Bioinspired leaf vein-architected gold nanowire ecoflexible biosensors for ultrasensitive occlusal force monitoring

Abstract

Flexible biosensors and bioelectronics for real-time healthcare monitoring require high sensitivity and durability, yet their high-cost materials and complex fabrication often hinder clinical translation. Emerging bio-templated electronics leverage evolutionarily optimized natural architectures to overcome these synthetic limitations. Here, we harness the bioinspired, hierarchical structure of natural leaf veins to create an ecoflexible, high-performance sensor, which feature a unique hierarchical, multibranching structure that enhances both mechanical performance and sensing efficiency. By integrating gold nanowires with the leaf vein framework through a gradient-decellularization process, we developed a sensor that demonstrates exceptional stretchability, sensitivity, and stability. The resulting piezoresistive sensor achieves a remarkable gauge factor (GF = 2.17 × 10²), a wide sensing range (∼60 kPa), and rapid response time (∼210 ms for response and ∼190 ms for recovery). Furthermore, it maintains excellent long-term stability, consistently performing over 1000 cycles at 40% strain. Such bioinspired leaf vein-architected gold nanowire ecoflexible biosensors offer a cost-effective, scalable solution for real-time occlusal force monitoring and broader medical applications, paving the way for multifunctional, flexible biosensors in wearable electronics and personalized healthcare.

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New concepts

We propose an ecoflexible biosensor that integrates the hierarchical architecture of leaf veins with gold nanowires, forming a high-performance, cost-effective sensing platform. Unlike traditional flexible electronics, which depend on synthetic materials and intricate fabrication processes, this approach exploits multibranched designs found in nature to enhance mechanical and sensing capabilities while streamlining production via gradient decellularization. This bio-templated strategy diverges from existing bioinspired sensors, which often prioritize sensitivity over scalability or durability, by achieving all three through a single, naturally derived framework. Our work demonstrates how evolutionary-optimized structures can synergistically enhance nanowire-based synthesis methods, offering a scalable solution for applications like occlusal force monitoring. For the field of sensing electrode materials design, this concept provides inspirational insight into leveraging leaf vein-architected templates to reduce fabrication complexity, blending ecological inspiration with nanomaterial functionality. It establishes a pathway for designing sustainable, multifunctional materials, broadening the scope of flexible electronics for healthcare and beyond.

Introduction

Wearable and flexible sensors have revolutionized healthcare monitoring, human–machine interfaces, and soft robotics by enabling real-time and non-invasive detection of biomechanical and physiological signals.^1–7 The growing demand for high-performance flexible sensors has led to extensive research on novel materials and device architectures that offer enhanced sensitivity, durability, and mechanical adaptability.^8–11 Among various strategies, nanomaterial-based flexible sensors have gained significant attention due to their ability to convert mechanical stimuli into electrical signals with high precision.^12–16 However, achieving a balance between flexibility, mechanical robustness, and long-term stability remains a key challenge in the development of next-generation wearable sensors.^17,18

A wide range of materials have been explored for flexible sensor fabrication, including carbon-based nanomaterials (e.g., graphene^19,20 and carbon nanotubes^21,22), conducting polymers (e.g., polyaniline and PEDOT:PSS),²³ and metallic nanostructures (e.g., silver nanowires,²⁴ platinum nanoparticles,²⁵ gold nanowires,^26–29 and gold nanoparticles³⁰). While carbon-based materials offer good flexibility and mechanical stability, they often suffer from lower electrical conductivity, requiring additional surface modifications to improve their performance. Conducting polymers exhibit excellent stretchability, but their electrical stability degrades over time. Among metallic nanomaterials, silver nanowires (AgNWs) are widely used due to their high conductivity and flexibility,³¹ but they are prone to oxidation and degradation, limiting their long-term reliability in practical applications.^32,33 Gold nanowires (AuNWs), on the other hand, provide an ideal alternative due to their superior electrical conductivity, chemical inertness, and biocompatibility.^34–37 Unlike AgNWs, AuNWs exhibit excellent resistance to oxidation and environmental degradation, ensuring stable electrical performance over prolonged use. Furthermore, the high aspect ratio of AuNWs facilitates the formation of highly conductive percolation networks, leading to enhanced strain sensitivity and lower detection limits. However, despite these advantages, the effective integration of AuNWs into flexible substrates remains a significant challenge, as conventional fabrication methods often lead to poor mechanical stability and inconsistent sensor performance under dynamic deformations.

