Quantification of cell adhesion strength on artificial surfaces with a microfluidic shear force device

Adhesion strength is a measure to determine the interaction between cells and their environment. Numerous types of devices and coatings are developed in order to meet medical and non medical issues and surface properties can be tuned in order to evoke specific cell response. In this work various properties of solid surfaces were investigated towards their impact on adhesion process and adhesion strength of mammalian cells, which both give information on the cell interaction with the substrate. Therefore a sophisticated assay to observe cell adhesion and measure cell adhesion strength on artificial surfaces was developed. Its capability to measure cell adhesion strength in the order of five magnitudes with a high reliability and quantitative output was applied to synthetic surfaces with different degree of hydration, anisotropic topography, bioactivity and different polarizations. Investigation of fibroblast adhesion on ethylene glycol self assembled monolayers showed that cell adhesion strength is reduced by increasing degree of hydration. At the same time it was found that cell adhesion strength was independent of cell spreading area, in particular when a certain spreading size was reached. This finding may strengthen the zipper detachment mechanism by which the cell detachment occurs after distinct bonds are broken. Another study on hydrogel like polysaccharides confirmed the inability of fibroblasts to attach to hydrated surfaces. At the same time it was found that hematopoietic progenitor cells expressing CD44 receptors overcome the inertness and attach to the coating by shear force induction through a hydrodynamic flow. This finding may explain the fact that the presence of hyaluronan is a prerequisite in the stem cell homing and engraftment process into the bone marrow. Besides receptor ligand interactions more basic surface polarity effects were studied, which have been reported to have a minor impact towards cell adhesion. Here it was shown by investigation of fibroblast adhesion on periodically poled ferroelectric lithium tantalite crystals, that the gradient between two opposite polarities can be sensed by cells but not the polarity itself. The cells do not distinguish the overall polarity of a surface, but avoid placing the nucleus in proximity to the sharp borders in between to inverse polarities as the cells start to spread. Even though this astonishing reaction is unexpected it is not contradictive to the absence of polarity sensing because sensing of a polarity gradient is different from a distinct polarization spread over a large area. Instead of a gradient, anisotropic surface properties can be achieved by directional surface texture. Anisotropically textured poly(p-xylylene) surfaces, which consist of dense packed tilted nanorods, revealed a force directional dependence of fibroblast cell adhesion strength. The hydrodynamic shear force applied with the direction of nanorod tilting revealed a reduced cell adhesion strength compared to force application perpendicular and against the tilting. This finding could be explained by a model which accounts for cell filopodia attaching between nanorods of the surface. In order to prove the filopodia attachment theory more sophisticated imaging, which reveals ultrastructural components, was needed. Therefore, cell preparation protocols were established with special attention to preserve cellular structure to image via X-ray holography under ultrahigh vacuum conditions. The imaging project was conducted in a consortium of researchers and first successful imaging was demonstrated

Adherent cells avoid polarization gradients on periodically poled LiTaO\u3csub\u3e3\u3c/sub\u3e ferroelectrics

The response of fibroblast cells to periodically poled LiTaO3 ferroelectric crystals has been studied. While fibroblast cells do not show morphological differences on the two polarization directions, they show a tendency to avoid the field gradients that occur between polarization domains of the ferroelectric. The response to the field gradients is fully established after one hour, a time at which fibroblasts form their first focal contacts. If suspension cells, with a lower tendency to establish strong surface contacts are used, no influence of the field gradients is observed

Adherent cells avoid polarization gradients on periodically poled LiTaO\u3csub\u3e3\u3c/sub\u3e ferroelectrics

The response of fibroblast cells to periodically poled LiTaO3 ferroelectric crystals has been studied. While fibroblast cells do not show morphological differences on the two polarization directions, they show a tendency to avoid the field gradients that occur between polarization domains of the ferroelectric. The response to the field gradients is fully established after one hour, a time at which fibroblasts form their first focal contacts. If suspension cells, with a lower tendency to establish strong surface contacts are used, no influence of the field gradients is observed

2-Octyl-cyanoacrylate for wound closure in cervical and lumbar spinal surgery

It is claimed that wound closure with 2-octyl-cyanoacrylate has the advantages that band-aids are not needed in the postoperative period, that the wound can get in contact with water and that removal of stitches is not required. This would substantially enhance patient comfort, especially in times of reduced in-hospital stays. Postoperative wound infection is a well-known complication in spinal surgery. The reported infection rates range between 0% and 12.7%. The question arises if the advantages of wound closure with 2-octyl-cyanoacrylate in spinal surgery are not surpassed by an increase in infection rate. This study has been conducted to identify the infection rate of spinal surgery if wound closure was done with 2-octyl-cyanoacrylate. A total of 235 patients with one- or two-level surgery at the cervical or lumbar spine were included in this prospective study. Their pre- and postoperative course was evaluated. Analysis included age, sex, body mass index, duration and level of operation, blood examinations, 6-week follow-up and analysis of preoperative risk factors. The data were compared to infection rates of similar surgeries found in a literature research and to a historical group of 503 patients who underwent wound closure with standard skin sutures after spine surgery. With the use of 2-octyl-cyanoacrylate, only one patient suffered from postoperative wound infection which accounts for a total infection rate of 0.43%. In the literature addressing infection rate after spine surgery, an average rate of 3.2% is reported. Infection rate was 2.2% in the historical control group. No risk factor could be identified which limited the usage of 2-octyl-cyanoacrylate. 2-Octyl-cyanoacrylate provides sufficient wound closure in spinal surgery and is associated with a low risk of postoperative wound infection

A single molecule assay to probe monovalent and multivalent bonds between hyaluronan and its key leukocyte receptor CD44 under force

Glycosaminoglycans (GAGs), a category of linear, anionic polysaccharides, are ubiquitous in the extracellular space, and important extrinsic regulators of cell function. Despite the recognized significance of mechanical stimuli in cellular communication, however, only few single molecule methods are currently available to study how monovalent and multivalent GAG•protein bonds respond to directed mechanical forces. Here, we have devised such a method, by combining purpose-designed surfaces that afford immobilization of GAGs and receptors at controlled nanoscale organizations with single molecule force spectroscopy (SMFS). We apply the method to study the interaction of the GAG polymer hyaluronan (HA) with CD44, its receptor in vascular endothelium. Individual bonds between HA and CD44 are remarkably resistant to rupture under force in comparison to their low binding affinity. Multiple bonds along a single HA chain rupture sequentially and independently under load. We also demonstrate how strong non-covalent bonds, which are versatile for controlled protein and GAG immobilization, can be effectively used as molecular anchors in SMFS. We thus establish a versatile method for analyzing the nanomechanics of GAG•protein interactions at the level of single GAG chains, which provides new molecular-level insight into the role of mechanical forces in the assembly and function of GAG-rich extracellular matrices