STAT6-targeting antisense oligonucleotides against solitary fibrous tumor.

Solitary fibrous tumor (SFT) is a rare, non-hereditary soft tissue sarcoma thought to originate from fibroblastic mesenchymal stem cells. The etiology of SFT is thought to be due to an environmental intrachromosomal gene fusion between NGFI-A-binding protein 2 (NAB2) and signal transducer and activator protein 6 (STAT6) genes on chromosome 12, wherein the activation domain of STAT6 is fused with the DNA-binding domain of NAB2 resulting in the oncogenesis of SFT. All NAB2-STAT6 fusion variations discovered in SFTs contain the C-terminal of STAT6 transcript, and thus can serve as target site for antisense oligonucleotides (ASOs)-based therapies. Indeed, our in vitro studies show the STAT6 3' untranslated region (UTR)-targeting ASO (ASO 993523) was able to reduce expression of NAB2-STAT6 fusion transcripts in multiple SFT cell models with high efficiency (half-maximal inhibitory concentration: 116-300 nM). Encouragingly, in vivo treatment of SFT patient-derived xenograft mouse models with ASO 993523 resulted in acceptable tolerability profiles, reduced expression of NAB2-STAT6 fusion transcripts in xenograft tissues (21.9%), and, importantly, reduced tumor growth (32.4% decrease in tumor volume compared with the untreated control). Taken together, our study established ASO 993523 as a potential agent for the treatment of SFTs.

Reduction of Tumor Growth with RNA-Targeting Treatment of the NAB2-STAT6 Fusion Transcript in Solitary Fibrous Tumor Models.

Solitary fibrous tumor (SFT) is a rare soft-tissue sarcoma. This nonhereditary cancer is the result of an environmental intrachromosomal gene fusion between NAB2 and STAT6 on chromosome 12, which fuses the activation domain of STAT6 with the repression domain of NAB2. Currently there is not an approved chemotherapy regimen for SFTs. The best response on available pharmaceuticals is a partial response or stable disease for several months. The purpose of this study is to investigate the potential of RNA-based therapies for the treatment of SFTs. Specifically, in vitro SFT cell models were engineered to harbor the characteristic NAB2-STAT6 fusion using the CRISPR/SpCas9 system. Cell migration as well as multiple cancer-related signaling pathways were increased in the engineered cells as compared to the fusion-absent parent cells. The SFT cell models were then used for evaluating the targeting efficacies of NAB2-STAT6 fusion-specific antisense oligonucleotides (ASOs) and CRISPR/CasRx systems. Our results showed that fusion specific ASO treatments caused a 58% reduction in expression of fusion transcripts and a 22% reduction in cell proliferation after 72 h in vitro. Similarly, the AAV2-mediated CRISPR/CasRx system led to a 59% reduction in fusion transcript expressions in vitro, and a 55% reduction in xenograft growth after 29 days ex vivo.

Automated finite element approach to generate anatomical patient-specific biomechanical models of atherosclerotic arteries from virtual histology-intravascular ultrasound.

Despite advancements in early detection and treatment, atherosclerosis remains the leading cause of death across all cardiovascular diseases (CVD). Biomechanical analysis of atherosclerotic lesions has the potential to reveal biomechanically instable or rupture-prone regions. Treatment decisions rarely consider the biomechanics of the stenosed lesion due in-part to difficulties in obtaining this information in a clinical setting. Previous 3D FEA approaches have incompletely incorporated the complex curvature of arterial geometry, material heterogeneity, and use of patient-specific data. To address these limitations and clinical need, herein we present a user-friendly fully automated program to reconstruct and simulate the wall mechanics of patient-specific atherosclerotic coronary arteries. The program enables 3D reconstruction from patient-specific data with heterogenous tissue assignment and complex arterial curvature. Eleven arteries with coronary artery disease (CAD) underwent baseline and 6-month follow-up angiographic and virtual histology-intravascular ultrasound (VH-IVUS) imaging. VH-IVUS images were processed to remove background noise, extract VH plaque material data, and luminal and outer contours. Angiography data was used to orient the artery profiles along the 3D centerlines. The resulting surface mesh is then resampled for uniformity and tetrahedralized to generate the volumetric mesh using TetGen. A mesh convergence study revealed edge lengths between 0.04 mm and 0.2 mm produced constituent volumes that were largely unchanged, hence, to save computational resources, a value of 0.2 mm was used throughout. Materials are assigned and finite element analysis (FEA) is then performed to determine stresses and strains across the artery wall. In a representative artery, the highest average effective stress was in calcium elements with 235 kPa while necrotic elements had the lowest average stress, reaching as low as 0.79 kPa. After applying nodal smoothening, the maximum effective stress across 11 arteries remained below 288 kPa, implying biomechanically stable plaques. Indeed, all atherosclerotic plaques remained unruptured at the 6-month longitudinal follow up diagnosis. These results suggest our automated analysis may facilitate assessment of atherosclerotic plaque stability.

