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1.
Am J Orthod Dentofacial Orthop ; 156(3): 326-336, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31474262

RESUMO

INTRODUCTION: Orthodontic mini-implants aid in the correction of distocclusions via direct anchorage (pull from mini-implant to teeth) and indirect anchorage (teeth pulled against other teeth anchored by the mini-implant). The aim of this study was to compare stress levels on the periodontal ligament (PDL) of maxillary buccal teeth in direct and indirect distalization against orthodontic mini-implants and accounting for individual variation in maxillary anatomy and biomechanical characteristics of the compact bone. METHODS: A 3D model of the maxilla containing the different components (teeth, PDL, trabecular and cortical bones) was generated from a computed tomographic scan. Cortical bone was divided into several areas according to previously defined zones. Bone stiffness and thickness data, obtained from 11 and 12 cadavers, respectively, were incorporated into the initial model to simulate the individual cortical bone variation at the different locations. Subsequently, a finite element analysis was used to simulate the distalization modalities. RESULTS: Stresses at the buccal, palatal, mesial, and distal surfaces were significantly different between adjacent teeth under stiffness but not thickness variation. In both distalization modalities, low or no significant correlations were found between stress values and corresponding cortical bone thicknesses. High significant and inverted correlations were observed at the first molar between stress amounts and cortical bone stiffness (direct modality: -0.68 < r < -0.72; indirect modality: -0.80 < r < -0.82; P <0.05). CONCLUSIONS: With the use of a novel finite element approach that integrated human data on variations in bone properties, findings suggested that cortical bone stiffness may influence tooth movement more than bone thickness. Significant clinical implications could be related to these findings.


Assuntos
Análise do Estresse Dentário/métodos , Análise de Elementos Finitos , Técnicas de Movimentação Dentária/métodos , Fenômenos Biomecânicos , Parafusos Ósseos , Simulação por Computador , Implantes Dentários , Humanos , Imagem Tridimensional/métodos , Maxila/anatomia & histologia , Maxila/diagnóstico por imagem , Modelos Anatômicos , Dente Molar , Procedimentos de Ancoragem Ortodôntica/instrumentação , Procedimentos de Ancoragem Ortodôntica/métodos , Desenho de Aparelho Ortodôntico , Ligamento Periodontal , Estresse Mecânico , Técnicas de Movimentação Dentária/instrumentação , Torção Mecânica
2.
Am J Orthod Dentofacial Orthop ; 156(2): 203-209, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31375230

RESUMO

INTRODUCTION: The objective of this clinical prospective study was to evaluate the effect of the 2 treatment strategies, translation or controlled tipping, followed by root correction on canine retraction efficiency, specifically canine movement rate. METHODS: Twenty-one patients who needed bilateral maxillary canine retraction to close extraction space as part of their treatment plan were selected for this study. Segmental T-loops designed for controlled tipping or for translation were applied randomly to each side. Two digital maxillary dental casts (taken before and after treatment) were used to measure the tooth displacements of each patient. The coordinate system located at the center of canine crown on the pretreatment model with the 3 axes defined in the mesial-distal (M-D), buccal-lingual, and occlusal-gingival directions was used to express the 6 tooth displacement components. The movement rates on the occlusal plane and in the M-D direction were computed. Movement rates were calculated by dividing the M-D displacements or the resultant displacement on the occlusal plane with the corresponding treatment time. RESULTS: T-Loops for controlled tipping moved canines faster (33.3% on occlusal plane and 38.5% in the M-D direction) than T-loops for translation. The differences were statistically significant (P = 0.041 on the occlusal plane and 0.020 in the M-D direction). CONCLUSIONS: Moment-to-force ratio (M/F) affects the canine movement rate in a maxillary canine retraction treatment with the use of a segmented T-loop mechanism. Within the neighborhood of the ratio for translation, lower M/F moves the canine faster than higher M/F both on the occlusal plane and in the M-D direction.