To address these challenges, bioinspired strategies have emerged as promising approaches to enhance the mechanical robustness and sensitivity of flexible sensors.^38,39 Leaf vein structures, for instance, offer a lightweight, flexible scaffold with well-defined surface topographies that enhance nanomaterial deposition efficiency.^40,41 Several studies have explored the use of bioinspired architectures for flexible electronics. For example, the slits near the leg joints of spiders serve as highly sensitive mechanoreceptors, capable of detecting minute mechanical stress variations. Inspired by this natural mechanism, researchers have developed flexible sensors based on nanoscale crack junctions, achieving ultra-high sensitivity to strain and vibration.⁴² Despite these advances, the direct integration of plant-derived substrates with functional nanomaterials for biomechanical sensing remains largely unexplored, presenting an opportunity to bridge natural templates with advanced sensing technologies.

Herein, we present an ecoflexible biosensor inspired by leaf vein architectures and integrated with AuNWs, addressing critical needs for high sensitivity, stretchability, cost-effectiveness, and sustainability. The sensor employs gold nanostars (AuNSs) as nucleation sites to mediate the growth of vertically aligned AuNWs in a jellyfish-like configuration, ensuring robust structural stability and electrical performance. Additionally, the incorporation of polydimethylsiloxane (PDMS) enhances its overall mechanical properties, yielding exceptional sensitivity, rapid response, effective recovery, and long-term stability. Beyond its remarkable sensitivity and mechanical resilience, this sensor exhibits multifunctionality, functioning effectively as both a strain and pressure sensor. We validated its practical utility through real-time bite force monitoring, underscoring its potential as a cost-effective tool for early dental disease screening. Given its outstanding performance, this leaf vein-architected AuNW ecoflexible sensor holds significant promise for applications in oral medicine, particularly in addressing the demand for low-cost, high-efficiency diagnostic solutions with substantial clinical potential.

Results and discussion

Fabrication of the leaf vein-architected AuNW ecoflexible electrode

Leaf veins, as a natural three-dimensional (3D) vascular structure, possess advantages such as a high surface-to-volume ratio, transparency, breathability, and flexibility. The high surface-to-volume ratio provides a vast interface for material deposition, enhancing adhesion and facilitating efficient charge transport.⁴³ The structure of the leaf vein provides excellent flexibility, enabling it to conform to complex surface shapes while maintaining stable performance during deformation. The network structure of the leaf vein also provides a circular curved surface in contact with external pressure, thereby enhancing the interaction between the sensing material and external pressure and improving the signal response capability.^44–46 Therefore, the microfractals of leaf skeletons can serve as highly advantageous substrates for flexible electronics.

Compared to other flexible sensor substrates, the fabrication process of leaf vein materials is simple and cost-effective.⁴⁶ The leaf veins of Osmanthus fragrans were etched using a sodium hydroxide (NaOH) solution (Fig. S1, ESI†), effectively removing the mesophyll cells while preserving a well-defined three-dimensional network framework (Fig. S2, ESI†). During the etching process, the NaOH solution reacted with the cell walls of the leaf, causing the mesophyll cells to dissolve and ultimately leaving a robust leaf vein framework. Following etching, the treated leaf veins were naturally dried to ensure morphological stability and subsequently stored for future functionalization and application. To further enhance flexibility and facilitate nanowire growth, a uniform layer of PDMS was attached to the leaf vein. By employing a modified seed-mediated method, programmable growth of AuNWs was induced on the PDMS substrate, thereby fabricating the leaf vein-architected AuNW ecoflexible electrode (Fig. 1(a)). In brief, the process started with the O₂ plasma treatment of leaf veins, which were previously adhered to PDMS, to improve their hydrophilicity. This treatment could significantly improve the surface adhesion properties of the leaf veins. Next, the surface was functionalized with 3-aminopropyltriethoxysilane (APTES), resulting in an amino-exposed surface that provides stable binding sites for subsequent nanoparticle modification. Following this, surfactant-free gold nanostars, serving as seed nanoparticles, were covalently anchored onto the PDMS-coated leaf vein surface via Au–N bonds. This ensures a uniform distribution of gold nanostars, forming an ideal foundation for the growth of AuNWs. Subsequently, the gold nanostar-anchored leaf veins were carefully transferred onto a clean glass slide, providing a stable support platform for the controlled growth of AuNWs. Finally, PDMS was immersed in a growth solution containing gold precursors, ligands, and reducing agents, thereby initiating the growth of the AuNWs. After approximately 15 minutes, jellyfish-like AuNW structures successfully formed on the leaf veins (Fig. S3, ESI†).

Fig. 1 Fabrication of the leaf vein-architected AuNW ecoflexible electrode. (a) Schematic illustration of the fabrication process for the leaf vein-architected AuNW ecoflexible electrode. (b) Optical images of the unmodified leaf vein and leaf vein-architected AuNW ecoflexible electrode. (c) 3D Network structure of the leaf vein-architected AuNW ecoflexible electrode at different magnifications. Scale bars (left to right): 5 mm, 1 mm, and 500 μm.

