Micro-/Nanohierarchical Structures Physically Engineered on Surfaces: Analysis and Perspective.

The high demand for micro-/nanohierarchical structures as components of functional substrates, bioinspired devices, energy-related electronics, and chemical/physical transducers has inspired their in-depth studies and active development of the related fabrication techniques. In particular, significant progress has been achieved in hierarchical structures physically engineered on surfaces, which offer the advantages of wide-range material compatibility, design diversity, and mechanical stability, and numerous unique structures with important niche applications have been developed. This review categorizes the basic components of hierarchical structures physically engineered on surfaces according to function/shape and comprehensively summarizes the related advances, focusing on the fabrication strategies, ways of combining basic components, potential applications, and future research directions. Moreover, the physicochemical properties of hierarchical structures physically engineered on surfaces are compared based on the function of their basic components, which may help to avoid the bottlenecks of conventional single-scale functional substrates. Thus, the present work is expected to provide a useful reference for scientists working on multicomponent functional substrates and inspire further research in this field.

Highly Sensitive Soft Pressure Sensors for Wearable Applications Based on Composite Films with Curved 3D Carbon Nanotube Structures.

Soft pressure sensors based on 3D microstructures exhibit high sensitivity in the low-pressure range, which is crucial for various wearable and soft touch applications. However, it is still a challenge to manufacture soft pressure sensors with sufficient sensitivity under small mechanical stimuli for wearable applications. This work presents a novel strategy for extremely sensitive pressure sensors based on the composite film with local changes in curved 3D carbon nanotube (CNT) structure via expandable microspheres. The sensitivity is significantly enhanced by the synergetic effects of heterogeneous contact of the microdome structure and changes of percolation network within the curved 3D CNT structure. The finite-element method simulation is used to comprehend the relationships between the sensitivity and mechanical/electrical behavior of microdome structure under the applied pressure. The sensor shows an excellent sensitivity (571.64 kPa-1 ) with fast response time (85 ms), great repeatability, and long-term stability. Using the developed sensor, a wireless wearable health monitoring system to avoid carpel tunnel syndrome is built, and a multi-array pressure sensor for realizing a variety of movements in real-time is demonstrated.

Correction: A wearable colorimetric sweat pH sensor-based smart textile for health state diagnosis.

Correction for 'A wearable colorimetric sweat pH sensor-based smart textile for health state diagnosis' by Ji-Hwan Ha et al., Mater. Horiz., 2023, 10, 4163-4171, https://doi.org/10.1039/d3mh00340j.

A wearable colorimetric sweat pH sensor-based smart textile for health state diagnosis.

Sweat pH is an important indicator for diagnosing disease states, such as cystic fibrosis. However, conventional pH sensors are composed of large brittle mechanical parts and need additional instruments to read signals. These pH sensors have limitations for practical wearable applications. In this study, we propose wearable colorimetric sweat pH sensors based on curcumin and thermoplastic-polyurethane (C-TPU) electrospun-fibers to diagnose disease states by sweat pH monitoring. This sensor aids in pH monitoring by changing color in response to chemical structure variation from enol to di-keto form via H-atom separation. Its chemical structure variation changes the visible color due to light absorbance and reflectance changes. Furthermore, it can rapidly and sensitively detect sweat pH due to its superior permeability and wettability. By O2 plasma activation and thermal pressing, this colorimetric pH sensor can be easily attached to various fabric substrates such as swaddling and patient clothing via surface modification and mechanical interlocking of C-TPU. Furthermore, the diagnosable clothing is durable and reusable enough to neutral washing conditions due to the reversible pH colorimetric sensing performance by restoring the enol form of curcumin. This study contributes to the development of smart diagnostic clothing for cystic fibrosis patients who require continuous sweat pH monitoring.

Battery-Free, Wireless, Cuff-Type, Multimodal Physical Sensor for Continuous Temperature and Strain Monitoring of Nerve.

