Clinical measurement of arterial stiffness obtained from noninvasive pressure waveforms

Optimizing Input Feature Sets Using Catch-22 and Personalization for an Accurate and Reliable Estimation of Continuous, Cuffless Blood Pressure

Nocturnal monitoring of continuous, cuffless blood pressure (BP) can unleash a whole new world for the prognostication of cardiovascular and other diseases due to its strong predictive capability. Nevertheless, the lack of an accurate and reliable method, primarily due to confounding variables, has prevented its widespread clinical adoption. Herein, we demonstrate how optimized machine learning using the Catch-22 features, when applied to the photoplethysmogram waveform and personalized with direct BP data through transfer learning, can accurately estimate systolic and diastolic BP. After training with a hemodynamically compromised VitalDB "calibration-free" dataset (n = 1293), the systolic and diastolic BP tested on a distinct VitalDB dataset that met AAMI criteria (n = 116) had acceptable error biases of -1.85 mm Hg and 0.11 mm Hg, respectively [within the 5 mm Hg IEC/ANSI/AAMI 80601-2-30, 2018 standard], but standard deviation (SD) errors of 19.55 mm Hg and 11.55 mm Hg, respectively [exceeding the stipulated 8 mm Hg limit]. However, personalization using an initial calibration data segment and subsequent use of transfer learning to fine-tune the pretrained model produced acceptable mean (-1.31 mm Hg and 0.10 mm Hg) and SD (7.91 mm Hg and 4.59 mm Hg) errors for systolic and diastolic BP, respectively. Levene's test for variance found that the personalization method significantly outperformed (p < 0.05) the calibration-free method, but there was no difference between three machine learning methods. Optimized multimodal Catch-22 features, coupled with personalization, demonstrate great promise in the clinical adoption of continuous, cuffless blood pressure estimation in applications such as nocturnal BP monitoring.

Low hysteresis and high sensitivity TPU/carbonized wood cellulose sponge sensors for monitoring dynamic pulses

The importance of continuous and reliable pulse wave monitoring is constantly being increased in health signal monitoring and disease diagnoses. Flexible pressure sensors with high sensitivity, low hysteresis and fast response time are an effective means for monitoring pulses. Herein, a special wave-shaped layered porous structure of carbonized wood cellulose sponge (CWCS) was constructed based on natural wood (NW). Thermoplastic polyurethane (TPU)/CWCS (PCWCS) composite flexible pressure sensitive elements were formed by immersing a TPU solution into the CWCS skeleton. The PCWCS-4 % based sensors exhibited high sensitivity of 164.77 kPa-1 (0.01-0.5 kPa), low hysteresis (0.70 %), short response time (21 ms), low detection limit and good cycling stability. The exceptional sensing performance was attributed to the wave-shaped layered porous structure of the PCWCS, which rapidly established conductive pathways and reduced stress concentrations during compression. Due to the high sensitivity and low hysteresis of sensors, more comprehensive pulse and other physiological signals could be obtained. Therefore, the PCWCS flexible pressure sensor possesses great potential for application in smart wearable and healthcare.

Vascular dysfunction in women with recurrent pregnancy loss: Possible association with antiphospholipid antibodies

OBJECTIVE

Antiphospholipid antibodies (aPL) are recognized to have a pivotal role in recurrent pregnancy loss (RPL) and cardiovascular disease. Therefore, we assessed the vascular function of women with RPL and examined the association with each type of aPL.

METHODS

In this retrospective study, 569 women with RPL and 55 healthy women who had never experienced pregnancy loss were recruited. We performed blood tests for aPL and acceleration plethysmography (APG) to evaluate peripheral vascular function.

RESULTS

The differential pulse wave index (DPI), indicating vascular elasticity, was significantly lower in women with RPL (115.6 ± 4.1) compared to the control group (117.0 ± 2.3). DPI in RPL women with anti-β2 glycoprotein I (aβ2GPI) IgG was significantly lower than those without. Remained blood volume (RBV), indicating post-vasoconstriction blood content, was significantly higher in RPL women with aβ2GI IgG than in those without. Regression analysis showed aβ2GPI IgG and body mass index (BMI) linked negatively with DPI.

CONCLUSION

Women with RPL have subclinical vascular dysfunction even at reproductive age. It is possible that aβ2GPI IgG is associated with vascular dysfunction in RPL women.

Boosting Sensitivity of Cellulose Pressure Sensor via Hierarchically Porous Structure

Pressure sensors are essential for a wide range of applications, including health monitoring, industrial diagnostics, etc. However, achieving both high sensitivity and mechanical ability to withstand high pressure in a single material remains a significant challenge. This study introduces a high-performance cellulose hydrogel inspired by the biomimetic layered porous structure of human skin. The hydrogel features a novel design composed of a soft layer with large macropores and a hard layer with small micropores, each of which contribute uniquely to its pressure-sensing capabilities. The macropores in the soft part facilitate significant deformation and charge accumulation, providing exceptional sensitivity to low pressures. In contrast, the microporous structure in the hard part enhances pressure range, ensuring support under high pressures and preventing structural failure. The performance of hydrogel is further optimized through ion introduction, which improves its conductivity, and as well the sensitivity. The sensor demonstrated a high sensitivity of 1622 kPa-1, a detection range up to 160 kPa, excellent conductivity of 4.01 S m-1, rapid response time of 33 ms, and a low detection limit of 1.6 Pa, outperforming most existing cellulose-based sensors. This innovative hierarchically porous architecture not only enhances the pressure-sensing performance but also offers a simple and effective approach for utilizing natural polymers in sensing technologies. The cellulose hydrogel demonstrates significant potential in both health monitoring and industrial applications, providing a sensitive, durable, and versatile solution for pressure sensing.

Blood pressure waveform morphology assessed using a transmission line model and harmonic distortion analysis

A major determinant of blood pressure waveform (BPW) morphology is vascular impedance, governed by material properties of the arterial wall and hemodynamics of blood flow. Analysis of BPW morphology can be an effective means of assessing cardiovascular health. A transmission line model of the mechanical impedance of the arterial tree was implemented to recreate physiologically realistic BPWs. We then examined the sensitivity of existing vascular measures, including augmentation index (AI), pulse wave velocity (PWV), and the recently proposed harmonic distortion (HD), to structural and mechanical parameters of vessel walls and blood flow. All three measures are primarily sensitive to structural stiffness while HD and AI also correlate strongly with geometric parameters. Further, in a simulated set of randomly constructed arterial trees using model parameters within a physiological range, the indexes are strongly correlated with stiffness. When controlling for all confounding factors, HD demonstrates a stronger correlation with arterial stiffness than AI for stiffness values higher than the average. Our study provides a mechanistic understanding of the determinants of AI and HD, with the latter being a promising measure of cardiovascular risk due to its ease of calculation and access, meeting key limitations set by AI and PWV.

Stretchable Multimodal Photonic Sensor for Wearable Multiparameter Health Monitoring

Stretchable sensors that can conformally interface with the skins for wearable and real-time monitoring of skin deformations, temperature, and sweat biomarkers offer critical insights for early disease prediction and diagnosis. Integration of multiple modalities in a single stretchable sensor to simultaneously detect these stimuli would provide a more comprehensive understanding of human physiology, which, however, has yet to be achieved. Here, this work reports, for the first time, a stretchable multimodal photonic sensor capable of simultaneously detecting and discriminating strain deformations, temperature, and sweat pH. The multimodal sensing abilities are enabled by realization of multiple sensing mechanisms in a hydrogel-coated polydimethylsiloxane (PDMS) optical fiber (HPOF), featured with high flexibility, stretchability, and biocompatibility. The integrated mechanisms are designed to operate at distinct wavelengths to facilitate stimuli decoupling and employ a ratiometric detection strategy for improved robustness and accuracy. To simplify sensor interrogation, spectrally-resolved multiband emissions are generated upon the excitation of a single-wavelength laser, utilizing upconversion luminescence (UCL) and radiative energy transfer (RET) processes. As proof of concept, this work demonstrates the feasibility of simultaneous monitoring of the heartbeat, respiration, body temperature, and sweat pH of a person in real-time, with only a single sensor.

