Aniruddha Bagchi | University of Minnesota - Twin Cities (original) (raw)

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Papers by Aniruddha Bagchi

Composites Science and Technology, 2006

In this paper, a theoretical model has been developed for predicting the effective thermal conduc... more In this paper, a theoretical model has been developed for predicting the effective thermal conductivity of an aligned multi-walled nanotube polymer composite. This model is based on an effective medium theory that has been developed for composites containing aligned spheroidal inclusions with imperfect interfaces. To incorporate the nanotube structure into this theory, a continuum model of the nanotube geometry is developed by considering its structure and the mechanism of heat conduction through it. Results show that the overall conductivity will be much lower than expected due to the fact that in the composite, the outer nanotube layer carries the bulk of the heat flowing through the nanotube. It is also seen that the high nanotube-matrix boundary resistance does not significantly affect the overall conductivity. The effective conductivity was also found to be highly sensitive to the nanotube diameter.

Regenerative Medicine, 2010

The expansion of cellular therapeutics will require large-scale manufacturing processes to expand... more The expansion of cellular therapeutics will require large-scale manufacturing processes to expand and package cell products, which may not be feasible with current blood-banking bag technology. This study investigated the potential for freezing, storing and shipping cell therapy products using novel pharmaceutical-grade Crystal Zenith((R)) (CZ) plastic vials. CZ vials (0.5, 5 and 30 ml volume) with several closure systems were filled with mesenchymal stem cells and stored at either -85 or -196 degrees C for 6 months. Vials were tested for their ability to maintain cell viability, proliferative and differentiation capacity, as well as durability and integrity utilizing a 1-m drop test. As controls, 2 ml polypropylene vials were investigated under the same conditions. Post-thaw viability utilizing a dye exclusion assay was over 95% in all samples. Stored cells exhibited rapid recovery 2 h post-thaw and cultures were approximately 70% confluent within 5-7 days, consistent with nonfrozen controls and indicative of functional recovery. Doubling times were consistent over all vials. The doubling rate for cells from CZ vials were 2.14 + or - 0.83 days (1 week), 1.84 + or - 0.68 days (1 month) and 1.79 + or - 0.71 days (6 months), which were not significantly different compared with frozen and fresh controls. Cells recovered from the vials exhibited trilineage differentiation consistent with controls. As part of vial integrity via drop testing, no evidence of external damage was found on vial surfaces or on closure systems. Furthermore, the filled vials stored for 6 months were tested for container closure integrity. Vials removed from freezer conditions were transported to the test laboratory on dry ice and tested using pharmaceutical packaging tests, including dye ingress and microbial challenge. The results of all stoppered vials indicated container closure integrity with no failures. Pharmaceutical-grade plastic CZ vials, which are commercially used to package pharmaceutical products, are suitable for low-temperature storage and transport of mesenchymal stem cells, and are a scalable container system for commercial manufacturing and fill-finish operation of cell therapy products.

International Journal of Heat and Mass Transfer, 2011

A numerical study of two-dimensional natural convection in fluid–superposed porous layers heated ... more A numerical study of two-dimensional natural convection in fluid–superposed porous layers heated locally from below is reported based on the one-domain formulation of the conservation equations. The effects of five dimensionless parameters on overall Nusselt number are ...

International Journal of Heat and Mass Transfer, 2012

An experimental study of natural convection in fluid-superposed porous layers heated locally from... more An experimental study of natural convection in fluid-superposed porous layers heated locally from below is reported. Measurements are made in a rectangular chamber with 3 mm DIA glass beads as the porous layer and distilled water as the saturating fluid. The effects of the heater-to-cavity length ratio and the porous layer-to-cavity height ratio on the overall heat transfer coefficients are reported. Average heat transfer coefficients over the heated surface increase with a decrease in porous layer-to-cavity height ratio, but no clear effect of heater-to-cavity length ratio is seen. Temperature profiles in the domain reveal a plume like flow with a single pair of circulating cells and evidence of convective motion inside the porous layer.

