Hot stamping: manufacturing functional optimized components

Due to rising requirements regarding passenger safety and weight reduction hot stamped components get more and more important regarding security relevant parts because of their high strength. Currently, the new challenge is manufacturing components with locally adjusted mechanical properties in order to simultaneously guarantee structural integrity and energy absorption in case of a crash. Therefore, the so called Tailored Tempering process is a promising strategy controlling the cooling rate of the austenitized blank by local heating of the tool and consequently adjusting microstructure development and resulting mechanical properties. As the adjustment of mechanical properties is a temperature dependent process which is also influenced by process parameters and contact conditions, accurate process knowledge is essential. Within this paper the influence of tool temperature and applied contact pressure on the resulting heat transfer coefficient as well as contact condition between the surfaces of former investigations will be shown in a short overview. Based on the results of these fundamental investigations, design principles for Tailored Tempering process will be derived. Furthermore, a hat-profile geometry will be investigated experimentally and characterized by mechanical tests as well as geometrical aspects like sheet thickness and distortion. Additionally, an FE-Modell based on the results of the thermo-mechanical characterization is build up and validated by comparison with the results of experimental work.     

Temperature analysis of steel structures protected by intumescent paint with steel claddings in fire

It is of great interest to understand the stabilization effect of steel structures by steel claddings in fire. Structural fire analysis using finite-element method, including temperature analysis and structural analysis, is important to investigate the stabilization effect. However, temperature-dependent thermal material data for the insulation layer of sandwich panels and the intumescent paint for fire protection of steel sections are still scarce. In this paper, the available thermal properties of these materials from the literature are summarized, and 2D and 3D temperature analyses were carried out for steel sections with steel claddings, such as sandwich panels with mineral wool and polyisocyanurate (PIR) cores and trapezoidal sheeting with mineral wool insulation. The analysis results were compared with the fire tests conducted in European research project STABFI (Stabilization of Steel Structures by Steel Claddings in Fire). The study shows reasonable accuracy of modeling using existing thermal material data for temperature-dependent insulation properties and thermal data for intumescent paint, for intumescent coatings (IC) protected steel beam with mineral wool sandwich panel and trapezoidal sheeting claddings. Larger discrepancy between finite element (FE) prediction and test measurement was observed for the case of sandwich cladding with PIR core. Gaps for further research were identified. The study also shows the heat sink effect of the steel section by sandwich panels with a mineral wool core. Therefore, it is recommended that the sandwich panels should be included in the thermal analysis model for steel sections with sandwich claddings.     

Current Status of Cell-Based Therapy in Patients with Critical Limb Ischemia

(1) Background: The treatment of peripheral arterial disease (PAD) is focused on improving perfusion and oxygenation in the affected limb. Standard revascularization methods include bypass surgery, endovascular interventional procedures, or hybrid revascularization. Cell-based therapy can be an alternative strategy for patients with no-option critical limb ischemia who are not eligible for endovascular or surgical procedures. (2) Aims: The aim of this narrative review was to provide an up-to-date critical overview of the knowledge and evidence-based medicine data on the position of cell therapy in the treatment of PAD. The current evidence on the cell-based therapy is summarized and future perspectives outlined, emphasizing the potential of exosomal cell-free approaches in patients with critical limb ischemia. (3) Methods: Cochrane and PubMed databases were searched for keywords “critical limb ischemia and cell therapy”. In total, 589 papers were identified, 11 of which were reviews and 11 were meta-analyses. These were used as the primary source of information, using cross-referencing for identification of additional papers. (4) Results: Meta-analyses focusing on cell therapy in PAD treatment confirm significantly greater odds of limb salvage in the first year after the cell therapy administration. Reported odds ratio estimates of preventing amputation being mostly in the region 1.6–3, although with a prolonged observation period, it seems that the odds ratio can grow even further. The odds of wound healing were at least two times higher when compared with the standard conservative therapy. Secondary endpoints of the available meta-analyses are also included in this review. Improvement of perfusion and oxygenation parameters in the affected limb, pain regression, and claudication interval prolongation are discussed. (5) Conclusions: The available evidence-based medicine data show that this technique is safe, associated with minimum complications or adverse events, and effective.     

