Data-driven inverse design of flexible pressure sensors.

Artificial skins or flexible pressure sensors that mimic human cutaneous mechanoreceptors transduce tactile stimuli to quantitative electrical signals. Conventional trial-and-error designs for such devices follow a forward structure-to-property routine, which is usually time-consuming and determines one possible solution in one run. Data-driven inverse design can precisely target desired functions while showing far higher productivity, however, it is still absent for flexible pressure sensors because of the difficulties in acquiring a large amount of data. Here, we report a property-to-structure inverse design of flexible pressure sensors, exhibiting a significantly greater efficiency than the conventional routine. We use a reduced-order model that analytically constrains the design scope and an iterative "jumping-selection" method together with a surrogate model that enhances data screening. As an exemplary scenario, hundreds of solutions that overcome the intrinsic signal saturation have been predicted by the inverse method, validating for a variety of material systems. The success in property design on multiple indicators demonstrates that the proposed inverse design is an efficient and powerful tool to target multifarious applications of flexible pressure sensors, which can potentially advance the fields of intelligent robots, advanced healthcare, and human-machine interfaces.

Characterization of an underwater metamaterial made of aluminum honeycomb panels at low frequencies.

This paper presents a method to characterize the effective properties of inertial acoustic metamaterial unit cells for underwater operation. The method is manifested by a fast and reliable parameter retrieval procedure utilizing both numerical simulations and measurements. The effectiveness of the method was proved to be self-consistent by a metamaterial unit cell composed of aluminum honeycomb panels with soft rubber spacers. Simulated results agree well with the measured responses of this metamaterial in a water-filled resonator tube. A sub-unity density ratio and an anisotropic mass density are simultaneously achieved by the metamaterial unit cell, making it useful in implementations of transformation acoustics. The metamaterial, together with the approach for its characterization, are expected to be useful for underwater acoustic devices.

Novel pyrene-pyridine oligomer nanorods for super-sensitive fluorescent detection of Pd2.

Conjugated polymers (CPs) can be fabricated into conjugated polymer nanoparticles of various shapes, thus tuning the hydrophobicity and sensing performances of the parent polymers. Herein, two new hydrophobic oligomeric CPs containing pyrene-pyridyl moieties, P1 and P2, were directly prepared and conveniently converted into hydrophilic nanorods, i.e. P1NRs and P2NRs (about 4-21 and 6-20 nm in diameter), by a modified microemulsion method. Notably, separated P1NRs exhibit excellent stability while P2NRs tend to stack on each other perhaps due to their different rigidity of π-delocalized backbones, which may have a profound effect on their fluorescence properties. In addition, Pd2+ can coordinate with the pyridyl N atoms, thereby causing ultrasensitive fluorescence quenching of P1NRs and P2NRs owing to the aggregation of oligomeric CP nanorods. These two simple nanosensors can help to determine Pd2+ with detection limits as low as 1 and 70 nM, respectively. It is worth noting that biocompatible P1NRs with bright blue fluorescence can be employed for efficient imaging of trace level Pd2+ ions in live cells.

Predictors of Medical Care Delay or Avoidance Among Chinese Adults During the COVID-19 Pandemic.

Purpose: Medical care delay or avoidance increases morbidity and mortality risk and is costly for the national healthcare system. The objective of this study was to identify factors associated with medical care delay or avoidance among Chinese adults during the COVID-19 pandemic. Materials and Methods: A cross-sectional analysis was conducted using data from the 2020 China Family Panel Study (CFPS). The CFPS was conducted from July to December 2020 during the COVID-19 pandemic. The final sample included 4369 adults. A logistic regression model was employed to identify the factors associated with medical care delay or avoidance. Results: The empirical results indicate that regardless of rural-urban residence, older adults and adults with chronic conditions were less likely to delay or avoid medical care during the pandemic. However, individuals who had completed more than three years of college showed a higher likelihood of delaying or avoiding medical care. In urban areas, larger family sizes, greater general trust in physicians, and higher provider structural quality were associated with a decreased probability of delaying or avoiding medical care during the pandemic. In contrast, employed adults were more likely to delay or avoid medical care. In rural areas, current smokers were more likely to delay or avoid medical care during the pandemic. Conclusion: This study has identified several factors affecting medical care delay or avoidance, some of which are amenable to policy changes. Policymakers can help improve the utilization of health facilities and patient health outcomes by implementing a series of reforms.

Employment intentions among rural order-oriented medical students in inner mongolia autonomous region, China.

