Biomimetic Applications Research Articles

Electromechanics of stretchable hybrid response pressure sensors based on porous nanocomposites

Stretchable pressure sensors are a key enabler of human-mimetic e-skin technology, with promising applications in soft robotics, prosthetics, biomimetics, and biosensors. Stretchable hybrid response pressure sensor (SHRPS) is an emerging type of soft pressure sensor that employs hybrid piezoresistive and piezocapacitive responses. A unique feature of SHRPS based on barely conductive porous nanocomposite (PNC) is its exceptional pressure sensitivity which trivializes its sensitivity to lateral stretch or shear. In this work, we experimentally characterize the electromechanical responses of SHRPS under various loading conditions and provide theoretical explanations through an equivalent circuit model. The capacitance and resistance of the PNC are described by a parallel mixing law and Archie’s law, respectively. Our model can reasonably predict the responses of SHRPS. Our findings reveal that SHRPS exhibits minimal sensitivity to stretch and shear because the hybrid response mechanism is activated only under compression. The effects of PNC-electrode contact impedance and fringe effects are discussed.

Evaluating Stacked Dielectric Elastomer Actuators as Soft Motor Units for Forming Artificial Muscles in Biomimetic Rehabilitation Robots

The recent commercial availability of stacked dielectric elastomer actuators (SDEAs) has unlocked new opportunities for their application as “artificial skeletal muscles” in rehabilitation robots and powered exoskeletons. Composed of multiple layers of thin, elastic capacitors, these actuators present a lightweight, soft, and acoustically noiseless alternative to traditional DC motor actuators commonly used in rehabilitation robotics, thereby enhancing the natural feel of such systems. Building on our previous research, this study aimed to evaluate the most recent version of commercial SDEAs to assess their potential for mechanizing rehabilitation robots. We quantified the stress and strain behavior and stiffness of these actuators in both single and 1 × 3 configurations (with three SDEAs connected in series). The actuators demonstrated the capability to generate up to 25 N of force and 115 KPa, a value surpassing human biceps, with a longitudinal strain measured at about 11%. The significant increase in force generation from 10 N in the previous version to 25 N and displacement from 3.3% to 11% substantially enhances the applicability of this actuator in rehabilitation robotics. SDEAs’ high force generation capability, combined with their strain and stress characteristics comparable to that of human biological muscles, make them ideal alternative actuators for biomimetic robots and applications where actuators must operate in the vicinity of the human body.

High Spatiotemporal Resolution Biomimetic Thermoreceptors Realizing by Jointless p‐n Integration Thermoelectric Composites

AbstractHuman body temperature is a critical physiological indicator, reflecting metabolism and temperature regulation. Biomimetic temperature sensors with high temporal and spatial resolution are highly desired to emulate human skin's temperature perception capabilities. Here, a selective filtration method is proposed to fabricate a jointless p‐n thermoelectric module, integrating p‐type and n‐type materials with minimal interfacial barriers. The structure enables rapid response, minimal signal variation, and a robust linear relationship between open circuit voltage and temperature difference, making it suitable as a biomimetic thermoreceptor for enhancing humanoid robots with intelligent sensing capabilities. A smart thermoelectric sensing system with a high temporal and spatial resolution is developed using with jointless p‐n module as the sensing element. In temporal thermal sensing, the sensing system can timely and effectively identify the heat source, with a fast response time of <0.1 s. In addition, in spatial thermal sensing, the system reliably detects thermal stimuli within discrete regions of each measuring area of <1 × 1 cm2. This study provides an effective strategy for temperature sensors in thermoelectric sensing and biomimetic thermoreceptor applications.

Investigating the nonlinear dynamics of photosensitive Belousov-Zhabotinsky gels via bifurcation analyses.

