Characterizing the Suture Pullout Force for Human Small Bowel.

Performing a small bowel anastomosis, or reconnecting small bowel segments, remains a core competency and critical step for the successful surgical management of numerous bowel and urinary conditions. As surgical education and technology moves toward improving patient outcomes through automation and increasing training opportunities, a detailed characterization of the interventional biomechanical properties of the human bowel is important. This is especially true due to the prevalence of anastomotic leakage as a frequent (3.02%) postoperative complication of small bowel anastomoses. This study aims to characterize the forces required for a suture to tear through human small bowel (suture pullout force, SPOF), while analyzing how these forces are affected by tissue orientation, suture material, suture size, and donor demographics. 803 tests were performed on 35 human small bowel specimens. A uni-axial test frame was used to tension sutures looped through 10 × 20 mm rectangular bowel samples to tissue failure. The mean SPOF of the small bowel was 4.62±1.40 N. We found no significant effect of tissue orientation (p = 0.083), suture material (p = 0.681), suture size (p = 0.131), age (p = 0.158), sex (p = .083), or body mass index (BMI) (p = 0.100) on SPOF. To our knowledge, this is the first study reporting human small bowel SPOF. Little research has been published about procedure-specific data on human small bowel. Filling this gap in research will inform the design of more accurate human bowel synthetic models and provide an accurate baseline for training and clinical applications.

Variability of tissue mechanical response in Sus Domesticus porcine models from in vivo to ex vivo conditions.

BACKGROUND: Healthcare simulators have been demonstrated to be a valuable resource for training several technical and nontechnical skills. A gap in the fidelity of tissues has been acknowledged as a barrier to application for current simulators; especially for interventional procedures. Inaccurate or unrealistic mechanical response of a simulated tissue to a given surgical tool motion may result in negative training transfer and/or prevents the "suspension of disbelief" necessary for a trainee to engage in the activity. Thus, where it is relevant to training outcomes, there should be an effort to create healthcare simulators with simulated tissue mechanical responses that match or represent those of biological tissues. Historically, this data is most often gathered from preserved (post mortem) tissue; however, there is a concern that the mechanical properties of preserved tissue, that lacks blood flow, may lack adequate accuracy to provide the necessary training efficacy of simulators. METHODS AND FINDINGS: This work explores the effect of the "state" of the tissue testing status on liver and peritoneal tissue by using a customized handheld grasper to measure the mechanical responses of representative porcine (Sus domesticus) tissues in n = 5 animals across five test conditions: in vivo, post mortem (in-situ), ex vivo (immediately removed from fresh porcine cadaver), post-refrigeration, and post-freeze-thaw cycle spanning up to 72 hours after death. No statistically significant difference was observed in the mechanical responses due to grasping between in vivo and post-freeze conditions for porcine liver and peritoneum tissue samples (p = 0.05 for derived stiffness at grasping force values F = 5N and 6.5N). Furthermore, variance between in vivo and post-freeze conditions within each animal, was comparable to the variance of the in vivo condition between animals. CONCLUSIONS: Results of this study further validate the use of preserved tissue in the design of medical simulators via observing tissue mechanical responses of post-freeze tissue comparable to in vivo tissue. Therefore, the use of thawed preserved tissue for the further study and emulation of mechanical perturbation of the liver and peritoneum can be considered. Further work in this area should investigate these trends further, particularly in regard to other tissues and the potential effects varying preservation methods may yield.

AMX - the highly automated macromolecular crystallography (17-ID-1) beamline at the NSLS-II.

The highly automated macromolecular crystallography beamline AMX/17-ID-1 is an undulator-based high-intensity (>5 × 1012 photons s-1), micro-focus (7 µm × 5 µm), low-divergence (1 mrad × 0.35 mrad) energy-tunable (5-18 keV) beamline at the NSLS-II, Brookhaven National Laboratory, Upton, NY, USA. It is one of the three life science beamlines constructed by the NIH under the ABBIX project and it shares sector 17-ID with the FMX beamline, the frontier micro-focus macromolecular crystallography beamline. AMX saw first light in March 2016 and started general user operation in February 2017. At AMX, emphasis has been placed on high throughput, high capacity, and automation to enable data collection from the most challenging projects using an intense micro-focus beam. Here, the current state and capabilities of the beamline are reported, and the different macromolecular crystallography experiments that are routinely performed at AMX/17-ID-1 as well as some plans for the near future are presented.

