Force-based assessment of tissue handling skills in simulation training for robot-assisted surgery

INTRODUCTION

Although robotic-assisted surgery is increasingly performed, objective assessment of technical skills is lacking. The aim of this study is to provide validity evidence for objective assessment of technical skills for robotic-assisted surgery.

METHODS

An international multicenter study was conducted with participants from the academic hospitals Heidelberg University Hospital (Germany, Heidelberg) and the Amsterdam University Medical Centers (The Netherlands, Amsterdam). Trainees with distinctly different levels of robotic surgery experience were divided into three groups (novice, intermediate, expert) and enrolled in a training curriculum. Each trainee performed six trials of a standardized suturing task using the da Vinci Surgical System. Using the ForceSense system, five force-based parameters were analyzed, for objective assessment of tissue handling skills. Mann-Whitney U test and linear regression were used to analyze performance differences and the Wilcoxon signed-rank test to analyze skills progression.

RESULTS

A total of 360 trials, performed by 60 participants, were analyzed. Significant differences between the novices, intermediates and experts were observed regarding the total completion time (41 s vs 29 s vs 22 s p = 0.003), mean non zero force (29 N vs 33 N vs 19 N p = 0.032), maximum impulse (40 Ns vs 31 Ns vs 20 Ns p = 0.001) and force volume (38 N³ vs 32 N³ vs 22 N³ p = 0.018). Furthermore, the experts showed better results in mean non-zero force (22 N vs 13 N p = 0.015), maximum impulse (24 Ns vs 17 Ns p = 0.043) and force volume (25 N³ vs 16 N³ p = 0.025) compared to the intermediates (p ≤ 0.05). Lastly, learning curve improvement was observed for the total task completion time, mean non-zero force, maximum impulse and force volume (p ≤ 0.05).

CONCLUSION

Construct validity for force-based assessment of tissue handling skills in robot-assisted surgery is established. It is advised to incorporate objective assessment and feedback in robot-assisted surgery training programs to determine technical proficiency and, potentially, to prevent tissue trauma.

Two-Point Optical Manipulation of Cell Junctions in the Early Epithelium of the Drosophila Embryo

Laser manipulation is widely used to study mechanics from the molecular to the tissue scale. We implemented optical tweezers to directly manipulate single cell-cell junctions in a developing tissue. We further extended the approach to two-point laser manipulation to enable extensive remodeling of cell-cell junctions. Here, we describe two-point laser manipulation and its implementation to probe the mechanics of cell junctions in the Drosophila embryo.

Adaptations of dragonfly larvae and their exuviae (Insecta: Odonata), attachment devices and their crucial role during emergence

Moulting, especially in 'hemimetabolous' insects that emerge upside down, is a crucial moment in their live. Losing their attachment during this situation can be fatal for survival. We here studied the emergence of dragonfly adults, describe structures involved in larval attachment to the substrate, and biomechanically test the pull-off forces of exuviae to natural substrates. Confocal laser scanning microscopy and scanning electron microscopy were used to describe both morphology and material composition of the leg cuticle of Anax imperator larvae. The results show that the combination of morphological and behavioral adaptations provides reliable anchorage of exuviae to the substrates. We determined a safety factor of 14, and demonstrated that this staggered safety system experiencing several unlocking and relocking events withstand multiple disturbances before the entire exuvia is completely detaches. This furthers our understanding of interlocking and anchorage of insects in general and may allow for future applications.

Under pressure: force resistance measurements in box mites (Actinotrichida, Oribatida)

Background

Mechanical defenses are very common and diverse in prey species, for example in oribatid mites. Here, the probably most complex form of morphological defense is known as ptychoidy, that enables the animals to completely retract the appendages into a secondary cavity and encapsulate themselves. The two groups of ptychoid mites constituting the Ptyctima, i.e. Euphthiracaroidea and Phthiracaroidea, have a hardened cuticle and are well protected against similar sized predators. Euphthiracaroidea additionally feature predator-repelling secretions. Since both taxa evolved within the glandulate group of Oribatida, the question remains why Phthiracaroidea lost this additional protection. In earlier predation bioassays, chemically disarmed specimens of Euphthiracaroidea were cracked by the staphylinid beetle Othius punctulatus, whereas equally sized specimens of Phthiracaroidea survived. We thus hypothesized that Phthiracaroidea can withstand significantly more force than Euphthiracaroidea and that the specific body form in each group is key in understanding the loss of chemical defense in Phthiracaroidea. To measure force resistance, we adapted the principle of machines applying compressive forces for very small animals and tested the two ptyctimous taxa as well as the soft-bodied mite Archegozetes longisetosus.

Results

Some Phthiracaroidea individuals sustained about 560,000 times their body weight. Their mean resistance was about three times higher, and their mean breaking point in relation to body weight nearly two times higher than Euphthiracaroidea individuals. The breaking point increased with body weight and differed significantly between the two taxa. Across taxa, the absolute force resistance increased sublinearly (with a 0.781 power term) with the animal's body weight. Force resistance of A. longisetosus was inferior in all tests (about half that of Euphthiracaroidea after accounting for body weight). As an important determinant of mechanical resistance in ptychoid mites, the individuals' cuticle thickness increased sublinearly with body diameter and body mass as well and did not differ significantly between the taxa.