Notably, a distinct chromatic distinction was observed between the unmodified leaf veins and the leaf vein-architected AuNW ecoflexible electrode (Fig. 1(b)). The leaf vein-architected AuNW ecoflexible electrode exhibited black coloration against a white background while manifesting a distinctive bronzed-gold hue against a black background (Fig. S4, ESI†). In contrast, the unmodified leaf veins retained their characteristic pale-yellow appearance (Fig. S3 and S4, ESI†). Furthermore, magnifying the leaf vein-architected AuNW ecoflexible electrode at different magnifications reveals an interconnected network structure, which accounts for its electrical conductivity (Fig. 1(c)). Those distinct optical behaviors demonstrate the successful integration and modification of the vascular structure by the jellyfish-like AuNWs. Moreover, despite the growth of AuNWs, the material retains exceptional flexibility, lightness, and thinness (Fig. 1(b) and Fig. S5 and S6, ESI†). These preserved characteristics render the modified structure highly suitable for applications demanding both adaptability and high performance.

Scanning electron microscopy (SEM) images (Fig. 2(a)–(f)) reveal the 3D layered structure of the leaf vein-architected AuNW ecoflexible electrode. The hierarchical architecture comprises distinct gold nanostructures: a top layer of gold nanostars superimposed over a bottom layer forming a densely packed gold nanowire array. Notably, the growth pattern of AuNWs on the leaf veins differs significantly from those reported on flat substrates. While flat films typically exhibit densely packed parallel nanowires, the leaf veins-supported nanowires demonstrate a unique curved growth mode, radiating outward from the branches of leaf veins with more prominent and larger interstitial gaps (Fig. 2(c)). Under pressure, the gold nanowires experience more noticeable changes, resulting in superior performance in pressure sensing compared to the flat-film grown gold nanowires. Additionally, the vein-like structure of the leaf facilitates the high-density attachment of AuNWs, which in turn enhances its strain sensing performance (Fig. 2(d) and (e)).

Fig. 2 Characterization of the leaf vein-architected AuNW ecoflexible electrode. (a)–(f) SEM images of the ecoflexible electrode at different magnifications. (g)–(l) EDS mapping of the leaf vein-architected AuNW ecoflexible electrode. (m) XRD spectrum of the leaf vein-architected AuNW ecoflexible electrode. (n) XPS spectrum of the leaf vein-architected AuNW ecoflexible electrode.

Fig. 2(f) further demonstrates the vertical alignment and density of the gold nanowires. The jellyfish-like AuNWs exhibit multiple individual AuNWs attached to a single gold nanostar, with an average nanowire length of approximately 1.5 μm. To further investigate the growth characteristics, we used 4 nm gold nanoparticles as seeds to induce the growth of jellyfish-like AuNWs on the leaf veins. In comparison, the leaf vein-architected AuNWs formed using 4 nm gold nanoparticles appeared gold-colored (Fig. S7, ESI†) but exhibited a relatively low sheet resistance of about 23.05 Ω sq⁻¹ (Fig. S8, ESI†). This low sheet resistance caused minimal changes in the electrical resistance under strain or pressure, resulting in poor sensor sensitivity. Through energy-dispersive X-ray spectroscopy (EDS) analysis, the relative composition and spatial distribution of the Au element within the leaf vein structure are comprehensively demonstrated (Fig. 2(g)–(l)). Furthermore, the X-ray diffraction (XRD) pattern displaying characteristic peaks of gold further confirms the growth of AuNWs on the leaf vein structure (Fig. 2(m)). X-ray photoelectron spectroscopy (XPS) analysis also provides additional evidence of the presence of AuNWs (Fig. 2(n)). It can be observed that the Au element constitutes the highest proportion and is uniformly distributed across the leaf vein network, which is closely related to the overall conductivity and sensitivity of the material.

Additionally, we investigated the growth of jellyfish-like AuNWs on various types of leaf veins and observed that robust and uniform growth was achieved across all examined leaf species. Upon visual inspection, the AuNWs on the leaf vein displayed a distinct black color against a white background (Fig. S9 and S10, ESI†), confirming the successful deposition and integration of the jellyfish-like AuNWs onto the leaf surface. This color contrast also suggests an efficient formation of the conductive network, which is critical for applications requiring high electrical conductivity.

To assess the potential of these gold wire-decorated leaf veins for practical applications, we performed gas permeability characterization. Remarkably, the leaf vein-architected AuNW ecoflexible electrode exhibited nearly 100% permeability (Fig. S11, ESI†), which indicates the retention of the intrinsic porosity of the leaf structure despite the gold wire deposition. This high permeability is particularly advantageous for applications in flexible and breathable electronic devices, where gas exchange or moisture diffusion is essential for maintaining performance and durability under varied environmental conditions. Furthermore, the near-perfect permeability suggests that the AuNW growth process maintains the integrity of the natural microstructure of the leaf, preserving both its functionality and the three-dimensional mesh structure of the leaf veins. These findings demonstrate the adaptability of AuNW growth on different leaf types, presenting a promising avenue for the development of sustainable materials with broad applications in flexible, transparent, and breathable sensor technologies.

