Measurement of Forces Acting on Single T-Cell Receptors

Molecular forces are increasingly recognized as an important parameter to understand cellular signaling processes. In the recent years, evidence accumulated that also T-cells exert tensile forces via their T-cell receptor during the antigen recognition process. To measure such intercellular pulling forces, one can make use of the elastic properties of spider silk peptides, which act similar to Hookean springs: increased strain corresponds to increased stress applied to the peptide. Combined with Förster resonance energy transfer (FRET) to read out the strain, such peptides represent powerful and versatile nanoscopic force sensing tools. In this paper, we provide a detailed protocol how to synthesize a molecular force sensor for application in T-cell antigen recognition and hands-on guidelines on experiments and analysis of obtained single molecule FRET data.

Compliant human-robot object transfer based on modular 3-axis force sensor for collaborative manufacturing

The primary motivation of this paper is to present a compliant and cost-effective solution for object transfer between human and robot. The application prospect of this study is robot-human collaboration in manufacturing. To achieve above goals, a novel modular 3-axis force sensor is proposed for the grasping system to achieve interactive force sensing. Compliant object transfer control strategy, which is composed of incremental force control mode and gravity balance control mode, is proposed for object transfer between human and robot. A prototype of underactuated grasping system which is mounted on the proposed modular 3-axis force sensor is fabricated to investigate the effectiveness of the proposed interactive control strategy. Experimental results reveal that the incremental force control mode is suitable for the lighter objects with a higher interactive sensitivity. For transferring heavier objects, the gravity balance control mode is more suitable. In gravity balance control mode, the human hand could achieve a quasi-static equilibrium with the object, and achieve a compliant transfer operation. Due to the above characteristic, the proposed control strategy has the potentials to enhance the object transfer compliance and safety in the human-robot object transfer process.

Efficacy of post-operative partial weight-bearing after total knee arthroplasty - a prospective observational trial

PURPOSE

There is little evidence proving the concept of partial weight-bearing to be efficient and feasible. Using insole pressure measurement systems, this study aimed to explore the compliance to prescribed weight-bearing restrictions after total knee arthroplasty (TKA).

METHODS

50 patients after TKA were recruited in a prospective manner. They were advised to limit weight-bearing of the affected limb to 200 N. True load was measured via insole force-sensors on day one after surgery (M1) and before discharge (M2). Compliance to the rehabilitation protocol was the primary outcome parameter.

RESULTS

At M1 and M2 compliance to the rehabilitation protocol was 0% und 2%, respectively. 84% (M1) and 90% (M2) of patients overloaded the affected limb during every step. The affected limb was loaded with 50% ± 14% (M1) and 57% ± 17% (M2) of body weight. Patients older than 65 loaded the affected limb on average 17% (M1) and 34% (M2) more than their younger counterparts did. This difference was even more pronounced when walking stairs up (49% increase on average) and down (53% increase on average).

CONCLUSION

Surgeons must take into consideration that the ability to maintain partial weight-bearing after TKA is highly dependent on the age of the patient and the achievable load reduction is determined by the patient's body weight.

Estimation of microtubule-generated forces using a DNA origami nanospring

Microtubules are dynamic cytoskeletal filaments that can generate forces when polymerizing and depolymerizing. Proteins that follow growing or shortening microtubule ends and couple forces to cargo movement are important for a wide range of cellular processes. Quantifying these forces and the composition of protein complexes at dynamic microtubule ends is challenging and requires sophisticated instrumentation. Here we present an experimental approach to estimate microtubule-generated forces through the extension of a fluorescent spring-shaped DNA origami molecule. Optical readout of the spring extension enables recording of force production simultaneously with single-molecule fluorescence of proteins getting recruited to the site of force generation. DNA nanosprings enable multiplexing of force measurements and only require a fluorescence microscope and basic laboratory equipment. We validate the performance of DNA nanosprings against results obtained using optical trapping. Finally, we demonstrate the use of the nanospring to study proteins that couple microtubule growth and shortening to force generation.

A force-sensing retractor for robot-assisted transoral surgery

PURPOSE

In robot-assisted transoral surgery, frequent retraction operations are essential to leave space for the surgical procedure. Commercial clinical retractors are simply composed of mechanical parts and cannot sense the touching force.

