Biomimetic electrochemistry from conducting polymers. A review

Thermodynamic model for voltammetric responses in conducting redox polymers

Electroactive polymer materials are known to play important roles in a vast spectrum of modern applications such as in supercapacitors, fuel cells, batteries, medicine, and smart materials, etc. They are usually divided into two main groups: first, conducting π-conjugated organic polymers, which conduct electricity by cation-radicals delocalized over a polymer chain; second, redox polymers, which conduct electricity via an electron-hopping mechanism. Polymer materials belonging to these two main groups have been thoroughly studied and their thermodynamic and kinetic models have been built. However, in recent decades a lot of mixed-type materials have been discovered and investigated. To the best of our knowledge, a thermodynamic-based description of conducting redox polymers (CRPs) has not been provided yet. In this work, we present a thermodynamic model for voltammetric responses of conducting redox polymers. The derived model allows one to extract thermodynamic parameters of a CRP including the polaron delocalization degree and redox active groups interaction constant. The model was verified with voltammetric experiments on three recently synthesized CRPs and showed a satisfactory predictive ability. The simulated data are in good agreement with the experiment. We believe that developing theoretical descriptions for CRPs and other types of electroactive materials with the ability to simulate their electrochemical responses may help in future realization of new systems with superior characteristics for electrochemical energy storage, chemical sensors, pharmacological applications, etc.

Neural repair and regeneration interfaces: a comprehensive review

Neural interfaces play a pivotal role in neuromodulation, as they enable precise intervention into aberrant neural activity and facilitate recovery from neural injuries and resultant functional impairments by modulating local immune responses and neural circuits. This review outlines the development and applications of these interfaces and highlights the advantages of employing neural interfaces for neural stimulation and repair, including accurate targeting of specific neural populations, real-time monitoring and control of neural activity, reduced invasiveness, and personalized treatment strategies. Ongoing research aims to enhance the biocompatibility, stability, and functionality of these interfaces, ultimately augmenting their therapeutic potential for various neurological disorders. The review focuses on electrophysiological and optophysiology neural interfaces, discussing functionalization and power supply approaches. By summarizing the techniques, materials, and methods employed in this field, this review aims to provide a comprehensive understanding of the potential applications and future directions for neural repair and regeneration devices.

Reaction Induced Conformational Change in Polyindole: Polyindole/PVA Film as Biomimetic Sensors of Temperature and Electrical Energetic Conditions

Conducting polymers can mimic the sensing characteristics of biological muscles through utilizing their unique electrochemical reactions. As these reactions occur, alterations in composition prompt changes in biomimetic properties, such as shifts in volume, brought about by the insertion of anions and solvent molecules, resulting in conformational movements. Similar to biological muscles, these electrochemical reaction senses the working variables affecting the reaction rate, through the same two connecting wires. The influence of working temperature and electrical energetic condition on the conformational movements of polyindole manifested as the cooperative actuation of the polymer chain is verified here using a polyindole-coated polyvinyl alcohol (PIN/PVA) film. Cyclic voltammetric (CV) studies revealed that the extent of reaction of polyindole varies linearly with temperature and scan rate. The logarithmic dependence of redox charge obtained from coulovoltammogram with inverse of temperature further proved the temperature sensing characteristics and the influence of temperature on the cooperative actuation of the film. The conformational relaxation increases as the temperature increases through hosting higher number of counter anions with the solvent molecule. The extension of the redox reaction was found to decrease as the scan rate increases. The double logarithmic relation between the consumed redox charge and the scan rate has proved that the electrical energetic condition can influence the conformational movement in a reversible manner. It is also verified from Chronopotentiometric (CP) studies that the consumed electrical energy during the reaction varies linearly with the change in temperature. The results suggest that the PIN/PVA film can act as a biomimetic macro molecular sensor of working temperature and electrical energetic condition as biological muscles do.

