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Non-Newtonian standard viscosity fluids
International Communications in Heat and Mass Transfer 49 (2013) 1–4
Contents lists available at ScienceDirect
International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt
Non-Newtonian standard viscosity fluids☆ Jin M. Jung a,1, Dong H. Lee b,⁎, Young I. Cho a a b
Department of Mechanical Eng. and Mechanics, Drexel University, Philadelphia, PA 19104, USA Department of Mechanical Design Eng., Chonbuk National University, Jeonju 561-756, South Korea
a r t i c l e
i n f o
Available online 5 November 2013 Keywords: Non-Newtonian shear-thinning fluid Blood viscosity Standard viscosity fluid Blood viscometer
a b s t r a c t The objective of the present study was to develop and validate a new non-Newtonian shear-thinning standard viscosity fluid (SVF). The SVF exhibiting the non-Newtonian shear-thinning viscosity behavior of whole blood was necessary to evaluate the analytical performance of a blood viscometer according to Clinical Laboratory and Standards Institute (CLSI) guideline. The study utilized three different concentrations of maltose solution in water to cover high-, medium-, and low-viscosity ranges of whole blood. The SVFs could simulate whole blood viscosity over a wide range of shear rates and showed a long-term stability for at least 56 days with the coefficients of variations less than 5% in the viscosity measurements. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction Whole blood exhibits non-Newtonian shear-thinning behavior due to multiple factors, which include a large amount of cells suspended in plasma such as erythrocytes, as well as lipid molecules and plasma proteins such as fibrinogen and immunoglobulins. These plasma constituents affect the aggregation of erythrocytes and, in turn, blood viscosity, particularly when blood moves slowly in small vessels [1–3]. Elevated blood viscosity has been reported to be associated with increased risk of cardiovascular and microvascular diseases [4–6]. Should blood viscosity assessment become increasingly common in the diagnosis of vascular diseases, accurate measurement of blood viscosity will be essential. When a blood viscometer is used in a clinical laboratory setting, regular calibration tests are necessary. For this purpose, a control fluid or a SVF having a known viscosity profile demonstrating non-Newtonian shear-thinning behavior over a range of shear rates is needed. Furthermore, SVFs are needed when one wants to evaluate the analytical performance of the blood viscometer according to Clinical Laboratory and Standards Institute (CLSI) guideline EP-5A2 [7]. Since the CLSI guideline requires two separate runs per day (i.e., one in the morning and the other in the afternoon) for 20 days [8], one cannot use human blood as its viscosity changes approximately 48 h after drawn from the body by venipuncture [9]. Blood viscosity varies over a wide range in normal subjects because hematocrit, one of the primary determinants of the blood viscosity, varies over a wide range. Hence, one needs to have multiple SVFs that
☆ Communicated by W.J. Minkowycz. ⁎ Corresponding author. E-mail address: [email protected] (D.H. Lee). 1 Present address of Jin M. Jung: Chonbuk National University, Jeonju 561-756, South Korea. 0735-1933/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.icheatmasstransfer.2013.10.011
can demonstrate accuracy of viscometry instrumentation at high-, medium-, and low-viscosity ranges for whole blood. Standard viscosity fluids have long been in use for calibration of rotational viscometers. Illustrative examples include mineral oils, such as silicone, (Cannon Instrument Company, State College, PA). Note, silicone oil behaves as a Newtonian fluid, and its viscosity levels do not vary with the shear rate, whereas whole blood viscosity increases 4–8 times as the shear rate decreases from 300 to 1 s− 1, depending on the aggregability of erythrocytes [10,11]. As such, silicone oil and similar mineral oils cannot serve conveniently as a controlled SVF for calibration of a blood viscometer. The literature describes the use of blood analog fluids for hemodynamics studies which were based on water-soluble high-molecular-weight polymer materials [11–13]. A critical drawback of such blood analog fluids is the degradation of the fluid with time, as the long chain molecules (i.e., Mw N 106) are broken under high-shear flow conditions, altering the non-Newtonian shearthinning viscosity profile over time [13,14]. The objective of the present study was to develop and validate a new SVF that not only exhibits non-Newtonian shear-thinning viscosity characteristics over a physiologic range of shear rates but also stables over an extended period of time. 2. Methods The present study utilized a maltose solution, which was produced by adding enzymes such as α-amylase, β-amylase, and pullulanase to a mixture of cornstarch and water. The advantage of the maltose solution against the aforementioned aqueous high-molecular-weight polymer solutions was its relatively low molecular weight (i.e., Mw ~ 342), which is essential in maintaining stability. Three different levels of SVFs, i.e., high, medium, and low concentration samples, were prepared to mimic high, medium, and low non-Newtonian shear-thinning viscosity profiles of whole blood.
