Saline Bath Research Articles

Transprosthetic Fenestration With Electrified Wires. Experimental Evaluation of Three Multifilament Endografts.

In situ fenestration of aortic endografts is an alternative endovascular technique for treatment of complex aortic aneurysms. While this technique has been carried out also to pass stent-grafts in individual cases, its feasibility and safety using different stent-grafts needs to be evaluated. In a saline bath at water temperature of 37°C, a 0.018" Astato 30 guidewire was advanced through 3 different stent-grafts (RelayPro, Zenith and Endurant II) by applying external current of 180 W via an electrosurgery pencil. Puncture efficacy and quality of the fenestration after ballooning with a 6 mm percutaneous transluminal angioplasty (PTA) catheter were assessed. Then, balloon-expandable covered stents were deployed in the fenestrations and evaluated for stenosis, using microscopy and radiography. Crossing of the electrified guidewire was instantaneous in the Zenith (n:10) and RelayPro (n:10) groups but not in 3 of 10 punctures in the Endurant group (p<.05). The fenestration area created after PTA was significantly larger in the RelayPro (5.3 mm2 ± 1.8, interquartile range [IQR] 1.6) and Zenith group (6.7 mm2 ± 0.7, IQR 0.5) compared to Endurant (2.3 mm2 ± 0.4, IQR 0.5, p<.001). Fraying was observed in all groups while graft shredding was found in 8 cases after PTA of the Zenith and Endurant endografts and in 5 of the RelayPro group, but the difference was not significant. Vertical tearing was detected after RelayPro (2 out of 10) and Zenith (6 out of 10) fenestrations, no damage was found in the Endurant group (p<.01). Residual stenosis at the level of the fenestration after implantation of a 6 × 79 mm VBX stent had to be corrected in all Endurant cases with a high-pressure PTA catheter. No stenosis was found in the RelayPro and Zenith groups before and after flaring. The "electrified wire" technique is a feasible tool that can be used to perform in situ fenestration by perforation of the endograft fabric. Based on this experimental evaluation the "ideal graft" for this technique could not be identified. Long-term fatigue tests and comparison with other fenestration techniques are required. In situ endograft fenestration can be a useful technique in emergent aortic repair. Recently, the electrified wire technique has been proposed as alternative option to laser, radiofrequency and needle-based techniques. In comparison to these methods, the use of electrified wires can be performed without modifications of routine equipment. Additionally, the material costs can be substantially reduced. However, the effectiveness of this approach for fenestration of different prosthetic grafts is unknown. Based on our experimental studies, the electrified wire technique is feasible but the Endurant endograft requires more attempts, and the placement of a bridging stent should be completed with high-pressure balloons.

Evaluation of pulsed field ablation lesion characteristics using an in vitro vegetable model.

In vitro models to evaluate cardiac pulsed field ablation (PFA) have not been well established. We sought to create a standardized vegetable model and staining protocol for assessing unipolar PFA using a surface electrode. We exposed potato slabs to unipolar PFA in a saline bath using a 3.5mm electrode catheter and grounding pad connected to a custom-built high-voltage generator. Lesions were clearly visualized after staining with 2,3,5-triphenyltetrazolium chloride (TTC) using a timed protocol to reveal a necrotic center and a periphery of electroporated cells with intact mitochondria. Lesion volume increased linearly with increasing voltage and logarithmically with repetitive PFA applications. The findings observed in this vegetable model using a TTC staining protocol are consistent with findings observed with cardiomyocytes.

A Dynamic, Self-Tensioning Suture Contracts in Saline to Counteract Changes in Loop Length From Cyclic Loading

To compare the biomechanical performance of a suture with proposed dynamic self-tensioning properties with that of commonly used high-tensile sutures by evaluating suture loop length changes, responses to cyclic loading, and failure testing with intermittent saline soaks. Six knots each of 4 different sutures were studied: 3 high-tensile sutures (ORTHOCORD, FiberWire, and ETHIBOND), and a dynamically self-tensioning suture (DYNACORD). After we measured loop length, knots were soaked in 37°C saline for 24 hours. Loop lengths were remeasured and tensile testing was performed. Cyclic elongation, first-cycle excursion, and elongation amplitude were recorded. Knots were then resoaked and retested. Finally, knots were pulled to failure, and peak load and stiffness were measured. Values were compared using nonparametric statistical tests. DYNACORD loop length decreased by 27% after the first soak (P= .002), whereas the other sutures demonstrated no length change (P > .05). Although DYNACORD loop length increased during cyclic load testing (P= .009), it was still significantly reduced after the second saline soak compared withits initial length (P= .002), whereas all other suture loops had elongated. ETHIBOND (P= .004) and ORTHOCORD (P= .002) had significantly less cyclic elongation from cycle I to cycle II testing compared with the other sutures. ETHIBOND had the lowest peak load at failure (P= .002). FiberWire had the greatest stiffness (P= .006). Compared with other suture types, the self-tensioning suture showed dynamic properties, demonstrating a decrease in loop length when soaked in a saline bath. This length was maintained after a second soak despite increased loop length during interval cyclic loading. Knot and loop security are of paramount importance to arthroscopic soft-tissue procedures. The ability for a suture to self-tension has implications for how it may interact with tissues invivo to increase construct stability after arthroscopic soft tissue repair procedures.

