Development and evaluation of a fluidic facemask for airborne transmission mitigation.

Recently, a fluidic facemask concept was proposed to mitigate the transmission of virus-laden aerosol and droplet infections, such as SARS-CoV-2 (COVID-19). This paper describes an experimental investigation of the first practical fluidic facemask prototype, or "Air-Screen". It employs a small, high-aspect-ratio, crossflow fan mounted on the visor of a filter-covered cap to produce a rectangular air jet, or screen, in front of the wearer's face. The entire assembly weighs less than 200 g. Qualitative flow visualization experiments using a mannequin clearly illustrated the Air-Screen's ability to effectively block airborne droplets (∼100 µm) from the wearer's face. Quantitative experiments to simulate droplets produced during sneezing or a wet cough (∼102 µm) were propelled (via a transmitter) at an average velocity of 50 m/s at 1 m from the mannequin or a target. The Air-Screen blocked 62% of all droplets with a diameter of less than 150 µm. With an Air-Screen active on the transmitter, 99% of all droplets were blocked. When both mannequin and transmitter Air-Screens were active, 99.8% of all droplets were blocked. A mathematical model, based on a weakly-advected jet in a crossflow, was employed to gain greater insight into the experimental results. This investigation highlighted the remarkable blocking effect of the Air-Screen and serves as a basis for a more detailed and comprehensive experimental evaluation.

Energetic analysis and experiments of earthworm-like locomotion with compliant surfaces.

The energy consumption of worm robots is composed of three parts: heat losses in the motors, internal friction losses of the worm device and mechanical energy locomotion requirements which we refer to as the cost of transport (COT). The COT, which is the main focus of this paper, is composed of work against two types of external factors: (i) the resisting forces, such as weight, tether force, or fluid drag for robots navigating inside wet environments and (ii) sliding friction forces that may result from sliding either forward or backward. In a previous work, we determined the mechanical energy requirement of worm robot locomotion over compliant surfaces, independently of the efficiency of the worm device. Analytical results were obtained by summing up the external work done on the robot and alternatively, by integrating the actuator forces over the actuator motions. In this paper, we present experimental results for an earthworm robot fitted with compliant contacts and these are post-processed to estimate the energy expenditure of the device. The results show that due to compliance, the COT of our device is increased by up to four-fold compared to theoretical predictions for rigid-contact worm-like locomotion.

Validation of a stereo camera system to quantify brain deformation due to breathing and pulsatility.

PURPOSE: A new stereo vision system is presented to quantify brain shift and pulsatility in open-skull neurosurgeries. METHODS: The system is endowed with hardware and software synchronous image acquisition with timestamp embedding in the captured images, a brain surface oriented feature detection, and a tracking subroutine robust to occlusions and outliers. A validation experiment for the stereo vision system was conducted against a gold-standard optical tracking system, Optotrak CERTUS. A static and dynamic analysis of the stereo camera tracking error was performed tracking a customized object in different positions, orientations, linear, and angular speeds. RESULTS: The system is able to detect an immobile object position and orientation with a maximum error of 0.5 mm and 1.6° in all depth of field, and tracking a moving object until 3 mm/s with a median error of 0.5 mm. Three stereo video acquisitions were recorded from a patient, immediately after the craniotomy. The cortical pulsatile motion was captured and is represented in the time and frequency domain. The amplitude of motion of the cloud of features' center of mass was inferior to 0.8 mm. Three distinct peaks are identified in the fast Fourier transform analysis related to the sympathovagal balance, breathing, and blood pressure with 0.03-0.05, 0.2, and 1 Hz, respectively. CONCLUSIONS: The stereo vision system presented is a precise and robust system to measure brain shift and pulsatility with an accuracy superior to other reported systems.

Accurate multi-robot targeting for keyhole neurosurgery based on external sensor monitoring.

Robotics has recently been introduced in surgery to improve intervention accuracy, to reduce invasiveness and to allow new surgical procedures. In this framework, the ROBOCAST system is an optically surveyed multi-robot chain aimed at enhancing the accuracy of surgical probe insertion during keyhole neurosurgery procedures. The system encompasses three robots, connected as a multiple kinematic chain (serial and parallel), totalling 13 degrees of freedom, and it is used to automatically align the probe onto a desired planned trajectory. The probe is then inserted in the brain, towards the planned target, by means of a haptic interface. This paper presents a new iterative targeting approach to be used in surgical robotic navigation, where the multi-robot chain is used to align the surgical probe to the planned pose, and an external sensor is used to decrease the alignment errors. The iterative targeting was tested in an operating room environment using a skull phantom, and the targets were selected on magnetic resonance images. The proposed targeting procedure allows about 0.3 mm to be obtained as the residual median Euclidean distance between the planned and the desired targets, thus satisfying the surgical accuracy requirements (1 mm), due to the resolution of the diffused medical images. The performances proved to be independent of the robot optical sensor calibration accuracy.