Assuntos
Dente Canino , Estresse Mecânico , Técnicas de Movimentação Dentária/métodos , Adolescente , Adulto , Fenômenos Biomecânicos , Dente Canino/anatomia & histologia , Feminino , Análise de Elementos Finitos , Humanos , Masculino , Maxila , Desenho de Aparelho Ortodôntico , Estudos Prospectivos , Coroa do Dente , Adulto Jovem
3.
Am J Orthod Dentofacial Orthop ; 156(2): 210-219, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31375231

RESUMO

INTRODUCTION: More patients are choosing customized orthodontic appliances because of their excellent esthetics. It is essential that clinicians understand the biomechanics of the tooth movement tendency in customized lingual orthodontics. This study aimed to evaluate the tooth movement tendency during space closure in maxillary anterior teeth with the use of miniscrew anchorage in customized lingual orthodontics with various power arm locations. METHODS: Three-dimensional finite element models of the maxilla were created with miniscrews and power arms; the positions were varied to change the force directions. A retraction force (1.5 N) was applied from the top of the miniscrews to the selected points on the power arm, and the initial displacements of the reference nodes of the maxillary teeth were analyzed. RESULTS: After applying force in different directions, power arms located at the distal side of the canines led to larger initial lingual crown tipping and occlusal crown extrusion of the maxillary incisors compared with power arms located at the midpoint between the lateral incisors and canines, and caused a decreasing trend of the intercanine width. CONCLUSIONS: In customized lingual orthodontic treatment, power arms located at the distal side of the canines are unfavorable for anterior teeth torque control and intercanine width control. Power arms located at the midpoint between the lateral incisors and canines can get better torque control, but still cannot achieve excepted torque without extra torque control methods, no matter whether its force application point is higher than, lower than, or equal to the level of the top of the miniscrews.


Assuntos
Parafusos Ósseos , Análise de Elementos Finitos , Procedimentos de Ancoragem Ortodôntica/instrumentação , Procedimentos de Ancoragem Ortodôntica/métodos , Fechamento de Espaço Ortodôntico , Técnicas de Movimentação Dentária/instrumentação , Técnicas de Movimentação Dentária/métodos , Adulto , Fenômenos Biomecânicos , Simulação por Computador , Dente Canino/patologia , Humanos , Imagem Tridimensional/métodos , Incisivo/patologia , Maxila , Modelos Biológicos , Desenho de Aparelho Ortodôntico , Aparelhos Ortodônticos , Braquetes Ortodônticos , Fechamento de Espaço Ortodôntico/instrumentação , Fechamento de Espaço Ortodôntico/métodos , Fios Ortodônticos , Planejamento de Assistência ao Paciente , Estresse Mecânico , Coroa do Dente , Torque , Resultado do Tratamento
4.
Am J Orthod Dentofacial Orthop ; 156(2): 220-228, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31375232

RESUMO

INTRODUCTION: The primary aim of this in vitro study was to compare the insertion torque (IT) and anchorage force (AF) values of 4 different sizes of orthodontic mini-implants with 2 different angles. The second aim was to evaluate the relationship between IT and AF values under different diameter, length, and insertion angle variables. METHODS: A total of 160 mini-implants, including 20 implants in each group, with 4 different sizes (1.6 × 8 mm, 1.6 × 10 mm, 2.0 × 8 mm, and 2.0 × 10 mm) at 2 different angles (70° and 90°), were inserted into bovine iliac bone segments. The IT and AF values leading to 1.5 mm deflection were compared. The correlations between IT and AF values under different variables were also analyzed. RESULTS: The mini-implants with greater diameter and length showed greater IT and AF values (P <0.05). The IT and AF values of mini-implants inserted at 70° angle were significantly greater than those of mini-implants inserted at 90° angle (P <0.001). Significant correlations were found between IT and AF values in all variables. CONCLUSIONS: The diameter, length, and insertion angle of orthodontic mini-implants have significant effects on IT and AF values. Insertion angle and diameter of mini-implants are more effective than implant length on skeletal anchorage. Significant correlations are present between IT and AF values of mini-implants regardless of their diameters, lengths, and insertion angles.


