Advances in Flexible and Wearable Electronics for Continuous Human Health Monitoring

Abstract

Wearable electronics have emerged as a pivotal technology in healthcare, offering non‑invasive, real‑time monitoring of vital physiological parameters. By leveraging soft, skin‑conformable substrates, these devices capture data such as pulse, temperature, and glucose levels, enabling proactive health management. This review surveys the most widely used sensor types—force, temperature, biochemical, and multifunctional—detailing their operating principles, structural innovations, and recent breakthroughs. We also discuss critical functional modules, including self‑powered sources and signal‑processing units, that enhance practicality. Finally, we outline the remaining challenges and prospective research directions that will propel wearable health monitoring toward mainstream adoption.

Introduction

Since the advent of silicon‑based semiconductors in the 1950s, the electronics industry has been reshaped by continuous innovation. Yet, the rigidity of conventional silicon devices limits their integration into flexible, wearable formats required for personalized health care. Flexible and wearable electronics—crafted from elastomeric, textile, or biocompatible materials—offer unmatched conformability, low weight, and durability, making them ideal for continuous physiological monitoring.

Increasingly, these devices provide real‑time data on heart rate, respiration, temperature, and biochemical markers, enabling timely alerts for clinicians and users alike. Their versatility extends to applications such as electronic skin, motion capture, and telemedicine, positioning them as a cornerstone of next‑generation healthcare.

Recent advances in materials, fabrication techniques, and sensing mechanisms have driven performance improvements across sensor categories. Figure 1 illustrates the evolution of wearable sensors for health monitoring and summarizes the key design strategies explored in this review.

A visual summary of recent development of wearable electronics for monitoring human health information

Flexible Force Sensors

Force sensors translate mechanical stimuli—tension, pressure, strain—into electrical signals. Conventional metal or semiconductor force sensors are bulky and rigid, limiting their use in wearables. In contrast, elastomeric substrates (e.g., PDMS, PU, SEBS) yield flexible, transparent, and stretchable sensors that can be seamlessly integrated into clothing or directly onto skin.

These sensors are categorized into resistive, capacitive, and piezoelectric types, each with distinct advantages.

Resistive Force Sensors

Resistive sensors detect changes in electrical resistance caused by deformation. Active materials often combine conductive fillers—graphene, carbon nanotubes, metallic nanowires, or conductive polymers—within an elastomer matrix. Resistance variations arise from geometry changes, filler separation, or interfacial contact shifts. Piezoresistive designs are prized for low power consumption and straightforward fabrication.

Microstructured elastomeric substrates, such as micropyramid arrays, dramatically enhance sensitivity by amplifying deformation at the conductive network. For instance, Choong et al. demonstrated a micropyramid PDMS array that achieved a ten‑fold increase in pressure sensitivity. However, traditional mold fabrication is costly, prompting alternative low‑cost templating methods like silk or natural leaves.

Incorporating porous conductive networks—formed by embedding microcapsules or carbonized tissue—creates a 3‑D network that deforms more readily under load, further boosting sensitivity and response speed. Wang et al. leveraged sunflower pollen microcapsules to fabricate a hollow‑sphere composite that exhibited superior strain and pressure detection on a human finger or throat.

Capacitive Force Sensors

Capacitive sensors measure changes in capacitance due to variations in dielectric thickness or electrode area. Using flexible dielectric layers (PDMS, SEBS) and conductive electrodes (CNTs, Ag nanowires), these devices offer high sensitivity and low detection limits. Microstructuring either the dielectric or the electrodes further improves performance by increasing compressibility and introducing controllable air voids that modulate permittivity under load.

Integrating organic field‑effect transistors (OFETs) with microstructured dielectrics yields ultrahigh sensitivity (8.4 kPa⁻¹) and rapid (<10 ms) response, ideal for pulse wave detection. Despite their strengths, capacitive sensors can suffer from nonlinearity and parasitic capacitance, which require careful circuit design.

Piezoelectric Force Sensors

Piezoelectric sensors convert mechanical deformation into voltage. Materials such as P(VDF‑TrFE), ZnO nanowires, and PZT nanostructures are frequently employed. P(VDF‑TrFE) offers excellent flexibility and a large piezoelectric coefficient, enabling detection of minute pressures (≈0.1 Pa) in applications like robotic touch sensing.

While piezoelectric sensors excel at capturing dynamic events, they cannot detect static pressure due to the lack of continuous voltage output. Hybrid designs—e.g., PTNWs/graphene heterostructures—convert strain‑induced polarization changes into carrier mobility variations, enabling static pressure measurement with enhanced sensitivity.

a Fabrication process of micropyramid PDMS array. b Sensing principle under external force. c Sensitivity comparison. d Linear pressure response. Adapted from ref. 10.

a Hollow‑sphere mechanism. b Transient response comparison. c Relaxation time. d Stability test. e SEM of carbon paper. f Breath monitoring. g Gesture monitoring. Adapted from ref. 63.

Flexible Temperature Sensors

Accurate skin‑temperature monitoring is vital for early detection of fever, anemia, or other systemic conditions. Flexible temperature sensors fall into resistive, pyroelectric, and thermistor categories.

Resistive Temperature Sensors

These sensors rely on the temperature coefficient of resistance (TCR) of metal or carbon‑based composites. Strategies to overcome limited stretchability include wrinkle‑buckled films, horseshoe structures, and rigid‑island designs, achieving strain tolerances up to 30% with minimal performance loss. PEDOT:PSS–CNT composites and graphene‑based thermistors offer higher TCRs (0.25–0.63 %/°C) and intrinsic stretchability, though strain‑induced resistance changes still pose a challenge.

