was observed after applying an external voltage to the conductive textiles. A smartwatch with a heart rate sensor was paired with the mask to display sensor data on the mask through wireless transmission. Therefore, this sensor-integrated mask system with AR technology provides the first line of defense to combat global threats from pathogens and air pollutants.

A Review of the Fabrication Methods, Testing, and Performance of Face Masks

Improvement in the performance and compatibility of face masks has remained the focus of researchers in recent years, especially after the emergence of the COVID pandemic. Although a lot of progress in the design, tolerability, and comfort of the mask has been reported, there are certain limitations, requiring further improvement. The present review aims to highlight the filtration efficacy, comfort, and associated characteristic of various types of face masks and respirators as a function of their design and structure. In addition, the air pollutants, their adverse effects on health, certified respirators, and face masks are also discussed. The present review also provides an insight into different types of commercially available face masks in terms of their materials, filtration efficiency, and limitations. The role of emerging trends (such as nanotechnology and high-performance polymers) in the improvement and development of face masks and respirators is also discussed.

Saving 80% Polypropylene in Facemasks by Laser-Assisted Melt-Blown Nanofibers

The ongoing coronavirus (COVID-19) pandemic requires enormous production of facemasks and related personal protection materials, thereby increasing the amount of nondegradable plastic waste. The core material for facemasks is melt-blown polypropylene (PP) fiber. Each disposable facemask consumes ∼0.7 g of PP fibers, resulting in annual global consumption and disposal of more than 1 150 000 tons of PP fibers annually. Herein, we developed a laser-assisted melt-blown (LAMB) technique to manufacture PP nanofibers with a quality factor of 0.17 Pa^-1 and significantly reduced the filter's weight. We demonstrated that a standard surgical facemask could be made with only 0.13 g of PP nanofibers, saving approximately 80% of the PP materials used in commercial facemasks. Theoretical analysis and modeling were also conducted to understand the LAMB process. Importantly, nanofibers can be easily scaled up for mass production by upgrading traditional melt blown line with scanning laser-assisted melt-blown (SLAMB).

Stretchable and Self-Adhesive PEDOT:PSS Blend with High Sweat Tolerance as Conformal Biopotential Dry Electrodes

Dry epidermal electrodes that can always form conformal contact with skin can be used for continuous long-term biopotential monitoring, which can provide vital information for disease diagnosis and rehabilitation. But, this application has been limited by the poor contact of dry electrodes on wet skin. Herein, we report a biocompatible fully organic dry electrode that can form conformal contact with both dry and wet skin even during physical movement. The dry electrodes are prepared by drop casting an aqueous solution consisting of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), poly(vinyl alcohol) (PVA), tannic acid (TA), and ethylene glycol (EG). The electrodes can exhibit a conductivity of 122 S cm^-1 and a mechanical stretchability of 54%. Moreover, they are self-adhesive to not only dry skin but also wet skin. As a result, they can exhibit a lower contact impedance to skin than commercial Ag/AgCl gel electrodes on both dry and sweat skins. They can be used as dry epidermal electrodes to accurately detect biopotential signals including electrocardiogram (ECG) and electromyogram (EMG) on both dry and wet skins for the users at rest or during physical movement. This is the first time to demonstrate dry epidermal electrodes self-adhesive to wet skin for accurate biopotential detection.

Electrospun PAN-HNTs composite nanofiber membranes for efficient electrostatic capture of particulate matters

The fine particulate matter (PM) pollution has become a serious concern to public health. As the core part of PM air filters, high-performance electrostatic nanofiber membranes are urgently needed. However, the existing air filters remain challenging to further decrease the pressure drop to improve the wearer comfort. On the other hand, the rapidly disappearing static electricity of the existing electrostatic nanofiber inevitably gives rise to a relatively short service life. Here, we demonstrate a novel and enhanced electrostatic nanofiber membrane by introducing the halloysite nanotubes (HNTs) to the traditional electrospun PAN nanofiber membrane. The optimal PAN-HNTs nanofiber membrane shows a high removal efficiency of 99.54%, a low pressure drop of 39 Pa, and a high quality factor of 0.89 Pa^-1. This greatly improved filtration performance can be attributed to the increased surface area and diameter of nanofiber after introducing the HNTs as additives with suitable doping concentrations. More importantly, compared with the pure PAN nanofiber membrane, the electrostatic capacity of the PAN-HNTs nanofiber membrane is significantly enhanced, which is confirmed by the leaf electroscope. After introducing the HNTs as additives, the surface of the PAN-HNTs nanofiber membrane becomes hydrophilic, which benefits for preventing foulants from attaching to the surface. We anticipate that the PAN-HNTs nanofibers as high-performance membrane air filters will bring great benefits to public health.