Conclusion

We showed the feasibility of the force resistance measurement method, and our results were consistent with the hypothesis that Phthiracaroidea compensated its lack of chemical secretions by a heavier mechanical resistance based on a different body form and associated build-up of hemolymph pressure (defensive trade-off).

Biomechanical assessment of the aortic root using novel force transducers

In recent years the use of valve sparing techniques has become more common in selected patients with aortic valve insufficiency. However, limited experimental research has been performed to document the biomechanical effect of these techniques. One experimental platform is to evaluate how the normal physiological aortic root forces are altered or re-established after the surgical intervention. Hence, the aim of this project was to develop new implantable force transducers for a biomechanical description of various aortic root repair techniques. Two novel force transducers were developed. Both transducers were manufactured using rapid prototyping and were instrumented with miniature strain gauges. Before implantation both transducers were calibrated using a dedicated setup, yielding very linear correlation between the applied load and transducer output. The developed force transducers were implanted and tested in an 80kg porcine model. In the post-cardioplegic heart, the peak annular forces varied in the range of 2-4N and the commissural forces varied from 0.4 to 0.8N with a left ventricular pressure of 111mmHg. In conclusion, the two new force transducers to measure forces in the aortic root have successfully been developed. With these new devices a novel versatile and direct force measurement system has been provided.

Beyond the Hookean Spring Model: Direct Measurement of Optical Forces Through Light Momentum Changes

The ability to measure forces in the range of 0.1-100 pN is a key feature of optical tweezers used for biophysical and cell biological studies. Analysis of the interactions between biomolecules and the forces that biomolecular motors generate at the single-molecule level has provided valuable insights in the molecular mechanisms that govern key cellular functions such as gene expression and the long-distance transport of organelles. Methods for determining the minute forces that biomolecular motors generate exhibit notable constraints that limit their application for studies other than the well-controlled in vitro experiments (although recent advances have been made that permit more quantitative optical tweezers studies insight living cells). One constraint comes from the linear approximation of the distance vs. force relationship used to extract the force from the position of the bead in the trap. This commonly employed "indirect" approach, although usually sufficiently precise, restricts the use of optical tweezers to a limited range of displacements (typically up to ±150 nm for small beads). Measurements based on the detection of the light-momentum changes, on the other hand, offer a "direct" and precise way to determine forces even when the generated displacements reach the escape point, thus covering the complete force range developed by the trap. In this chapter, we detail the requirements for the design of a force-sensor instrument based on light-momentum changes using a high-numerical-aperture objective lens and provide insights into its construction. We further discuss the calibration of the system and the main steps for its routine operation.

Laser Ablation to Probe the Epithelial Mechanics in Drosophila

Laser ablation is nowadays a widespread technique to probe tissue mechanics during development. Here we describe the setup of one such ablation system and ablation experiments performed on the embryo and pupa of Drosophila. We describe in detail the process of sample preparation, how to disrupt single-cell junctions and perform linear or circular cuts at the tissue scale, and how to analyze the data to determine relevant mechanical parameters.

In Vivo Wireless Monitoring System of Cardiovascular Force Data

Biotelemetry provides the possibility to measure physiological data in awake, free-ranging animals without the effects of anesthesia and repeated surgery. In this project a fully implantable, telemetric system to measure biomechanical force data of the moving structures of the heart along with the ECG of experimental animals was developed. The system is based on a microcontroller with a built in bidirectional radio frequency transceiver, which allows for the implant to both receive and send data wirelessly. ECG was acquired using electrodes placed directly onto the heart, and the forces were collected using a miniature force transducer. The system was tested in a porcine model (60 kg body weight), where the system transmitted ECG and force data at a range of 5 m between the implant and the receiver. The data was displayed and saved to the hard drive of a laptop computer using a custom built software user interface. It was shown feasible to wirelessly measure forces simultaneously with physiological data from the cardiovascular system of living animals. The current system was optimized to measure forces and ECG, and more channels can be added to increase the number of parameters recorded.

Actin filament dynamics using microfluidics

We describe how combining microfluidics with TIRF and epifluorescence microscopy can greatly facilitate the quantitative analysis of actin assembly dynamics and its regulation, as well as the exploration of issues that were often out of reach with standard single-filament microscopy, such as the kinetics of processes linked to actin self-assembly or the kinetics of interaction with regulators. We also show how the viscous drag force exerted by fluid flowing on the filaments can be calibrated in order to assess the mechanosensitivity of end-binding protein machineries such as formins or adhesion proteins. We also discuss how microfluidics, in conjunction with other techniques, could be used to address the mechanism of coordination between heterogeneous populations of filaments, or the behavior of individual filaments during regulated treadmilling. These techniques also can be applied to study the assembly and regulation of other cytoskeletal polymers such as microtubules, septins, intermediate filaments, as well as the transport of cargoes by molecular motors under a flow-produced load.