Assuntos
Implantes Dentários , Procedimentos de Ancoragem Ortodôntica/instrumentação , Desenho de Aparelho Ortodôntico/instrumentação , Animais , Parafusos Ósseos , Bovinos , Implantação Dentária Endo-Óssea , Análise do Estresse Dentário , Falha de Equipamento , Procedimentos de Ancoragem Ortodôntica/métodos , Desenho de Aparelho Ortodôntico/métodos , Estresse Mecânico , Torque
5.
Sheng Wu Yi Xue Gong Cheng Xue Za Zhi ; 36(4): 590-595, 2019 Aug 25.
Artigo em Chinês | MEDLINE | ID: mdl-31441259

RESUMO

In order to study the mechanical behavior of degeneration and nucleotomy of lumbar intervertebral disc, compression experiments with porcine lumbar intervertebral discs were carried out. The lumbar intervertebral discs with trypsin-treated and nucleus nucleotomy served as the experimental group and the normal discs as the control group. Considering the effects of load magnitude and loading rate, the relationship between stress and strain, instantaneous elastic modulus and creep property of intervertebral disc were obtained. The creep constitutive model was established. The results show that the strain and creep strain of the experimental group increase significantly with the increase of compression load and loading rate, whereas the instantaneous elastic modulus decreases obviously, compared with the control group. It indicates that the effect of load magnitude and loading rate on load-bearing capacity of intervertebral disc after nucleotomy is larger obviously than that of normal disc. The creep behavior of the experimental group can be still predicted by the Kelvin three-parameter solid model. The results will provide theoretical foundation for clinical treatment and postoperative rehabilitation of intervertebral disc disease.


Assuntos
Disco Intervertebral/fisiologia , Disco Intervertebral/cirurgia , Estresse Mecânico , Animais , Fenômenos Biomecânicos , Vértebras Lombares , Suínos , Suporte de Carga
6.
Sheng Wu Yi Xue Gong Cheng Xue Za Zhi ; 36(4): 596-603, 2019 Aug 25.
Artigo em Chinês | MEDLINE | ID: mdl-31441260

RESUMO

The mechanical properties of the aorta tissue is not only important for maintaining the cardiovascular health, but also is closely related to the development of cardiovascular diseases. There are obvious differences between the ventral and dorsal tissues of the descending aorta. However, the cause of the difference is still unclear. In this study, a biaxial tensile approach was used to determine the parameters of porcine descending aorta by analyzing the stress-strain curves. The strain energy functions Gasser-Ogden-Holzapfel was adopted to characterize the orthotropic parameters of mechanical properties. Elastic Van Gieson (EVG) and Sirius red stain were used to observe the microarchitecture of elastic and collagen fibers, respectively. Our results showed that the tissue of descending aorta had more orthotropic and higher elastic modulus in the dorsal region compared to the ventral region in the circumferential direction. No significant difference was found in hyperelastic constitutive parameters between the dorsal and ventral regions, but the angle of collagen fiber was smaller than 0.785 rad (45°) in both dorsal and ventral regions. The arrangement of fiber was inclined to be circumferential. EVG and Sirius red stain showed that in outer-middle membrane of the descending aorta, the density of elastic fibrous layer of the ventral region was higher than that of the dorsal region; the amount of collagen fibers in dorsal region was more than that of the ventral region. The results suggested that the difference of mechanical properties between the dorsal and ventral tissues in the descending aorta was related to the microstructure of the outer membrane of the aorta. In the relatively small strain range, the difference in mechanical properties between the ventral and dorsal tissues of the descending aorta can be ignored; when the strain is higher, it needs to be treated differently. The results of this study provide data for the etiology of arterial disease (such as arterial dissection) and the design of artificial blood vessel.


Assuntos
Aorta Torácica/fisiologia , Animais , Fenômenos Biomecânicos , Colágeno , Módulo de Elasticidade , Estresse Mecânico , Suínos
7.
Sheng Wu Yi Xue Gong Cheng Xue Za Zhi ; 36(4): 604-612, 2019 Aug 25.
Artigo em Chinês | MEDLINE | ID: mdl-31441261

RESUMO

In vitro experimental test for mechanical properties of a vascular stent is a main method to evaluate its effectiveness and safety, which is of great significance to the clinical applications. In this study, a comparative study of planar, V-groove and radial compression methods for the radial support property test were performed, and the effects of compression rate and circumferential position on the test results were conducted. Based on the three-point bending method, the influences of compression rate and circumferential position on flexibility were also explored. And then a best test proposal was selected to evaluate the radial support property and flexibility of the three self-designed stents and the comparative biodegradable vascular stent (BVS) (BVS1.1, Abbott Vascular, USA) with different outside diameters of 1.4 mm, 1.7 mm and 2.4 mm. The results show that the developing trends of the compression load with the compression displacement measured by the three radial support property test methods are the same, but normalized radial force values are quite different. The planar compression method is more suitable for comparing the radial support properties of stents with different diameters and structures. Compression rate has no obvious effect on the testing results of both the radial support property and flexibility. Compression circumferential position has a great impact on testing radial support property with the planar or V-groove compression methods and testing flexibility with three-point bending method. The radial support properties of all the three self-designed stents are improved at a certain degree compared to that of the BVS stent. The study has better guide significance and reference value for testing mechanical properties of vascular stents.