Simultaneous Sensing and Actuating Capabilities of a Triple-Layer Biomimetic Muscle for Soft Robotics

This work presents the fabrication and characterization of a triple-layered biomimetic muscle constituted by polypyrrole (PPy)-dodecylbenzenesulfonate (DBS)/adhesive tape/PPy-DBS demonstrating simultaneous sensing and actuation capabilities. The muscle was controlled by a neurobiologically inspired cortical neural network sending agonist and antagonist signals to the conducting polymeric layers. Experiments consisted of controlled voluntary movements of the free end of the muscle at angles of ±20°, ±30°, and ±40° while monitoring the muscle's potential response. Results show the muscle's potential varies linearly with applied current amplitude during actuation, enabling current sensing. A linear dependence between muscle potential and temperature enabled temperature sensing. Electrolyte concentration changes also induced exponential variations in the muscle's potential, allowing for concentration sensing. Additionally, the influence of the electric current density on the angular velocity, the electric charge density, and the desired angle was studied. Overall, the conducting polymer-based soft biomimetic muscle replicates properties of natural muscles, permitting simultaneous motion control, current, temperature, and concentration sensing. The integrated neural control system exhibits key features of biological motion regulation. This muscle actuator with its integrated sensing and control represents an advance for soft robotics, prosthetics, and biomedical devices requiring biomimetic multifunctionality.

From Nature to Technology: Exploring Bioinspired Polymer Actuators via Electrospinning

Nature has always been a source of inspiration for the development of novel materials and devices. In particular, polymer actuators that mimic the movements and functions of natural organisms have been of great interest due to their potential applications in various fields, such as biomedical engineering, soft robotics, and energy harvesting. During recent years, the development and actuation performance of electrospun fibrous meshes with the advantages of high permeability, surface area, and easy functional modification, has received extensive attention from researchers. This review covers the recent progress in the state-of-the-art electrospun actuators based on commonly used polymers such as stimuli-sensitive hydrogels, shape-memory polymers (SMPs), and electroactive polymers. The design strategies inspired by nature such as hierarchical systems, layered structures, and responsive interfaces to enhance the performance and functionality of these actuators, including the role of biomimicry to create devices that mimic the behavior of natural organisms, are discussed. Finally, the challenges and future directions in the field, with a focus on the development of more efficient and versatile electrospun polymer actuators which can be used in a wide range of applications, are addressed. The insights gained from this review can contribute to the development of advanced and multifunctional actuators with improved performance and expanded application possibilities.

Electrochemical control of bone microstructure on electroactive surfaces for modulation of stem cells and bone tissue engineering

Controlling stem cell behavior at the material interface is crucial for the development of novel technologies in stem cell biology and regenerative medicine. The composition and presentation of bio-factors on a surface strongly influence the activity of stem cells. Herein, we designed an electroactive surface that mimics the initial process of trabecular bone formation, by immobilizing chondrocyte-derived plasma membrane nanofragments (PMNFs) on its surface for rapid mineralization within 2 days. Moreover, the electroactive surface was based on the conducting polymer polypyrrole (PPy), which enabled dynamic control of the presentation of PMNFs on the surface via electrochemical redox switching, further resulting in the formation of bone minerals with different morphologies. Furthermore, bone minerals with contrasting surface morphologies had differential effects on the differentiation of human bone marrow-derived stem cells (hBMSCs) cultured on the surface. Together, this electroactive surface showed multifunctional characteristics, not only allowing dynamic control of PMNF presentation but also promoting the formation of bone minerals with different morphologies within 2 days. This electroactive substrate could be valuable for more precise control of stem cell growth and differentiation, and further development of more suitable microenvironments containing bone apatite for housing a bone marrow stem cell niche, such as biochips/bone-on-chips.

Smart biomaterials and their potential applications in tissue engineering

Smart biomaterials have been rapidly advancing ever since the concept of tissue engineering was proposed. Interacting with human cells, smart biomaterials can play a key role in novel tissue morphogenesis. Various aspects of biomaterials utilized in or being sought for the goal of encouraging bone regeneration, skin graft engineering, and nerve conduits are discussed in this review. Beginning with bone, this study summarizes all the available bioceramics and materials along with their properties used singly or in conjunction with each other to create scaffolds for bone tissue engineering. A quick overview of the skin-based nanocomposite biomaterials possessing antibacterial properties for wound healing is outlined along with skin regeneration therapies using infrared radiation, electrospinning, and piezoelectricity, which aid in wound healing. Furthermore, a brief overview of bioengineered artificial skin grafts made of various natural and synthetic polymers has been presented. Finally, by examining the interactions between natural and synthetic-based biomaterials and the biological environment, their strengths and drawbacks for constructing peripheral nerve conduits are highlighted. The description of the preclinical outcome of nerve regeneration in injury healed with various natural-based conduits receives special attention. The organic and synthetic worlds collide at the interface of nanomaterials and biological systems, producing a new scientific field including nanomaterial design for tissue engineering.

