Correlating flow induced shear stress and chondrocytes activity in micro-porous scaffold using computational fluid dynamics and rapid prototyping

Flow induced shear stress plays an important role in regulating cell growth and distribution in scaffolds. This study sought to correlate wall shear stress and chondrocytes activity for engineering design of micro-porous osteochondral grafts based on the hypothesis that it is possible to capture and discriminate between the transmitted force and cell response at the inner irregularities. Unlike common tissue engineering therapies with perfusion bioreactors in which flow-mediated stress is the controlling parameter, this work assigned the associated stress as a function of porosity to influence in vitro proliferation of chondrocytes. D-optimality criterion was used to accommodate three pore characteristics for appraisal in a mixed level fractional design of experiment (DOE); namely, pore size (4 levels), distribution pattern (2 levels) and density (3 levels). Micro-porous scaffolds (n=12) were fabricated according to the DOE using rapid prototyping of an acrylic-based bio-photopolymer. Computational fluid dynamics (CFD) models were created correspondingly and used on an idealized boundary condition with a Newtonian fluid domain to simulate the dynamic microenvironment inside the pores. In vitro condition was reproduced for the 3D printed constructs seeded by high pellet densities of human chondrocytes and cultured for 72 hours. The results showed that cell proliferation was significantly different in the constructs (p<0.05). Inlet fluid velocity of 3×10-2mms-1 and average shear stress of 5.65×10-2 Pa corresponded with increased cell proliferation for scaffolds with smaller pores in hexagonal pattern and lower densities. Although the analytical solution of a Poiseuille flow inside the pores was found insufficient for the description of the flow profile probably due to the outside flow induced turbulence, it showed that the shear stress would increase with cell growth and decrease with pore size. This correlation demonstrated the basis for determining the relation between the induced stress and chondrocyte activity to optimize microfabrication of engineered cartilaginous constructs.

Edexcel AS History: Stalin´s Russia, 1924-53.

Esta guía ha sido escrita por un examinador y explica los requisitos de cada unidad, resume el contenido relevante de cada unidad e incluye una serie de preguntas y respuestas. Cumple los requisitos establecidos para aprobar el examen de historia del nivel Edexcel AS que pertenece al segundo ciclo de enseñanza secundaria. El tema principal del libro es la Rusia de Stalin, 1924-53, los otros temas que trata el libro son: la lucha por el liderazgo, la economía en 1930, las políticas sociales de Stalin, terror y propaganda en la Rusia de Stalin, la guerra mundial y la guerra fría.

The saturated magnetic field of the neutron stars

Considering the ferromagnetic screening for the decay of the X-ray neutron star magnetic field in the binary accretion phase, the phase transition of ferromagnetic materials in the crust of neutron star induces the ferromagnetic screening saturation of the accreted crust, which results in the minimum surface magnetic field of the accreting neutron star, about 108 G, if the accreted matter has completely replaced the crust mass of the neutron star. The magnetic field evolution versus accreted mass is given as Bs ∝ ΔM-0.9, and the obtained magnetic field versus spin period relation is consistent with the distribution of the binary X-ray sources and recycled pulsars. The further thermal effect on the magnetic evolution is also studied.

CT coronary angiography versus conventional invasive coronary angiography - the view of the referring physician

PURPOSE Assessment of experience gained by local referring physicians with the procedure of coronary computed tomographic angiography (CCTA) in the everyday clinical routine. MATERIALS AND METHODS A 25-item questionnaire was sent to 179 physicians, who together had referred a total of 1986 patients for CCTA. They were asked about their experience to date with CCTA, the indications for coronary imaging, and their practice in referring patients for noninvasive CCTA or invasive catheter angiography. RESULTS 53 questionnaires (30 %) were assessable, corresponding to more than 72 % of the patients referred. Of the referring physicians who responded, 94 % saw a concrete advantage of CCTA in the treatment of patients, whereby 87 % were 'satisfied' or 'very satisfied' with the reporting. For excluding coronary heart disease (CHD) where there was a low pre-test probability of disease, the physicians considered CCTA to be superior to conventional coronary diagnosis (4.2 on a scale of 1 - 5) and vice versa for acute coronary syndrome (1.6 of 5). The main reasons for unsuitability of CCTA for CT diagnosis were claustrophobia and the absence of a sinus rhythm. The level of exposure to radiation in CCTA was estimated correctly by only 42 % of the referring physicians. 90 % of the physicians reported that their patients evaluated their coronary CT overall as 'positive' or 'neutral', while 87 % of the physicians whose patients had undergone both procedures reported that the patients had experienced CCTA as the less disagreeable of the two. CONCLUSION CCTA is accepted by the referring physicians as an alternative imaging procedure for the exclusion of CHD and received a predominantly positive assessment from both the referring physicians and the patients.