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Downstream Processing
Published in Maik W. Jornitz, Filtration and Purification in the Biopharmaceutical Industry, 2019
Density gradient centrifugation is similar to differential sedimentation in that the principle is to exploit centrifugal force to separate feed components on the basis of particle size or density. However, the distinguishing feature is that the medium in the centrifuge tube is heterogeneous, and the density of the solution increases along the axis of rotation. This is usually achieved by varying the concentration of solute along the centrifuge tube prior to sample loading. As well as pelleting very dense particles, density gradient centrifugation also achieves the separation of particles within the density range of the solution into different bands. In rate zonal centrifugation, all particles will eventually form a pellet so the run must be interrupted to isolate particles in the desired density range. In isopycnic centrifugation, a very dense solution is used and particles or molecules in the density range will never form a pellet but will remain suspended at a specific distance along the density gradient. Such processes are common in laboratory-scale preparations but are rarely used on an industrial scale.
Downstream processing of viral-based vaccines
Published in Amine Kamen, Laura Cervera, Bioprocessing of Viral Vaccines, 2023
Rita P. Fernandes, Piergiuseppe Nestola, Cristina Peixoto
Complexity of the purification processes holds in the fact that viruses are quite large when compared with other biomolecules present in the harvested cell lysate such as proteins, peptides, sugars, and nucleic acids. For example, proteins typically range from 0.005 to 0.006 × 106 Da, whereas viruses are around 5 × 106 Da. They present sizes up to 1,000 nm, although the most common viruses produced have sizes between 20–400 nm [7]. This is why the first purification strategies implemented in vaccine manufacturing were based on virus size and density properties. Ultracentrifugation and density gradient centrifugation, later combined with filtration techniques, were the first methods to be used for the purification of viral particles.
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Published in Luis Liz-Marzán, Colloidal Synthesis of Plasmonic Nanometals, 2020
Jose M. Romo-Herrera, Ramón A. Alvarez-Puebla, Luis M. Liz-Marzán
The first separation methods employed were chromatography82-84 and size-selective precipitation,85-87 for very small NPs (1–10 nm size range). These methods show great capabilities to improve the size monodispersity but are commonly used in a size regime smaller than the one considered here. Plasmonic building blocks correspond to a larger size regime, for which the reported separation methods can be sorted into three main classes, as a function of their driving force: (i) sedimentation, (ii) electrophoresis, and (iii) density gradient centrifugation.
From the vapour–liquid coexistence region to the supercritical fluid: the van der Waals fluid
Published in Molecular Physics, 2023
In the coexistence (interfacial) region, or the interface area, the unstable system is composed of heterogeneous nanoscale clusters and the equilibrium thermodynamic (the mean-field theory alone) fails to apply. By using a perturbation approach van der Waals proposed the density gradient theory [1], which is later enriched and finalised by Cahn and Hilliard [6]. In the density gradient theory, a position-dependent density function, known as the density profile, is introduced to bridge the discontinuous bulk densities so that a continuous density variable can be used to define any state in the region. Various local (position-dependent) properties are composed of two parts: (1) a homogeneous contribution from the mean-field theory with the local density; (2) a heterogeneous counterpart, which is expressed in terms of the density gradients (derivatives). The basic assumption is that conventional (classic) thermodynamics formalisms hold in the interface area as the heterogeneous contribution is considered.
A method for separation and purification of mouse splenocytes by density gradient centrifugation
Published in Preparative Biochemistry & Biotechnology, 2021
Yao Lu, Chenghao Fu, Chao Xia, Shiliang Ma
Our results showed that mouse lymphocytes and MDSCs from tumor-bearing mouse spleen can be separated successfully with a higher purity by density gradient centrifugation. And the density gradient centrifugation does show many advantages in cell separation. Firstly, it has minimal impact on the cells as well as is beneficial to subsequent research. The separation solution does not contain any biological elements, therefore it protects the cell surface receptors from activating. Secondly, the whole separation process makes cells go through minimal mechanical damage, which keeps the cell surface receptors intact. Furthermore, unlike immunomagnetic bead enrichment and flow cytometry sorting, which require antibody labeling and need time-consuming steps, density gradient centrifugation does not need antibody labeling and is easy to operate. Therefore, the separation solution can both keep the cells in the most primitive state and obtain a high cell recovery. Also, the solution keeps cells from external simulating factors, thus it provides a reliable basis for subsequent research.
Study on Topology Optimization Method of Particle Moving Based on Element-Free Galerkin Method
Published in International Journal for Computational Methods in Engineering Science and Mechanics, 2018
Shu-guang Gong, Yong-bao Wei, Gui-lan Xie, Jian-ping Zhang
The density gradient operator can be used to represent the degree of density change between particles. For given density function , assuming that the coordinate vector of any two isolated particle and in the influence field is and , respectively, then the density gradient vector (as shown in Fig. 3) between two points can be given as following