Fabrication of Polyaniline Ni-Complex Catalytic Electrode by Plasma Deposition for Electrochemical Detection of Phosphate through Glucose Redox Reaction as Mediator

We report here the preparation and characterization of polyaniline Ni-complex catalytic electrode by one-pot plasma deposition for the electrochemical detection of phosphate via the redox reaction of glucose. We first prepared a precursory solution by combining NiCl2 and 3-aminobenzoic acid in a mixed solution of methanol (MeOH) and water, and adding aniline as a conductive polymeric precursor for increasing the electron transfer potential. We then synthesized the catalytic electrode in a one-step cold plasma process by preparing the precursors on ITO glass. We characterized the obtained Ni-coordinate catalytic electrode via X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (SEM), and electrochemical methods. Electrochemical characterization produced stable redox properties of Ni3+/Ni2+ couples in a 0.1 M NaOH solution. Cyclic voltametric experiments have drastically increased electrocatalytic oxidation and reduction of glucose by increasing the concentration of phosphate (PO43−) ions using the prepared Ni-modified catalytic electrodes. From these results, the prepared catalytic electrode could be used as the electrochemical sensor for phosphate in actual water.

In Vivo Organic Bioelectronics for Neuromodulation

The nervous system poses a grand challenge for integration with modern electronics and the subsequent advances in neurobiology, neuroprosthetics, and therapy which would become possible upon such integration. Due to its extreme complexity, multifaceted signaling pathways, and ∼1 kHz operating frequency, modern complementary metal oxide semiconductor (CMOS) based electronics appear to be the only technology platform at hand for such integration. However, conventional CMOS-based electronics rely exclusively on electronic signaling and therefore require an additional technology platform to translate electronic signals into the language of neurobiology. Organic electronics are just such a technology platform, capable of converting electronic addressing into a variety of signals matching the endogenous signaling of the nervous system while simultaneously possessing favorable material similarities with nervous tissue. In this review, we introduce a variety of organic material platforms and signaling modalities specifically designed for this role as “translator”, focusing especially on recent implementation in in vivo neuromodulation. We hope that this review serves both as an informational resource and as an encouragement and challenge to the field.

Quantum dot decorated polyaniline plastic as a multifunctional nanocomposite: experimental and theoretical approach

AgO, CoO, and ZnO (ACZ) mixed metal quantum dots (QDs) were synthesized by the sol–gel process. Polyaniline (PANI) was prepared by the chemical-oxidative technique. An in situ approach was used for the synthesis of ACZ decorated PANI plastic nanocomposites (NCs). TEM, FTIR, FESEM, UV-visible, DSC, Raman, photoluminescence, and XRD techniques were used for characterizing the QDs, PANI, and ACZ decorated PANI NCs. Experimental and theoretical (DFT) studies were used to support the results. NCs were studied for their adsorption, magnetic, photocatalytic, electrical, thermal, photoluminescence, antibacterial, and anticorrosive activities. The plastic NCs of size 35 nm (observed from XRD and TEM) were found to be paramagnetic. UV-visible spectroscopy and DFT techniques were used to observe the optical band gap of NCs and show an almost equal band gap i.e., 2.75 eV. In 1.0 M H₂SO₄, the NCs show an 82.0% corrosion inhibition efficiency for mild steel. The adsorption power of the silica gel + NCs packed column was higher than normal silica gel column. A very small low-intensity D band in the Raman spectra confirms defect-free NCs. The photocatalytic activity was observed against methyl-red dye in visible light. The thermal stability of plastic NCs was higher than pure PANI and QDs. The NCs were investigated for bactericidal activity against Gram (positive and negative) microorganisms. The ACZ decorated PANI NCs acted as good nanomaterials for adsorption, separation, magnetic, photocatalytic, photoluminescence, antibacterial, electrical, thermal insulator, and anticorrosive agent.

PANI based plastic NCs shows good adsorption power, anticorrosive and thermal stability. The photocatalytic activity was observed against methyl-red dye. The NCs also shows good magnetic, antibacterial, and electrical properties.