Influence of Jellyfish-like AuNW growth time on mechanical properties

A systematic investigation was conducted to elucidate the correlation between growth time and the resultant electrical and mechanical properties of the AuNW-modified material. While the AuNW length substantially influences electrical conductivity, its impact on mechanical characteristics remains to be fully elucidated. To further explore this effect, the growth process was examined at five different time intervals: 3 min, 6 min, 9 min, 12 min, and 15 min. Electrical characterization revealed that jellyfish-like AuNWs grown for 3 minutes exhibited substantially high sheet resistance (3914.2 Ω sq⁻¹) (Fig. S12, ESI†), indicating poor conductivity. The sheet resistance demonstrated an exponential decay with increasing growth duration, reaching a plateau after approximately 9 min (Fig. S12, ESI†). SEM images revealed an evolution from initially sparse and truncated nanowires to progressively denser and elongated structures with extended growth periods. This observation corroborates the inverse relationship between growth duration and electrical resistance, where enhanced conductivity correlates with increased nanowire length (Fig. 3(a)–(f)).

Fig. 3 Performance characterization of the leaf vein-architected AuNW ecoflexible electrode/sensor. (a)–(f) SEM images of the leaf vein-architected AuNW ecoflexible electrode under varying growth time. (g)–(k) Optical images of the leaf vein-architected AuNW ecoflexible electrode under bending angles ranging from 0° to 720°. (l) Optical image of the leaf vein-architected AuNW ecoflexible electrode adhered to an arm. (m) Tensile stress–strain curves of the ecoflexible sensor under different AuNW growth time. (n) Tensile stress–strain curves of the leaf vein-architected AuNW ecoflexible sensor with different PDMS encapsulation thicknesses. (o) Relative resistance changes versus applied strains, with the GF calculated from the slopes of the curve under different strains.

We further investigated the mechanical properties and found that all growth time intervals allowed for significant bending of the leaf vein-architected AuNW ecoflexible electrode (Fig. 3(g)–(k)) while maintaining excellent flexibility and transparency (Fig. 3(l)). This demonstrates that the growth time has no impact on the intrinsic flexibility and transparency of the leaf vein-architected AuNW ecoflexible electrode. Subsequently, external copper wires were connected to the leaf vein-architected AuNW electrodes using silver paste, forming reliable electrical contacts (Fig. S13, ESI†). Then, these copper wire-connected electrodes, as well as unmodified leaf veins (not connected by copper wires), were encapsulated in PDMS to ensure structural integrity and facilitate subsequent testing (Fig. S14, ESI†). To ensure a uniform thickness, a spin-coating process was employed. As shown in Fig. 3(m), strain–stress curves indicated that the mechanical properties of the sensors were largely unaffected by the variation in AuNW growth time. To systematically assess the impact of AuNW modification on the mechanical behavior of leaf vein-architected AuNW ecoflexible sensors, a comparative study was conducted focusing on Young's modulus within a 50% tensile strain range, as well as tensile strength and elongation at break calculated from standard stress–strain curves. As shown in Fig. S15a (ESI†), the Young's modulus values for the unmodified and AuNW-modified samples remain nearly identical under 50% tensile strain, indicating that the inherent flexibility of the material is preserved after AuNW deposition. Moreover, both the tensile strength (Fig. S15b, ESI†) and elongation at break (Fig. S15c, ESI†) derived from the corresponding stress–strain curves exhibit no significant differences between the two groups, suggesting comparable strength and ductility under mechanical loading. In conclusion, these findings demonstrate that the integration of AuNWs enhances electrical functionality while preserving the intrinsic mechanical properties of natural leaf veins, thereby maintaining their inherent flexibility and toughness.