2
J.M. Jung et al. / International Communications in Heat and Mass Transfer 49 (2013) 1–4
Maltose solution and distilled water were precisely measured using a digital balance (CUX-420H, CAS, Korea) with a resolution of 0.001 g and mixed according to the formulas given in Table 1. The mixture was first stirred manually until string-like dense maltose globules were dissolved, and then the beaker containing the mixture was placed on a magnetic stirrer (HSD-180, Mtops, Korea) for an additional 10 min at room temperature. In order to investigate the non-Newtonian shear-thinning characteristics of SVFs, a scanning capillary viscometer (SCV) (Bio-Visco, Korea) was used, which gave the viscosity of SVFs at 37 °C over a range of shear rates, i.e., from 1 to 1000 s−1. The SCV utilized a U-shaped disposable tube with a capillary tube of 0.8 mm ID positioned in between two vertical tubes of 3 mm ID. The height difference of the SVF in the two vertical tubes was continuously monitored over time using two charge-coupled devices (CCDs) and two light-emitting diodes (LEDs) installed along the two vertical tubes. A detailed procedure of determining the blood viscosity from the height change at the SCV using the Casson model was described elsewhere [15,16]. Since the height variation was measured with the CCD-LED sensor, the SCV requires an opaque fluid that can block the transmission of light. Food dye in the form of aqueous solution (Black color, McCormick, MD) was added to the mixture of the maltose solution and distilled water at 0.1–0.4% by weight to make the SVFs opaque. Note that the viscosity of an aqueous solution does not vary for dye concentration of up to 2% [17]. Three different levels of SVFs (high, medium, and low concentrations) were prepared with concentrations of 32.0, 26.9, and 23.7 wt.% of the maltose solution, respectively. For each case, a SVF of 35–50 g was prepared in a beaker (see Table 1) and then divided into 12–15 plain vials, which were then stored at a refrigerator and kept at 4 °C until viscosity measurement. This procedure was repeated to make a total number of 60 SVF samples for each level of SVF. Repeatability tests were carried out every 24 h for six consecutive days by measuring the viscosity of each SVF sample six times. For each SVF test, two vials were randomly selected from the refrigerator, and the viscosities of both samples were measured. For longitudinal testing for SVF degradation, the viscosity of each SVF was measured every 7 days over six months. In each case, two vial samples were randomly selected from the refrigerator every 7 days, and the viscosities of both samples were measured. The data obtained in the repeatability and long-term degradation tests were averaged, and the coefficient of variations was calculated to quantify the dispersion or scatter of the measured viscosities of the SVFs in terms of a normalized distribution.
Fig. 1. Viscosity profiles of three different levels of SVFs and whole blood over shear rate ranges from 1 to 1000 s−1.
13 samples for each level of SVF, the mean values of the viscosity measured at a shear rate of 1 s− 1 were 56.32 ± 1.60, 22.35 ± 0.82, and 8.70 ± 0.29 cP for high, medium, and low SVFs, respectively, whereas those measured at a shear rate of 300 s− 1 were 7.16 ± 0.42, 3.90 ± 0.12, and 2.99 ± 0.13 cP for high, medium, and low SVFs, respectively. The effect of the concentration of the maltose solution on the viscosity of SVFs is shown in Fig. 2. By varying the concentration of the maltose solution, the viscosities measured from 13 samples for each level of SVF at a shear rate of 1 s−1 varied from 8.70 ± 0.29 to 56.32 ± 1.60 cP, whereas those measured at a shear rate of 300 s−1 varied from 2.99 ± 0.13 cP to 7.16 ± 0.42 cP. The results from the repeatability tests showed that the coefficient of variations was less than 5% for all three levels of SVFs over the range of shear rates. Fig. 3a–c shows the results of the viscosity measurements of three different SVFs prepared in plain vials with no-additive measured every 7 days over a period of six months. Based on the results shown in Fig. 3a–c, the viscosities of the SVFs prepared in plain vials showed no long-term degradation in the first 56 days. After that, the viscosity of SVF samples began to show some changes particularly in the medium SVF case despite continuous storage of the samples in a 4 °C environment. The coefficient of variations over the period of 56 days was also less than 5%.