METHODS

We propose a new retractor for robot-assisted transoral surgery. It supports sensing of the touching force when retracting the tissues. By designing the structure of the force sensors based on small piezoresistive elements, we build a sensory system that is well integrated with the retractor for transoral surgery. After calibration of the system, a simple equation is computed to decode the resultant force as well as the center of the contact location.

RESULTS

A standard measuring test is designed for the force-sensing retractor. The result shows that the measured force is up to 15 N, and the sensed force precision reaches 0.08 N with a sampling rate of 98 Hz. The dimensions of the sensory system fit the retractor well.

CONCLUSION

The experimental results demonstrate the potential of the proposed retractor in robot-assisted surgery. The retractor supports the provision of force feedback in an interactive manipulation mode and produces haptic information for the remote side in a teleoperated surgical robot system.

Design and Fabrication of Biological Wires for Cardiac Fibrosis Disease Modeling

Extensive progress has been made in developing engineered models for elucidating human cardiac disease. Cardiac fibrosis is often associated with all forms of cardiac disease and has a direct deleterious effect on cardiac function. As currently there is no effective therapeutic strategy specifically designed to target fibrosis, in vitro diagnostic platforms for drug testing have generated significant interest. In this context, we have developed an innovative approach to generate human cardiac fibrotic tissues on Biowire II platform and established a compound screening system. The disease model is constructed to recapitulate contractile, biomechanical, and electrophysiological complexities of fibrotic myocardium. Additionally, an integrated model with fibrotic and healthy cardiac tissues coupled together can be created to mimic focal fibrosis. The methods for constructing the Biowire fibrotic model will be described here.

Digitizing abdominal palpation with a pressure measurement and positioning device

An abdominal physical examination is one of the most important tools in evaluating patients with acute abdominal pain. We focused on palpation, in which assessment is made according to the patient’s response and force feedback. Since palpation is performed manually by the examiner, the uniformity of force and location is difficult to achieve during examinations. We propose an integrated system to quantify palpation pressure and location. A force sensor continuously collects pressure data, while a camera locates the precise position of contact. The system recorded, displayed average and maximum pressure by creating a pressure/time curve for computer-aided diagnosis. Compared with previous work on pressure sensors of quantifying abdominal palpation, our proposed system is the integrated approach to measure palpation force and track the corresponding position at the same time, for further diagnosis. In addition, we only make use of a sensing device and a general web camera, rather than commercial algometry and infrared cameras used in the previous work. Based on our clinical trials, the statistics of palpation pressure values and the corresponding findings are also reported. We performed abdominal palpation with our system for twenty-three healthy participants, including fourteen males and nine females. We applied two grades of force on the abdomen (light and deep) by four-quadrant and nine-region schemes, record the value of pressure and location. In the four-quadrant scheme, the average pressures of abdominal palpation with light and deep force levels were 0.506(N) and 0.552(N), respectively. In the nine-region scheme, the average pressures were 0.496(N) and 0.577(N), respectively. Two episodes of contact dermal reaction were identified. According to our experiment statistics, there is no significant difference in the force level between the four-quadrant and nine-region scheme. Our results have the potential to be used as a reference guide while designing digital abdominal palpation devices.

The use of a piezoelectric force sensor in the magnetic force microscopy of thin permalloy films

A piezoelectric force sensor is suggested for magnetic force microscopy (MFM) purposes. Added between the piezoelectric resonator and the magnetic probe is a mechanical force amplifier in the form of a thin, long resonant arm with an integral micro-rod whereby the amplitude of the force acting on the probe is amplified by a factor of 20 to 40 at a low noise level. When the sensor was operated in air, its noise floor was found to be 1.4 pN (RMS) at a bandwidth of 100 Hz. The piezoelectric sensor requires no repeated calibration; and it is capable of operating in a vacuum, and at cryogenic temperatures. By using this sensor we carried out the MFM of ultrathin (1.5- and 3-nm-thick) Ni₇₉Fe₂₁ permalloy films. The 1.5-nm-thick permalloy films studied have a nanoisland structure, whereas 3-nm-thick ones are contiouous. Domain structures were found in both. The MFM image was found to suffer substantial changes when the external magnetic field was altered by 1 Oe. The structures under study featured both "elastic" and "viscous" magnetic force components.