Controlling the dynamics of active stimuli-responsive smart materials is essential to replicate the biomimetic functionalities at different length scales for a variety of biological systems-based applications. Photosensitive Belousov-Zhabotinsky (BZ) gels, powered by a nonlinear chemical oscillator, called a BZ reaction are one of the stimuli-responsive smart materials in demand due to their ability to continuously transduce chemical oscillations into mechanical deformations. The chemical oscillations in a BZ reaction and subsequent mechanical oscillations in photosensitive BZ gels occur due to the redox cycle of photosensitive ruthenium complex-based catalysts. In this work, our objective is to identify how the behavior of photosensitive BZ gels can be tuned and used for biomimetic applications by investigating its dynamical characteristics using bifurcation analyses. Specifically, we use the normal form approach and perform linear and nonlinear stability analyses to identify high-order bifurcations by computing higher-order Lyapunov and frequency coefficients. We revealed the existence of domains that encompass coexisting stable and unstable limit cycles (LCs), which merge to form a semi-stable LC at the limit point of cycle (LPC). Their existence shows how a slight variation in the BZ gel recipe can significantly alter its dynamics. Subsequently, we quantify the amplitude and frequency of oscillations in different domains under the effect of variation of BZ reaction formulations. We believe that the outcomes of our work serve as an efficient template for the design and control of BZ gel-based applications. The usage of a normal form and a systematic representation of nonlinear dynamics allow our framework to be extended for other nonlinear dynamical systems.

Biomimetic Strategies for Sustainable Resilient Cities: Review across Scales and City Systems.

Biomimicry applications in different domains, from material science to technology, have proven to be promising in inspiring innovative solutions for present-day challenges. However, biomimetic applications in the built environment face several barriers including the absence of biological knowledge of architects and planners and the lack of an adequate common means to transfer biomimetic concepts into strategies applicable in the urban context. This review aims to create a multidimensional relational database of biomimetic strategies from successful precedent case studies in the built environment across different city systems and on different application scales. To achieve this, a thorough systematic search of the literature was implemented to map relevant biomimetic case studies, which are analyzed to extract biomimetic strategies that proved to be applicable and successful in an urban context. These strategies are then classified and documented in a relational database. This will provide a guide for architects and planners on how to transfer biomimetic strategies to strategies applicable in the urban context, thus bridging the gap of their lack of biological knowledge. The resulting matrix of strategies provides potential strategies across most of the different city systems and scales with few exceptions. This gap will be covered in a future work, currently in progress, to expand the database to include all city systems and scales.

Biomimetic Scaffolds of Calcium-Based Materials for Bone Regeneration.

Calcium-based materials, such as calcium carbonate, calcium phosphate, and calcium silicate, have attracted significant attention in biomedical research, owing to their unique physicochemical properties and versatile applications. The distinctive characteristics of these materials, including their inherent biocompatibility and tunable structures, hold significant promise for applications in bone regeneration and tissue engineering. This review explores the biomedical applications of calcium-containing materials, particularly for bone regeneration. Their remarkable biocompatibility, tunable nanostructures, and multifaceted functionalities make them pivotal for advancing regenerative medicine, drug delivery system, and biomimetic scaffold applications. The evolving landscape of biomedical research continues to uncover new possibilities, positioning calcium-based materials as key contributors to the next generation of innovative biomaterial scaffolds.

Unmatched resilience and fatigue resistance in a novel cellulose-derived ionic gel with hierarchical superstructured synergy for advanced human-computer interaction

Unlike traditional hydrogels, solvent-free ionic gels eliminate leakage and solvent volatilization, making them suitable for applications in electronic skin, sensing, and other fields due to their excellent conductivity and flexibility. However, designing solvent-free ionic gels with exceptional fatigue resistance, high ionic conductivity, and toughness remains a significant challenge. We address this challenge by employing small molecule/polymer heating self-assembly to regulate the synergistic effects of various components on the hierarchical superstructure. A multi-stage network was formed through the free radical polymerization of 3-Ethyl-1-vinyl-1H-imidazol-3-ium bromide ([C2VIm]Br), lipoic acid (LA), acrylic acid (AA), and hydroxypropyl cellulose (HPC), stabilized by dense hydrogen bonding and polymer chain entanglement. The resulting HPC/LA/AA/iLs (HLAI) ionic gel exhibits exceptional properties: excellent flexibility (with an elongation at break of 4222 %), toughness (1.03 MJ/m3), high ionic conductivity (3.29 × 10−2 S/m), and outstanding fatigue resistance (with a resilience of 91.9 % after 1000 load-unloading cycles at 50 % strain). Additionally, it shows low sensitivity to crack propagation (50 % notched sample can be stretched to 9 times without breaking) and good environmental stability, demonstrating excellent sensing sensitivity and stability (GF=3.23). The conductive ionic gel features a sophisticated hierarchical superstructure that synergistically enhances its properties at the molecular level. The integration of dynamic disulfide bonds, achieved through the polymerization of Lipoic acid, imparts remarkable self-healing capabilities and superior fatigue resistance. Additionally, the incorporation of a rigid HPC structure with dense cross-linking points bolsters elasticity, fracture resistance, and resilience. The gel’s ionic conductivity and sensing sensitivity are significantly enhanced by the inclusion of ionic liquids with polymerizable double bonds, making it an ideal material for applications requiring both flexibility and conductivity. This work presents a novel strategy for designing high-performance multi-stage network solvent-free ionic gels, opening up exciting possibilities for biomimetic electronic skin applications.

