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1.
Proc Natl Acad Sci U S A ; 118(27)2021 07 06.
Artigo em Inglês | MEDLINE | ID: mdl-34183402

RESUMO

Negative drag coefficients are normally associated with a vessel outfitted with a sail to extract energy from the wind and propel the vehicle forward. Therefore, the notion of a heavy vehicle, that is, a semi truck, that generates negative aerodynamic drag without a sail or any external appendages may seem implausible, especially given the fact that these vehicles have some of the largest drag coefficients on the road today. However, using both wind tunnel measurements and computational fluid dynamics simulations, we demonstrate aerodynamically integrated vehicle shapes that generate negative body-axis drag in a crosswind as a result of large negative frontal pressures that effectively "pull" the vehicle forward against the wind, much like a sailboat. While negative body-axis drag exists only for wind yaw angles above a certain analytical threshold, the negative frontal pressures exist at smaller yaw angles and subsequently produce body-axis drag coefficients that are significantly less than those of modern heavy vehicles. The application of this aerodynamic phenomenon to the heavy vehicle industry would produce sizable reductions in petroleum use throughout the United States.

2.
Sci Adv ; 6(47)2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-33208366

RESUMO

We demonstrate an additive manufacturing approach to produce gradient refractive index glass optics. Using direct ink writing with an active inline micromixer, we three-dimensionally print multimaterial green bodies with compositional gradients, consisting primarily of silica nanoparticles and varying concentrations of titania as the index-modifying dopant. The green bodies are then consolidated into glass and polished, resulting in optics with tailored spatial profiles of the refractive index. We show that this approach can be used to achieve a variety of conventional and unconventional optical functions in a flat glass component with no surface curvature.

3.
Biofabrication ; 13(1)2020 10 16.
Artigo em Inglês | MEDLINE | ID: mdl-32977323

RESUMO

Various types of embolization devices have been developed for the treatment of cerebral aneurysms. However, it is challenging to properly evaluate device performance and train medical personnel for device deployment without the aid of functionally relevant models. Currentin vitroaneurysm models suffer from a lack of key functional and morphological features of brain vasculature that limit their applicability for these purposes. These features include the physiologically relevant mechanical properties and the dynamic cellular environment of blood vessels subjected to constant fluid flow. Herein, we developed three-dimensionally (3D) printed aneurysm-bearing vascularized tissue structures using gelatin-fibrin hydrogel of which the inner vessel walls were seeded with human cerebral microvascular endothelial cells (hCMECs). The hCMECs readily exhibited cellular attachment, spreading, and confluency all around the vessel walls, including the aneurysm walls. Additionally, thein vitroplatform was directly amenable to flow measurements via particle image velocimetry, enabling the direct assessment of the vascular flow dynamics for comparison to a 3D computational fluid dynamics model. Detachable coils were delivered into the printed aneurysm sac through the vessel using a microcatheter and static blood plasma clotting was monitored inside the aneurysm sac and around the coils. This biomimeticin vitroaneurysm model is a promising method for examining the biocompatibility and hemostatic efficiency of embolization devices and for providing hemodynamic information which would aid in predicting aneurysm rupture or healing response after treatment.


Assuntos
Bioimpressão , Embolização Terapêutica , Aneurisma Intracraniano , Prótese Vascular , Células Endoteliais , Humanos , Aneurisma Intracraniano/terapia
4.
Med Eng Phys ; 75: 65-71, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31672456

RESUMO

To prevent aneurysmal rupture, intracranial aneurysms are often treated with endovascular metal coils that fill the aneurysm sac and stimulate thrombus formation, thereby isolating the aneurysm from the arterial flow. Despite its widespread use, this method can result in suboptimal outcomes leading to aneurysm recurrence. Recently, shape memory polymer foam has been proposed as an alternative aneurysm filler. In this work, a computational thrombus model is used to predict the clotting response within idealized 2D aneurysms virtually treated with foam. The results are compared to previously reported clot formation predictions in identical 2D aneurysm geometries filled with simplified endovascular metal coil shapes. Each of the foam-filled aneurysms reached at least 94% thrombus occlusion regardless of foam pore size or orientation, whereas the final thrombus occlusion within the coil-filled aneurysms varied from 80.8 to 92.2% with many of the cases leaving large areas in the aneurysm neck unfilled. Based on the simulations presented here, shape memory polymer foams may be able to produce more predictable, uniform, and complete clotting results than bare metal coils, independent of foam geometry or orientation.