Assessment with clinical data of a coupled bio-hemodynamics numerical model to predict leukocyte adhesion in coronary arteries.

Numerical simulations of coupled hemodynamics and leukocyte transport and adhesion inside coronary arteries have been performed. Realistic artery geometries have been obtained for a set of four patients from intravascular ultrasound and angiography images. The numerical model computes unsteady three-dimensional blood hemodynamics and leukocyte concentration in the blood. Wall-shear stress dependent leukocyte adhesion is also computed through agent-based modeling rules, fully coupled to the hemodynamics and leukocyte transport. Numerical results have a good correlation with clinical data. Regions where high adhesion is predicted by the simulations coincide to a good approximation with artery segments presenting plaque increase, as documented by clinical data from baseline and six-month follow-up exam of the same artery. In addition, it is observed that the artery geometry and, in particular, the tortuosity of the centerline are a primary factor in determining the spatial distribution of wall-shear stress, and of the resulting leukocyte adhesion patterns. Although further work is required to overcome the limitations of the present model and ultimately quantify plaque growth in the simulations, these results are encouraging towards establishing a predictive methodology for atherosclerosis progress.

In Silico Tissue Engineering: A Coupled Agent-Based Finite Element Approach.

Over the past two decades, the increase in prevalence of cardiovascular diseases and the limited availability of autologous blood vessels and saphenous vein grafts have motivated the development of tissue-engineered vascular grafts (TEVGs). However, compliance mismatch and poor mechanical properties of the TEVGs remain as two major issues that need to be addressed. Researchers have investigated the role of various culture conditions and mechanical conditioning in deposition and orientation of collagen fibers, which are the key structural components in the vascular wall; however, the intrinsic complexity of mechanobiological interactions demands implementing new engineering approaches that allow researchers to investigate various scenarios more efficiently. In this study, we utilized a coupled agent-based finite element analysis (AB-FEA) modeling approach to study the effect of various loading modes (uniaxial, biaxial, and equibiaxial), boundary conditions, stretch magnitudes, and growth factor concentrations on growth and remodeling of smooth muscle cell-populated TEVGs, with specific focus on collagen deposition and orientation. Our simulations (12 weeks of culture) showed that biaxial cyclic loading (and not uniaxial or equibiaxial) leads to alignment of collagen fibers in the physiological directions. Moreover, axial boundary conditions of the TEVG act as determinants of fiber orientations. Decreasing the serum concentration, from 10% to 5% or 1%, significantly decreased the growth and remodeling speed, but only affected the fiber orientation in the 1% serum case. In conclusion, in silico tissue engineering has the potential to evolve the future of tissue engineering, as it will allow researchers to conceptualize various interactions and investigate numerous scenarios with great speed. In this study, we were able to predict the orientation of collagen fibers in TEVGs using a coupled AB-FEA model in less than 8 h. Impact Statement Tissue-engineered vascular grafts (TEVGs) hold potential to replace the current gold standard of vascular grafting, saphenous vein grafts. However, developing TEVGs that mimic the mechanical performance of the native tissue remains a challenging task. We developed a computational model of the grafts' remodeling processes and studied the effects of various loading mechanisms and culture conditions on collagen fiber orientation, which is a key factor in mechanical performance of the grafts. We were able to predict the fiber orientations accurately and show that biaxial loading and axial boundary conditions are important factors in collagen fiber organization.

Stress distribution in a tooth treated through minimally invasive access compared to one treated through traditional access: A finite element analysis study.

INTRODUCTION: The purpose of this study was to compare the stress distributions in the teeth treated through minimally invasive access (MIA) designs to those of the teeth treated through traditional straight-line access and their relationship to the final restoration using three-dimensional finite element analysis (FEA). MATERIALS AND METHODS: Four FEA models of an extracted mandibular first molar were constructed. An intact model served as the control, whereas the other three were prepared with either an MIA or traditional straight-line access. Simulated composite access fillings with or without a simulated gold crown were applied to the models, followed by application of an occlusal load of 100 N. Von Mises stresses in the teeth were then calculated and analyzed. RESULTS: Stress values within the dentin for baseline, MIA with composite filling, MIA with composite filling and crown, and traditional access with composite filling and crown were 10.14 MPa, 6.98 MPa, 11.79 MPa, and 16.81 MPa, respectively. Higher stress values indicate that the tooth is more prone to fracture. CONCLUSIONS: A traditional endodontic access cavity may render a tooth more susceptible to fracture compared with an MIA design.