The amine modified acrylic copolymers as catalysts in the reaction of octylbromide with sodium cyanide

Summary Amine-modified and alkylated (with butyl bromide or hexyl bromide) acrylonitrile-butyl acrylate-divinylbenzene terpolymers and alkyl acrylate-divinylbenzene copolymers (where alkyl=methyl, ethyl or butyl) were used as catalysts in the reaction of octyl bromide with cyanide anions. The dependence of catalytic activity as a function of the acrylate content and swelling properties was investigated. The most effective catalyst was butyl acrylate-divinylbenzene copolymer. This sample showed maximum toluene uptake from the toluene/water mixture.     

Macroporous membranes. 3. Properties of macroporous membranes synthesized from glycidyl methacrylate,ethylene dimethacrylate and alkyl- or hydroxyalkyl methacrylate

A series of macroporous membrances composed either of glycidyl methacrylate and ethylene dimethacrylate with an addition of other monomer chosen from a group comprising 2-hydroxyethyl methacrylate, butyl methacrylate, octyl methacrylate or dodecyl methacrylate, or of a copolymer of 2-hydroxyethyl methacrylate and ethylene dimethacrylate were synthesized and their properties were determined. The addition of a third monomer changes the porous properties only when the concentration of the monomer in the polymerization feed is rather high. The presence of bulkier alkyl side chains in a polymer matrix raises hydrophobicity and reduces the water regain while the strength of the membrane increases.     

Implication of Mesenchymal Stem Cells and Their Derivates for Osteochondral Regeneration

Healing of articular cartilage defects presents a challenging issue, due to its regenerative shortcomings. Lacking vascularity and innervation of cartilage and low proliferative potential of chondrocytes are the main reasons for the limited healing potential of articular cartilage. Traditional reparative approaches are limited in their efficiency, hence there is a demand for novel reparative treatments. Mesenchymal stromal cells, preferred for clinical uses, can be readily derived from various sources and have been proven to have a therapeutic effect on cartilage and subchondral bone. Therefore, mesenchymal stromal cells, their derivates, and scaffolds have been utilized in research targeting osteochondral regeneration. The present review aims to comprehensively outline and discuss literature considering this topic published within last 5 years.     

Semipreparative capillary electrochromatography

Capillaries with inner diameters of 550 microm have successfully been packed with 1.5-microm octadecyl silica particles using frits made of macroporous polymers by the UV photopolymerization of a solution of glycidyl methacrylate and trimethylolpropane trimethacrylate. This type of frit is found superior to one made of low-melting point poly(styrene-co-divinylbenzene) beads. Bubble formation is not observed to occur within these capillary columns under our experimental conditions. Separations can be achieved with sample injection volumes as high as 1 microL. To demonstrate its semipreparative use, a mixture of 500 nL of taxol (20 mM) and its precursor, baccatin III (30 mM), is separated using such a column with a Tris buffer.     

Hierarchical Micro‐ and Mesoporous Zn‐Based Metal–Organic Frameworks Templated by Hydrogels: Their Use for Enzyme Immobilization and Catalysis of Knoevenagel Reaction

Encapsulation of enzymes in metal–organic frameworks (MOFs) is often obstructed by the small size of the orifices typical of most reported MOFs, which prevent the passage of larger‐size enzymes. Here, the preparation of hierarchical micro‐ and mesoporous Zn‐based MOFs via the templated emulsification method using hydrogels as a template is presented. Zinc‐based hydrogels featuring a 3D interconnecting network are first produced via the formation of hydrogen bonds between melamine and salicylic acid in which zinc ions are well distributed. Further coordination with organic linkers followed by the removal of the hydrogel template produces hierarchical Zn‐based MOFs containing both micropores and mesopores. These new MOFs are used for the encapsulation of glucose oxidase and horseradish peroxidase to prove the concept. The immobilized enzymes exhibit a remarkably enhanced increased operational stability and enzymatic activity with a k_cat/k_m value of 85.68 mm s^–1. This value is 7.7‐fold higher compared to that found for the free enzymes in solution, and 2.7‐fold higher than enzymes adsorbed on conventional microporous MOFs. The much higher catalytic activity of the mesoporous conjugate for Knoevenagel reactions is demonstrated, since the large pores enable easier access to the active sites, and compared with that observed for catalysis using microporous MOFs.