Degradation behavior of novel Fe/ß-TCP composites produced by powder injection molding for cortical bone replacement

When it comes to bone replacement in load-bearing areas, there are currently no adequate biodegradable implants available. Several non-degradable metallic materials fulfill the requirements of biocompatibility and mechanical strength. However, besides magnesium, only iron is a degradable metallic material. The aim of this long-term degradation study was to investigate the effects of iron beta-tricalcium phosphate interpenetrating phase composite on degradation rate and strength in comparison to pure iron. Cylindrical samples with 0–50 vol% beta-tricalcium phosphate (ß-TCP) were prepared by powder injection molding. In addition to dense samples, porous iron samples with a porosity of 60.3 % were produced with polyoxymethylene as a placeholder. Dense and porous samples were immersed in 0.9 % sodium chloride solution (NaCl) or in phosphate buffered saline solution (PBS) for 56 days. Following immersion, the degradation rate, compressive yield strength, and ion release were determined. A maximum degradation rate of 196 µm/year was observed after 56 days for iron with 40 vol% ß-TCP. This was found to be 28 % higher than for pure iron. After immersion, the compressive yield strength of pure iron decreased by 44 % (NaCl) and 48 % (PBS). In comparison, iron with 40 % ß-TCP samples lost <1 % (NaCl) and 9 % (PBS) of strength following immersion. It was demonstrated that the solubility of calcium phosphate enhanced the corrosion processes and led to an increase in degradation, thus showing that the addition of ß-TCP to pure iron can be a promising route for a novel degradable bone substitute material, particularly for load-bearing areas due to the increased strength.     

Information and communication theory in molecular biology

The DNA sequencing efforts of the past years together with rapid progress in sequencing technology have generated a huge amount of sequence data available in public molecular databases. This recent development makes it statistically feasible to apply universal concepts from Shannon’s information theory to problems in molecular biology, e.g to use mutual information for gene mapping and phylogenetic classification. Additionally, the genetic information in the cell is continuously subject to mutations. However, it has to be passed from generation to generation with high fidelity, raising the question of existence of error protection and correction mechanisms similar to those used in technical communication systems. Finally, better understanding of genetic information processing on the molecular level in the cell can be acquired by looking for parallels to well established models in communication theory, e.g. there exist analogies between gene expression and frame synchronization.     

Catalytic effects of activated carbon on hydrolysis reactions of chlorinated organic compounds: Part 2. 1,1,2,2-Tetrachloroethane

The hydrolysis reaction of 1,1,2,2-tetrachloroethane (TeCA) is significantly enhanced by sorption on activated carbon. TeCA is quantitatively transformed into trichloroethene (TCE) at moderate pH values. This transformation is exploited as the basic step of a site-adapted groundwater-cleanup technology. The volatility of TCE is a factor of 23 higher than that of TeCA such that the partially dehydrochlorinated product can be easily stripped out of the groundwater flow. The base-mediated and the neutral dehydrochlorination of TeCA were studied as a function of temperature and pH value in batch and column experiments. Surprisingly, it was found that despite high loadings of the sorbent with TeCA and TCE (≥20 wt.%) the TeCA remains available for the hydrolysis reaction.     

Forced periodic temperature cycling of chemical reactions in microstructure devices

In this publication, several stainless steel microstructure reactors specially designed to obtain rapid and periodic temperature changes are presented. Different microstructure reactor designs have been manufactured and tested for their thermal behaviour and equally by running a test reaction under stationary and non-stationary temperature conditions. The devices were continuously electrically heated and periodically cooled by a deionized water flow. The objective of the experimental measurements was to demonstrate that non-stationary temperature conditions may lead to an increase in the reaction rate compared to the stationary conditions. The heterogeneously catalysed oxidation of CO was chosen as the test reaction. The catalyst used was a dispersion of platinum on a porous alumina support generated by sol-gel technology. The experiments realized under non-stationary temperature conditions with a temperature oscillation amplitude of 41 K and a period duration of 21 s show an increase in the mean CO₂ concentration of a factor 1.72 compared to the mean concentration under quasi-stationary temperature conditions. The simulations of a simple monomolecular reaction under non-stationary temperature conditions indicate that the presence of a transitional surface coverage generated by the temperature oscillations may be a possible explanation for the observed phenomenon.     

