Focusing of sub-micrometer particles and bacteria enabled by two-dimensional acoustophoresis.

Handling of sub-micrometer bioparticles such as bacteria are becoming increasingly important in the biomedical field and in environmental and food analysis. As a result, there is an increased need for less labor-intensive and time-consuming handling methods. Here, an acoustophoresis-based microfluidic chip that uses ultrasound to focus sub-micrometer particles and bacteria, is presented. The ability to focus sub-micrometer bioparticles in a standing one-dimensional acoustic wave is generally limited by the acoustic-streaming-induced drag force, which becomes increasingly significant the smaller the particles are. By using two-dimensional acoustic focusing, i.e. focusing of the sub-micrometer particles both horizontally and vertically in the cross section of a microchannel, the acoustic streaming velocity field can be altered to allow focusing. Here, the focusability of E. coli and polystyrene particles as small as 0.5 µm in diameter in microchannels of square or rectangular cross sections, is demonstrated. Numerical analysis was used to determine generic transverse particle trajectories in the channels, which revealed spiral-shaped trajectories of the sub-micrometer particles towards the center of the microchannel; this was also confirmed by experimental observations. The ability to focus and enrich bacteria and other sub-micrometer bioparticles using acoustophoresis opens the research field to new microbiological applications.

Ultrasound-induced acoustophoretic motion of microparticles in three dimensions.

We derive analytical expressions for the three-dimensional (3D) acoustophoretic motion of spherical microparticles in rectangular microchannels. The motion is generated by the acoustic radiation force and the acoustic streaming-induced drag force. In contrast to the classical theory of Rayleigh streaming in shallow, infinite, parallel-plate channels, our theory does include the effect of the microchannel side walls. The resulting predictions agree well with numerics and experimental measurements of the acoustophoretic motion of polystyrene spheres with nominal diameters of 0.537 and 5.33 µm. The 3D particle motion was recorded using astigmatism particle tracking velocimetry under controlled thermal and acoustic conditions in a long, straight, rectangular microchannel actuated in one of its transverse standing ultrasound-wave resonance modes with one or two half-wavelengths. The acoustic energy density is calibrated in situ based on measurements of the radiation dominated motion of large 5-µm-diameter particles, allowing for quantitative comparison between theoretical predictions and measurements of the streaming-induced motion of small 0.5-µm-diameter particles.

Effects of long-term phenobarbital treatment on the liver in dogs.

Long-term administration of phenobarbital has been reported to cause hepatic injury in dogs. Phenobarbital induces hepatic enzymes, and it may be difficult to distinguish the effect of enzyme induction on serum liver enzyme activities from actual hepatic damage. The hepatotoxicity of phenobarbital and the impact of enzyme induction on serum liver enzyme activity were investigated prospectively in 12 normal dogs. Phenobarbital was administered for 29 weeks at 5 mg per kilogram of body weight (range, 4.8-6.6 mg/kg) PO q12h, resulting in therapeutic serum phenobarbital concentrations (20-40 microg/mL). Serum alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate transaminase (AST), gamma-glutamyltransferase (GGT), fasted bile acids (fBA), total bilirubin, and albumin were determined before and during treatment. Lateral abdominal radiographs, abdominal ultrasounds, and histopathologic examinations of liver tissue obtained by ultrasound-guided biopsy were performed before and during treatment. Radiographs revealed a moderate increase in liver size in most dogs. Ultrasonographic examination revealed no change in liver echogenicity or architecture. No evidence of morphologic liver damage was observed histopathologically. ALP and ALT increased significantly (P < .05), GGT increased transiently, and albumin decreased transiently during the study. There were no significant changes in AST, bilirubin, and fBA. These results suggest that increases in serum ALP, ALT, and GGT may reflect enzyme induction rather than hepatic injury during phenobarbital treatment in dogs. Serum AST, fBA, and bilirubin, and ultrasonographic evaluation of the liver are not affected by the enzyme-inducing effect of phenobarbital and can therefore be helpful to assess liver disease in dogs treated with the drug.

Effects of long-term phenobarbital treatment on the thyroid and adrenal axis and adrenal function tests in dogs.

Phenobarbital can interfere with the thyroid axis in human beings and rats by accelerating hepatic thyroxine metabolism because of enzyme induction. In human beings, it also can interfere with the low-dose dexamethasone suppression test (LDDST) used to assess adrenal function by accelerating dexamethasone metabolism. This effect can cause a lack of suppression of pituitary ACTH and subsequent adrenal cortisol release after dexamethasone administration. The effects of phenobarbital on the thyroid axis, the adrenal axis, and adrenal function tests were prospectively investigated in 12 normal, adult dogs. Phenobarbital was administered at 5 mg per kilogram of body weight (range, 4.8-6.6 mg/kg) PO q12h for 29 weeks, resulting in therapeutic serum concentrations (20-40 microg/mL). Serum total thyroxine (TT4), free thyroxine (FT4) by equilibrium dialysis, total triiodothyronine (TT3), thyrotropin (TSH), and cholesterol were determined before and during phenobarbital treatment. LDDST, ACTH stimulation tests, and ultrasonographic evaluation of the adrenal glands were performed before and during treatment. TT4 and FT4 decreased significantly (P < or = .05), TT3 had minimal fluctuation, TSH had only a delayed compensatory increase, and cholesterol increased during phenobarbital treatment. The delayed increase in TSH, despite persistent hypothyroxinemia, suggests that accelerated hepatic thyroxine elimination may not be the only effect of phenobarbital on the thyroid axis. There was no significant effect of phenobarbital on either of the adrenal function tests. With the methods employed, we did not find any effects of the drug on the hormonal equilibrium of the adrenal axis.

Efeitos ambientais de inverno sobre o consumo de matéria seca por vacas holandesas estabuladas e vacas holandesas desabrigadas / Winter environmental effects on dry-matter intake of stabled and unsheltered holstein cows

A pesquisa, desenvolvida em Santa Maria, Estado do Rio Grande do Sul, durante os meses de julho e agosto de 1986, teve como objetivo determinar a variaçäo no consumo de matéria seca, em funçäo da diminuiçäo da temperatura ambiente, por vacas holandesas abrigadas e desabrigadas, durante o inverno em clima subtropical úmido. Foram utilizadas 12 vacas alimentadas "ad libitum" com raçäo à base de silagem de milho, distribuídas em dois tratamentos: vacas estabuladas (Grupo I) e vacas mantidas em piquetes sem abrigo (Grupo II), num delineamento inteiramente casualizado. O consumo diário, que foi de 0,077 mais ou menos 0,005 e 0,095 mais ou menos 0,006 kgMS/kg elevado à 0,75 potência nos Grupos I e II, respectivamente, apresentou diferença significativa (P < 0,01). A temperatura ambiente, umidade relativa do ar, velocidade do vento e precipitaçäo correlacionaram-se significativamente (P < 0,05) com o consumo de MS das vacas desabrigadas, cujos coeficientes de correlaçäo variaram de -0,58 a 0,51, enquanto o consumo das vacas estabuladas apresentou correlaçäo significativa (P < 0,05) com a temperatura ambiental às 7 horas, com coeficiente de -0,27. Concluiu-se que as temperaturas baixas determinaram aumento no consumo de volumoso em vacas holandesas, sendo que os animais desabrigados consumiram em média 0,36 kgMS/vaca a mais que os estabulados, para cada unidade de diminuiçäo da temperatura do ar e aumento da umidade relativa e velocidade do vento, às 7 e 21 horas, simultaneamente