Simultaneous measurement of turgor pressure and cell wall elasticity in growing pollen tubes

Plant growth and morphogenesis are tightly controlled processes of division and expansion of individual cells. To fully describe the factors that influence cell expansion, it is necessary to quantify the counteracting forces of turgor pressure and cell wall stiffness, which together determine whether and how a cell expands. Several methods have been developed to measure these parameters, but most of them provide only values for one or the other, and thus require complex models to derive the missing quantity. Furthermore, available methods for turgor measurement are either accurate but invasive, like the pressure probe; or they lack accuracy, such as incipient plasmolysis or indentation-based methods that rely on information about the mechanical properties of the cell wall. Here, we describe a system that overcomes many of the above-mentioned disadvantages using growing pollen tubes of Lilium longiflorum as a model. By combining non-invasive microindentation and cell compression experiments, we separately measure turgor pressure and cell wall elasticity on the same pollen tube in parallel. Due to the modularity of the setup and the large range of the micro-positioning system, our method is not limited to pollen tubes but could be used to investigate the biomechanical properties of many other cell types or tissues.

Quantification of Mechanical Forces and Physiological Processes Involved in Pollen Tube Growth Using Microfluidics and Microrobotics

Pollen tubes face many obstacles on their way to the ovule. They have to decide whether to navigate around cells or penetrate the cell wall and grow through it or even within it. Besides chemical sensing, which directs the pollen tubes on their path to the ovule, this involves mechanosensing to determine the optimal strategy in specific situations. Mechanical cues then need to be translated into physiological signals, which eventually lead to changes in the growth behavior of the pollen tube. To study these events, we have developed a system to directly quantify the forces involved in pollen tube navigation. We combined a lab-on-a-chip device with a microelectromechanical systems-based force sensor to mimic the pollen tube's journey from stigma to ovary in vitro. A force-sensing plate creates a mechanical obstacle for the pollen tube to either circumvent or attempt to penetrate while measuring the involved forces in real time. The change of growth behavior and intracellular signaling activities can be observed with a fluorescence microscope.

Force Metrics and Suspension Times for Microlaryngoscopy Procedures

OBJECTIVE

To determine the difference in force metrics measured by the laryngeal force sensor for various suspension microlaryngoscopy (SML) procedures and their perioperative narcotic requirements.

STUDY DESIGN

Prospective observational study.

SETTING

Academic tertiary center.

METHODS

The laryngeal force sensoris a force sensor designed for SML procedures. Prospectively enrolled patients had dynamic recordings of maximum force, average force, suspension time, and total impulse. Procedures were grouped into excision of striking zone lesions, nonstriking zone lesions, endoscopic cancer surgery with margin control, and airway dilation. Narcotic administration in the intraoperative period and postanesthesia care unit was also recorded and converted into IV morphine equivalents. Surgeons were blinded to the force recordings during surgery to prevent operator bias.

RESULTS

In total, 110 patients completed the study. There was no significant difference in average force across different procedures, however, a significant difference was seen for maximum force (P = 0.025), suspension time (P < 0.001), and total impulse (P = 0.002). The highest values were seen for endoscopic cancer surgeries with margin control with a mean maximum force of 49.4 lbf (95%CI, 37.1-61.7), mean suspension time of 60.2 minutes (95%CI, 40.5-79.9), and mean total impulse of 31.3 ton*s (95%CI, 15.2-47.3). A significant difference (P < 0.01) in perioperative narcotic requirements was also seen, with endoscopic cancer surgery cases having the highest requirements at 27.6 mg of ME (95%CI, 16.1-39.2 mg).

CONCLUSION

Significant differences in force metrics exist between various SML procedures. Endoscopic cancer surgery is associated with higher force metrics and perioperative narcotic requirements.