3D-Printed Models of Cleft Lip and Palate for Surgical Training and Patient Education.

BACKGROUND: Sculpted physical models and castings of the anatomy of cleft lip and palate are used for parent, patient, and trainee education of cleft lip and palate conditions. In this study, we designed a suite of digital 3-dimensional (3D) models of cleft lip and palate anatomy with additive manufacturing techniques for patient education. METHODS: CT scans of subjects with isolated cleft palate, unilateral and bilateral cleft lip and palate, and a control were obtained. Soft tissue and bony structures were segmented and reconstructed into digital 3D models. The oral soft tissues overlying the cleft palate were manually molded with silicone putty and scanned using CT to create digital 3D models. These were then combined with the original model to integrate with segmentable soft tissues. Bone and soft tissues were 3D printed in different materials to mimic the rigidity/softness of the relevant anatomy. These models were presented to the parents/patients at our craniofacial clinic. Visual analog scale (VAS) surveys were obtained pertaining to the particular use of the models, to ascertain their value in parental education. RESULTS: A total of 30 parents of children with cleft conditions completed VAS evaluations. The models provided the parents with a better understanding of their child's condition with an overall evaluation score of 9.35 ± 0.5. CONCLUSIONS: We introduce a suite of 3D-printed models of cleft conditions that has a useful role in patient, parental, and allied health education with highly positive feedback.

Mechanobiological model of arterial growth and remodeling.

A coupled agent-based model (ABM) and finite element analysis (FEA) computational framework is developed to study the interplay of bio-chemo-mechanical factors in blood vessels and their role in maintaining homeostasis. The agent-based model implements the power of REPAST Simphony libraries and adapts its environment for biological simulations. Coupling a continuum-level model (FEA) to a cellular-level model (ABM) has enabled this computational framework to capture the response of blood vessels to increased or decreased levels of growth factors, proteases and other signaling molecules (on the micro scale) as well as altered blood pressure. Performance of the model is assessed by simulating porcine left anterior descending artery under normotensive conditions and transient increases in blood pressure and by analyzing sensitivity of the model to variations in the rule parameters of the ABM. These simulations proved that the model is stable under normotensive conditions and can recover from transient increases in blood pressure. Sensitivity studies revealed that the model is most sensitive to variations in the concentration of growth factors that affect cellular proliferation and regulate extracellular matrix composition (mainly collagen).

A finite element analysis of novel vented dental abutment geometries for cement-retained crown restorations.

Recent literature indicates that the long-term success of dental implants is, in part, attributed to how dental crowns are attached to their associated implants. The commonly utilized method for crown attachment - cementation, has been criticized because of recent links between residual cement and peri-implant disease. Residual cement extrusion from crown-abutment margins post-crown seating is a growing concern. This study aimed at (1) identifying key abutment features, which would improve dental cement flow characteristics, and (2) understanding how these features would impact the mechanical stability of the abutment under functional loads. Computational fluid dynamic modeling was used to evaluate cement flow in novel abutment geometries. These models were then evaluated using 3D-printed surrogate models. Finite element analysis also provided an understanding of how the mechanical stability of these abutments was altered after key features were incorporated into the geometry. The findings demonstrated that the key features involved in improved venting of the abutment during crown seating were (1) addition of vents, (2) diameter of the vents, (3) location of the vents, (4) addition of a plastic screw insert, and (5) thickness of the abutment wall. This study culminated in a novel design for a vented abutment consisting of 8 vents located radially around the abutment neck-margin plus a plastic insert to guide the cement during seating and provide retrievability to the abutment system.Venting of the dental abutment has been shown to decrease the risk of undetected residual dental cement post-cement-retained crown seating. This article will utilize a finite element analysis approach toward optimizing dental abutment designs for improved dental cement venting. Features investigated include (1) addition of vents, (2) diameter of vents, (3) location of vents, (4) addition of plastic screw insert, and (5) thickness of abutment wall.

Stereoscopically observed deformations of a compliant abdominal aortic aneurysm model.