Assuntos
Implantes Absorvíveis , Fenômenos Mecânicos , Stents , Polímeros , Desenho de Prótese , Estresse Mecânico
8.
Sheng Wu Yi Xue Gong Cheng Xue Za Zhi ; 36(4): 619-626, 2019 Aug 25.
Artigo em Chinês | MEDLINE | ID: mdl-31441263

RESUMO

Aiming at the problem of the influence of preloading force on its mechanical response in soft tissue compression experiments, an elimination method of preloading force based on linear loading region is proposed. Unconfined compression experiments under a variety of different preloading forces are performed. The influence of the preloading force on the parameters of constitutive model is analyzed. In the preload phase, the mechanical response of the soft tissue is taken as a linear model. The preloading force is eliminated by taking the preloading phase into account throughout the response process. According to five different preloading forces of the unconfined compression experiments, the elimination method is validated with two different constitutive models of soft tissue, and the error between the models obtained by the preloading force elimination method and the traditional method with the experimental results is compared. The results show that the error obtained by preloading force elimination method is significantly smaller than the traditional method. The preloading force elimination method can eliminate the influence of preloading force on mechanical response to a certain extent, and constitutive model parameters which are closer to the true properties of soft tissue can be obtained.


Assuntos
Modelos Biológicos , Pressão , Elasticidade , Modelos Lineares , Estresse Mecânico
9.
Pharm Res ; 36(10): 139, 2019 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-31359156

RESUMO

PURPOSE: To identify the minimum interfacial bonding strength (IBS) required for bilayer tablets to sustain the stresses experienced during manufacturing, transportation, and handling. METHODS: Bilayer tablets of a number of formulations with systematically varied IBS were prepared on a materials testing macine. Five bilayer tablets with the same IBS were repeatedly dropped at a fixed height in a friabilator and integrity of the interface was periodically examined. The number of tablets free from observable defects at the interface was plotted as a function of the number of drops. The IBS for all five tablets to remain intact after 1000 drops was taken as the minimum IBS for a given formulation. RESULTS: The minimum IBS depends on both layer composition and tablet size. For bilayer tablets made with more brittle materials or a larger size, a higher minimum IBS is required to pass the survival test. The incorporation of HPMC leads to a lower minimum IBS. An IBS of 0.26 MPa is sufficient for all bilayer tablet formulations and sizes to pass the survival test in this work. CONCLUSIONS: A minimum IBS of 0.26 MPa is recommended as a tentative criterion for bilayer tablets of most materials to avoid quality issues arising from inadequate IBS.


Assuntos
Excipientes/química , Comprimidos/química , Celulose/química , Composição de Medicamentos/métodos , Estabilidade de Medicamentos , Lactose/química , Tamanho da Partícula , Estresse Mecânico , Propriedades de Superfície , Resistência à Tração
10.
Soft Matter ; 15(30): 6237-6246, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31334527

RESUMO

Mechanical testing of connective tissues such as tendons and ligaments can lead to collagen denaturation even in the absence of macroscale damage. The following tensile loading protocols, ramp loading to failure, overloading and release, cyclic overloading and cyclic fatigue loading, all yield molecular damage in rat or bovine tendons. Single collagen fibrils extracted from the positional common digital extensor tendon of the forelimb also show molecular damage after tensile loading to failure. Using fibrils from the same source we assess changes to the molecular and supramolecular structure after tensile stress relaxation at strains between 4 and 22% followed by release. We observe no broken fibril and no significant change in D-band spacing. However, we observe significant binding of a fluorescent collagen hybridizing peptide to the fibrils indicating that collagen denaturation occurs in a strain dependent way for relaxation times between 1 s and 1500 s. We also show that peptide binding is associated with a decrease of the cross-sectional area of the fibrils providing an estimate of the dry volume loss due to molecular denaturation as well as an estimate of the mechanical energy density required, 25-110 MJ m-3. In summary we show that collagen molecular damage can occur in the absence of fibril failure and without visible changes to the supramolecular structure.