First Series Using Ultrasonic Propulsion and Burst Wave Lithotripsy to Treat Ureteral Stones.

PURPOSE: Our goal was to test transcutaneous focused ultrasound in the form of ultrasonic propulsion and burst wave lithotripsy to reposition ureteral stones and facilitate passage in awake subjects. MATERIALS AND METHODS: Adult subjects with a diagnosed proximal or distal ureteral stone were prospectively recruited. Ultrasonic propulsion alone or with burst wave lithotripsy was administered by a handheld transducer to awake, unanesthetized subjects. Efficacy outcomes included stone motion, stone passage, and pain relief. Safety outcome was the reporting of associated anticipated or adverse events. RESULTS: Twenty-nine subjects received either ultrasonic propulsion alone (n = 16) or with burst wave lithotripsy bursts (n = 13), and stone motion was observed in 19 (66%). The stone passed in 18 (86%) of the 21 distal ureteral stone cases with at least 2 weeks follow-up in an average of 3.9±4.9 days post-procedure. Fragmentation was observed in 7 of the burst wave lithotripsy cases. All subjects tolerated the procedure with average pain scores (0-10) dropping from 2.1±2.3 to 1.6±2.0 (P = .03). Anticipated events were limited to hematuria on initial urination post-procedure and mild pain. In total, 7 subjects had associated discomfort with only 2.2% (18 of 820) propulsion bursts. CONCLUSIONS: This study supports the efficacy and safety of using ultrasonic propulsion and burst wave lithotripsy in awake subjects to reposition and break ureteral stones to relieve pain and facilitate passage.

Ureteral Strictures Following Ureteroscopy for Kidney Stone Disease: A Population-based Assessment.

PURPOSE: As the prevalence of urolithiasis increases and ureteroscopy is used more frequently, the risks of uncommon complications such as ureteral stricture may become more notable. Our objective is to assess the rate and associated risk factors of ureteral stricture formation in patients undergoing ureteroscopy. MATERIALS AND METHODS: Utilizing the IBM MarketScan research database, we evaluated data from 2008 to 2019 and compared ureteral stricture rates and their management following ureteroscopy to subjects who had shock wave lithotripsy. Shock wave lithotripsy was used as a comparison group to represent the rate of stricture from stone disease alone. A third group of those having both shock wave lithotripsy and ureteroscopy was included. Patients and secondary procedures were identified using Current Procedural Terminology, and International Classification of Diseases-9 and -10 codes. RESULTS: A total of 329,776 patients received ureteroscopy, shock wave lithotripsy, or shock wave lithotripsy+ureteroscopy between 2008 and 2019. Stricture developed in 2.9% of patients after ureteroscopy, 1.5% after shock wave lithotripsy, and 2.6% after shock wave lithotripsy+ureteroscopy. In the multivariable model, rates of stricture were 1.7-fold higher after ureteroscopy vs shock wave lithotripsy (OR:1.71, 95% CI 1.62-1.81). Preoperative hydronephrosis, age, prior stones/intervention, and concurrent kidney and ureteral stones were associated with increased risk of stricture. Of those with strictures incurred after ureteroscopy, 35% required drainage, 21% had endoscopic intervention, 4.8% required reconstructive surgery, and 1.7% underwent nephrectomy. CONCLUSIONS: Ureteral stricture rate after ureteroscopy of nearly 3% was higher than expected and approximately twice the rate attributable to stone disease alone. Factors associated with the stone as well as instrumentation were found to be risk factors. The morbidity of stricture disease following ureteroscopy was significant.

Serial crystallography with multi-stage merging of thousands of images.