Manufacturable Ti/ZrO2/Cu memristor-based synapses and biomimetic memory applications with circuit implementation

Manufacturable Ti/ZrO2/Cu memristor-based synapses and biomimetic memory applications with circuit implementation

Constructing inkjet printed dielectric elastomers with modified silicon carbide nanowire surfaces to enhance electromechanical performance

AbstractDielectric elastomers (DEs), have attracted interest because they can replicate the behavior of muscles. They can change shape when subjected to an electric field. A novel DE is proposed in this study that incorporates silicon carbide (SiC) nanowires into silicone rubber (SR). The nanowires were propagated using polycarbosilane via a chemical vapor reaction (CVR). A boronate polymer was employed to promote compatibility between SR and SiC nanowires which modified the nanowire surfaces, leveraging a strong adhesive quality of the catechol moiety. Electrohydrodynamic (EHD) inkjet printing was then used to form the DEs into various shapes. These DEs had substantial dielectric constants of the order of 4.46. Significantly, one of the DEs achieved the highest actuated area strain of 20.36% in an electric field of 16.5 V/μm, demonstrating excellent driving performance. Furthermore, when used the fabricated DEs showed pronounced long‐term stability, meaning they are capable of finding applications in artificial intelligence, biomimetics, aerospace, and other disciplines.Highlights The SiC nanowires were obtained through a chemical vapor reaction. A boronate polymer with catechol moiety was used to modify the SiC nanowires. DEs were formed various shapes by inkjet printing. DEs achieved very large actuated strains of up to 20.36% at 16.5 V/μm.

Bridging Nature and Engineering: Protein-Derived Materials for Bio-Inspired Applications.

The sophisticated, elegant protein-polymers designed by nature can serve as inspiration to redesign and biomanufacture protein-based materials using synthetic biology. Historically, petro-based polymeric materials have dominated industrial activities, consequently transforming our way of living. While this benefits humans, the fabrication and disposal of these materials causes environmental sustainability challenges. Fortunately, protein-based biopolymers can compete with and potentially surpass the performance of petro-based polymers because they can be biologically produced and degraded in an environmentally friendly fashion. This paper reviews four groups of protein-based polymers, including fibrous proteins (collagen, silk fibroin, fibrillin, and keratin), elastomeric proteins (elastin, resilin, and wheat glutenin), adhesive/matrix proteins (spongin and conchiolin), and cyanophycin. We discuss the connection between protein sequence, structure, function, and biomimetic applications. Protein engineering techniques, such as directed evolution and rational design, can be used to improve the functionality of natural protein-based materials. For example, the inclusion of specific protein domains, particularly those observed in structural proteins, such as silk and collagen, enables the creation of novel biomimetic materials with exceptional mechanical properties and adaptability. This review also discusses recent advancements in the production and application of new protein-based materials through the approach of synthetic biology combined biomimetics, providing insight for future research and development of cutting-edge bio-inspired products. Protein-based polymers that utilize nature's designs as a base, then modified by advancements at the intersection of biology and engineering, may provide mankind with more sustainable products.

Exploring Enzyme-Mimicking Metal-Organic Frameworks for CO2 Conversion through Vibrational Spectra-Based Machine Learning.

In pursuing the benefits of natural enzyme catalysts while overcoming their limitations, we find metal-organic frameworks (MOFs), renowned for their highly tunable functionalities, stand out in biomimetic applications. We used unsupervised machine learning on density functional theory-computed vibrational infrared and Raman spectral features to screen 300 Zn-MOFs for CO2 conversion, similar to carbonic anhydrase (CA). Our findings confirmed that MOFs with spectroscopic attributes closely resembling those of CA hold the potential for replicating CA's electronic and catalytic properties. Unlike previous studies that relied on heuristic or trial-and-error methods and focused on geometric configurations, our research uses vibrational spectral features to explore structure-property relationships, making them more accessible through spectroscopy. Moreover, we highlight vibrational spectral features as efficient carriers for highly dimensional chemical information, enabling the simultaneous optimization of multiple performance parameters. These findings pave the way for pioneering designs of enzyme-mimetic MOFs and concurrently expand the application scope of spectroscopic tools in biomimetic catalysis.

