Patient-specific tissue engineered vascular graft for aortic arch reconstruction.

Objectives: The complexity of aortic arch reconstruction due to diverse 3-dimensional geometrical abnormalities is a major challenge. This study introduces 3-dimensional printed tissue-engineered vascular grafts, which can fit patient-specific dimensions, optimize hemodynamics, exhibit antithrombotic and anti-infective properties, and accommodate growth. Methods: We procured cardiac magnetic resonance imaging with 4-dimensional flow for native porcine anatomy (n = 10), from which we designed tissue-engineered vascular grafts for the distal aortic arch, 4 weeks before surgery. An optimal shape of the curved vascular graft was designed using computer-aided design informed by computational fluid dynamics analysis. Grafts were manufactured and implanted into the distal aortic arch of porcine models, and postoperative cardiac magnetic resonance imaging data were collected. Pre- and postimplant hemodynamic data and histology were analyzed. Results: Postoperative magnetic resonance imaging of all pigs with 1:1 ratio of polycaprolactone and poly-L-lactide-co-ε-caprolactone demonstrated no specific dilatation or stenosis of the graft, revealing a positive growth trend in the graft area from the day after surgery to 3 months later, with maintaining a similar shape. The peak wall shear stress of the polycaprolactone/poly-L-lactide-co-ε-caprolactone graft portion did not change significantly between the day after surgery and 3 months later. Immunohistochemistry showed endothelization and smooth muscle layer formation without calcification of the polycaprolactone/poly-L-lactide-co-ε-caprolactone graft. Conclusions: Our patient-specific polycaprolactone/poly-L-lactide-co-ε-caprolactone tissue-engineered vascular grafts demonstrated optimal anatomical fit maintaining ideal hemodynamics and neotissue formation in a porcine model. This study provides a proof of concept of patient-specific tissue-engineered vascular grafts for aortic arch reconstruction.

Faceted wrinkling by contracting a curved boundary.

Single-mode deformations of two-dimensional materials, such as the Miura-ori zig-zag fold, are important to the design of deployable structures because of their robustness; these usually require careful pre-patterning of the material. Here we show that inward contraction of a curved boundary produces a fine wrinkle pattern with a novel structure that suggests similar single-mode characteristics, but with minimal pre-patterning. Using finite-element representation of the contraction of a thin circular annular sheet, we show that these sheets wrinkle into a structure well approximated by an isometric structure composed of conical sectors and flat, triangular facets. Isometry favours the restriction of such deformations to a robust low-bending energy channel that avoids stretching. This class of buckling offers a novel way to manipulate sheet morphology via boundary forces.

Disturbed flow in the juxta-anastomotic area of an arteriovenous fistula correlates with endothelial loss, acute thrombus formation, and neointimal hyperplasia.

Clinical failure of arteriovenous neointimal hyperplasia (NIH) fistulae (AVF) is frequently due to juxta-anastomotic NIH (JANIH). Although the mouse AVF model recapitulates human AVF maturation, previous studies focused on the outflow vein distal to the anastomosis. We hypothesized that the juxta-anastomotic area (JAA) has increased NIH compared with the outflow vein. AVF was created in C57BL/6 mice without or with chronic kidney disease (CKD). Temporal and spatial changes of the JAA were examined using histology and immunofluorescence. Computational techniques were used to model the AVF. RNA-seq and bioinformatic analyses were performed to compare the JAA with the outflow vein. The jugular vein to carotid artery AVF model was created in Wistar rats. The neointima in the JAA shows increased volume compared with the outflow vein. Computational modeling shows an increased volume of disturbed flow at the JAA compared with the outflow vein. Endothelial cells are immediately lost from the wall contralateral to the fistula exit, followed by thrombus formation and JANIH. Gene Ontology (GO) enrichment analysis of the 1,862 differentially expressed genes (DEG) between the JANIH and the outflow vein identified 525 overexpressed genes. The rat jugular vein to carotid artery AVF showed changes similar to the mouse AVF. Disturbed flow through the JAA correlates with rapid endothelial cell loss, thrombus formation, and JANIH; late endothelialization of the JAA channel correlates with late AVF patency. Early thrombus formation in the JAA may influence the later development of JANIH.NEW & NOTEWORTHY Disturbed flow and focal endothelial cell loss in the juxta-anastomotic area of the mouse AVF colocalizes with acute thrombus formation followed by late neointimal hyperplasia. Differential flow patterns between the juxta-anastomotic area and the outflow vein correlate with differential expression of genes regulating coagulation, proliferation, collagen metabolism, and the immune response. The rat jugular vein to carotid artery AVF model shows changes similar to the mouse AVF model.