The Effects of Previous Amenorrhea on Endothelial and Vascular Function

Introduction: Endogenous estrogen has a protective cardiovascular effect. Estrogen loss, such as during menopause and amenorrhea, results in stiffer vessels and endothelial dysfunction. It is unknown if reversing amenorrhea and regaining a regular menstrual cycle leads to the restoration of cardiovascular function. Methods: Sixteen women were divided into groups: eumenorrheic (n = 10; 23 ± 3 years) women who had a consistent menstrual cycle and amenorrheic (n = 6; 22 ± 1 year) women who previously were without their menstrual cycle for at least 6 consecutive months. Endothelial function, arterial stiffness, and brachial and aortic blood pressure were assessed. Results: There were no differences between groups in endothelial function or arterial stiffness measures. The previously amenorrheic group displayed lower brachial systolic and mean pressures and aortic systolic, diastolic, and mean pressures. When controlling for physical activity, only central pressure remained significantly lower in the amenorrheic group. Conclusions: Previous amenorrhea in young women does not result in long-term cardiovascular consequences in arterial and endothelial function measures assuming regular menstruation resumes. Physical activity shows a blood pressure-lowering effect in the peripheral arteries, while the previously amenorrheic group demonstrated lower central pressures, independent of physical activity.

Different effects of mechano- and metaboreflex on the central blood pressure waveform

Introduction

The effect of mechanoreflex on central blood pressure (BP) is unclear, although the influence of metaboreflex has been investigated. A relatively small contribution of the mechanoreflex to the pressor response to exercise has been considered in humans because many studies have failed to isolate the mechanoreflex-mediated pressor response. In a recent study, we successfully isolated a mechanoreflex-mediated pressor response using static passive stretching (SPS) in the forearm. Thus, it is possible to isolate the effect of the mechanoreflex on the central BP using this recently developed method. We investigated the effect of muscle mechanoreflex on central BP and compared the changes in the shape of the central BP waveform during mechanoreflex and metaboreflex.

Methods

We measured 12 healthy males (age, 26 ± 2 years; height, 171.1 ± 5.2 cm; body mass, 63.3 ± 10.3 kg; body fat, 16.7% ± 3.9%; means ± standard deviation [SD]) in this study. All participants performed static passive stretching (SPS) of the forearm for 60 s to isolate the muscle mechanoreflex. They also performed 120 s of isometric handgrip (IHG) at 30% maximal voluntary contraction and underwent 180 s of post-exercise ischemia (PEI) to isolate the muscle metaboreflex. The carotid BP (cBP) waveform was obtained from the right common carotid artery as the central BP waveform. We evaluated the first systolic peak (P1) and second systolic peak (P2) from the cBP waveform.

Results

SPS increased cBP with an increase in P1 (p < 0.05), whereas PEI increased cBP with an increase in P2 (p < 0.05). SPS did not alter augmentation pressure (AP) (p > 0.05), whereas PEI increased it (p < 0.05). The relative change from rest (Δ) in P1 during SPS was positively correlated with that in stroke volume (r = 0.68; p < 0.05), and the ΔAP during PEI was positively correlated with that in total peripheral resistance TPR (r = 0.61; p < 0.05).

Conclusion

These results suggest different effects of mechano- and metaboreflex on the change in shape of the central BP waveform; mechanoreflex and metaboreflex deform P1 and P2, respectively.

Developing technologies to assess vascular ageing: a roadmap from VascAgeNet

Vascular ageing (vascular ageing) is the deterioration of arterial structure and function which occurs naturally with age, and which can be accelerated with disease. Measurements of vascular ageing are emerging as markers of cardiovascular risk, with potential applications in disease diagnosis and prognosis, and for guiding treatments. However, vascular ageing is not yet routinely assessed in clinical practice. A key step towards this is the development of technologies to assess vascular ageing. In this Roadmap, experts discuss several aspects of this process, including: measurement technologies; the development pipeline; clinical applications; and future research directions. The Roadmap summarises the state of the art, outlines the major challenges to overcome, and identifies potential future research directions to address these challenges.

Ultra-Stretchable Composite Organohydrogels Polymerized Based on MXene@Tannic Acid-Ag Autocatalytic System for Highly Sensitive Wearable Sensors

Conductive hydrogels have attracted widespread attention in the fields of biomedicine and health monitoring. However, their practical application is severely hindered by the lengthy and energy-intensive polymerization process and weak mechanical properties. Here, a rapid polymerization method of polyacrylic acid/gelatin double-network organohydrogel is designed by integrating tannic acid (TA) and Ag nanoparticles on conductive MXene nanosheets as catalyst in a binary solvent of water and glycerol, requiring no external energy input. The synergistic effect of TA and Ag NPs maintains the dynamic redox activity of phenol and quinone within the system, enhancing the efficiency of ammonium persulfate to generate radicals, leading to polymerization within 10 min. Also, ternary composite MXene@TA-Ag can act as conductive agents, enhanced fillers, adhesion promoters, and antibacterial agents of organohydrogels, granting them excellent multi-functionality. The organohydrogels exhibit excellent stretchability (1740%) and high tensile strength (184 kPa). The strain sensors based on the organohydrogels exhibit ultrahigh sensitivity (GF = 3.86), low detection limit (0.1%), and excellent stability (>1000 cycles, >7 days). These sensors can monitor the human limb movements, respiratory and vocal cord vibration, as well as various levels of arteries. Therefore, this organohydrogel holds potential for applications in fields such as human health monitoring and speech recognition.

High-Performance Supercapacitive Pressure Sensors via Height-Grading Micro-Domes of Ionic Conductive Elastomer

Soft capacitive sensors present numerous appealing characteristics, including simple structure, low power consumption, and fast response. However, they often suffer from low sensitivity and a limited linear sensing range. Herein, a concept is presented to enhance the sensitivity and linearity of supercapacitive pressure sensors by functionally grading the heights of macrodomes constructed from a highly elastic and ionic conductive elastomer made of poly(vinyl alcohol) and phosphoric acid (PVA/H3PO4). The resultant supercapacitive sensors exhibit a high sensitivity (423.42 kPa-1), wide linear sensing range (0-400 kPa), ultralow limit of detection (0.48 Pa), and high durability (stable signal outputs up to 5000 cycles of loading/unloading). Additionally, the sensors can maintain consistent sensing performance within a temperature range of 25-40 °C. The potential of the sensor in health monitoring is demonstrated through ultrahigh-resolution weight measurement, pulse detection, and respiration monitoring.

Ultrathin crystalline silicon-based omnidirectional strain gauges for implantable/wearable characterization of soft tissue biomechanics

Monitoring soft-tissue biomechanics is of interest in biomedical research and clinical treatment of diseases. An important focus is biointegrated strain gauges that track time-dependent mechanics of targeted tissues with deforming surfaces over multidirections. Existing methods provide limited gauge factors, tailored for sensing within specific directions under quasi-static conditions. We present development and applicability of implantable/wearable strain gauges that integrate multiple ultrathin monocrystalline silicon-based sensors aligned with different directions, in stretchable formats for dynamically monitoring direction angle-sensitive strain. We experimentally and computationally establish operational principles, with theoretical systems that enable determination of intensities and direction of applied strains at an omnidirectional scale. Wearable evaluations range from cardiac pulse to intraocular pressure monitoring of eyeballs. The device can evaluate cardiac disorders of myocardial infarction and hypoxia of living rats and locate the pathological orientation associated with infarction, in designs with possibilities as biodegradable implants for stable operation. These findings create clinical significance of the devices for monitoring complex dynamic biomechanics.

Pilot study on the effect of flavonoids on arterial stiffness and oxidative stress in chronic kidney disease

BACKGROUND

Flavonoids, the main class of polyphenols, exhibit antioxidant and antihypertensive properties.

AIM

To prospectively investigate the impact of flavonoids on arterial stiffness in patients with chronic kidney disease (CKD) stages I-IV.

METHODS

In this prospective, single-arm study, CKD patients with arterial hypertension and diabetes mellitus were enrolled. Baseline demographic, clinical, and laboratory variables were recorded. Patients received daily treatment with a phenol-rich dietary supplement for 3 months. Blood pressure, arterial stiffness (carotid-femoral pulse wave velocity, central pulse pressure), and oxidative stress markers (protein carbonyls, total phenolic compound, total antioxidant capacity) were measured at baseline and at study end.

RESULTS

Sixteen patients (mean age: 62.5 years, 87.5% male) completed the study. Following intervention, peripheral systolic blood pressure decreased significantly by 14 mmHg (P < 0.001). Carotid-femoral pulse wave velocity decreased from 8.9 m/s (baseline) to 8.2 m/s (study end) (P < 0.001), and central pulse pressure improved from 59 mmHg to 48 mmHg (P = 0.003). Flavonoids also reduced oxidative stress markers including protein carbonyls (P < 0.001), total phenolic compound (P = 0.001), and total antioxidant capacity (P = 0.013).

