In silico analysis of rib force distribution in postscapulothoracic arthrodesis model.

Scapulothoracic arthrodesis (STA) is carried out by fixing the scapula to thoracic ribs which in turn allows the patient suffering from Facioscapulohumeral Muscular Dystrophy to carry out shoulder-joint dependent activities of daily living. A biomechanical analysis of this procedure has not been conducted in the literature and, for the first time, this study investigates the finite element calculated glenohumeral-applied load distributions on ribs by creating a post-STA model. Three loading directions on the glenohumeral joint are designated: anterior-posterior, superior-inferior, and lateral-medial. Reaction forces on the ribs are calculated based on the glenoid force percent. Simulations are repeated by removing a singular rib contact to observe the change in force distributions in the case of missing levels or failed bonding as well as the impact of clavicle osteotomy. Total load distribution is observed highest at T2 followed by T3 and T6. In the T2 missing scenario, total loads on T3 and T4 increase. In the T4 missing case, the most affected level is T3. In the T6 missing scenario, total loads on T5 and T7 increase. In the clavicular osteotomy scenario, all levels' loads increase; the highest is recorded in T7 by 460%, followed by T5, T4, T2, T6, and T3. While all levels contribute to fixation strength, T2 is subjected to the highest loads, and, in the missing level scenarios, the loads are tolerated sufficiently by the remaining levels. Missing T4 scenario has the least effect on the system, which is interpreted as potentially the only skippable level of fixation. Clavicular osteotomy has the highest effect on the arthrodesis site.

Development of a non-invasive ventilator for emergency and beyond.

The SARS-CoV-2 pandemic led to the development and implementation of emergency ventilators owing to the shortage of ventilators globally. Using invasive ventilators for patient intubation has medical experts concerned about increasing mortality. Early intervention with oxygen and respiratory therapy reduces the need for intubation, increases survival rates, and reduces the stress of critical care ventilators in hospitals. This study explores the capabilities of an easy-to-build and accessible non-invasive ventilator during an emergency and the practical implementation of the ventilator beyond the scope of the emergency. The proposed system consists of a high-pressure turbine integrated with a microcontroller and pressure and flow sensors assembled in a portable design. The non-invasive pressure support system is tested with a single-chamber high-precision lung simulator capable of simulating multiple lung diseases. The system is operated in a spontaneous pressure support mode as a Bi-level Ventilator for varying degrees of pressure level and lung conditions. The proposed study implements two most commonly adapted non-invasive patient circuits, i.e., single passive limb leak circuit and single limb active circuit. Both circuits are tested with and without leakage compensation. Two clinically accepted ventilation modes, i.e., pressure support and volume-assured pressure support ventilation, are presented. The results demonstrate the feasibility of using this type of device for non-invasive respiratory support and highlight the need for further testing to assess its safety and effectiveness in various clinical settings.

Intraoperative fluoroscopic safety assessment of femoral head implants with 3-dimensional risk parameters to minimize cut-out.

OBJECTIVE: This study aimed to introduce a method to extract the 3-dimensional spatial position of the femoral head implant from 2-dimensional fluoroscopic projections, allowing surgeons to assess fixation much more accurately and prevent cut-out complications in proximal femoral nailing. METHODS: To define a safety region for the tip in the femoral head, a novel 3-dimensional distance-based risk parameter called TSD3D was introduced. An intersection algorithm was developed that solely takes the fluoroscopic anteroposterior and lateral distances to reveal the 3-dimensional location of the screw or Kirschner wire tip, enabling the utilization of the 3-dimensional parameter. Orthogonal per- spectives of 6 femur proximal bone substitutes with randomly inserted Kirschner wires were imaged under fluoroscopy. The developed algorithm was used to calculate the implant tip location in 3-dimensional from 2-dimensional images for each case. Algorithm accuracy was validated with the computed tomography-obtained 3-dimensional models of the same femur substitutes. RESULTS: The newly introduced risk parameter successfully visualizes 3-dimensional safety regions. Utilizing the 2-dimensional fluoro- scopic distances as inputs to the algorithm, the 3-dimensional position of the implanted Kirschner wire tip is calculated with a maximum of 9.8% error for a single Cartesian-coordinate measurement comparison. CONCLUSION: By incorporating the newly introduced 3-dimensional risk parameter, surgeons can more precisely evaluate the position of the implant and avoid cut-out complications, instead of relying solely on misleading 2-dimensional fluoroscopic projections of the femoral head.