Social Determinants of Health Factors and Loss-To-Follow-Up in the Field of Vascular Surgery.

BACKGROUND: It is estimated that 22-57% of vascular patients are lost to follow-up (LTF) which is of concern as the Society of Vascular Surgery recommends annual patient follow-up. The purpose of this report was to identify social determinants of health factors (SDoH) and their relationship to LTF in vascular patients. METHODS: The methods employed were a systematic literature review of 29 empirical articles and a retrospective quality improvement report with 27 endovascular aortic repair (EVAR) and thoracic endovascular aortic repair (TEVAR) patients at the University of Chicago. RESULTS: The systematic literature review resulted in 2,931 articles which were reduced to 29 articles meeting the inclusion criteria. Demographic variables were more frequently cited than SDoH factors, but the most common were smoking, transportation, and socioeconomic status/insurance. Additionally, 176 EVAR and TEVAR patients were called resulting in 27 patients who completed a SDoH questionnaire. Twenty-six percent indicated they had missed at least 1 appointment with the top reasons being work or family responsibilities. Due to limited patient size no statistical analyses were performed, but frequencies of responses to SDoH questions were reported to augment the existing limited literature and guide future research into variables such as one's ability to pay for basics like food or mortgage. CONCLUSIONS: SDoH factors are important yet understudied aspects of endovascular repairs that require more research to understand their impact on vascular surgery follow-up rates and outcomes. Additional research is needed as lack of consideration of such factors may impact the generalizability of existing research and such knowledge may help in informing clinician treatment plans.

The geometric evolution of aortic dissections: Predicting surgical success using fluctuations in integrated Gaussian curvature.

Clinical imaging modalities are a mainstay of modern disease management, but the full utilization of imaging-based data remains elusive. Aortic disease is defined by anatomic scalars quantifying aortic size, even though aortic disease progression initiates complex shape changes. We present an imaging-based geometric descriptor, inspired by fundamental ideas from topology and soft-matter physics that captures dynamic shape evolution. The aorta is reduced to a two-dimensional mathematical surface in space whose geometry is fully characterized by the local principal curvatures. Disease causes deviation from the smooth bent cylindrical shape of normal aortas, leading to a family of highly heterogeneous surfaces of varying shapes and sizes. To deconvolute changes in shape from size, the shape is characterized using integrated Gaussian curvature or total curvature. The fluctuation in total curvature (δK) across aortic surfaces captures heterogeneous morphologic evolution by characterizing local shape changes. We discover that aortic morphology evolves with a power-law defined behavior with rapidly increasing δK forming the hallmark of aortic disease. Divergent δK is seen for highly diseased aortas indicative of impending topologic catastrophe or aortic rupture. We also show that aortic size (surface area or enclosed aortic volume) scales as a generalized cylinder for all shapes. Classification accuracy for predicting aortic disease state (normal, diseased with successful surgery, and diseased with failed surgical outcomes) is 92.8±1.7%. The analysis of δK can be applied on any three-dimensional geometric structure and thus may be extended to other clinical problems of characterizing disease through captured anatomic changes.

Ridge localization driven by wrinkle packets.

