Controlling the Motion of Ferrofluid Droplets Using Surface Tension Gradients and Magnetoviscous Pinning.

This work demonstrates the controlled motion and stopping of individual ferrofluid droplets due to a surface tension gradient and a uniform magnetic field. The surface tension gradients are created by patterning hydrophilic aluminum regions, shaped as wedges, on a hydrophobic copper surface. This pattern facilitates the spontaneous motion of water-based ferrofluid droplets down the length of the wedge toward the more hydrophilic aluminum end due to a net capillarity force created by the underlying surface wettability gradient. We observed that applying a magnetic field parallel to the surface tension gradient direction has little or no effect on the droplet's motion, while a moderate perpendicular magnetic field can stop the motion altogether effectively "pinning" the droplet. In the absence of the surface tension gradient, droplets elongate in the presence of a parallel field but do not travel. This control of the motion of individual droplets might lend itself to some biomedical and lab-on-a-chip applications. The directional dependence of the magnetoviscosity observed in this work is believed to be the consequence of the formation of nanoparticle chains in the fluid due to the existence of a minority of relatively larger magnetic particles.

Vitamin A requirements assessed by plasma response to supplementation during pregnancy.

Plasma vitamin A responses were examined in 30 low income pregnant women before and after supplementation with vitamin A. In the groups of women who had an initial (at < 20 weeks) plasma vitamin A of less than 30 micrograms/dl retinol, typical changes representing a peak at mid gestation and a significant decline at term were observed. Supplementation with vitamin A tablets equivalent to 1800 micrograms of retinol daily for 12 weeks was able to raise the plasma vitamin A content at term. On the other hand, those women who had an initial plasma vitamin A concentration of more than 30 micrograms/dl did not show any appreciable changes even with vitamin A supplementation. Consistent beneficial effects of supplementation on maternal and cord vitamin A and maternal hemoglobin and progesterone were noted in our previous studies only when the supplementation lasted for 12 weeks and not after 10 weeks. Using these data with dietary intake obtained from other studies, an attempt was made to estimate the requirements of vitamin A during pregnancy. The approximate requirement of 780 retinol equivalents (RE) obtained, is in agreement with earlier recommendations of FAO and Indian Council of Medical Research (ICMR) Expert Committees, but is higher than the recent ICMR recommendations.

A new model for producing vitamin A deficiency in rats.

To produce a rapid depletion of vitamin A, an experimental approach based on partial hepatectomy (60%) to remove stores and feeding a vitamin A deficient diet during recovery was tested in weanling and adult wistar rats. Plasma and liver vitamin A levels were determined at appropriate time points along with food intakes and body weights. Adult rats fed a deficient diet for a period of one month during regeneration, exhibited significantly lower values (mean +/- SE) of liver vitamin A (176 +/- 19 micrograms/g) compared to controls (256 +/- 41 micrograms/g) receiving vitamin A supplements. However, these levels are not in the deficient range and the plasma vitamin A levels were not altered. Therefore, adult animals were not considered a suitable model for such experiments. In similar experiments with weanling rats, sham-operated controls kept on a vitamin A-free diet showed a liver vitamin A concentration of 16 +/- 1.2 micrograms/g after six weeks. Hepatectomized animals kept on a similar diet showed 5.2 +/- 1.1 micrograms/g liver in contrast to those fed on a vitamin A supplemented diet (328 +/- 27 micrograms/g). Also, the plasma vitamin A of hepatectomized animals on a vitamin A-deficient diet was very low (4.3 +/- 1.5 micrograms/dl) as compared to that in either supplemented or sham-operated controls. Thus rapid deficiency of nutrients like vitamin A could be produced using a hepatectomy and regeneration model in weanling rats, which otherwise may take much longer time.

Assessment of vitamin A status in pregnant women as reflected by in vitro destruction of vitamin A by hemolysates and urinary ammonium nitrogen to creatinine ratio.

To investigate the significance of the lowered plasma vitamin A during the last few weeks of pregnancy, the capacity of erythrocyte lysates to destroy vitamin A in vitro and the alteration in ammonium nitrogen to creatinine ratio (Am N/Cr) in random urine samples was followed up at different gestational ages in women from low income groups. One group received no supplementation and the other received supplements of 1800 retinol equivalents (RE) and at most points the number of observations were not less than 12. In the unsupplemented women there was a significant increase in the capacity of erythrocytes to destroy vitamin A in vitro, which reflects an increased oxidative stress as compared to the supplemented group. While differences in mean Am N/Cr did not follow any consistent pattern, there was a strong association between lowered plasma vitamin A (< 35 micrograms/dl) and increased Am N/Cr ratio (> 0.5). This was true only when combined data of both groups were considered till 26 weeks of gestation and not beyond. As expected in supplemented women there was no significant fall in the plasma vitamin A during term. These data reveal that the lowered plasma vitamin A levels are suggestive of greater risk of hypovitaminosis A during pregnancy as indicated by the oxidative stress in erythrocytes.

Effect of vitamin A supplementation of plasma progesterone and estradiol levels during pregnancy.

The effect of vitamin A supplementation on plasma estrogen and progesterone were studied in pregnant women. While there was no change in the estrogen concentration, the mean increment in plasma progesterone in the supplemented group was significant when compared to the unsupplemented group. It is suggested that vitamin A supplementation to undernourished pregnant women may have beneficial effect on feto-placental function.

Effect of vitamin A supplementation on haemoglobin and vitamin A levels during pregnancy.

About 450 pregnant women from a low-income group were recruited to study the effect of vitamin A supplementation on plasma vitamin A levels in the mother and cord and on the birth weights of the neonates. Results showed that supplementation with 1800 micrograms vitamin A/d for more than 12 weeks prevented the decline in plasma vitamin A that otherwise occurs during the last few weeks of pregnancy. This improvement in maternal values for vitamin A at a critical time of development favourably affected availability to the fetus, as reflected by the marked elevation in cord levels. Supplementation for a period of 12 weeks was found to be sufficient, since subsequent discontinuation did not alter the beneficial response. Apart from increasing maternal and cord vitamin A levels, vitamin A supplementation along with iron prevented, in this study, the significant decline in haemoglobin occurring at 26-28 weeks of gestation. The birth weights were not altered by vitamin A supplementation.

Plasma levels of estradiol & progesterone at different gestational ages in Indian women.

Plasma levels of estradiol and progesterone were determined at different gestational ages in Indian pregnant women from the low socio-economic group. The levels of estradiol and progesterone progressively increased with gestation and reached maximum values (14.35 +/- 1.092 and 145.9 +/- 7.69 ng/ml, respectively) by term. Though the estradiol values were comparable to those reported in literature, the term values of progesterone were found to be lower (145.9 +/- 7.69 ng/ml) than those reported from Western countries (160 +/- 7.5 ng/ml) at 34-38 wk of gestation. These low progesterone values may have physiological implication in placental function.

Evaluation of a colorimetric method for vitamin A estimation.

A simple colorimetric procedure for plasma vitamin A is evaluated, which does not require sophisticated or expensive equipment. Vitamin A values obtained with 30 human plasma samples and 11 liver samples obtained from lactating rabbits, using a colorimetric procedure based on Carr-Price reaction with ferric chloride and acetyl chloride were compared with those obtained with spectrophotometric and spectrofluorimetric micro methods. With widely varying plasma samples, the values showed a high degree correlation and good agreement. The intraassay variation was 3% which is in the acceptable range. The plasma samples could be analysed within 4 weeks and the reagents, were found to be stable, unlike some batches of trifluoro acetic acid (TFA).