BACKGROUND: The program of the "Free Training of Chinese Rural Order-Oriented Medical Students" is a plan to train general practitioners who can work at rural medical institutions. However, many students have been unwilling to fulfill their commitments and actually work in their assigned locations. OBJECTIVE: This study aimed to provide some explanation by exploring factors influencing the employment intentions of rural order-oriented medical students in Inner Mongolia Autonomous Region of China to provide a basis for formulating relevant supporting policies to help increase the fulfillment rate of medical students. METHODS: We conducted a cross-sectional study with a stratified cluster sampling method at four medical universities in Inner Mongolia using a survey questionnaire. Multivariate logistic regression was used to identify factors that were significantly associated with employment intentions. RESULTS: Approximately 67% of students were willing to work in rural areas, whereas 33% were not. Order-oriented medical students who were dissatisfied with, or indifferent to, training, were unclear about policy, were of Han ethnicity, or came from an urban area, had lower intentions to accept employment in rural areas. The training satisfaction in particular had the greatest predictive effect. CONCLUSION: The implementation of the program "Free Training of Chinese Rural Order-Oriented Medical Students" has been affected by the low actual employment intentions. This study may provide a useful basis on which medical educators and health policy makers can formulate relevant supporting policies and develop strategies to increase the number of order-oriented medical students who working in rural areas where they are most needed.

3D Printing of Interpenetrating Network Flexible Hydrogels with Enhancement of Adhesiveness.

3D printing of hydrogels has been widely explored for the rapid fabrication of complex soft structures and devices. However, using 3D printing to customize hydrogels with both adequate adhesiveness and toughness remains a fundamental challenge. Here, we demonstrate mussel-inspired (polydopamine) PDA hydrogel through the incorporation of a classical double network (2-acrylamido-2-methylpropanesulfonic acid) PAMPS/(polyacrylamide) PAAm to achieve simultaneously tailored adhesiveness, toughness, and biocompatibility and validate the 3D printability of such a hydrogel into customized architectures. The strategy of combining PDA with PAMPS/PAAm hydrogels leads to favorable adhesion on either hydrophilic or hydrophobic surfaces. The hydrogel also shows excellent flexibility, which is attributed to the reversible cross-linking of PDA and PAMPS, together with the long-chain PAAm cross-linking network. Among them, the reversible cross-linking of PDA and PAMPS is capable of dissipating mechanical energy under deformation. Meanwhile, the long-chain PAAm network contributes to maintaining a high deformation capability. We establish a theoretical framework to quantify the contribution of the interpenetrating networks to the overall toughness of the hydrogel, which also provides guidance for the rational design of materials with the desired properties. Our work manifests a new paradigm of printing adhesive, tough, and biocompatible interpenetrating network hydrogels to meet the requirements of broad potential applications in biomedical engineering, soft robotics, and intelligent and superabsorbent devices.

In Situ Wide-Field Visualization of Palladium Hydrogenation.

Visualizing hydrogenation processes in palladium (Pd) in real-time is important to various hydrogen-involved applications. However, observing hydrogen diffusion of Pd was limited by its small permittivity variation, and the kinetics of lateral diffusion of hydrogen in Pd film was not reported. Here, we proposed an optical microscopy-based visualization of Pd hydrogenation from the diffusion surface to the interior by introducing a fast-response mechanical platform that transforms the hydrogen diffusion into self-organized ordered wrinkles with sharp optical contrast. This platform is a Au/Pd double layer on an elastomer, which results in directional hydrogenation from the sidewall to the interior. The kinetics of hydrogenation in the interior of the palladium along the diffusion direction was monitored in real-time. This platform will enable in situ visualization of atom/ion diffusion on metals that are crucial in energy storage and hydrogen detection.

Skin-electrode iontronic interface for mechanosensing.

Electrodermal devices that capture the physiological response of skin are crucial for monitoring vital signals, but they often require convoluted layered designs with either electronic or ionic active materials relying on complicated synthesis procedures, encapsulation, and packaging techniques. Here, we report that the ionic transport in living systems can provide a simple mode of iontronic sensing and bypass the need of artificial ionic materials. A simple skin-electrode mechanosensing structure (SEMS) is constructed, exhibiting high pressure-resolution and spatial-resolution, being capable of feeling touch and detecting weak physiological signals such as fingertip pulse under different skin humidity. Our mechanical analysis reveals the critical role of instability in high-aspect-ratio microstructures on sensing. We further demonstrate pressure mapping with millimeter-spatial-resolution using a fully textile SEMS-based glove. The simplicity and reliability of SEMS hold great promise of diverse healthcare applications, such as pulse detection and recovering the sensory capability in patients with tactile dysfunction.

Ultrafine fluorene-pyridine oligoelectrolyte nanoparticles for supersensitive fluorescence sensing of heparin and protamine.