Development of a Low-cost Epimysial Electromyography Electrode: A Simplified Workflow for Fabrication and Testing.

Electromyography (EMG) is a valuable diagnostic tool for detecting neuromuscular abnormalities. Implantable epimysial electrodes are commonly used to measure EMG signals in preclinical models. Although classical resources exist describing the principles of epimysial electrode fabrication, there is a sparsity of illustrative information translating electrode theory to practice. To remedy this, we provide an updated, easy-to-follow guide on fabricating and testing a low-cost epimysial electrode. Electrodes were made by folding and inserting two platinum-iridium foils into a precut silicone base to form the contact surfaces. Next, coated stainless steel wires were welded to each contact surface to form the electrode leads. Lastly, a silicone mixture was used to seal the electrode. Ex vivo testing was conducted to compare our custom-fabricated electrode to an industry standard electrode in a saline bath, where high levels of signal agreement (sine [intraclass correlation - ICC= 0.993], square [ICC = 0.995], triangle [ICC = 0.958]), and temporal-synchrony (sine [r = 0.987], square [r = 0.990], triangle [r= 0.931]) were found across all waveforms. Low levels of electrode impedance were also quantified via electrochemical impedance spectroscopy. An in vivo performance assessment was also conducted where the vastus lateralis muscle of a rat was surgically instrumented with the custom-fabricated electrode and signaling was acquired during uphill and downhill walking. As expected, peak EMG activity was significantly lower during downhill walking (0.008 ± 0.005 mV) than uphill (0.031 ± 0.180 mV, p = 0.005), supporting the validity of the device. The reliability and biocompatibility of the device were also supported by consistent signaling during level walking at 14 days and 56 days post implantation (0.01 ± 0.007 mV, 0.012 ± 0.007 mV respectively; p > 0.05) and the absence of histological inflammation. Collectively, we provide an updated workflow for the fabrication and testing of low-cost epimysial electrodes.

Overloading effect on the osmo-viscoelastic and recovery behavior of the intervertebral disc.

In vitro studies investigating the effect of high physiological compressive loads on the intervertebral disc mechanics as well as on its recovery are rare. Moreover, the osmolarity effect on the disc viscoelastic behavior following an overloading is far from being studied. This study aims to determine whether a compressive loading-unloading cycle exceeding physiological limits could be detrimental to the cervical disc, and to examine the chemo-mechanical dependence of this overloading effect. Cervical functional spine units were subjected to a compressive loading-unloading cycle at a high physiological level (displacement of 2.5 mm). The overloading effect on the disc viscoelastic behavior was evaluated through two relaxation tests conducted before and after cyclic loading. Afterward, the disc was unloaded in a saline bath during a rest period, and its recovery response was assessed by a third relaxation test. The chemo-mechanical coupling in the disc response was further examined by repeating this protocol with three different saline concentrations in the external fluid bath. It was found that overloading significantly alters the disc viscoelastic response, with changes statistically dependent on osmolarity conditions. The applied hyper-physiological compressive cycle does not cause damage since the disc recovers its original viscoelastic behavior following a rest period. Osmotic loading only influences the loading-unloading response; specifically, increasing fluid osmolarity leads to a decrease in disc relaxation after the applied cycle. However, the disc recovery is not impacted by the osmolarity of the external fluid.

Safety Criteria in Ecotourism Activities: The Case of a Marine Salt Pan During the Covid-19 Pandemic

This study used the analytic hierarchy process (AHP) to examine the application of the main safety rules in ecotourism activities in a marine salt pan during the COVID-19 pandemic. The results suggest that, among the activities analyzed, the best way perceived to maintain social distance was the guided tour activity, while hand hygiene was seen as the most important in the saline bath and in the combined activity. Mask was generally removed in activities involving immersion in water by tourists. These measures were crucial to ensure a sense of security and well-being both for tourists and employees of the tourism and hospitality industry.

Time-Resolved Mid-Infrared Photothermal Microscopy for Imaging Water-Embedded Axon Bundles.

