V. S. K. Sajja

Auburn University, Auburn, Alabama, United States

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Publications (7)6.12 Total impact

  • Suan Shi, V. S. K. Sajja, Y. Y. Lee
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    ABSTRACT: Paper mill sludge is a solid waste composed of pulp residues and ash generated from pulping and paper making processes. The carbohydrate portion of the sludge has chemical and physical characteristics similar to pulp. It can be biologically converted to value-added products without pretreatment. Most of the hemicellulose fraction of pulp mill feedstock is released into black liquor during the pulping process and combusted to recover energy. It is feasible to recover this fraction of carbohydrate for bioconversion. The prehydrolysate can be produced by steam or hot-water treatment. The sugar concentration, however, is far below the level usable as fermentation feed. In this study, we have investigated a bioconversion scheme in which the mixture of these two feedstocks is converted to lactic acid. For this purpose, simultaneous saccharificiaton and fermentation (SSF) was applied using Lactobacillus delbrueckii (ATCC 7830) and cellulose enzyme (Novozyme CTec-2). The bioreactor feed was prepared mixing Kraft pulp mill sludge and the prehydrolysate generated from pine wood by hot-water extraction. The prehydrolysate was detoxified by overliming and charcoal treatment. The SSF was carried out without pH control since calcium carbonate in the sludge, the main inorganic ingredient in the ash, acted as a neutralizing reagent. The main carbohydrate in the prehydrolysate, mannose, and the Kraft sludge were converted efficiently giving above 80% of theoretical yield with enzyme loading less than 10 FPU/g-hexose. The performance data and the details of the bioprocess, prehydrolysate preparation, and detoxification procedures are presented in this paper.
    12 AIChE Annual Meeting; 11/2012
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    ABSTRACT: In the Quadrupole Magnetic Sorter (QMS) magnetic particles enter a vertical flow annulus and are separated from non-magnetic particles by radial deflection into an outer annulus where the purified magnetic particles are collected via a flow splitter. The purity of magnetically isolated particles in QMS is affected by the migration of nonmagnetic particles across transport lamina in the annular flow channel. Computational Fluid Dynamics (CFD) simulations were used to predict the flow patterns, pressure drop and nonspecific crossover in QMS flow channel for the isolation of pancreatic islets of Langerhans. Simulation results were compared with the experimental results to validate the CFD model. Results of the simulations were used to show that one design gives up to 10% less nonspecific crossover than another and this model can be used to optimise the flow channel design to achieve maximum purity of magnetic particles.
    The Canadian Journal of Chemical Engineering 10/2011; 89(5):1068-1075. · 1.00 Impact Factor
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    ABSTRACT: Magnetic isolation is a promising method for separating and concentrating pancreatic islets of Langerhans for transplantation in Type 1 diabetes patients. We are developing a continuous magnetic islet sorter to overcome the restrictions of current purification methods that result in limited yield and viability. In Quadrupole Magnetic Sorting (QMS) islets are magnetized by infusing superparamagnetic microbeads into islets' vasculature via arteries that serve the pancreas. The performance of the islet sorter depends on the resulting speed of the islets in an applied magnetic field, a property known as magnetophoretic mobility. Essential to the design and successful operation of the QMS is a method to measure the magnetophoretic mobilities of magnetically infused islets. We have adapted a Magnetic Particle Tracking Velocimeter (MPTV) to measure the magnetophoretic mobility of particles up to 1,000 µm in diameter. Velocity measurements are performed in a well-characterized uniform magnetic energy gradient using video imaging followed by analysis of the video images with a computer algorithm that produces a histogram of absolute mobilities. MPTV was validated using magnetic agarose beads serving as islet surrogates and subjecting them to QMS. Mobility distributions of labeled porcine islets indicated that magnetized islets have sufficient mobility to be captured by the proposed sorting method, with this result confirmed in test isolations of magnetized islets.
    Biotechnology and Bioengineering 04/2011; 108(9):2107-17. · 4.16 Impact Factor
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    ABSTRACT: Despite significant advances, widespread applicability of islet cell transplantation remains elusive. Refinement of current islet isolation protocols may improve transplant outcomes. Islet purification by magnetic separation has shown early promise. However, surgical protocols must be optimized to maximize the incorporation of paramagnetic microparticles (MP) within a greater number of islets. This study explores the impact of MP concentration and infusion method on optimizing MP incorporation within islets. Five porcine pancreata were procured from donors after cardiac death. Splenic lobes were isolated and infused with varying concentrations of MP (8, 16, and 32 × 10(8) MP/L of cold preservation solution) and using one of two delivery techniques (hanging bag versus hand-syringe). After procurement and infusion, pancreata were stored at 0°C to 4°C during transportation (less than 1 hour), fixed in 10% buffered formalin, and examined by standard magnetic resonance imaging (MRI) and histopathology. T2*-weighted MRI showed homogeneous distribution of MP in all experimental splenic lobes. In addition, histologic analysis confirmed that MP were primarily located within the microvasculature of islets (82% to 85%), with few MP present in acinar tissue (15% to 18%), with an average of five to seven MP per islet (within a 5-μm thick section). The highest MP incorporation was achieved at a concentration of 16 × 10(8) MP/L using the hand-syringe technique. This preliminary study suggests that optimization of a surgical protocol, MP concentrations, and applied infusion pressures may enable more uniform distribution of MP in the porcine pancreas and better control of MP incorporation within islets. These results may have implications in maximizing the efficacy of islet purification by magnetic separation.