Assuntos
Colágeno/química , Estresse Mecânico , Tendões/metabolismo , Animais , Fenômenos Biomecânicos , Bovinos , Membro Anterior/metabolismo , Ratos , Tendões/química
11.
Zhongguo Gu Shang ; 32(6): 564-568, 2019 Jun 25.
Artigo em Chinês | MEDLINE | ID: mdl-31277543

RESUMO

OBJECTIVE: To introduce the design of customized pelvic prosthesis, to evaluate the biomechanical property under three load conditions of customized pelvic prosthesis under three load cinditions. METHODS: A titanium alloy prosthesis for reconstruction of pelvic tumors was designed by CAD software. The strength and stiffness of the custom prosthesis under static and slow gait conditions were analyzed and evaluated by finite element method. RESULTS: The results of the finite element analysis suggested that the maximum von Mises stress in the pelvic under three load conditions were 39.0, 202.8 and 42.4 MPa; the maximum displacement were 0.199, 0.766 and 0.847 mm. The maximum von Mises stress in the prosthesis under three load conditions were 62.3, 318 and 468 MPa. The maximum Von Mises stress in the Ti-alloy prosthesis and pelvic was far smaller than the yield strength of Ti-alloy. CONCLUSIONS: The study can design the size and shape of prosthesis accurately according to patient's condition. The finite element method can reduce the bone stress level and fracture risk, prolong the service life of prostheses, and ensure the safety and stability of the postoperative patients under normal gait.


Assuntos
Fraturas Ósseas , Próteses e Implantes , Fenômenos Biomecânicos , Análise de Elementos Finitos , Marcha , Humanos , Desenho de Prótese , Estresse Mecânico
12.
Phys Rev Lett ; 122(21): 218102, 2019 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-31283330

RESUMO

Dynamically cross-linked semiflexible biopolymers such as the actin cytoskeleton govern the mechanical behavior of living cells. Semiflexible biopolymers nonlinearly stiffen in response to mechanical loads, whereas the cross-linker dynamics allow for stress relaxation over time. Here we show, through rheology and theoretical modeling, that the combined nonlinearity in time and stress leads to an unexpectedly slow stress relaxation, similar to the dynamics of disordered systems close to the glass transition. Our work suggests that transient cross-linking combined with internal stress can explain prior reports of soft glassy rheology of cells, in which the shear modulus increases weakly with frequency.


Assuntos
Citoesqueleto/química , Citoesqueleto de Actina/química , Actinas/química , Humanos , Modelos Químicos , Dinâmica não Linear , Reologia , Estresse Mecânico
13.
Zhonghua Kou Qiang Yi Xue Za Zhi ; 54(7): 463-468, 2019 Jul 09.
Artigo em Chinês | MEDLINE | ID: mdl-31288326

RESUMO

Objective: To investigate effect of the contact surface between the bridge and the adjacent teeth on the stress distribution of the implant and bone tissue and the displacement of the prosthesis in the cantilever fixed implant bridge restoring missing mandibular central incisors. Methods: Two-dimensional images of the mandible and dentition in healthy adults were obtained using CT data. A three-dimensional finite element model of cantilever fixed bridge supported by implants with mandibular central incisor was established by computer reconstruction technique.The contact surface between the bridge and the adjacent natural tooth was designed as "oval" and "trapezoid". The "trapezoid" has a slightly smaller median diameter on the labial side and a slightly larger medial diameter on the lingual side. Loading of 120 N was applied on the tangential margin of the middle line of the long axis of the bridge 41. The direction was set at 0°, which was parallel to the long axis of the tooth and downward. The buccal to lingual and downward angles were 30°, 45° and 60°, respectively, perpendicular to the long axis of the tooth and 90° to the lingual side.The stress distribution of the implant and surrounding bone tissue and the displacement of the prosthesis were compared between the two models. Results: Under axial and buccolingual loading, the maximum equivalent stress peak in the implant and surrounding bone tissue in the cantilever with trapezoidal contact surface design and the maximum displacement of the prosthesis were lower. Moreover, the distribution of stress was more balanced and the concentration range of stress was smaller. With the loading angle increasing, this trend was more obvious. When loading angle increased to 90°, the maximum equivalent stress and the maximum displacement of the elliptic contact surface model implant and surrounding bone tissue were 196 and 101 MPa and 0.196 mm, respectively, while the trapezoidal contact surface model were 157 and 72 MPa and 0.164 mm, respectively. Conclusions: The trapezoidal contact surface of the bridge and the adjacent teeth in the cantilever fixed bridge supported by implants with mandibular central incisor is beneficial to reduce the impact of the leverage on the implant and surrounding bone tissue.