CONCLUSION

Flavonoid supplementation in CKD patients shows promise in improving blood pressure, arterial stiffness, and oxidative stress markers.

MXenes for Wearable Physical Sensors toward Smart Healthcare

The gradual rise of personal healthcare awareness is accelerating the deployment of wearable sensors, whose ability of acquiring physiological vital signs depends on sensing materials. MXenes have distinct chemical and physical superiorities over other 2D nanomaterials for wearable sensors. This review presents a comprehensive summary of the latest advancements in MXenes-based materials for wearable physical sensors. It begins with an introduction to special structural features of MXenes for sensing performance, followed by an in-depth exploration of versatile functionalities. A detailed description of different sensing mechanisms is also included to illustrate the contribution of MXenes to the sensing performance and its improvement. In addition, the real-world applications of MXenes-based physical sensors for monitoring different physiological signs are included as well. The remaining challenges of MXenes-based materials for wearable physical sensors and their promising opportunities are finally narrated, in conjunction with a prospective for future development.

E-Selectin and Asymmetric Dimethylarginine Levels in Adult Cyanotic Congenital Heart Disease: Their Relation to Biochemical Parameters, Vascular Function, and Clinical Status

Background and Aim: Patients with cyanosis secondary to congenital heart disease (CHD) are characterized by erythrocytosis and increased blood viscosity, which contribute to endothelial dysfunction, increased arterial stiffness, and impaired vascular function, which may affect the final clinical presentation. Asymmetric dimethylarginine (ADMA) and e-selectin (e-sel) are valuable biomarkers for endothelial and vascular dysfunction. Their concentration levels in blood serum have the potential to be an accessible tool that reflects the severity of the disease. We aimed to assess e-sel and ADMA levels and their relationship with the clinical status and endothelial and vascular function. Methods: A cross-sectional study, including 36 adult CHD cyanotic patients [(17 males) (42.3 ± 16.3 years)] with an arterial blood oxygen saturation less than 92% and 20 healthy controls [(10 males) (38.2 ± 8.5 years)], was performed. All the patients underwent a clinical examination, blood testing, and cardiopulmonary tests. Their endothelial function was assessed using the intima media thickness and flow-mediated dilatation. Vascular function, using applanation tonometry methods, was determined using the aortic systolic pressure, aortic pulse pressure, augmentation pressure, augmentation index, pulse pressure amplification, and pulse wave velocity. Results: The concentrations of e-sel and ADMA were significantly higher in the patients with CHD. The E-sel levels correlated positively with red blood cells, hemoglobin concentration, hematocrit, and augmentation pressure; they correlated negatively with blood oxygen saturation, the forced expiratory one-second volume, forced vital capacity, and oxygen uptake. The ADMA levels were found to correlate only with age. Conclusions: The E-sel level, unlike ADMA concentration, reflects the severity of erythrocytosis and hypoxia and, thus, the physical status of patients with cyanotic CHD.

Changes of pulse wave transit time after haemodynamic manoeuvres in healthy adults: a prospective randomised observational trial (PWTT volunteer study)

Background

Pulse wave transit time (PWTT) shows promise for monitoring intravascular fluid status intraoperatively. Presently, it is unknown how PWTT mirrors haemodynamic variables representing preload, inotropy, or afterload.

Methods

PWTT was measured continuously in 24 adult volunteers. Stroke volume was assessed by transthoracic echocardiography. Volunteers underwent four randomly assigned manoeuvres: 'Stand-up' (decrease in preload), passive leg raise (increase in preload), a 'step-test' (adrenergic stimulation), and a 'Valsalva manoeuvre' (increase in intrathoracic pressure). Haemodynamic measurements were performed before and 1 and 5 min after completion of each manoeuvre. Correlations between PWTT and stroke volume were analysed using the Pearson correlation coefficient.

Results

'Stand-up' caused an immediate increase in PWTT (mean change +55.9 ms, P-value <0.0001, 95% confidence interval 46.0-65.7) along with an increase in mean arterial pressure and heart rate and a drop in stroke volume (P-values <0.0001). Passive leg raise caused an immediate drop in PWTT (mean change -15.4 ms, P-value=0.0024, 95% confidence interval -25.2 to -5.5) along with a decrease in mean arterial pressure (P-value=0.0052) and an increase in stroke volume (P-value=0.001). After 1 min, a 'step-test' caused no significant change in PWTT measurements (P-value=0.5716) but an increase in mean arterial pressure and heart rate (P-values <0.0001), without changes in stroke volume (P-value=0.1770). After 5 min, however, PWTT had increased significantly (P-value <0.0001). Measurements after the Valsalva manoeuvre caused heterogeneous results.

Conclusion

Noninvasive assessment of PWTT shows promise to register immediate preload changes in healthy adults. The clinical usefulness of PWTT may be hampered by late changes because of reasons different from fluid shifts.

Clinical trial registration

German clinical trial register (DRKS, ID: DRKS00031978, https://www.drks.de/DRKS00031978).

The Impact of Cardiopulmonary Rehabilitation on Ventriculoarterial Coupling in Post-Coronavirus Disease-2019 Patients

PURPOSE

Coronavirus disease-2019 (COVID-19) affects the cardiovascular system even after the acute phase of the disease. Cardiopulmonary rehabilitation may improve post-COVID-19 symptoms. This study aims to evaluate the impact of a cardiopulmonary rehabilitation program after acute COVID-19 on arterial stiffness, left ventricular function, and ventriculoarterial coupling (VAC).

METHODS

Forty-eight adults were examined 1 (T0) and 3-mo (T1) following recovery from COVID-19 and randomized 1:1 to participate or not in a 3-mo rehabilitation program. Matched subjects were enrolled as a non-COVID-19 group. Arterial stiffness was evaluated by carotid-femoral pulse wave velocity (PWV). Left ventricular (LV) systolic performance was evaluated with global longitudinal strain (GLS). The PWV/LV-GLS ratio was calculated as an index of VAC. High-sensitivity C reactive protein (hs-CRP) was measured.

RESULTS

At T0, convalescent patients with COVID-19 had impaired PWV ( P = .001) and reduced VAC ( P = .001) compared to non-COVID-19 subjects. PWV (8.15 ± 1.37 to 6.55 ± 0.98 m/sec, P < .001) and LV-GLS (-19.67 ± 1.98 to -21.3 ± 1.93%, P < .001) improved only in convalescent patients with COVID-19 undergoing rehabilitation. Similarly, VAC was only improved in the rehabilitation group (-0.42 ± 0.11 to -0.31 ± 0.06 m · sec -1  ·% -1 , P < .001). A significant improvement in VO 2max was noted after rehabilitation (15.70 [13.05, 21.45] to 18.30 [13.95, 23.75] ml · kg -1  · min -1 , P = .01). Finally, hs-CRP was improved in both groups with a significantly greater improvement in the rehabilitation group.

CONCLUSION

A 3-mo rehabilitation program in convalesced patients with COVID-19 enhances the recovery of arterial stiffness, left ventricular function, and VAC, highlighting the beneficial mechanisms of rehabilitation in this patient population.

A Flexible Skin Bionic Thermally Comfortable Wearable for Machine Learning-Facilitated Ultrasensitive Sensing

Tremendous popularity is observed for multifunctional flexible electronics with appealing applications in intelligent electronic skins, human-machine interfaces, and healthcare sensing. However, the reported sensing electronics, mostly can hardly provide ultrasensitive sensing sensitivity, wider sensing range, and robust cycling stability simultaneously, and are limited of efficient heat conduction out from the contacted skin interface after wearing flexible electronics on human skin to satisfy thermal comfort of human skin. Inspired from the ultrasensitive tactile perception microstructure (epidermis/spinosum/signal transmission) of human skin, a flexible comfortably wearable ultrasensitive electronics is hereby prepared from thermal conductive boron nitride nanosheets-incorporated polyurethane elastomer matrix with MXene nanosheets-coated surface microdomes as epidermis/spinosum layers assembled with interdigitated electrode as sensing signal transmission layer. It demonstrates appealing sensing performance with ultrasensitive sensitivity (≈288.95 kPa-1), up to 300 kPa sensing range, and up to 20 000 sensing cycles from obvious contact area variation between microdome microstructures and the contact electrode under external compression. Furthermore, the bioinspired electronics present advanced thermal management by timely efficient thermal dissipation out from the contacted skin surface to meet human skin thermal comfort with the incorporated thermal conductive boron nitride nanosheets. Thus, it is vitally promising in wearable artificial electronic skins, intelligent human-interactive sensing, and personal health management.