3. Results Fig. 1 shows the non-Newtonian shear-thinning viscosity profiles of three different SVFs (high, medium, and low concentrations) over a range of shear rates. Based on the viscosity profiles measured from
Table 1 Mixing formula to prepare three different levels of SVFs having high, medium, and low viscosities. Black color food dye was obtained from McCormick, MD. Range of viscosity
Formula
High
Maltose Distilled water Dye Maltose Distilled water Dye Maltose Distilled water Dye
Medium
Low
Weight concentration of maltose solution 11.42 14.97 0.10 12.10 23.00 0.10 12.10 29.00 0.10
g g g g g g g g g
32.0%
26.9%
23.7% Fig. 2. Viscosity curves at three shear rates of 1, 5, and 300 s−1 at different concentrations of a maltose solution.
J.M. Jung et al. / International Communications in Heat and Mass Transfer 49 (2013) 1–4
3
The WBV using the SCV showed comparable results with the Brookfield viscometer at a wall shear rate of 300 s−1 in the Passing–Bablok regression analysis (slope 1.08; 95% CI, 0.98 to 1.18 and intercept −3.14; 95% CI, −7.09 to 0.60) [8]. In addition, the blood viscosity data obtained from the Couette low-shear viscometer (i.e., Contraves LS-30) were compared with those from SCV at shear rates of 1.29, 3.23, 8.11, 15.0, and 51.2 s−1. Compared to average Couette values, the mean difference for the SCV was −1.4 ± 1.5% for blood at native hematocrit [18]. Hence, these comparison studies indicate that the SCV provides accurate and reproducible viscosity data in both high and low shear rate ranges as long as the wall shear rate is used for viscosity measurements in the SCV. The present study selected three concentrations of the maltose solution as shown in Table 1 as these three concentrations could cover a wide range of whole blood viscosity occurring in clinical practice. If one desires a SVF with a different viscosity range, the concentration of the maltose solution corresponding to the different range could easily be selected from the graphs in Fig. 2. One of the concerns in developing SVF is how variable the maltose solution is as it is produced commercially. In this regard, the present study recommends that whenever a batch of a SVF is prepared, the viscosity of the SVF should be measured and accompanied with the SVF. In fact, this is a common practice for most standard fluids used for the quality-control procedure in laboratory medicine. 5. Conclusions The present study investigated non-Newtonian standard viscosity fluids (SVFs). By utilizing different concentrations of maltose solution in water, the SVFs could cover a wide range of blood viscosity. Both the repeatability and long-term degradation tests gave the coefficients of variations less than 5%. When the SVFs were stored at 4 °C environment, the viscosities of the SVFs were found unchanged for at least 56 days. The present study demonstrated that the SVFs could be used for the CLSI analytical performance evaluation of a blood viscometer. Acknowledgment The present work was partially supported by a grant from the Ministry of Education, Science and Technology of Korea through the National Research Foundation (project no. 2013-027389). References
Fig. 3. Results of long-term stability tests with a) high SVF, b) medium SVF, and c) low SVF stored for six months in plain vials.
4. Discussion A capillary tube viscometer is one of the oldest viscometer types used for liquid viscosity measurements. However, it does not have a constant shear rate at the tube cross-section as the flow velocity in the tube has a parabolic profile. On the other hand, the rotating viscometers such as cone-and-plate and Couette types have a constant shear rate between cone and plate or two cylinders. Hence, one might say that the viscosity should also be measured using a rotating viscometer and compare the results with those from the SCV. In this regard, the comparison test of the viscosity measurements between Brookfield cone-and-plate rotating viscometer and the SVC was reported, where 227 whole human blood samples were used [8].
