Review of cathodic electroactive bacteria: Species, properties, applications and electron transfer mechanisms.

Cathodic electroactive bacteria (C-EAB) which are capable of accepting electrons from solid electrodes provide fresh avenues for pollutant removal, biosensor design, and electrosynthesis. This review systematically summarized the burgeoning applications of the C-EAB over the past decade, including 1) removal of nitrate, aromatic derivatives, and metal ions; 2) biosensing based on biocathode; 3) electrosynthesis of CH4, H2, organic carbon, NH3, and protein. In addition, the mechanisms of electron transfer by the C-EAB are also classified and summarized. Extracellular electron transfer and interspecies electron transfer have been introduced, and the electron transport mechanism of typical C-EAB, such as Shewanella oneidensis MR-1, has been combed in detail. By bringing to light this cutting-edge area of the C-EAB, this review aims to stimulate more interest and research on not only exploring great potential applications of these electron-accepting bacteria, but also developing steady and scalable processes harnessing biocathodes.

Electric wiring of bacteria using redox polymers and selective measurement of metabolic activity in the presence of surrounding planktonic bacteria.

Non-electroactive bacteria (n-EAB), constituting the majority of known bacteria to date, have been underutilized in electrochemical conversion technologies due to their lack of direct electron transfer to electrodes. In this study, we established an electric wiring between n-EAB (gram-positive Bacillus subtilis and gram-negative Escherichia coli) and an extracellular electrode via a ferrocene-polyethyleneimine-based redox polymer (Fc-PEI). Chronoamperometry recordings indicated that Fc-PEI can transfer intracellular electrons to the extracellular electrode regardless of the molecular organization of PEI (linear or branched) and the membrane structure of bacteria (gram-positive or -negative). As fluorescence staining suggested, Fc-PEI improves the permeability of the bacterial cell membrane, enabling electron carriers in the cell to react with Fc. In addition, experiments with Fc-immobilized electrodes without PEI suggested the existence of an alternative electron transfer pathway from B. subtilis to the extracellular Fc adsorbed onto the cell membrane. Furthermore, we proposed for the first time that the bacteria/Fc-linear PEI modified structure enables selective measurement of immobilized bacterial activity by physically blocking contact between the electrode surface and planktonic cells co-existing in the surrounding media. Such electrodes can be a powerful analytical tool for elucidating the metabolic activities of specific bacteria wired to the electrode even within complex bacterial communities.

The surface charge of electroactive materials governs cell behaviour through its effect on protein deposition.

The precise mechanisms underlying the cellular response to static electric cues remain unclear, limiting the design and development of biomaterials that utilize this parameter to enhance specific biological behaviours. To gather information on this matter we have explored the interaction of collagen type-I, the most abundant mammalian extracellular protein, with poly(vinylidene fluoride) (PVDF), an electroactive polymer with great potential for tissue engineering applications. Our results reveal significant differences in collagen affinity, conformation, and interaction strength depending on the electric charge of the PVDF surface, which subsequently affects the behaviour of mesenchymal stem cells seeded on them. These findings highlight the importance of surface charge in the establishment of the material-protein interface and ultimately in the biological response to the material. STATEMENT OF SIGNIFICANCE: The development of new tissue engineering strategies relies heavily on the understanding of how biomaterials interact with biological tissues. Although several factors drive this process and their driving principles have been identified, the relevance and mechanism by which the surface potential influences cell behaviour is still unknown. In our study, we investigate the interaction between collagen, the most abundant component of the extracellular matrix, and poly(vinylidene fluoride) with varying surface charges. Our findings reveal substantial variations in the binding forces, structure and adhesion of collagen on the different surfaces, which collectively explain the differential cellular responses. By exposing these differences, our research fills a critical knowledge gap and paves the way for innovations in material design for advanced tissue regeneration strategies.

Towards rapid formation of electroactive biofilm: insights from thermodynamics and electric field manipulation.