Few experimental tools exist for performing label-free imaging of biological samples in a water-rich environment due to the high infrared absorption of water, overlapping with major protein and lipid bands. A novel imaging modality based on time-resolved mid-infrared photothermal microscopy is introduced and applied to imaging axon bundles in a saline bath environment. Photothermally induced spatial gradients at the axon bundle membrane interfaces with saline and surrounding biological tissue are observed and temporally characterized by a high-speed boxcar detection system. Localized time profiles with an enhanced signal-to-noise, hyper-temporal image stacks, and two-dimensional mapping of the time decay profiles are acquired without the need for complex post image processing. Axon bundles are found to have a larger distribution of time decay profiles compared to the water background, allowing background differentiation based on these transient dynamics. The quantitative analysis of the signal evolution over time allows characterizing the level of thermal confinement at different regions. When axon bundles are surrounded by complex heterogeneous tissue, which contains smaller features, a stronger thermal confinement is observed compared to a water environment, thus shedding light on the heat transfer dynamics across aqueous biological interfaces.

AB-452674-4 SHORT AND SWEET: EXPLORING HIGH POWER, SHORT DURATION RADIOFREQUENCY ABLATION STRATEGIES FOR OPTIMAL LESION FORMATION

High power, short duration (HPSD) radiofrequency (RF) ablation allows for wider, more uniform ablation lesion formation as compared to moderate power, moderate duration ablation. Ablation with HPSD capitalizes on the resistive heating phase providing immediate heating to the target tissue while preventing the consequences of conductive heating. Understanding the threshold where resistive heating transitions to conductive heating may allow for optimization of parameters to favor resistive heating. Additionally, HPSD lesion application has been associated with a lower risk of complications, including cardiac perforation and atrioesophageal fistulas. To assess lesion formation with variations in RF duration and contact force utilizing a HPSD strategy in an ex vivo model. This study utilized recently harvested swine heart tissue ablated using a contact force sensing irrigation ablation catheter submerged in a saline bath with a target temperature of 36 °C and an impedance of 140 Ω. Step 1 compared various RF durations (1-5, 8, and 10 seconds(s)) with 50 Watts (W) and an average of 10g of force applied to the epicardial surface of the left ventricle. Six lesions were applied for each time duration. For step two of the procedure, we assessed the impact of contact force (1g, 5g, 10g, 20g) on lesion size and depth using 50 W and 5s RF duration. Five lesions were applied for each amount of contact force. The tissue was stained in a 2,3,5-Triphenyltetrazolium chloride bath prior to measurements. Of the 42 lesions created utilizing HPSD with variable durations of RF duration, application of >3s resulted in the creation of visual lesions within the tissue. There was an increase in lesion volume with longer duration ablation application (50W/10g), with 5, 8 and 10s durations generating lesion volumes of 16.8mm3, 26.8mm3 and 40.6mm3, respectively. All 20 lesion applications with varying degrees of contact force (50W/5s) resulted in visual lesions. There was an increase in lesion volume with higher contact force plateauing at 10 g, compared to 20g (28.9mm3 vs 31.9mm3, respectively). In an animal model, a HPSD ablation strategy focused on short duration lesion application with lower contact forces (50W/5s/10g) created lesions of similar volume to 20g of force application. In the initial 10s of lesion formation, a force >10g may have a lesser role and may potentially represent a transition point between resistive and conductive heating.

PO-03-042 A COOL DRINK OF WATER: CONVECTIVE ESOPHAGEAL COOLING PREVENTS THERMAL INJURY FROM RADIOFREQUENCY HEATING IN AN EX VIVO SWINE ESOPHAGUS MODEL

Esophageal heating and subsequent thermal injury are concerning adverse effects of radiofrequency (RF) energy ablation on the posterior wall of the left atrium. Active intraluminal esophageal cooling may provide thermal protection, allowing for effective delivery of RF energy to overlying myocardium without collateral damage to the underlying esophagus. To evaluate the impact of esophageal luminal cooling with a closed loop continuous flow irrigation on esophageal heating and thermal injury using an ex vivo model. A flexible tube was placed through the lumen of a swine esophagus and connected to a closed loop circuit consisting of a pump and water bath (Figure 1, panel A). The esophagus was submerged in a saline bath with a temperature of 36 °C and an impedance of 140 ohms. Ten non-contiguous RF lesions were delivered at 50 watts for 8 seconds directly on the outer esophageal wall with 4 mm irrigated RF ablation catheter. This was performed without irrigation (control), irrigation at 1.5 L/min with room temperature water (20 °C), and irrigation at 1.5 L/min with ice water (0 °C). Esophageal tissue samples were obtained from immunohistochemistry and the esophagus was cross sectioned and lesions were measured with digital calipers. Closed loop continuous flow esophageal irrigation with ice water yielded esophageal lesions with the smallest surface area (Figure 1, panel A), depth, and volume (Figure 1, panel B). Continuous esophageal irrigation with room temperature water resulted in the second smallest lesions. RF lesions without esophageal irrigation resulted in the largest and deepest lesion, as well as evidence of luminal esophageal injury (Figure 1, panel C & D). Histology showed preserved smooth muscle, glands, basement membrane and epithelium with cooled esophagus and transmural lesions with non-irrigated esophagus (Figure 1, panel C & D). Continuous endoluminal esophageal cooling reduced lesion size with RF energy delivery. There was no luminal injury with room temperature and ice water esophageal irrigation. Thus, both may be useful in prevention of endoluminal esophageal injury during poster wall RF ablation.