KAMO and BLEND provide particularly effective tools to automatically manage the merging of large numbers of data sets from serial crystallography. The requirement for manual intervention in the process can be reduced by extending BLEND to support additional clustering options such as the use of more accurate cell distance metrics and the use of reflection-intensity correlation coefficients to infer `distances' among sets of reflections. This increases the sensitivity to differences in unit-cell parameters and allows clustering to assemble nearly complete data sets on the basis of intensity or amplitude differences. If the data sets are already sufficiently complete to permit it, one applies KAMO once and clusters the data using intensities only. When starting from incomplete data sets, one applies KAMO twice, first using unit-cell parameters. In this step, either the simple cell vector distance of the original BLEND or the more sensitive NCDist is used. This step tends to find clusters of sufficient size such that, when merged, each cluster is sufficiently complete to allow reflection intensities or amplitudes to be compared. One then uses KAMO again using the correlation between reflections with a common hkl to merge clusters in a way that is sensitive to structural differences that may not have perturbed the unit-cell parameters sufficiently to make meaningful clusters. Many groups have developed effective clustering algorithms that use a measurable physical parameter from each diffraction still or wedge to cluster the data into categories which then can be merged, one hopes, to yield the electron density from a single protein form. Since these physical parameters are often largely independent of one another, it should be possible to greatly improve the efficacy of data-clustering software by using a multi-stage partitioning strategy. Here, one possible approach to multi-stage data clustering is demonstrated. The strategy is to use unit-cell clustering until the merged data are sufficiently complete and then to use intensity-based clustering. Using this strategy, it is demonstrated that it is possible to accurately cluster data sets from crystals that have subtle differences.

Hepatitis C virus NS3/4A inhibitors and other drug-like compounds as covalent binders of SARS-CoV-2 main protease.

Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), threatens global public health. The world needs rapid development of new antivirals and vaccines to control the current pandemic and to control the spread of the variants. Among the proteins synthesized by the SARS-CoV-2 genome, main protease (Mpro also known as 3CLpro) is a primary drug target, due to its essential role in maturation of the viral polyproteins. In this study, we provide crystallographic evidence, along with some binding assay data, that three clinically approved anti hepatitis C virus drugs and two other drug-like compounds covalently bind to the Mpro Cys145 catalytic residue in the active site. Also, molecular docking studies can provide additional insight for the design of new antiviral inhibitors for SARS-CoV-2 using these drugs as lead compounds. One might consider derivatives of these lead compounds with higher affinity to the Mpro as potential COVID-19 therapeutics for further testing and possibly clinical trials.

Characterization of Puncture Forces of the Human Trachea and Cricothyroid Membrane.

Accurate human tissue biomechanical data represents a critical knowledge gap that will help facilitate the advancement of new medical devices, patient-specific predictive models, and training simulators. Tissues related to the human airway are a top priority, as airway medical procedures are common and critical. Placement of a surgical airway, though less common, is often done in an emergent (cricothyrotomy) or urgent (tracheotomy) fashion. This study is the first to report relevant puncture force data for the human cricothyroid membrane and tracheal annular ligaments. Puncture forces of the cricothyroid membrane and tracheal annular ligaments were collected from 39 and 42 excised human donor tracheas, respectively, with a mechanized load frame holding various surgical tools. The average puncture force of the cricothyroid membrane using an 11 blade scalpel was 1.01 ± 0.36 N, and the average puncture force of the tracheal annular ligaments using a 16 gauge needle was 0.98 ± 0.34 N. This data can be used to inform medical device and airway training simulator development as puncture data of these anatomies has not been previously reported.

A simple technique to classify diffraction data from dynamic proteins according to individual polymorphs.

One often observes small but measurable differences in the diffraction data measured from different crystals of a single protein. These differences might reflect structural differences in the protein and may reveal the natural dynamism of the molecule in solution. Partitioning these mixed-state data into single-state clusters is a critical step that could extract information about the dynamic behavior of proteins from hundreds or thousands of single-crystal data sets. Mixed-state data can be obtained deliberately (through intentional perturbation) or inadvertently (while attempting to measure highly redundant single-crystal data). To the extent that different states adopt different molecular structures, one expects to observe differences in the crystals; each of the polystates will create a polymorph of the crystals. After mixed-state diffraction data have been measured, deliberately or inadvertently, the challenge is to sort the data into clusters that may represent relevant biological polystates. Here, this problem is addressed using a simple multi-factor clustering approach that classifies each data set using independent observables, thereby assigning each data set to the correct location in conformational space. This procedure is illustrated using two independent observables, unit-cell parameters and intensities, to cluster mixed-state data from chymotrypsinogen (ChTg) crystals. It is observed that the data populate an arc of the reaction trajectory as ChTg is converted into chymotrypsin.