Assuntos
Aneurisma/complicações , Simulação por Computador , Polímeros/farmacologia , Trombose/complicações , Trombose/prevenção & controle , Polímeros/química
5.
Biomech Model Mechanobiol ; 17(6): 1821-1838, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30074100

RESUMO

Cardiovascular implantable devices alter the biofluid dynamics and biochemistry of the blood in which they are placed. These perturbations can lead to thrombus formation which may or may not be desired, depending on the application. In this work, a computational model is developed that couples biofluid dynamics and biochemistry to predict the clotting response of blood to such devices. The model consists of 28 advection-diffusion-reaction partial differential equations to track proteins in the blood involved in clotting and utilizes boundary flux terms to model the initiation of the intrinsic clotting pathway at thrombogenic device surfaces. We use this model to simulate the transient clot growth within a 2D idealized bifurcation aneurysm filled with various distributions of bare metal coils with similar packing densities. The clot model predicts initial clot formation to occur in areas along coil surfaces where flow is minimal and where time-averaged shear rates are the smallest. Among the six coil-filled aneurysm cases simulated, maximum thrombus occlusion ranged between 80.8 and 92.2% of the post-treatment aneurysm volume and was achieved 325-450 s after treatment. With further refinement and validation, the computational clotting model will be a valuable engineering tool for evaluating and comparing the relative performance of cardiovascular implantable devices.


Assuntos
Procedimentos Endovasculares/instrumentação , Aneurisma Intracraniano/fisiopatologia , Aneurisma Intracraniano/cirurgia , Metais/química , Trombose/fisiopatologia , Algoritmos , Animais , Coagulação Sanguínea , Velocidade do Fluxo Sanguíneo , Simulação por Computador , Difusão , Humanos , Hidrodinâmica , Cinética , Modelos Cardiovasculares , Próteses e Implantes , Reprodutibilidade dos Testes , Tromboembolia
6.
Sci Rep ; 7: 43401, 2017 03 06.
Artigo em Inglês | MEDLINE | ID: mdl-28262669

RESUMO

Here we report the first example of a class of additively manufactured carbon fiber reinforced composite (AMCFRC) materials which have been achieved through the use of a latent thermal cured aromatic thermoset resin system, through an adaptation of direct ink writing (DIW) 3D-printing technology. We have developed a means of printing high performance thermoset carbon fiber composites, which allow the fiber component of a resin and carbon fiber fluid to be aligned in three dimensions via controlled micro-extrusion and subsequently cured into complex geometries. Characterization of our composite systems clearly show that we achieved a high order of fiber alignment within the composite microstructure, which in turn allows these materials to outperform equivalently filled randomly oriented carbon fiber and polymer composites. Furthermore, our AM carbon fiber composite systems exhibit highly orthotropic mechanical and electrical responses as a direct result of the alignment of carbon fiber bundles in the microscale which we predict will ultimately lead to the design of truly tailorable carbon fiber/polymer hybrid materials having locally programmable complex electrical, thermal and mechanical response.

7.
J Mech Behav Biomed Mater ; 40: 102-114, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-25222869

RESUMO

Predominantly closed-cell low density shape memory polymer (SMP) foam was recently reported to be an effective aneurysm filling device in a porcine model (Rodriguez et al., Journal of Biomedical Materials Research Part A 2013: (http://dx.doi.org/10.1002/jbm.a.34782)). Because healing involves blood clotting and cell migration throughout the foam volume, a more open-cell structure may further enhance the healing response. This research sought to develop a non-destructive reticulation process for this SMP foam to disrupt the membranes between pore cells. Non-destructive mechanical reticulation was achieved using a gravity-driven floating nitinol pin array coupled with vibratory agitation of the foam and supplemental chemical etching. Reticulation resulted in a reduced elastic modulus and increased permeability, but did not impede the shape memory behavior. Reticulated foams were capable of achieving rapid vascular occlusion in an in vivo porcine model.


