Hans-Joerg Fecht

Tuning nanoscopic water layers on hydrophobic and hydrophilic surfaces with laser light.

The evolutional function of ordered interfacial water near solid surfaces was postulated by Szent-Györgyi: Life actually, may have started with building these water structures. Here we report their tunability with laser light on both hydrophobic and hydrophilic surfaces. On the former, the light caused their depletion--on the latter, an increase in fluidity--as measured by atomic force acoustic microscopy. Interfacial water layers play a key role in cellular recognition. Their tunability promises to revolutionize various fields in biomedical engineering and life sciences.

The Top of the Biomimetic Triangle

There is increasing observational evidence indicating that crystalline interfacial water layers play a central role in evolution and biology. For instance in cellular recognition processes, in particular during first contact events, where cells decide upon survival or entering apoptosis. Understanding water layers is thus crucial in biomedical engineering, specifically in the design of biomaterials inspired by biomimetic principles. Whereas there is ample experimental evidence for crystalline interfacial water layers on surfaces in air, their subaquatic presence could not be verified directly, so far. Analysing a polarity dependent asymmetry in the surface conductivity on hydrogenated nanocrystalline diamond, we show that crystalline interfacial water layers persist subaquatically. Nanoscopic interfacial water layers with an order different from that of bulk water have been identified at room temperature on both hydrophilic and hydrophobic model surfaces — in air and subaquatically. Their generalization and systematic inclusion into the catalogue of physical and chemical determinants of biocompatibility complete the biomimetic triangle.

On the Social Behaviour of Cells

Polystyrene Petri dishes are in use in hundreds of thousands of laboratories world wide. Cell culture experiments performed in them provide fundamental information in a wide range of applications, including but not limited to testing novel biomaterials and pharmaceuticals, and stem cell research. These experiments cost billions of dollars per year. In this study we report on a potential deficiency of polystyrene Petri dishes, possibly caused by an increase in interfacial pH under relevant culture conditions and affecting cell performance. We conclude that cell performance on Petri dishes could be improved by improving the Petri dishes. As a spin-off of our study we postulate the concept that cancer cells and stem cells are social. It is impossible to validate this concept on the basis of the model established in this paper. However, the coherence of our insights may encourage further study and lead to the development of a qualitative improvement of cell culture devices, including Petri dishes and culture flasks, to the identification of potential strategies for chemotherapy and chemoprevention that could suppress progression of metastasis, and to the establishment of improved settings for tissue engineering and stem cell research. An immediate recommendation of our study is to use chemically and biologically inert substrates for important cell culture experiments, for example, nanocrystalline diamond.

It is Time for a Change: Petri Dishes Weaken Cells

We wish to draw the attention to a potential deficiency in the biocompatibility of polystyrene cell culture dishes which is caused by a softening of the material under relevant culture conditions. The finding confirms the central hypothesis of our previous model study. In it we assumed a local increase in pH at the interface between the hydrophilic polymer and liquid. The finding is of considerable biological interest. Polystyrene tissue culture dishes are now in use for 50 years. To the best of our knowledge their biocompatibility has never been challenged. Here we report the first experimental proof that exposure to water softens the surface of polystyrene Petri dishes. We expect that our results will stimulate the development of a new generation of cell culture devices, including Petri dishes and culture flasks, and the establishment of improved biomimetic settings for tissue engineering and stem cell research. New non-swelling biomaterials or nanocoatings designed to reduce the swelling of polymer culture dishes could improve cell performance. The need for further study is clear.

Surface tension and viscosity of industrial alloys from parabolic flight experiments — Results of theThermoLab project

The surface tension and the viscosity of a series of industrial alloys have been measured by the oscillating drop technique with an electromagnetic levitation device under reduced gravity conditions in several parabolic flights. It was demonstrated that the 20 seconds of reduced gravity available in a parabola were sufficient for melting, heating into the liquid phase, and cooling to solidification of typically 7 mm diameter metallic specimen. The surface tension and the viscosity were obtained from the frequency and the damping time constant of the oscillation which were evaluated from the temperature signal of a highresolution pyrometer. Alloys processed included steels, Ni-based superalloys, and Ti-alloys which were supplied by industrial partners to the project. Three to four parabolas were sufficient to obtain the surface tension and the viscosity over a large range in temperature.

Body Building on Diamonds

Whereas conservative therapies aim to stall the advance of disease, regenerative medicine strives to reverse it. The capacity of most tissues to regenerate derives from stem cells, but there are a number of barriers which have to be circumvented before it will be possible to use stem-cell-based therapies. Such therapies, however, are expected to improve human health enormously, and knowledge gained from studying stem cells in culture and in model organisms is now laying the groundwork for a new era of regenerative medicine. One of the most prominent methods to study stem cell differentiation is to let them to form embryoid bodies. Under favourable conditions any stem cell line will form embryoid bodies. However, the mechanism of the formation of embryoid bodies is not very well understood, and to produce them in the laboratory is in no way trivial — an important technical barrier in stem cell research. Recently, the embryoid body cultivation step has been successfully circumvented for the derivation of osteogenic cultures of embryonic stem cells. Here we report on a simple and reusable system to cultivate embryoid bodies in extremely short times. The method is inspired by the principles that lead to the establishment of the biomimetic triangle.

Subaquatic Fly Locomotion — Principles

The theoretical criteria essential for underwater superhydrophobicity follow from the analysis on the conditions of heterogeneous wetting. Such surfaces, when immersed in water are not wetted — a layer of air is trapped between them and the surrounding water. Here we provide an observational evidence that house flies can survive under water by exploiting underwater superhydrophobicity in association with underwater adhesion. The adhesion — resisting updraft — is probably mediated by a glue-like interfacial water layer formed on the top of the pathogens collected on the terminal setae.

Nondestructive characterization and application of doped and undoped polycrystalline diamond films

In this overview the mechanical, thermal and electrical properties of CVD (Chemical Vapor Deposition) diamond, determined by various non-destructive techniques, are highlighted and compared with calculations. In the case of Youngs modulus the measurement results of high quality samples leads to an average value of 1126 GPa which is in good agreement with the calculated value of 1143 GPa and close to the Young+s modulus of single crystalline diamond. However, values as low as 242 GPa were determined on 300 +m thick bulk CVD diamond. The differences in the measurement results can be traced back to extended voids in the sample. A traditional heated bar technique was used to measure the temperature dependent thermal conductivity of CVD-diamond. High quality polycrystalline diamond films reached a room temperature thermal conductivity of 20.5 W cm-1 K-1. This value is comparable to the thermal conductivity of the best single crystal diamonds available. For the lower quality samples, boundary scattering and point defects are most likely responsible for the lower thermal conductivity. The electrical properties of B-doped polycrystalline diamond films were characterized by temperature dependent Hall and conductivity measurements. These measurements together with a semi-empirical model give insight in to the current transport mechanism. The model indicates, that the electrical mobility in diamond thin films is lower compared with single crystal diamond. However, the current conduction mechanism are essentially the same when compared with single crystal diamond.