Adhesion of biological cells

SURFACE MODIFICATIONS TO INFLUENCE ADHESION OF BIOLOGICAL CELLS AND ADSORPTION OF GLOBULAR PROTEINS... 

Such cell probes allow the direct meastirement of the adhesion of biological cells to membranes. Interpretation of the data for such cell probes is more difficult than for colloid or modified colloid probes, as the cell can distort during the measurements. However, the data show that the XP117 development membrane has lower adhesion and hence lower fouling propensity, also for yeast cells. 

Pearce-Pratt, R. and Phillips, D. M. Studies of adhesion of lymphocytic cells implications for sexual transmission of human immuno dehciency virus. Biology of Reproduction 1993, 48, 431-45. 

We have already seen from Example 10.1 that van der Waals forces play a major role in the heat of vaporization of liquids, and it is not surprising, in view of our discussion in Section 10.2 about colloid stability, that they also play a significant part in (or at least influence) a number of macroscopic phenomena such as adhesion, cohesion, self-assembly of surfactants, conformation of biological macromolecules, and formation of biological cells. We see below in this chapter (Section 10.7) some additional examples of the relation between van der Waals forces and macroscopic properties of materials and investigate how, as a consequence, measurements of macroscopic properties could be used to determine the Hamaker constant, a material property that represents the strength of van der Waals attraction (or repulsion see Section 10.8b) between macroscopic bodies. In this section, we present one illustration of the macroscopic implications of van der Waals forces in thermodynamics, namely, the relation between the interaction forces discussed in the previous section and the van der Waals equation of state. In particular, our objective is to relate the molecular van der Waals parameter (e.g., 0n in Equation (33)) to the parameter a that appears in the van der Waals equation of state ... 

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. 

Collagen molecules undergo self-assembly by lateral associations into fibrils and fibers and are able, therefore, along with other biological functions, to ensure the mechanical support of the connective tissue. Collagen also plays an important role in many bioadhesion processes. Collagen molecules bound to implant materials enhance adhesion of epidermal cells to the surfaces of biomaterials and prevent implant failure. 

The so-called London dispersion or van der Waais interactions are those between molecules that have neither a net charge nor a permanent dipole moment. This interaction is essentially due to the interactions between a transient electrical dipole in one molecule and its induced electrical dipole in the other molecule. TTiis type of electrical interaction plays an important role in biological systems (e.g., in surface tension, stability of biological membranes, condensation properties, adhesion and fusion of biological cell membranes, enzyme-substrate recognition, etc.). 

Thus, bioadhesion is sensitive to factors of electrical and compositional nature. This offers various ways to manipulate cell adhesion, for example, by changing the pH and/or ionic strength of the medium and by adding adsorbing or nonadsorbing polymer molecules of different sizes. These possibilities can be exploited for immobilization of biological cells in bioreactors, for bioremediation of soils and sediments, and for many other applications. 

In biological adhesion, roughness also plays an important role. For example, roughness is routinely used to enhance cell adhesion to titanium implants that are designed to integrate with bone, such as those in hip-joint or tooth replacements. However, it is also clear that roughness does not affect the adhesion of all cells in a similar manner , and the biochemical aspects of cell responses to roughness remain a much-explored research topic (see Chapter 3c). 

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