A new experimental setup has been implemented to precisely measure the deformations of an entire model abdominal aortic aneurysm (AAA). This setup addresses a gap between the computational and experimental models of AAA that have aimed at improving the limited understanding of aneurysm development and rupture. The experimental validation of the deformations from computational approaches has been limited by a lack of consideration of the large and varied deformations that AAAs undergo in response to physiologic flow and pressure. To address the issue of experimentally validating these calculated deformations, a stereoscopic imaging system utilizing two cameras was constructed to measure model aneurysm displacement in response to pressurization. The three model shapes, consisting of a healthy aorta, an AAA with bifurcation, and an AAA without bifurcation, were also evaluated with computational solid mechanical modeling using finite elements to assess the impact of differences between material properties and for comparison against the experimental inflations. The device demonstrated adequate accuracy (surface points were located to within 0.07 mm) for capturing local variation while allowing the full length of the aneurysm sac to be observed at once. The experimental model AAA demonstrated realistic aneurysm behavior by having cyclic strains consistent with reported clinical observations between pressures 80 and 120 mm Hg. These strains are 1-2%, and the local spatial variations in experimental strain were less than predicted by the computational models. The three different models demonstrated that the asymmetric bifurcation creates displacement differences but not cyclic strain differences within the aneurysm sac. The technique and device captured regional variations of strain that are unobservable with diameter measures alone. It also allowed the calculation of local strain and removed rigid body motion effects on the strain calculation. The results of the computations show that an asymmetric aortic bifurcation created displacement differences but not cyclic strain differences within the aneurysm sac.

Trans-thrombus blood pressure effects in abdominal aortic aneurysms.

How much and how the thrombus supports the wall of an abdominal aortic aneurysm (AAA) is unclear. While some previous studies have indicated that thrombus lacks the mechanical integrity to support much load compared with the aneurysm wall, others have shown that removing thrombus in computational AAA models drastically changes aneurysm wall stress. Histopathological studies have shown that thrombus properties vary through the thickness and it can be porous. The goal of this study is to explore the variations in thrombus properties, including the ability to isolate pressure from the aneurysm wall, incomplete attachment, and their effects on aneurysm wall stress, an important parameter in determining risk for rupture. An analytical model comprised of cylinders and two patient specific models were constructed with pressurization boundary conditions applied at the lumen or the thrombus/aneurysm wall interface (to simulate complete transmission of pressure through porous thrombus). Aneurysm wall stress was also calculated in the absence of thrombus. The potential importance of partial thrombus attachment was also analyzed. Pressurizing at either surface (lumen versus interface) made little difference to mean von Mises aneurysm wall stress values with thrombus completely attached (3.1% analytic, 1.2% patient specific) while thrombus presence reduced mean von Mises stress considerably (79% analytic, 40-46% patient specific) in comparison to models without it. Peak von Mises stresses were similarly influenced with pressurization surface differing slightly (3.1% analytic, 1.4% patient specific) and reductions in stress by thrombus presence (80% analytic, 28-37% patient specific). The case of partial thrombus attachment was investigated using a cylindrical model in which there was no attachment between the thrombus and aneurysm wall in a small area (10 deg). Applying pressure at the lumen resulted in a similar stress field to fully attached thrombus, whereas applying pressure at the interface resulted in a 42% increase in peak aneurysm wall stress. Taken together, these results show that the thrombus can have a wall stress reducing role even if it does not shield the aneurysm wall from direct pressurization--as long as the thrombus is fully attached to the aneurysm wall. Furthermore, the potential for porous thrombus to transmit pressure to the interface can result in a considerable increase in aneurysm wall stress in cases of partial attachment. In the search for models capable of accurately assessing the risk for rupture, the nature of the thrombus and its attachment to the aneurysm wall must be carefully assessed.

Effects of stent design and atherosclerotic plaque composition on arterial wall biomechanics.

PURPOSE: To examine the solid mechanical effects of varying stent design and atherosclerotic plaque stiffness on the biomechanical environment induced in a diseased artery wall model. METHODS: Computational modeling techniques were employed to investigate the final radius of the lumen and artery wall stresses after stent implantation. Two stent designs were studied (one stiff and one less stiff). The stenotic artery was modeled as an axisymmetrical diseased vessel with a 20% stenosis by diameter. The material properties of the diseased tissue in the artery models varied. Atherosclerotic plaques half as stiff (0.5x), of equal stiffness (1.0x), or twice as stiff (2.0x) as the artery wall were investigated. RESULTS: Final lumen radius was dependent on stent design, and the stiffer stent deformed the artery to an approximately 10% greater radius than the more compliant design. Alternatively, circumferential stress levels were dependent on both stent design and plaque material properties. Overall, the stiffer stent subjected the artery wall to much higher stress values than the more compliant design, with differences in peak values of 0.50, 0.31, and 0.09 MPa for the 2.0x, 1.0x, and 0.5x stiff plaques, respectively. CONCLUSION: Evidence suggests that a judicious choice of stent design can minimize stress while maintaining a patent lumen in stenotic arteries. If confronted with a rigid, calcified plaque, stent design is more important, as design differences can impose dramatically different stress fields, while still providing arterial patency. Alternatively, stent design is not as much of an issue when treating a soft, lipid-laden plaque, as stress fields do not vary significantly among stent designs.