AB-452672-3 PRE-CLINICAL PULSED-FIELD ABLATION (PFA) USING A SINGLE-SHOT CIRCULAR LINEAR ABLATION CATHETER FOR PV ISOLATION

Pulsed field ablation (PFA) is becoming the preferred energy treatment for pulmonary vein (PV) isolation. PFA application appears safe and effective and shortens procedure time. A circular linear ablation catheter may have advantages for single-shot delivery of PFA for PV isolation. To evaluate the feasibility of pusled field ablation for PV isolation with a circular linear ablation catheter. The Fiore™ catheter (EP Frontiers S.p.A., Italy; Figure) has two unique features: (1) an over the wire anchor and (2) an ablation element with linear electrodes. The anchor is positioned in the PV and guides the Circular Linear Ablation (CLA). The CLA can deliver PFA from a customized generator. Optimization of PFA parameters was conducted with a potato model in a saline bath by testing various energy pulses with bipolar and biphasic energy (500-1000 volts, pulse duration of 10-100 μs, interpulse pause of 10-400 μs, with a changing number of repetitions). The goal was to create circular ablations with a minimal depth of 3-4 mm. Following energy application images were acquired acutely and 18-24 hours after. Porcine in vivo testing (n=5 swine under general anaesthesia) with a deflectable sheath, evaluated PFA application at the left and right superior pulmonary vein, superior vena cava, and lateral wall of the right atrium with histopathology. In vitro ablations with three separate pulse trains demonstrated circular lesions with a diameter of up to 40 mm that were visible hours after the energy delivery. Average cross section of the circular lesions revealed an average depth of 3.2 mm with a surface width of 36 mm (Figure). Four applications (vs eight), from linear electrodes resulted in the most optimal and controlled circular lesions with central sparing and no off-target tissue destruction. Under fluoroscopic guidance, all positions in left and right atria, were easily accessed in all 5 animals (Figure). During PFA delivery, minimal skeletal muscle contraction was observed, without thermal ablation effect. Histopathology examination revealed acute changes in the atrial muscle structure. Chronic animal testing is ongoing to provide optimization of pulse trains and electrode to electrode sequencing to allow precise measurements of the PFA lesions depth. Following lesion optimization in an in vitro model, we demonstrate feasibility of delivering reproducible single-shot circumferential PFA lesions using a unique designed circular linear ablation catheter.

PO-04-072 THERMOCHROMIC HEART PHANTOM TO MODEL RADIOFREQUENCY ABLATION

We have previously developed a conductive hydrogel for use as an intermediate between heart tissue and catheter tips in cardiac ablation, providing a more uniform and precisely shaped lesion with the goal of minimizing the occurrence of steam pops and repeat procedures in arrythmia patients. Characterization of the gel has involved the repeated use of porcine hearts for an approximation of ablation behavior in human models. As this gel will require testing and iterative development to characterize its performance in ablation, a more conservative, safe, and affordable model of the heart is paramount. The heart phantom is to mimic the visible formation of lesions in ventricular myocardial tissue upon contact with a catheter that imparts radiofrequency (RF) energy. To predict lesion formation as mediated with the hydrogel, we seek to produce a heart model with similar thermally conductive properties as myocardial tissue. Various gel materials were prepared and evaluated for similarity to physiological myocardium, visual appeal, and ease of use for multiple trials, among other factors. Each gel was mixed with a thermochromic pigment (transition temperature of 60 C) and placed in a water bath of normal saline at 37 C for at least ten minutes for temperature equilibration. Preliminary tests were conducted with bare catheters alone instead of with hydrogel. An RF generator was set to 30 then 50 Watts, then Thermocool SF non-irrigated catheters were lightly applied to the gel surface in the saline bath for thirty seconds (Fig 1C). Lesions (white) are formed as shown in the figure for tests with silicone and black pigment, the most successful material combination thus far (Fig 1A and 1B). Compared to lesions formed in prior ex vivo experiments with ventricular myocardial tissue, the width and depth of the lesions formed in the gel model varied up to 22% and 76% from the ex vivo values, respectively. A thermochromic phantom heart for lesion characterization is feasible. Further development of this model seeks to better mimic myocardial tissue by selecting or synthesizing a material that matches the heart's experimental thermal conductivity and designing the phantom to contain similar anatomical compartments as in the left ventricular region. Once the phantom material displays lesions approximately equal in size to those formed in heart tissue, it may be used as a substitute for further characterization of the conductive hydrogel.

PO-01-004 DEVELOPMENT OF A THERMOCHROMIC BENCHTOP MODEL FOR A RAPID, EFFICIENT, AND COST-EFFECTIVE OPTIMIZATION OF PULSED FIELD ABLATION THERAPIES

Pulsed Field Ablation (PFA) is a non-thermal alternative to RF providing a tissue preferential therapy with no thermal necrosis. PFA applies high voltage, short electrical pulses to create irreversible cell membrane pores causing cell death. Since energy application intrinsically leads to Joule heating, parameters optimization is vital to obtain a therapy that limits temperature below 50°C, the cardiac thermal damage threshold. This constraint creates a complex multi-variable problem, requiring multiple in vivo studies to mitigate the likelihood of thermal damage, which can be inefficient and costly. Bench methods using ex vivo tissue or gels with thermal probes are inadequate as they rely on orientation and proximity to hotspots. The aim of this research was to develop a thermochromic phantom gel model that changes color when temperature exceeds the critical thermal damage threshold, enabling better visualization of thermal profile for PFA systems. The development of this gel model included a combination of saline with polyacrylic acid and a reversible thermochromic pigment that changes color ≥45°C. The gel allows any catheter to be coated. The coated Abbott VoltTM PFA catheter was placed in a 32°C heated saline bath (to obtain ΔT of 13°C, analogous to that observed between 37°C and 50°C) and PFA was applied using VoltTM PFA Generator. During ablation, real-time gel color change is noted (Purple<Threshold≤Light blue). Using this model, we compared an optimized PFA waveform to a Positive Control waveform known to cause thermal damage in vivo (N=1 section from 1 animal). Three gel batches were used to understand batch variability (N=15 at each batch). The positive control showed color change in 84% of trials. During ablation, light blue spots appeared on electrodes that enlarged with continued ablation, highlighting heat stacking for the Positive Control waveform. No color change was observed for the optimized waveform (N=45). The non-thermal nature of the lesion created by the optimized VoltTM PFA waveform was also confirmed in in vivo studies via histopathology (N=6 sections from 2 animals). This study demonstrated that the gel model can capture thermal damage risk with a Positive Control (84%). The optimized VoltTM PFA system waveform via the gel model is thermally safe, as confirmed via histopathology. This bench model offers an efficient and cost-effective method for optimizing PFA waveforms.

Ambient circulation surrounding an ablation catheter tip affects ablation lesion characteristics.

The association between ambient circulating environments (CEs) and ablation lesions has been largely underexplored. Viable bovine myocardium was placed in a saline bath in an ex vivo endocardial model. Radiofrequency (RF) ablation was performed using three different ablation catheters: 3.5 mm open irrigated (OI), 4, and 8 mm. Variable flow rates of surrounding bath fluids were applied to simulate standard flow, high flow, and no flow. For in vivo epicardial ablation, 24 rats underwent a single OI ablation and performed with circulating saline (30 ml/min; n = 12), versus those immersed in saline without circulation (n = 12). High flow reduced ablation lesion volumes for all three catheters. In no-flow endocardial CE, both 4 mm and OI catheters produced smaller lesions compared with standard flow. However, the 8 mm catheter produced the largest lesions in a no-flow CE. Ablation performed in an in vivo model with CE resulted in smaller lesions compared with ablation performed in a no-flow environment. No statistically significant differences in steam pops were found among the groups. A higher endocardial CE flow can decrease RF effectiveness. Cardiac tissue subjected to no endocardial CE flow may also limit RF for 4 mm catheters, but not for OI catheters; these findings may have implications for RF ablation safety and efficacy, especially in the epicardial space without circulating fluid or in the endocardium under varying flow conditions.

Poster 199: The Hip Suction Seal Restoration Using the Circumferential Labral Reconstruction. The Role of The Graft Width