However, the presence of PDMS greatly enhanced the tensile properties of the leaf vein. To further explore the influence of PDMS thickness on the mechanical performance of the sensors, four different thickness gradients (1 mm, 1.25 mm, 1.5 mm, and 1.75 mm) were examined. The stress–strain curves demonstrated that as the PDMS thickness increased, the mechanical performance of the device gradually declined (Fig. 3(n)). Therefore, thinner PDMS encapsulation is preferred. However, excessive thinning may expose the surface of leaf veins, rendering the pressure sensing function ineffective. After careful consideration, we selected 1 mm as the optimal thickness, as it offers a balance between superior mechanical performance and effective pressure sensing with high sensitivity. In order to assess the reliability of the sensor under dynamic mechanical conditions, we examined its resistance behavior during a complete stretch-release cycle from 0% to 50% strain and back to 0% (Fig. S16, ESI†). The leaf vein-architected AuNW ecoflexible sensor exhibited favorable stability and mechanical reversibility. Notably, the resistance increased progressively during the stretching phase and decreased along a comparable path during the releasing phase, indicating relatively low hysteresis. Furthermore, this consistent electrical response implies that the conductive network remains intact and recoverable throughout deformation, highlighting the potential of the sensor for practical and repeatable strain sensing applications. We also measured the gauge factor (GF) of the leaf vein-architected AuNW ecoflexible sensor based on the formula: GF = (ΔR/R₀)/ε, where ΔR, R₀, and ε represent the resistance variation, the baseline resistance, and the applied strain, respectively. As shown in Fig. 3(o), the GF of the leaf vein-architected AuNW ecoflexible sensor increased progressively with strain, ultimately reaching a maximum value of 3.53 × 10⁴. However, mechanical failure had already occurred in the high-strain region, rendering the corresponding GF value unreliable. Therefore, we adopted the GF values calculated within the moderate strain range of 40–60%. A distinct two-stage response behavior is observed in Fig. S17 (ESI†): at small strains, a low GF of 1.4 is attributed to minor structural adjustments between adjacent conductive elements; as the strain exceeds the percolation threshold, a sharp transition occurs, leading to a high GF of 2.17 × 10² due to significant disruption of the conductive network. This two-stage response mechanism is clearly demonstrated in sensors based on natural leaf vein substrates, where the intrinsic hierarchical architecture offers a favorable framework for the strain-induced evolution of the conductive pathways.^47–49 To further investigate the advantages of natural leaf vein substrates over conventional ones, a comparative sensitivity test was conducted using a PDMS film-based substrate (Fig. S18, ESI†). Compared to the PDMS film-based sensor, the leaf vein-architected AuNW ecoflexible sensor exhibits a significantly higher resistance change under strain, particularly beyond 50% elongation. This enhanced sensitivity can be attributed to the intrinsic hierarchical porous structure of the leaf vein substrate,^50–52 which effectively amplifies the deformation-induced disruption within the gold nanowire network. In addition, the natural vein pathways facilitate more efficient strain transfer and localized stress concentration, resulting in a more pronounced electrical response.

Leaf vein-architected AuNW ecoflexible sensors for strain monitoring in human motion

To further explore the potential applications of the leaf vein-architected AuNW ecoflexible sensors in strain sensing, the encapsulated leaf vein-architected AuNW ecoflexible sensors were affixed to the human skin using adhesive tape, and a series of motion monitoring experiments, including both large-scale and subtle movements, were conducted (Fig. 4). The results presented in Fig. 4(a)–(d) demonstrate that the sensor is capable of accurately and real-time monitoring the bending angles of the finger, wrist, elbow, and knee joints with high sensitivity and precision. As the bending angle increases (from 30°, 60°, and 90° to 120°), the resistance change measured by the sensor shows a consistent and reproducible relationship with the angle increase, indicating that the sensor has rapid response capability and strong structural stability, making it effective for monitoring joint motion over a wide range of angles. Such strain-dependent resistance characteristics are well demonstrated in the current–voltage (I–V) profiles, as shown in Fig. S19 (ESI†). Under different tensile strains of 0%, 10%, 20%, 30%, and 40%, the leaf vein-architected AuNW ecoflexible sensor consistently exhibits linear I–V curves, indicating ohmic behavior across all tested conditions. This stable ohmic response reflects the preservation of both structural continuity and conductive network integrity during mechanical deformation. As the strain increases, a slight reduction in the slope of the I–V curves is observed, which can be attributed to the elongation and rearrangement of the conductive pathways. Nonetheless, the overall linearity remains intact, underscoring the excellent electrical reliability of the sensor under sustained strain. Such performance is particularly critical for high-fidelity flexible electronics, especially in real-time human motion monitoring applications.

Fig. 4 Application of the leaf vein-architected AuNW ecoflexible sensors in physiological motion monitoring. (a) Finger bending. (b) Wrist bending. (c) Elbow bending. (d) Knee bending. (e) Throat movements identifying drinking behavior. (f) Long-term stability of the leaf vein-architected AuNW ecoflexible sensor during more than 1000 stretch-release cycles under 40% strain.

In addition to joint bending monitoring, the leaf vein-architected AuNW ecoflexible sensor also exhibited excellent detection of subtle movements. For instance, when monitoring minute activities in the throat region, the sensor was able to respond in real-time with remarkable sensitivity (Fig. 4(e)). Furthermore, the sensor demonstrated the capability to capture real-time human pulse signals at the wrist, as shown in Fig. S20 (ESI†). Periodic waveforms corresponding to pulse movements were recorded, clearly reflecting the systolic and diastolic phases. This feature highlights the broad dynamic range of the sensor in the field of flexible strain sensing, enabling it to distinguish both micro deformations and large-scale movements, thus meeting the demands for a variety of motion monitoring applications. This ultra-high sensitivity allows the leaf vein-architected AuNW ecoflexible sensor to not only detect large-scale movements but also capture subtle muscular activity changes, providing broad potential applications in health monitoring, sports tracking, and biological signal analysis.

