Urinary Bladder Volume Reconstruction Based on Bioimpedance Measurements: Ex Vivo and In Vivo Validation Through Implanted Patch and Needle Electrodes

Restoring bladder sensation in patients with bladder dysfunctions by performing urinary volume monitoring is an ambitious goal. The bioimpedance technique has shown promising results in wearable solutions but long-term validation and implantable systems are not available, yet. In this work, we propose to implant commercial bioimpedance sensors on bladder walls to perform bladder volume estimation. Two commercial sensor types (Ag/AgCl patch and needle electrodes) were selected to this purpose. Injected current frequency of 1.337 MHz and electrodes pair on the same face of the bladder allowed to correlate the changes in impedance with increasing volumes. Two volume reconstruction algorithms have been proposed, based on the direct correlation between bioimpedance readings and bladder volume (Algorithm A) or bioimpedance readings and inter-electrode distance (Algorithm B, bladder shape approximated to a sphere). For both algorithms, a better fit with a second-degree fitting polynomial was obtained. Algorithm A obtained lower estimation errors with an average of 20.35% and 21.98% (volumes greater than 150 ml) for patch and needle electrodes, respectively. The variations in ions concentration led to a slight deterioration of volume estimation, however the presence of tissues surrounding the bladder did not influence the performance. Although Algorithm B was less affected by the experimental conditions and inter-subject biological variability, it featured higher estimation errors. In vivo validation on suine model showed average errors of 29.36% (volumes greater than 100 ml), demonstrating the potential of the proposed solution and paving the way towards a novel implantable volume monitoring system

Real-time imaging and tracking of microrobots in tissues using ultrasound phase analysis

Ultrasound B-mode imaging has been employed to monitor single agents and collective swarms of microrobots in vitro and ex vivo in controlled experimental conditions. However, low contrast and spatial resolution still limit the effective employment of such a method in a medical microrobotic scenario. Doppler-based ultrasound appears as a promising tool for tracking microrobots in echogenic and dynamic environments as biological tissues. In this Letter, we demonstrate that microrobot displacements can be used as a special signature for their visualization within echogenic media, where B-mode fails. To this aim, we induced vibrations of a magnetic soft microrobot through alternated magnetic fields and used ultrasound phase analysis to derive microrobot features such as size and position over time. By exploiting vibrations, we were able to perform imaging and tracking of a low contrast microrobot both in tissue-mimicking phantom and in chicken breast. The axial resolution was 38 μm, which is four times smaller than the B-mode resolution with the employed equipment. We also performed real-time tracking of the microrobot's positions along linear trajectories with a linear velocity up to 1 mm/s. Overall, the reported results pave the way for the application of the proposed approach for the robust monitoring of medical microrobots in tissue

Miniaturized peristaltic rotary pump for non-continuous drug dosing

Micro dosing pumps are the beating heart of infusion systems. Among many technologies to inject micro quantities of fluids, peristaltic pumps show high precision and the possibility to not alter the fluid properties. However, in real drug delivery applications, the continuous release behavior of typical peristaltic pumps is not favorable. In this paper, we investigate the intermittent performance of two prototypes of peristaltic pumps, based on four and five rollers, used to occlude the tube. The pump performances are reported for different rotation speeds and lag times between consecutive infusions. The proposed pumps showed a good volumetric precision (2.88 μL for the five rollers pump and 4.11 μL for the four rollers pump) without any dependency on rotation speed and lag time

Contrast-enhanced ultrasound tracking of helical propellers with acoustic phase analysis and comparison with color Doppler

