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The ability to program collective cell migration can allow us to control critical multicellular processes in development, regenerative medicine, and invasive disease. However, while various technologies exist to make individual cells migrate, translating these tools to control myriad, collectively interacting cells within a single tissue poses many challenges. For instance, do cells within the same tissue interpret a global migration ‘command’ differently based on where they are in the tissue? Similarly, since no stimulus is permanent, what are the long-term effects of transient commands on collective cell dynamics? We investigate these questions by bioelectrically programming large epithelial tissues to globally migrate ‘rightward’ via electrotaxis. Tissues clearly developed distinct rear, middle, side, and front responses to a single global migration stimulus. Furthermore, at no point post-stimulation did tissues return to their pre-stimulation behavior, instead equilibrating to a third, new migratory state. These unique dynamics suggested that programmed migration resets tissue mechanical state, which was confirmed by transient chemical disruption of cell-cell junctions, analysis of strain wave propagation patterns, and quantification of cellular crowd dynamics. Overall, this work demonstrates how externally driving the collective migration of a tissue can reprogram baseline cell-cell interactions and collective dynamics, even well beyond the end of the global migratory cue, and emphasizes the importance of considering the supracellular context of tissues and other collectives when attempting to program crowd behaviors.

Genetic circuits that encode extracellular electron transfer (EET) pathways allow the intracellular state of Escherichia coli to be electronically monitored and controlled. However, relatively low electron flux flows through these pathways, limiting the degree of control by these circuits. Since the EET pathway is composed of multiple multiheme cytochromes c (cyts c) from Shewanella oneidensis MR-1, we hypothesized that lower expression levels of cyt c may explain this low EET flux and may be caused by the differences in the cyt c maturation (ccm) machinery between these two species. Here, we constructed random mutations within ccmH by error-prone PCR and screened for increased cyt c production. We identified two ccmH mutants, ccmH-132 and ccmH-195, that exhibited increased heterologous cyt c expression, but had different effects on EET. The ccmH-132 strain reduced WO3 nanoparticles faster than the parental control, whereas the ccmH-195 strain reduced more slowly. The same trend is reflected in electrical current generation: ccmH-132, which has only a single mutation from WT, drastically increased current production by 77%. The percentage of different cyt c proteins in these two mutants suggests that the stoichiometry of the S. oneidensis cyts c is a key determinant of current production by Mtr-expressing E. coli. Thus, we conclude that modulating cyt c maturation effectively improves genetic circuits governing EET in engineered biological systems, enabling better bioelectronic control of E. coli.

We consider the problem of controlling an invasive mechanical ventilator for pressure-controlled ventilation: a controller must let air in and out of a sedated patient’s lungs according to a trajectory of airway pressures specified by a clinician.Hand-tuned PID controllers and similar variants have comprised the industry standard for decades, yet can behave poorly by over- or under-shooting their target or oscillating rapidly.We consider a data-driven machine learning approach: First, we train a simulator based on data we collect from an artificial lung. Then, we train deep neural network controllers on these simulators. We show that our controllers are able to track target pressure waveforms significantly better than PID controllers.We further show that a learned controller generalizes across lungs with varying characteristics much more readily than PID controllers do.

There is a growing interest in bioelectric wound treatment and electrotaxis, the process by which cells detect an electric field and orient their migration along its direction, has emerged as a potential cornerstone of the endogenous wound healing response. Despite recognition of the importance of electrotaxis in wound healing, no experimental system to date demonstrates that the actual closing of a wound can be accelerated solely by the electrotaxis response itself, and in vivo systems are too complex to resolve cell migration from other healing stages such as proliferation and inflammation. This uncertainty has led to a lack of standardization between stimulation methods, model systems, and electrode technology required for device development. In this paper, we present a ‘healing-on-chip’ approach that is a standardized, low-cost, model for investigating electrically accelerated wound healing. Our device provides the first convergent field geometry used in a stimulation device. We validate this device by using electrical stimulation to close a 1.5 mm gap between two large (30 mm2) primary skin keratinocyte layers to double the rate of healing over an unstimulated tissue. This proves that convergent electrotaxis is both possible and can accelerate healing, and offers a new ‘healing-on-a-chip’ platform to explore future bioelectric interfaces.

We present a fully open ventilator platform–The People’s Ventilator: PVP1– with complete documentation and detailed build instructions, and a DIY cost of $1,300 USD. Here, we validate PVP1 against key performance criteria specified in the U.S. Food and Drug Administration’s Emergency Use Authorization for Ventilators. Notably, PVP1 performs well over a wide range of test conditions and has been demonstrated to perform stably for a minimum of 72,000 breath cycles over three days with a mechanical test lung. As an open project, PVP1 can enable both future educational, academic, and clinical developments in the ventilator space.

Directed cell migration is critical across biological processes spanning healing to cancer invasion, yet no existing tools allow real-time interactive guidance over such migration. We present a new bioreactor that harnesses electrotaxis—directed cell migration along electric field gradients—by integrating four independent electrodes under computer control to dynamically program electric field patterns, and hence steer cell migration. Using this platform, we programmed and characterized multiple precise, two-dimensional collective migration maneuvers in renal epithelia and primary skin keratinocyte ensembles. First, we demonstrated on-demand, 90-degree collective turning. Next, we developed a universal electrical stimulation scheme capable of programming arbitrary 2D migration maneuvers such as precise angular turns and migration in a complete circle. Our stimulation scheme proves that cells effectively time-average electric field cues, helping to elucidate the transduction time scales in electrotaxis. Together, this work represents an enabling platform for controlling cell migration with broad utility across many cell types.

The coordination of cell proliferation and migration in growing tissues is crucial in development and regeneration but remains poorly understood. Here, we find that, while expanding with an edge speed independent of initial conditions, millimeter-scale epithelial monolayers exhibit internal patterns of proliferation and migration that depend not on the current but on the initial tissue size, indicating memory effects. Specifically, the core of large tissues becomes very dense, almost quiescent, and ceases cell-cycle progression. In contrast, initially-smaller tissues develop a local minimum of cell density and a tissue-spanning vortex. To explain vortex formation, we propose an active polar fluid model with a feedback between cell polarization and tissue flow. Taken together, our findings suggest that expanding epithelia decouple their internal and edge regions, which enables robust expansion dynamics despite the presence of size- and history-dependent patterns in the tissue interior., eLife digest Cells do not exist in isolation. Instead, they form tissues, where individual cells make contact with their neighbors and form microscopic ‘architectures’. Epithelia are a type of tissue where cells are arranged in flat sheets, and are found in organs such as the lining of the kidney or the skin. Tissues need to grow, especially early in life. If tissues are damaged – for example, if the skin is cut or grazed – cells also need to divide (to create new healthy cells) and move as a group (to close the wound). Such coordinated motions result in cells exhibiting distinct group behaviors, similar to those observed within crowds of people or schools of fish. If coordination breaks down, problems can happen such as uncoordinated tissue growth seen in cancer. However, how cell movements are coordinated is still not fully understand. For example, researchers know that cells’ positions within a group can determine how they behave, meaning that even the same type of cell could behave differently at the edge or center of a tissue. This suggests that the initial size and shape of a tissue should influence its subsequent growth and behavior; however, the nature of this influence is still largely unknown. Heinrich et al. therefore wanted to determine the differences in the way larger and smaller tissues grow. Microscope imaging was used to track the growth of circular, artificial tissues made from single-layered sheets of dog kidney cells grown in the laboratory. Comparing how quickly the tissues expanded revealed that the area of tissue circles that started out smaller increased at a much faster rate than that of tissue circles that were larger to begin with. This turned out to be because the edges of the tissues grew at a constant speed, independent of their initial size or shape, but circles with a smaller area have a larger proportion of cells on their edges. The motions of the cells at the center of the tissues had no effect on how the edges of the tissue grew. A final observation was that the way tissues of a given size behaved depended on whether they had grown to be that size, or they started off that big. These results shed light on how groups of cells interact in growing tissues. In the future, this information could be used to predict how different tissues grow over time, potentially helping scientists engineer better artificial tissues or organs for transplantation.

Directed cell migration is critical across biological processes spanning healing to cancer invasion, yet no tools allow such migration to be interactively guided. We present a new bioreactor that harnesses electrotaxis — directed cell migration along electric field gradients — by integrating multiple independent electrodes under computer control to dynamically program electric field patterns, and hence steer cell migration. Using this platform, we programmed and characterized multiple precise, two-dimensional collective migration maneuvers in renal epithelia and primary skin keratinocyte ensembles. First, we demonstrated on-demand, 90-degree collective turning. Next, we developed a universal electrical stimulation scheme capable of programming arbitrary 2D migration maneuvers such as precise angular turns and directing cells to migrate in a complete circle. Our stimulation scheme proves that cells effectively time-average electric field cues, helping to elucidate the transduction time scales in electrotaxis. Together, this work represents a fundamentally different platform for controlling cell migration with broad utility across fields.

There is a growing interest in bioelectric wound treatment and electrotaxis, the process by which cells detect an electric field and orient their migration along its direction, has emerged as a potential cornerstone of the endogenous wound healing response. Despite recognition of the importance of electrotaxis in wound healing, no experimental demonstration to date has shown that the actual closing of a wound can be accelerated solely by the electrotaxis response itself, and in vivo systems are too complex to resolve cell migration from other healing stages such as proliferation and inflammation. This uncertainty has led to a lack of standardization between stimulation methods, model systems, and electrode technology required for device development. In this paper, we present a ‘healing-on-chip’ approach that is a standardized, low-cost, model for investigating electrically accelerated wound healing. Our device provides a biomimetic convergent field geometry that more closely resembles actual wound fields. We validate this device by using electrical stimulation to close a 1.5 mm gap between two large (30 mm2) layers of primary skin keratinocyte to completely heal the gap twice as quickly as in an unstimulated tissue. This demonstration proves that convergent electrotaxis is both possible and can accelerate healing and offers an accessible ‘healing-on-a-chip’ platform to explore future bioelectric interfaces.

