Challenges for successful implantation of biofuel cells

Two-Ply Carbon Nanotube Fiber-Typed Enzymatic Biofuel Cell Implanted in Mice

Implantable devices have emerged as a promising industry. It is inevitable that these devices will require a power source to operate in vivo. Thus, to power implantable medical devices, biofuel cells (BFCs) that generate electricity using glucose without an external power supply have been considered. Although implantable BFCs have been developed for application in vivo, they are limited by their bulky electrodes and low power density. In the present study, we attempted to apply to living mice an implantable enzymatic BFC (EBFC) that was previously reported to be a high-power EBFC comprising carbon nanotube yarn electrodes. To improve their mechanical properties and for convenient implantation, the electrodes were coated with Nafion and twisted into a micro-sized, two-ply, one-body system. When the two-ply EBFC system was implanted in the abdominal cavity of mice, it provided a high-power density of 0.3 mW/cm². The two-ply EBFC system was injected through a needle using a syringe without surgery and the inflammatory response in vivo initially induced by the injection of the EBFC system was attenuated after 7 days, indicating the biocompatibility of the system in vivo.

The biocompatibility of biofuel cells operating inside the body

In 1968 Wolfson et al. published the concept for producing energy inside the body using catalytic electrodes exposed to the body fluid as an electrolyte and utilising naturally occurring fuels such as glucose. Since then, the technology has advanced to enhance the levels of power using enzymes immobilised within three-dimensional bioelectrodes that are nanostructured. Current research in the field of enzymatic fuel cells is directed toward applying electrochemical and nanostructural expertise to increase the energy density, to increase the power density, to increase the operational stability, and to increase the voltage output. Nonetheless, biocompatibility remains the major challenge for increasing the life-time for implanted enzymatic biofuel cells. Here, we discuss the current issues for biocompatibility and suggest directions to enhance the design of biofuel cells so as to increase the life-time of implantation whilst maintaining sufficient performance to provide power for implanted medical devices.

Challenges for the Implantation of Symbiotic Nanostructured Medical Devices

We discuss the perspectives of designing implantable medical devices that have the criterion of being symbiotic. Our starting point was whether the implanted device is intended to have any two-way (“duplex”) communication of energy or materials with the body. Such duplex communication extends the existing concepts of a biomaterial and biocompatibility to include the notion that it is important to consider the intended functional use of the implanted medical device. This demands a biomimetic approach to design functional symbiotic implantable medical devices that can be more efficient in mimicking what is happening at the molecular and cellular levels to create stable interfaces that allow for the unfettered exchanges of molecules between an implanted device and a body. Such a duplex level of communication is considered to be a necessary characteristic of symbiotic implanted medical devices that are designed to function for long periods of time inside the body to restore and assist the function of the body. We illustrate these perspectives with experience gained from implanting functional enzymatic biofuel cells.

Application of Electrically Conducting Nanocomposite Material Polythiophene@NiO/Frt/GOx as Anode for Enzymatic Biofuel Cells

In this work, nano-inspired nickel oxide nanoparticles (NiO) and polythiophene (Pth) modified bioanode was prepared for biofuel cell applications. The chemically prepared nickel oxide nanoparticles and its composite with polythiophene were characterized for elemental composition and microscopic characterization while using scanning electron microscopy. The electrochemical characterizations of polythiophene@NiO composite, biocompatible mediator ferritin (Frt) and glucose oxidase (GOx) catalyst modified glassy carbon (GC) electrode were carried out using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and charge-discharge studies. The current density of Pth@NiO/Frt/GOx bioanode was found to be 5.4 mA/cm². The bioanode exhibited a good bio-electrocatalytic activity towards the oxidation of the glucose. The experimental studies of the bioanode are justifying its employment in biofuel cells. This will cater a platform for the generation of sustainable energy for low temperature devices.

Materials Strategies and Device Architectures of Emerging Power Supply Devices for Implantable Bioelectronics

Implantable bioelectronics represent an emerging technology that can be integrated into the human body for diagnostic and therapeutic functions. Power supply devices are an essential component of bioelectronics to ensure their robust performance. However, conventional power sources are usually bulky, rigid, and potentially contain hazardous constituent materials. The fact that biological organisms are soft, curvilinear, and have limited accommodation space poses new challenges for power supply systems to minimize the interface mismatch and still offer sufficient power to meet clinical-grade applications. Here, recent advances in state-of-the-art nonconventional power options for implantable electronics, specifically, miniaturized, flexible, or biodegradable power systems are reviewed. Material strategies and architectural design of a broad array of power devices are discussed, including energy storage systems (batteries and supercapacitors), power devices which harvest sources from the human body (biofuel cells, devices utilizing biopotentials, piezoelectric harvesters, triboelectric devices, and thermoelectric devices), and energy transfer devices which utilize sources in the surrounding environment (ultrasonic energy harvesters, inductive coupling/radiofrequency energy harvesters, and photovoltaic devices). Finally, future challenges and perspectives are given.