Effects of Electroactive materials on nerve cell behaviors and applications in peripheral nerve repair

Peripheral nerve damage can lead to loss of function or even complete disability, which bring about a huge burden on both the patient and society. Regulating nerve cell behavior and...

Electroactive macromolecular motors as model materials of ectotherm muscles

The electrochemical reaction in liquid electrolytes of conducting polymers, carbon nanotubes, graphenes, among other materials, replicates the active components (macromolecular electro-chemical motors, ions and solvent) and volume variation of the sarcomere in any natural muscles during actuation, allowing the development of electro-chemo-mechanical artificial muscles. Materials, reactions and artificial muscles have been used as model materials, model reactions and model devices of the muscles from ectotherm animals. We present in this perspective the experimental results and a quantitative description of the thermal influence on the reaction extension and energetic achievements of those muscular models using different experimental methodologies. By raising the temperature for 40 °C keeping the extension of the muscular movement the cooperative actuation of the macromolecular motors harvest, saving chemical energy, up to 60% of the reaction energy from the thermal environment. The synergic thermal influence on either, the reaction rate (Arrhenius), the conformational movement rates of the motors (ESCR model) and the diffusion coefficients of ions across polymer matrix (WLF equation) can support the physical chemical foundations for the selection by nature of ectotherm muscles. Macromolecular motors act, simultaneously, as electro-chemo-mechanical and thermo-mechanical transducers. Technological and biological perspectives are presented.

Printing Multi-Material Organic Haptic Actuators

Haptic actuators generate touch sensations and provide realism and depth in human-machine interactions. A new generation of soft haptic interfaces is desired to produce the distributed signals over large areas that are required to mimic natural touch interactions. One promising approach is to combine the advantages of organic actuator materials and additive printing technologies. This powerful combination can lead to devices that are ergonomic, readily customizable, and economical for researchers to explore potential benefits and create new haptic applications. Here, an overview of emerging organic actuator materials and digital printing technologies for fabricating haptic actuators is provided. In particular, the focus is on the challenges and potential solutions associated with integration of multi-material actuators, with an eye toward improving the fidelity and robustness of the printing process. Then the progress in achieving compact, lightweight haptic actuators by using an open-source extrusion printer to integrate different polymers and composites in freeform designs is reported. Two haptic interfaces-a tactile surface and a kinesthetic glove-are demonstrated to show that printing with organic materials is a versatile approach for rapid prototyping of various types of haptic devices.

Highly Conductive Collagen by Low-Temperature Atomic Layer Deposition of Platinum

In modern biomaterial-based electronics, conductive and flexible biomaterials are gaining increasing attention for their wide range of applications in biomedical and wearable electronics industries. The ecofriendly, biodegradable, and self-resorbable nature of these materials makes them an excellent choice in fabricating green and transient electronics. Surface functionalization of these biomaterials is required to cater to the need of designing electronics based on these substrate materials. In this work, a low-temperature atomic layer deposition (ALD) process of platinum (Pt) is presented to deposit a conductive thin film on collagen biomaterials, for the first time. Surface characterization revealed that a very thin ALD-deposited seed layer of TiO₂ on the collagen surface prior to Pt deposition is an alternative for achieving a better nucleation and 100% surface coverage of ultrathin Pt on collagen surfaces. The presence of a pure metallic Pt thin film was confirmed from surface chemical characterization. Electrical characterization proved the existence of a continuous and conductive Pt thin film (∼27.8 ± 1.4 nm) on collagen with a resistivity of 295 ± 30 μΩ cm, which occurred because of the virtue of TiO₂. Analysis of its electronic structures showed that the presence of metastable state due to the presence of TiO₂ enables electrons to easily flow from valence into conductive bands. As a result, this turned collagen into a flexible conductive biomaterial.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Poly-3-thienylboronic acid: a chemosensitive derivative of polythiophene

Poly-3-thiopheneboronic acid was synthesized by electrochemical polymerization from 3-thienylboronic acid dissolved in the mixture of boron trifluoride diethyl etherate and acetonitrile. Cyclic voltammetry during electropolymerization shows oxidative and reductive peaks growing in each next cycle. An investigation by scanning electron microscopy displayed the polymer layer like a highly flexible film of 110 nm thick with grains of 60–120 nm in size. Strong negative solvatochromic effect was observed. Optical spectra of poly-3-thienylboronic acid at different potentials and pH were studied. Potential cycling leads to a well reversible electrochromic effect. At pH 7.4, the increase of potential leads to the decrease in the absorption band at 480 nm and to the rise in the absorption band at 810 nm with an isosbestic point at 585 nm. Spectroelectrochemical behavior of poly-3-thienylboronic acid and polythiophene was compared. Binding of sorbitol at fixed electrode potential leads to an increase in the absorbance in the shortwave band and to the decrease in the longwave band; the effect depends on the electrode potential and pH. Perspectives of application of poly-3-thienylboronic acid as new chemosensitive material are discussed.

