The adhesion strength of cells depends on the properties of the surface they attach to. Varying the surface properties can trigger different cellular responses such as differentiation. In order to study cell adhesion quantitatively, we developed a microfluidic shear force assay which allows the variation of applied shear stress by five orders of magnitude. With this device we can determine the critical shear stress which is necessary to remove 50% of the adherent cells. As an application we investigated the adhesion strength of cells on a series of oligo(ethylene glycol) (OEG) containing self-assembled monolayers (SAMs). By varying the number of ethylene oxide units, the hydration properties of the monolayers are changed. We found that cell adhesion strength for mammalian fibroblasts decreases if the hydration of the surface is increased. As the cell spreading area changes with the substrate properties, the adhesion strength per unit area was additionally determined.

Highly porous thin films based on a [Cu(bdc)(2)](n) (bdc = benzene-1,4-dicarboxylic acid) metal-organic framework, MOF, grown using liquid-phase epitaxy (LPE) show remarkable stability in pure water as well as in artificial seawater. This opens the possibility to use these highly porous coatings for environmental and life science applications. Here we characterize in detail the stability of these SURMOF 2 thin films under aqueous and cell culture conditions. We find that the material degrades only very slowly in water and artificial seawater (ASW) whereas in typical cell culture media (PBS and DMEM) a rapid dissolution is observed. The release of Cu(2+) ions resulting from the dissolution of the SURMOF 2 in the liquids exhibits no adverse effect on the adhesion of fibroblasts, prototype eukaryotic cells, to the substrate and their subsequent proliferation, thus demonstrating the biocompatibility of SURMOF 2 surface coatings. Thus, the results are an important step toward application of these porous materials as a slow release matrix, for example, for pharmaceuticals and growth factors.

No abstract

Leukemic cells and human hematopoietic progenitor cells expressing CD44 receptors have the ability to attach and roll on hyaluronan. We investigated quantitatively the adhesion behavior of leukemic cell lines and hematopoietic progenitor cells on thin films of the polysaccharides hyaluronan and alginate in a microfluidic system. An applied flow enhances the interaction between CD44-positive cells and hyaluronan if a threshold shear stress of 0.2 dyn/cm(2) is exceeded. At shear stress ∼1 dyn/cm(2), the cell rolling speed reaches a maximum of 15 μm/s. Leukemic Jurkat and Kasumi-1 cells lacking CD44-expression showed no adhesion or rolling on the polysaccharides whereas the CD44-expressing leukemic cells KG-1a, HL-60, K-562, and hematopoietic progenitor cells attached and rolled on hyaluronan. Interestingly, the observations of flow-induced cell rolling are related to those found in the recruitment of leukocytes to inflammatory sites and the mechanisms of stem-cell homing into the bone marrow.