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1.
J Mech Behav Biomed Mater ; 89: 150-161, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30286374

RESUMO

OBJECTIVES: This study aimed to develop a simple and efficient numerical modeling approach for characterizing strain and total strain energy in bone scaffolds implanted in patient-specific anatomical sites. MATERIALS AND METHODS: A simplified homogenization technique was developed to substitute a detailed scaffold model with the same size and equivalent orthotropic material properties. The effectiveness of the proposed modeling approach was compared with two other common homogenization methods based on periodic boundary conditions and the Hills-energy theorem. Moreover, experimental digital image correlation (DIC) measurements of full-field surface strain were conducted to validate the numerical results. RESULTS: The newly proposed simplified homogenization approach allowed for fairly accurate prediction of strain and total strain energy in tissue scaffolds implanted in a large femur mid-shaft bone defect subjected to a simulated in-vivo loading condition. The maximum discrepancy between the total strain energy obtained from the simplified homogenization approach and the one obtained from detailed porous scaffolds was 8.8%. Moreover, the proposed modeling technique could significantly reduce the computational cost (by about 300 times) required for simulating an in-vivo bone scaffolding scenario as the required degrees of freedom (DoF) was reduced from about 26 million for a detailed porous scaffold to only 90,000 for the homogenized solid counterpart in the analysis. CONCLUSIONS: The simplified homogenization approach has been validated by correlation with the experimental DIC measurements. It is fairly efficient and comparable with some other common homogenization techniques in terms of accuracy. The proposed method is implicating to different clinical applications, such as the optimal selection of patient-specific fixation plates and screw system.


Assuntos
Osso e Ossos/citologia , Análise de Elementos Finitos , Estresse Mecânico , Tecidos Suporte , Fenômenos Biomecânicos , Fêmur/citologia , Modelos Biológicos , Porosidade
2.
J Formos Med Assoc ; 117(7): 640-645, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29254683

RESUMO

Under the time-based criteria, patients with unknown onset stroke (UOS) are ineligible for reperfusion therapies. However, previous studies suggest that some patients with UOS may benefit from reperfusion. Several imaging modalities have been suggested to select patients for intervention, but the optimal imaging criteria are still controversial. Herein we present a series of four cases using 10-point CT-ASPECTS to support our decision of reperfusion therapy. We decided based on history, symptoms, and the 10-point CT-ASPECTS alone. Each patient's history suggested that the stroke just took place. All four patients had apparent clinical symptoms, with 10-point CT-ASPECTS. All of them had a reduction in their NIHSS after the reperfusion therapy. 10-point CT-ASPECTS could be used to support the presumption that the stroke just happens in patients with UOS. Further study is warranted to elucidate the value of CT-ASPECTS for UOS patients.


Assuntos
Isquemia Encefálica/terapia , Fibrinolíticos/uso terapêutico , Acidente Vascular Cerebral/diagnóstico por imagem , Acidente Vascular Cerebral/terapia , Ativador de Plasminogênio Tecidual/uso terapêutico , Idoso , Angiografia por Tomografia Computadorizada , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Índice de Gravidade de Doença , Trombectomia , Resultado do Tratamento
3.
Artigo em Inglês | MEDLINE | ID: mdl-26916052

RESUMO

Design of prosthetic implants to ensure rapid and stable osseointegration remains a significant challenge, and continuous efforts have been directed to new implant materials, structures and morphology. This paper aims to develop and characterise a porous titanium dental implant fabricated by metallic powder injection-moulding. The surface morphology of the specimens was first examined with a scanning electron microscope (SEM), followed by microscopic computerised tomography (µ-CT) scanning to capture its 3D microscopic features non-destructively. The nature of porosity and pore sizes were determined statistically. A homogenisation technique based on the Hills-energy theorem was adopted to evaluate its directional elastic moduli, and the conservation of mass theorem was employed to quantify the oxygen diffusivity for bio-transportation feature. This porous medium was found to have pore sizes varying from 50 to 400 µm and the average porosity of 46.90 ± 1.83%. The anisotropic principal elastic moduli were found fairly close to the upper range of cortical bone, and the directional diffusivities could potentially enable radial osseous tissue ingrowth and vascularisation. This porous titanium successfully reduces the elastic modulus mismatch between implant and bone for dental and orthopaedic applications, and provides improved capacity for transporting oxygen, nutrient and waste for pre-vascular network formation. Copyright © 2016 John Wiley & Sons, Ltd.


Assuntos
Implantes Dentários , Titânio , Microtomografia por Raio-X/métodos , Difusão , Módulo de Elasticidade , Humanos , Teste de Materiais , Microscopia Eletrônica de Varredura , Osseointegração , Oxigênio/metabolismo , Porosidade , Propriedades de Superfície
4.
Mater Sci Eng C Mater Biol Appl ; 33(6): 3146-52, 2013 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-23706194

RESUMO

Cuttlebone is a natural marine cellular material possessing the exceptional mechanical properties of high compressive strength, high porosity and high permeability. This combination of properties is exceedingly desirable in biomedical applications, such as bone tissue scaffolds. In light of recent studies, which converted raw cuttlebone into hydroxyapatite tissue scaffolds, the impact of morphological variations in the microstructure of this natural cellular material on the effective mechanical properties is explored in this paper. Two extensions of the finite element-based homogenization method are employed to account for deviations from the assumption of periodicity. Firstly, a representative volume element (RVE) of cuttlebone is systematically varied to reflect the large range of microstructural configurations possibly among different cuttlefish species. The homogenization results reveal the critical importance of pillar formation and aspect ratio (height/width of RVE) on the effective bulk and shear moduli of cuttlebone. Secondly, multi-cell analysis domains (or multiple RVE domains) permit the introduction of random variations across neighboring cells. Such random variations decrease the bulk modulus whilst displaying minimal impact on the shear modulus. Increasing the average size of random variations increases the effect on bulk modulus. Also, the results converge rapidly as the size of the analysis domain is increased, meaning that a relatively small multi-cell domain can provide a reasonable approximation of the effective properties for a given set of random variation parameters. These results have important implications for the proposed use of raw cuttlebone as an engineering material. They also highlight some potential for biomimetic design capabilities for materials inspired by the cuttlebone microstructure, which may be applicable in biomedical applications such as bone tissue scaffolds.


Assuntos
Materiais Biomiméticos/química , Osso e Ossos/química , Animais , Osso e Ossos/patologia , Decapodiformes/metabolismo , Durapatita/química , Análise de Elementos Finitos , Modelos Moleculares , Porosidade
5.
Nanotechnology ; 20(11): 115401, 2009 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-19420438

RESUMO

In quantum mechanics, a wavefunction contains two factors: the amplitude and the phase. Only when the probing beam is fully phase coherent, can complete information be retrieved from a particle beam based experiment. Here we use the electron beam field emitted from a noble-metal covered W(111) single-atom tip to image single-walled carbon nanotubes (SWNTs) in an electron point projection microscope (PPM). The interference fringes of an SWNT bundle exhibit a very high contrast and the fringe pattern extends throughout the entire beam width. This indicates good phase correlation at all points transverse to the propagation direction. Application of these sources can significantly improve the performance and expand the capabilities of current electron beam based techniques. New instrumentation based on the full spatial coherence may allow determination of the three-dimensional atomic structures of nonperiodic nanostructures and make many advanced experiments possible.

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