Medical microrobots (MRs) hold the potential to radically transform several interventional procedures. However, to guarantee therapy success when operating in hard-to-reach body districts, a precise and robust imaging strategy is required for monitoring and controlling MRs in real-time. Ultrasound (US) may represent a powerful technology, but MRs' visibility with US needs to be improved, especially when targeting echogenic tissues. In this context, motions of MRs have been exploited to enhance their contrast, e.g., by Doppler imaging. To exploit a more selective contrast-enhancement mechanism, in this study, we analyze in detail the characteristic motions of one of the most widely adopted MR concepts, i.e., the helical propeller, with a particular focus on its interactions with the backscattered US waves. We combine a kinematic analysis of the propeller 3D motion with an US acoustic phase analysis (APA) performed on the raw radio frequency US data in order to improve imaging and tracking in bio-mimicking environments. We validated our US-APA approach in diverse scenarios, aimed at simulating realistic in vivo conditions, and compared the results to those obtained with standard US Doppler. Overall, our technique provided a precise and stable feedback to visualize and track helical propellers in echogenic tissues (chicken breast), tissue-mimicking phantoms with bifurcated lumina, and in the presence of different motion disturbances (e.g., physiological flows and tissue motions), where standard Doppler showed poor performance. Furthermore, the proposed US-APA technique allowed for real-time estimation of MR velocity, where standard Doppler failed

Retrieval of magnetic medical microrobots from the bloodstream

Untethered magnetic microrobots hold the potential to penetrate hard-to-reach areas of the human body and to perform therapy in a controlled way. In the past decade, impressive advancements have been made in this field but the clinical adoption of magnetoresponsive microrobots is still hampered by safety issues. A tool appointed for magnetic microrobots retrieval within body fluids could enable a real paradigm change, fostering their clinical translation.By starting from the general problem to retrieve magnetic microrobots injected into the bloodstream, the authors introduce a magnetic capture model that allows to design retrieval tools for magnetic cores of different diameters (down to 10 nm) and in different environmental conditions (fluid speed up to 7 cms-1). The model robustness is demonstrated by the design and testing of a retrieval catheter. In its optimal configuration, the catheter includes 27 magnets and fits a 12 F catheter. The model provides a good prediction of capture efficiency for 250 nm magnetic particles (experimental data: 77.6%, model prediction: 65%) and a very good prediction for 500 nm particles (experimental data: 93.6%, model prediction: 94%). The results support the proposed model-based design approach, which can be extended to retrieve other magnetoresponsive agents from body compartments

3D Printing of Small-Scale Soft Robots with Programmable Magnetization

status: publishe

Extracting information from multiplex networks

11 pages; 5 figure

Visibility graphs of random scalar fields and spatial data

The family of visibility algorithms were recently introduced as mappings between time series and graphs. Here we extend this method to characterize spatially extended data structures by mapping scalar fields of arbitrary dimension into graphs. After introducing several possible extensions, we provide analytical results on some topological properties of these graphs associated to some types of real-valued matrices, which can be understood as the high and low disorder limits of real-valued scalar fields. In particular, we find a closed expression for the degree distribution of these graphs associated to uncorrelated random fields of generic dimension, extending a well known result in one-dimensional time series. As this result holds independently of the field's marginal distribution, we show that it directly yields a statistical randomness test, applicable in any dimension. We showcase its usefulness by discriminating spatial snapshots of two-dimensional white noise from snapshots of a two-dimensional lattice of diffusively coupled chaotic maps, a system that generates high dimensional spatio-temporal chaos. We finally discuss the range of potential applications of this combinatorial framework, which include image processing in engineering, the description of surface growth in material science, soft matter or medicine and the characterization of potential energy surfaces in chemistry, disordered systems and high energy physics. An illustration on the applicability of this method for the classification of the different stages involved in carcinogenesis is briefly discussed

Evolution of the cosmic ray anisotropy above 10^{14} eV

The amplitude and phase of the cosmic ray anisotropy are well established experimentally between 10^{11} eV and 10^{14} eV. The study of their evolution into the energy region 10^{14}-10^{16} eV can provide a significant tool for the understanding of the steepening ("knee") of the primary spectrum. In this letter we extend the EAS-TOP measurement performed at E_0 around 10^{14} eV, to higher energies by using the full data set (8 years of data taking). Results derived at about 10^{14} and 4x10^{14} eV are compared and discussed. Hints of increasing amplitude and change of phase above 10^{14} eV are reported. The significance of the observation for the understanding of cosmic ray propagation is discussed.Comment: 4 pages, 3 figures, accepted for publication on ApJ Letter