Expert Review of Medical Devices, 2008

Over the last half the 20th Century, reproductive medicine has become a critically important bran... more Over the last half the 20th Century, reproductive medicine has become a critically important branch of modern medical science. Fertility preservation is a vital branch of reproductive medicine and involves the preservation of gametes (sperm and oocytes), embryos, and reproductive tissues (ovarian and testicular tissues) for use in artificial reproduction. This technology gives millions of people suffering from reproductive ailments, cancer patients who have their reproductive functions destroyed by therapy (chemotherapy and radiation) and people undergoing sterilization, a chance to conceive. The most common fertility preservation technique is cryopreservation, which involves freezing cells and tissues at cryogenic temperatures. Cryopreserved cells and tissues can endure storage for centuries with almost no change in functionality or genetic information, making this storage method highly attractive. However, developing efficient cryopreservation techniques is challenging, as both freezing and thawing exposes cells to severe stresses, potentially causing cell death. There are two major techniques for cryopreservation: freeze-thaw processes and vitrification. The major difference between them is the total avoidance of ice formation in vitrification. The use of both theoretical models that describe cell response to freezing and thawing, and experimental investigations of freezing behavior, has led to the development of successful freeze-thaw and vitrification procedures for a number of cell types. Among reproductive cells, there exist efficient cryopreservation techniques for spermatozoa and embryos. Oocytes, however, present significant hurdles in achieving successful cryopreservation, primarily due to their sensitive microtubule structure. Recently, cryopreservation of ovarian and testicular tissues has been investigated with success reported. Ovarian cryopreservation can help circumvent many of the problems associated with oocyte cryopreservation, while testicular tissue preservation may be helpful when insufficient sperm counts are available for routine semen preservation.

Cryobiology, 2008

Macromolecules and salts are ubiquitous in biology in both intra-and extracellular solutions. As ... more Macromolecules and salts are ubiquitous in biology in both intra-and extracellular solutions. As both of these solutes exhibit non-ideal behaviour at very low concentrations, they have a marked effect on the solution thermodynamics, especially when the solutes are concentrated during freezing by the removal of water as ice. We have previously shown that salts alone or salts in combination with certain small molecules have osmotic behaviour that is well predicted by our osmotic virial equation. However, it has been shown that the solution behaviour of macromolecules is altered when the salt concentration is varied, but equations have not been developed to predict the osmolality of these solutions accurately. The objective of this study was to determine the osmotic virial coefficients for macromolecules in various salt solutions and investigate the changes in these coefficients as a function of the salt concentration. The phase diagrams for hydroxyethyl starch (HES) in varying concentrations of NaCl were obtained from the literature for mass ratios (R values) ranging from 0.5 to 20. Our multisolute osmotic virial equation was fit to each HES + NaCl phase diagram, using the osmotic virial coefficients for NaCl that were previously determined, to obtain the osmotic virial coefficients for HES at each R value. The osmotic virial coefficients were plotted as a function of R value and analyzed in order to obtain equations to determine the osmotic virial coefficient dependence on salt concentration. The effect of salt on macromolecules should be taken into account when modeling these solutions. The osmotic virial coefficients show a strong dependence on the R value, which may lead to the development of equations to predict osmotic virial coefficients as a function of the salt concentration. (Conflicts of interest: None declared.

Cryobiology, 2010

Partial phase diagrams are of considerable utility in the development of optimized cryobiological... more Partial phase diagrams are of considerable utility in the development of optimized cryobiological procedures. Recent theoretical predictions of the melting points of ternary solutions of interest to cryobiology have caused us to re-examine measurments that our group made for the ethylene-glycol-sodium chloride-water phase diagram. Here we revisit our previous experiments by measuring melting points at five ethylene-glycol to sodium chloride ratios (R values; R = 5, 10, 15, 30, and 45) and five levels of concentration for each ratio. Melting points were averaged from three measurements and plotted as a function of total solute concentration for each R value studied. The new measurements differed from our original experimental values and agreed with predicted values from both theoretical models. Additionally, the data were fit to the polynomial described in our previous report and the resulting equation was obtained:

Composites Science and Technology, 2006

In this paper, a theoretical model has been developed for predicting the effective thermal conduc... more In this paper, a theoretical model has been developed for predicting the effective thermal conductivity of an aligned multi-walled nanotube polymer composite. This model is based on an effective medium theory that has been developed for composites containing aligned spheroidal inclusions with imperfect interfaces. To incorporate the nanotube structure into this theory, a continuum model of the nanotube geometry is developed by considering its structure and the mechanism of heat conduction through it. Results show that the overall conductivity will be much lower than expected due to the fact that in the composite, the outer nanotube layer carries the bulk of the heat flowing through the nanotube. It is also seen that the high nanotube-matrix boundary resistance does not significantly affect the overall conductivity. The effective conductivity was also found to be highly sensitive to the nanotube diameter.

Regenerative Medicine, 2010

The expansion of cellular therapeutics will require large-scale manufacturing processes to expand... more The expansion of cellular therapeutics will require large-scale manufacturing processes to expand and package cell products, which may not be feasible with current blood-banking bag technology. This study investigated the potential for freezing, storing and shipping cell therapy products using novel pharmaceutical-grade Crystal Zenith((R)) (CZ) plastic vials. CZ vials (0.5, 5 and 30 ml volume) with several closure systems were filled with mesenchymal stem cells and stored at either -85 or -196 degrees C for 6 months. Vials were tested for their ability to maintain cell viability, proliferative and differentiation capacity, as well as durability and integrity utilizing a 1-m drop test. As controls, 2 ml polypropylene vials were investigated under the same conditions. Post-thaw viability utilizing a dye exclusion assay was over 95% in all samples. Stored cells exhibited rapid recovery 2 h post-thaw and cultures were approximately 70% confluent within 5-7 days, consistent with nonfrozen controls and indicative of functional recovery. Doubling times were consistent over all vials. The doubling rate for cells from CZ vials were 2.14 + or - 0.83 days (1 week), 1.84 + or - 0.68 days (1 month) and 1.79 + or - 0.71 days (6 months), which were not significantly different compared with frozen and fresh controls. Cells recovered from the vials exhibited trilineage differentiation consistent with controls. As part of vial integrity via drop testing, no evidence of external damage was found on vial surfaces or on closure systems. Furthermore, the filled vials stored for 6 months were tested for container closure integrity. Vials removed from freezer conditions were transported to the test laboratory on dry ice and tested using pharmaceutical packaging tests, including dye ingress and microbial challenge. The results of all stoppered vials indicated container closure integrity with no failures. Pharmaceutical-grade plastic CZ vials, which are commercially used to package pharmaceutical products, are suitable for low-temperature storage and transport of mesenchymal stem cells, and are a scalable container system for commercial manufacturing and fill-finish operation of cell therapy products.

International Journal of Heat and Mass Transfer, 2011

A numerical study of two-dimensional natural convection in fluid–superposed porous layers heated ... more A numerical study of two-dimensional natural convection in fluid–superposed porous layers heated locally from below is reported based on the one-domain formulation of the conservation equations. The effects of five dimensionless parameters on overall Nusselt number are ...

International Journal of Heat and Mass Transfer, 2012

An experimental study of natural convection in fluid-superposed porous layers heated locally from... more An experimental study of natural convection in fluid-superposed porous layers heated locally from below is reported. Measurements are made in a rectangular chamber with 3 mm DIA glass beads as the porous layer and distilled water as the saturating fluid. The effects of the heater-to-cavity length ratio and the porous layer-to-cavity height ratio on the overall heat transfer coefficients are reported. Average heat transfer coefficients over the heated surface increase with a decrease in porous layer-to-cavity height ratio, but no clear effect of heater-to-cavity length ratio is seen. Temperature profiles in the domain reveal a plume like flow with a single pair of circulating cells and evidence of convective motion inside the porous layer.