Effect of elasticity on electrospun styrene-butadiene-styrene fibrous membrane cell culture behaviors

In this study, elastic styrene-butadiene-styrene (SBS), non-elastic SBS and their blends at different ratios were electrospun into fibrous membranes and their cell biocompatibility was evaluated. The as-spun fibers showed an average fiber diameter of 2 µm, and the fibrous membranes had pore size of 8 ± 0.01 µm. The blending ratios of the elastic with non-elastic SBSs showed little effect on fibrous structure, but affected the mechanical properties. All SBS membrane showed no cytotoxicity on endothelial cells (ECs). ECs attached and proliferated on all the SBS fibrous membrane scaffolds regardless of their elasticity. ECs maintained their polygonal shape on the scaffolds and they tended to orient along the fiber length. The SBS fibrous samples with elastic:non-elastic SBS weight ratios of 1:1 and 2:3 showed better cell viability than that of elastic and non-elastic SBS.

A Biomimetic Approach to Increasing Soft Actuator Performance by Friction Reduction

While increasing power output is the most straight-forward solution for faster and stronger motion in technology, sports, or elsewhere, efficiency is what separates the best from the rest. In nature, where the possibilities of power increase are limited, efficiency of motion is particularly important; the same principle can be applied to the emerging biomimetic and bio-interacting technologies. In this work, by applying hints from nature, we consider possible approaches of increasing the efficiency of motion through liquid medium of bilayer ionic electroactive polymer actuations, focusing on the reduction of friction by means of surface tension and hydrophobicity. Conducting polyethylene terephthalate (PET) bilayers were chosen as the model actuator system. The actuation medium consisted of aqueous solutions containing tetramethylammonium chloride and sodium dodecylbenzenesulfonate in different ratios. The roles of ion concentrations and the surface tension are discussed. Hydrophobicity of the PET support layer was further tuned by adding a spin-coated silicone layer to it. As expected, both approaches increased the displacement-the best results having been obtained by combining both, nearly doubling the bending displacement. The simple approaches for greatly increasing actuation motion efficiency can be used in any actuator system operating in a liquid medium.

Structural Control of Charge Storage Capacity to Achieve 100% Doping in Vapor Phase-Polymerized PEDOT/Tosylate

Vapor phase polymerization (VPP) is used to fabricate a series of tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes on carbon paper. The series of VPP PEDOT/tosylate coatings has varying levels of crystallinity and electrical conductivity because of the use (or not) of nonionic triblock copolymers in the oxidant solution during synthesis. As a result, the impact of the structure on charge storage capacity is investigated using tetra-n-butylammonium hexafluorophosphate (0.1 M in acetonitrile). The ability to insert anions, and hence store charge, of the VPP PEDOT/tosylate is inversely related to its electrical conductivity. In the case of no nonionic triblock copolymer employed, the VPP PEDOT/tosylate achieves electrochemical doping levels of 1.0 charge per monomer or greater (≥100% doping level). Such high doping levels are demonstrated to be plausible by molecular dynamics simulations and density functional theory calculations. Experiments show that this high doping level is attainable when the PEDOT structure is weakly crystalline with (relatively) large crystallite domains.