Electroactive biofilm (EAB) has garnered significant attention due to its effectiveness in pollutant remediation, electricity generation, and chemical synthesis. However, achieving precise control over the rapid formation of EAB presents challenges for the practical implementation of bioelectrochemical technology. In this study, we investigated the regulation of EAB formation by manipulating applied electric potential. We developed a modified XDLVO model for the applied electric field and quantitatively assessed the feasibility of existing rapid formation strategies for EAB. Our results revealed that electrostatic (EL) force significantly influenced EAB formation in the presence of the applied electric field, with the potential difference between the electrode and the microbial solution being the primary determinant of EL force. Compared to -0.2 V and 0 V vs.Ag/AgCl, EAB exhibited the highest electrochemical performance at 0.2 V vs.Ag/AgCl, with a maximum current density of 6.044 ± 0.10 A/m2, surpassing that at -0.2 V vs.Ag/AgCl and 0 V vs.Ag/AgCl by 1.73 times and 1.31 times, respectively. Furthermore, EAB demonstrated the highest biomass accumulation, measuring a thickness of 25 ± 2 µm at 0.2 V vs. Ag/AgCl, representing increases of 1.67 and 1.25 times compared to -0.2 V vs.Ag/AgCl and 0 V vs.Ag/AgCl, respectively. The strong electrostatic attraction under the anodic potential promoted the formation of a monolayer of biofilm. Additionally, the hydrophilicity and hydrophobicity of the biofilm were altered following inversion culture. The Lewis acid-base (AB) attraction offset the electrostatic repulsion caused by negative charges, it is beneficial for the formation of biofilms. This study, for the first time, elucidated the difference in the formation of cathode and anode biofilm from a thermodynamic perspective in the context of electric field introduction, laying the theoretical foundation for the directional regulation of the rapid formation of typical electroactive biofilms.

Intermittent electrostimulation-modified direct interspecies electron transfer for enhanced methanogenesis in anaerobic digestion of sulfate-rich wastewater.

Methane recovery and organics removal in sulfate (SO42-)-rich wastewater anaerobic digestion are hindered by electron competition between methanogenesis and sulfidogenesis. Here, intermittently electrostimulated bioelectrodes were developed to facilitate direct interspecies electron transfer (DIET)-driven syntrophic methanogenesis, increasing substrate competition among methanogenic archaea (MA). By optimising the electrochemical environment, MA was able to employ electron transfer more efficiently than sulfate-reducing bacteria (SRB), resulting in significant methane accumulation (58.1 ± 1.0 mL-CH4/m3reactor) and COD removal (90.5 ± 0.5 %) at lower COD/SO42- ratio. Intermittent electrostimulation improved the metabolic pathway for electroactive bacteria to utilize acetate and direct electrons to electrotrophic MA, decreasing SRB abundance and affecting the sulfate reduction pathway. Intermittently electrostimulated biofilms significantly increased gene levels of key enzymes in electron transport for cytochrome and e-pili biosynthesis, crucial for DIET, demonstrating enhanced DIET-driven syntrophic methanogenesis. This study provides a strategic approach to optimize methanogenesis in sulfate-rich wastewater anaerobic digestion.

Integrating Graphene Oxide-Hydrogels and Electrical Stimulation for Controlled Neurotrophic Factor Encapsulation: A Promising Approach for Efficient Nerve Tissue Regeneration.

Nerve growth factor (NGF) plays a crucial role in cellular growth and neurodifferentiation. To achieve significant neuronal regeneration and repair using in vitro NGF delivery, spatiotemporal control that follows the natural neuronal processes must be developed. Notably, a challenge hindering this is the uncontrolled burst release from the growth factor delivery systems. The rapid depletion of NGF reduces treatment efficacy, leading to poor cellular response. To address this, we developed a highly controllable system using graphene oxygen (GO) and GelMA hydrogels modulated by electrical stimulation. Our system showed superior control over the release kinetics, reducing the burst up 30-fold. We demonstrate that the system is also able to sequester and retain NGF up to 10-times more efficiently than GelMA hydrogels alone. Our controlled release system enabled neurodifferentiation, as revealed by gene expression and immunostaining analysis. The increased retention and reduced burst release from our system show a promising pathway for nerve tissue engineering research toward effective regeneration.

Chlorophyll a acts as a natural photosensitizer to drive nitrate reduction in nonphotosynthetic microorganisms.

