Petr Ponížil

Grain Size Estimation in Anisotropic Materials

The estimation of grain size (volume) by using computer database of tessellations is explained and demonstrated. As model material was selected an anisotropic material formed by compression-moulded pellets of PVC. The pellets were first covered with carbon paste to highlight borders of grains in final specimen and then moulded; their volumes were exactly known. Standard profile and intercept counts were carried out on the planar sections of the specimen and used to estimate the grain size by means of computer database. The obtained estimates were then compared with the known pellet characteristics. The estimation of grain volume and of other suitable characteristics by inspection of section planes is necessary in opaque materials (e.g. metal alloys, crystalline polymers, ceramics), where their values are inaccessible by direct measurements. The aim of this work is show that the standard approaches can be improved with the help of a suitably prepared computer database.

Hyaluronan hydrogels modified by glycinated Kraft lignin: Morphology, swelling, viscoelastic properties and biocompatibility

Effects of the addition of water soluble glycinated Kraft lignin (WS/KL) on the mechanical stability and biocompatibility of hyaluronan (NaHy) hydrogels were evaluated in this work. Water soluble lignin was obtained by the modification of Kraft lignin via a Mannich reaction. It was found that WS/KL is highly compatible with hyaluronan due to its improved water solubility, which favours its use in designing new advanced composite hydrogels. The effects of the concentration of WS/KL on morphological, swelling and creep/recovery behaviours of hyaluronan hydrogels were investigated. It was detected that the creep resistance and creep recovery of NaHy hydrogels was improved by the incorporation of up to 3% (w/w) of WS/KL. In contrast, the swelling capacity of hydrogels was decreased. The cytotoxicity tests proved that glycinated KL lignin limits the viability of cells only slightly, and the final hyaluronan/lignin hydrogels were non-toxic materials.

Quantitative characterization of microstructure in copper processed by equal-channel angular pressing

Experiments were conducted on extremely coarse-grained pure copper to evaluate the effect of equal-channel angular pressing (ECAP) on microstructure evolution in the as-pressed state and after creep exposure using various stereological methods. The microstructure formed by severe plastic deformation is an unusual structure which can be hardly characterized only by the mean grain size especially after low number of ECAP passes. The purpose of this paper is a detailed examination of (sub)boundaries and grain boundaries in the microstructures of the pressed material. The inhomogeneity of deformed microstructures is also evaluated. The detailed description of ECAP microstructures should contribute to the better understanding of mechanical properties of the pressed materials.

Electrorheological flow patterns analysis

A method of image analysis of flow patterns, which are developed in electrorheological fluids, is presented. Due to the process of preparation, electrorheological samples show a radial symmetry. Numerical transformations are necessary to remove sample deformation and obtain correct radial dependence of image intensity as the function characterizing the sample image. Parameters describing the radial symmetrical image are suggested. Then the influence of electrorheological parameters on properties of final sample is studied.

Polyaniline cryogels: Biocompatibility of novel conducting macroporous material

Polyaniline cryogel is a new unique form of polyaniline combining intrinsic electrical conductivity and the material properties of hydrogels. It is prepared by the polymerization of aniline in frozen poly(vinyl alcohol) solutions. The biocompatibility of macroporous polyaniline cryogel was demonstrated by testing its cytotoxicity on mouse embryonic fibroblasts and via the test of embryotoxicity based on the formation of beating foci within spontaneous differentiating embryonic stem cells. Good biocompatibility was related to low contents of low-molecular-weight impurities in polyaniline cryogel, which was confirmed by liquid chromatography. The adhesion and growth of embryonic stem cells, embryoid bodies, cardiomyocytes, and neural progenitors prove that polyaniline cryogel has the potential to be used as a carrier for cells in tissue engineering or bio-sensing. The surface energy as well as the elasticity and porosity of cryogel mimic tissue properties. Polyaniline cryogel can therefore be applied in bio-sensing or regenerative medicine in general, and mainly in the tissue engineering of electrically excitable tissues.

Classification and Computer Simulation of 2D tessellations

In an analogy to the 3D tool of tessellation classification – w−s diagram, a similar graphical device is proposed for 2D tessellations. Any tessellation is represented by a point in the Cartesian coordinate system with the axes Ep (the mean cell perimeter) and CV a (the coefficient of cell area variation). Images of tessellations and p−CV a diagrams for selected tessellations with low and high values of CV a are shown as examples.