Acausal Modelling of Advanced-Stage Heart Failure and the Istanbul Heart Ventricular Assist Device Support with Patient Data.

BACKGROUND: In object-oriented or acausal modelling, components of the model can be connected topologically, following the inherent structure of the physical system, and system equations can be formulated automatically. This technique allows individuals without a mathematics background to develop knowledge-based models and facilitates collaboration in multidisciplinary fields like biomedical engineering. This study conducts a preclinical evaluation of a ventricular assist device (VAD) in assisting advanced-stage heart failure patients in an acausal modelling environment. METHODS: A comprehensive object-oriented model of the cardiovascular system with a VAD is developed in MATLAB/SIMSCAPE, and its hemodynamic behaviour is studied. An analytically derived pump model is calibrated for the experimental prototype of the Istanbul Heart VAD. Hemodynamics are produced under healthy, diseased, and assisted conditions. The study features a comprehensive collection of advanced-stage heart failure patients' data from the literature to identify parameters for disease modelling and to validate the resulting hemodynamics. RESULTS: Regurgitation, suction, and optimal speeds are identified, and trends in different hemodynamic parameters are observed for the simulated pathophysiological conditions. Using pertinent parameters in disease modelling allows for more accurate results compared to the traditional approach of arbitrary reduction in left ventricular contractility to model dilated cardiomyopathy. CONCLUSION: The current research provides a comprehensive and validated framework for the preclinical evaluation of cardiac assist devices. Due to its object-oriented nature, the featured model is readily modifiable for other cardiovascular diseases for studying the effect of pump operating conditions on hemodynamics and vice versa in silico and hybrid mock circulatory loops. The work also provides a potential teaching tool for understanding the pathophysiology of heart failure, diagnosis rationale, and degree of assist requirements.

In-silico hemodynamic ramp testing of ventricular assist device implanted patients using acausal cardiovascular-VAD modeling.

BACKGROUND: While cardiovascular system and mechanical circulatory support devices are efficiently model the effect of disease and assistance, they can also lend valuable insights into clinical procedures. This study demonstrates the use of a CVS-VAD model for an invasive procedure; hemodynamic ramp testing, in-silico. METHODS: The CVS model is developed using validated models in literature, using Simscape™. An analytically derived pump model is calibrated for the HeartWare VAD. Dilated cardiomyopathy is used as an illustrative example of heart failure, and heart failure patients are created virtually by calibrating the model with requisite disease parameters obtained from published patient data. A clinically applied ramp study protocol is adopted whereby speed optimization is performed following clinically accepted hemodynamic normalization criteria. Trends in hemodynamic variables in response to pump speed increments are obtained. Optimal speed ranges are obtained for the three virtual patients based on target values of central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO), and mean arterial pressure (MAP) for hemodynamic stabilization. RESULTS: Appreciable speed changes in the mild case (300 rpm), slight changes in the moderate case (100 rpm), and no changes in the simulated severe case are possible. CONCLUSION: The study demonstrates a novel application of cardiovascular modeling using an open-source acausal model, which can be potentially beneficial for medical education and research.

Investigation of lattice infill parameters for additively manufactured bone fracture plates to reduce stress shielding.

BACKGROUND: Stress shielding is a detrimental phenomenon caused by the stiffness mismatch between metallic bone plates and bone tissue, which can hamper fracture healing. Additively manufactured plates can decrease plate stiffness and alleviate the stress shielding effect. METHODS: Rectilinear lattice plates with varying cell sizes, wall thicknesses, and orientations are computationally generated. Finite element analysis is used to calculate the four-point bending stiffness and strength of the plates. The mechanical behaviors of three different lattice plates are also simulated under a simple diaphyseal fracture fixation scenario. RESULTS: The study shows that with different combinations of lattice infill parameters, plates with up to 68% decrease in stiffness compared to the 100% infill plate can be created. Moreover, in the fixation simulations, the least stiff lattice plate displays 53% more average stress distribution at the healing callus region compared to the 100% infill plate. CONCLUSIONS: Using computational techniques, it has been demonstrated that additively manufactured stiffness-reduced bone plates can successfully address stress shielding with the strategic modulation of lattice infill parameters. Lattice plates with design versatility have the potential for use in various fracture fixation scenarios.

A new checklist surgical hand scrub to replace time-based methods - A pixel intensity analysis.