Giant Iontronic Flexoelectricity in Soft Hydrogels Induced by Tunable Biomimetic Ion Polarization.

Flexoelectricity features the strain gradient-induced mechanoelectric conversion using materials not limited by their crystalline symmetry, but state-of-the-art flexoelectric materials exhibit very small flexoelectric coefficients and are too brittle to withstand large deformations. Here, inspired by the ion polarization in living organisms, this paper reports the giant iontronic flexoelectricity of soft hydrogels where the ion polarization is attributed to the different transfer rates of cations and anions under bending deformations. The flexoelectricity is found to be easily regulated by the types of anion-cation pairs and polymer networks in the hydrogel. A polyacrylamide hydrogel with 1m NaCl achieves a record-high flexoelectric coefficient of ≈1160 µC m-1, which can even be improved to ≈2340 µC m-1 by synergizing with the effects of ion pairs and extra polycation chains. Furthermore, the hydrogel as flexoelectric materials can withstand larger bending deformations to obtain higher polarization charges owing to its intrinsic low modulus and high elasticity. A soft flexoelectric sensor is then demonstrated for object recognition by robotic hands. The findings greatly broaden the flexoelectricity to soft, biomimetic, and biocompatible materials and applications.

Study on biomimetic superhydrophobic mechanisms and existing issues

The realm of biomimetic superhydrophobic surfaces encompasses a diverse range of applications, yet the specific biomimetic mechanisms, theories, models, and preparation methods remain shrouded in ambiguity. To address this gap, a meticulous examination of the current theories and preparation methods is imperative for guiding further biomimetic superhydrophobic research. This study, adopting a dual perspective from superhydrophobic theory and the intricate interplay between droplets and surfaces, intricately synthesizes the relevant theories and models pertaining to biomimetic superhydrophobic microstructures. Delving into the existing challenges in theoretical research and preparation methods within the field of biomimetic superhydrophobics, the research not only identifies current limitations but also lays the groundwork for future explorations. This systematic inquiry contributes not only to a nuanced understanding of existing biomimetic superhydrophobic surfaces but also provides a robust foundation for future studies and technological innovations. As the research unfolds, it propels the scientific community towards a more comprehensive grasp of biomimetic superhydrophobic phenomena, promising advancements, and applications across various scientific and technological domains.

Multistimulus‐Responsive Miniature Soft Actuator with Programmable Shape‐Morphing Design for Biomimetic and Biomedical Applications

AbstractMiniature soft actuators have garnered attention across healthcare, military, and industrial fields; however, soft actuators mostly have functions and applications in nature‐inspired biomimetic locomotion, without any specific approaches reported for biomedical applications. In biomedical applications, soft actuators must be biodegradable, biocompatible, and visible in vivo. This study presents a multifunctional soft actuator comprising chitosan and magnetic nanoparticles (MNPs) fabricated via facile casting and laser micromachining. The actuator demonstrates programmable shape morphing and responds swiftly to six stimuli: humidity, chemical solvents, near‐infrared (NIR) light, radio‐frequency (RF) heating, temperature, and magnetic fields. This actuator shows feasibility for biomimetic applications, such as flower, leaf, larva, and finger. Furthermore, the actuator demonstrates magnetic locomotion, real‐time X‐ray visibility, biocompatibility, and biodegradability both in vitro and in vivo. The multistimulus‐responsive shape‐morphing performance of the soft actuator has potential as a wireless miniature robot in various fields, including biomimetic and biomedical applications.

Bioinspired sensing-memory-computing integrated vision systems: biomimetic mechanisms, design principles, and applications

Bioinspired sensing-memory-computing integrated vision systems: biomimetic mechanisms, design principles, and applications

Mechanisms of anisotropic fracture resistance of nacreous structure and design: Essential role of cracking modes of organic interfaces

Nacreous structure holds significant promise for biomimetic design applications due to its excellent mechanical properties. In this paper, the influence of loading direction on the mechanical properties of nacreous structure was investigated to understand its mechanisms of anisotropic fracture resistance. The results revealed significant anisotropy in the mechanical properties of nacre when loaded along different directions (perpendicular to y and z axes). When loaded perpendicular to the top face, nacre exhibits better mechanical properties and greater resistance to fracture compared to loading perpendicular to the side face. This distinction can be attributed to different cracking modes of organic interfaces in nacreous structure, where the nacreous structure loaded perpendicular to the top face exhibits more tortuous crack deflection, larger fracture stepped surface area and microcrack zones. Furthermore, the theoretical analysis indicates that the differences in the volume fraction of organic interfaces and the main crack deflection along organic interfaces are important factors leading to different cracking modes of organic interfaces in nacreous structure. Based on the analysis of the mechanisms of anisotropic fracture resistance, the critical parameters to characterize the anisotropic mechanical properties of the nacreous structure were proposed. The research results provide a reference and basis for future biomimetic application design.

