Cameron N. Riviere

Autonomous robotic-assisted surgery (RAS) has emerged as a promising objective in biomedical technology, further enhanced by miniaturization toward microrobotic-assisted surgery (μ-RAS). This reduction in scale promises minimally invasive, partially or fully automated surgical procedures, with the potential to reduce patient recovery times, lower medical costs, and enable previously unavailable procedural options. This perspective highlights the specific advances in RAS that potentially map to the microscale (μ-RAS), organized across five surgical domains: endovascular, endoluminal, laparoscopic, ophthalmic, and orthopedic. We examine both clinical demands and technological advances in surgical robotics and identify the key innovations required for progress across these surgical fields. Our contribution is distinct in combining the perspectives of both surgical experts and bioengineering innovators, outlining a roadmap for the advancement and eventual integration of autonomous RAS and μ-RAS into mainstream surgical practice.

Electromagnetic trackers (EMTs) are position sensors that enable surgical navigation and robotic guidance by measuring the six degree of freedom motion of a magnetic sensor with respect to a fixed source field. Metallic interference is a major limitation for EMTs in clinical and industrial applications. We systematically examined this problem using our In-Loop Electromagnetic Tracker (ILEMT) with dual-frequency capability (300 Hz and 10 kHz) and compared results with commercial pulsed DC modulation. We tested six metals in rod, tube, and sheet forms across multiple positions and orientations, including both ferromagnetic and non-ferromagnetic materials with varying conductivities. Low-frequency modulations (300 Hz and pulsed DC) produced nearly identical interference despite different tracker hardware, validating ILEMT’s low-frequency channel as equivalent to pulsed DC systems. The effect of low-frequency modulation varied dramatically from 260× reduction to 5.5× increase in interference depending on metal type, shape, and orientation. Contrary to simple models, large metal sheets showed unexpected behavior where material properties had minimal effect and ferromagnetic metals sometimes produced less interference at low frequencies. Shape and orientation significantly affected interference, with interference decreasing with distance following power laws with exponents ranging from -3 to -6 rather than the -6 predicted by dipole theory. These findings provide practical guidance for EMT workspace configuration and demonstrate the potential of dual-frequency systems for adaptive interference mitigation.

BACKGROUND: HeartPrinter is a flexible parallel wire robot that adheres to the beating heart with vacuum suction at three bases. An injector head actuated by cables delivers gene therapy injections within the bounds of the bases. To deploy onto the epicardium, an introducer mechanism is required. On the heart, the robot's workspace and anatomical model registration to its pose are needed. METHODS: We present HeartPrinter's components and introducer mechanism, and assess them on an artificial beating heart. We evaluate accuracy for position determination of the bases and registering a three-dimensional heart scan. RESULTS: The introducer mechanism successfully positioned HeartPrinter, and the bases adhered to the beating heart. The base positions and registration were calculated accurately with errors under 4 and 2 mm. CONCLUSIONS: The introducer mechanism can deploy HeartPrinter on the epicardium, and HeartPrinter's components can operate on the heart. Workspace determination and registration demonstrate feasibility as preliminary concepts.

BACKGROUND: Virtual fixtures in robot-assisted retinal surgery require knowledge of the position of the retina with respect to the surgical tool to be effective. Retinal surface estimation is a difficult problem due to the lack of features in the captured microscope imagery and a complex light path. A laser aiming beam attached to the tool can be easily detected in the microscope imagery and provide valuable information about the location of the surface. METHODS: We propose using the area of a laser aiming beam attached to the surgical tool to determine the distance of the tool from the retina. This area was modified in accordance with the tool width to ensure independence from microscope magnification. Retinal distance is predicted using a dual Kalman filter that combines distance inferred from this metric with information from an optical tracker that tracks the position of the tool in a global coordinate system. This updates both the state and parameters of the system in parallel and allows us to predict retinal distance even with errors in initial parameters. RESULTS: The laser metric's independence from microscope magnification is demonstrated by plotting the metric at 3 different magnifications for a number of angles. We also predict the distance of the tool from the retina for various random angles at each magnification with median errors of less than 100 μm. Finally, we predict distance at each magnification during freehand motion and validate our results using a force sensor placed underneath the phantom. CONCLUSIONS: Using the area of laser aiming beam attached to the surgical tool, our method can predict the distance of the surgical tool to the retina with errors that are acceptable for implementing virtual fixtures during robot-assisted retinal surgery. The predicted distance is also independent of microscope magnification and can work when initial parameters are not precisely known. Future work will involve adapting this method to in vivo environments and further reduction in prediction errors.

HeartLander is a miniature mobile robot designed to navigate on the surface of the heart using a crawling motion and is well-suited for delivering myocardial injections. Previous work has incorporated a cooling system to enable delivery of a thermally responsive anti-ventricular remodeling hydrogel to a target injection site. However, the previous setup required the saline coolant to be discharged at the distal end of the system and into the patient's pericardial space, hindering the hydrogel from forming a deposit at the target site, presenting an additional burden to the surgeon's workflow, and increasing the risk to the patient. To prevent this, we redesigned the system to include a return channel for the coolant, which discharges to a reservoir outside the patient. We validated this design with a multiphysics simulation, static water bath tests, and by demonstration of controlled injections in an ovine heart ex vivo at 37°C.

An electromagnetic position and orientation tracker must be calibrated so that magnetic measurements can be converted into spatial data, and the accuracy must also be characterized to know what accuracy is obtained. We describe a magnetic calibration matrix model which is extensible to the common coil configurations. We detail data representations and discuss successful approaches to the calibration optimization. An accurate positioning device is necessary for both calibration and characterization. We discuss the effect of positioning error on calibration accuracy and some design tradeoffs for positioning. We characterize the calibrated accuracy with two different source coil designs and several calibration variations, with the best configuration achieving 208 μm/0.27° uncertainty, an accuracy exceeding published values for commercial EMTs (tested by other methods). We use local measurement nonlinearity to characterize the expected accuracy across small motions, including the cross-coupling between position and orientation. All software described is open source (Apache License 2.0).

HeartPrinter is a novel under-constrained 3-cable parallel wire robot designed for minimally invasive epicardial interventions. The robot adheres to the beating heart using vacuum suction at its anchor points, with a central injector head that operates within the triangular workspace formed by the anchors, and is actuated by cables for multipoint direct gene therapy injections. Minimizing cable tensions can reduce forces on the heart at the anchor points while supporting rapid delivery of accurate injections and minimizing procedure time, risk of damage to the robot, and strain to the heart. However, cable tensions must be sufficient to hold the injector head's position as the heart moves and to prevent excessive cable slack. We pose a linear optimization problem to minimize the sum of cable tension magnitudes for HeartPrinter while ensuring the injector head is held in static equilibrium and the tensions are constrained within a feasible range. We use Karush-Kuhn-Tucker optimality conditions to derive conditional algebraic expressions for optimal cable tensions as a function of injector head position and workspace geometry, and we identify regions of injector head positions where particular combinations of cable tensions are optimally at minimum allowable tensions. The approach can rapidly solve for the minimum set of cable tensions for any robot workspace geometry and injector head position and determine whether an injection site is attainable.