Objectives: Background:Favorable patient-reported outcomes has been reported following circumferential labral reconstruction (CLR);however, there is a paucity on biomechanical data following CLR.Purpose:To evaluate the role of the CLR using iliotibial band (ITB) allograft on the restoration of the distractive stability force (suction seal), and to evaluate whether any correlation existed between ITB allograft width and the distractive stability restoration after CLR.Hypothesis:1) CLR using a wider ITB allograft would restore the distractive stability force to a level comparable to the intact labrum. 2) Wider CLR would achieve significantly superior distractive stability force when compared to CLR using smaller width allograft.Methods:14 fresh-frozen cadaveric hips consisting of hemipelvis and proximal femur with intact labra and without osteoarthritis (Tönnis > 1) were dissected free of all soft tissue including the hip capsule. Each hip underwent two CLR using ITB allograft, width > 6.5mm (7.5-8.0mm) and width <6.5mm (4.5-5.0mm), the order of the reconstruction was assigned in a randomized fashion. Each hemipelvis was potted, placed in the saline bath, and securely fixed to the frame of a hydraulic testing system with the hip being placed in 30° of abduction. A 500N·m compressive load was applied to the acetabulum followed by a distraction at the rate of 5.0mm/s. Force and displacement were recorded throughout the distraction until the suction seal ruptured. Measures were performed in each hip for intact labrum, deficient (excised) labrum, first CLR, and second CLR.Results:The distraction force was comparable between the intact state and the CLR >6.5mm (P = 0.587). Further, the distraction force was comparable between the deficient state and the CLR <6.5mm (P = 0.418). When comparing the CLR <6.5mm and CLR >6.5mm, the distraction force was significantly higher for the latest (P = 0.01). Also, the CLR >6.5mm outperformed the deficient state (P = 0.001). Similarly, the distance to suction seal rupture was comparable between the intact state and the CLR >6.5 mm (P = 0.587), comparable for the deficient state and the CLR < 6.5mm (P = 0.418), significant longer for the CLR >6.5mm when compared to the CLR < 6.5mm and the deficient state (P = 0.01 and P = 0.001, respectively).[MOU1].Conclusions:The allograft width following CLR was found to be correlated with the hip suction seal restoration in a cadaveric model. CLR using an ITB allograft > 6.5mm was found to restore the distractive stability force to values comparable to the native intact labral state. Further, when compared to the CLR using ITB allograft with a width < 6.5mm, the CRL >6.5 mm outperformed by demonstrating significantly superior distractive stability force restoration.Clinical Relevance:The allograft width for CRL was correlated with the hip suction seal effect restoration in a cadaveric model. Although further studies would be required to identify the clinical effects of the CLR allograft width, it seems appropriate to selecting allograft > 6.5mm in the clinical setting.Figure 1.The images corresponded to a right hip following a circumferential labral reconstruction. The tank was clamped to the hydraulic mechanical testing system (MTS). A. The acetabular pot has been secured to the tank and the femoral pot was fastened to the MTS actuator. B. The tank was filled with phosphate-buffered saline solution heated to 37°CFigure 2.This images corresponded to the same right hip. The most antcromedial aspect (AM) and posterolateral (PL) aspect of the acetabulum (A), and the most antcromedial (*) and posterolateral (▲) points of the transverse acetabular ligament have been marked. A. The native labium has been excised, and the anchor drill holes (black arrows) have been made. B. The circumferential labral reconstruction has been performed using an iliotibial band allograft (G). Eleven 2.4mm CinchLock SS PEEK knotlcss anchor with No. 1 ultra-high molecular weight polyethylene suture (Pivot Stryker) were used in this specimen. Femoral head (FH), ligamentous teres (LT)Figure 3.This images corresponded to the same right hip. The most anteromedial aspect (AM) and posterolateral (PL) aspect of the acetabulum (A), and the most anteromedial (*) and posterolateral (▲) points of the transverse acetabular ligament have been marked. A. A circumferential labral reconstruction (CLR) with an iliotibial allograft (G) 36.5mm has been performed. B. A CLR with G <6.5mm its shown. Femoral head (FH), ligamentous teres (LT).Figure 4.

An Increased Allograft Width for Circumferential Labral Reconstruction Better Restores Distractive Stability of the Hip: A Cadaveric Biomechanical Analysis

Background: Questions remain about whether circumferential labral reconstruction (CLR) using an iliotibial band (ITB) allograft can effectively restore the labral suction seal of the hip. Hypotheses: (1) CLR with an ITB allograft >6.5 mm would restore distractive stability force to that of the intact labrum. (2) CLR with an ITB allograft >6.5 mm would achieve significantly superior distractive stability force compared with CLR with an ITB allograft <6.5 mm. Study Design: Controlled laboratory study. Methods: A total of 6 fresh-frozen pelves with attached femurs (n = 12 matched hemipelves) from male donors were procured and dissected free of all soft tissue, including the hip capsule but preserving the native labrum, transverse acetabular ligament, and ligamentum teres. Potted hemipelves were placed in a saline bath and securely fixed to the frame of a hydraulic testing system. A 500-N compressive load was applied, followed by femoral distraction at a rate of 5.0 mm/s until the suction seal ruptured. Force and femoral displacement were continually recorded. Force versus displacement curves were plotted, the maximum force was recorded, and the amount of femoral distraction to rupture the suction seal was determined. After intact testing, the labrum was excised, and specimens were retested using the same protocol. CLR was subsequently performed twice in a randomized fashion using (1) an ITB allograft with a width >6.5 mm (7.5-9.0 mm) and (2) an ITB allograft with a width <6.5 mm (4.5-6.0 mm). Specimens were retested after each CLR procedure. Force (in Newtons) and femoral distraction (in millimeters) required to rupture the suction seal were measured and compared between the 4 testing states (intact, deficient, CLR <6.5 mm, and CLR >6.5 mm) using repeated-measures analysis of variance. Results: On average, intact specimens required 148.4 ± 33.1 N of force to rupture the hip suction seal, which significantly decreased to 44.3 N in the deficient state (P < .001). CLR with ITB allografts <6.5 mm did not improve the maximum force (63 ± 62 N) from the deficient state (P = .42) and remained significantly lower than the intact state (P < .01). CLR with ITB allografts >6.5 mm recorded significantly greater force to rupture the suction seal (135.8 ± 44.6 N) compared with both the deficient and CLR <6.5 mm states (P < .01), with a mean force comparable with the intact labrum (P = .59). The amount of femoral distraction to rupture the suction seal demonstrated similar findings. Conclusion: In a cadaveric model, CLR using ITB allografts >6.5 mm restored the distractive force and distance to the suction seal rupture to values comparable with hips with an intact labrum. CLR using ITB allografts >6.5 mm outperformed CLR with ITB allografts <6.5 mm, demonstrated by a significantly higher force to rupture the suction seal and increased distraction before the rupture. Clinical Relevance: The results of this cadaveric investigation suggest that using wider labral allografts during CLR will provide the distractive force required to rupture the suction seal and immediate postoperative stability of the hip, although further studies are required to determine if these results translate to improved clinical outcomes.