A new fluorene-pyridine oligoelectrolyte (OFP) is rationally proposed and readily synthesized via a simple one-pot Sonogashira approach. Hence, an unexpectedly small cationic oligomer nanosensor (i.e. OFPNPs, ∼ 1.2 nm in diameter) was conveniently fabricated owing to the enhanced flexibility endowed by the meta-substituted pyridyl unit. Inspiringly, this facile nanoplatform with low cytotoxicity favors the ultrasensitive fluorescence assay for heparin and protamine with a detection limit (LOD, S/N = 3) as low as 1.2 ng mL-1 and 0.5 ng mL-1, respectively, involving heparin-induced aggregation of OFPNPs through electrostatic interaction or competitive rebinding of protamine to heparin.

Electromechanically reconfigurable optical nano-kirigami.

Kirigami, with facile and automated fashion of three-dimensional (3D) transformations, offers an unconventional approach for realizing cutting-edge optical nano-electromechanical systems. Here, we demonstrate an on-chip and electromechanically reconfigurable nano-kirigami with optical functionalities. The nano-electromechanical system is built on an Au/SiO2/Si substrate and operated via attractive electrostatic forces between the top gold nanostructure and bottom silicon substrate. Large-range nano-kirigami like 3D deformations are clearly observed and reversibly engineered, with scalable pitch size down to 0.975 µm. Broadband nonresonant and narrowband resonant optical reconfigurations are achieved at visible and near-infrared wavelengths, respectively, with a high modulation contrast up to 494%. On-chip modulation of optical helicity is further demonstrated in submicron nano-kirigami at near-infrared wavelengths. Such small-size and high-contrast reconfigurable optical nano-kirigami provides advanced methodologies and platforms for versatile on-chip manipulation of light at nanoscale.

Continuous 3D printing from one single droplet.

3D printing has become one of the most promising methods to construct delicate 3D structures. However, precision and material utilization efficiency are limited. Here, we propose a one-droplet 3D printing strategy to fabricate controllable 3D structures from a single droplet ascribing to the receding property of the three-phase contact line (TCL) of the resin droplet. The well-controlled dewetting force of liquid resin on the cured structure results in the minimization of liquid residue and the high wet and net material utilization efficiency in forming a droplet into a 3D structure. Additionally, extra curing induced protruding or stepped sidewalls under high printing speed, which require high UV intensity, can be prevented. The critical is the free contact surface property of the droplet system with the introduction of the receding TCL, which increased the inner droplet liquid circulation and reduces the adhesion properties among the liquid resin, cured resin, and resin vat.

A novel fluorescent nanosensor based on small-sized conjugated polyelectrolyte dots for ultrasensitive detection of phytic acid.

A novel nanosensor is developed for selective and highly sensitive detection of phytic acid (PA) based on small-sized conjugated polyelectrolyte dots (Pdots) fabricated from a new conjugated polymer (P1) by a modified reprecipitation method. P1 featuring a π-delocalized backbone bearing meta-substituted pyridyl groups can be endowed with enhanced flexibility and hence is beneficial for the synthesis of ultrasmall Pdots (i.e. Pdot-1, ∼3.8 nm in average diameter) as well as for the binding of Fe3+, thus leading to the obvious fluorescence quenching of Pdot-1 (∼444 nm) in the presence of Fe3+ via an electron transfer (ET) process. In addition, phytic acid with six phosphate groups exhibits strong chelating ability. When phytic acid is added, phytic acid readily binds to Fe3+ and the fluorescence of Pdot-1 around 444 nm can be recovered, rendering the supersensitive and selective sensing of PA. Under the optimum conditions, this ultra-small Pdot-based nanoprobe favors the fluorescent determination of PA with the detection limit as low as 10 nM. Particularly, Pdot-1 with bright blue fluorescence exhibits low cytotoxicity. Furthermore, the small-sized and biocompatible Pdot-1 can be applied to the sensitive fluorescence assay for PA in cell extracts and the efficient imaging of PA in live cells.

[In vivo noninvasive detection of vulnerable atherosclerotic plaque by (99)Tc(m)-Annexin V imaging in an atherosclerotic rabbit model.].

OBJECTIVE: Apoptosis contributes to the instability of the atherosclerotic (AS) lesions. The vulnerable plaque was identified in vivo by detecting the apoptosis with radiolabeled annexin V in an atherosclerotic rabbit model. METHODS: Eight male New Zealand white rabbits on 2% cholesterol diet for 2 weeks had abdominal aortic balloon injury and fed a 2% cholesterol diet for another 15 weeks (AS group), 3 rabbits fed a normal rabbit chow for 17 weeks without balloon injury served as controls. Annexin V labeled with (99)Tc(m) was then intravenously administered and planar whole-body images were captured using a gamma camera in the left lateral position. The entire length of the abdominal aorta was explanted for ex vivo imaging with gamma camera. The aorta then was divided into several segments according to the severity of AS. The segments were separated weighted and counted in an gamma counter for the absorptive dose of annexin per gram of tissue. Histology examinations were made on specimens. RESULTS: At 2 hours post annexin V injection, clear delineation of radiolabel within the abdominal aorta could be evidenced in vivo gamma imaging. After explanation of the aorta, ex vivo imaging showed a robust uptake of radiotracer in the infradiaphragmatic aorta corresponding to the in vivo images and conforming to the macroscopic distribution of atherosclerotic lesions. The uptake of radiolabel was absent in areas without grossly visible atherosclerotic lesions. The in vivo and ex vivo images identified plaque areas were identical and corresponded histological results on the explanted specimen. The aortic specimen was divided into 18 segments on lesions. The magority of the lesions (14/18) manifested as type IV or type V lesions of AHA classification (vulnerable lesions), except segments 1 - 4, which manifested as type I or type II lesions. The thickness of fibrous cap (TFC) and the ratio of cap and lipid nuclear (RCN) were significantly reversely correlated to the unit radioactivity counts, and the correlation between RCN and the unit radioactivity counts was more significant than that between TFC and the unit radioactivity counts (r = -0.904, P < 0.01, and r = -0.8, P < 0.01). Apoptosis detection (TUNEL): annexin V intake in plaques was positively correlated to apoptotic index(r = 0.651, P = 0.012). CONCLUSION: Noninvasive Annexin V imaging could be used to detect vulnerable atherosclerotic plaques in vivo.

Nano-kirigami with giant optical chirality.

Kirigami enables versatile shape transformation from two-dimensional (2D) precursors to 3D architectures with simplified fabrication complexity and unconventional structural geometries. We demonstrate a one-step and on-site nano-kirigami method that avoids the prescribed multistep procedures in traditional mesoscopic kirigami or origami techniques. The nano-kirigami is readily implemented by in situ cutting and buckling a suspended gold film with programmed ion beam irradiation. By using the topography-guided stress equilibrium, rich 3D shape transformation such as buckling, rotation, and twisting of nanostructures is precisely achieved, which can be predicted by our mechanical modeling. Benefiting from the nanoscale 3D twisting features, giant optical chirality is achieved in an intuitively designed 3D pinwheel-like structure, in strong contrast to the achiral 2D precursor without nano-kirigami. The demonstrated nano-kirigami, as well as the exotic 3D nanostructures, could be adopted in broad nanofabrication platforms and could open up new possibilities for the exploration of functional micro-/nanophotonic and mechanical devices.

Engineered 3D-printed artificial axons.

Myelination is critical for transduction of neuronal signals, neuron survival and normal function of the nervous system. Myelin disorders account for many debilitating neurological diseases such as multiple sclerosis and leukodystrophies. The lack of experimental models and tools to observe and manipulate this process in vitro has constrained progress in understanding and promoting myelination, and ultimately developing effective remyelination therapies. To address this problem, we developed synthetic mimics of neuronal axons, representing key geometric, mechanical, and surface chemistry components of biological axons. These artificial axons exhibit low mechanical stiffness approaching that of a human axon, over unsupported spans that facilitate engagement and wrapping by glial cells, to enable study of myelination in environments reflecting mechanical cues that neurons present in vivo. Our 3D printing approach provides the capacity to vary independently the complex features of the artificial axons that can reflect specific states of development, disease, or injury. Here, we demonstrate that oligodendrocytes' production and wrapping of myelin depend on artificial axon stiffness, diameter, and ligand coating. This biofidelic platform provides direct visualization and quantification of myelin formation and myelinating cells' response to both physical cues and pharmacological agents.

[Lymphoscintigraphy in sentinel lymph node biopsy of breast cancer].

OBJECTIVE: To evaluate the feasibility of lymphoscintigraphy in sentinel lymph node biopsy of breast cancer. METHOD: Lymphoscintigraphy was performed after peritumoral or subdermal injection of radioactive colloid. Then, sentinel lymph node (SLN) biopsy guided by gamma detector probe was performed. Factors correlated with identification-detection rate were assessed. RESULTS: Lymphatic drainage was present in preoperative lymphoscintigraphy in 88(93%) out of 95 patients, with 39 (44.3%) positive for lymphatic drainage other than in the axilla. A total of 91 (95.8%) patients had their SLN identified in the intraoperative procedure. The quality of lymphoscintigraphic image was closely related to SLN identification-detection rate in the intraoperative procedure (P = 0.025). CONCLUSION: Sentinel lymph node outside the axilla can be detected by lymphoscintigraphy. The combination of lymphoscintigraphy and gamma detector probe for sentinel lymph node biopsy of breast cancer not only is acceptable but promising.