While buckling is a time independent phenomenon for filaments or films bonded to soft elastic substrates, time evolution plays an important role when the substrate is a viscous fluid. Here we show that buckling instabilities in fluid-structure interactions can be reduced to the analysis of a growth function that amplifies the initial noise characterizing experimental or numerical error. The convolution between a specific growth function and noise leads to natural imperfections that emerge in the form of wave packets with a large scale modulation that can transform into localized structures depending on nonlinear effects. Specifically, we provide an experimental example where these wave packets are amplified into ridges for sufficiently low compression rates or are diluted into wrinkles for high compression rates.

To Operate or Not? Balancing Advanced Imaging, Machine Learning, and the Doctor-Patient Relationship in Complex Clinical Decision Making.

Advances in high-resolution, cross-sectional imaging have changed the practice of medicine. These innovations have clearly benefited patient care yet have also led to a decreased dependence on the art of medicine, with its emphasis on obtaining a thoughtful history and thorough physical examination to elicit the same diagnosis that imaging provides. What remains to be determined is how physicians can balance these technological advances with their own ability to use clinical experience and judgment. This can be seen not only with the use of high-level imaging but also with the increasing use of machine-learning models throughout medicine. The authors contend that these should be seen not as a replacement for the physician, but as another tool in their arsenal in determining management decisions. These issues are salient for surgeons, who, given the serious undertaking required to operate on a person, must develop trust-based relationship with their patients. Navigating this new field brings with it several ethical conundrums that must be addressed, with the final goal being to provide optimal patient care without sacrificing the human element involved, from either the physician or the patient. The authors examine these less-than-simple challenges, which will continue to develop as physicians use the increasing amount of machine-based knowledge available to them.

Topographic de-adhesion in the viscoelastic limit.

The superiority of many natural surfaces at resisting soft, sticky biofoulants have inspired the integration of dynamic topography with mechanical instability to promote self-cleaning artificial surfaces. The physics behind this novel mechanism is currently limited to elastic biofoulants where surface energy, bending stiffness and topographical wavelength are key factors. However, the viscoelastic nature of many biofoulants causes a complex interplay between these factors with time-dependent characteristics such as material softening and loading rate. Here, we enrich the current elastic theory of topographic de-adhesion using analytical and finite-element models to elucidate the nonlinear, time-dependent interaction of three physical, dimensionless parameters: biofoulant's stiffness reduction, the product of relaxation time and loading rate, and the critical strain for short-term elastic de-adhesion. Theoretical predictions, in good agreement with numerical simulations, provide insight into tuning these control parameters to optimize surface renewal via topographic de-adhesion in the viscoelastic regime.

Usage of a percutaneous closure device to repair an iatrogenic subclavian artery injury.

OBJECTIVES: Inadvertent subclavian artery cannulation during attempted subclavian central venous access is more likely to occur during rushed trauma resuscitations when anatomic landmarks are used for placement. Traditional supraclavicular and infraclavicular approaches for direct repair of the resultant arteriotomy are painful, morbid procedures that should be replaced with more minimally invasive techniques. METHODS: This case report describes the usage of a percutaneous suture-mediated device (Perclose Proglide, Abbott Laboratories) to repair an iatrogenic subclavian artery arteriotomy. RESULTS: Two patients had their injuries successfully repaired using a percutaneous closure device. CONCLUSIONS: The use of a percutaneous closure device to repair iatrogenic subclavian artery injuries is a safe and effective method of repair that precludes a more invasive exposure and repair.

Contemporary Unplanned Readmission Trends Following Management of Type B Aortic Dissection.