Peripheral nerve injuries cause various disabilities related to loss of motor and sensory functions. The treatment of these injuries typically requires surgical operations for improving functional recovery of the nerve. However, capabilities for continuous nerve monitoring remain a challenge. Herein, a battery-free, wireless, cuff-type, implantable, multimodal physical sensing platform for continuous in vivo monitoring of temperature and strain from the injured nerve is introduced. The thin, soft temperature, and strain sensors wrapped around the nerve exhibit good sensitivity, excellent stability, high linearity, and minimum hysteresis in relevant ranges. In particular, the strain sensor integrated with circuits for temperature compensation provides reliable, accurate strain monitoring with negligible temperature dependence. The system enables power harvesting and data communication to wireless, multiple implanted devices wrapped around the nerve. Experimental evaluations, verified by numerical simulations, with animal tests, demonstrate the feasibility and stability of the sensor system, which has great potential for continuous in vivo nerve monitoring from an early stage to complete regeneration.

Nanoscale three-dimensional fabrication based on mechanically guided assembly.

The growing demand for complex three-dimensional (3D) micro-/nanostructures has inspired the development of the corresponding manufacturing techniques. Among these techniques, 3D fabrication based on mechanically guided assembly offers the advantages of broad material compatibility, high designability, and structural reversibility under strain but is not applicable for nanoscale device printing because of the bottleneck at nanofabrication and design technique. Herein, a configuration-designable nanoscale 3D fabrication is suggested through a robust nanotransfer methodology and design of substrate's mechanical characteristics. Covalent bonding-based two-dimensional nanotransfer allowing for nanostructure printing on elastomer substrates is used to address fabrication problems, while the feasibility of configuration design through the modulation of substrate's mechanical characteristics is examined using analytical calculations and numerical simulations, allowing printing of various 3D nanostructures. The printed nanostructures exhibit strain-independent electrical properties and are therefore used to fabricate stretchable H2 and NO2 sensors with high performances stable under external strains of 30%.

Battery-Free, Wireless, Ionic Liquid Sensor Arrays to Monitor Pressure and Temperature of Patients in Bed and Wheelchair.

Repositioning is a common guideline for the prevention of pressure injuries of bedridden or wheelchair patients. However, frequent repositioning could deteriorate the quality of patient's life and induce secondary injuries. This paper introduces a method for continuous multi-site monitoring of pressure and temperature distribution from strategically deployed sensor arrays at skin interfaces via battery-free, wireless ionic liquid pressure sensors. The wirelessly delivered power enables stable operation of the ionic liquid pressure sensor, which shows enhanced sensitivity, negligible hysteresis, high linearity and cyclic stability over relevant pressure range. The experimental investigations of the wireless devices, verified by numerical simulation of the key responses, support capabilities for real-time, continuous, long-term monitoring of the pressure and temperature distribution from multiple sensor arrays. Clinical trials on two hemiplegic patients confined on bed or wheelchair integrated with the system demonstrate the feasibility of sensor arrays for a decrease in pressure and temperature distribution under minimal repositioning.

Sutureless transplantation ofin vivopriming human mesenchymal stem cell sheet promotes the therapeutic potential for cardiac repair.

The heart, contrary to its small size, vigorously pumps oxygen and nutrients to our entire body indeterminably; and thus, its dysfunction could be devastating. Until now, there ave been several major obstacles to applying a cardiac patch for the treatment for myocardial infarction, including poor integration and low engraftment rates, due to the highly-curved surface of the heart and its dynamic nature. Here, we demonstrate a novel way for a comprehensive cardiac repair achieved by the sutureless transplantation of a highly integrablein vivopriming bone marrow mesenchymal stem cell (BMSC) sheet based on the utilization of a highly aligned thermoresponsive nanofiber membrane. Moreover, we developed a BMSC sheet specialized for vascular regeneration through 'in-vivopriming' using human umbilical vein endothelial cells. A prolonged secretion of multiple angiogenic cytokines, such as vascular endothelial growth factor, angiopoietin-1, insulin-like growth factor-1, which was observedin vitrofrom the specialized BMSC sheet seemed to lead a significant improvement in the cardiac function, including intrinsic contractibility and remodeling. In this study, we provide strong evidence thatin vivopriming of a human BMSC sheet develops the therapeutic potential for cardiac repair.

Battery-free, wireless soft sensors for continuous multi-site measurements of pressure and temperature from patients at risk for pressure injuries.

Capabilities for continuous monitoring of pressures and temperatures at critical skin interfaces can help to guide care strategies that minimize the potential for pressure injuries in hospitalized patients or in individuals confined to the bed. This paper introduces a soft, skin-mountable class of sensor system for this purpose. The design includes a pressure-responsive element based on membrane deflection and a battery-free, wireless mode of operation capable of multi-site measurements at strategic locations across the body. Such devices yield continuous, simultaneous readings of pressure and temperature in a sequential readout scheme from a pair of primary antennas mounted under the bedding and connected to a wireless reader and a multiplexer located at the bedside. Experimental evaluation of the sensor and the complete system includes benchtop measurements and numerical simulations of the key features. Clinical trials involving two hemiplegic patients and a tetraplegic patient demonstrate the feasibility, functionality and long-term stability of this technology in operating hospital settings.

Improved chondrogenic performance with protective tracheal design of Chitosan membrane surrounding 3D-printed trachea.

In recent tracheal tissue engineering, limitations in cartilage reconstruction, caused by immature delivery of chondrocyte-laden components, have been reported beyond the complete epithelialization and integration of the tracheal substitutes with the host tissue. In an attempt to overcome such limitations, this article introduces a protective design of tissue-engineered trachea (TraCHIM) composed of a chitosan-based nanofiber membrane (CHIM) and a 3D-printed biotracheal construct. The CHIM was created from chitosan and polycaprolactone (PCL) using an electrospinning process. Upon addition of chitosan to PCL, the diameter of electrospun fibers became thinner, allowing them to be stacked more closely, thereby improving its mechanical properties. Chitosan also enhances the hydrophilicity of the membranes, preventing them from slipping and delaminating over the cell-laden bioink of the biotracheal graft, as well as protecting the construct. Two weeks after implantation in Sprague-Dawley male rats, the group with the TraCHIM exhibited a higher number of chondrocytes, with enhanced chondrogenic performance, than the control group without the membrane. This study successfully demonstrates enhanced chondrogenic performance of TraCHIM in vivo. The protective design of TraCHIM opens a new avenue in engineered tissue research, which requires faster tissue formation from 3D biodegradable materials, to achieve complete replacement of diseased tissue.

Arterial Internal Elastic Lamina-Inspired Membrane for Providing Biochemical and Structural Cues in Developing Artery-on-a-Chip.

In vitro artery models constructed on a membrane-based microfluidic chip, called an artery-on-a-chip, have been spotlighted as a powerful platform for studying arterial physiology. However, due to the use of a flat and porous membrane that cannot mimic the in vivo internal elastic lamina (IEL), the physiological similarity in the phenotypes and the arrangements of the endothelial cells (ECs) and aortic smooth muscle cells (AoSMCs) has been limited in the previously developed artery-on-a-chips. Herein, we developed an innovative membrane mimicking the structures of IEL by utilizing electrospun aligned silk fibroin/polycaprolactone nanofiber membranes. An arterial IEL-mimicking (AIM) membrane was about 5 µm thick and composed of orthogonally aligned nanofibers with a diameter of around 400 nm, which were highly comparable to the IEL. Such structural similarity was found to induce the ECs and SMCs to be elongated and orthogonally aligned as in the in vivo artery. In particular, the SMCs cultured on the AIM membrane maintained a healthy state showing increased αSMA mRNA expression, which was easily lost on the conventional membrane. We constructed an AIM membrane-integrated artery-on-a-chip having an orthogonal arrangement of ECs and SMCs, which was desirable but difficult to be realized with the previous artery-on-a-chip.