Marangoni-driven deterministic formation of softer, hollow microstructures for sensitivity-enhanced tactile system

Microengineering the dielectric layers with three-dimensional microstructures has proven effective in enhancing the sensitivity of flexible pressure sensors. However, the widely employed geometrical designs of solid microstructures exhibit limited sensitivity over a wide range of pressures due to their inherent but undesired structural compressibility. Here, a Marangoni-driven deterministic formation approach is proposed for fabricating hollow microstructures, allowing for greater deformation while retarding structural stiffening during compression. Fluid convective deposition enables solute particles to reassemble in template microstructures, controlling the interior cavity with a void ratio exceeding 90%. The hollow micro-pyramid sensor exhibits a 10-fold sensitivity improvement across wider pressure ranges over the pressure sensor utilizing solid micro-pyramids, and an ultra-low detect limit of 0.21 Pa. With the advantages of facilitation, scalability, and large-area compatibility, such an approach for hollow microstructures can be expanded to other sensor types for superior performance and has considerable potential in robotic tactile and epidermal devices.

Development of Highly Flexible Piezoelectric PVDF-TRFE/Reduced Graphene Oxide Doped Electrospun Nano-Fibers for Self-Powered Pressure Sensor

The demand for self-powered, flexible, and wearable electronic devices has been increasing in recent years for physiological and biomedical applications in real-time detection due to their higher flexibility and stretchability. This work fabricated a highly sensitive, self-powered wearable microdevice with Poly-Vinylidene Fluoride-Tetra Fluoroethylene (PVDF-TrFE) nano-fibers using an electrospinning technique. The dielectric response of the polymer was improved by incorporating the reduced-graphene-oxide (rGO) multi-walled carbon nano-tubes (MWCNTs) through doping. The dielectric behavior and piezoelectric effect were improved through the stretching and orientation of polymeric chains. The outermost layer was attained by chemical vapor deposition (CVD) of conductive polymer poly (3,4-ethylenedioxythiophene) to enhance the electrical conductivity and sensitivity. The hetero-structured nano-composite comprises PVDF-TrFE doped with rGO-MWCNTs over poly (3,4-ethylenedioxythiophene) (PEDOT), forming continuous self-assembly. The piezoelectric pressure sensor is capable of detecting human physiological vital signs. The pressure sensor exhibits a high-pressure sensitivity of 19.09 kPa-1, over a sensing range of 1.0 Pa to 25 kPa, and excellent cycling stability of 10,000 cycles. The study reveals that the piezoelectric pressure sensor has superior sensing performance and is capable of monitoring human vital signs, including heartbeat and wrist pulse, masticatory movement, voice recognition, and eye blinking signals. The research work demonstrates that the device could potentially eliminate metallic sensors and be used for early disease diagnosis in biomedical and personal healthcare applications.

Investigating the relationship between early cardiovascular disease markers and loneliness in young adults

Loneliness is recognised as a risk factor for cardiovascular disease development. However, it is unclear whether loneliness itself or other closely related mental health symptoms, such as depression and social anxiety, are associated with the development of cardiovascular disease. In the present study, we examined the relationship between loneliness and several early cardiovascular disease markers in young adults, after controlling for depression and social anxiety. Sixty-six young adults (18-35 years old, Mage = 22.70; 75.8% females) completed psychological questionnaires and took part in several physiological tests assessing cardiovascular health (e.g., vascular function). Results revealed higher loneliness was significantly associated with shorter pulse transit time (β = - 0.70, p = 0.002; shorter pulse transit time is a subclinical marker for arterial stiffness). Additionally, results show that while loneliness and depression were both related to vascular dysfunction in young adults, the underlining physiological mechanisms through which they affect vascular function may be different. Specifically, higher loneliness was associated with increased arterial stiffness, whereas depression was associated with increased endothelial dysfunction (β = - 0.43, p = 0.04). Our findings indicate that presence of loneliness and depression in young adults may be accompanied by early indicators of poor cardiovascular health, such as arterial stiffness and endothelial dysfunction. Results from the study further support the link between loneliness and cardiovascular disease development.

A Novel Hollow Graphene/Polydimethylsiloxane Composite for Pressure Sensors with High Sensitivity and Superhydrophobicity

Flexible pressure sensors have attracted great interest as they play an important role in various fields such as health monitoring and human-machine interactions. The design of the pressure sensors still faces challenges in achieving a high sensitivity for a wide sensing range, and the interference of water restricts the applications of the sensors. Herein, we developed a graphene-polydimethylsiloxane film combining a hierarchical surface with nanowrinkles on it and a hollow structure. The microstructure design of the composite can be facilely controlled to improve the sensing and hydrophobic performance by tailoring the microsphere building units. Attributed to the irregular surface and hollow structure of the sensing layer, the optimized sensor exhibits a superior sensitivity of 1085 kPa-1 in a 50 kPa linear range. For practical applications, the nanowrinkles on the surface of the microspheres and the polymer coating endow the composite with waterproof properties. Inspired by the dual receptors of the skin, two designed microstructured films can simply integrate into one with double-sided microstructures. The sensing performance and the water-repellence property allow the sensor to detect physiological signals under both ambient and underwater conditions. Furthermore, underwater stimuli detection and communication are demonstrated. This method of fabricating a flexible sensor shows great potential in wearable and robotic fields.

Determinants of hand pulse wave velocity and hand pulse transit time in healthy adults

Arterial pulse wave velocity (PWV) is recognized as a convenient method to assess peripheral vascular stiffness. This study explored the clinical characteristics of hand PWV (hPWV) and hand pulse transit time (hPTT) in healthy adults (sixty males = 42.4 ± 13.9 yrs; sixty-four females = 42.8 ± 13.9 yrs) voluntarily participated in this study. The arterial pulse waveform and the anatomical distance from the radial styloid process to the tip of the middle finger of both hands were recorded in the sitting position. The hPWV was calculated as the traversed distance divided by hPTT between those two points. Male subjects showed significantly greater hPWV, systolic blood pressure, and pulse pressure than age-matched female subjects, while the hPTT was not significantly different between genders. Multiple linear regression analysis showed that gender is a common determinant of hPWV and hPTT, and that age and heart rate (HR) were negatively correlated with hPWV and hPTT, respectively. We conclude that male subjects have greater hPWV than female subjects. Ageing is associated with decreased hPWV, while increased HR is associated with a smaller hPTT. The hPWV and hPTT might be used as non-invasive indices to characterise the ageing and arterial stiffness of peripheral blood vessels.

Artery Pulse Waveform Acquired with a Fabry-Perot Interferometer

For most patients admitted to a hospital, it is a requirement to continuously monitor their vital signs. Among these are the waveforms from ECG and the pulmonary arterial pulse. At present, there are several electronic devices that can measure the arterial pulse waveform. However, they can be affected by electromagnetic wave radiation, and the fabrication of electronic sensors is complicated and contributes to the e-waste, among other problems. In this paper, we propose an optical method to measure arterial pulse based on a Fabry-Perot interferometer composed of two mirrors. A pulse sensor formed by an acrylic cell with a thin membrane is used to gather the vasodilatation of the wrist, forming an air pulse that is enacted by means of a tube to a metallic cell containing a mirror that is glued to a thin silicone membrane. When the air pulse arrives, a displacement of the mirror takes place and produces a shift of the interference pattern fringes given by the Fabry-Perot. A detector samples the fringe intensity. With this method, an arterial pulse waveform is obtained. We characterize this optical device as a test of concept, and its application to measuring artery pulse is presented. The optical device is compared to other electronic devices.

Flow in temporally and spatially varying porous media: a model for transport of interstitial fluid in the brain

Flow in a porous medium can be driven by the deformations of the boundaries of the porous domain. Such boundary deformations locally change the volume fraction accessible by the fluid, creating non-uniform porosity and permeability throughout the medium. In this work, we construct a deformation-driven porous medium transport model with spatially and temporally varying porosity and permeability that are dependent on the boundary deformations imposed on the medium. We use this model to study the transport of interstitial fluid along the basement membranes in the arterial walls of the brain. The basement membrane is modeled as a deforming annular porous channel with the compressible pore space filled with an incompressible, Newtonian fluid. The role of a forward propagating peristaltic heart pulse wave and a reverse smooth muscle contraction wave on the flow within the basement membranes is investigated. Our results identify combinations of wave amplitudes that can induce either forward or reverse transport along these transport pathways in the brain. The magnitude and direction of fluid transport predicted by our model can help in understanding the clearance of fluids and solutes along the Intramural Periarterial Drainage route and the pathology of cerebral amyloid angiopathy.