Assuntos
Implantes Dentários , Prótese Parcial Fixa , Análise de Elementos Finitos , Incisivo , Humanos , Modelos Teóricos , Estresse Mecânico , Tomografia Computadorizada por Raios X
14.
Int J Nanomedicine ; 14: 2693-2703, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31354260

RESUMO

Background: Silver, incorporation with natural or synthetic polymers, has been used as an effective antibacterial agent since decades. Silver has potential applications in healthcare especially in nanoparticles form but silver sulfadiazine (AgSD) is the most efficient antibacterial agent especially for burn wound dressings. Method: In this report, mechanical, structural, and antibacterial properties of PAN nanofibers incorporation with silver sulfadiazine are mainly focused. AgSD was loaded for the first time on electrospinning as well as self-synthesized AgSD on PAN nanofibers by solution immersion method and then compared the results of both. Results: Occurrence of chemical reaction among the functional groups of AgSD and PAN were analyzed using FTIR, for both types of specimen. Morphological and surface properties of prepared nanofiber mats were characterized by scanning electron microscope, and it resulted in uniform nanofibers without bead formation. Diameter of nanofibers was slightly increased with addition of AgSD by in situ and immersion methods respectively. Nanoparticles distribution was analyzed by transmission electron microscopy. Thermal properties were analyzed by thermo-gravimetric analyzer and it was observed that AgSD decreased thermal stability of PAN which is better from biomedical perspective. X-ray diffraction declared crystalline structure of nanofiber mats. Presence of Ag and S contents in nanofiber mats was analyzed by X-ray photo spectroscopy. Antibacterial properties of nanofiber mats were investigated by disc diffusion method was carried out. E. coli and Bacillus bacteria strain were used as gram-negative and gram-positive respectively. Zone inhibition of the bacteria was used as a tool to determine effectiveness of AgSD released from PAN nanofiber mats. The antibacterial properties of PAN nanofibers impregnated with AgSD were determined with both types of bacteria strains to compare with control one. Conclusion: On the basis of characterization results it is concluded that PAN/AgSD (immersion) nanofiber mats have better structural and antibacterial properties than that of PAN/AgSD (in situ) nanofiber mats. So, from our point of view, self-synthesized AgSD is recommended for further production of nanofiber mats for antibacterial applications.


Assuntos
Resinas Acrílicas/química , Antibacterianos/farmacologia , Nanofibras/química , Sulfadiazina de Prata/farmacologia , Bacillus/efeitos dos fármacos , Módulo de Elasticidade , Escherichia coli/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Nanofibras/ultraestrutura , Espectroscopia Fotoeletrônica , Espectrometria por Raios X , Espectroscopia de Infravermelho com Transformada de Fourier , Estresse Mecânico , Resistência à Tração , Termogravimetria , Difração de Raios X
15.
Soft Matter ; 15(27): 5511-5520, 2019 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-31241632

RESUMO

Red blood cells in shear flow show a variety of different shapes due to the complex interplay between hydrodynamics and membrane elasticity. Malaria-infected red blood cells become generally adhesive and less deformable. Adhesion to a substrate leads to a reduction in shape variability and to a flipping motion of the non-spherical shapes during the mid-stage of infection. Here, we present a complete state diagram for wall adhesion of red blood cells in shear flow obtained by simulations, using a particle-based mesoscale hydrodynamics approach, multiparticle collision dynamics. We find that cell flipping at a substrate is replaced by crawling beyond a critical shear rate, which increases with both membrane stiffness and viscosity contrast between the cytosol and suspending medium. This change in cell dynamics resembles the transition between tumbling and tank-treading for red blood cells in free shear flow. In the context of malaria infections, the flipping-crawling transition would strongly increase the adhesive interactions with the vascular endothelium, but might be suppressed by the combined effect of increased elasticity and viscosity contrast.