Purpose: Large studies have demonstrated improved survival outcomes with thoracic endovascular aortic repair (TEVAR) at two and five years compared to medical therapy; however, early TEVAR for acute type B aortic dissection (TBAD) remains controversial. We aimed to evaluate trends and clinical predictors of hospital readmissions in patients undergoing medical management and TEVAR for acute TBADs. Materials and Methods: The Nationwide Readmissions Database was queried for all 30-day and 90-day index readmissions (30D-IR and 90D-IR, respectively) after a diagnosis of a TBAD from January 2012 to September 2015. Data on readmission diagnosis, patient demographics, and hospital characteristics were collected from readmitted patients and analyzed. Multivariable logistic regression models were used to identify the predictors of readmission after TEVAR or medical medical management of TBAD. Results: We identified 53,117 patients with acute TBAD. Medical management was the initial treatment modality in 46,985 (88.4%) patients, while 6,132 (11.5%) underwent TEVAR. Factors including older patient age, lower household income, severity of comorbidities, initial hospital length of stay, and urgent procedure demonstrated an increased likelihood of experiencing 30D-IR and 90D-IR (P<0.05). The rate of unplanned readmission for patients undergoing medical management remained stable (11.3% vs. 10.0% for 30D-IR; 19.1% vs. 15.5% for 90D-IR). Reasons for unplanned readmission in the TEVAR cohort were largely related to technical complications. There was no significant difference in readmission costs between medical management and TEVAR. Conclusion: Number of unplanned readmissions in the TEVAR arm decreased significantly over time, whereas the number of readmissions for medical management remained stable.

Computational analysis of endovascular aortic repair proximal seal zone preservation with endoanchors: A case study in cylindrical neck anatomy.

BACKGROUND: Endovascular aortic repair is the common approach for abdominal aortic aneurysms, but endoleaks remain a significant problem with long-term success. Endoanchors have been found to reduce the incidence of type 1A endoleaks and can treat intraoperative type 1a endoleaks. However, little is known about the optimal number and position of endoanchors to achieve the best outcome. METHODS: Using image segmentation and a computational model derived from a reconstructed native patient abdominal aortic aneurysm geometry, the stability of the proximal seal zone was examined through finite element analysis in Abaqus (Dassault Systèmes, Providence, RI). The biomechanical parameter of contact area was compared for varying numbers (0, 2, 4, 8) and positions (proximal, medial, distal) of endoanchors under different adhesion strengths and physiologic pressure conditions. RESULTS: In every simulation, an increase in adhesion strength is associated with maintenance of proximal seal. For biologically plausible adhesion strengths, under conditions of normal blood pressure (120 mm Hg), the addition of any number of endoanchors increases the stability of the endograft-wall interface at the proximal seal zone by approximately 10% compared with no endoanchors. At hypertensive pressures (200 mm Hg), endoanchors increase the stability of the interface by 20% to 60% compared with no endoanchors. The positioning of endoanchors within the proximal seal zone has a greater effect at hypertensive pressures, with proximal positioning increasing stability by 15% compared with medial and distal positioning and 30% compared with no endoanchors. CONCLUSIONS: Endoanchors improve fixation within the proximal seal zone particularly under conditions of high peak systolic pressure. Seal zone stabilization provides a mechanism through which endoanchor addition may translate into lower rates of type 1a endoleaks for patients.

Multiscale geometry and mechanics of lipid monolayer collapse.

Langmuir monolayers at gas/liquid interfaces provide a rich framework to investigate the interplay between multiscale geometry and mechanics. Monolayer collapse is investigated at a topological and geometric level by building a scale space M from experimental imaging data. We present a general lipid monolayer collapse phase diagram, which shows that wrinkling, folding, crumpling, shear banding, and vesiculation are a continuous set of mechanical states that can be approached by either tuning monolayer composition or temperature. The origin of the different mechanical states can be understood by investigating the monolayer geometry at two scales: fluorescent vs atomic force microscopy imaging. We show that an interesting switch in continuity occurs in passing between the two scales, CAFM∈MAFM≠CFM∈M. Studying the difference between monolayers that fold vs shear band, we show that shear banding is correlated to the persistence of a multi-length scale microstructure within the monolayer at all surface pressures. A detailed analytical geometric formalism to describe this microstructure is developed using the theory of structured deformations. Lastly, we provide the first ever finite element simulation of lipid monolayer collapse utilizing a direct mapping from the experimental image space M into a simulation domain P. We show that elastic dissipation in the form of bielasticity is a necessary and sufficient condition to capture loss of in-plane stability and shear banding.