N-Terminal Pro-Brain Type Natriuretic Peptide Predicts Cardiovascular Events Independently of Arterial Stiffness, Assessed By Carotid-to-Femoral Pulse Wave Velocity, in Apparently Healthy Subjects

AIM

This study aimed to evaluate whether N-terminal pro-brain natriuretic peptide (NT-proBNP) and carotid-to-femoral pulse wave velocity (PWV) carried independent prognostic value in predicting cardiovascular events in apparently healthy individuals beyond traditional risk factors.

METHODS

A total of 1,872 participants aged 41, 51, 61, or 71 years from the MONItoring of trends and determinants in CArdiovascular disease (MONICA) study were included. Traditional risk factors were assessed, including: smoking status; mean systolic and diastolic blood pressure; body mass index; fasting plasma glucose; serum triglycerides; total, high-density, and low-density lipoprotein cholesterol; NT-proBNP; and PWV. The principal endpoint that was assessed during 16 years of follow-up was a composite of major adverse cardiovascular events (MACE). The secondary endpoints were cardiovascular mortality (CVM), hospitalisation for coronary artery disease (CAD), and a composite of hospitalisation for heart failure (HF) or atrial fibrillation (AF).

RESULTS

At baseline, NT-proBNP was associated with PWV (β=0.14; p<0.001), but not after adjustment for traditional risk factors (β=-0.01; p=0.67). In models including traditional risk factors and PWV, NT-proBNP was associated with all four outcomes (HRMACE=1.33, 95% CI 1.16-1.52; HRCVM=2.02, 95% CI 1.65-2.48; HRCAD=1.29, 95% CI 1.07-1.55; and HRHF or AF=1.79, 95% CI 1.40-2.28). In the same model, PWV was only associated with CVM (HRCVM=1.20, 95% CI 1.01-1.41). No interactions between NT-proBNP and PWV were found. N-terminal pro-brain natriuretic peptide significantly improved net reclassification (NRI) for MACE (NRI=0.12; p=0.03), CVM (NRI=0.33; p<0.001), and HF or AF (NRI=0.33; p<0.001) beyond traditional risk factors, while PWV did not aid in net reclassification improvement for any endpoint.

CONCLUSIONS

In apparently healthy individuals, NT-proBNP and PWV predicted cardiovascular events independently. N-terminal pro-brain natriuretic peptide improved reclassification for the prediction of MACE, CVM, and hospitalisation for HF or AF beyond traditional risk factors, while PWV did not.

Sensitive, Robust, Wide-Range, and High-Consistency Capacitive Tactile Sensors with Ordered Porous Dielectric Microstructures

Flexible capacitive tactile sensors show great promise in personalized healthcare monitoring and human-machine interfaces, but their practical application is normally hindered because they rarely possess the required comprehensive performance, that is, high pressure sensitivity and fast response within a broad pressure range, high structure robustness, performance consistency, etc. This paper aims to engineer flexible capacitive pressure sensors with highly ordered porous dielectric microstructures and a 3D-printing-based fully solution-processable fabrication process. The proposed dielectric layer with uniformly distributed interior microporous can not only increase its compressibility and dynamic response within an extended pressure range but also enlarge its contact area with electrodes, contributing to a simultaneous improvement in the sensitivity, response speed, detection range, and structure robustness. Meanwhile, owing to its superior abilities in complex structure manufacturing and dimension controlling, the proposed 3D-printing-based fabrication process enables the consistent fabrication of the porous microstructure and thus guarantees device consistency. As a result, the prepared pressure sensors exhibit a high sensitivity of 0.21 kPa-1, fast response and relaxation times of 112 and 152 ms, an interface bonding strength of more than 455.2 kPa, and excellent performance consistency (≤5.47% deviation among different batches of sensors) and tunability. Encouraged by this, the pressure sensor is further integrated with a wireless readout circuit and realizes wireless wearable monitoring of various biosignals (pulse waves and heart rate) and body movements (from slight finger touch to large knee bending). Finally, the influence law of the feature parameters of the porous microstructure on device performance is established by the finite element method, paving the way for sensor optimization. This study motivates the development of flexible capacitive pressure sensors toward practical application.

A review of nanomaterials for biosensing applications

A biosensor is a device that reacts with the analyte to be analyzed, detects its concentration, and generates readable information, which plays an important role in medical diagnosis, detection of physiological indicators, and disease prevention. Nanomaterials have received increasing attention in the fabrication and improvement of biosensors due to their unique physicochemical and optical properties. In this paper, the properties of nanomaterials such as the size effect, optical and electrical properties, and their advantages in the field of biosensing are briefly summarized, and the application of nanomaterials can effectively improve the sensitivity and reduce the detection limit of biosensors. The advantages of commonly used nanomaterials such as gold nanoparticles (AuNPs), carbon nanotubes (CNTs), quantum dots (QDs), graphene, and magnetic nanobeads for biosensor applications are also reviewed. Besides, the two main types of biosensors using nanomaterials involved in their construction and their working principles are described, and the toxicity and biocompatibility of nanomaterials and the future direction of nanomaterial biosensors are discussed.

High-Fidelity, Low-Hysteresis Bionic Flexible Strain Sensors for Soft Machines

Stretchable flexible strain sensors based on conductive elastomers are rapidly emerging as a highly promising candidate for popular wearable flexible electronic and soft-mechanical sensing devices. However, due to the intrinsic limitations of low fidelity and high hysteresis, existing flexible strain sensors are unable to exploit their full application potential. Herein, a design strategy for a successive three-dimensional crack conductive network is proposed to cope with the uncoordinated variation of the output resistance signal arising from the conductive elastomer. The electrical characteristics of the sensor are dominated by the successive crack conductive network through a greater resistance variation and a concise sensing mechanism. As a result, the developed elastomer bionic strain sensors exhibit excellent sensing performance in terms of a smaller overshoot response, a lower hysteresis (∼2.9%), and an ultralow detection limit (0.00179%). What's more, the proposed strategy is universal and applicable to many conductive elastomers with different conductive fillers (including 0-D, 1-D, and 2-D conductive fillers). This approach improves the sensing signal accuracy and reliability of conductive elastomer strain sensors and holds promising potential for various applications in the fields of e-skin and soft robotic systems.

Validation of Noninvasive Derivation of the Central Aortic Pressure Waveform from Fingertip Photoplethysmography Using a Novel Selective Transfer Function Method

Introduction

Central aortic pressure waveform analyses can provide clinically relevant information beyond conventional brachial blood pressure (BP) assessment. This waveform can be reproduced noninvasively through application of a generalized transfer function (GTF) on a peripheral waveform, as conventionally performed by applanation tonometry. Photoplethysmography (PPG) is an alternate approach; however, differences in measurement site and modality demand the use of a transfer function (TF) specific for those differences. This study aimed to compare central aortic waveform features generated from radial tonometry (reference) using a proprietary GTF with a central aortic waveform and its features generated from a simultaneous fingertip PPG measurement using a selective method where one of three different TFs is chosen based on the input signal harmonic profile.

Methods

Brachial BP was measured in triplicate under resting conditions and was used for subsequent calibration. Multiple simultaneous radial tonometry (SphygmoCor CVMS) and fingertip PPG measurements were then performed in individual participants (n = 21, 10 females, age: 39 ± 16 years). Measurements were converted into central aortic waveforms with their respective TFs. Twenty central aortic pressure waveform parameters were compared through correlation analysis, Bland-Altman plots, and a repeated measure mixed-effects ANOVA model. Central aortic waveform shape was compared using the root-mean-squared error (RMSE).

Results

Correlation (r) of PPG-derived parameters with radially tonometry-derived central aortic parameters was high ranging from 0.79 to 0.99. Mean differences of pressure-related parameters were within 1.3 mm Hg, and differences of time-related parameters ranged from -2.2 to 3.4%. While some parameters were statistically different, these differences are not physiologically meaningful. Central aortic waveform shape had an average RMSE of 1.8 ± 0.9%.

Conclusion

Fingertip PPG-derived central aortic waveform parameters using a novel selective TF were comparable to central aortic waveform features derived from radial tonometry using a previously validated GTF.

