Shear cell types

In experiments with cultured cells it has been shown that osteocytes, but not periosteal fibroblasts, are extremely sensitive to fluid flow, resulting in increased prostaglandin as well as nitric oxide production [104, 105], Three different cell populations, namely osteocytes, osteoblasts, and periosteal fibroblasts, were subjected to two stress regimes, pulsatile fluid flow and intermittent hydrostatic compression [104], Intermittent hydrostatic compression was applied at 0.3 Hz with a 13-kPa peak pressure. The pulsatile fluid flow was a fluid flow with a mean shear stress of 0.5 Pa with cyclic variations of 0.02 Pa at 5 Hz. The maximal hydrostatic pressure rate was 130 kPa/sec and the maximal fluid shear stress rate was 12 Pa/sec. Under both stress regimes, osteocytes appeared more sensitive than osteoblasts, and osteoblasts more sensitive than periosteal fibroblasts. However, despite the large difference in peak stress and peak stress rate, pulsatile fluid flow was more effective than intermittent hydrostatic compression. Osteocytes, but not the other cell types, responded to 1 hour pulsatile fluid flow treatment with a sustained prostaglandin E2 upregula-... 

The weaknesses associated with the flow through an orifice and angle of repose measurements limit their application for powder flow studies and hopper designs. Consequently, several powder shear testers and methods that permit a more thorough and precisely defined assessment of powder flow characteristics were developed. Shear testers that measure the frictional characteristics of a powder bed under load yield valuable information with regard to powder flow in high-speed tablet equipment. A number of types of shear cell testers are available, but the most common types used in the pharmaceutical industry are the Jenike shear cell and the Schulze ring shear tester.61,62... 

There are several different methods available for determining the flow properties of powders. Shear cell methods provide an assessment of powder flow properties as a function of consolidation load and time. There are a number of types of shear cells available, the most common being the Jenike shear cell [21]. 

This basic assay is susceptible to be modified in order to measure the ability of adherent cells to withstand increasing shear forces, which can be obtained by increasing the rate of mixing. Using this approach, the strength of cell adhesion to different substrates, or the strength of adhesion of different cell types to the same substrate, can be compared. 

Fig. 8 The plate-type shear cell. Key (A) lower plate (B) template (C) upper plate (D) tow line (E) cantilever strain gauge (F) screw jack. (From York, P. Int. J. Pharm. 1980, 6, 100.)...

As with the Jenike cell, this process is time-consuming. Amidon and Houghton, " however, used a single yield locus with this cell for comparative purposes. Hiestand et al., ° in comparing this apparatus to the Jenike cell, claimed that this simple shear cell can be used to provide characterization of the unconfined yield strengths of powders. The results from the two devices are not identical. However, as much as the Hiestand device requires less powder and the consolidation step is more automated and consistent, it provides an inexpensive alternative to the Jenike-type cell to characterize pharmaceutical powders. Amidon and Houghton used the cell to examine the effect of moisture on the powder flow properties of microcrystalline cellulose. ... 

Literature reports have used the following reactor parameters to correlate the effects of agitation intensity with cell injury in bioreactors agitator rpm, impeller tip speed, integrated shear factor and Kolmogorov eddy size. Additional parameters have been used for microcarrier bioreactors (discussed below). All correlations of cell injury with a bioreactor parameter should be used only qualitatively. These correlations are, at present, indicative of various trends or mechanistic hypotheses and should not be used for quantitative bioreactor scale-up. In addition, such correlations are applicable to the specific cell type, because different cell types are likely to exhibit different responses to fluid forces. 

These findings suggest that the shear-protective effects of these additives in the bioreactor are physical in nature, and specifically purely fluid-mechanical, i.e. due to changes in the interactions between bubbles, draining films and the cells. If their effect was biological, cells would have been protected in both shear environments (viscometer and bioreactor). Other experiments suggest that the protection mechanism may vary for different cell types. 

In summary, the effect of dextrans can be positive or negative depending on the cell type, bioreactor or even dextran grade and make used, but all experimental evidence so far suggests that dextran offers no mechanical protection. Dextrans and modified starches should not be used as protectants against shear damage. 

The so-called shear cells are used for direct shear tests, where the powder specimen is consolidated in the vertical direction and then sheared in a horizontal plane. There are basically two types of shear cells in use today the Jenike shear cell (sometimes referred to more generally as the translational shear box) and the annular (or ring) shear cell (the rotational shear box). As the equipment needed is highly specialized (and hence outside the scope of this Guide) and as manufacturers instructions are usually adequate, the following contains only an outline description of both the hardware and the test procedures. 

There is another type of shear cell, known as the ring cell or Peschl Shear Tester84. The cell is in the form of a full ring and is rotated like the annular shear cell. It is a very easy device for comparative measurements and another report from BMHB84,... 

The Cohesion Tester has been used in industry, mainly as a quality control-type test. It can be useful as an aid to assessment of flow properties and of power requirements in mixers, bulk conveyors and feeders. The original developers of the tester, Warren Spring Laboratories35, have even tried to correlate the cohesion value with unconfined yield stress determined with the Jenike shear cell and found a good correlation for some powders (fc = 6 x C). The tester is, quite obviously, only useful with fine, cohesive powders because ... 

Taken together, these studies revealed that confluent cell layers in contact to the resonator lead to a significant increase of energy dissipation from the shear oscillation [33] as we had learned already from the QCM-D experiments presented in Sect. 2.4. The impact of the cells on energy dissipation is individual and dependent on the cell type. It is important to mention in this context that different batches of a certain cell line may also cause a different QCM response within certain limits. This is not surprising for cell biologists since cells of the same kind but taken from different batches may show a certain variance in their behavior and it underlines that the QCM is capable of picking up these subtle differences. 

We consider these studies to be strong evidence that the protein content of the cell, and in particular the cytoskeleton, is a prominent if not the predominant contributor to the acoustic load that is created on shear wave resonators by adherent cells. The reduction of A Zl after disassembly of the actin cytoskeleton supports this hypothesis. Please note that all the experiments described in this paragraph have been performed with MDCK II cells. In order to exclude that the observed increase in acoustic load after fixation is a cell-type-specific phenomenon of MDCK II cells, analog experiments were performed with other cell types and returned the same answer. Only the numerical value of the increase in A Zl varied to some extend. 

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