Evaluation of the pressure on the dorsal surface of the distal radius using a cadaveric and computational model: clinical considerations in intersection syndrome and Colles' fracture

The fibers of the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) muscles intersect the distal radius. This anatomical structure puts pressure on the dorsal surface of the distal radius when various wrist positions are adopted. An increase in this pressure is associated with the risk of intersection syndrome and with immobilization after Colles' fracture. However, the relationship between the pressure on the distal radius and various wrist positions remains unclear. This study was established to provide quantitative data on the mechanical effect of the pressure exerted by the APL and EPB. Ten cadaveric wrist models containing a force sensor were prepared and used to record pressure levels at various wrist positions, such as pronation, supination, flexion and dorsiflexion, and radial and ulnar deviation. A three-dimensional simulation model comprising four bones, one muscle, one tendon, and one tendon sheath was constructed and analyzed in detail using the finite element method. The contribution of the APL and EPB to the pressure exerted on the distal radius was quantified by dissecting muscles while measuring pressure. The position (pronation and ulnar deviation without flexion/dorsiflexion) associated with a strong force being exerted on the distal radius was determined by measuring and analyzing the mechanical effect. We concluded that this position increases the risk of intersection syndrome but provides effective immobilization after Colles' fracture. The cadaveric and computational method presented herein is the first to identify the anatomical relationship between the pressure on the distal radius and various wrist positions.

Biaxial sensing suture breakage warning system for robotic surgery

The number of procedures performed with robotic surgery may exceed one million globally in 2018. The continual lack of haptic feedback, however, forces surgeons to rely on visual cues in order to avoid breaking sutures due to excessive applied force. To mitigate this problem, the authors developed and validated a novel grasper-integrated system with biaxial shear sensing and haptic feedback to warn the operator prior to anticipated suture breakage. Furthermore, the design enables facile suture manipulation without a degradation in efficacy, as determined via measured tightness of resulting suture knots. Biaxial shear sensors were integrated with a da Vinci robotic surgical system. Novice subjects (n = 17) were instructed to tighten 10 knots, five times with the Haptic Feedback System (HFS) enabled, five times with the system disabled. Seven suture failures occurred in trials with HFS enabled while seventeen occurred in trials without feedback. The biaxial shear sensing system reduced the incidence of suture failure by 59% (p = 0.0371). It also resulted in 25% lower average applied force in comparison to trials without feedback (p = 0.00034), which is relevant because average force was observed to play a role in suture breakage (p = 0.03925). An observed 55% decrease in standard deviation of knot quality when using the HFS also indicates an improvement in consistency when using the feedback system. These results suggest this system may improve outcomes related to knot tying tasks in robotic surgery and reduce instances of suture failure while not degrading the quality of knots produced.

A force sensor that converts fluorescence signal into force measurement utilizing short looped DNA

A force sensor concept is presented where fluorescence signal is converted into force information via single-molecule Förster resonance energy transfer (smFRET). The basic design of the sensor is a ~100 base pair (bp) long double stranded DNA (dsDNA) that is restricted to a looped conformation by a nucleic acid secondary structure (NAS) that bridges its ends. The looped dsDNA generates a tension across the NAS and unfolds it when the tension is high enough. The FRET efficiency between donor and acceptor (D&A) fluorophores placed across the NAS reports on its folding state. Three dsDNA constructs with different lengths were bridged by a DNA hairpin and KCl was titrated to change the applied force. After these proof-of-principle measurements, one of the dsDNA constructs was used to maintain the G-quadruplex (GQ) construct formed by thrombin binding aptamer (TBA) under tension while it interacted with a destabilizing protein and stabilizing small molecule. The force required to unfold TBA-GQ was independently investigated with high-resolution optical tweezers (OT) measurements that established the relevant force to be a few pN, which is consistent with the force generated by the looped dsDNA. The proposed method is particularly promising as it enables studying NAS, protein, and small molecule interactions using a highly-parallel FRET-based assay while the NAS is kept under an approximately constant force.

Impact sites representing potential bruising locations associated with bed falls in children

Bruising can occur as a result of accidental or abusive trauma in children. Bruises are an early sign of child abuse and their locations on the body can be an effective delineator of abusive trauma. Since falls are often reported as false histories in abuse, the ability to predict potential bruising locations in falls could be valuable when attempting to differentiate between abuse and accident. In our study we used an anthropomorphic test device (ATD), a surrogate representing a 12 month old child, adapted with a custom developed force sensing skin to predict potential bruising locations during simulated bed falls. The sensing skin is made of custom resistive force sensors integrated into a conformable skin, adapted to fit the contours of the ATD. The sensing skin measured and displayed recorded force data on a computerized body image mapping system when sensors were activated. Simulated bed fall experiments were performed from two initial positions (FF - facing forward and FR - facing rearward) and two fall heights of 61cm (24 in) and 91cm (36 in) onto a padded carpet impact surface. Findings indicated potential bruising primarily in two planes of the ATD body. The majority of contact regions and greater forces were recorded in one plane, with fewer regions of contact and decreased force exhibited in an adjoining second plane. Additionally, no contact was recorded in the two planes opposite the impact planes. Differences in contact regions were observed for varying heights and initial position. Limitations of ATD biofidelity and soft tissue properties must be considered when interpreting these findings.

Tensile strength and failure load of sutures for robotic surgery

BACKGROUND

Robotic surgical platforms have seen increased use among minimally invasive gastrointestinal surgeons (von Fraunhofer et al. in J Biomed Mater Res 19(5):595-600, 1985. doi: 10.1002/jbm.820190511 ). However, these systems still suffer from lack of haptic feedback, which results in exertion of excessive force, often leading to suture failures (Barbash et al. in Ann Surg 259(1):1-6, 2014. doi: 10.1097/SLA.0b013e3182a5c8b8 ). This work catalogs tensile strength and failure load among commonly used sutures in an effort to prevent robotic surgical consoles from exceeding identified thresholds. Trials were thus conducted on common sutures varying in material type, gauge size, rate of pulling force, and method of applied force.

METHODS

Polydioxanone, Silk, Vicryl, and Prolene, gauges 5-0 to 1-0, were pulled till failure using a commercial mechanical testing system. 2-0 and 3-0 sutures were further tested for the effect of pull rate on failure load at rates of 50, 200, and 400 mm/min. 3-0 sutures were also pulled till failure using a da Vinci robotic surgical system in unlooped, looped, and at the needle body arrangements.

RESULTS

Generally, Vicryl and PDS sutures had the highest mechanical strength (47-179 kN/cm²), while Silk had the lowest (40-106 kN/cm²). Larger diameter sutures withstand higher total force, but finer gauges consistently show higher force per unit area. The difference between material types becomes increasingly significant as the diameters decrease. Comparisons of identical suture materials and gauges show 27-50% improvement in the tensile strength over data obtained in 1985 (Ballantyne in Surg Endosc Other Interv Tech 16(10):1389-1402, 2002. doi: 10.1007/s00464-001-8283-7 ). No significant differences were observed when sutures were pulled at different rates. Reduction in suture strength appeared to be strongly affected by the technique used to manipulate the suture.

CONCLUSIONS

Availability of suture tensile strength and failure load data will help define software safety protocols for alerting a surgeon prior to suture failure during robotic surgery. Awareness of suture strength weakening with direct instrument manipulation may lead to the development of better techniques to further reduce intraoperative suture breakage.

Visual-perceptual mismatch in robotic surgery

BACKGROUND

The principal objective of the experiment was to analyze the effects of the clutch operation of robotic surgical systems on the performance of the operator. The relative coordinate system introduced by the clutch operation can introduce a visual-perceptual mismatch which can potentially have negative impact on a surgeon's performance. We also assess the impact of the introduction of additional tactile sensory information on reducing the impact of visual-perceptual mismatch on the performance of the operator.

METHODS

We asked 45 novice subjects to complete peg transfers using the da Vinci IS 1200 system with grasper-mounted, normal force sensors. The task involves picking up a peg with one of the robotic arms, passing it to the other arm, and then placing it on the opposite side of the view. Subjects were divided into three groups: aligned group (no mismatch), the misaligned group (10 cm z axis mismatch), and the haptics-misaligned group (haptic feedback and z axis mismatch). Each subject performed the task five times, during which the grip force, time of completion, and number of faults were recorded.

RESULTS

Compared to the subjects that performed the tasks using a properly aligned controller/arm configuration, subjects with a single-axis misalignment showed significantly more peg drops (p = 0.011) and longer time to completion (p < 0.001). Additionally, it was observed that addition of tactile feedback helps reduce the negative effects of visual-perceptual mismatch in some cases. Grip force data recorded from grasper-mounted sensors showed no difference between the different groups.