BACKGROUND: Hand scrubbing is an absolute precaution to avoid surgical site infections. World Health Organization (WHO) recommends 4-min overall scrubbing (4MS) for surgical hand hygiene. However, we hypothesize that the more methodical 10-stroke counting technique (10SS) via locational partitioning of the arm is superior to WHO's superficial guideline dictating only the duration. PURPOSE: The mechanical efficiency of 4MS and 10SS techniques are compared. METHODS: 24 healthcare professionals were recruited for the study. A novel methodology was devised to quantify the average brightness change of skin-applied UV ink before and after scrubbing via pixel intensity analysis. A black-box setup is constructed with an integrated high-resolution camera to photograph the UV-stained dorsal arm. Each stain was then digitally isolated for brightness comparison. RESULTS: It was observed that the 10SS technique was overall more successful in removing the UV ink in comparison to the 4MS method (p = 0.014). In addition, a bias was observed in removing more percentage of the proximal stains when compared to middle and distal stains with the 4MS technique (p = 0.0027), while location-based brightness change averages were statistically equal with the 10SS technique (p = 0.423). CONCLUSIONS AND CLINICAL RELEVANCE: 10SS provided not only a more mechanically efficient scrubbing but also a more homogenous cleaning than 4MS. We recommend the use of the 10SS technique to achieve more effective pre-surgical hand hygiene.

Ruthenium-induced corneal collagen crosslinking under visible light.

Corneal collagen crosslinking (CXL) is a commonly used minimally invasive surgical technique to prevent the progression of corneal ectasias, such as keratoconus. Unfortunately, riboflavin/UV-A light-based CXL procedures have not been successfully applied to all patients, and result in frequent complications, such as corneal haze and endothelial damage. We propose a new method for corneal crosslinking by using a Ruthenium (Ru) based water-soluble photoinitiator and visible light (430 nm). Tris(bipyridine)ruthenium(II) ([Ru(bpy)3]2+) and sodium persulfate (SPS) mixture covalently crosslinks free tyrosine, histidine, and lysine groups under visible light (400-450 nm), which prevents UV-A light-induced cytotoxicity in an efficient and time saving collagen crosslinking procedure. In this study, we investigated the effects of the Ru/visible blue light procedure on the viability and toxicity of human corneal epithelium, limbal, and stromal cells. Then bovine corneas crosslinked with ruthenium mixture and visible light were characterized, and their biomechanical properties were compared with the customized riboflavin/UV-A crosslinking approach in the clinics. Crosslinked corneas with a ruthenium-based CXL approach showed significantly higher young's modulus compared to riboflavin/UV-A light-based method applied to corneas. In addition, crosslinked corneas with both methods were characterized to evaluate the hydrodynamic behavior, optical transparency, and enzymatic resistance. In all biomechanical, biochemical, and optical tests used here, corneas that were crosslinked with ruthenium-based approach demonstrated better results than that of corneas crosslinked with riboflavin/ UV-A. This study is promising to be translated into a non-surgical therapy for all ectatic corneal pathologies as a result of mild conditions introduced here with visible light exposure and a nontoxic ruthenium-based photoinitiator to the cornea. STATEMENT OF SIGNIFICANCE: Keratoconus, one of the most frequent corneal diseases, could be treated with riboflavin and ultraviolet light-based photo-crosslinking application to the cornea of the patients. Unfortunately, this method has irreversible side effects and cannot be applied to all keratoconus patients. In this study, we exploited the photoactivation behavior of an organoruthenium compound to achieve corneal crosslinking. Ruthenium-based organic complex under visible light demonstrated significantly better biocompatibility and superior biomechanical results than riboflavin and ultraviolet light application. This study promises to translate into a new fast, efficient non-surgical therapy option for all ectatic corneal pathologies.

In silico evaluation of lattice designs for additively manufactured total hip implants.