    Transplantation Proceedings 12/2010; 42(10):4209-12. · 0.95 Impact Factor
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    ABSTRACT: Magnetic isolation is a promising method for separating and concentrating pancreatic islets for transplantation in Type 1 Diabetes patients. We are developing a continuous magnetic islet sorter to overcome the restrictions of current purification methods that result in limited yield, viability and purity of the isolated islets. Islets are magnetized by infusing superparamagnetic microbeads into islets' vasculature via arteries that serve the pancreas. The performance of the islet sorter depends on the resulting speed of the islets in an applied magnetic field, a property known as magnetophoretic mobility. Essential to the design and operation of the magnetic sorter is a method to measure the magnetophoretic mobilities of magnetically infused islets. We have developed a magnetic particle tracking velocimeter (MPTV) to measure the magnetophoretic mobility of particles up to 1000 microns in diameter. Velocity measurements are performed in a well-characterized uniform magnetic energy gradient using video imaging followed by analysis of the video images using a computer algorithm that produces an absolute histogram of mobilities. High-density Ficoll solutions were used to suspend magnetically-labeled islets and surrogate particles, such as 200 to 350 micron alginate beads. Mobility distributions obtained indicated that magnetized islets have sufficient mobility to be captured by the proposed sorting method, with this result confirmed in test isolations of magnetized islets.
    2010 AIChE Annual Meeting; 11/2010
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    ABSTRACT: Isolation of the pancreatic islets is the important step in preparing islets for the transplantation in type 1 diabetes patients. Quadrupole magnetic flow sorting (QMS), effective in the separation of suspensions of single cells, is being modified for isolation of pancreatic islets. The separating mechanism in QMS is created by the magnetic field strength and gradient induced by a modified Halbach quadrupole magnet assembly and applied to an annular channel of separands flowing through the magnet bore. Thus, islets are subjected to vertical parallel annular flows, horizontal magnetic force, vertical sedimentation and flow through inlet and outlet spreaders and splitters as well as through peristaltic pumps. Computational fluid dynamics (CFD) models were used to simulate the islet separation in the flow channel and flow distributors in the QMS channel. Analyses of particle trajectories, splitter geometries and transport lamina were performed. The CFD results provided an adequate match with the experimental data. Keywords: magnetic flow sorter, pancreatic islets, computational fluid dynamics, pulsatile flow
    2009 AIChE Annual Meeting; 11/2009
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    ABSTRACT: Diabetes, a group of metabolic diseases affecting 8 per cent of the US population, costs the US economy more than $132 billion per year. Insulin treatment cannot fully prevent chronic complications, and intensive insulin treatment to improve metabolic control is paralleled by an increased risk of severe hypoglycemia. Pancreatic islet transplantation offers a viable option to achieve permanent metabolic control in Type 1 diabetes patients. However, large quantities of pure viable donor islet cells are necessary for transplantation. Using currently available islet isolation methods multiple donor organs are required to achieve successful transplantation, and there is a demand for an isolation method with high islet yield and viability. Quadrupole Magnetic Sorting (QMS), a single cell separation method, is being modified for the isolation of pancreatic islets. QMS is a split flow thin channel form of continuous separation device, which consists of two substantial components: an automated processing system that contains a high energy density Halbach quadrupole magnet assembly and a disposable annular flow channel capable of providing the fluid transport to separate the magnetically labeled cells. Islets or surrogate islets are labeled with 4.6m Dynal Dynabeads and separated continuously with QMS. Studies of pancreatic digests with the modified flow channel indicate high purities with less than 2 per cent crossover of acinar tissue into the magnetic fraction. In the parallel flow streams of QMS islets are rapidly removed from the harmful enzymes and competing acinar tissue in the digest fluid. Presence of Dynabeads in the islets after the isolation does not affect the islet functionality. QMS subjects islets to less mechanical and chemical stress when compared to other separation techniques like density gradient methods, potentially increasing the number of islets that survive transplantation. Keywords: magnetic flow sorter, pancreatic islets, magnetic particles, diabetes This research is supported by National Institute for Diabetes and Digestive and Kidney Disease Research, grant SR44DK.
    2009 AIChE Annual Meeting; 11/2009