Assuntos
Eritrócitos/citologia , Eritrócitos/fisiologia , Adesão Celular , Movimento Celular , Forma Celular , Simulação por Computador , Elasticidade , Membrana Eritrocítica/fisiologia , Cinética , Fenômenos Físicos , Resistência ao Cisalhamento , Estresse Mecânico , Propriedades de Superfície , Viscosidade
16.
Plant Physiol Biochem ; 141: 431-445, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31238253

RESUMO

S-adenosylmethionine synthetase (SAMS) catalyzes methionine and ATP to generate S-adenosyl-L-methionine (SAM). In plants, accumulating SAMS genes have been characterized and the majority of them are reported to participate in development and stress response. In this study, two putative SAMS genes (CsSAMS1 and CsSAMS2) were identified in cucumber (Cucumis Sativus L.). They displayed 95% similarity and had a high identity with their homologous of Arabidopsis thaliana and Nicotiana tabacum. The qRT-PCR test showed that CsSAMS1 was predominantly expressed in stem, male flower, and young fruit, whereas CsSAMS2 was preferentially accumulated in stem and female flower. And they displayed differential expression profiles under stimuli, including NaCl, ABA, SA, MeJA, drought and low temperature. To elucidate the function of cucumber SAMS, the full-length CDS of CsSAMS1 was cloned, and prokaryotic expression system and transgenic materials were constructed. Expressing CsSAMS1 in Escherichia coli BL21 (DE3) improved the growth of the engineered strain under salt stress. Overexpression of CsSAMS1 significantly increased MDA content, H2O2 content, and POD activity in transgenic lines under non-stress condition. Under salt stress, however, the MDA content of transgenic lines was lower than that of the wild type, the H2O2 content remained high, the polyamine and ACC synthesis in transgenic lines exhibited a CsSAMS1-expressed dependent way. Taken together, our results suggested that both CsSAMS1 and CsSAMS2 were involved in plant development and stress response, and a proper increase of expression level of CsSAMS1 in plants is benificial to improving salt tolerance.


Assuntos
Cucumis sativus/enzimologia , Cucumis sativus/fisiologia , Metionina Adenosiltransferase/metabolismo , Tolerância ao Sal , Antioxidantes/metabolismo , Arabidopsis/metabolismo , Secas , Perfilação da Expressão Gênica , Regulação Enzimológica da Expressão Gênica , Regulação da Expressão Gênica de Plantas , Peróxido de Hidrogênio/química , Metionina Adenosiltransferase/genética , Filogenia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Poliaminas/química , Sais , Estresse Mecânico , Estresse Fisiológico/genética , Tabaco/metabolismo
17.
Hua Xi Kou Qiang Yi Xue Za Zhi ; 37(2): 115-123, 2019 Apr 01.
Artigo em Chinês | MEDLINE | ID: mdl-31168976

RESUMO

Current biomechanical research of dental implants focuses on the mechanical damage and enhancement mechanism of the implant-abutment interface as well as how to obtain better mechanical strength and longer fatigue life of dental implants. The mechanical properties of implants can be comprehensively evaluated by strain gauge analysis, photo elastic stress analysis, digital image correlation, finite element analysis, implant bone bonding strength test, and measurement of mechanical properties. Finite element analysis is the most common method for evaluating stress distribution in dental implants, and static pressure and fatigue tests are commonly used in mechanical strength test. This article reviews biomechanical research methods and evaluation indices of dental implants. Results provide methodology guidelines in the field of biomechanics by introducing principles, ranges of application, advantages, and limitations, thereby benefitting researchers in selecting suitable methods. The influencing factors of the experimental results are presented and discussed to provide implant design ideas for researchers.


Assuntos
Projeto do Implante Dentário-Pivô , Implantes Dentários , Planejamento de Prótese Dentária , Fenômenos Biomecânicos , Simulação por Computador , Consenso , Dente Suporte , Análise do Estresse Dentário , Análise de Elementos Finitos , Estresse Mecânico
18.
Hua Xi Kou Qiang Yi Xue Za Zhi ; 37(2): 162-167, 2019 Apr 01.
Artigo em Chinês | MEDLINE | ID: mdl-31168982