Additive manufacturing restructures the fabrication of custom medical implants and transforms the design, topology optimization, and material selection perspectives in biomechanical applications. Additionally, it facilitated the design and fabrication of patient-oriented hip implants. Selection of proper lattice type is critical in additive manufacturing of hip implants. The lattice types reduce the implant mass and, due to higher stress distribution and deformations as compared to the rigid implants, it brings down the stress shielding issues. This study introduces a rigid shell structure and infill lattice hip implant. Additionally, the effect of various lattice unit cell thickness (0.2-1 mm) and elemental size (2.5-5 mm) while applying 2300 N axial force is explored numerically. A cubic structure with two rigid surfaces on the top and bottom is outlined to separate the effect of the hip implant cross-sectional area variations. The stress distribution and deformation characteristics are validated with the hip implant design. The Finite Element Analysis (FEA) demonstrated that the Weaire-Phelan lattice structure exhibits the least stress and deformation among the other types at various design parameters. Additionally, the same methodology is applied to three biocompatible hip implant materials as Ti-6Al-4V, TA15 (Ti-6Al-2Zr-1Mo-1V), and CoCr28Mo6. Finally, the effect of the unit cell thickness and size on the implant's mass reduction considering the lattice's safety factor is investigated for the mentioned materials. The selection of a Weaire-Phelan lattice with the optimized safety factor and mass reduction is represented considering all the results. The optimized parameters for Titanium-based alloys are approximately 3.5 mm unit cell size with 0.6 mm beam thickness. However, the CoCr Mo-based alloy requires a thicker beam size (about 0.8 mm) due to lower safety factors.

Impact of the Amyotrophic Lateral Sclerosis Disease on the Biomechanical Properties and Oxidative Stress Metabolism of the Lung Tissue Correlated With the Human Mutant SOD1G93A Protein Accumulation.

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease, and ALS incidence is increasing worldwide. Patients with ALS have respiratory failure at the disease's end stages, leading to death; thus, the lung is one of the most affected organs during disease progression. Tissue stiffness increases in various lung diseases because of impaired extracellular matrix (ECM) homeostasis leading to tissue damage and dysfunction at the end. According to the literature, oxidative stress is the major contributor to ECM dysregulation, and mutant protein accumulation in ALS have been reported as causative to tissue damage and oxidative stress. In this study, we used SOD1G93A and SOD1WT rats and measured lung stiffness of rats by using a custom-built stretcher, where H&E staining is used to evaluate histopathological changes in the lung tissue. Oxidative stress status of lung tissues was assessed by measuring glucose 6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6-PGD), glutathione reductase (GR), glutathione s-transferase (GST), catalase (CAT), and superoxide dismutase 1 (SOD1) levels. Western blot experiments were performed to evaluate the accumulation of the SOD1G93A mutated protein. As a result, increased lung stiffness, decreased antioxidant status, elevated levels of oxidative stress, impaired mineral and trace element homeostasis, and mutated SOD1G93A protein accumulation have been found in the mutated rats even at the earlier stages, which can be possible causative of increased lung stiffness and tissue damage in ALS. Since lung damage has altered at the very early stages, possible therapeutic approaches can be used to treat ALS or improve the life quality of patients with ALS.

A novel lower bound for tip-apex distance.

PURPOSE: The cut-out of the cephalomedullary nail is among the most common post-surgery complications for intertrochanteric fractures. As a risk predictor, a tip-apex distance (TAD) below 25 mm, observed from orthogonal fluoroscopic views, is recommended in the literature. This study aims to demonstrate that TAD < 25 mm is a mathematically insufficient risk definition and to complement the TAD upper bound with an appropriate lower bound, with the introduction of a novel distance parameter, TADX, based on the orthogonal projection of the nail tip on the central femoral midline. METHOD: Through a mathematical simulation software, all the possible points that lie inside the AP and lateral views of the proximal femoral hemisphere are utilized to create a 3D grid that is sorted into geometrically safe and risk-bearing regions. Extending this methodology, TAD < 25 mm, 10 mm < TAD < 25 mm, and the ideal tip position volumes are simulated. Finally, intersection volumes are created by a combination of different candidate lower TADX bounds and TAD < 25 mm upper bound to determine satisfactory TADX limits. RESULTS: Simulation of TAD-bound zones exposed that TAD is only a mathematically suitable parameter for defining the upper boundary but not the lower boundary for the optimal region. However, using a TADX lower limit creates a 3D volume that is much closer to the optimal tip region volumetrically and can still be as quickly calculated from 2D AP and lateral views. CONCLUSIONS: According to the mathematical simulations, the use of a TADX lower bound of 9 mm for small, 7.5 mm for medium, and 7 mm for large femoral heads in conjunction with a TAD upper bound of 25 mm is suggested.

Comparison of the Morphologic and Mechanical Features of Human Cranial Dura and Other Graft Materials Used for Duraplasty.

OBJECTIVE: This study aimed to compare the thickness and mechanical properties of the frontal; parietal; temporal; occipital human dura; autogenous grafts (facia lata, temporal fascia, galea aponeurotica); and artificial dura. METHODS: Sagittal and transverse dura samples were obtained from standard regions of the cranial dura from 30 autopsies for histologic and mechanical property measurements. Identical measurements were made for the autogenous grafts artificial dura, and the results were statistically analyzed. RESULTS: The thickness of the temporal (0.35 ± 0.11 mm), parietal (0.44 ± 0.13 mm), frontal (0.38 ± 0.12 mm), and occipital (0.46 ± 0.18 mm) dura showed regional variations. The parietal and occipital dura were significantly thicker than the temporal dura. The occipital dura was considerably thicker than the frontal dura. The frontal and temporal dura of males were significantly thicker than females. The sagittal maximum tensile force measurements were significantly greater than transverse, for the frontal, temporal, and occipital dura. The stiffness measurements in sagittal direction were greater than the measurements in transverse direction for the frontal dura. The mechanical properties and thickness of the autogenous and artificial dura were not similar to the human dura. CONCLUSIONS: The thickness and mechanical properties of the regional cranial dura should be taken into consideration for a better cure and fewer complications. The mechanical properties of sagittal and transverse dura should be kept in mind for the preference of dura material. The present study's data can pave the way to produce artificial regional dura by mimicking the thickness and mechanical properties of the human dura.

In silico analysis of modular bone plates.

BACKGROUND: Inventory management or immediate availability of fracture plates can be problematic since for each surgical intervention a specific plate of varying size and functionality must be ordered. Modularization of the standard monolithic plate is proposed to address this issue. METHODS: The effects of four different unit module design parameters (type, degree of modularization, connector screw diameter, sandwich ratio) on the plate bending stiffness and failure are investigated in a finite element four-point-bending analysis. A chosen, best-performing modular plate is then tested in silico for a simple diaphyseal tibial fracture scenario under anatomical compressional, torsional, and bending loads. RESULTS: A modularization strategy is proposed to match the monolithic plate bending properties as closely as possible. With the best combination of design parameters, a fully modularized equivalent length plate with a 42.3% decrease in stiffness and 46.2% decrease in strength could be assembled. The chosen modular plate also displayed sufficient mechanical performance under the fracture fixation scenarios for a potentially successful osteosynthesis. CONCLUSIONS: Via computational methods, the viability of the modularization strategy as an alternate to the traditional monolithic plate is demonstrated. As a further realized advantage, the modular plates can alleviate stress shielding thanks to the reduced stiffness.

In Silico Analysis of Elastomer-Coated Cerclage for Reducing Sternal Cut-Through in High-Risk Patients.

BACKGROUND: AISI 316 L stainless steel wire cerclage routinely used in sternotomy closure causes lateral cut-through damage and fracture, especially in cases of high-risk patients, which leads to postoperative complications. A biocompatible elastomer (Pellethane®) coating on the standard wire is proposed to mitigate the cut-through effect. METHODS: Simplified peri-sternal and transsternal, sternum-cerclage contact models are created and statically analyzed in a finite element (FE) software to characterize the stress-reduction effect of the polymer coating for thicknesses between 0.5 and 1.125 mm. The performance of the polymer-coated cerclage in alleviating the detrimental cortical stresses is also compared to the standard steel cerclage in a full sternal closure FE model for the extreme cough loading scenario. RESULTS: It was observed via the simplified contact simulations that the cortical stresses can be substantially decreased by increasing the coating thickness. The full closure coughing simulation on the human sternum further corroborated the simplified contact results. The stress reduction effect was found to be more prominent in the transsternal contacts in comparison to peri-sternal contacts. CONCLUSIONS: Bearing in mind the promising numerical simulation results, it is put forth that a standard steel wire coated with Pellethane will majorly address the cut-through complication.

The safety and accuracy of the fluoroscopic imaging during proximal femoral fixation: A computerized 3D reappraisal of the joint penetration risk.