With the death and decomposition of widely distributed photosynthetic organisms, free natural pigments are often detected in surface water, sediment and soil. Whether free pigments can act as photosensitizers to drive biophotoelectrochemical metabolism in nonphotosynthetic microorganisms has not been reported. In this work, we provide direct evidence for the photoelectrophic relationship between extracellular chlorophyll a (Chl a) and nonphotosynthetic microorganisms. The results show that 10 µg of Chl a can produce significant photoelectrons (∼0.34 A/cm2) upon irradiation to drive nitrate reduction in Shewanella oneidensis. Chl a undergoes structural changes during the photoelectric process, thus the ability of Chl a to generate a photocurrent decreases gradually with increasing illumination time. These changes are greater in the presence of microorganisms than in the absence of microorganisms. Photoelectron transport from Chl a to S. oneidensis occurs through a direct pathway involving the cytochromes MtrA, MtrB, MtrC and CymA but not through an indirect pathway involving riboflavin. These findings reveal a novel photoelectrotrophic linkage between natural photosynthetic pigments and nonphototrophic microorganisms, which has important implications for the biogeochemical cycle of nitrogen in various natural environments where Chl a is distributed.

Interspecies ecological competition rejuvenates decayed Geobacter electroactive biofilm.

Bioelectrochemical systems (BESs) exploit electroactive biofilms (EABs) for promising applications in biosensing, wastewater treatment, energy production, and chemical biosynthesis. However, during the operation of BESs, EABs inevitably decay. Seeking approaches to rejuvenate decayed EABs is critical for the sustainability and practical application of BESs. Prophage induction has been recognized as the primary reason for EAB decay. Herein, we report that introducing a competitive species of Geobacter uraniireducens suspended prophage induction in Geobacter sulfurreducens and thereby rejuvenated the decayed G. sulfurreducens EAB. The transcriptomic profile of G. sulfurreducens demonstrated that the addition of G. uraniireducens significantly affected the expression of metabolism- and stress response system-related genes and in particular suppressed the induction of phage-related genes. Mechanistic analyses revealed that interspecies ecological competition exerted by G. uraniireducens suppressed prophage induction. Our findings not only reveal a novel strategy to rejuvenate decayed EABs, which is significant for the sustainability of BESs, but also provide new knowledge for understanding phage-host interactions from an ecological perspective, with implications for developing therapies to defend against phage attack.

Electroactive Ionic Polymer of Intrinsic Microporosity for High-Performance Capacitive Energy Storage.

Here, we report an ionic polymer of intrinsic microporosity (PIM) as a high-functioning supercapacitor electrode without the need for conductive additives or binders. The performance of this material is directly related to its large accessible surface area. By comparing electrochemical performance between a porous viologen PIM and a non-porous viologen polymer, we reveal that the high energy and power density are both due to the ability of ions to rapidly access the ionic PIM. In 0.1 M H2SO4 electrolyte, a pseudocapacitve energy of 315 F g-1 is observed, whereas in 0.1 M Na2SO4, a capacitive energy density of 250 F g-1 is obtained. In both cases, this capacity is retained over 10,000 charge-discharge cycles, without the need for stabilizing binders or conductive additives even at moderate loadings (5 mg cm-2). This desirable performance is maintained in a prototype symmetric two-electrode capacitor device, which had >99% Coloumbic efficiency and a <10 mF capacity drop over 2000 cycles. These results demonstrate that ionic PIMs function well as standalone supercapacitor electrodes and suggest ionic PIMs may perform well in other electrochemical devices such as sensors, ion-separation membranes, or displays. This article is protected by copyright. All rights reserved.

Design Optimization of Printed Multi-Layered Electroactive Actuators Used for Steerable Guidewire in Micro-Invasive Surgery.

To treat cardiovascular diseases (i.e., a major cause of mortality after cancers), endovascular-technique-based guidewire has been employed for intra-arterial navigation. To date, most commercially available guidewires (e.g., Terumo, Abbott, Cordis, etc.) are non-steerable, which is poorly suited to the human arterial system with numerous bifurcations and angulations. To reach a target artery, surgeons frequently opt for several tools (guidewires with different size integrated into angulated catheters) that might provoke arterial complications such as perforation or dissection. Steerable guidewires would, therefore, be of high interest to reduce surgical morbidity and mortality for patients as well as to simplify procedure for surgeons, thereby saving time and health costs. Regarding these reasons, our research involves the development of a smart steerable guidewire using electroactive polymer (EAP) capable of bending when subjected to an input voltage. The actuation performance of the developed device is assessed through the curvature behavior (i.e., the displacement and the angle of the bending) of a cantilever beam structure, consisting of single- or multi-stack EAP printed on a substrate. Compared to the single-stack architecture, the multi-stack gives rise to a significant increase in curvature, even when subjected to a moderate control voltage. As suggested by the design framework, the intrinsic physical properties (dielectric, electrical, and mechanical) of the EAP layer, together with the nature and thickness of all materials (EAP and substrate), do have strong effect on the bending response of the device. The analyses propose a comprehensive guideline to optimize the actuator performance based on an adequate selection of the relevant materials and geometric parameters. An analytical model together with a finite element model (FEM) are investigated to validate the experimental tests. Finally, the design guideline leads to an innovative structure (composed of a 10-stack active layer screen-printed on a thin substrate) capable of generating a large range of bending angle (up to 190°) under an acceptable input level of 550 V, which perfectly matches the standard of medical tools used for cardiovascular surgery.