Furthermore, we systematically investigated the long-term stability and durability of leaf vein-architected AuNW ecoflexible sensors to assess their feasibility for practical applications. A cyclic stretching test involving 1000 cycles at 40% strain was conducted (Fig. 4(f)), and the results indicated that the sensor maintained stable performance with high sensitivity, exhibiting no significant degradation or failure.

Leaf vein-architected AuNW ecoflexible sensor for occlusal force monitoring

To evaluate the pressure sensing characteristics, a pressure sensor was designed using a leaf vein-architected AuNW ecoflexible electrode. This sensor features a unique 3D mesh structure, where the AuNW-based leaf vein not only reinforces the mechanical properties but also demonstrates exceptional sensitivity to external pressure. The design of this structure aims to maximize sensitivity and response speed of the sensor while ensuring long-term stability. Furthermore, the pressure response characteristics were systematically analyzed by measuring resistance variations under different pressure gradients.

Initially, the resistance variation of the sensor was measured under the biting conditions of different teeth positions in an adult male. As illustrated in Fig. 5(a)–(c), the sensor provides clear and stable responses in actual occlusion environments, indicating its ability to function effectively in complex physiological conditions and adapt to dynamic loads. Similarly, as with strain, such pressure-dependent resistance characteristics are also clearly reflected in the I–V curves, as shown in Fig. S21 (ESI†). Under applied pressures of 0, 2.5, 5, 10, 15, and 20 kPa, the leaf vein-architected AuNW ecoflexible sensor exhibits well-defined linear I–V characteristics, indicating that its electrical behavior remains ohmic under varying pressure conditions. This consistent ohmic response confirms the structural integrity and conductive network stability of the sensor. Notably, as the applied pressure increases, the slope of the I–V curves gradually decreases, corresponding to an increase in overall resistance. This increase in resistance can be attributed to microstructural changes in the AuNW conductive network under external pressure.^53–55 Specifically, when pressure is applied to the sensor, the AuNWs modified on the naturally three-dimensional leaf vein framework undergo localized deformation. Owing to the branched and non-coplanar geometry of the leaf vein structure, the AuNW pathways are not entirely confined to a single plane. During compression, this structural non-uniformity causes local buckling of the AuNWs, thereby increasing the spacing between adjacent conductive paths and reducing the effective contact area (Fig. S22a, ESI†). Moreover, the inherently three-dimensional architecture of the leaf vein can hinder lateral contact and overlapping between adjacent AuNWs under compressive stress, thereby further impairing the overall electron transport efficiency (Fig. S22b, ESI†). Similar to the sparse conductive pathways induced by outward extension of the AuNW network under tensile strain, this pressure-induced microstructural rearrangement also exerts a significant impact on the conductive behavior of the sensor (Fig. S22c, ESI†). Therefore, the responsive geometric deformation of the AuNW network supported by the leaf vein substrate is a key mechanism underlying the observed resistance increase with rising pressure.

Fig. 5 Pressure sensing performance of the leaf vein-architected AuNW ecoflexible sensor. (a) Bite force response curve at the incisor region. (b) Bite force response curve at the canine region. (c) Bite force response curve at the molar region. (d) Dynamic pressure-sensitive response of the leaf vein-architected AuNW ecoflexible sensor at different pressure levels. (e) Pressure response and recovery time of the leaf vein-architected AuNW ecoflexible sensor. (f) Long-term stability of the leaf vein-architected AuNW ecoflexible sensor over 1000 pressure-release cycles at 2.5 kPa.

Subsequently, the pressure response curves were measured under five different pressure gradients (2.5 kPa to 20 kPa) (Fig. 5(d)). The sensor exhibited distinct and progressively increasing ΔR/R₀ responses with rising pressure levels, demonstrating stable signal output, good sensitivity, and clear differentiation across the pressure range. To better determine the wide detection range of the leaf vein-architected AuNW ecoflexible sensor, a series of continuous pressure response tests were conducted, and the limit of detection (LOD) was calculated accordingly. As illustrated in Fig. S23 (ESI†), the sensor exhibits a clear and stable stepwise signal increase with progressively applied pressure, indicating excellent linear sensitivity and repeatability. Based on the slope fitting of the response curve, the sensitivity (S) was determined to be 0.06914 kPa⁻¹ (Fig. S24, ESI†). Meanwhile, statistical analysis of the blank signal yielded a standard deviation of σ = 0.0007071, and the limit of detection was estimated using the following formula:

Thus, the calculated LOD of the pressure sensor is:

This low detection limit indicates that the sensor can reliably detect subtle pressure variations with high resolution. Furthermore, the final plateau in the response curve confirms that the sensor is capable of detecting pressures up to 60 kPa, demonstrating its applicability for wide-range pressure sensing. The results demonstrated that the sensor exhibited consistent and stable resistance changes across the entire pressure range, confirming its high sensitivity and reliability for monitoring varying external pressure. Beyond its linear response characteristics, the response time and recovery time at low pressures were also evaluated. Under a small applied pressure of 2 kPa, the sensor achieved a response time of 210 ms and a recovery time of 190 ms (Fig. 5(e)). A continuous loading-unloading test was further conducted to reveal the hysteresis behavior of the sensor. The ΔR/R₀ profile, as presented in Fig. S25 (ESI†), exhibits a narrow and symmetric hysteresis loop, reflecting a minimal discrepancy between the loading and unloading processes. This minor hysteresis implies that the sensing layer possesses excellent structural reversibility and fast elastic recovery, which are critical parameters for maintaining output stability under repeated operation. Such behavior can be attributed to the viscoelastic optimization of the material system and the robust interfacial bonding, which jointly contribute to the achievement of high mechanical reliability without sacrificing sensitivity. This indicates that the sensor can quickly respond to external pressure changes and recover to its original state within a very short time, which is crucial for high-frequency dynamic pressure monitoring in practical applications.

Traditionally, pressure sensors for occlusal force monitoring have primarily been developed based on aerogel structures. In comparison to conventional composite aerogel-based pressure sensors, the leaf vein-architected AuNW ecoflexible sensor exhibits an expanded pressure response range and enhanced practical applicability (Table 1). The sensor exhibits a wide detectable pressure range of up to 60 kPa, significantly surpassing most composite aerogels that operate within 0–20 kPa. This broad response range enables the sensor to adapt to complex and dynamic environments, making it particularly suitable for applications such as biomechanical sensing, wearable electronics, and intelligent health monitoring. Although the sensitivity of the current design still falls short of that achieved by traditional aerogel-based materials, the sensor offers clear advantages in terms of cost-effectiveness and material accessibility. Leaf veins, as naturally abundant and structurally sophisticated biological templates, allow for sustainable, low-cost material sourcing. Combined with straightforward metal deposition techniques, this results in an eco-friendly and economical fabrication process suitable for large-scale production. Moreover, the incorporation of leaf vein AuNW structures represents a novel convergence of material innovation and structural functionality. The inherent 3D microchannel network of plant veins serves as an ideal conductive structure, providing excellent flexibility and skin-conformability while also offering a unique platform for the integration of functional nanomaterials (e.g., conductive polymers, AuNWs, and graphene). To enhance sensitivity in the future, the following strategies are proposed: (1) development of nanomaterials with high compatibility to the vein network for optimized signal transduction;⁵⁶ (2) introduction of multifunctional encapsulation layers to improve interfacial charge transfer and mechanical consistency;⁵⁷ and (3) bioinspired structural tuning to control the sensing pathways and force distribution more precisely.⁵⁸ In conclusion, these results indicate that the leaf vein AuNW pressure sensor not only maintains stable sensing performance over prolonged and repeated use but also demonstrates notable advantages in applicability, cost-effectiveness, and material innovation. Its broad pressure response range is particularly critical for accurate bite force monitoring, and the integration of novel nanomaterials with bioinspired structures offers promising directions for future advancements in flexible sensing technologies.

Table 1 Comparison with other conventional composite aerogel piezoresistive sensors

Materials	Pressure range (kPa)	Sensitivity (kPa^−1)	Response/recovery time (ms)	Ref.
rGO/MXene	∼1	4.05	<200	59
Graphene/MXene	0–0.7	31.6	167/121	60
Chitosan/MXene	∼5	80.4	109.6/110.6	61
PAN/rGO/MXene	0–0.5	331	71/15	62
rGO/MXene	∼3.8	0.06	80.5	63
	3.8–4.3	0.37
	4.3–5.5	2.25
Cellulose/MXene	∼10	45.5	189	64
PANI/BC/MXene	∼3	327.22	350	65
	3–20	1.59
This work	∼60	0.06914	210/190

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To assess the long-term stability of the sensor, more than 1000 loading and unloading cycles were performed (Fig. 5(f)). Throughout this process, the response curve shape of the sensor remained almost unchanged, demonstrating its high stability even under repeated pressure stimuli. Notably, the sensor exhibited no significant degradation in performance during the early, middle, or late stages of the test, further confirming its excellent cycling stability.

The excellent sensing performance can be attributed to the unique leaf vein 3D mesh structure, which effectively disperses external forces and undergoes mechanical deformation in multiple directions, thereby enhancing the sensitivity and reliability of the sensor. Additionally, the PDMS encapsulation further improves flexibility and durability of the sensor, enabling it to adapt to a variety of complex environments and prolonged use. Through optimized structural design and material selection, the pressure sensor achieves high precision, high sensitivity, rapid response, and excellent cyclic stability. This innovation provides a novel solution for monitoring and treating dental diseases, particularly in real-time monitoring of dental occlusion forces, evaluating treatment outcomes and preventing dental damage, demonstrating its broad application potential.

Conclusions

In conclusion, we present a novel leaf vein-architected AuNW ecoflexible sensor designed for bite force monitoring, facilitating early detection and diagnosis of dental disease. Leveraging jellyfish-like AuNW configuration within a three-dimensional leaf vein framework, this sensor enhances mechanical robustness and electrical performance, exhibiting superior sensing capabilities under stretching and deformation. Encapsulation with polydimethylsiloxane (PDMS) yields a flexible, stable platform capable of monitoring both large-scale human motions (e.g., joint bending) and subtle physiological signals (e.g., pulse and throat movements). The unique 3D leaf vein architecture, combined with jellyfish-like AuNW, enables highly sensitive and precise bite force detection, offering a promising tool for early dental health assessment. Furthermore, the use of an environmentally friendly leaf vein structure substantially reduces the cost of oral health diagnostics, addressing the increasing demand for sustainable and cost-effective healthcare solutions. This sensor technology exhibits transformative potential for widespread adoption in biomedical and dental applications, addressing the escalating demand for cost-efficient, environmentally sustainable solutions with significant clinical impact.

Author contributions

Yi Chen: conceptualization (lead), supervision (lead), investigation (equal), writing – original draft (equal), writing – review & editing (equal). Wuxing Zhang: investigation (lead), formal analysis (lead), writing – original draft (equal), writing – review & editing (equal). Heng Zhang: conceptualization (equal), supervision (equal), investigation (lead), writing – original draft (equal), writing – review & editing (equal). Gangsheng Chen: investigation (equal), writing – review & editing (equal). Biao Ma: investigation (equal), writing – review & editing (equal). Yang Xia: investigation (equal), writing – review & editing (equal).

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

The authors declare no competing financial interest.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (82472106, 21501027, and 92163213), the National Key Research and Development Program of China (2024YFF0508602 and 2021YFA1201403), the Natural Science Foundation of Jiangsu Province (BK20231420), the Basic Research Program of Suzhou (SYG202317, SYG201911, and SYC2022099), and the Fundamental Research Funds for the Central Universities (SEU Instrumentation Analysis and Testing Fund). Y. Chen acknowledges the support from the Young Elite Scientists Sponsorship Program by China Association for Science and Technology (2015QNRC001), the Innovative and Entrepreneurial Talent Project of Jiangsu Province, Analysis and Testing Center of SEU, and the Monash-JITRI Collaboration Fund. H. Zhang would like to acknowledge the financial aid from the SEU Innovation Capability Enhancement Plan for Doctoral Students (CXJH_SEU 24141). The authors also acknowledge the support from the Yangtze River Delta Medical Advanced Technology Innovation Center, the Collaborative Innovation Center of Suzhou Nano Science and Technology, the Suzhou Dushu Lake Science and Education Innovation District Administrative Committee (Visiting Academic Engineers Program), and the Innovation Platform of Key Laboratory of Biomedical Materials and Technology (YZCXPT2022102).

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Footnotes

† Electronic supplementary information (ESI) available: Section 1: Materials and methods. Section 2: Preparation of leaf vein venation skeleton. Section 3: Leaf vein-architected AuNW electrode. Section 4: Leaf vein-architected AuNW electrode induced by 4 nm gold nanoparticle. Section 5: AuNW growth on various types of leaf veins. Section 6: Permeability characterization. Section 7: Sheet resistance of the vein-architected AuNW electrode under different growth time. Section 8: Vein-architected AuNW ecoflexible sensor. Section 9: Comparison of mechanical properties between unmodified and AuNW-modified sensors. Section 10: The resistance responses during a stretch-release cycle. Section 11: Gauge factor (GF) evaluation. Section 12: Comparison between leaf vein-architected AuNW ecoflexible sensor and PDMS film-based AuNW sensor. Section 13: Current–voltage response under strain. Section 14: Real-time detection of wrist pulse signals. Section 15: Current–voltage response under pressure. Section 16: Mechanism of resistance variation under mechanical deformation. Section 17: Stepwise pressure response curve of the leaf vein-architected AuNW ecoflexible sensor”. See DOI: https://doi.org/10.1039/d5mh00460h

‡ These authors contributed equally to this work.

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