One-Pot Aqueous Synthesis of Icosahedral Au as Bifunctional Candidates for Enhanced Glucose Electrooxidation and Surface-Enhanced Raman Scattering

Bifunctional candidates, which could provide catalytic and plasmonic properties simultaneously, could activate a promising development for biomedicine. Here, we kinetically controlled and synthesized a penta-twinned icosahedral Au (Ih Au) by a facile wet-chemical protocol without assistance of stabilizers. Benefiting from icosahedral morphology and kinetic synthesis process, the Ih Au nanoparticles (NPs) incorporate three key advantages: (i) ample active sites/"hot spots" and surface strain, (ii) good stability/chemical inertness and easy functionalization, and (iii) biological compatibility and a clean surface, which could promote their electrocatalysis and photonic capacity. Ih Au NPs, as bifunctional nanomaterials, exert excellent electrocatalytic and surface-enhanced Raman scattering (SERS) performances. Ih Au delivers the highest glucose electrooxidation (GEO) peak current density with 6.87 mA cm^-2, which is 14 times larger than that of Turkevich Au (0.49 mA cm^-2) under the same condition. Moreover, the SERS signals of rhodamine 6G (R6G) on Ih Au are much stronger than that on the other corresponding Au counterparts. Particularly, the SERS intensity of R6G on Ih Au increases by about four times compared to that on Au NPs. This study motivates the great prospect for combining Ih Au's bifunctionalities and indicates the potential of bifunctional nanomaterials in biologically implanted devices.

Long duration stabilization of porous silicon membranes in physiological media: Application for implantable reactors

The natural biodegradabilty of porous silicon (pSi) in physiological media limits its wider usage for implantable systems. We report the stabilization of porous silicon (pSi) membranes by chemical surface oxidation using RCA1 and RCA2 protocols, which was followed by a PEGylation process using a silane-PEG. These surface modifications stabilized the pSi to allow a long period of immersion in PBS, while leaving the pSi surface sufficiently hydrophilic for good filtration and diffusion of several biomolecules of different sizes without any blockage of the pSi structure. The pore sizes of the pSi membranes were between 5 and 20 nm, with the membrane thickness around 70 μm. The diffusion coefficient for fluorescein through the membrane was 2 × 10^-10 cm² s^-1, and for glucose was 2.2 × 10^-9 cm² s^-1. The pSi membrane maintained that level of glucose diffusion for one month of immersion in PBS. After 2 months immersion in PBS the pSi membrane continued to operate, but with a reduced glucose diffusion coefficient. The chemical stabilization of pSi membranes provided almost 1 week stable and functional biomolecule transport in blood plasma and opens the possibility for its short-term implantation as a diffusion membrane in biocompatible systems.

Nature-inspired electrocatalysts and devices for energy conversion

A NICE approach for the design of nature-inspired electrocatalysts and electrochemical devices for energy conversion.

Recent development of biofuel cell based self-powered biosensors

BFC-based SPBs have been used as power sources for other devices and as sensors for detecting toxicity and BOM.

Recent advancement and strategy on bio-hydrogen production from photosynthetic microalgae

Recently, ensuring energy security is a key challenge to political and economic strength in the world. Bio-hydrogen production from microalgae is the promising alternative source for potential renewable and self-sustainability energy but still in the initial phase of development. Practically and sustainability of microalgae hydrogen production is still debatable. The genetic engineering and metabolic pathway engineering of hydrogenase and nitrogenase play a key role to enhance hydrogen production. Microalgae have photosynthetic efficiency and synthesize huge carbohydrate biomass, used as 4th generation feedstock to generate bio-hydrogen. Recent genetically modified strains of microalgae are the attractive source for enhancing bio-hydrogen production in the future. The potential of hydrogen production from microRNAs are gaining great interest of researcher. The main objective of this review is attentive discussed recent approaches on new molecular genetics engineering and metabolic pathway developments, modern photo-bioreactors efficiency, economic assessment, limitations and knowledge gap of bio-hydrogen production from microalgae.

The Future of Cardiovascular Stents: Bioresorbable and Integrated Biosensor Technology

Cardiovascular disease is the greatest cause of death worldwide. Atherosclerosis is the underlying pathology responsible for two thirds of these deaths. It is the age-dependent process of "furring of the arteries." In many scenarios the disease is caused by poor diet, high blood pressure, and genetic risk factors, and is exacerbated by obesity, diabetes, and sedentary lifestyle. Current pharmacological anti-atherosclerotic modalities still fail to control the disease and improvements in clinical interventions are urgently required. Blocked atherosclerotic arteries are routinely treated in hospitals with an expandable metal stent. However, stented vessels are often silently re-blocked by developing "in-stent restenosis," a wound response, in which the vessel's lumen renarrows by excess proliferation of vascular smooth muscle cells, termed hyperplasia. Herein, the current stent technology and the future of biosensing devices to overcome in-stent restenosis are reviewed. Second, with advances in nanofabrication, new sensing methods and how researchers are investigating ways to integrate biosensors within stents are highlighted. The future of implantable medical devices in the context of the emerging "Internet of Things" and how this will significantly influence future biosensor technology for future generations are also discussed.