Mechanical modeling of stents deployed in tapered arteries.

The biomechanical interaction of stents and the arteries into which they are deployed is a potentially important consideration for long-term success. Adverse arterial reactions to excessive stress and the resulting damage have been linked to the development of restenosis. Complex geometric features often encountered in these procedures can confound treatment. In some cases, it is desirable to deploy a stent across a region in which the diameter decreases significantly over the length of the stent. This study aimed to assess the final arterial diameter and circumferential stress in tapered arteries into which two different stents were deployed (one stiff and one less stiff). The artery wall was assumed to be made of a strain stiffening material subjected to large deformations, with a 10% decrease in diameter over the length of the stent. A commercially available finite element code was employed to solve the contact problem between the two elastic bodies. The stiffer stent dominated over arterial taper, resulting in a nearly constant final diameter along the length of the stent, and very high stresses, particularly at the distal end. The less stiff stent followed more closely the tapered contour of the artery, resulting in lower artery wall stresses. More compliant stents should be considered for tapered artery applications, perhaps even to the exclusion of tapered stents.

Stented artery biomechanics and device design optimization.

The deployment of a vascular stent aims to increase lumen diameter for the restoration of blood flow, but the accompanied alterations in the mechanical environment possibly affect the long-term patency of these devices. The primary aim of this investigation was to develop an algorithm to optimize stent design, allowing for consideration of competing solid mechanical concerns (wall stress, lumen gain, and cyclic deflection). Finite element modeling (FEM) was used to estimate artery wall stress and systolic/diastolic geometries, from which single parameter outputs were derived expressing stress, lumen gain, and cyclic artery wall deflection. An optimization scheme was developed using Lagrangian interpolation elements that sought to minimize the sum of these outputs, with weighting coefficients. Varying the weighting coefficients results in stent designs that prioritize one output over another. The accuracy of the algorithm was confirmed by evaluating the resulting outputs of the optimized geometries using FEM. The capacity of the optimization algorithm to identify optimal geometries and their resulting mechanical measures was retained over a wide range of weighting coefficients. The variety of stent designs identified provides general guidelines that have potential clinical use (i.e., lesion-specific stenting).

Effects of stent design parameters on normal artery wall mechanics.

A stent is a device designed to restore flow through constricted arteries. These tubular scaffold devices are delivered to the afflicted region and deployed using minimally invasive techniques. Stents must have sufficient radial strength to prop the diseased artery open. The presence of a stent can subject the artery to abnormally high stresses that can trigger adverse biologic responses culminating in restenosis. The primary aim of this investigation was to investigate the effects of varying stent "design parameters" on the stress field induced in the normal artery wall and the radial displacement achieved by the stent. The generic stent models were designed to represent a sample of the attributes incorporated in present commercially available stents. Each stent was deployed in a homogeneous, nonlinear hyperelastic artery model and evaluated using commercially available finite element analysis software. Of the designs investigated herein, those employing large axial strut spacing, blunted corners, and higher amplitudes in the ring segments induced high circumferential stresses over smaller areas of the artery's inner surface than all other configurations. Axial strut spacing was the dominant parameter in this study, i.e., all designs employing a small stent strut spacing induced higher stresses over larger areas than designs employing the large strut spacing. Increasing either radius of curvature or strut amplitude generally resulted in smaller areas exposed to high stresses. At larger strut spacing, sensitivity to radius of curvature was increased in comparison to the small strut spacing. With the larger strut spacing designs, the effects of varying amplitude could be offset by varying the radius of curvature and vice versa. The range of minimum radial displacements from the unstented diastolic radius observed among all designs was less than 90 microm. Evidence presented herein suggests that stent designs incorporating large axial strut spacing, blunted corners at bends, and higher amplitudes exposed smaller regions of the artery to high stresses, while maintaining a radial displacement that should be sufficient to restore adequate flow.