A Friction Testing-Bioreactor Device for Study of Synovial Joint Biomechanics, Mechanobiology, and Physical Regulation.

In primary osteoarthritis (OA), normal 'wear and tear' associated with aging inhibits the ability of cartilage to sustain its load-bearing and lubrication functions, fostering a deleterious physical environment. The frictional interactions of articular cartilage and synovium may influence joint homeostasis through tissue level wear and cellular mechanotransduction. To study these mechanical and mechanobiological processes, a device capable of replicating the motion of the joint is described. The friction testing device controls the delivery of reciprocal translating motion and normal load to two contacting biological counterfaces. This study adopts a synovium-on-cartilage configuration, and friction coefficient measurements are presented for tests performed in a phosphate-buffered saline (PBS) or synovial fluid (SF) bath. The testing was performed for a range of contact stresses, highlighting the lubricating properties of SF under high loads. This friction testing device can be used as a biomimetic bioreactor for studying the physical regulation of living joint tissues in response to applied physiologic loading associated with diarthrodial joint articulation.

Biomechanics of human trabecular meshwork in healthy and glaucoma eyes via dynamic Schlemm's canal pressurization

Background and objectiveThe trabecular meshwork (TM) consists of extracellular matrix (ECM) with embedded collagen and elastin fibers providing its mechanical support. TM stiffness is considerably higher in glaucoma eyes. Emerging data indicates that the TM moves dynamically with transient intraocular pressure (IOP) fluctuations, implying the viscoelastic mechanical behavior of the TM. However, little is known about TM viscoelastic behavior. We calculated the viscoelastic mechanical properties of the TM in n = 2 healthy and n = 2 glaucoma eyes. MethodsA quadrant of the anterior segment was submerged in a saline bath, and a cannula connected to an adjustable saline reservoir was inserted into Schlemm's canal (SC). A spectral domain-OCT (SD-OCT) provided continuous cross-sectional B-scans of the TM/JCT/SC complex during pressure oscillation from 0 to 30 mmHg at two locations. The TM/JCT/SC complex boundaries were delineated to construct a 20-µm-thick volume finite element (FE) mesh. Pre-tensioned collagen and elastin fibrils were embedded in the model using a mesh-free penalty-based cable-in-solid algorithm. SC pressure was represented by a position- and time-dependent pressure boundary; floating boundary conditions were applied to the other cut edges of the model. An FE-optimization algorithm was used to adjust the ECM/fiber mechanical properties such that the TM/JCT/SC model and SD-OCT imaging data best matched over time. ResultsSignificantly larger short- and long-time ECM shear moduli (p = 0.0032), and collagen (1.82x) and elastin (2.72x) fibril elastic moduli (p = 0.0001), were found in the TM of glaucoma eyes compared to healthy controls. ConclusionsThese findings provide additional clarity on the mechanical property differences in healthy and glaucomatous outflow pathway under dynamic loading. Understanding the viscoelastic properties of the TM may serve as a new biomarker in early diagnosis of glaucoma.