Conditions for worm-robot locomotion in a flexible environment: theory and experiments.

Biological vessels are characterized by their substantial compliance and low friction that present a major challenge for crawling robots for minimally invasive medical procedures. Quite a number of studies considered the design and construction of crawling robots; however, very few focused on the interaction between the robots and the flexible environment. In a previous study, we derived the analytical efficiency of worm locomotion as a function of the number of cells, friction coefficients, normal forces, and local (contact) tangential compliance. In this paper, we introduce the structural effects of environment compliance, generalize our previous analysis to include dynamic and static coefficients of friction, determine the conditions of locomotion as function of the external resisting forces, and experimentally validate our previous and newly obtained theoretical results. Our experimental setup consists of worm robot prototypes, flexible interfaces with known compliance and a Vicon motion capture system to measure the robot positioning. Separate experiments were conducted to measure the tangential compliance of the contact interface that is required for computing the analytical efficiency. The validation experiments were performed for both types of compliant conditions, local and structural, and the results are shown to be in clear match with the theoretical predictions. Specifically, the convergence of the tangential deflections to an arithmetic series and the partial and overall loss of locomotion verify the theoretical predictions.

Force feedback in a piezoelectric linear actuator for neurosurgery.

BACKGROUND: Force feedback in robotic minimally invasive surgery allows the human operator to manipulate tissues as if his/her hands were in contact with the patient organs. A force sensor mounted on the probe raises problems with sterilization of the overall surgical tool. Also, the use of off-axis gauges introduces a moment that increases the friction force on the bearing, which can easily mask off the signal, given the small force to be measured. METHODS: This work aims at designing and testing two methods for estimating the resistance to the advancement (force) experienced by a standard probe for brain biopsies within a brain-like material. The further goal is to provide a neurosurgeon using a master-slave tele-operated driver with direct feedback on the tissue mechanical characteristics. Two possible sensing methods, in-axis strain gauge force sensor and position-position error (control-based method), were implemented and tested, both aimed at device miniaturization. The analysis carried out was aimed at fulfilment of the psychophysics requirements for force detection and delay tolerance, also taking into account safety, which is directly related to the last two issues. Controller parameters definition is addressed and consideration is given to development of the device with integration of a haptic interface. RESULTS: Results show better performance of the control-based method (RMSE < 0.1 N), which is also best for reliability, sterilizability, and material dimensions for the application addressed. CONCLUSIONS: The control-based method developed for force estimation is compatible with the neurosurgical application and is also capable of measuring tissue resistance without any additional sensors. Force feedback in minimally invasive surgery allows the human operator to manipulate tissues as if his/her hands were in contact with the patient organs.

Analysis of wormlike robotic locomotion on compliant surfaces.

An inherent characteristic of biological vessels and tissues is that they exhibit significant compliance or flexibility, both in the normal and tangential directions. The latter in particular is atypical of standard engineering materials and presents additional challenges for designing robotic mechanisms for navigation inside biological vessels by crawling on the tissue. Several studies aimed at designing and building wormlike robots have been carried out, but little was done on analyzing the interactions between the robots and their flexible environment. In this study, we will analyze the interaction between earthworm robots and biological tissues where contact mechanics is the dominant factor. Specifically, the efficiency of locomotion of earthworm robots is derived as a function of the tangential flexibility, friction coefficients, number of cells in the robot, and external forces.

Clinical acceptance and accuracy assessment of spinal implants guided with SpineAssist surgical robot: retrospective study.