Fragmentation of Stones by Burst Wave Lithotripsy in the First 19 Humans.

PURPOSE: We report stone comminution in the first 19 human subjects by burst wave lithotripsy (BWL), which is the transcutaneous application of focused, cyclic ultrasound pulses. MATERIALS AND METHODS: This was a prospective multi-institutional feasibility study recruiting subjects undergoing clinical ureteroscopy (URS) for at least 1 stone ≤12 mm as measured on computerized tomography. During the planned URS, either before or after ureteroscope insertion, BWL was administered with a handheld transducer, and any stone fragmentation and tissue injury were observed. Up to 3 stones per subject were targeted, each for a maximum of 10 minutes. The primary effectiveness outcome was the volume percent comminution of the stone into fragments ≤2 mm. The primary safety outcome was the independent, blinded visual scoring of tissue injury from the URS video. RESULTS: Overall, median stone comminution was 90% (IQR 20, 100) of stone volume with 21 of 23 (91%) stones fragmented. Complete fragmentation (all fragments ≤2 mm) within 10 minutes of BWL occurred in 9 of 23 stones (39%). Of the 6 least comminuted stones, likely causative factors for decreased effectiveness included stones that were larger than the BWL beamwidth, smaller than the BWL wavelength or the introduction of air bubbles from the ureteroscope. Mild reddening of the papilla and hematuria emanating from the papilla were observed ureteroscopically. CONCLUSIONS: The first study of BWL in human subjects resulted in a median of 90% comminution of the total stone volume into fragments ≤2 mm within 10 minutes of BWL exposure with only mild tissue injury.

Advanced Modular Manikin and Surgical Team Experience During a Trauma Simulation: Results of a Single-Blinded Randomized Trial.

BACKGROUND: Our aim was assess whether an integrated Advanced Modular Manikin (AMM) provides improved participant experience compared with use of peripheral simulators alone during a standardized trauma team scenario. Simulation-based team training has been shown to improve team performance. To address limitations of existing manikin simulators, the AMM platform was created that enables interconnectedness, interoperability, and integration of multiple simulators ("peripherals") into an adaptable, comprehensive training system. METHODS: A randomized single-blinded, crossover study with 2 conditions was used to assess learner experience differences when using the integrated AMM platform vs peripheral simulators. First responders, anesthesiologists, and surgeons rated their experience and workload with the conditions in a 3-scene standardized trauma scenario. Participant ratings were compared and focus groups conducted to obtain insight into participant experience. RESULTS: Fourteen teams (n = 42) participated. Team experience ratings were higher for the integrated AMM condition compared with peripherals (Cohen's d = .25, p = 0.016). Participant experience varied by background with surgeons and first responders rating their experience significantly higher compared with anesthesiologists (p < 0.001). Higher workload ratings were observed with the integrated AMM condition (Cohen's d = .35, p = 0.014) driven primarily by anesthesiologist ratings. Focus groups revealed that participants preferred the integrated AMM condition based on its increased realism, physiologic responsiveness, and feedback provided on their interventions. CONCLUSIONS: This first comprehensive evaluation suggests that integration with the AMM platform provides benefits over individual peripheral simulators and has the potential to expand simulation-based learning opportunities and enhance learner experience, especially for surgeons.

FMX - the Frontier Microfocusing Macromolecular Crystallography Beamline at the National Synchrotron Light Source II.