Expert Review of Medical Devices, 2008

Over the last half the 20th Century, reproductive medicine has become a critically important bran... more Over the last half the 20th Century, reproductive medicine has become a critically important branch of modern medical science. Fertility preservation is a vital branch of reproductive medicine and involves the preservation of gametes (sperm and oocytes), embryos, and reproductive tissues (ovarian and testicular tissues) for use in artificial reproduction. This technology gives millions of people suffering from reproductive ailments, cancer patients who have their reproductive functions destroyed by therapy (chemotherapy and radiation) and people undergoing sterilization, a chance to conceive. The most common fertility preservation technique is cryopreservation, which involves freezing cells and tissues at cryogenic temperatures. Cryopreserved cells and tissues can endure storage for centuries with almost no change in functionality or genetic information, making this storage method highly attractive. However, developing efficient cryopreservation techniques is challenging, as both freezing and thawing exposes cells to severe stresses, potentially causing cell death. There are two major techniques for cryopreservation: freeze-thaw processes and vitrification. The major difference between them is the total avoidance of ice formation in vitrification. The use of both theoretical models that describe cell response to freezing and thawing, and experimental investigations of freezing behavior, has led to the development of successful freeze-thaw and vitrification procedures for a number of cell types. Among reproductive cells, there exist efficient cryopreservation techniques for spermatozoa and embryos. Oocytes, however, present significant hurdles in achieving successful cryopreservation, primarily due to their sensitive microtubule structure. Recently, cryopreservation of ovarian and testicular tissues has been investigated with success reported. Ovarian cryopreservation can help circumvent many of the problems associated with oocyte cryopreservation, while testicular tissue preservation may be helpful when insufficient sperm counts are available for routine semen preservation.

Cryobiology, 2008

Macromolecules and salts are ubiquitous in biology in both intra-and extracellular solutions. As ... more Macromolecules and salts are ubiquitous in biology in both intra-and extracellular solutions. As both of these solutes exhibit non-ideal behaviour at very low concentrations, they have a marked effect on the solution thermodynamics, especially when the solutes are concentrated during freezing by the removal of water as ice. We have previously shown that salts alone or salts in combination with certain small molecules have osmotic behaviour that is well predicted by our osmotic virial equation. However, it has been shown that the solution behaviour of macromolecules is altered when the salt concentration is varied, but equations have not been developed to predict the osmolality of these solutions accurately. The objective of this study was to determine the osmotic virial coefficients for macromolecules in various salt solutions and investigate the changes in these coefficients as a function of the salt concentration. The phase diagrams for hydroxyethyl starch (HES) in varying concentrations of NaCl were obtained from the literature for mass ratios (R values) ranging from 0.5 to 20. Our multisolute osmotic virial equation was fit to each HES + NaCl phase diagram, using the osmotic virial coefficients for NaCl that were previously determined, to obtain the osmotic virial coefficients for HES at each R value. The osmotic virial coefficients were plotted as a function of R value and analyzed in order to obtain equations to determine the osmotic virial coefficient dependence on salt concentration. The effect of salt on macromolecules should be taken into account when modeling these solutions. The osmotic virial coefficients show a strong dependence on the R value, which may lead to the development of equations to predict osmotic virial coefficients as a function of the salt concentration. (Conflicts of interest: None declared.

Cryobiology, 2010

Partial phase diagrams are of considerable utility in the development of optimized cryobiological... more Partial phase diagrams are of considerable utility in the development of optimized cryobiological procedures. Recent theoretical predictions of the melting points of ternary solutions of interest to cryobiology have caused us to re-examine measurments that our group made for the ethylene-glycol-sodium chloride-water phase diagram. Here we revisit our previous experiments by measuring melting points at five ethylene-glycol to sodium chloride ratios (R values; R = 5, 10, 15, 30, and 45) and five levels of concentration for each ratio. Melting points were averaged from three measurements and plotted as a function of total solute concentration for each R value studied. The new measurements differed from our original experimental values and agreed with predicted values from both theoretical models. Additionally, the data were fit to the polynomial described in our previous report and the resulting equation was obtained: