Multiwavelength light-responsive Au/B-TiO2 Janus micromotors

Conventional photocatalytic micromotors are limited to the use of specific wavelengths of light due to their narrow light absorption spectrum, which limits their effectiveness for applications in biomedicine and environmental remediation. We present a multiwavelength light-responsive Janus micromotor consisting of a black TiO₂ microsphere asymmetrically coated with a thin Au layer. The black TiO₂ microspheres exhibit absorption ranges between 300 and 800 nm. The Janus micromotors are propelled by light, both in H₂O₂ solutions and in pure H₂O over a broad range of wavelengths including UV, blue, cyan, green, and red light. An analysis of the particles' motion shows that the motor speed decreases with increasing wavelength, which has not been previously realized. A significant increase in motor speed is observed when exploiting the entire visible light spectrum (>400 nm), suggesting a potential use of solar energy, which contains a great portion of visible light. Finally, stop-go motion is also demonstrated by controlling the visible light illumination, a necessary feature for the steerability of micro- and nanomachines

How Much Will Safe Sanitation for all Cost? Evidence from Five Cities

Global sustainable development goals call for universal access to safely managed sanitation by 2030. Here, we demonstrate methods to estimate the financial requirements for meeting this commitment in urban settings of low-income countries. Our methods considered two financial requirements: (i) the subsidies needed to bridge the gap between the willingness-to-pay of low-income households and actual market prices of toilets and emptying services and (ii) the amounts needed to expand the municipal waste management infrastructure for unserved populations. We applied our methods in five cities– Kisumu, Malindi, Nakuru in Kenya; Kumasi in Ghana; and Rangpur in Bangladesh and compared three to five sanitation approaches in each city. We collected detailed cost data on the sanitation infrastructure, products, and services from 76 key informants across the five cities, and we surveyed a total of 2381 low-income households to estimate willingness-to-pay. We found that the total financial requirements for achieving universal sanitation in the next 10 years and their breakdown between household subsidies and municipal infrastructure varied greatly between sanitation approaches. Across our study cities, sewerage was the costliest approach (total financial requirements of 16–24 USD/person/year), followed by container-based sanitation (10–17 USD/person/year), onsite sanitation (2–14 USD/person/year), and mini-sewers connecting several toilets to communal septic tanks (3–5 USD/person/year). Further applications of our methods can guide sanitation planning in other cities

Remote Magnetic Navigation and Applications in Ophthalmic Surgery

Magnetism has entertained a close relationship with medicine throughout history, but its ability to navigate therapeutic devices inside the human body has emerged in the last few decades thanks to technological improvements in the fabrication, and control of magnetic devices. Remote magnetic navigation of untethered devices, also known as micro or nanorobots, or tethered surgical devices including catheters, endoscopes, and needles can be achieved by generating magnetic fields from outside the human body, using a magnetic navigation system. This thesis is divided in two parts. The first part discusses the prediction of generated magnetic fields, a fundamental task of remote magnetic navigation that is required for simulating, controlling, and localizing magnetically navigated devices. We first explore interpolation based methods, which create continuous representations of magnetic fields using pre-existing data. Several interpolation methods are compared based on their ability to accurately predict magnetic fields and magnetic field gradients, and how well they respect certain physical constraints obeyed by magnetic fields. Magnetic navigation systems using electromagnets that are large enough to perform magnetic navigation at human scales exhibit nonlinear magnetic saturation. We first propose a strategy that can correct for electromagnet saturation in existing linear models. Machine learning based methods are capable of modeling such complex nonlinear behavior with multiple inputs and outputs from data alone. We show an artificial neural network that achieved superior field prediction accuracy to both linear and corrected methods. This was followed by the application of a generative convolutional neural network that far outperformed all other methods. The second part of the thesis concerns the application of remote magnetic navigation for the control of tethered surgical devices in ophthalmology. Surgery on the retina is exceedingly challenging, involves movements and forces that are at the limits of human ability and perception, and for that reason has long been proposed as a candidate for the application of medical robotics. Differing from existing robots that use mechanical transfer of motion to navigate tools inside the cavity of the eye, this work presents flexible devices that are navigated using magnetic fields. Such devices combine fine position control, extreme miniaturization, and enhanced safety over existing rigid tools. We first describe a magnetically navigated laser probe that could be used for treating advanced forms of diabetic retinopathy, a rapidly growing and already leading cause of vision loss. By tracking the laser position in real-time using computer vision, the probe is navigated in closed-loop, and the procedure, which is repetitive, lengthy, and painful for patients, can be automated. There is active research in the development of new therapies for treating diseases that cause degeneration of the retina, particularly age-related macular degeneration, the leading cause of blindness in the developed world. New treatments including virus-carried gene therapies and stem cells need to be delivered close to the targeted areas of the retina for them to be effective. Subretinal injections have been proposed as the most promising pathway for delivery of such therapeutics, but they are a challenging surgical procedure with significant associated risks. We have developed a magnetically navigated cannula that can be navigated throughout the retina with micrometer precision, and with much greater ease than with handheld cannulas. Combined with optical coherence tomography, an increasingly popular imaging method in ophthalmology that enables high-definition 3D visualization of the retina, we show that a cannula can be placed precisely, for safe injections in the subretinal space. Injections were demonstrated in ex-vivo porcine eyes, as a first step towards subretinal delivery in human patients