Two new macromolecular crystallography (MX) beamlines at the National Synchrotron Light Source II, FMX and AMX, opened for general user operation in February 2017 [Schneider et al. (2013). J. Phys. Conf. Ser. 425, 012003; Fuchs et al. (2014). J. Phys. Conf. Ser. 493, 012021; Fuchs et al. (2016). AIP Conf. Proc. SRI2015, 1741, 030006]. FMX, the micro-focusing Frontier MX beamline in sector 17-ID-2 at NSLS-II, covers a 5-30 keV photon energy range and delivers a flux of 4.0 × 1012 photons s-1 at 1 Šinto a 1 µm × 1.5 µm to 10 µm × 10 µm (V × H) variable focus, expected to reach 5 × 1012 photons s-1 at final storage-ring current. This flux density surpasses most MX beamlines by nearly two orders of magnitude. The high brightness and microbeam capability of FMX are focused on solving difficult crystallographic challenges. The beamline's flexible design supports a wide range of structure determination methods - serial crystallography on micrometre-sized crystals, raster optimization of diffraction from inhomogeneous crystals, high-resolution data collection from large-unit-cell crystals, room-temperature data collection for crystals that are difficult to freeze and for studying conformational dynamics, and fully automated data collection for sample-screening and ligand-binding studies. FMX's high dose rate reduces data collection times for applications like serial crystallography to minutes rather than hours. With associated sample lifetimes as short as a few milliseconds, new rapid sample-delivery methods have been implemented, such as an ultra-high-speed high-precision piezo scanner goniometer [Gao et al. (2018). J. Synchrotron Rad. 25, 1362-1370], new microcrystal-optimized micromesh well sample holders [Guo et al. (2018). IUCrJ, 5, 238-246] and highly viscous media injectors [Weierstall et al. (2014). Nat. Commun. 5, 3309]. The new beamline pushes the frontier of synchrotron crystallography and enables users to determine structures from difficult-to-crystallize targets like membrane proteins, using previously intractable crystals of a few micrometres in size, and to obtain quality structures from irregular larger crystals.

The Advanced Modular Manikin Open Source Platform for Healthcare Simulation.

INTRODUCTION: Current thinking in healthcare education stipulates a holistic approach with a focus on patient management, bringing together technical skills, decision-making, and team performance. In parallel, training opportunities with actual patients have diminished, and the number of different interventions to master has increased. Training on simulators has become broadly accepted; however, requirements for such training devices have outpaced the development of new simulators. The Department of Defense (DoD) targeted this gap with a development challenge. This article introduces the Advanced Modular Manikin (AMM) platform and describes the path followed to address the challenge. MATERIALS AND METHODS: Under Contract # W81XWH-14-C-0101, our interdisciplinary team of healthcare providers, educators, engineers, and scientists, together with partners in industry and the government collaborated to establish a set of comprehensive requirements and develop an overarching system architecture and specifications to meet healthcare simulation needs. In order to instantiate the architecture and investigate usability of the platform, a demonstration modular manikin was created that incorporated physical and digital peripherals. RESULTS: The system architecture and corresponding data models have been completed and published as open source. A developer's tool kit has been created, including instructional materials and required hardware and software for interested parties to develop AMM-compatible modules. A reference manikin was created based on the platform specifications and successfully supported a usability study that was performed by the American College of Surgeons, Education Division at the Naval Medical Center San Diego. CONCLUSIONS: The formal release of a functional modular, interoperable open-source healthcare simulation platform is complete. Next steps involve a strategy for maintaining the open standards and verification of AMM-compatibility for modules. Increasing awareness of this powerful tool and prioritization of module-development to address the wide range of healthcare education needs could lead to a renaissance in military and civilian healthcare simulation-based training.

Nephrolithiasis in Pregnancy: Treating for Two.