Biofouling effects on the performance of microbial fuel cells and recent advances in biotechnological and chemical strategies for mitigation

The occurrence of biofouling in MFC can cause severe problems such as hindering proton transfer and increasing the ohmic and charge transfer resistance of cathodes, which results in a rapid decline in performance of MFC. This is one of the main reasons why scaling-up of MFCs has not yet been successfully accomplished. The present review article is a wide-ranging attempt to provide insights to the biofouling mechanisms on surfaces of MFC, mainly on proton exchange membranes and cathodes, and their effects on performance of MFC based on theoretical and practical evidence. Various biofouling mitigation techniques for membranes are discussed, including preparation of antifouling composite membranes, modification of the physical and chemical properties of existing membranes, and coating with antifouling agents. For cathodes of MFC, use of Ag nanoparticles, Ag-based composite nanoparticles, and antifouling chemicals is outlined in considerable detail. Finally, prospective techniques for mitigation of biofouling are discussed, which have not been given much previous attention in the field of MFC research. This article will help to enhance understanding of the severity of biofouling issues in MFCs and provides up-to-date solutions. It will be beneficial for scientific communities for further strengthening MFC research and will also help in progressing this cutting-edge technology to scale-up, using the most efficient methods as described here.

Tackling the Challenges of Enzymatic (Bio)Fuel Cells

The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourth, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.

Frontiers of Medical Robotics: From Concept to Systems to Clinical Translation

Medical robotics is poised to transform all aspects of medicine—from surgical intervention to targeted therapy, rehabilitation, and hospital automation. A key area is the development of robots for minimally invasive interventions. This review provides a detailed analysis of the evolution of interventional robots and discusses how the integration of imaging, sensing, and robotics can influence the patient care pathway toward precision intervention and patient-specific treatment. It outlines how closer coupling of perception, decision, and action can lead to enhanced dexterity, greater precision, and reduced invasiveness. It provides a critical analysis of some of the key interventional robot platforms developed over the years and their relative merit and intrinsic limitations. The review also presents a future outlook for robotic interventions and emerging trends in making them easier to use, lightweight, ergonomic, and intelligent, and thus smarter, safer, and more accessible for clinical use.

Transition-Metal-Doped Molybdenum Diselenides with Defects and Abundant Active Sites for Efficient Performances of Enzymatic Biofuel Cell and Supercapacitor Applications

We have demonstrated the synthesis of defect-rich Ni-doped MoSe₂ nanoplates (NiMoSe₂) and their application as an efficient electrocatalyst for enzymatic biofuel cells and electrochemical pseudocapacitors. In this study, a new type of interpretation is proposed that a defective surface facilitates the effective entrapment of enzymes (glucose oxidase (GOD), laccase) for biofuel cells and additional ion diffusion for Faradic charge-discharge reaction. The transmission electron microscopy and UV-vis spectroscopy techniques scrutinized the formation of defects/distortions and the resultant successful entrapment of enzymes. The performed electrochemical characterizations of enzyme-immobilized NiMoSe₂/nickel foam (NF) bioanode (NiMoSe₂/GOD/NF) and biocathode (NiMoSe₂/laccase/NF) exhibited better direct charge conductive behavior at the interface of enzymes and electrode material. Herein, the assembled biofuel cells exhibited an open-circuit voltage ( V_OC = 0.6 V) and a short-circuit current density ( J_SC = 8.629 mA cm^-2) with a maximum power density ( P_max) of 1.2 mW cm^-2. For the electrochemical pseudocapacitor application, the proposed NiMoSe₂/NF exhibited excellent specific capacitance (535.74 F g^-1), with 86.7% rate performance. Finally, this work suggests new insights into both enzymatic biofuel cell and supercapacitor applications.

A Critical View of Microbial Fuel Cells: What Is the Next Stage?

Microbial fuel cells (MFCs) have garnered interest from the scientific community since the beginning of this century and this has caused a considerable increase in the scientific production of MFCs. However, the ability of MFCs to generate power has not increased considerably within this timeframe. In recent years, the power generated by MFCs has remained at an almost contact level owing to difficulties in the scale-up of the technology and thus the application of MFCs for powering systems with high energy demands will not be fully developed, at least within a short temporal horizon. Scale-up by increasing the size of the electrodes has failed, because of the wrong assumption that a linear function describes the relationship between the amount of power generated by a MFC and its size. However, more efficient energy generation upon working with small MFCs has been described. This has led to a new approach for scaling up on the basis of miniaturization and replication. Then, MFCs can be connected electrically in series to increase the overall potential and in parallel to increase the overall current. However, cell-voltage reversal and ionic short-circuit issues must be solved for this approach to be successful. Nowadays, the applicability of MFC technology in wastewater treatment does not make any sense in light of the power levels reached, despite the fact that MFCs were seen as a paramount opportunity less than a decade ago. However, MFCs can be used for wastewater treatment with coupled energy generation, as well as for other technologies such as biosensors and biologically inspired robots.

Electrochemical performance and microbial community analysis in air cathode microbial fuel cells fuelled with pyroligneous liquor

Microbial fuels cells (MFCs) have been applied for the degradation of pyroligneous liquor (PL) derived from apple tree branches, at different concentrations. The substrate removal, electrochemical properties, and microbial community characteristics were analysed to evaluate the performance of MFCs. Maximum current density (1.94 A/m²), coulombic efficiency (28%), and phenol removal rate (84%) were achieved with MFCs fed with PL at the optimal concentration of 1 g chemical oxygen demand (COD)/L. The polarisation test, cyclic voltammetry, and electrochemical impedance of the electrode redox reaction further explained how the addition of PL could stimulate formation of the electrochemically active biofilm, at the optimal concentration of 1 g COD/L. The microbial community of the anodic biofilm demonstrated that MFCs fed with 1 g COD/L had the highest relative abundance of the typical electrogenic bacteria Geobacter (33%), followed by Sphaerochaeta (6%) and Clostridium (4%). The results revealed that syntrophic interaction of these functional microorganisms contributed significantly to the PL degradation and electrical current generation.

Flexible Laser-Induced Graphene for Nitrogen Sensing in Soil

Flexible graphene electronics are rapidly gaining interest, but their widespread implementation has been impeded by challenges with ink preparation, ink printing, and postprint annealing processes. Laser-induced graphene (LIG) promises a facile alternative by creating flexible graphene electronics on polyimide substrates through the one-step laser writing fabrication method. Herein, we demonstrate the use of LIG, created with a low-cost UV laser, for electrochemical ion-selective sensing of plant-available nitrogen (i.e., both ammonium and nitrate ions: NH₄⁺ and NO₃^-) in soil samples. The laser used to create the LIG was operated at distinct pulse widths (10, 20, 30, 40, and 50 ms) to maximize the LIG electrochemical reactivity. Results illustrated that a laser pulse width of 20 ms led to a high percentage of sp² carbon (77%) and optimal peak oxidation current of 120 μA during cyclic voltammetry of ferro/ferricyanide. Therefore, LIG electrodes created with a 20 ms pulse width were consequently functionalized with distinct ionophores specific to NH₄⁺ (nonactin) or NO₃^- (tridodecylmethylammonium nitrate) within poly(vinyl chloride)-based membranes to create distinct solid contact ion-selective electrodes (SC-ISEs) for NH₄⁺ and NO₃^- ion sensing, respectively. The LIG SC-ISEs displayed near Nernstian sensitivities of 51.7 ± 7.8 mV/dec (NH₄⁺) and -54.8 ± 2.5 mV/dec (NO₃^-), detection limits of 28.2 ± 25.0 μM (NH₄⁺) and 20.6 ± 14.8 μM (NO₃^-), low long-term drift of 0.93 mV/h (NH₄⁺ sensors) and -5.3 μV/h (NO₃^- sensors), and linear sensing ranges of 10^-5-10^-1 M for both sensors. Moreover, soil slurry sensing was performed, and recovery percentages of 96% and 95% were obtained for added NH₄⁺ and NO₃^-, respectively. These results, combined with a facile fabrication that does not require metallic nanoparticle decoration, make these LIG electrochemical sensors appealing for a wide range of in-field or point-of-service applications for soil health management.

Tackling the Concept of Symbiotic Implantable Medical Devices with Nanobiotechnologies

This review takes an approach to implanted medical devices that considers whether the intention of the implanted device is to have any communication of energy or materials with the body. The first part describes some specific examples of three different classes of implants, analyzed with regards to the type of signal sent to cells. Through several examples, the authors describe that a one way signaling to the body leads to encapsulation or degradation. In most cases, those phenomena do not lead to major problems. However, encapsulation or degradation are critical for new kinds of medical devices capable of duplex communication, which are defined in this review as symbiotic devices. The concept the authors propose is that implanted medical devices that need to be symbiotic with the body also need to be designed with an intended duplex communication of energy and materials with the body. This extends the definition of a biocompatible system to one that requires stable exchange of materials between the implanted device and the body. Having this novel concept in mind will guide research in a new field between medical implant and regenerative medicine to create actual symbiotic devices.