PEDOT-Based Conducting Polymer Actuators

Conducting polymers, particularly poly(3,4-ethylenedioxythiophene) (PEDOT) and its complex with poly(styrene sulfonate) (PEDOT:PSS), provide a promising materials platform to develop soft actuators or artificial muscles. To date, PEDOT-based actuators are available in the field of bionics, biomedicine, smart textiles, microactuators, and other functional applications. Compared to other conducting polymers, PEDOT provides higher conductivity and chemical stability, lower density and operating voltages, and the dispersion of PEDOT with PSS further enriches performances in solubility, hydrophility, processability, and flexibility, making them advantageous in actuator-based applications. However, the actuators fabricated by PEDOT-based materials are still in their infancy, with many unknowns and challenges that require more comprehensive understanding for their current and future development. This review is aimed at providing a comprehensive understanding of the actuation mechanisms, performance evaluation criteria, processing technologies and configurations, and the most recent progress of materials development and applications. Lastly, we also elaborate on future opportunities for improving and exploiting PEDOT-based actuators.

Cell Responses to Electrical Pulse Stimulation for Anticancer Drug Release

Electrical stimulation is an attractive approach to tune on-demand drug release in the body as it relies on simple setups and requires typically 1 V or less. Although many studies have been focused on the development of potential smart materials for electrically controlled drug release, as well as on the exploration of different delivery mechanisms, progress in the field is slow because the response of cells exposed to external electrical stimulus is frequently omitted from such investigations. In this work, we monitor the behavior of prostate and breast cancer cells (PC-3 and MCF7, respectively) exposed to electroactive platforms loaded with curcumin, a hydrophobic anticancer drug. These consist in conducting polymer nanoparticles, which release drug molecules by altering their interactions with polymer, and electrospun polyester microfibres that contain electroactive nanoparticles able to alter the porosity of the matrix through an electro-mechanical actuation mechanism. The response of the cells against different operating conditions has been examined considering their viability, metabolism, spreading and shape. Results have allowed us to differentiate the damage induced in the cell by the electrical stimulation from other effects, as for example, the anticancer activity of curcumin and/or the presence of curcumin-loaded nanoparticles or fibres, demonstrating that these kinds of platforms can be effective when the dosage of the drug occurs under restricted conditions.

Free-Standing Faradaic Motors Based on Biocompatible Nanoperforated Poly(lactic Acid) Layers and Electropolymerized Poly(3,4-ethylenedioxythiophene)

The electro-chemo-mechanical response of robust and flexible free-standing films made of three nanoperforated poly(lactic acid) (pPLA) layers separated by two anodically polymerized poly(3,4-ethylenedioxythiophene) (PEDOT) layers has been demonstrated. The mechanical and electrochemical properties of these films, which are provided by pPLA and PEDOT, respectively, have been studied by nanoindentation, cyclic voltammetry, and galvanostatic charge-discharge assays. The unprecedented combination of properties obtained for this system is appropriated for its utilization as a Faradaic motor, also named artificial muscle. Application of square potential waves has shown important bending movements in the films, which can be repeated for more than 500 cycles without damaging its mechanical integrity. Furthermore, the actuator is able to push a huge amount of mass, as it has been proved by increasing the mass of the passive pPLA up to 328% while keeping the mass of electroactive PEDOT unaltered.

Conjugated Polymer Actuators and Devices: Progress and Opportunities

Conjugated polymers (CPs), as exemplified by polypyrrole, are intrinsically conducting polymers with potential for development as soft actuators or "artificial muscles" for numerous applications. Significant progress has been made in the understanding of these materials and the actuation mechanisms, aided by the development of physical and electrochemical models. Current research is focused on developing applications utilizing the advantages that CP actuators have (e.g., low driving potential and easy to miniaturize) over other actuating materials and on developing ways of overcoming their inherent limitations. CP actuators are available as films, filaments/yarns, and textiles, operating in liquids as well as in air, ready for use by engineers. Here, the milestones made in understanding these unique materials and their development as actuators are highlighted. The primary focus is on the recent progress, developments, applications, and future opportunities for improvement and exploitation of these materials, which possess a wealth of multifunctional properties.

Visual detection of odorant geraniol enabled by integration of a human olfactory receptor into polydiacetylene/lipid nano-assembly

A new polydiacetylene lipid/human olfactory receptor nano-assembly was fabricated for the visual detection of an odorant for the first time. The assembly consisted of phospholipid-mixed polydiacetylenes (PDAs) and human olfactory receptors (hORs) in detergent micelles. To overcome the limitations of bioelectronic noses, hOR-embedded chromatic complexes (PDA/hORs) were developed, introducing PDAs that showed color and fluorescence transitions against various stimuli. The chromatic nanocomplexes reacted with target molecules, showing a fluorescence intensity increase in a dose-dependent manner and target selectivity among various odorants. As a result, a color transition of the assembly from blue to purple occurred, allowing the visual detection of the odorant geraniol. Through circular dichroism (CD) spectroscopy and a tryptophan fluorescence quenching method, the structural and functional properties of the hORs embedded in the complexes were confirmed. Based on this first work, future array devices, integrating multiple nano-assemblies, can be substantiated and utilized in environmental assessment and analysis of food quality.