RESUMO

OBJECTIVE: The purpose of this study is to investigate the potential effects of sclerostin (SOST) on the biological funtions and related mechanisms of cementoblasts under mechanical stress. METHODS: OCCM-30 cells were treated with varying doses of SOST (0, 25, 50, and 100 ng·mL⁻¹) and were loaded with uniaxial compressive stress (2 000 µ strain with a frequency of 0.5 Hz) for six hours. Western blot was utilized to detect the expressions of ß-catenin, p-smad1/5/8, and smad1/5/8 proteins. Alkaline phosphatase (ALP) activity was determined, and reverse transcription polymerase chain reaction was used to measure the expressions of runt-related transcription factor 2 (Runx-2), osteocalcin (OCN), bone sialoproteins (BSP), receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) mRNA. RESULTS: The expression of p-smad
1/5/8 was significantly downregulated with increasing SOST. ß-catenin and smad1/5/8 exhibited no difference. ALP activity decreased under mechanical compressive stress with increasing SOST concentrations. Runx-2 expression was reduced with increasing SOST concentrations, and a similar trend was observed for the BSP and OCN expressions. When the SOST concentration was enhanced, RANKL expression gradually increased, whereas the expression of OPG decreased. CONCLUSIONS: Under mechanical comprehensive stress, SOST can adjust the bone morphogenetic protein (BMP) /smad signal pathway. Osteosclerosis inhibits the mineralization of cementoblasts under mechanical compressive stress, which may be achieved by inhibiting the expressions of osteogenesis factors (Runx2, OCN, BSP, and others) and by promoting the ratio of cementoclast-related factors (RANKL/OPG) through BMP signal pathways.


Assuntos
Proteínas Morfogenéticas Ósseas , Cemento Dentário , Proteínas Morfogenéticas Ósseas/metabolismo , Subunidade alfa 1 de Fator de Ligação ao Core , Osteocalcina , Proteínas Smad/metabolismo , Estresse Mecânico
19.
Nat Commun ; 10(1): 2487, 2019 06 06.
Artigo em Inglês | MEDLINE | ID: mdl-31171776

RESUMO

Lack or excess expression of the surface ectoderm-expressed transcription factor Grainyhead-like2 (Grhl2), each prevent spinal neural tube closure. Here we investigate the causative mechanisms and find reciprocal dysregulation of epithelial genes, cell junction components and actomyosin properties in Grhl2 null and over-expressing embryos. Grhl2 null surface ectoderm shows a shift from epithelial to neuroepithelial identity (with ectopic expression of N-cadherin and Sox2), actomyosin disorganisation, cell shape changes and diminished resistance to neural fold recoil upon ablation of the closure point. In contrast, excessive abundance of Grhl2 generates a super-epithelial surface ectoderm, in which up-regulation of cell-cell junction proteins is associated with an actomyosin-dependent increase in local mechanical stress. This is compatible with apposition of the neural folds but not with progression of closure, unless myosin activity is inhibited. Overall, our findings suggest that Grhl2 plays a crucial role in regulating biomechanical properties of the surface ectoderm that are essential for spinal neurulation.


Assuntos
Embrião de Mamíferos/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Tubo Neural/embriologia , Células Neuroepiteliais/metabolismo , Neurulação/genética , Fatores de Transcrição/genética , Actomiosina/genética , Actomiosina/metabolismo , Animais , Fenômenos Biomecânicos , Caderinas/metabolismo , Ectoderma/citologia , Ectoderma/embriologia , Ectoderma/metabolismo , Células Epiteliais/metabolismo , Junções Intercelulares/genética , Junções Intercelulares/metabolismo , Camundongos , Tubo Neural/metabolismo , Fatores de Transcrição SOXB1/metabolismo , Estresse Mecânico , Fatores de Transcrição/metabolismo
20.
Nat Commun ; 10(1): 2512, 2019 06 07.
Artigo em Inglês | MEDLINE | ID: mdl-31175307

RESUMO

DNA is a common biomaterial in nature as well as a good building block for producing useful structures, due to its fine feature size and liquid crystalline phase. Here, we demonstrate that a combination of shear-induced flow and microposts can be used to create various kinds of interesting microstructure DNA arrays. Our facile method provides a platform for forming multi-scale hierarchical orientations of soft- and biomaterials, using a process of simple shearing and controlled evaporation on a patterned substrate. This approach enables potential patterning applications using DNA or other anisotropic biomaterials based on their unique structural characteristics.


Assuntos
DNA/ultraestrutura , Microtecnologia , Estresse Mecânico , Materiais Biocompatíveis , Microscopia Confocal , Análise de Sequência com Séries de Oligonucleotídeos
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