Cell size distribution

Fig. 9.20 Typical example of cell size distribution offoamed PLA/...

By means of the Coulter channelizer 256 module an optional extra on the model ZM but built-in on the multisizer, enables biological cell-size distributions to be measured. This provides an ability to measure suspension... 

While the quahty of the foam was not discussed, changes in surfactant type and concentration were the primary determinants of cell size, distribution, and type and doubtless affected the cell effectiveness and retention of cells in the foams. 

We discussed reticulated foams earlier in this book. They appear to have many desirable properties of ideal scaffolds. Depending on the feedstock, the manufacturers can produce a wide variety of pore sizes. Foams made specifically for reticulation have very narrow pore size distributions. If we compare the reported cell size distribution with that of Zeltringer, we can illustrate the precision of the reticulated foam process in the context of scaffolds for cell growth. Caution is advised in reviewing the Figure 7.6 plot. It is qualitative and assumes a normal distribution for both systems. It estimates the Zeltringer data based on the published standard deviation. 

The cell size distribution is very easy to get if the cells are perfectly closed. If the closed cells are connected, the cell size distribution can be determined according to two methods (Maire et al., 2003). The first possibility is to try to close the cells within the digital image using morphological operations such as erosion/dilation. When this activity is done successfully, it is possible to extract some morphological 3D parameters of cells such as volume, surface, aspect ratio, and sphericity. The cell size distribution can be easily obtained... 

In order to specify the size of a circular section, instead of the absolute area A, the Saltykov method adopts the ratio A/Amilx, where A max is the maximum circular section area in the whole population. The first step in determining the cell size distribution is to measure all the 2D circular sections, identifying the largest cell section in the total cell section population found on the section planes. This maximum area can be used to divide the size distribution of the cell sections into 12 classes and to determine the total number of sections in each class. 

The cell size distribution in products, such as marshmallow, muffin, and mousse, was also fitted by a lognormal distribution. 

Microcellular foaming, bimodal cell size distributions, and high open-celled contents of molecular composites of HT-polymers were reported by Sun et al. [33], investigating blends of a rod-like polymer polybenzimidazole with an aminated PSU and poly(phenyl sulfone) by using carbon dioxide as a blowing agent. The complex foaming behavior was related to phase separation within the otherwise... 

By foaming an immiscible blend system of a poly(ethylene glycol)PEG/ polystyrene (PEG/PS), Taki et al. detected a similar foaming behavior as well as a bimodal cell size distribution [78], While smaller cells formed in the more... 

A strong similarity is found for the present blends with a PPE/PS ratio of 50/50, as reflected by a similar bimodal cell size distribution for all SAN contents. Small differences can be related to the distinct foaming kinetics of the PPE/PS blend phase. Compared to the PPE/PS 75/25 blend phase, the higher content of PS in the PPE/PS 50/50 phase leads to a cell nucleation and growth kinetics close to the SAN phase. Nevertheless, the PPE/PS phase still appears to restrict the cell growth and expansion in the SAN phase to some extent, and smaller cells are found within the cell walls. Independent of the SAN content, cell growth within the dispersed SAN phase proceeds under the constraints of the continuous, higher Tg PPE/PS phase. 

The cellular structure of the quaternary blend systems after foaming at 180°C for 10 s is highlighted in Fig. 33. An excellent homogeneity down to the microscale can be detected for all foamed blend compositions. As already discussed in the previous section, simultaneous foaming of the PPE/PS and the SAN phase in the noncompatibilized blend leads to a bimodal cell size distribution. Besides larger cells induced by the highly expanded SAN phase, smaller cells are formed in the PPE/PS phase (Fig. 33a). 

In order to overcome this drawback, the concept of selective blending was exploited. Selective blending of PPE with low-viscous PS allowed one to control the microstructure, to refine the phase size, and to adjust the foaming characteristics of the individual phases of PPE/SAN blends. Appropriate blend compositions allowed simultaneous nucleation and cooperative expansion of both phases, generally leading to bimodal cell size distributions in the micron range. Due to cell nucleation and growth in both blend phases, the density could be further reduced when compared to PPE/SAN blends. Moreover, the presence of coalesced foam structure and particularly macroscopic defects could be avoided, and the matrix of the foamed structure was formed by the heat resistant PPE/PS phase. 