[1] M.H. Mansour, N.W. Bressloff, C.P. Shearman, Red blood cell migration in microvessels, Biorheology 47 (1) (2010) 73–93. [2] Y.I. Cho, D.J. Cho, Hemorheology and microvascular disorders, Korean Circ. J. 41 (6) (2011) 287–295. [3] G. Cokelet, Hemorheology and Hemodynamics, Morgan & Claypool Life Sciences, 2011. 27–56. [4] G. De Simone, R.B. Devereux, S. Chien, M.H. Alderman, S.A. Atlas, J.H. Laragh, Relation of blood viscosity to demographic and physiologic variables and to cardiovascular risk factors in apparently normal adults, Circulation 81 (1) (1990) 107–117. [5] K.R. Kensey, The mechanistic relationships between hemorrheological characteristics and cardiovascular disease, Curr. Med. Res. Opin. 19 (7) (2003) 587–596. [6] G. Lowe, F. Fowkes, J. Dawes, P. Donnan, S. Lennie, E. Housley, Blood viscosity, fibrinogen, and activation of coagulation and leukocytes in peripheral arterial disease and the normal population in the Edinburgh Artery Study, Circulation 87 (6) (1993) 1915–1920. [7] D.W. Tholen, Evaluation of Precision Performance of Quantitative Measurement Methods: Approved Guideline, Second edition National Committee for Clinical Laboratory Standards, 2004. [8] H. Kim, Y.I. Cho, D.-H. Lee, C.-M. Park, H.-W. Moon, M. Hur, J.Q. Kim, Y.-M. Yun, Analytical performance evaluation of the scanning capillary tube viscometer for measurement of whole blood viscosity, Clin. Biochem. 46 (2013) 139–142. [9] O.K. Baskurt, M. Boynard, G.C. Cokelet, P. Connes, B.M. Cooke, S. Forconi, F. Liao, M.R. Hardeman, F. Jung, H.J. Meiselman, New guidelines for hemorheological laboratory techniques, Clin. Hemorheol. Microcirc. 42 (2) (2009) 75–97. [10] O.K. Baskurt, H.J. Meiselman, Blood rheology and hemodynamics, Semin. Thromb. Hemost. 29 (5) (2003) 435–450. [11] Y.I. Cho, K.R. Kensey, Effects of the non-NEWTONIAN viscosity of blood on flows in a diseased arterial vessel. Part 1: steady flows, Biorheology 28 (3–4) (1991) 241–262. [12] D. Mann, J. Tarbell, Flow of non-Newtonian blood analog fluids in rigid curved and straight artery models, Biorheology 27 (5) (1990) 711.
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[13] T. Naiki, Y. Yamai, K. Hayashi, Evaluation of high polymer solutions as blood analog fluid—for the model study of hemodynamics, J. Jpn. Soc. Biorheol. 9 (1995) 84–89. [14] N. Srivastava, M.A. Burns, Analysis of non-Newtonian liquids using a microfluidic capillary viscometer, Anal. Chem. 78 (5) (2006) 1690–1696. [15] S. Kim, Y.I. Cho, W.N. Hogenauer, K.R. Kensey, A method of isolating surface tension and yield stress effects in a U-shaped scanning capillary-tube viscometer using a Casson model, J. Non-Newtonian Fluid Mech. 103 (2–3) (2002) 205–219.
[16] S. Kim, B. Namgung, P.K. Ong, Y.I. Cho, K.J. Chun, D. Lim, Determination of rheological properties of whole blood with a scanning capillary-tube rheometer using constitutive models, J. Mech. Sci. Technol. 23 (6) (2009) 1718–1726. [17] S. Kim, Y.I. Cho, The effect of dye concentration on the viscosity of water in a scanning capillary-tube viscometer, J. Non-Newtonian Fluid Mech. 111 (1) (2003) 63–68. [18] T. Alexy, R.B. Wenby, E. Pais, L.J. Goldstein, W. Hogenauer, H.J. Meiselman, An automated tube-type blood viscometer: validation studies, Biorheology 42 (3) (2005) 237–247.
