Eating, Drinking, Living, Dying and Decaying Soft Robots

Soft robotics opens up a whole range of possibilities that go far beyond conventional rigid and electromagnetic robotics. New smart materials and new design and modelling methodologies mean we can start to replicate the operations and functionalities of biological organisms, most of which exploit softness as a critical component. These range from mechanical responses, actuation principles and sensing capabilities. Additionally, the homeostatic operations of organisms can be exploited in their robotic counterparts. We can, in effect, start to make robotic organisms, rather than just robots. Important new capabilities include the fabrication of robots from soft bio-polymers, the ability to drive the robot from bio-energy scavenged from the environment, and the degradation of the robot at the end of its life. The robot organism therefore becomes an entity that lives, dies, and decays in the environment, just like biological organisms. In this chapter we will examine how soft robotics have the potential to impact upon pressing environmental pollution, protection and remediation concerns

The dawn of biodegradable robots

Robotics is a field that is not normally associated with green technology or sustainability. Robots are generally constructed using materials that are non-biodegradable, toxic and expensive. These factors can limit the potential uses that an artificial agent might have, especially if operation is required outside and away from where humans live. Things are further complicated when considering the robot’s power supply.In most cases, batteries are used that will inevitably run out and require recharging from charging stations.Imagine then, an environmentally friendly robot, one that can safely roam a targeted area whether that is within agricultural fields, rain forests or remote jungles. Movement would not be random but with a preset purpose built-in perhaps to identify pests, clean up human-made waste and generate electricity from it, or simply monitor/sense environmental conditions

Investigating the effects of fluidic connection between microbial fuel cells

Microbial fuel cells (MFCs) can 'treat' wastewater but individually are thermodynamically restricted. Scale-up might, therefore, require a plurality of units operating in a stack which could introduce losses simply through fluidic connections. Experiments were performed on two hydraulically joined MFCs (20 cm apart) where feedstock flowed first through the upstream unit (MFCup) and into the downstream unit (MFCdown) to explore the interactive effect of electrical load connection, influent make-up and flow-rate on electrical outputs. This set-up was also used to investigate how calculating total internal resistance based on a dynamic open circuit voltage (OCV) might differ from using the starting OCV. When fed a highly conductive feedstock (∼4,800 μS) MFCdown dropped approximately 180 mV as progressively heavier loads were applied to MFCup (independent of flow-rate) due to electron leakages through the medium. The conductivities of plain acetate solutions (5 and 20 mM) were insufficient to induce losses in MFCdown even when MFCup was operating at high current densities. However, at the highest flow-rate (240 mL/h) MFCdown dropped by approximately 100 mV when using 5 and 220 mV using 20 mM acetate. When the distance between MFCs was reduced by 5 cm, voltage drops were apparent even at lower flow-rates, (30 mL/h decreased the voltage by 115 mV when using 20 mM acetate). Shear flow-rates can introduce dissolved oxygen and turbulence all capable of affecting the anodic biofilm and redox conditions. Calculating total internal resistance using a dynamic OCV produced a more stable curve over time compared to that based on the starting constant OCV. © 2010 Springer-Verlag

Cast and 3D printed ion exchange membranes for monolithic microbial fuel cell fabrication

© 2015 Elsevier B.V. All rights reserved. We present novel solutions to a key challenge in microbial fuel cell (MFC) technology; greater power density through increased relative surface area of the ion exchange membrane that separates the anode and cathode electrodes. The first use of a 3D printed polymer and a cast latex membrane are compared to a conventionally used cation exchange membrane. These new techniques significantly expand the geometric versatility available to ion exchange membranes in MFCs, which may be instrumental in answering challenges in the design of MFCs including miniaturisation, cost and ease of fabrication. Under electrical load conditions selected for optimal power transfer, peak power production (mean 10 batch feeds) was 11.39 μW (CEM), 10.51 μW (latex) and 0.92 μW (Tangoplus). Change in conductivity and pH of anolyte were correlated with MFC power production. Digital and environmental scanning electron microscopy show structural changes to and biological precipitation on membrane materials following long term use in an MFC. The cost of the novel membranes was lower than the conventional CEM. The efficacy of two novel membranes for ion exchange indicates that further characterisation of these materials and their fabrication techniques, shows great potential to significantly increase the range and type of MFCs that can be produced

Complete microbial fuel cell fabrication using additive layer manufacturing

Improving the efficiency of microbial fuel cell (MFC) technology by enhancing the system performance and reducing the production cost is essential for commercialisation. In this study, building an additive manufacturing (AM)-built MFC comprising all 3D printed components such as anode, cathode and chassis was attempted for the first time. 3D printed base structures were made of low-cost, biodegradable polylactic acid (PLA) filaments. For both anode and cathode, two surface modification methods using either graphite or nickel powder were tested. The best performing anode material, carbon-coated non-conductive PLA filament, was comparable to the control modified carbon veil with a peak power of 376.7 µW (7.5 W m−3) in week 3. However, PLA-based AM cathodes underperformed regardless of the coating method, which limited the overall performance. The membrane-less design produced more stable and higher power output levels (520−570 µW, 7.4−8.1 W m−3) compared to the ceramic membrane control MFCs. As the final design, four AM-made membrane-less MFCs connected in series successfully powered a digital weather station, which shows the current status of low-cost 3D printed MFC development

The power of glove: Soft microbial fuel cell for low-power electronics

A novel, soft microbial fuel cell (MFC) has been constructed using the finger-piece of a standard laboratory natural rubber latex glove. The natural rubber serves as structural and proton exchange material whilst untreated carbon veil is used for the anode. A soft, conductive, synthetic latex cathode is developed that coats the outside of the glove. This inexpensive, lightweight reactor can without any external power supply, start up and energise a power management system (PMS), which steps-up the MFC output (0.06-0.17 V) to practical levels for operating electronic devices (>3 V). The MFC is able to operate for up to 4 days on just 2 mL of feedstock (synthetic tryptone yeast extract) without any cathode hydration. The MFC responds immediately to changes in fuel-type when the introduction of urine accelerates the cycling times (35 vs. 50 min for charge/discharge) of the MFC and PMS. Following starvation periods of up to 60 h at 0 mV the MFC is able to cold start the PMS simply with the addition of 2 mL fresh feedstock. These findings demonstrate that cheap MFCs can be developed as sole power sources and in conjunction with advancements in ultra-low power electronics, can practically operate small electrical devices.© 2013 Elsevier B.V. All rights reserved

Urine in bioelectrochemical systems: An overall review

In recent years, human urine has been successfully used as an electrolyte and organic substrate in bioelectrochemical systems (BESs) mainly due of its unique properties. Urine contains organic compounds that can be utilised as a fuel for energy recovery in microbial fuel cells (MFCs) and it has high nutrient concentrations including nitrogen and phosphorous that can be concentrated and recovered in microbial electrosynthesis cells and microbial concentration cells. Moreover, human urine has high solution conductivity, which reduces the ohmic losses of these systems, improving BES output. This review describes the most recent advances in BESs utilising urine. Properties of neat human urine used in state‐of‐the‐art MFCs are described from basic to pilot‐scale and real implementation. Utilisation of urine in other bioelectrochemical systems for nutrient recovery is also discussed including proofs of concept to scale up systems

Scaling-up of a novel, simplified MFC stack based on a self-stratifying urine column

© 2016 Walter et al. Background: The microbial fuel cell (MFC) is a technology in which microorganisms employ an electrode (anode) as a solid electron acceptor for anaerobic respiration. This results in direct transformation of chemical energy into electrical energy, which in essence, renders organic wastewater into fuel. Amongst the various types of organic waste, urine is particularly interesting since it is the source of 75 % of the nitrogen present in domestic wastewater despite only accounting for 1 % of the total volume. However, there is a persistent problem for efficient MFC scale-up, since the higher the surface area of electrode to volume ratio, the higher the volumetric power density. Hence, to reach usable power levels for practical applications, a plurality of MFC units could be connected together to produce higher voltage and current outputs; this can be done by combinations of series/parallel connections implemented both horizontally and vertically as a stack. This plurality implies that the units have a simple design for the whole system to be cost-effective. The goal of this work was to address the built configuration of these multiple MFCs into stacks used for treating human urine. Results: We report a novel, membraneless stack design using ceramic plates, with fully submerged anodes and partially submerged cathodes in the same urine solution. The cathodes covered the top of each ceramic plate whilst the anodes, were on the lower half of each plate, and this would constitute a module. The MFC elements within each module (anode, ceramic, and cathode) were connected in parallel, and the different modules connected in series. This allowed for the self-stratification of the collective environment (urine column) under the natural activity of the microbial consortia thriving in the system. Two different module sizes were investigated, where one module (or box) had a footprint of 900 mL and a larger module (or box) had a footprint of 5000 mL. This scaling-up increased power but did not negatively affect power density (≈12 W/m3), a factor that has proven to be an obstacle in previous studies. Conclusion: The scaling-up approach, with limited power-density losses, was achieved by maintaining a plurality of microenvironments within the module, and resulted in a simple and robust system fuelled by urine. This scaling-up approach, within the tested range, was successful in converting chemical energy in urine into electricity

A review into the use of ceramics in microbial fuel cells

© 2016 The Authors. Microbial fuel cells (MFCs) offer great promise as a technology that can produce electricity whilst at the same time treat wastewater. Although significant progress has been made in recent years, the requirement for cheaper materials has prevented the technology from wider, out-of-the-lab, implementation. Recently, researchers have started using ceramics with encouraging results, suggesting that this inexpensive material might be the solution for propelling MFC technology towards real world applications. Studies have demonstrated that ceramics can provide stability, improve power and treatment efficiencies, create a better environment for the electro-active bacteria and contribute towards resource recovery. This review discusses progress to date using ceramics as (i) the structural material, (ii) the medium for ion exchange and (iii) the electrode for MFCs