Highly adjustable 3D nano-architectures and chemistries via assembled 1D biological templates

Porous metal nanofoams have made significant contributions to a diverse set of technologies from separation and filtration to aerospace. Nonetheless, finer control over nano and microscale features must be gained to reach the full potential of these materials in energy storage, catalytic, and sensing applications. As biologics naturally occur and assemble into nano and micro architectures, templating on assembled biological materials enables nanoscale architectural control without the limited chemical scope or specialized equipment inherent to alternative synthetic techniques. Here, we rationally assemble 1D biological templates into scalable, 3D structures to fabricate metal nanofoams with a variety of genetically programmable architectures and material chemistries. We demonstrate that nanofoam architecture can be modulated by manipulating viral assembly, specifically by editing the viral surface coat protein, as well as altering templating density. These architectures were retained over a broad range of compositions including monometallic and bi-metallic combinations of noble and transition metals of copper, nickel, cobalt, and gold. Phosphorous and boron incorporation was also explored. In addition to increasing the surface area over a factor of 50, as compared to the nanofoam's geometric footprint, this process also resulted in a decreased average crystal size and altered phase composition as compared to non-templated controls. Finally, templated hydrogels were deposited on the centimeter scale into an array of substrates as well as free standing foams, demonstrating the scalability and flexibility of this synthetic method towards device integration. As such, we anticipate that this method will provide a platform to better study the synergistic and de-coupled effects between nano-structure and composition for a variety of applications including energy storage, catalysis, and sensing.

Soft Robotics: Academic Insights and Perspectives Through Bibliometric Analysis

Soft robotics is of growing interest in the robot community as well as in public media, and there is an increase in the quality and quantity of publications related to this topic. To formally elaborate this growth, we have used a bibliometric analysis to evaluate the publications in the field from 1990 to 2017 based on the Science Citation Index Expanded database. We present a detailed overview and discussion based on keywords, citation, h-index, year, journal, institution, country, author, and review articles. The results show that the United States takes the leading position in this research field, followed by China and Italy. Harvard University has the most publications, high average number of citations per publication and the highest h-index. IEEE Transactions on Robotics ranks first among the top 20 academic journals publishing articles related to this field, whereas Soft Robotics holds the top position in journals categorized with "ROBOTICS." Actuator, fabrication, control, material, sensing, simulation, bionics, stiffness, modeling, power, motion, and application are the hot topics of soft robotics. Smart materials, bionics, morphological computation, and embodiment control are expected to contribute to this field in the future. Application and commercialization appear to be the initial driving force and final goal for soft robots.

Electroactive polymers for tissue regeneration: Developments and perspectives

Human body motion can generate a biological electric field and a current, creating a voltage gradient of -10 to -90 mV across cell membranes. In turn, this gradient triggers cells to transmit signals that alter cell proliferation and differentiation. Several cell types, counting osteoblasts, neurons and cardiomyocytes, are relatively sensitive to electrical signal stimulation. Employment of electrical signals in modulating cell proliferation and differentiation inspires us to use the electroactive polymers to achieve electrical stimulation for repairing impaired tissues. Electroactive polymers have found numerous applications in biomedicine due to their capability in effectively delivering electrical signals to the seeded cells, such as biosensing, tissue regeneration, drug delivery, and biomedical implants. Here we will summarize the electrical characteristics of electroactive polymers, which enables them to electrically influence cellular function and behavior, including conducting polymers, piezoelectric polymers, and polyelectrolyte gels. We will also discuss the biological response to these electroactive polymers under electrical stimulation. In particular, we focus this review on their applications in regenerating different tissues, including bone, nerve, heart muscle, cartilage and skin. Additionally, we discuss the challenges in tissue regeneration applications of electroactive polymers. We conclude that electroactive polymers have a great potential as regenerative biomaterials, due to their ability to stimulate desirable outcomes in various electrically responsive cells.