Wired for Success: Probing the Effect of Tissue-Engineered Neural Interface Substrates on Cell Viability.

This study investigates the electrochemical behavior of GelMA-based hydrogels and their interactions with PC12 neural cells under electrical stimulation in the presence of conducting substrates. Focusing on indium tin oxide (ITO), platinum, and gold mylar substrates supporting conductive scaffolds composed of hydrogel, graphene oxide, and gold nanorods, we explored how the substrate materials affect scaffold conductivity and cell viability. We examined the impact of an optimized electrical stimulation protocol on the PC12 cell viability. According to our findings, substrate selection significantly influences conductive hydrogel behavior, affecting cell viability and proliferation as a result. In particular, the ITO substrates were found to provide the best support for cell viability with an average of at least three times higher metabolic activity compared to platinum and gold mylar substrates over a 7 day stimulation period. The study offers new insights into substrate selection as a platform for neural cell stimulation and underscores the critical role of substrate materials in optimizing the efficacy of neural interfaces for biomedical applications. In addition to extending existing work, this study provides a robust platform for future explorations aimed at tailoring the full potential of tissue-engineered neural interfaces.

Stimuli-responsive microcarriers and their application in tissue repair: A review of magnetic and electroactive microcarrier.

Microcarrier applications have made great advances in tissue engineering in recent years, which can load cells, drugs, and bioactive factors. These microcarriers can be minimally injected into the defect to help reconstruct a good microenvironment for tissue repair. In order to achieve more ideal performance and face more complex tissue damage, an increasing amount of effort has been focused on microcarriers that can actively respond to external stimuli. These microcarriers have the functions of directional movement, targeted enrichment, material release control, and providing signals conducive to tissue repair. Given the high controllability and designability of magnetic and electroactive microcarriers, the research progress of these microcarriers is highlighted in this review. Their structure, function and applications, potential tissue repair mechanisms, and challenges are discussed. In summary, through the design with clinical translation ability, meaningful and comprehensive experimental characterization, and in-depth study and application of tissue repair mechanisms, stimuli-responsive microcarriers have great potential in tissue repair.

A Microactuator Array Based on Ionic Electroactive Artificial Muscles for Cell Mechanical Stimulation.

Mechanical stimulation is prevalent within organisms, and appropriate regulation of such stimulation can significantly enhance cellular functions. Consequently, the in vitro construction and simulation of mechanical stimulation have emerged as a research hotspot in biomechanics. In recent years, a class of artificial muscles named electroactive polymers (EAPs), especially ionic EAPs, have shown promising applications in biomechanics. While several techniques utilizing ionic EAPs for cell mechanical stimulation have been reported, further research is needed to advance and enhance their practical applications. Here, we prepared a microactuator array based on ionic EAP artificial muscles for cell mechanical stimulation. As a preliminary effort, we created a 5 × 5 microactuator array on a supporting membrane by employing laser cutting. We evaluated the electro-actuation performance of the microactuators through experimental testing and numerical simulations, affirming the potential use of the microactuator array for cell mechanical stimulation. The devised approach could inspire innovative design concepts in the development of miniaturized intelligent electronic devices, not only in biomechanics and biomimetics but also in other related fields.

A biocompatible electrode/exoelectrogens interface augments bidirectional electron transfer and bioelectrochemical reactions.

