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1.
Wien Med Wochenschr ; 161(19-20): 493-502, 2011 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-21792522

RESUMO

Composite materials based on a polyamide fabric (aramid) and a polydymethylsiloxane (PDMS) matrix were designed for application in bone surgery. In order to increase the bioactivity, 2, 5, 10, 15, 20, and 25 vol.% of nano/micro hydroxyapatite (HA) and tricalcium phosphate (TCP) were added. We studied the effect of the additives on the biocompatibility of the composite. It appears that nano additives have a more favorable effect on mechanical properties than microparticles. 15 vol.% of nano hydroxyapatite additive is an optimum amount for final application of the composites as substitutes for bone tissue: in this case both the mechanical properties and the biological properties are optimized without distinct changes in the inner structure of the composite.


Assuntos
Substitutos Ósseos/química , Substitutos Ósseos/normas , Osso e Ossos/cirurgia , Fosfatos de Cálcio , Dimetilpolisiloxanos , Durapatita , Teste de Materiais/métodos , Nylons , Polímeros , Animais , Apatitas , Elasticidade , Humanos , Microscopia Eletrônica de Varredura , Microtecnologia , Nanoestruturas , Osseointegração/fisiologia , Plasma , Coelhos , Software , Propriedades de Superfície
2.
Med Hypotheses ; 60(6): 936-7, 2003 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-12699729

RESUMO

Hypothesis of regulation of proteosynthetic activity of chondrocytes is suggested. A deformation of the cartilage caused by contact hip joint stress and consequent deformation of the chondrocytes are considered as main factors that could influence the metabolism of the cartilage.


Assuntos
Adaptação Fisiológica/fisiologia , Cartilagem Articular/fisiologia , Condrócitos/fisiologia , Articulação do Quadril/fisiologia , Homeostase/fisiologia , Mecanotransdução Celular/fisiologia , Suporte de Carga/fisiologia , Animais , Humanos , Modelos Biológicos , Estresse Mecânico
3.
Med Eng Phys ; 25(5): 379-85, 2003 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-12711235

RESUMO

The stress gradient index (G(p)) is introduced for the assessment of dysplasia in human hip joint. The absolute value of G(p) is equal to the magnitude of the gradient of the contact stress at the lateral acetabular rim. The parameter G(p) normalized with respect to the body weight (W(B)) is determined from the standard anteroposterior radiographs of adult human hips and pelvises using the mathematical model. The average value of G(p)/W(B) was determined for the group of dysplastic hips and for the group of normal hips. In the group of normal hips the average value of G(p)/W(B) is smaller (-0.445x10(5) m(-3)) than in the group of dysplastic hips (+1.481x10(5) m(-3)). The difference is statistically significant P<0.001. The average value of G(p)/W(B) changes its sign at the value of the centre-edge angle theta(CE) approximately 20( composite function ) which is usually considered as the boundary value of theta(CE) (lower limit) for the normal hips. Accordingly we suggest a new definition for the hip dysplasia with respect to the size and sign of the normalized stress gradient index G(p)/W(B). The hips with positive G(p)/W(B) are considered to be dysplastic while the hips with negative G(p)/W(B) are considered to be normal. The statistically significant correlation between the value of the Harris hip score, used in the clinical assessment of the hip dysplasia, and the normalized stress gradient index was found.


Assuntos
Luxação Congênita de Quadril/diagnóstico por imagem , Luxação Congênita de Quadril/fisiopatologia , Modelos Biológicos , Peso Corporal , Simulação por Computador , Feminino , Fricção , Articulação do Quadril/diagnóstico por imagem , Articulação do Quadril/fisiopatologia , Humanos , Masculino , Radiografia , Valores de Referência , Estresse Mecânico , Suporte de Carga
4.
Biomed Mater Eng ; 12(2): 121-34, 2002.
Artigo em Inglês | MEDLINE | ID: mdl-12122236

RESUMO

An analytical model has been used to simulate the effects of tissue aging on residual strain, constitutive relations and stiffness parameter in the main right and left (ramus circumflexus) human coronary arteries, based on experimental data. The experimental opening angle theta scatters considerably with age. The optimum angle theta(op) approximately equals 70 degrees, which makes the circumferential stress uniform in the arterial wall at a normal blood pressure, is approximately constant throughout aging. Above age of the 15 years the estimated and experimental values of theta are greater than theta(op) and therefore the mechanical load of the inner layers of the media and the intima decreases and the adventitia is overloaded. On the basis of nonlinear regression analysis, age-related constitutive laws of arterial wall circumferential stiffness have been determined. Above the age of 30, arterial wall hardening increases rapidly. The left coronary artery is stiffer than the right artery for groups from 35 to 45 years of age. Hyperelasticity theory has been used to identify age-related multiaxial stress through wall thickness. A theoretical model based on the reduced Green strain provides a very good representation of the coronary artery circumferential mechanical response and predicts its nearly isotropic behavior. Bio-composite material forms non-homogeneous stresses and, in the course of aging, it increases the adventitia loading. In groups aged from 10 to 15 years, whose coronary artery residual strains are low, the circumferential stress distribution has a classic form. Stiffness parameter beta gradually increases with age and this increase is significant above the age of 60. Parameter beta tends to decrease when the opening angle theta increases.


Assuntos
Envelhecimento/fisiologia , Vasos Coronários/fisiologia , Modelos Cardiovasculares , Músculo Liso Vascular/fisiologia , Túnica Íntima/fisiologia , Túnica Média/fisiologia , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Pressão Sanguínea , Vasos Coronários/ultraestrutura , Elasticidade , Feminino , Hemodinâmica , Humanos , Masculino , Pessoa de Meia-Idade , Músculo Liso Vascular/ultraestrutura , Pressão , Análise de Regressão , Sensibilidade e Especificidade , Fatores Sexuais , Estresse Mecânico , Túnica Íntima/ultraestrutura , Túnica Média/ultraestrutura
5.
Clin Orthop Relat Res ; 447: 92-9, 2006 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-16505705

RESUMO

Contact stress distribution in the articular surface of the hip is considered a factor in the development of osteoarthritis, a common complication in hips with aseptic necrosis of the femoral head. We present evidence supporting the hypothesis that osteoarthritis in hips with aseptic necrosis of the femoral head can be caused by elevated contact stress related to the reduced load-bearing ability of the necrotic bone. By using a previously validated mathematical model, we observed that hip contact stress may increase considerably if the load-bearing capacity of the necrotic lesion is decreased, if the size of the necrotic segment is increased, and if the necrotic segment is located more laterally. These effects are affected by the intrinsic shape of the hip. As the estimated values of stress in hips with osteonecrosis are in the range obtained by the same method in dysplastic hips, osteoarthritis in hips with osteonecrosis can be caused by elevated contact stress.


Assuntos
Fenômenos Biomecânicos , Necrose da Cabeça do Fêmur/etiologia , Articulação do Quadril/fisiologia , Osteoartrite do Quadril/etiologia , Força Compressiva , Necrose da Cabeça do Fêmur/fisiopatologia , Humanos , Modelos Anatômicos , Modelos Teóricos , Osteoartrite do Quadril/fisiopatologia , Medição de Risco , Sensibilidade e Especificidade , Estresse Mecânico , Suporte de Carga
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