Assuntos
Materiais Biocompatíveis/química , Materiais Biocompatíveis/farmacologia , Vasos Sanguíneos/efeitos dos fármacos , Teste de Materiais , Fenômenos Mecânicos , Polímeros/química , Polímeros/farmacologia , Ligas/química , Animais , Vasos Sanguíneos/citologia , Vasos Sanguíneos/fisiologia , Membrana Celular/efeitos dos fármacos , Hemostasia/efeitos dos fármacos , Permeabilidade , Suínos
8.
Biomed Eng Online ; 12: 103, 2013 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-24120254

RESUMO

BACKGROUND: Shape memory polymer (SMP) foams are being investigated as an alternative aneurysm treatment method to embolic coils. The goal of both techniques is the reduction of blood flow into the aneurysm and the subsequent formation of a stable thrombus, which prevents future aneurysm rupture. The purpose of this study is to experimentally determine the parameters, permeability and form factor, which are related to the flow resistance imposed by both media when subjected to a pressure gradient. METHODS: The porous media properties-permeability and form factor-of SMP foams and mock embolic coils (MECs) were measured with a pressure gradient method by means of an in vitro closed flow loop. We implemented the Forchheimer-Hazen-Dupuit-Darcy equation to calculate these properties. Mechanically-reticulated SMP foams were fabricated with average cell sizes of 0.7E-3 and 1.1E-3 m, while the MECs were arranged with volumetric packing densities of 11-28%. RESULTS: The permeability of the SMP foams was an order of magnitude lower than that of the MECs. The form factor differed by up to two orders of magnitude and was higher for the SMP foams in all cases. The maximum flow rate of all samples tested was within the inertial laminar flow regime, with Reynolds numbers ranging between 1 and 35. CONCLUSIONS: The SMP foams impose a greater resistance to fluid flow compared to MECs, which is a result of increased viscous and inertial losses. These results suggest that aneurysms treated with SMP foam will have flow conditions more favorable for blood stasis than those treated with embolic coils having packing densities ≤ 28%.


Assuntos
Procedimentos Endovasculares/instrumentação , Polímeros , Hidrodinâmica , Aneurisma Intracraniano/cirurgia , Permeabilidade , Porosidade
9.
IEEE Trans Biomed Eng ; 54(9): 1722-4, 2007 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-17867367

RESUMO

A deployable, shape memory polymer adapter is investigated for reducing the hemodynamic stress caused by dialysis needle flow impingement within an arteriovenous graft. Computational fluid dynamics simulations of dialysis sessions with and without the adapter demonstrate that the adapter provides a significant decrease in the wall shear stress. Preliminary in vitro flow visualization measurements are made within a graft model following delivery and actuation of a prototype shape memory polymer adapter. Both the simulations and the qualitative flow visualization measurements demonstrate that the adapter reduces the severity of the dialysis needle flow impingement on the vascular access graft.


Assuntos
Anastomose Cirúrgica/instrumentação , Prótese Vascular , Diálise/instrumentação , Agulhas , Polímeros/química , Materiais Biocompatíveis/química , Pressão Sanguínea , Diálise/métodos , Elasticidade , Desenho de Equipamento , Análise de Falha de Equipamento , Estresse Mecânico
10.
J Biomed Opt ; 12(3): 030504, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-17614707

RESUMO

Conventional embolization of cerebral aneurysms using detachable coils is time-consuming and often requires retreatment. These drawbacks have prompted the development of new methods of aneurysm occlusion. We present the fabrication and laser deployment of a shape memory (SMP) polymer expanding foam device. Data acquired in an in vitro basilar aneurysm model with and without flow showed successful treatment, with the flow rate affecting foam expansion and the temperature at the aneurysm wall.


Assuntos
Aneurisma/terapia , Embolização Terapêutica/instrumentação , Embolização Terapêutica/métodos , Lasers , Polímeros/química , Polímeros/uso terapêutico , Animais , Materiais Biocompatíveis/química , Materiais Biocompatíveis/efeitos da radiação , Materiais Biocompatíveis/uso terapêutico , Gases/química , Humanos , Teste de Materiais , Projetos Piloto , Polímeros/efeitos da radiação
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