Seewoster T, Lehmann J (1997), Cell size distribution as a parameter for the predetermination of exponential growth during repeated batch cultivation of CHO cells, Biotechnol. Bioeng. 55 793-797. 

These three forms of presenting the cell size distribution are interrelated through Equations (3) and (4). 

Cell size distribution of HeLa cells grown in serum-free culture medium (Luebberstedt, 2000), presented as (A) frequency and (B) cumulative undersize (y) and oversize (z) distributions. 

In addition, the use of gates or windows in the Coulter counter model ZM enables cell sizes to be accurately determined after the machine has been calibrated with pollen grains of known size. Thus ragweed pollen has a mean volume of 3800 ju,m3. When coupled to a Channelyzer a histogram of the cell size distribution is automatically recorded (Fig. 7.3). 

Related Calculations. In biotechnology separations such as this, data such as those for the density difference, viscosity, and cell size distribution are typically notknown with certainty, so the calculation here can be regarded as providing only an approximate value for more precision, experimental means must be used. E. coli suspensions with cell sizes between 0.8 and 1.8 gm have in practice been separated, with efficiencies of over 98%, at rates of 200 to 400 L/h. This suggests that the approximation made here is a good one. 

Figure 9.9 Cell size distribution depends on the quantity of unbranched PE (M 1500 dispersity, 0.18 degree of crystallinity, 87%)...

Microporous polymer systems consisting of essentially spherical, interconnected voids with a narrow range of pore- and cell-size distribution have been produced from a variety of thermoplastic resins by phase separation [94]. If a polyolefin or polystyrene is insoluble in a solvent at low temperatures but soluble at high temperatures, the solvent can be used to prepare a microporous polymer. When the solution containing 10-70% polymer is cooled to ambient temperature, the polymer separates as a second phase. The remainder can be extracted. These microporous polymers may be used in microfiltration or as controlled-release carriers for chemicals. 

Cell filterability is influenced by a variety of biological and technological factors (Nordt, 1983). Thus, in order to be reliable and reproducible, Nucleopore filtration techniques must fulfil certain criteria, and namely (1) the most part of the input cells must be recovered in the filtrate (2) cellular aggregation should be minimized by choosing conditions which permit relatively short filtration times (3) cell viability should be high and not lost on filtration (4) cell size distribution should not be influenced by filtration and (5) differences in cell to filter and cell to cell adhesion of different cell lines should not be responsible for differences in filterability. In order to fulfil these criteria, experimental parameters such as cell to pore ratio, filtration pressure and cell culmre conditions have to be standardized. The following optimal conditions have been established for filtration of B16 melanoma cells (mean cell diameter 17.4 0.21 /xm, mean diameter of cell nuclei 9.8 0.27/xm) 20 cm H2O driving pressure, cell-to-pore ratio 1 1, temperature 22°C (Ochalek et al., 1988). Care has to be taken to derive tumor cells from similar culture conditions, since cell density has been found to influence filterability. 

Finally, the cell size distribution is not Gaussian but a normal logarithmic one. This implies that, according to the theory of statistical analysis, the totality of cells consists of several, at least two, groups of cells. The cells of these groups markedly differ both in size and in number. This is confirmed by a further analysis of the data available (F. 2). 

This survey deals with the fundamental morphological parameters of foamed polymers including size, shape and number of cells, closeness of cells, cellular structure anisotropy, cell size distribution, surface area etc. The methods of measurement and calculation of these parameters are discussed. Attempts are made to evaluate the effect and the contribution of each of these parameters to the main physical properties of foamed polymers namely apparent density, strength and thermoconductivity. The cellular structure of foamed polymers is considered as a particular case of porous statistical systems. Future trends and tasks in the study of the morphology and cellular structure-properties relations are discussed. 

Influence of Mechanical Deformation on the Cell Size Distribution. 198... 

However, a real foam structure is composed of cells having differing shapes, sizes and volumes. In studying the properties of foamed polymers as well as in developing and elaborating preparative processes, it is necessary to find out cell size, shape and volume distribution. The methods for calculating the respective distribution functions will be discussed in Sect. 9.2, 9.3 here, we only note that the cell size distribution function is a most comprehensive and valuable characteristic of plastic foam structures. 

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