Contents lists available at ScienceDirect
International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt
Non-Newtonian standard viscosity fluids☆ Jin M. Jung a,1, Dong H. Lee b,⁎, Young I. Cho a a b
Department of Mechanical Eng. and Mechanics, Drexel University, Philadelphia, PA 19104, USA Department of Mechanical Design Eng., Chonbuk National University, Jeonju 561-756, South Korea
a r t i c l e
i n f o
Available online 5 November 2013 Keywords: Non-Newtonian shear-thinning fluid Blood viscosity Standard viscosity fluid Blood viscometer
a b s t r a c t The objective of the present study was to develop and validate a new non-Newtonian shear-thinning standard viscosity fluid (SVF). The SVF exhibiting the non-Newtonian shear-thinning viscosity behavior of whole blood was necessary to evaluate the analytical performance of a blood viscometer according to Clinical Laboratory and Standards Institute (CLSI) guideline. The study utilized three different concentrations of maltose solution in water to cover high-, medium-, and low-viscosity ranges of whole blood. The SVFs could simulate whole blood viscosity over a wide range of shear rates and showed a long-term stability for at least 56 days with the coefficients of variations less than 5% in the viscosity measurements. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction Whole blood exhibits non-Newtonian shear-thinning behavior due to multiple factors, which include a large amount of cells suspended in plasma such as erythrocytes, as well as lipid molecules and plasma proteins such as fibrinogen and immunoglobulins. These plasma constituents affect the aggregation of erythrocytes and, in turn, blood viscosity, particularly when blood moves slowly in small vessels [1–3]. Elevated blood viscosity has been reported to be associated with increased risk of cardiovascular and microvascular diseases [4–6]. Should blood viscosity assessment become increasingly common in the diagnosis of vascular diseases, accurate measurement of blood viscosity will be essential. When a blood viscometer is used in a clinical laboratory setting, regular calibration tests are necessary. For this purpose, a control fluid or a SVF having a known viscosity profile demonstrating non-Newtonian shear-thinning behavior over a range of shear rates is needed. Furthermore, SVFs are needed when one wants to evaluate the analytical performance of the blood viscometer according to Clinical Laboratory and Standards Institute (CLSI) guideline EP-5A2 [7]. Since the CLSI guideline requires two separate runs per day (i.e., one in the morning and the other in the afternoon) for 20 days [8], one cannot use human blood as its viscosity changes approximately 48 h after drawn from the body by venipuncture [9]. Blood viscosity varies over a wide range in normal subjects because hematocrit, one of the primary determinants of the blood viscosity, varies over a wide range. Hence, one needs to have multiple SVFs that
☆ Communicated by W.J. Minkowycz. ⁎ Corresponding author. E-mail address: [email protected] (D.H. Lee). 1 Present address of Jin M. Jung: Chonbuk National University, Jeonju 561-756, South Korea. 0735-1933/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.icheatmasstransfer.2013.10.011
can demonstrate accuracy of viscometry instrumentation at high-, medium-, and low-viscosity ranges for whole blood. Standard viscosity fluids have long been in use for calibration of rotational viscometers. Illustrative examples include mineral oils, such as silicone, (Cannon Instrument Company, State College, PA). Note, silicone oil behaves as a Newtonian fluid, and its viscosity levels do not vary with the shear rate, whereas whole blood viscosity increases 4–8 times as the shear rate decreases from 300 to 1 s− 1, depending on the aggregability of erythrocytes [10,11]. As such, silicone oil and similar mineral oils cannot serve conveniently as a controlled SVF for calibration of a blood viscometer. The literature describes the use of blood analog fluids for hemodynamics studies which were based on water-soluble high-molecular-weight polymer materials [11–13]. A critical drawback of such blood analog fluids is the degradation of the fluid with time, as the long chain molecules (i.e., Mw N 106) are broken under high-shear flow conditions, altering the non-Newtonian shearthinning viscosity profile over time [13,14]. The objective of the present study was to develop and validate a new SVF that not only exhibits non-Newtonian shear-thinning viscosity characteristics over a physiologic range of shear rates but also stables over an extended period of time. 2. Methods The present study utilized a maltose solution, which was produced by adding enzymes such as α-amylase, β-amylase, and pullulanase to a mixture of cornstarch and water. The advantage of the maltose solution against the aforementioned aqueous high-molecular-weight polymer solutions was its relatively low molecular weight (i.e., Mw ~ 342), which is essential in maintaining stability. Three different levels of SVFs, i.e., high, medium, and low concentration samples, were prepared to mimic high, medium, and low non-Newtonian shear-thinning viscosity profiles of whole blood.