STUDY DESIGN: Retrospective, multicenter study of robotically-guided spinal implant insertions. Clinical acceptance of the implants was assessed by intraoperative radiograph, and when available, postoperative computed tomography (CT) scans were used to determine placement accuracy. OBJECTIVE: To verify the clinical acceptance and accuracy of robotically-guided spinal implants and compare to those of unguided free-hand procedures. SUMMARY OF BACKGROUND DATA: SpineAssist surgical robot has been used to guide implants and guide-wires to predefined locations in the spine. SpineAssist which, to the best of the authors' knowledge, is currently the sole robot providing surgical assistance in positioning tools in the spine, guided over 840 cases in 14 hospitals, between June 2005 and June 2009. METHODS: Clinical acceptance of 3271 pedicle screws and guide-wires inserted in 635 reported cases was assessed by intraoperative fluoroscopy, where placement accuracy of 646 pedicle screws inserted in 139 patients was measured using postoperative CT scans. RESULTS: Screw placements were found to be clinically acceptable in 98% of the cases when intraoperatively assessed by fluoroscopic images. Measurements derived from postoperative CT scans demonstrated that 98.3% of the screws fell within the safe zone, where 89.3% were completely within the pedicle and 9% breached the pedicle by up to 2 mm. The remaining 1.4% of the screws breached between 2 and 4 mm, while only 2 screws (0.3%) deviated by more than 4 mm from the pedicle wall. Neurologic deficits were observed in 4 cases yet, following revisions, no permanent nerve damage was encountered, in contrast to the 0.6% to 5% of neurologic damage reported in the literature. CONCLUSION: SpineAssist offers enhanced performance in spinal surgery when compared to free-hand surgeries, by increasing placement accuracy and reducing neurologic risks. In addition, 49% of the cases reported herein used a percutaneous approach, highlighting the contribution of SpineAssist in procedures without anatomic landmarks.

A self-propelled inflatable earthworm-like endoscope actuated by single supply line.

Design of a self-propelling endoscope has been of interest for decades, as it allows for simplified medical examination techniques and improved patient comfort, together with advanced analysis capacity. In this paper, we describe the development of a fully automatic, multiple-balloon system achieving peristaltic locomotion, controlled by a single supply channel. The system employs the nonlinear pressure-radius characteristics of elastic balloons to simultaneously control numerous balloons with a constant inlet pressure. The balloons are connected in series and the flow is controlled by small orifices, which delay the flow between them. The proposed multiple-balloon system requires no moving parts, no electronics, and relies on dynamics of the fluid flow between serially interconnected inflatable balloons. The entire system is made of disposable silicone and is plastic-modeled by injection molding. Additionally, the cost of such a system is expected to be low and suitable for numerous biomedical applications as it can be easily scaled down due to the need for only one supply line. Mathematical modeling, and simulation and experimental results of a system prototype are presented in this paper. Experimental results in the straight cylinder show close correlation to simulated system.

Ultrasound-guided robot for flexible needle steering.

The success rate of medical procedures involving needle insertion is often directly related to needle placement accuracy. Due to inherent limitations of commonly used freehand needle placement techniques, there is a need for a system providing for controlled needle steering for procedures that demand high positional accuracy. This paper describes a robotic system developed for flexible needle steering inside soft tissues under real-time ultrasound imaging. An inverse kinematics algorithm based on a virtual spring model is applied to calculate needle base manipulations required for the tip to follow a curved trajectory while avoiding physiological obstacles. The needle tip position is derived from ultrasound images and is used in calculations to minimize the tracking error, enabling a closed-loop needle insertion. In addition, as tissue stiffness is a necessary input to the control algorithm, a novel method to classify tissue stiffness from localized tissue displacements is proposed and shown to successfully distinguish between soft and stiff tissue. The system performance was experimentally verified by robotic manipulation of the needle base inside a phantom with layers of varying stiffnesses. The closed-loop experiment with updated tissue stiffness parameters demonstrated a needle-tip tracking error of approximately 1 mm and proved to be significantly more accurate than the freehand method.

Bone-mounted miniature robotic guidance for pedicle screw and translaminar facet screw placement: part 2--Evaluation of system accuracy.

OBJECTIVE: To evaluate the accuracy of a novel bone-mounted miniature robotic system for percutaneous placement of pedicle and translaminar facet screws. METHODS: Thirty-five spinal levels in 10 cadavers were instrumented. Each cadaver's entire torso was scanned before the procedure. Surgeons planned optimal entry points and trajectories for screws on reconstructed three-dimensional virtual x-rays of each vertebra. Either a clamp or a minimally invasive external frame was attached to the bony anatomy. Anteroposterior and lateral fluoroscopic images using targeting devices were obtained and automatically registered with the virtual x-rays of each vertebra generated from the computed tomographic scan obtained before the procedure. A miniature robot was mounted onto the clamp and external frame and the system controlled the robot's motions to align the cannulated drill guide along the planned trajectory. A drill bit was introduced through the cannulated guide and a hole was drilled through the cortex. Then, K-wires were introduced and advanced through the same cannulated guide and left inside the cadaver. The cadavers were scanned with computed tomography after the procedure and the system's accuracy was evaluated in three planes, comparing K-wire positions with the preoperative plan. A total of fifty-five procedures were evaluated. RESULTS: Twenty-nine of 32 K-wires and all four screws were placed with less than 1.5 mm of deviation; average deviation was 0.87 +/- 0.63 mm (range, 0-1.7 mm) from the preoperative plan in this group. Sixteen of 19 K-wires were placed with less than 1.5 mm of deviation. There was one broken and one bent K-wire. Another K-wire was misplaced because of collision with the previously placed wire on the contralateral side of the same vertebra because of a mistake in planning, resulting in a 6.5-mm deviation. When this case was excluded, average deviation was 0.82 +/- 0.65 mm (range, 0-1.5 mm). CONCLUSION: These results verify the system's accuracy and support its use for minimally invasive spine surgery in selected patients.