Bidirectional electron transfer is about that exoelectrogens produce bioelectricity via extracellular electron transfer at anode and drive cytoplasmic biochemical reactions via extracellular electron uptake at cathode. The key factor to determine above bioelectrochemical performances is the electron transfer efficiency under biocompatible abiotic/biotic interface. Here, a graphene/polyaniline (GO/PANI) nanocomposite electrode specially interfacing exoelectrogens (Shewanella loihica) and augmenting bidirectional electron transfer was conducted by in-situ electrochemical modification on carbon paper (CP). Impressively, the GO/PANI@CP electrode tremendously improved the performance of exoelectrogens at anode for wastewater treatment and bioelectricity generation (about 54 folds increase of power density compared to blank CP electrode). The bacteria on electrode surface not only showed fast electron release but also exhibited high electricity density of extracellular electron uptake through the proposed direct electron transfer pathway. Thus, the cathode applications of microbial electrosynthesis and bio-denitrification were developed via GO/PANI@CP electrode, which assisted the close contact between microbial outer-membrane cytochromes and nanocomposite electrode for efficient nitrate removal (0.333 mM/h). Overall, nanocomposite modified electrode with biocompatible interfaces has great potential to enhance bioelectrochemical reactions with exoelectrogens.

Optimizing bioelectromethanosynthesis of CO2 and membrane fouling mitigation in MECs via in-situ biogas recirculation.

The CO2 bioelectromethanosynthesis via two-chamber microbial electrolysis cell (MEC) holds tremendous potential to solve the energy crisis and mitigate the greenhouse gas emissions. However, the membrane fouling is still a big challenge for CO2 bioelectromethanosynthesis owing to the poor proton diffusion across membrane and high inter-resistance. In this study, a new MEC bioreactor with biogas recirculation unit was designed in the cathode chamber to enhance secondary-dissolution of CO2 while mitigating the contaminant adhesion on membrane surface. Biogas recirculation improved CO2 re-dissolution, reduced concentration polarization, and facilitated the proton transmembrane diffusion. This resulted in a remarkable increase in the cathodic methane production rate from 0.4 mL/L·d to 8.5 mL/L·d. A robust syntrophic relationship between anodic organic-degrading bacteria (Firmicutes 5.29%, Bacteroidetes 25.90%, and Proteobacteria 6.08%) and cathodic methane-producing archaea (Methanobacterium 65.58%) enabled simultaneous organic degradation, high CO2 bioelectromethanosynthesis, and renewable energy storage.

Green and Heavy-Duty Anticorrosion Coatings: Waterborne Epoxy Thermoset Composites Modified through Variation of Zinc Dust Loading and Incorporation of Amine-Capped Aniline Trimer and Graphene Oxide.

In this study, an array of environmentally friendly and heavy-duty anticorrosion composite coatings were prepared. The synthesis involved amine-capped aniline trimer (ACAT) produced by an oxidative coupling reaction and graphene oxide (GO) prepared based on Hummer's method, and later, the waterborne epoxy thermoset composite (WETC) coatings were prepared by thermal ring-opening polymerization of EP 147w, a commercial waterborne epoxy resin, in the presence of ACAT and/or GO with zinc dust (ZD). A synergistic effect was observed by replacing a significant amount of the ZD loading in the WETC by simultaneously incorporating a small amount of ACAT and GO. The electrochemical corrosion measurements of the as-prepared WETC coatings indicated that incorporating 5% w/w ACAT or 0.5% w/w GO separately replaced approximately 30% w/w or 15% w/w of the ZD, respectively. Moreover, the WETC coatings containing 5% w/w ACAT and 0.5% w/w GO simultaneously were found to replace 45% w/w of the ZD. A salt spray test based on ASTM B-117 also showed a consistent trend with the electrochemical results. Incorporating small amounts of ACAT and GO in WETC coatings instead of ZD not only maintains the anticorrosion performance but also enhances adhesion and abrasion resistance, as demonstrated by the adhesion and abrasion tests.

Electron Transfer in the Biogeochemical Sulfur Cycle.

Microorganisms are key players in the global biogeochemical sulfur cycle. Among them, some have garnered particular attention due to their electrical activity and ability to perform extracellular electron transfer. A growing body of research has highlighted their extensive phylogenetic and metabolic diversity, revealing their crucial roles in ecological processes. In this review, we delve into the electron transfer process between sulfate-reducing bacteria and anaerobic alkane-oxidizing archaea, which facilitates growth within syntrophic communities. Furthermore, we review the phenomenon of long-distance electron transfer and potential extracellular electron transfer in multicellular filamentous sulfur-oxidizing bacteria. These bacteria, with their vast application prospects and ecological significance, play a pivotal role in various ecological processes. Subsequently, we discuss the important role of the pili/cytochrome for electron transfer and presented cutting-edge approaches for exploring and studying electroactive microorganisms. This review provides a comprehensive overview of electroactive microorganisms participating in the biogeochemical sulfur cycle. By examining their electron transfer mechanisms, and the potential ecological and applied implications, we offer novel insights into microbial sulfur metabolism, thereby advancing applications in the development of sustainable bioelectronics materials and bioremediation technologies.

Single-Walled Carbon Nanotube-Reinforced PEDOT: PSS Hybrid Electrodes for High-Performance Ionic Electroactive Polymer Actuator.

Ionic electroactive polymer (iEAP) actuators are recognized as exceptional candidates for artificial muscle development, with significant potential applications in bionic robotics, space exploration, and biomedical fields. Here, we developed a new iEAP actuator utilizing high-purity single-walled carbon nanotubes (SWCNTs)-reinforced poly(3, 4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT: PSS, PP) hybrid electrodes and a Nafion/EMIBF4 ion-exchange membrane via a straightforward and efficient spray printing technique. The SWCNT/PP actuator exhibits significantly enhanced electric conductivity (262.9 S/cm) and specific capacitance (22.5 mF/cm2), benefitting from the synergistic effect between SWCNTs and PP. These improvements far surpass those observed in activated carbon aerogel bucky-gel-electrode-based actuators. Furthermore, we evaluated the electroactive behaviors of the SWCNT/PP actuator under alternating square-wave voltages (1-3 V) and frequencies (0.01-100 Hz). The results reveal a substantial bending displacement of 6.44 mm and a high bending strain of 0.61% (at 3 V, 0.1 Hz), along with a long operating stability of up to 10,000 cycles (at 2 V, 1 Hz). This study introduces a straightforward and efficient spray printing technique for the successful preparation of iEAP actuators with superior electrochemical and electromechanical properties as intended, which hold promise as artificial muscles in the field of bionic robotics.

Nonelectroactive clostridium obtains extracellular electron transfer-capability after forming chimera with Geobacter.

Extracellular electron transfer (EET) of microorganisms is a major driver of the microbial growth and metabolism, including reactions involved in the cycling of C, N, and Fe in anaerobic environments such as soils and sediments. Understanding the mechanisms of EET, as well as knowing which organisms are EET-capable (or can become so) is fundamental to electromicrobiology and geomicrobiology. In general, Gram-positive bacteria very seldomly perform EET due to their thick non-conductive cell wall. Here, we report that a Gram-positive Clostridium intestinale (C.i) attained EET-capability for ethanol metabolism only after forming chimera with electroactive Geobacter sulfurreducens (G.s). Mechanism analyses demonstrated that the EET was possible after the cell fusion of the two species was achieved. Under these conditions, the ethanol metabolism pathway of C.i was integrated by the EET pathway of G.s, by which achieved the oxidation of ethanol for the subsequent reduction of extracellular electron acceptors in the coculture. Our study displays a new approach to perform EET for Gram-positive bacteria via recruiting the EET pathway of an electroactive bacterium, which suggests a previously unanticipated prevalence of EET in the microbial world. These findings also provide new perspectives to understand the energetic coupling between bacterial species and the ecology of interspecies mutualisms.

Osteogenic differentiation of human mesenchymal stem cells on electroactive substrates.

This study investigates the effect of electroactivity and electrical charge distribution on the biological response of human bone marrow stem cells (hBMSCs) cultured in monolayer on flat poly(vinylidene fluoride), PVDF, substrates. Differences in cell behaviour, including proliferation, expression of multipotency markers CD90, CD105 and CD73, and expression of genes characteristic of different mesenchymal lineages, were observed both during expansion in basal medium before reaching confluence and in confluent cultures in osteogenic induction medium. The crystallisation of PVDF in the electrically neutral α-phase or in the electroactive phase ß, both unpoled and poled, has been found to have an important influence on the biological response. In addition, the presence of a permanent positive or negative surface electrical charge distribution in phase ß substrates has also shown a significant effect on cell behaviour.