2
J.M. Jung et al. / International Communications in Heat and Mass Transfer 49 (2013) 1–4
Maltose solution and distilled water were precisely measured using a digital balance (CUX-420H, CAS, Korea) with a resolution of 0.001 g and mixed according to the formulas given in Table 1. The mixture was first stirred manually until string-like dense maltose globules were dissolved, and then the beaker containing the mixture was placed on a magnetic stirrer (HSD-180, Mtops, Korea) for an additional 10 min at room temperature. In order to investigate the non-Newtonian shear-thinning characteristics of SVFs, a scanning capillary viscometer (SCV) (Bio-Visco, Korea) was used, which gave the viscosity of SVFs at 37 °C over a range of shear rates, i.e., from 1 to 1000 s−1. The SCV utilized a U-shaped disposable tube with a capillary tube of 0.8 mm ID positioned in between two vertical tubes of 3 mm ID. The height difference of the SVF in the two vertical tubes was continuously monitored over time using two charge-coupled devices (CCDs) and two light-emitting diodes (LEDs) installed along the two vertical tubes. A detailed procedure of determining the blood viscosity from the height change at the SCV using the Casson model was described elsewhere [15,16]. Since the height variation was measured with the CCD-LED sensor, the SCV requires an opaque fluid that can block the transmission of light. Food dye in the form of aqueous solution (Black color, McCormick, MD) was added to the mixture of the maltose solution and distilled water at 0.1–0.4% by weight to make the SVFs opaque. Note that the viscosity of an aqueous solution does not vary for dye concentration of up to 2% [17]. Three different levels of SVFs (high, medium, and low concentrations) were prepared with concentrations of 32.0, 26.9, and 23.7 wt.% of the maltose solution, respectively. For each case, a SVF of 35–50 g was prepared in a beaker (see Table 1) and then divided into 12–15 plain vials, which were then stored at a refrigerator and kept at 4 °C until viscosity measurement. This procedure was repeated to make a total number of 60 SVF samples for each level of SVF. Repeatability tests were carried out every 24 h for six consecutive days by measuring the viscosity of each SVF sample six times. For each SVF test, two vials were randomly selected from the refrigerator, and the viscosities of both samples were measured. For longitudinal testing for SVF degradation, the viscosity of each SVF was measured every 7 days over six months. In each case, two vial samples were randomly selected from the refrigerator every 7 days, and the viscosities of both samples were measured. The data obtained in the repeatability and long-term degradation tests were averaged, and the coefficient of variations was calculated to quantify the dispersion or scatter of the measured viscosities of the SVFs in terms of a normalized distribution.
Fig. 1. Viscosity profiles of three different levels of SVFs and whole blood over shear rate ranges from 1 to 1000 s−1.
13 samples for each level of SVF, the mean values of the viscosity measured at a shear rate of 1 s− 1 were 56.32 ± 1.60, 22.35 ± 0.82, and 8.70 ± 0.29 cP for high, medium, and low SVFs, respectively, whereas those measured at a shear rate of 300 s− 1 were 7.16 ± 0.42, 3.90 ± 0.12, and 2.99 ± 0.13 cP for high, medium, and low SVFs, respectively. The effect of the concentration of the maltose solution on the viscosity of SVFs is shown in Fig. 2. By varying the concentration of the maltose solution, the viscosities measured from 13 samples for each level of SVF at a shear rate of 1 s−1 varied from 8.70 ± 0.29 to 56.32 ± 1.60 cP, whereas those measured at a shear rate of 300 s−1 varied from 2.99 ± 0.13 cP to 7.16 ± 0.42 cP. The results from the repeatability tests showed that the coefficient of variations was less than 5% for all three levels of SVFs over the range of shear rates. Fig. 3a–c shows the results of the viscosity measurements of three different SVFs prepared in plain vials with no-additive measured every 7 days over a period of six months. Based on the results shown in Fig. 3a–c, the viscosities of the SVFs prepared in plain vials showed no long-term degradation in the first 56 days. After that, the viscosity of SVF samples began to show some changes particularly in the medium SVF case despite continuous storage of the samples in a 4 °C environment. The coefficient of variations over the period of 56 days was also less than 5%.