OBJECTIVES: To review the literature regarding the epidemiology of stone disease and develop a management algorithm based on current evidence and societal guidelines. METHODS: A structured literature review was performed to determine highest quality of evidence guiding care for pregnant patients with symptomatic nephrolithiasis. PUBMED and EMBASE databases were searched using terms "pregnancy," "nephrolithiasis," or "pregnancy" and "renal colic" alone and in combination with "stone", "kidney stone," "ultrasound," "MRI," "CT," "percutaneous nephrostomy," "ureteral stent," or "ureteroscopy." All English-language abstracts were reviewed for relevance and full-length articles were reviewed for content. Articles published prior to 1990 were excluded, and priority for inclusion was given to multi-institutional studies and larger institutional studies, reflecting the highest level of current available evidence and most contemporaneous practice patterns. RESULTS: Symptomatic nephrolithiasis affects less than 1% of pregnancies but poses unique diagnostic challenges due to the physiologic changes of pregnancy and risks of ionizing radiation exposure to the fetus. Ultrasound remains the imaging modality of choice. Most patients may be managed non-operatively, but drainage with percutaneous nephrostomy or ureteral stent may be performed if warranted. Growing evidence also supports the safety and efficacy of definitive stone treatment. CONCLUSIONS: Though rare, symptomatic nephrolithiasis poses significant clinical challenges due to the need to minimize risk for both mother and fetus with diagnostic and therapeutic interventions. A multi-disciplinary approach is paramount, as is shared decision making with the patient at each step of care.

Retained Digital Flexible Ureteroscope During Percutaneous Nephrolithotomy.

Background: During percutaneous nephrolithotomy, retrograde flexible ureteroscopy can be utilized to facilitate repositioning of stones, enable direct vision percutaneous access, minimize radiation exposure, reduce operating times, and improve stone-free rates. Although advancements in technique and flexible ureteroscope technology for the past decades have rendered complications rare, herein we report a case of a retained ureteroscope during percutaneous nephrolithotomy that was effectively managed endoscopically. Case Presentation: A 59-year-old Caucasian gentleman with a history of recurrent bilateral nephrolithiasis presents for a left-sided percutaneous nephrolithotomy for a large stone burden >4 cm. A ureteral access sheath was used and retrograde ureteroscopy was performed to first reposition several stones into the renal pelvis. During manipulation, we were unexpectedly unable to retract the ureteroscope from the access sheath. We describe procedural details leading up to the event and subsequent intraoperative management using an antegrade approach. Conclusion: A retained flexible ureteroscope is a rare but serious intraoperative complication that may require invasive open surgical management. However, careful endoscopic management may be feasible in select cases, allowing for preservation of ureter and instrument.

In-Office Ultrasound Facilitates Timely Clinical Care at a Multidisciplinary Kidney Stone Center.

INTRODUCTION: A considerable publication record exists comparing sensitivity and specificity of radiological ultrasound (including point of care ultrasound) to computerized tomography for stone disease. However, the practical application of in-office ultrasound to support the growing number of kidney stone centers around the world represents a nuanced topic that is ripe for study and discussion. METHODS: We provide a descriptive analysis of how in-office ultrasound is being used as an adjunct to clinical care based on our experience during 50 days in clinic at an institutionally affiliated, multidisciplinary kidney stone center. Clinic subjects gave consent and underwent ultrasound as part of research studies. Ultrasonograms were shared with and verified by the treating physician before the patient was discharged from care. We counted the number of times research imaging altered the care plan. RESULTS: Of the 60 patients enrolled the clinician used the information obtained from the studies in 20 (33%) to determine the course of clinical care that resulted in a change in treatment or process. CONCLUSIONS: Ultrasound has the potential to be a cost-effective and valuable tool that can provide more efficient workflow within a kidney stone center or urology clinic.

Inter-Resident Variability in Urologic Operative Case Volumes Over Time: A Review of the ACGME Case Logs From 2009 to 2016.

OBJECTIVES: To assess the effect of the changing landscape of urologic residency education and training on resident operative exposure and inter-resident variability. METHODS: The Accreditation Council for Graduate Medical Education (ACGME) case logs for graduating urology chief residents were reviewed from Academic Year (AY) 2009-2010 to 2016-2017. Cases were stratified into the 4 ACGME categories - general urology, endourology, oncology, and reconstruction. Linear regression models analyzed the association between training year, volume, and type of cases performed. Inter-resident variability in case exposure was calculated by the difference between the ACGME reported 10th and 90th percentiles. RESULTS: During the study period, the mean number of cases performed per resident was 1092 (standard deviation 32.7). Although there was no significant change in total case volume, there were changes within case categories. Endoscopic, retroperitoneal oncology, and male reconstruction case volume all increased significantly (Δ20.1%, Δ 5.1%, Δ 8.2%, respectively, all P < .05). This was balanced with a concomitant decrease in pelvic oncology and female reconstruction cases (Δ 10.0% and Δ 14.5%, respectively, both P < .05). There was a 27.8% increase in laparoscopic/robotic cases (P < .001). The ratio difference between the 10th percentile and 90th percentile ranged from a low of 2.5 for retroperitoneal oncology cases to a high of 5.2 for extracorporeal shock wave lithotripsy and percutaneous nephrolithotomy. CONCLUSION: From AY2009-2010 to 2016-2017, residency case volume has remained constant, but there has been a change in types of cases performed and proliferation of minimally invasive techniques. Significant variability of inter-resident operative experience was noted.

Monolithic 3D printing of embeddable and highly stretchable strain sensors using conductive ionogels.

Medical training simulations that utilize 3D-printed, patient-specific tissue models improve practitioner and patient understanding of individualized procedures and capacitate pre-operative, patient-specific rehearsals. The impact of these novel constructs in medical training and pre-procedure rehearsals has been limited, however, by the lack of effectively embedded sensors that detect the location, direction, and amplitude of strains applied by the practitioner on the simulated structures. The monolithic fabrication of strain sensors embedded into lifelike tissue models with customizable orientation and placement could address this limitation. The demonstration of 3D printing of an ionogel as a stretchable, piezoresistive strain sensor embedded in an elastomer is presented as a proof-of-concept of this integrated fabrication for the first time. The significant hysteresis and drift inherent to solid-phase piezoresistive composites and the dimensional instability of low-hysteresis piezoresistive liquids inspired the adoption of a 3D-printable piezoresistive ionogel composed of reduced graphene oxide and an ionic liquid. The shear-thinning rheology of the ionogel obviates the need to fabricate additional structures that define or contain the geometry of the sensing channel. Sensors are printed on and subsequently encapsulated in polydimethylsiloxane (PDMS), a thermoset elastomer commonly used for analog tissue models, to demonstrate seamless fabrication. Strain sensors demonstrate geometry- and strain-dependent gauge factors of 0.54-2.41, a high dynamic strain range of 350% that surpasses the failure strain of most dermal and viscus tissue, low hysteresis (<3.5% degree of hysteresis up to 300% strain) and baseline drift, a single-value response, and excellent fatigue stability (5000 stretching cycles). In addition, we fabricate sensors with stencil-printed silver/PDMS electrodes in place of wires to highlight the potential of seamless integration with printed electrodes. The compositional tunability of ionic liquid/graphene-based composites and the shear-thinning rheology of this class of conductive gels endows an expansive combination of customized sensor geometry and performance that can be tailored to patient-specific, high-fidelity, monolithically fabricated tissue models.

Conditions for reliable grip force and jaw angle estimation of da Vinci surgical tools.

PURPOSE: This work presents an estimation technique as well as corresponding conditions which are necessary to produce an accurate estimate of grip force and jaw angle on a da Vinci surgical tool using back-end sensors alone. METHODS: This work utilizes an artificial neural network as the regression estimator on a dataset acquired from custom hardware on the proximal and distal ends. Through a series of experiments, we test the effect of estimation accuracy due to change in operating frequency, using the opposite jaw, and using different tools. A case study is then presented comparing our estimation technique with direct measurements of material response curves on two synthetic tissue surrogates. RESULTS: We establish the following criteria as necessary to produce an accurate estimate: operate within training frequency bounds, use the same side jaw, and use the same tool. Under these criteria, an average root mean square error of 1.04 mN m in grip force and 0.17 degrees in jaw angle is achieved. Additionally, applying these criteria in the case study resulted in direct measurements which fell within the 95% confidence bands of our estimation technique. CONCLUSION: Our estimation technique, along with important training criteria, is presented herein to further improve the literature pertaining to grip force estimation. We propose the training criteria to begin establishing bounds on the applicability of estimation techniques used for grip force estimation for eventual translation into clinical practice.