Neue reaktive Mikrogele als Träger für Enzyme

By copolymerization of ethylene-dimethacrylate with acrylonitrile and glycidylmethacrylate, respectively, reactive microgels with diameters of approx. 50nm were obtained. Modification reactions led to functional groups (imidate or aldehyde groups) suitable for covalent enzyme coupling. When immobilizing the enzymes lactate dehydrogenase, alkaline phosphatase and proteinase K it was found that the residual activity of these conjugates was very much higher compared with conventional porous supports due to the absence of diffusional restrictance.     

The Effect of Different Sterilization Methods on the Mechanical Strength of Magnesium Based Implant Materials

The research on the development and characterization of potential magnesium biomaterials is a steadily expanding. Commonly, implants present a high risk of infection for their recipients. For this reason, a pre‐operative sterilizing process is required. Due to the temperatures and media which are used while sterilizing, effects may occur which cause a change in the mechanical strength of certain magnesium alloys. Four commonly used sterilization methods (autoclave sterilization, dry heat sterilization, gamma sterilization and ethylene oxide sterilization) were investigated to gain information about their influences on the quasi‐static mechanical behavior of LAE442 (Mg 90 m.%, Li 4 m.%, Al 4 m.%, RE 2 m.%), MgCa0.8 (Mg 99.2 m.%, Ca 0.8 m.%) magnesium alloys as well as pure magnesium. The mechanical properties exhibited by the sterilized and non‐sterilized alloys refer to susceptibilities of the mechanical strengths to the investigated sterilization methods. Such susceptibilities appear to be dependent on the combination of alloy and method of sterilization. However, the maximum changes in mechanical strength appear in the range of ±10%. Within this study, ETO sterilization caused the least changes in the mechanical strength of the alloys and appears to be the best performer.     

The Manufacture of Resorbable Suture Material from Magnesium – Drawing and Stranding of Thin Wires

With the aid of multiple wire drawing passes, the magnesium alloys ZEK100, MgCa0.8, and AL36 were reduced to monofilament wires possessing diameters between 0.5 and 0.1 mm. These filaments were subsequently twisted into poly‐filament suture material using stranding. In order to analyze the microstructural constituents and the mechanical‐tribological properties, metallographic specimens were prepared and tensile tests were performed on both monofilament as well as poly‐filament wire strands. Appropriate parameters were ascertained for the wire drawing process with regard to forming rate, temperature, and heat treatment. During the investigations, the alloy ZEK100 exhibited particularly interesting mechanical properties which, owing to its high tensile strengths (up to 550 MPa for monofilament) and fracture strains (up to 30% for poly‐filament), are comparable to those of conventional polymer‐based suture materials. In addition to this, integrating a core (internal, individual wire) into the poly‐filament mesh of wire strands represents an interesting alternative for future research in which structures composed of different materials, and the advantages of combining their properties are brought into particular focus.     

Establishment of a New Device for Electrical Stimulation of Non-Degenerative Cartilage Cells In Vitro

In cell-based therapies for cartilage lesions, the main problem is still the formation of fibrous cartilage, caused by underlying de-differentiation processes ex vivo. Biophysical stimulation is a promising approach to optimize cell-based procedures and to adapt them more closely to physiological conditions. The occurrence of mechano-electrical transduction phenomena within cartilage tissue is physiological and based on streaming and diffusion potentials. The application of exogenous electric fields can be used to mimic endogenous fields and, thus, support the differentiation of chondrocytes in vitro. For this purpose, we have developed a new device for electrical stimulation of chondrocytes, which operates on the basis of capacitive coupling of alternating electric fields. The reusable and sterilizable stimulation device allows the simultaneous use of 12 cavities with independently applicable fields using only one main supply. The first parameter settings for the stimulation of human non-degenerative chondrocytes, seeded on collagen type I elastin-based scaffolds, were derived from numerical electric field simulations. Our first results suggest that applied alternating electric fields induce chondrogenic re-differentiation at the gene and especially at the protein level of human de-differentiated chondrocytes in a frequency-dependent manner. In future studies, further parameter optimizations will be performed to improve the differentiation capacity of human cartilage cells.     

A fast and precise approach for computational saturation mutagenesis and its experimental validation by using an artificial (βα)8-barrel protein

We present a computational saturation mutagenesis protocol (CoSM) that predicts the impact on stability of all possible amino acid substitutions for a given site at an internal protein interface. CoSM is an efficient algorithm that uses a combination of rotamer libraries, side-chain flips, energy minimization, and molecular dynamics equilibration. Because CoSM considers full side-chain and backbone flexibility in the local environment of the mutated position, amino acids larger than the wild-type residue are also modeled in a proper manner. To assess the performance of CoSM, the effect of point mutations on the stability of an artificial (βα)(8)-barrel protein that has been designed from identical (βα)(4)-half barrels, was studied. In this protein, position 234(N) is a previously identified stability hot-spot that is located at the interface of the two half barrels. By using CoSM, changes in protein stability were predicted for all possible single point mutations replacing wild-type Val234(N). In parallel, the stabilities of 14 representative mutants covering all amino acid classes were experimentally determined. A linear correlation of computationally and experimentally determined energy values yielded an R(2) value of 0.90, which is statistically significant. This degree of coherence is stronger than the ones we obtained for established computational methods of mutational analysis.     

Recovery efficiency of Cryptosporidium from water with a crossflow system and continuous flow centrifugation: a comparison study

A crossflow system and continuous flow centrifugation were tested with regard to the recovery rate of Cryptosporidium oocysts from water. Equal volumes of tap water were contaminated with specific numbers of oocysts. With the crossflow system, an average recovery of 9.8% was obtained when using a concentration of 2 x 10(2) oocysts/L. Recovery rates achieved with the continuous flow centrifuge were more satisfactory: Starting with a concentration of 80 oocysts/L, we obtained an average recovery of 12.9%. The technique of continuous flow centrifugation was found to be more efficient for collection of Cryptosporidium oocysts from water than the crossflow system.     

Singular Nature of Preferential Conducting Paths at High Electric Fields in ZnO-Based Varistors

The ac electrical response of ZnO-based varistors was monitored as a function of frequency (50 Hzf2 MHz) and electric field (60% E_lmA/cm2EE_lmA/cm2, E_lmA/cm2 in the critical field at 1 mA/cm²) at room temperature, and these data were represented in the complex impedance (Z^*) plane. The finite depression angle observed in this plane was rationalized in terms of nonuniformity in the measured reactance between the terminals. The singular nature of the series-parallel combination of the uniform conducting paths between the electrodes was suggested when this depression angle diminished to 0° at high electric fields (EE_lmA/cm2).