Genetic circuits that encode extracellular electron transfer (EET) pathways allow the intracellular state of

Escherichia coli detects and follows chemical gradients in its environment in a process known as chemotaxis. The performance of chemotaxis approaches fundamental biosensor speed and sensitivity limits, but there have been relatively few attempts to incorporate the response into a functional biosensor. Toward that end, we have developed software to process digital microscope images of a large number of tethered E. coli responding to different chemical perturbations. Upwards of fifty cells can be recorded in one experiment, allowing for rapid labeling of the chemotactic responses of multiple cells. After we collected hundreds of wild-type chemotactic E. coli motor responses to dilutions of aspartate and leucine, we trained a support vector classifier (SVC) to estimate the order of magnitude of aspartate concentration between 0M, 100nM, and 1μM with a single cell classification subset accuracy of 69%. We trained another SVC to differentiate between aspartate and leucine with a single cell classification subset accuracy of 83%. Using a majority-vote method on a bacterial population of size N, estimates have 95% confidence for N = 27 bacteria for concentration detection and N = 9 bacteria for chemical differentiation. These methods are a step towards adaptable chemotaxis-based biosensing.

The front cover artwork is provided by the group of Dr. Caroline Ajo-Franklin at Berkeley Lab, USA. The cover image shows electrogenic E. coli transporting electrical energy, originating from its metabolism, to external metals. Read the full text of the article at 10.1002/celc.201402194.

This work incorporates an open-ended design experience into an introductory circuits laboratory with the intended outcome of increasing self-efficacy for circuit prototyping and design. The authors have implemented a tinkering-based laboratory, in which students spend each lab period building a component of an inexpensive robot. The course culminates in a four week open-ended final hack that adds functionality to the finished robot. This design project prompts students to make connections across disciplines and exercise design thinking in a low-stakes environment. To determine the impact of this design experience on student learning, self-efficacy was measured through optional surveys administered both before and after the final hack. The design project resulted in a significant increase in design self-efficacy for students with some prior electronics experience, as well as an increase in prototyping self-efficacy in less experienced students, indicating that the design requirement had a positive impact on self-efficacy overall. It also showed that undergraduates in this course were ready to engage in a structured open-ended design experience even though they did not have a classical foundation in all the relevant theory, a common justification for the omission of design projects from intermediate-level engineering curricula.

Predictions of the fourth-order small perturbation method (SPM) are examined for scattering from two rough surfaces in a layered geometry. Cross-polarized backscatter, in particular, is emphasized because use of the fourth-order SPM is required to obtain this quantity. The formulation of the SPM fields and incoherent ensemble-averaged normalized radar cross sections (NRCSs) up to the third and the fourth order in surface rms heights, respectively, are reviewed. It is shown that the fourth-order NRCS includes distinct contributions from upper and lower interface roughnesses, as well as an “interaction” term that couples the upper and lower interface roughnesses. A comparison with NRCS values computed using the “numerically exact” method of moments in the full bistatic scattering pattern is shown for verification, and NRCS values at the second and the fourth order are compared in order to assess the convergence of the SPM series. Although the number of parameters inherent in the two-layer rough surface scattering problem makes an exhaustive study of scattering effects difficult, several illustrative examples are presented to capture a range of scattering behaviors. The results emphasize the importance of interactions between the rough surfaces in producing cross-polarized backscattering and also indicate an increased significance of fourth-order contributions in the two-layer geometry as compared to the single-layer case.

We present a miniaturized, free-floating monitoring system which makes use of electron transfer in Shewanella oneidensis sequestered behind a permeable membrane while maintaining diffusive contact with the environment, allowing for sensing environmental conditions. The system makes use of a commercial off-the-shelf (COTS) integrated circuit (IC) which sets a potential between a working electrode and a Ag/AgCl reference electrode while recording the resulting current from the electroactive cells. We successfully sensed both pyruvate and the environmental presence of E. coli via changes in the currents sensed. This work will enable the development of mobile aquatic sensing systems which make use of bacterial electron transfer as a transduction method. Further miniaturization of the recording mote, electrodes, packaging, and system is discussed.

Flagellar motility in Escherichia coli is driven by the proton motive force (PMF); exogenous control of PMF could allow the use of flagellated bacteria as microactuators. Following recent work, we have engineered cells to express a fluorescent membrane protein (proteorhodopsin optical proton sensor, PROPS) to report PMF, allowing real-time monitoring of the membrane potential and its periodic depolarizations. We show that the timing characteristics of these fluctuations can be controlled by adjusting the availability of oxygen, suggesting a potential scheme of PMF control.