Evidence of increased vascular stiffness and left ventricular hypertrophy in children with cystic kidney disease

BACKGROUND

Cardiovascular disease (CVD) is the most common cause of mortality in chronic kidney disease (CKD). Children with early-onset CKD arguably experience the greatest lifetime CVD burden. We utilized data from the Chronic Kidney Disease in Children Cohort Study (CKiD) to evaluate two pediatric CKD cohorts: congenital anomalies of the kidney and urinary tract (CAKUT) and cystic kidney disease for CVD risks and outcomes.

METHODS

CVD risk factors and outcomes including blood pressures, left ventricular hypertrophy (LVH), left ventricular mass index (LVMI), and ambulatory arterial stiffness index (AASI) scores were evaluated.

RESULTS

Forty-one patients in the cystic kidney disease group were compared to 294 patients in the CAKUT group. Cystic kidney disease patients had higher cystatin-C levels, despite similar iGFR. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) indexes were higher in the CAKUT group, but a significantly higher proportion of cystic kidney disease patients was on anti-hypertensive medications. Cystic kidney disease patients had increased AASI scores and a higher incidence of LVH.

CONCLUSIONS

This study provides a nuanced analysis of CVD risk factors and outcomes including AASI and LVH in two pediatric CKD cohorts. Cystic kidney disease patients had increased AASI scores, higher incidence of LVH, and higher rates of anti-hypertensive medication use which could imply a greater burden of CVD despite similar GFR. Our work suggests that additional mechanisms may contribute to vascular dysfunction in cystic kidney disease, and that these patients may need additional interventions to prevent the development of CVD. A higher resolution version of the Graphical abstract is available as Supplementary information.

Cardiovascular variations in patients with major depressive disorder versus bipolar disorder

BACKGROUND

Differentiating depression in major depressive disorder and bipolar disorder is challenging in clinical practice. Therefore, reliable biomarkers are urgently needed to differentiate between these diseases. This study's main objective was to assess whether cardiac autonomic function can distinguish patients with unipolar depression (UD), bipolar depression (BD), and bipolar mania (BM).

METHODS

We recruited 791 patients with mood disorders, including 191 with UD, 286 with BD, and 314 with BM, who had been drug free for at least 2 weeks. Cardiovascular status was measured using heart rate variability (HRV) and pulse wave velocity (PWV) indicators via finger photoplethysmography during a 5-min rest period.

RESULTS

Patients with BD showed lower HRV but higher heart rates than those with UD and BM. The PWV indicators were lower in the UD group than in the bipolar disorder group. The covariates of age, sex, and body mass index affected the cardiovascular characteristics. After adjusting for covariates, the HRV and PWV variations among the three groups remained significant. Comparisons between the UD and BD groups showed that the variable with the largest effect size was the frequency-domain indices of HRV, very low and high frequency, followed by heart rate. The area under the receiver operating characteristic curve (AUC) for each cardiovascular variable ranged from 0.661 to 0.714. The High-frequency index reached the highest AUC.

LIMITATIONS

Cross-sectional design and the magnitude of heterogeneity across participants with mood disorders limited our findings.

CONCLUSION

Patients with BD, but not BM, had a greater extent of cardiac imbalance than those with UD. Thus, HRV may serve as a psychophysiological biomarker for the differential diagnosis of UD and BD.

Age and vascular aging: an unexplored frontier

Vascular age is an emerging field in cardiovascular risk assessment. This concept includes multifactorial changes in the arterial wall, with arterial stiffness as its most relevant manifestation, leading to increased arterial pressure and pulsatile flow in the organs. Today, the approved test for measuring vascular age is pulse wave velocity, which has been proven to predict cardiovascular events. Furthermore, vascular phenotypes, such as early vascular aging and "SUPERNOVA," representing phenotypic extremes of vascular aging, have been found. The identification of these phenotypes opens a new field of study in cardiovascular physiology. Lifestyle interventions and pharmacological therapy have positively affected vascular health, reducing arterial stiffness. This review aims to define the concepts related to vascular age, pathophysiology, measurement methods, clinical signs and symptoms, and treatment.

Rationally designed cellulose hydrogel for an ultrasensitive pressure sensor

Flexible pressure sensors with high sensitivity are required in fields such as human-machine interactions, electronic skin, and health tracking. In this work, we reported cellulose ion-conductive hydrogel (ICH) rationally designed from both nano and micron perspectives for ultrasensitive pressure sensors, via a zero-waste approach, without involving soft components. By introducing low molecular weight cellulose and using the idea of a rough surface, the piezocapacitive sensitivity of the ICH was increased from 0.04 kPa-1 to 89.81 kPa-1 in increments of 2245, which also has a high degree of transparency, excellent durability, and good electrical transmission. Moreover, the ICH demonstrated great potential as sensors and arrays practicable in various industries, including medical treatment and motion recognition. The design is also applicable for piezoresistive tactile sensors, which realize enhanced sensitivity. This affordable, effective, and environmentally friendly technology definitely offers novel perspectives and the potential to enhance the functionality of flexible pressure sensors.

Signatures of obstructions and expansions in the arterial frequency response

BACKGROUND AND OBJECTIVE

The blood pressure and flow waveforms carry valuable information about the condition of the cardiovascular system and a patient's health. Waveform analysis in health and pathological conditions can be performed in the time or frequency domains; the information to be emphasised defines the use of either domain. However, physicians are more familiar with the time domain, and the changes in the waveforms due to cardiovascular diseases and ageing are better characterised in such domain. On the other hand, the analysis of the vascular and geometrical variables determining the signatures in the frequency response of local vascular anomalies, such as aneurysms and stenoses, has not been thoroughly explored. This paper aims to characterise the signatures of obstructions (stenoses) and expansions (aneurysms) in the frequency response of tapered arteries.

METHODS

The first step in our methodology was to incorporate the viscous response of the arterial wall into a one-dimensional elastic formulation that solves the governing equations in the frequency domain. As a second step, we imposed a volumetric flow excitation in arteries simulating the aorta with increasing geometry complexity: from straight to tapered arteries with local expansions or obstructions; and we assessed the frequency response.

RESULTS

We found that the obstructions and expansions cause characteristic signatures in an artery's frequency response that are distinguishable from a health condition. The signatures of obstruction and expansions differ; the obstructions increase the magnitude of fundamental frequency and work as a close boundary condition. On the other hand, the expansions diminish the fundamental frequency and work as an open boundary condition. Furthermore, such signatures correlate to the distance between the artery's inlet and the anomaly's starting point and have the potential to pinpoint abnormalities non-invasively.

CONCLUSIONS

We found that the obstructions and expansions cause characteristic signatures in an artery's frequency response that have the potential to detect and follow up on the development of vascular abnormalities. For the latter purpose, constant monitoring may be required; despite this not being a common clinical practice, the new wearable technology offers the possibility of continuous monitoring of biophysical markers such as the pressure waveform.

Aortic blood pressure and pulse wave indices responses to exercise in peripheral artery disease

Peripheral artery disease (PAD) refers to obstructed blood flow in peripheral arteries typically due to atherosclerotic plaques. How PAD alters aortic blood pressure and pressure wave propagation during exercise is unclear. Thus, this study examined central blood pressure responses to plantar flexion exercise by investigating aortic pulse wave properties in PAD. Thirteen subjects with PAD and 13 healthy [age-, sex-, body mass index (BMI) matched] subjects performed rhythmic plantar flexion for 14 min or until fatigue (20 contractions/min; started at 2 kg with 1 kg/min increment up to 12 kg). Brachial (oscillometric cuff) and radial (SphygmoCor) blood pressure and derived-aortic waveforms were analyzed during supine rest and plantar flexion exercise. At rest, baseline augmentation index (P = 0.0263) and cardiac wasted energy (P = 0.0321) were greater in PAD due to earlier arrival of the reflected wave (P = 0.0289). During exercise, aortic blood pressure (aMAP) and aortic pulse pressure showed significant interaction effects (P = 0.0041 and P = 0.0109, respectively). In particular, PAD had a greater aMAP increase at peak exercise (P = 0.0147). Moreover, the tension time index was greater during exercise in PAD (P = 0.0173), especially at peak exercise (P = 0.0173), whereas the diastolic time index (P = 0.0685) was not different between the two groups. Hence, during exercise, the subendocardial viability ratio was lower in PAD (P = 0.0164), especially at peak exercise (P = 0.0164). The results suggest that in PAD, the aortic blood pressure responses and myocardial oxygen demand during exercise are increased compared with healthy controls.