On the Workspace of Electromagnetic Navigation Systems

In remote magnetic navigation, a magnetic navigation system is used to generate magnetic fields to apply mechanical wrenches to steer a magnetic object. This technique can be applied to navigate untethered micro- and nanorobots, as well as tethered magnetic surgical tools for minimally invasive medicine. The design and characterization of these systems have been extensively investigated over the past decade. The determination of the region in space in which these systems can operate has yet to be formalized within the research community. This region is commonly referred to as the “workspace” and constitutes a central concept for any class of robotic system. We focus on magnetic navigation systems comprised of electromagnets and propose a first set of definitions for a magnetic workspace, a methodology to determine it, and evaluation metrics to analyze its characteristics. Our methodology and tools are illustrated with several examples of planar and spatial electromagnetic magnetic navigation systems for both didactic and realistic navigation scenarios.ISSN:1552-3098ISSN:1042-296XISSN:1941-046

A Magnetically Steered Endolaser Probe for Automated Panretinal Photocoagulation

ISSN:2377-376

A Magnetically Navigated Microcannula for Subretinal Injections

Retinal disorders, including age-related macular degeneration, are leading causes of vision loss worldwide. New treatments, such as gene therapies and stem cell regeneration, require therapeutics to be introduced to the subretinal space due to poor diffusion to the active component of the retina. Subretinal injections are a difficult and risky surgical procedure and have been suggested as a candidate for robot-assisted surgery. We propose a different actuation paradigm to existing robotic approaches using remote magnetic navigation to control a flexible microcannula. A flexible cannula allows for high dexterity and considerable safety advantages over rigid tools, while maintaining the benefits of micrometer precision, hand tremor removal, and telemanipulation. The position of the cannula is tracked in real-time using near-infrared tip illumination, allowing for semi-automatic placement of the cannula and an intuitive user interface. Using this tool, we successfully performed several subretinal injections in ex-vivo porcine eyes under both microscope and optical coherence tomography visualization.ISSN:0018-9294ISSN:1558-253

Modeling Electromagnetic Navigation Systems

Remote magnetic navigation is used for the manipulation of untethered micro and nanorobots, as well as tethered magnetic surgical tools for minimally invasive medicine. Mathematical modeling of the magnetic fields generated by magnetic navigation systems is a fundamental task in the control of such tools for biomedical applications. In this article, we describe and compare several existing and newly developed methods for representations of continuous magnetic fields using interpolation in the context of remote magnetic navigation. Clinical-scale electromagnetic navigation systems feature nonlinear magnetization and magnetization interactions between electromagnets, which renders accurate magnetic field modeling challenging. We first introduce a method that can adapt existing linear models to correct for nonlinear magnetization, with similar performance to the current state-of-the-art nonlinear model. Furthermore, we present a method based on convolutional neural networks.ISSN:1552-3098ISSN:1042-296XISSN:1941-046