CONCLUSIONS

The visual-perceptual mismatch created by the misalignment of the robotic controls relative to the robotic arms has a negative impact on the operator of a robotic surgical system. Introduction of other sensory information and haptic feedback systems can help in potentially reducing this effect.

Versatile and inexpensive Hall-Effect force sensor for mechanical characterization of soft biological materials

Mismatch of hierarchical structure and mechanical properties between tissue-engineered implants and native tissue may result in signal cues that negatively impact repair and remodeling. With bottom-up tissue engineering approaches, designing tissue components with proper microscale mechanical properties is crucial to achieve necessary macroscale properties in the final implant. However, characterizing microscale mechanical properties is challenging, and current methods do not provide the versatility and sensitivity required to measure these fragile, soft biological materials. Here, we developed a novel, highly sensitive Hall-Effect based force sensor that is capable of measuring mechanical properties of biological materials over wide force ranges (μN to N), allowing its use at all steps in layer-by-layer fabrication of engineered tissues. The force sensor design can be easily customized to measure specific force ranges, while remaining easy to fabricate using inexpensive, commercial materials. Although we used the force sensor to characterize mechanics of single-layer cell sheets and silk fibers, the design can be easily adapted for different applications spanning larger force ranges (>N). This platform is thus a novel, versatile, and practical tool for mechanically characterizing biological and biomimetic materials.

Design of vessel ligation simulator for deliberate practice

BACKGROUND

Surgical residents develop technical skills at variable rates, often based on random chance of cases encountered. One such skill is tying secure knots without exerting excessive force. This study describes the design of a simulator using a force sensor to measure instantaneous forces exerted on a blood vessel analog during vessel ligation and the development of expert-derived performance goals.

MATERIALS AND METHODS

Vessel ligations were performed on Silastic tubing at an offset from a Vernier Force Sensor. Nine experts (surgical faculty and senior residents) and 10 novices (junior residents) were recruited to each perform 10 vessel ligations (two square knots each) with two-handed and one-handed techniques. Internal consistency for the series of vessel ligations was tested with Cronbach alpha. Maximum forces exerted by novices and experts were compared using Student t-test.

RESULTS

Internal consistency across the 10 ligations on the simulator was excellent (Cronbach alpha = 0.91). The expert group on average exerted a significantly lower maximum force when compared with novices while performing two-handed (0.76 ± 0.39 N versus 1.12 ± 0.49 N, P < 0.01) and one-handed (0.84 ± 0.32 N versus 1.36 ± 0.44 N, P < 0.01) vessel ligations.

CONCLUSIONS

Although the expert group performed vessel ligations with significantly lower peak force than the novice group, there were novices who performed at the expert level. This is consistent with the conceptual framework of milestones and suggests that the skill of gentle knot-tying can be measured and develops at different chronologic levels of training in different individuals. This simulator can be used as part of a deliberate practice curriculum with instantaneous visual feedback.

Myosin IIA deficient cells migrate efficiently despite reduced traction forces at cell periphery

Cell motility is a cornerstone of embryogenesis, tissue remodeling and repair, and cancer cell invasion. It is generally thought that migrating cells grab and exert traction force onto the extracellular matrix in order to pull the cell body forward. While previous studies have shown that myosin II deficient cells migrate efficiently, whether these cells exert traction forces during cell migration in the absence of the major contractile machinery is currently unknown. Using an array of micron-sized pillars as a force sensor and shRNA specific to each myosin II isoform (A and B), we analyzed how myosin IIA and IIB individually regulate cell migration and traction force generation. Myosin IIA and IIB localized preferentially to the leading edge where traction force was greatest, and the trailing edge, respectively. When individual myosin II isoforms were depleted by shRNA, myosin IIA deficient cells lost actin stress fibers and focal adhesions, whereas myosin IIB deficient cells maintained similar actin organization and focal adhesions as wild-type cells. Interestingly, myosin IIA deficient cells migrated faster than wild-type or myosin IIB deficient cells on both a rigid surface and a pillar array, yet myosin IIA deficient cells exerted significantly less traction force at the leading edge than wild-type or myosin IIB deficient cells. These results suggest that, in the absence of myosin IIA mediated force-generating machinery, cells move with minimal traction forces at the cell periphery, thus demonstrating the remarkable ability of cells to adapt and migrate.