BACKGROUND: To assess the success of proximal cephalomedullary nailing operations for treating trochanteric fractures, surgeons utilize 2D fluoroscopy to observe the relative positions of the femoral head and the implant. One distance-based risk parameter, observed from the AP and Lateral projections, is the Tip-Surface Distance(TSD) that dictates how close to the outer cortex should the implant tip be residing to avoid post-surgical complications such as cut-out or joint penetration. In this study, the safety and the accuracy of the orthogonal fluoroscopic imaging were evaluated. METHODS: A femoral head model was created and the risk zone was defined as a hemispherical shell of 5 mm thickness beneath the subchondral cortex, which should not be violated during screw insertion. The remaining hemisphere beneath the risk zone was designated as the safe zone. To assess the effect of head size, each simulation was conducted for 34, 47, and 60 mm diameter(Dfemur) femoral heads. The rate of safe zone violation was calculated for all possible screw endpoints with a TSD of at least 5 mm on fluoroscopic orthogonal views (TSDAP and TSDLat). RESULTS: The minimum risk of joint penetration was achieved when the TSDAP/TSDLat ratio was 1. For Dfemur of 34 mm there was a risk of 91.7% of the safe zone violation when each TSDAP and TSDLat were 5 mm and 0% for 9 mm. For Dfemur of 47 mm, the risk was 92.2% for 5 mm and 0% for 11 mm. For Dfemur of 60 mm, the risk was 92.3% for 5 mm and 0% for 13 mm. Safety maps were constructed for all possible TSD combinations for 34, 47, and 60 mm femoral heads. CONCLUSIONS: Depending solely on the orthogonal fluoroscopic images is not a safe and accurate technique for assessing joint penetration risk during proximal femoral fixation due to the spherical geometry of the femoral head. The screw tip can lie completely outside of the femoral head even when it appears inside, in both orthogonal fluoroscopic views. Evidently, when using TSD, more stringent distance limits should be chosen, contrary to the recommended 5 mm limit. Our safety maps for TSD combinations may be used to check the security of the implantation.

In silico analysis of Superelastic Nitinol staples for trans-sternal closure.

BACKGROUND: Superelastic Nitinol staples, utilized routinely in foot surgeries, are proposed to be used for sternal closure application in this study. It is hypothesized that the shape memory induced superelasticity will allow multiple staples placed along the sternum to promote fast and safe recovery by maintaining constant clamping pressure at the sternotomy midline. METHODS: Two different Nitinol staples of different alloying compositions, one representing the metal formed wire geometry and, the other, powder metallurgy manufactured rectangular geometry, are chosen from the literature. Austenite finish temperatures of both materials are confirmed to be appropriately below the body temperature for superelastic shape memory activation. The adopted finite element superelasticity model is first validated and, via design optimization of parametrized dimensions, the staple geometries for producing maximal clamping forces are identified. The performances of the optimized staples for full trans-sternal closure (seven staples for each) are then tested under lateral sternal loading in separate computational models. RESULTS: The optimized metal formed staple exerts 70.2 N and the optimized powder metallurgy manufactured staple exerts 245 N clamping force, while keeping the maximum localized stresses under the yield threshold for 90° leg bending. Testing the staple-sternum constructs under lateral sternal loading revealed that the former staple can be utilized for small-chested patients with lower expected physiological loading, while the latter staple can be used for high-risk patients, for which high magnitude valsalva maneuver is expected. CONCLUSION: Computational results prove that superelastic Nitinol staples are promising candidates as alternatives to routinely performed techniques for sternal closure.

A Short-Term In Vivo Evaluation of the Istanbul Heart Left Ventricular Assist Device in a Pig Model.

OBJECTIVES: A continuous-flow centrifugal blood pump system has been recently developed as an implantable left ventricular assist device for patients with endstage heart failure. The objective of this study was to evaluate the initial in vivo performance of a newly developed left ventricular assist device (iHeart or Istanbul heart; Manufacturing and Automation Research Center, Koc University, Istanbul, Turkey) in an acute setting using a pig model. MATERIALS AND METHODS: Three pigs (77, 83, 92 kg) received implants via a median sternotomy, with animals supported for up to 6 hours. An outflow cannula was anastomosed to the ascending aorta. Anticoagulation was applied by intravenous heparin administration. During the support period, pump performance was evaluated under several flow and operating conditions. All pigs were humanely sacrificied after the experiments, and organs were examined macroscopically and histopathologically. RESULTS: Flow rate ranged between 1.5 and 3.6 L/min with pump speeds of 1500 to 2800 revolutions/min and motor current of 0.6 to 1.3 A. Initial findings confirmed thatthe iHeart ventricular assist device had sufficient hydraulic performance to support the circulation. During the experimental period, plasma free hemoglobin levels were found to be within normalranges.Thrombus formation was not observed inside the pump in all experiments. CONCLUSIONS: The iHeart ventricular assist device demonstrated encouraging hemodynamic performance and good biocompatibility in the pig model for use as an implantable left ventricular assist device. Further acute in vivo studies will evaluate the short-term pump performance prior to chronic studies for long-term evaluation.

