33 research outputs found
Microscopic theory of quadrupolar ordering in TmTe
We have calculated the crystal electric field of TmTe (T>T_Q) and have
obtained that the ground state of a Tm 4f hole is the doublet in
agreement with Mossbauer experiments. We study the quadrupole interactions
arising from quantum transitions of 4f holes of Tm. An effective attraction is
found at the L point of the Brillouin zone, . Assuming that the
quadrupolar condensation involves a single arm of we show that
there are two variants for quadrupole ordering which are described by the space
groups C2/c and C2/m. The Landau free energy is derived in mean-field theory.
The phase transition is of second order. The corresponding quadrupole order
parameters are combinations of and components. The obtained
domain structure is in agreement with observations from neutron diffraction
studies for TmTe. Calculated lattice distortions are found to be different for
the two variants of quadrupole ordering. We suggest to measure lattice
displacements in order to discriminate between those two structures.Comment: 10 pages, 2 figures, 5 tables; accepted by PR
Mixing theory for culture and harvest in bioreactors of human mesenchymal stem cells on microcarriers
The use of human mesenchymal stem cells (hMSCs) in regenerative medicine is a potential major advance for the treatment of many medical conditions, especially with the use of allogeneic therapies where the cells from a single donor can be used to treat ailments in many patients. Such cells must be grown attached to surfaces and for large scale production, it is shown that stirred bioreactors containing ~200 Όm particles (microcarriers) can provide such a surface. It is also shown that the just suspended condition, agitator speed NJS, provides a satisfactory condition for cell growth by minimizing the specific energy dissipation rate, ΔT, in the bioreactor whilst still meeting the oxygen demand of the cells. For the cells to be used for therapeutic purposes, they must be detached from the microcarriers before being cryopreserved. A strategy based on a short period (~7 min) of very high ΔT, based on theories of secondary nucleation, is effective at removing >99% cells. Once removed, the cells are smaller than the Kolmogorov scale of turbulence and hence not damaged. This approach is shown to be successful for culture and detachment in 4 types of stirred bioreactors from 15 mL to 5 L
Scale-up of an intensified bioprocess for the expansion of bovine adipose-derived stem cells (bASCs) in stirred tank bioreactors
Cultivated meat is an emerging field, aiming to establish the production of animal tissue for human consumption in an in vitro environment, eliminating the need to raise and slaughter animals for their meat. To realise this, the expansion of primary cells in a bioreactor is needed to achieve the high cell numbers required. The aim of this study was to develop a scalable, microcarrier based, intensified bioprocess for the expansion of bovine adipose-derived stem cells as precursors of fat and muscle tissue. The intensified bioprocess development was carried out initially in spinner flasks of different sizes and then translated to fully controlled litre scale benchtop bioreactors. Bioprocess intensification was achieved by utilising the previously demonstrated bead-to-bead transfer phenomenon and through the combined addition of microcarrier and medium to double the existing surface area and working volume in the bioreactor. Choosing the optimal time point for the additions was critical in enhancing the cell expansion. A significant fold increase of 114.19â±â1.07 was obtained at the litre scale in the intensified bioprocess compared to the baseline (**pâ<â.005). The quality of the cells was evaluated pre- and post-expansion and the cells were found to maintain their phenotype and differentiation capacity
Numerical methods for the design and description of in vitro expansion processes of human mesenchymal stem cells
Human mesenchymal stem cells (hMSCs) are a valuable source of cells for clinical applications (e.g., treatment of acute myocardial infarction or inflammatory diseases), especially in the field of regenerative medicine. However, for autologous (patient-specific) and allogeneic (off-the-shelf) hMSC-based therapies, in vitro expansion is necessary prior to the clinical application in order to achieve the required cell numbers. Safe, reproducible, and economic in vitro expansion of hMSCs for autologous and allogeneic therapies can be problematic because the cell material is restricted and the cells are sensitive to environmental changes. It is beneficial to collect detailed information on the hydrodynamic conditions and cell growth behavior in a bioreactor system, in order to develop a so called âDigital Twinâ of the cultivation system and expansion process. Numerical methods, such as Computational Fluid Dynamics (CFD) which has become widely used in the biotech industry for studying local characteristics within bioreactors or kinetic growth modelling, provide possible solutions for such tasks.
In this review, we will present the current state-of-the-art for the in vitro expansion of hMSCs. Different numerical tools, including numerical fluid flow simulations and cell growth modelling approaches for hMSCs, will be presented. In addition, a case study demonstrating the applicability of CFD and kinetic growth modelling for the development of an microcarrier-based hMSC process will be shown
Novel probes for pH and dissolved oxygen measurements in cultivations from millilitre to benchtop scale
Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)pH value and the concentration of dissolved oxygen (DO) are key parameters to monitor and control cell growth in cultivation studies. Reliable, robust and accurate methods to measure these parameters in cultivation systems in real time guarantee high product yield and quality. This mini-review summarises the current state of the art of pH and DO sensors that are applied to bioprocesses from millilitre to benchtop scale by means of a short introduction on measuring principles and selected applications. Special emphasis is placed on single-use bioreactors, which have been increasingly employed in bioprocess development and production in recent years. Working principles, applications and the particular requirements of sensors in these cultivation systems are given. In such processes, optical sensors for pH and DO are often preferred to electrochemical probes, as they allow semi-invasive measurements and can be miniaturised to micrometre scale or lower. In addition, selected measuring principles of novel sensing technologies for pH and DO are discussed. These include solid-state sensors and miniaturised devices that are not yet commercially available, but show promising characteristics for possible use in bioprocesses in the near future
Controlled production of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) nanoparticles for targeted and sustained drug delivery
The ability to control the size and quality of nanoparticles (NPs) during production is critical for their success as a commercial product for clinical applications. Here, we employed a statistical design of experiment approach to identify the key process variables affecting the size of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) NPs during production via the solvent evaporation method. The number of sonication cycles had a standardzed effect on NP size of 55, with sonication power at 25, and PHBHHx concentration at 27 with a combination of these variables having a lower yet significant effect on NP size (p < 0.05). The PHBHHx NPs were stable for at least 7 days with an average polydispersity index of 0.18, a zeta potential of -10 to -40 mV, and an encapsulation efficiency of 63.5 ± 2%. These data were utilized to produce a prediction graph whereby particles could be produced with sizes ranging from 90 to 205 nm with a low mean curve prediction error of 1.96% for Haperzine-A-loaded NPs. Furthermore, a range of drug encapsulates NPs were produced and showed a sustained release of the encapsulated drug.
This study demonstrates the ability to control the size of drug-loaded particles by manipulation of the production variables, which will allow targeted and controlled drug release to fit a variety of applications
Structural, thermodynamic, and transport properties of Laves-phase ZrMn2 from x-ray and neutron diffraction and first principles
see attachmentJRC.E.6-Actinides researc