Reliable and Scalable Piezoresistive Sensors with an MXene/MoS2 Hierarchical Nanostructure for Health Signals Monitoring

The increased popularity of wearable electronic devices has led to a greater need for advanced sensors. However, fabricating pressure sensors that are flexible, highly sensitive, robust, and compatible with large-scale fabrication technology is challenging. This work investigates a piezoresistive sensor constructed from an MXene/MoS2 hierarchical nanostructure, which is obtained through an easy and inexpensive fabrication process. The sensor exhibits a high sensitivity of 0.42 kPa-1 (0-1.5 kPa), rapid response (∼36 ms), and remarkable mechanical durability (∼10,000 cycles at 13 kPa). The sensor has been demonstrated to be successful in detecting human motion, speech recognition, and physiological signals, particularly in analyzing human pulse. These data can be used to alert and identify irregularities in human health. Additionally, the sensing units are able to construct sensor arrays of various sizes and configurations, enabling pressure distribution imaging in a variety of application scenarios. This research proposes a cost-effective and scalable approach to fabricating piezoresistive sensors and sensor arrays, which can be utilized for monitoring human health and for use in human-machine interfaces.

Robust and flexible smart silk/PEDOT conductive fibers as wearable sensor for personal health management and information transmission

Flexible highly conductive fibers have attracted much attention due to their great potential in the field of wearable electronic devices. In this work, silk/PEDOT conductive fibers with a resistivity of 1.73 Ω·cm were obtained by oxidizing Ce3+ with H2O2 under alkaline conditions to produce CeO2 and further promote the in-situ polymerization of 3,4-ethylenedioxythiophene (EDOT) on the surface of silk fibers. The morphology and chemical composition of the silk/PEDOT conductive fibers were characterized and the results confirmed that a large amount of polythiophene was synthesized and deposited on the surface of silk fibers. The conductivity and electrochemical property stability of the silk/PEDOT conductive fibers were evaluated by soaping and organic solvent immersion, and the conductive silk fibers exhibited excellent environmental stability and durability. The silk/PEDOT conductive fibers show good pressure sensing and strain sensing performance, which exhibits high sensitivity, fast response and cyclability, and have excellent applications in personal health monitoring, human-machine information transmission, etc.

Response of cardiac pulse parameters in humans at various inclinations via 360° rotating platform for simulated microgravity perspective

On the Earth, the human body is designed and adapted to function under uniform gravitational acceleration. However, exposure to microgravity or weightlessness as experienced by astronauts in space causes significant alterations in the functioning of the human cardiovascular system. Due to limitations in using real microgravity platforms, researchers opted for various ground-based microgravity analogs including head-down tilt (HDT) at fixed inclination. However, in the present study, an investigation of response of various cardiac parameters and their circulatory adaptation in 18 healthy male subjects was undertaken by using an indigenously developed 360° rotating platform. Cardiac pulse was recorded from 0° to 360° in steps of 30° inclination using piezoelectric pulse sensor (MLT1010) and associated cardiac parameters were analyzed. The results showed significant changes in the pulse shape while an interesting oscillating pattern was observed in associated cardiac parameters when rotated from 0° to 360°. The response of cardiac parameters became normal after returning to supine posture indicating the ability of the cardiovascular system to reversibly adapt to the postural changes. The observed changes in cardiac parameters at an inclination of 270°, in particular, were found to be comparable with spaceflight studies. Based on the obtained results and the proposed extended version of fluid redistribution mechanism, we herewith hypothesize that the rotation of a subject to head down tilt inclination (270°) along with other inclinations could represent a better microgravity analog for understanding the cumulative cardiac response of astronauts in space, particularly for short duration space missions.

Tofogliflozin long-term effects on atherosclerosis progression and major clinical parameters in patients with type 2 diabetes mellitus lacking a history of cardiovascular disease: a 2-year extension study of the UTOPIA trial

BACKGROUND

This study aimed to assess the long-term effects of tofogliflozin, a sodium-glucose cotransporter 2 (SGLT2) inhibitor, on atherosclerosis progression and major clinical parameters in patients with type 2 diabetes lacking an apparent history of cardiovascular disease.

METHODS

This was a prospective observational 2-year extension study of the "Using TOfogliflozin for Possible better Intervention against Atherosclerosis for type 2 diabetes patients (UTOPIA)" trial, a 2-year randomized intervention study. The primary endpoints represented changes in the carotid intima-media thickness (IMT). Secondary endpoints included brachial-ankle pulse wave velocity (baPWV) and biomarkers for glucose metabolism, lipid metabolism, renal function, and cardiovascular risks.

RESULTS

The mean IMT of the common carotid artery (IMT-CCA) significantly decreased in both the tofogliflozin (- 0.067 mm, standard error 0.009, p < 0.001) and conventional treatment groups (- 0.080 mm, SE 0.009, p < 0.001) throughout the follow-up period; however, no significant intergroup differences in the changes (0.013 mm, 95% confidence interval (CI) - 0.012 to 0.037, p = 0.32) were observed in a mixed-effects model for repeated measures. baPWV significantly increased in the conventional treatment group (82.7 ± 210.3 cm/s, p = 0.008) but not in the tofogliflozin group (- 17.5 ± 221.3 cm/s, p = 0.54), resulting in a significant intergroup difference in changes (- 100.2 cm/s, 95% CI - 182.8 to - 17.5, p = 0.018). Compared to the conventional treatment group, tofogliflozin significantly improved the hemoglobin A1c and high-density lipoprotein cholesterol levels, body mass index, abdominal circumference, and systolic blood pressure. The frequencies of total and serious adverse events did not vary significantly between the groups.

CONCLUSIONS

Tofogliflozin was not associated with improved inhibition of carotid wall thickening but exerted long-term positive effects on various cardiovascular risk factors and baPWV while showing a good safety profile.

A Review of Epidermal Flexible Pressure Sensing Arrays

In recent years, flexible pressure sensing arrays applied in medical monitoring, human-machine interaction, and the Internet of Things have received a lot of attention for their excellent performance. Epidermal sensing arrays can enable the sensing of physiological information, pressure, and other information such as haptics, providing new avenues for the development of wearable devices. This paper reviews the recent research progress on epidermal flexible pressure sensing arrays. Firstly, the fantastic performance materials currently used to prepare flexible pressure sensing arrays are outlined in terms of substrate layer, electrode layer, and sensitive layer. In addition, the general fabrication processes of the materials are summarized, including three-dimensional (3D) printing, screen printing, and laser engraving. Subsequently, the electrode layer structures and sensitive layer microstructures used to further improve the performance design of sensing arrays are discussed based on the limitations of the materials. Furthermore, we present recent advances in the application of fantastic-performance epidermal flexible pressure sensing arrays and their integration with back-end circuits. Finally, the potential challenges and development prospects of flexible pressure sensing arrays are discussed in a comprehensive manner.

Multifunctional Starch-Based Sensor with Non-Covalent Network to Achieve "3R" Circulation

With the consumption of disposable electronic devices increasing, it is meaningful but also a big challenge to develop reusable and sustainable materials to replace traditional single-use sensors. Herein, a clever strategy for constructing a multifunctional sensor with 3R circulation (renewable, reusable, pollution-reducing biodegradable) is presented, in which silver nanoparticles (AgNPs) with multiple interactions are introduced into a reversible non-covalent cross-linking network composed of biocompatible and degradable carboxymethyl starch (CMS) and polyvinyl alcohol (PVA) to simultaneously obtain high mechanical conductivity and long-term antibacterial properties by a one-pot method. Surprisingly, the assembled sensor shows high sensitivity (gauge factor up to 4.02), high conductivity (0.1753 S m^-1 ), low detection limit (0.5%), long-term antibacterial ability (more than 7 days), and stable sensing performance. Thus, the CMS/PVA/AgNPs sensor can not only accurately monitor a series of human behavior, but also identify handwriting recognition from different people. More importantly, the abandoned starch-based sensor can form a 3R circulation. Especially, the fully renewable film still shows excellent mechanical performance, achieving reusable without sacrificing its original function. Therefore, this work provides a new horizon for multifunctional starch-based materials as sustainable substrates for replacing traditional single-use sensors.