Pacing electrodes to ablate, not to pace: what settings to use to create lesions even deep in the septum

Abstract Funding Acknowledgements Type of funding sources: None. Background Intramural septal ventricular arrhythmia remains challenging, requiring emergent technologies and experimental approaches. Although conduction system pacing (CSP) has allowed us to reach deep in the septum, ablation though pacing electrodes has not been examined yet. Purpose To evaluate lesion creation by radiofrequency ablation (RFA) through pacing electrodes. Methods A custom ex vivo swine model in a saline bath with an indifferent electrode was used to apply RFA with an 8 mm non-irrigated catheter (SJM, MN, USA) on the proximal end of pacing (CapSureFix 5086) or CSP-electrodes (SelectSecure 3830, Medtronic, MN, USA), screwed in perpendicularly to the slab. A generator (Ampere, SJM, MN, USA) applied RFA at varying settings (1-10 W, 1-20 sec). Lesion depth (D), width (W) and volume (V=3,14*W2*D/4) were assessed and analyzed (SPSS 23). Results A total of 80 lesions were used for analysis. Median RFA with 3 W over 6 sec resulted in an impedance drop from 200 to 140 Ω and a lesion of 2x3 mm or 9.4 mm3 (Figure 1). Higher energy settings caused impedance rise with abort (n=3, 4%) or charring (n=3, 4%). Compared to conventional electrodes, lesions with CSP-electrodes had similar volume (9.3±7 vs. 10.8±9 mm3, p=0.45) and width (2±0.8 vs. 2±0.7, p=0.58), but more depth (2.6±0.5 vs. 3±0.6, p=0.0.01). Regression analysis showed final-impedance (FI), power and duration (WS=W*Sec) as independent predictors of lesion volume (V=4.7WS-4.1WS2+4.5FI-4, p&amp;lt;0.001). Conclusions Effective ablation through pacing electrodes is possible, but lesion size is limited and low-power settings are necessary. Using CSP-electrodes for effective intramural lesions is possibly a new tool for septal arrhythmias. Further in vivo studies are warranted and bailout use should be considered.

High power bipolar ablation of a thick myocardium: ex-vivo study using externally-irrigated large-tip ablation catheters

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Bipolar radiofrequency catheter ablation (Bi-RFCA) can overcome some challenges related with treatment of intramural ventricular arrhythmias. However, there’s no data if Bi-RFCA can be effective in the setting of a thick myocardium. Aim To estimate safety and efficacy of high-power long-duration Bi-RFCA in the setting of a thick myocardium and to demonstrate feasibility of external irrigation for large-tip ablation catheters (AC). Methods The study was performed in a saline bath containing a fresh bovine heart. Bi-RFCA of the left ventricular (LV) and right free wall, interventricular septum, papillary muscle and LV summit at power settings of 70W was performed using two solid-tip 8mm AC in a parallel orientation. Irrigation using normal saline of each AC was provided from a long sheath advanced to the level of 2nd (distal irrigation – DI) or 3rd (proximal irrigation – PI) AC electrode. Post-Bi-RFCA lesions were evaluated macroscopically. Results Mean intercatheter distance was 28±11 mm, range 12-50 mm and a total number of 12 high-power Bi-RFCA lesions were performed. Mean Bi-RFCA time was 108±42s. Complete transmurality was achieved in 4 (33%) of lesions (mean 17±3 mm thickness, range 12-20 mm) whereas borderline transmurality was observed in further 2 (17%) lesions (mean 23±0,5 mm thickness, range 22-23 mm). No transmurality was present in the remaining 6 (50%) lesions (mean 38±7 mm thickness, range 30-50 mm). Steam pops occurred in 25% of Bi-RFCA applications. Temperature drop during external irrigation was significantly higher in the DG group vs PG 15°C vs 7°C, p=0,0046). Conclusions Bi-RFCA of a myocardial thickness above &amp;gt;30mm is challenging. High-power (70W) long-duration Bi-RFCA is associated with substantial incidence of steam pops. Further histopathological studies should evaluate levels of transmurality using high power Bi-RFCA at muscle thickness between 20-30mm. External irrigation of solid-tip large AC is feasible and can significantly reduce AC tip temperature.

Poisson's ratio and compressibility of arterial wall – Improved experimental data reject auxetic behaviour

Poisson's ratio of fibrous soft tissue is analyzed in this paper on the basis of direct experimental measurements of porcine arterial wall layer under uniaxial tension and immersed in tempered saline bath. The current study follows the previously published testing methodology but with a new totally redesigned testing apparatus allowing more credible and precise evaluation of arterial wall behaviour. The new results confirm most of previous findings focused on positivity/negativity of Poisson's ratio playing a crucial role in (in)validation aspects of some constitutive models widely used in recent computational vascular mechanics. The effect of frozen & thawed conditions is also evaluated in comparison with fresh specimens. The in-plane Poisson's ratio of arterial wall was identified in the range of 0.3–0.4, whereas its out-of-plane component is much higher ranging from 0.5 to 0.7. These results contrast with predictions of some frequently used constitutive models. The volumetric (in)compressibility of arterial specimens is also analyzed, quantified and discussed in the paper, as a key property of soft tissues closely related to the topic of their constitutive modelling.