3. Results Fig. 1 shows the non-Newtonian shear-thinning viscosity profiles of three different SVFs (high, medium, and low concentrations) over a range of shear rates. Based on the viscosity profiles measured from
Table 1 Mixing formula to prepare three different levels of SVFs having high, medium, and low viscosities. Black color food dye was obtained from McCormick, MD. Range of viscosity
Formula
High
Maltose Distilled water Dye Maltose Distilled water Dye Maltose Distilled water Dye
Medium
Low
Weight concentration of maltose solution 11.42 14.97 0.10 12.10 23.00 0.10 12.10 29.00 0.10
g g g g g g g g g
32.0%
26.9%
23.7% Fig. 2. Viscosity curves at three shear rates of 1, 5, and 300 s−1 at different concentrations of a maltose solution.
J.M. Jung et al. / International Communications in Heat and Mass Transfer 49 (2013) 1–4
3
The WBV using the SCV showed comparable results with the Brookfield viscometer at a wall shear rate of 300 s−1 in the Passing–Bablok regression analysis (slope 1.08; 95% CI, 0.98 to 1.18 and intercept −3.14; 95% CI, −7.09 to 0.60) [8]. In addition, the blood viscosity data obtained from the Couette low-shear viscometer (i.e., Contraves LS-30) were compared with those from SCV at shear rates of 1.29, 3.23, 8.11, 15.0, and 51.2 s−1. Compared to average Couette values, the mean difference for the SCV was −1.4 ± 1.5% for blood at native hematocrit [18]. Hence, these comparison studies indicate that the SCV provides accurate and reproducible viscosity data in both high and low shear rate ranges as long as the wall shear rate is used for viscosity measurements in the SCV. The present study selected three concentrations of the maltose solution as shown in Table 1 as these three concentrations could cover a wide range of whole blood viscosity occurring in clinical practice. If one desires a SVF with a different viscosity range, the concentration of the maltose solution corresponding to the different range could easily be selected from the graphs in Fig. 2. One of the concerns in developing SVF is how variable the maltose solution is as it is produced commercially. In this regard, the present study recommends that whenever a batch of a SVF is prepared, the viscosity of the SVF should be measured and accompanied with the SVF. In fact, this is a common practice for most standard fluids used for the quality-control procedure in laboratory medicine. 5. Conclusions The present study investigated non-Newtonian standard viscosity fluids (SVFs). By utilizing different concentrations of maltose solution in water, the SVFs could cover a wide range of blood viscosity. Both the repeatability and long-term degradation tests gave the coefficients of variations less than 5%. When the SVFs were stored at 4 °C environment, the viscosities of the SVFs were found unchanged for at least 56 days. The present study demonstrated that the SVFs could be used for the CLSI analytical performance evaluation of a blood viscometer. Acknowledgment The present work was partially supported by a grant from the Ministry of Education, Science and Technology of Korea through the National Research Foundation (project no. 2013-027389). References
Fig. 3. Results of long-term stability tests with a) high SVF, b) medium SVF, and c) low SVF stored for six months in plain vials.
4. Discussion A capillary tube viscometer is one of the oldest viscometer types used for liquid viscosity measurements. However, it does not have a constant shear rate at the tube cross-section as the flow velocity in the tube has a parabolic profile. On the other hand, the rotating viscometers such as cone-and-plate and Couette types have a constant shear rate between cone and plate or two cylinders. Hence, one might say that the viscosity should also be measured using a rotating viscometer and compare the results with those from the SCV. In this regard, the comparison test of the viscosity measurements between Brookfield cone-and-plate rotating viscometer and the SVC was reported, where 227 whole human blood samples were used [8].
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