Selective adsorption of solvents in a multiscale device

We have incorporated microspheres, from 50 to 80 μm in diameter, of periodic mesoporous organosilica (inner surfaces up to 1,000 m²/g and pore sizes in the nanometre range) with two types of organic functionalities (benzene and ethane bridges, respectively) inside microstructured channels (each 200 μm wide and 100 μm deep) and, exemplarily, monitored by Raman microscopy (Raman spectroscopy through microscope optics) that the temperature characteristics of the adsorption–desorption equilibria of benzene and ethanol vary significantly with the type of organic functionality of the microspheres and the pore morphology. The integration of this class of nanostructured material into devices by means of microchannels is a promising novel approach to, among others, substance separation in analytics, micro process engineering, and micro chemistry.     

Applicability of ToF-SIMS for monitoring compositional changes in bone in a long-term animal model

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a well-established technique in material sciences but has not yet been widely explored for implementation in life sciences. Here, we demonstrate the applicability and advantages of ToF-SIMS analysis for the study of minerals and biomolecules in osseous tissue. The locally resolved analysis of fragment ions deriving from the sample surface enables imaging and differentiation of bone tissue and facilitates histology on non-stained cross sections. In a rat model, bilateral ovariectomy combined with either a multi-deficiency diet or steroid treatment was carried out to create osteoporotic conditions. We focused our study on the Ca content of the mineralized tissue and monitored its decline. Calcium mass images of cross sections show the progressive degenerative changes in the bone. We observed a decreased Ca concentration in the edge region of the trabeculae and a decline in the Ca/P ratio. Additionally, we focused on the non-mineralized matrix and identified fragment ions that are characteristic for the collagen matrix. We observed trabeculae with wide ranges of non-mineralized collagen for the diet group owing to an impaired mineralization process. Here, the advantage of coeval monitoring of collagen and minerals indicated an osteomalacic model rather than an osteoporotic one.     

Parameter set selection for dynamic systems under uncertainty via dynamic optimization and hierarchical clustering

It is common that only a subset of the parameters of models can be accurately estimated. One approach for identifying a subset of parameters for estimation is to perform clustering of the parameters into groups based upon their sensitivity vectors. However, this has the drawback that uncertainty cannot be directly incorporated into the procedure as the sensitivity vectors are based upon the nominal values of the parameters. This article addresses this drawback by presenting a parameter set selection technique that can take uncertainty in the parameter space into account. This is achieved by defining sensitivity cones, where a sensitivity cone includes all sensitivity vectors of a parameter for different values, resulting from the uncertainty, in the parameter space. Parameter clustering can then be performed based upon the angles between the sensitivity cones, instead of the angle between sensitivity vectors. The presented technique is applied to two case studies. © 2013 American Institute of Chemical Engineers AIChE J, 60: 181–192, 2014     

Rotation-vibrational states of H3+ and the adiabatic approximation

We discuss recent progress in the calculation and identification of rotation-vibrational states of H3+ at intermediate energies up to 13,000 cm(-1). Our calculations are based on the potential energy surface of Cencek et al. which is of sub-microhartree accuracy. As this surface includes diagonal adiabatic and relativistic corrections to the fixed nuclei electronic energies, the remaining discrepancies between our calculated and experimental data should be due to the neglect of non-adiabatic coupling to excited electronic states in the calculations. To account for this, our calculated energy values were adjusted empirically by a simple correction formula. Based on our understanding of the adiabatic approximation, we suggest two new approaches to account for the off-diagonal adiabatic correction, which should work; however, they have not been tested yet for H3+. Theoretical predictions made for the above-barrier energy region of recent experimental interest are accurate to 0.35 cm(-1) or better.     

深入了解赛灵思System Generator中的时间参数

针对基于模型的设计,本文提出了采用赛灵思为DSP提供的SystemGenerator工具的系统化解决方案,详细介绍和分析了其中的比例-积分-微分(PID)控制器以及各时间参数的定义和选择.