Flexible needle steering for percutaneous therapies.

OBJECTIVE: A robotic system is presented for flexible needle steering and control in soft tissue. MATERIALS AND METHODS: Flexible needle insertion into a deformable tissue is modeled as a linear beam supported by virtual springs, where the stiffness coefficients of the springs can vary along the needle. Using this simplified model, the forward and inverse kinematics of the needle are solved analytically, thus enabling both path planning and path correction in real time. Given target and obstacle locations, the computer calculates the needle tip trajectory that will avoid the obstacle and hit the target. Using the inverse kinematics algorithm, the corresponding needle base maneuver needed to follow this trajectory is calculated. RESULTS: It is demonstrated that the needle tip path is not unique and can be optimized to minimize lateral pressure of the needle body on the tissue. Needle steering, i.e., the needle base movements that steer the needle tip, is not intuitive. Therefore, the needle insertion procedure is best performed by a robot. The model was verified experimentally on muscle and liver tissues by robotically assisted insertion of a flexible spinal needle. During insertion, the position and shape of the needle were recorded by X-ray. CONCLUSIONS: This study demonstrates the ability to curve a flexible needle by its base motion in order to achieve a planned tip trajectory.

Feasibility study of a mini, bone-attached, robotic system for spinal operations: analysis and experiments.

STUDY DESIGN: In this investigation, a new concept of a miniature, bone-attached, medical robotic system for spinal operations is presented. As part of the design parameters of the robot, the forces and moments applied by the physician during insertion of Kirschner wires to soft tissues and drilling in hard tissues were examined. A theoretical model for the expected error of the robotic system due to the applied force has been derived and verified experimentally. The results of a clinical experiment that was carried out on a cadaver support the theoretical model derived and the miniature, bone-attached, robotic concept. OBJECTIVES: 1) Examining the concept of attaching a miniature robotic system to the spinous process of the operated vertebra. 2) Measuring the forces applied by the physician during insertion of Kirschner wires to soft tissues and drilling in hard tissues. 3) Evaluating the expected error of the robot due to mechanical and anatomic deflection caused by the forces applied by the physician during operation. 4) Testing and verifying the theoretical background by a clinical experiment. SUMMARY OF BACKGROUND DATA: Spinal operations are reported in the literature to have a relatively low success rate (70%-90%). This low success rate is affected by misunderstanding of the disease and its indications, resulting in bad selection of patients. From the technical point of view, the low success rate is greatly affected by the physician's lack of experience and the complexity of the spinal anatomy. The development of a miniature bone-attached robotic system for spinal operations could improve the success rate of spinal operations, introduce new percutaneous procedures, and shorten recovery and hospitalization time. Moreover, it will reduce the use of fluoroscopic exposure during operation; consequently, it will decrease considerably exposure to radiation during spinal operations. METHODS: Forces and moments applied by the physician during operation were measured by a 6-DOF miniature sensor. The measurements were taken during K-wire insertion both to soft and to hard tissues of a sheep and a human cadaver. A theoretical model of the expected location error of a K-wire, inserted to selected vertebralanatomies by the robotic system, was derived and verified experimentally. RESULTS: The theoretical model agreed with the experimental results, meaning that the combination of the spinous process and the robotic structure is rigid enough to guide a K-wire accurately. The forces and moments were measured and analyzed, and the total expected error due to the forces and moments was calculated. The clinical experiments supported the theoretical model and proved the system's feasibility. CONCLUSIONS: The given results support the theoretical model developed. Moreover, a miniature robotic guiding system can be attached to the spinous process of a given vertebra. The deflection and system error resulting from the forces and moments acting during operation are within the allowable errors.

Approximating Functions by Neural Networks: A Constructive Solution in the Uniform Norm.

A method for constructively approximating functions in the uniform (i.e., maximal error) norm by successive changes in the weights and number of neurons in a neural network is developed. This is a realization of the approximation results of Cybenko, Hecht-Nielsen, Hornik, Stinchcombe, White, Gallant, Funahashi, Leshno et al., and others. The constructive approximation in the uniform norm is more appropriate for a number of examples, such as robotic arm motion, and stands in contrast with more standard methods, such as back-propagation, which approximate only in the average error norm. Copyright 1996 Elsevier Science Ltd