Advanced differential circuit designs, such as those using SWCNT transistors, suppress strain‑induced threshold voltage shifts, enabling accurate temperature readouts up to 50% strain. Gated devices based on R‑GO/PU composites have demonstrated superior sensitivity (1.34 %/°C) compared to resistive counterparts.

Pyroelectric Temperature Sensors

Pyroelectric materials (PZT, LiTaO₃, PVDF‑TrFE) generate surface charges in response to temperature changes. Flexible pyroelectric OFETs, incorporating P(VDF‑TrFE) with BaTiO₃ nanoparticles, can distinguish temperature effects from mechanical strain, enabling reliable sensing under complex deformation states.

a Unstructured vs. microstructured PDMS. b Response comparison. c Sensitivity testing. d Low‑pressure sensitivity. e Response under 1 Pa. Adapted from ref. 18.

a Microhair structure. b SEM of microhair arrays. c–f Radial artery test results. Adapted from ref. 54.

Flexible Physiological Biochemical Sensors

Non‑invasive monitoring of biochemical markers—glucose, electrolytes, lactate—has become feasible with flexible electrochemical platforms. These sensors exploit chemical reactions between analytes and recognition layers, converting them into measurable electrical changes.

Chen et al. introduced a skin‑level biosensor that uses subcutaneous electrochemical twin channels (ETCs) to draw blood glucose toward the skin surface, where it is detected by immobilized glucose oxidase. The sensor’s readings closely matched those of conventional glucometers over multi‑day testing.

For sweat analysis, Gao et al. fabricated a multifunctional patch incorporating separate micro‑electrodes for Na⁺, K⁺, glucose, and lactate. A flexible printed circuit board processed and wirelessly transmitted the data, enabling real‑time assessment of hydration and metabolic status.

a ETC schematic. b Biosensor on skin. c–d Glucose monitoring comparison. e–f Sweat sensor system. g–h Sweat analysis results. Adapted from refs. 48, 54.

Multifunctional Sensors

Combining strain, pressure, temperature, humidity, and gas sensing into a single, laminated e‑skin platform enables comprehensive physiological monitoring. Harada et al. demonstrated a triaxial tactile array and temperature sensor on a single print, while Ho et al. integrated graphene‑based humidity, thermal, and capacitive strain sensors into a 3 × 3 matrix.

These multilayer architectures preserve individual sensor specificity while minimizing crosstalk, a critical requirement for real‑world applications where multiple stimuli occur simultaneously.

a Multilayer sensor architecture. b 3 × 3 array image. c Fingerprint test results. d–e E‑skin schematic and circuit. f–h Performance of humidity, temperature, and pressure sensors. Adapted from ref. 55.

Functional Modules of Wearable Electronics

For a truly autonomous wearable system, power generation and data handling must be integrated into the device. Nanogenerators—based on triboelectric, piezoelectric, and pyroelectric effects—harvest mechanical or thermal energy from the body to power sensors or low‑power electronics.

Zi et al. presented a hybrid tribo‑pyro‑piezo cell that simultaneously harvests sliding motion and frictional heat, delivering sufficient voltage to drive LEDs and to sense subtle temperature or strain changes. Parallel studies have achieved high stretchability (up to 1160% strain) and transparency (>90%) in soft triboelectric generators, enabling seamless integration with skin or clothing.

Signal processing remains a bottleneck; most current systems pair flexible sensors with rigid silicon electronics. Emerging flexible printed circuit boards (FPCBs) and intrinsically stretchable ICs are beginning to bridge this gap, but challenges in full‑system integration—particularly in power management, real‑time data transmission, and form factor—persist.

a–d Hybrid cell structure. e Circuit integration. f LED illumination. g–h Temperature sensing schematic. i–j Measurement setup and force application. Adapted from ref. 56.

Conclusions and Outlook

Flexible and wearable electronics have matured into powerful tools for continuous health monitoring, thanks to advances in sensor sensitivity, durability, and integration. Yet several hurdles remain: accurate source‑discrimination of mechanical signals, simultaneous high stretchability and strain‑immune temperature sensing, improved biochemical accuracy, crosstalk‑free multifunctionality, and fully autonomous, in‑situ data processing.

1. Force sensors must reliably resolve pulse, muscle, and contact forces in a direction‑sensitive manner.

2. Temperature sensors should combine high stretchability, sensitivity, and strain decoupling.

3. Biochemical sensors require enhanced accuracy and deeper access to internal fluids, possibly via implantable or minimally invasive interfaces.

4. Multifunctional platforms must detect diverse stimuli without interference, demanding novel materials and architectures.

5. End‑to‑end integration of power, signal conditioning, and wireless transmission is essential for practical deployment.

Availability of Data and Materials

Not applicable.

Abbreviations

Au:

Aurum

Cu:

Cuprum

CVD:

Chemical vapor deposition

LED:

Light‑emitting diode

NW:

Nanowire

OFET:

Organic field‑effect transistor

P(VDF-TrFE):

Poly(vinylidenefluoride‑trifluoroethylene)

PAAm:

Polyacrylamide

PbTiO₃:

Lead titanate

PDMS:

Polydimethylsiloxane

Pt:

Platinum

PU:

Polyurethane

PZT:

Lead zirconate titanate

SEBS:

Styrene‑ethylene‑butylene‑styrene block copolymer

VHB:

Very high bond

ZnO:

Zinc oxide