Emerging sensing and modeling technologies for wearable and cuffless blood pressure monitoring

Cardiovascular diseases (CVDs) are a leading cause of death worldwide. For early diagnosis, intervention and management of CVDs, it is highly desirable to frequently monitor blood pressure (BP), a vital sign closely related to CVDs, during people's daily life, including sleep time. Towards this end, wearable and cuffless BP extraction methods have been extensively researched in recent years as part of the mobile healthcare initiative. This review focuses on the enabling technologies for wearable and cuffless BP monitoring platforms, covering both the emerging flexible sensor designs and BP extraction algorithms. Based on the signal type, the sensing devices are classified into electrical, optical, and mechanical sensors, and the state-of-the-art material choices, fabrication methods, and performances of each type of sensor are briefly reviewed. In the model part of the review, contemporary algorithmic BP estimation methods for beat-to-beat BP measurements and continuous BP waveform extraction are introduced. Mainstream approaches, such as pulse transit time-based analytical models and machine learning methods, are compared in terms of their input modalities, features, implementation algorithms, and performances. The review sheds light on the interdisciplinary research opportunities to combine the latest innovations in the sensor and signal processing research fields to achieve a new generation of cuffless BP measurement devices with improved wearability, reliability, and accuracy.

Reproduction of human blood pressure waveform using physiology-based cardiovascular simulator

This study presents a cardiovascular simulator that mimics the human cardiovascular system's physiological structure and properties to reproduce the human blood pressure waveform. Systolic, diastolic blood pressures, and its waveform are key indicators of cardiovascular health. The blood pressure waveform is closely related to the pulse wave velocity and the overlap of the forward and reflected pressure waves. The presented cardiovascular simulator includes an artificial aorta made of biomimetic silicone. The artificial aorta has the same shape and stiffness as the human standard and is encased with a compliance chamber. The compliance chamber prevents distortion of the blood pressure waveform from strain-softening by applying extravascular pressure. The blood pressure waveform reproduced by the simulator has a pressure range of 80-120 mmHg, a pulse wave velocity of 6.58 m/s, and an augmentation index of 13.3%. These values are in the middle of the human standard range, and the reproduced blood pressure waveform is similar to that of humans. The errors from the human standard values are less than 1 mmHg for blood pressure, 0.05 m/s for pulse wave velocity, and 3% for augmentation index. The changes in blood pressure waveform according to cardiovascular parameters, including heart rate, stroke volume, and peripheral resistance, were evaluated. The same pressure ranges and trends as in humans were observed for systolic and diastolic blood pressures according to cardiovascular parameters.

Ultrasensitive Linear Capacitive Pressure Sensor with Wrinkled Microstructures for Tactile Perception

Ultrasensitive flexible pressure sensors with excellent linearity are essential for achieving tactile perception. Although microstructured dielectrics have endowed capacitive sensors with ultrahigh sensitivity, the compromise of sensitivity with increasing pressure is an issue yet to be resolved. Herein, a spontaneously wrinkled MWCNT/PDMS dielectric layer is proposed to realize the excellent sensitivity and linearity of capacitive sensors for tactile perception. The synergistic effect of a high dielectric constant and wrinkled microstructures enables the sensor to exhibit linearity up to 21 kPa with a sensitivity of 1.448 kPa-1 and a detection limit of 0.2 Pa. Owing to these merits, the sensor monitors subtle physiological signals such as various arterial pulses and respiration. This sensor is further integrated into a fully multimaterial 3D-printed soft pneumatic finger to realize material hardness perception. Eight materials with different hardness values are successfully discriminated, and the capacitance of the sensor varies linearly (R2 > 0.975) with increasing hardness. Moreover, the sensitivity to the material hardness can be tuned by controlling the inflation pressure of the soft finger. As a proof of concept, the finger is used to discriminate pork fats with different hardness, paving the way for hardness discrimination in clinical palpation.

Recent Development of Mechanical Stimuli Detectable Sensors, Their Future, and Challenges: A Review

By virtue of their wide applications in transportation, healthcare, smart home, and security, development of sensors detecting mechanical stimuli, which are many force types (pressure, shear, bending, tensile, and flexure) is an attractive research direction for promoting the advancement of science and technology. Sensing capabilities of various force types based on structural design, which combine unique structure and materials, have emerged as a highly promising field due to their various industrial applications in wearable devices, artificial skin, and Internet of Things (IoT). In this review, we focus on various sensors detecting one or two mechanical stimuli and their structure, materials, and applications. In addition, for multiforce sensing, sensing mechanism are discussed regarding responses in external stimuli such as piezoresistive, piezoelectric, and capacitance phenomena. Lastly, the prospects and challenges of sensors for multiforce sensing are discussed and summarized, along with research that has emerged.

Switching ultra-stretchability and sensitivity in metal films for electronic skins: a pufferfish-inspired, interlayer regulation strategy

The booming development of electronic skins necessitates stretchable electrodes and flexible sensors that exhibit distinctly opposite requirements of electromechanical properties, both of which are difficult to be fulfilled on a single material. Here, a pufferfish-inspired, interlayer regulation strategy is proposed that realizes the above opposite properties in simple metal films, exhibiting either ultra-stretchability (295% strain) or sensitivity (maximum GF: ∼5500) on demand. It is revealed that the stretchability of the intrinsically strain-sensitive metal films can be improved by ∼20-fold via regulating the surface morphology of the inserted interlayer, accompanied by an intriguing transition in film cracking behavior from cut-through cracks to network patterns. By featuring these two antithetical but valuable properties, common metal films can be applied as diverse sensors and stretchable electrodes in electronic skins, showing application prospects in healthcare monitoring, human-machine interaction, and engineering services. Our proposed strategy substantially advances the application of metal film conductors in flexible electronics and broadens the horizons for developing more sophisticated electronic skins by interlayer engineering.

Engineering Smart Composite Hydrogels for Wearable Disease Monitoring

Growing health awareness triggers the public's concern about health problems. People want a timely and comprehensive picture of their condition without frequent trips to the hospital for costly and cumbersome general check-ups. The wearable technique provides a continuous measurement method for health monitoring by tracking a person's physiological data and analyzing it locally or remotely. During the health monitoring process, different kinds of sensors convert physiological signals into electrical or optical signals that can be recorded and transmitted, consequently playing a crucial role in wearable techniques. Wearable application scenarios usually require sensors to possess excellent flexibility and stretchability. Thus, designing flexible and stretchable sensors with reliable performance is the key to wearable technology. Smart composite hydrogels, which have tunable electrical properties, mechanical properties, biocompatibility, and multi-stimulus sensitivity, are one of the best sensitive materials for wearable health monitoring. This review summarizes the common synthetic and performance optimization strategies of smart composite hydrogels and focuses on the current application of smart composite hydrogels in the field of wearable health monitoring.

Multichannel Flexible Pulse Perception Array for Intelligent Disease Diagnosis System

Pressure sensors with high sensitivity, a wide linear range, and a quick response time are critical for building an intelligent disease diagnosis system that directly detects and recognizes pulse signals for medical and health applications. However, conventional pressure sensors have limited sensitivity and nonideal response ranges. We proposed a multichannel flexible pulse perception array based on polyimide/multiwalled carbon nanotube-polydimethylsiloxane nanocomposite/polyimide (PI/MPN/PI) sandwich-structure pressure sensor that can be applied for remote disease diagnosis. Furthermore, we established a mechanical model at the molecular level and guided the preparation of MPN. At the structural level, we achieved high sensitivity (35.02 kPa-1) and a broad response range (0-18 kPa) based on a pyramid-like bilayer microstructure with different upper and lower surfaces. A 27-channel (3 × 9) high-density sensor array was integrated at the device level, which can extract the spatial and temporal distribution information on a pulse. Furthermore, two intelligent algorithms were developed for extracting six-dimensional pulse information and automatic pulse recognition (the recognition rate reaches 97.8%). The results indicate that intelligent disease diagnosis systems have great potential applications in wearable healthcare devices.

Ultrasensitive Ionic Liquid Polymer Composites with a Convex and Wrinkled Microstructure and Their Application as Wearable Pressure Sensors

The development of pressure sensors with high sensitivity and effectiveness that exhibit linearity over a wide pressure range is crucial for wearable devices. In this study, we fabricated a novel ionic liquid (IL)/polymer composite with a convex and randomly wrinkled microstructure in a cost-effective and facile manner using an opaque glass and stretched polydimethylsiloxane template. The fabricated IL/polymer composite was used as the dielectric layer in a capacitive pressure sensor. The sensor exhibited a high linear sensitivity of 56.91 kPa^-1 owing to the high interfacial capacitance formed by the electrical double layer of the IL/polymer composite over a relatively wide range (0-80 kPa). We also demonstrated the sensor performance for various applications such as a glove-attached sensor, sensor array, respiration monitoring mask, human pulse, blood pressure measurement, human motion detection, and a wide range of pressure sensing. It would be expected that the proposed pressure sensor has sufficient potential for use in wearable devices.