Structural diversity of crustacean exoskeletons and its implications for biomimetics.

The crustacean cuticle is a biological composite material consisting of chitin-protein fibres in a mineralized matrix. Recent research has revealed a surprising range of fibre architectures and mineral compositions of crustacean skeletal structures adapted to various mechanical demands. It is becoming increasingly clear that the organic fibres in the cuticle may be organized in patterns differing from the standard twisted plywood model. Observed fibre architectures in protruding skeletal structures include longitudinal and circular parallel fibre arrays. Skeletal minerals often include calcium phosphates in addition to calcium carbonates. Furthermore, skeletal properties are affected by protein cross-linking, which replaces mineralization as a stiffening mechanism in some structures. Several common structural motifs, such as the stiffening of the outer skeletal layers, the incorporation of non-mineralized cuticle in exposed structures, and interchanging layers of parallel fibres and the twisted plywood structure, can be identified in skeletal elements with similar functions. These evolutionary solutions have the potential for biomimetic applications, particularly as manufacturing technologies advance. To make use of this potential, we need to understand the processes behind the formation of the crustacean exoskeleton and determine which features are truly adaptive and worth mimicking.

CFD analysis of the complex japanese pufferfish nest

Existing research on the pufferfish species (Torquigener Albomaculosus) has shown that its nest structure has a certain impact on flow velocity. This study aims to investigate the nest-building behavior by using different materials. A 3D model will be created based on nest geometry, and 2D simulations will be conducted by using computational fluid dynamics (CFD). Furthermore, the study examines the nest’s fluid dynamics characteristics in its original state, with varied materials and heights. Results demonstrate that the nest reduces flow velocity, adapts to external flow conditions, and enhances shear strength with rough materials. Additionally, nest height affects internal circulation area and pressure. This unique structure protects the spawning area, improves oxygen transport, and strengthens the nest. The study further expands biomimetic engineering applications and suggests future interdisciplinary research directions.

Hydrogel Ink for 3D Printing with High and Widely Tunable Mechanical Properties via the Salting‐Out Effect

AbstractDue to the difficulty of simultaneously ensuring printability and controlling their mechanical properties, 3D printed hydrogels thus far have low modulus, far less than that of many biological tissues and organs. Therefore, their feasibility toward various biomimetic applications is currently limited. Herein, Direct‐Ink‐Writing (DIW) based 3D printable hydrogel ink with broadly adjustable mechanical properties is introduced. The salting‐out effect is utilized to effectively lower the gelation temperature of hydrogel inks with a wide range of modulus (0.193–1.072 MPa), making them all 3D printable. As a proof of concept, multi‐layered synthetic blood vessels that mimic the mechanical properties of biological blood vessels are printed, and their practicability toward surgical training is demonstrated. The versatility and simplicity of this technique make it highly promising for use in various 3D‐printed hydrogel biomaterials applications.

Periodic implicit representation, design and optimization of porous structures using periodic B-splines

Porous structures are intricate solid materials with numerous small pores, extensively used in fields like medicine, chemical engineering, and aerospace. However, the design of such structures using computer-aided tools is a time-consuming and tedious process. In this study, we propose a novel representation method and design approach for porous units that can be infinitely spliced to form a porous structure. We use periodic B-spline functions to represent periodic or symmetric porous units. Starting from a voxel representation of a porous sample, the discrete distance field is computed. To fit the discrete distance field with a periodic B-spline, we introduce the constrained least squares progressive-iterative approximation algorithm, which results in an implicit porous unit. This unit can be subject to optimization to enhance connectivity and utilized for topology optimization, thereby improving the model’s stiffness while maintaining periodicity or symmetry. The experimental results demonstrate the potential of the designed complex porous units in enhancing the mechanical performance of the model. Consequently, this study has the potential to incorporate remarkable structures derived from artificial design or nature into the design of high-performing models, showing the promise for biomimetic applications.