A novel adjustable locking plate (ALP) for segmental bone fracture treatment.

A novel Ti6Al4V adjustable locking plate (ALP) is designed to provide enhanced bone stability for segmental bone fractures and to allow precise positioning of disconnected segments. The design incorporates an adjustable rack and pinion mechanism to perform compression, distraction and segment transfer during plate fixation surgery. The aim of this study is to introduce the advantages of the added feature and computationally characterize the biomechanical performance of the proposed design. Structural strength of the novel plate is analyzed using numerical methods for 4-point bending and fatigue properties, following ASTM standards. An additional mechanical failure finite element test is also conducted on the rack and pinion to reveal how much torque can be safely applied to the mechanism by the surgeon. Simulation results predict that the new design is sufficiently strong to not fail under regular anatomical loading scenarios with close bending strength and fatigue life properties to clinically used locking compression plates. The novel ALP design is expected to be a good candidate for addressing problems regarding fixation of multi-fragmentary bone fractures.

Defining a New Variable That May Impact Long-term Postoperative Nasal Tip Support: The Biomechanical Properties of the Columellar Strut Graft.

BACKGROUND: Although columellar strut grafts (CSGs) are considered among the fundamental steps for providing nasal tip support, a downward rotation of the nasal tip in patients with strut grafts can still be encountered. Patient-related factors such as nasal skin thickness can allow the plastic surgeon to anticipate certain drawbacks that can be encountered in the healing phase, but patient-based differences of nasal cartilage and the resulting impact have yet to be investigated. The purpose of this study was to evaluate the effect of the biomechanical properties of CSGs on late postoperative nasal tip position and support. METHODS: The study was undertaken with the participation of 20 patients undergoing closed-technique primary rhinoplasty with CSGs. Each cartilage specimen was biomechanically analyzed to calculate the modulus of elasticity. Preoperative and postoperative images were obtained to determine nasal tip position and rotation with quantitative measurements. Postoperative 3- and 12-month measurements were evaluated according to their relationship with the elasticity modulus of the utilized cartilages. RESULTS: The evaluation demonstrated that the elasticity modulus can impact the long-term support of the nasolabial angle in which an increase in the coefficient of elasticity can result in a decrease in long-term nasal tip support. CONCLUSION: The results of the study reveal a new objective variable that can impact nasal tip dynamics and patient-related differences following rhinoplasty. This study not only brings forth a different perspective in the evaluation of nasal tip dynamics but can also provide data for determining ideal values for cartilage prefabrication.

Effect of blade curvature on the hemolytic and hydraulic characteristics of a centrifugal blood pump.

AIMS:: Impeller design has a significant impact on the overall performance of a blood pump. In this study, the effect of the blade curvature was investigated by performing in silico and in vitro studies on a recently developed centrifugal blood pump. METHODS:: A computational fluid dynamics study was performed for the flow rates of 3-5 L/min at 2000 r/min. The computational fluid dynamics model was also applied on the US Food and Drug Administration (FDA) benchmark blood pump to validate our computational method. The relative hemolysis index was calculated with the Eulerian hemolysis estimation method for five impellers with the wrap angles ranging from 0° to 240°. Hydraulic experiments were conducted for the validation of computational fluid dynamics results. In addition, the curved-blade impeller (120°) and the straight-blade impeller (0°) were evaluated with in vitro hemolysis tests using human blood. RESULTS:: The wrap angle of 120° provided the best hydraulic and hemolytic performance. Pump achieved the physiologic operating pressures and flows with 85-115 mmHg at 2.5-5.9 L/min. Compared to the straight-blade impeller, the 120° model reduces the relative hemolysis index and the plasma-free hemoglobin near 72.8% and 56.7%, respectively. Comparison of in silico and in vitro results indicated the similar trend to the blade curvature. CONCLUSION:: Introducing a blade curvature enhanced the hydrodynamic and hemolytic performance compared to the straight-blade configuration for the investigated centrifugal blood pump. The findings of this study provide new insights into centrifugal blood pump design by examining the influence of the blade curvature.