Gaussian Surface Curvature Mapping Indicating High Risk Type B Thoracic Aortic Dissections.

BACKGROUND: Identifying fragile aortas that are more likely to lead to adverse clinical outcomes would provide surgeons with a better sense of how to balance the risks of surgical versus medical management in patients with type B dissections. We examine the progression of a type B dissection into a type A dissection in a patient and analyze changes in the Gaussian surface curvature distribution, as well as the response of the stress distribution at the lesser curve in response to pressurization. We hypothesize that examining the Gaussian curvature will provide us with a link between aortic surface geometry and the stress distribution, which is crucial to understanding the process driving aortic dissection. METHODS: Computed tomography scans of a patient before and after the type A dissection are obtained. These are segmented in Simpleware ScanIP. Centerline curvatures are calculated on segmented models in ScanIP. Models are then pressurized in the finite element analysis software Abaqus. The Gaussian curvature is calculated by exporting segmentations into the computational program Matlab and applying a modified previously published algorithm. RESULTS: The centerlines generated in ScanIP fail to capture the change in the acuity of the lesser curve before and after the type A dissection. Instead, Gaussian curvature analysis shows that the curvature distribution before the type A dissection is much wider compared with the distribution after the type A dissection. In addition, analyzing the stress distribution in response to pressurization reveals that before the type A dissection there is a large divergence in the principal stress vectors at the lesser curve but this transitions to a more uniform hoop stress after the type A dissection. CONCLUSIONS: Our analysis demonstrates that Gaussian surface curvature analysis captures changes in aortic geometry that are otherwise silent in centerline curvature analysis. Here, we show that as the aorta develops a type A dissection it is able to more smoothly handle the hoop stress at the lesser curve compared with the stress focusing seen in the before type A geometry. We propose that the geometric focusing before type A creates a higher energy stress state, which is relaxed on retrograde dissection. Thus, Gaussian curvature analysis may provide a window to capture underlying geometric instability in type B dissections.

Diagnostic Colour Duplex Ultrasound for Type IIIb Endoleak.

INTRODUCTION: This report presents the treatment of an aortic endovascular aneurysm repair (EVAR) device failure, focusing on the use of colour duplex ultrasound (CDUS) to diagnose and confirm effective treatment of a type IIIb endoleak. REPORT: An 89 year old man with a history of EVAR was transferred to the authors' centre with complaints of abdominal pain and a pressure sensation behind the umbilicus. A previously stable 11 cm aneurysm sac was visualised on computed tomography angiography in addition to a newly suspected type IIIb endoleak, which was confirmed via CDUS. He underwent successful endovascular repair with a stent across the limb defect. The patient was discharged uneventfully and was followed for surveillance. DISCUSSION: Type IIIb endoleak is an underreported complication after EVAR. CDUS of type IIIb endoleak aided in localisation and characterisation of the graft failure, and confirmed successful endovascular treatment of the endoleak defect in the side limb. Locating the point of graft failure using CDUS preceding endovascular repair of type IIIb endoleaks guides interventions and repair outcomes. It is a rare opportunity to report a case of acute type IIIb endoleak with CDUS that definitively localised an endograft defect.

Dynamic Luminal Topography: A Potential Strategy to Prevent Vascular Graft Thrombosis.

AIM: Biologic interfaces play important roles in tissue function. The vascular lumen-blood interface represents a surface where dynamic interactions between the endothelium and circulating blood cells are critical in preventing thrombosis. The arterial lumen possesses a uniform wrinkled surface determined by the underlying internal elastic lamina. The function of this structure is not known, but computational analyses of artificial surfaces with dynamic topography, oscillating between smooth and wrinkled configurations, support the ability of this surface structure to shed adherent material (Genzer and Groenewold, 2006; Bixler and Bhushan, 2012; Li et al., 2014). We hypothesized that incorporating a luminal surface capable of cyclical wrinkling/flattening during the cardiac cycle into vascular graft technology may represent a novel mechanism of resisting platelet adhesion and thrombosis. METHODS AND RESULTS: Bilayer silicone grafts possessing luminal corrugations that cyclically wrinkle and flatten during pulsatile flow were fabricated based on material strain mismatch. When placed into a pulsatile flow circuit with activated platelets, these grafts exhibited significantly reduced platelet deposition compared to grafts with smooth luminal surfaces. Constrained wrinkled grafts with static topography during pulsatile flow were more susceptible to platelet accumulation than dynamic wrinkled grafts and behaved similar to the smooth grafts under pulsatile flow. Wrinkled grafts under continuous flow conditions also exhibited marked increases in platelet accumulation. CONCLUSION: These findings provide evidence that grafts with dynamic luminal topography resist platelet accumulation and support the application of this structure in vascular graft technology to improve the performance of prosthetic grafts. They also suggest that this corrugated structure in arteries may represent an inherent, self-cleaning mechanism in the vasculature.

Wrinkling instabilities for biologically relevant fiber-reinforced composite materials with a case study of Neo-Hookean/Ogden-Gasser-Holzapfel bilayer.

Wrinkling is a ubiquitous surface phenomenon in many biological tissues and is believed to play an important role in arterial health. As arteries are highly nonlinear, anisotropic, multilayered composite systems, it is necessary to investigate wrinkling incorporating these material characteristics. Several studies have examined surface wrinkling mechanisms with nonlinear isotropic material relationships. Nevertheless, wrinkling associated with anisotropic constitutive models such as Ogden-Gasser-Holzapfel (OGH), which is suitable for soft biological tissues, and in particular arteries, still requires investigation. Here, the effects of OGH parameters such as fibers' orientation, stiffness, and dispersion on the onset of wrinkling, wrinkle wavelength and amplitude are elucidated through analysis of a bilayer system composed of a thin, stiff neo-Hookean membrane and a soft OGH substrate subjected to compression. Critical contractile strain at which wrinkles occur is predicted using both finite element analysis and analytical linear perturbation approach. Results suggest that besides stiffness mismatch, anisotropic features associated with fiber stiffness and distribution might be used in natural layered systems to adjust wrinkling and subsequent folding behaviors. Further analysis of a bilayer system with fibers in the (x-y) plane subjected to compression in the x direction shows a complex dependence of wrinkling strain and wavelength on fiber angle, stiffness, and dispersion. This behavior is captured by an approximation utilizing the linearized anisotropic properties derived from OGH model. Such understanding of wrinkling in this artery wall-like system will help identify the role of wrinkling mechanisms in biological artery in addition to the design of its synthetic counterparts.

Trends and Determinants of Readmissions to Another Facility After Endovascular Aortic Repair.

BACKGROUND: Endovascular aneurysm repair (EVAR) has become the procedure of choice for abdominal aortic aneurysms (AAAs). It has been previously reported that significant percentage of patients were being readmitted to another hospital after complications after EVAR. We aimed to evaluate trends and clinical predictors of readmission to another (secondary) hospital after index EVAR. METHODS: The Nationwide Readmissions Database (NRD) was queried for all 30-day readmissions after an index EVAR procedure from 2012 to 2014. Readmission diagnosis, patient demographics, and hospital characteristics were collected regarding those patients who were admitted to another care facility after EVAR. Univariate analysis and multivariable logistic regression model was used to identify predictors for readmission to a different hospital. RESULTS: Between 2012 and 2014, 3,215 patients were readmitted to another hospital within 30 days of their index EVAR constituting 22.8% of a total 14,073 readmissions during that time period. Comorbidities of patients examined were similar between those patients readmitted to the primary hospital versus the secondary hospital except for the incidence of hypothyroidism (P < 0.001). Higher proportion of patients admitted to a different hospital had Medicare and Medicaid insurance (P < 0.047). In addition, higher proportion of patients readmitted to secondary hospitals had EVAR performed at smaller (<100 beds) hospitals (P = 0.002). Univariate analysis demonstrated that patients readmitted to another hospital were slightly older and had higher index length of stay and higher index hospital cost after EVAR (P < 0.001). In a multivariate model, index EVAR at a small hospital (odds ratio [OR]: 1.7) and the diagnosis of hypothyroidism (OR: 1.54) were independent determinants of readmission to another care facility. CONCLUSIONS: Significant proportion of patients is being readmitted elsewhere after elective EVAR adding complexity to the determination of appropriate healthcare resource allocation. In our study, index EVAR at a small hospital (<100 beds) and pre-existing medical comorbidity of hypothyroidism were significant predictors for unanticipated readmission to a different hospital.

Dynamic seal at the aortic neck-endograft interface studied using a novel method of cohesive zone modeling.

BACKGROUND: Endovascular aortic stent graft technology radically altered aortic aneurysm repair from a maximally invasive procedure to a minimally invasive approach. Whereas the overall principle of the repair remained the same, the surgeon ceded control of the proximal seal when suturing was eliminated. In endovascular aneurysm repair (EVAR), no longer does the surgeon control the precise placement of mechanical fasteners (sutures) between graft and tissue; rather, the graft is kept in place by creation of a seal zone that often lacks any mechanical fastening. The kinematic coupling condition is replaced by contact mechanics between the outer graft surface and the aorta. METHODS: We develop a novel computational methodology to fully model and characterize the aorta-endograft seal zone within a fully integrated aorta-EVAR model. The aorta, endograft, and intraluminal thrombus are modeled by standard finite element analysis in the limit of elastic response under pressure loading conditions. The seal zone in our simulations is fully dynamic and modeled using the cohesive zone method. Our methodology allows full separation of the aorta and endograft, simulating loss of seal and endoleak. RESULTS: Using patient-specific geometry, we show that our approach is capable of predicting the location of rupture in an index patient who presented with a ruptured juxtarenal aneurysm. Applying our novel cohesive zone method analysis to the post-EVAR geometry, we studied the stability of the endograft under several seal zone strengths correlating to very weak, standard, and very strong seal. Loss of seal is shown to correlate to the propagation of an elastic front in the aortic neck. We propose that aortic neck dilation, which develops from graft deployment and pressurization, provides an energy release mechanism that drives seal zone failure: the elasto-adhesive seal model. CONCLUSIONS: We develop the first ever fully integrated computational model of aorta-endograft seal. Our elasto-adhesive seal model provides the first biomechanical model to evaluate seal loss. We hope that our method will provide a rich tool set with which to study the vexing problems of type I endoleak and help guide the development of technologies to optimize seal.

Active wrinkles to drive self-cleaning: A strategy for anti-thrombotic surfaces for vascular grafts.

The inner surfaces of arteries and veins are naturally anti-thrombogenic, whereas synthetic materials placed in blood contact commonly experience thrombotic deposition that can lead to device failure or clinical complications. Presented here is a bioinspired strategy for self-cleaning anti-thrombotic surfaces using actuating surface topography. As a first test, wrinkled polydimethylsiloxane planar surfaces are constructed that can repeatedly transition between smooth and wrinkled states. When placed in contact with blood, these surfaces display markedly less platelet deposition than control samples. Second, for the specific application of prosthetic vascular grafts, the potential of using pulse pressure, i.e. the continual variation of blood pressure between systole and diastole, to drive topographic actuation was investigated. Soft cylindrical tubes with a luminal surface that transitioned between smooth and wrinkled states were constructed. Upon exposure to blood under continual pressure pulsation, these cylindrical tubes also showed reduced platelet deposition versus control samples under the same fluctuating pressure conditions. In both planar and cylindrical cases, significant reductions in thrombotic deposition were observed, even when the wrinkles had wavelengths of several tens of µm, far larger than individual platelets. We speculate that the observed thrombo-resistance behavior is attributable to a biofilm delamination process in which the bending energy within the biofilm overcomes interfacial adhesion. This novel strategy to reduce thrombotic deposition may be applicable to several types of medical devices placed into the circulatory system, particularly vascular grafts.