Search

Surrogate technologies to monitor bed load discharge have been developed to supplement and ultimately take over traditional direct methods. Our research deals with passive acoustic monitoring of bed load flux using a hydrophone continuously deployed near a river bed. This passive acoustic technology senses any acoustic waves propagated in the river environment and particularly the sound due to interparticle collisions emitted during bed load movement. A data set has been acquired in the large Alpine gravel‐bedded Drau River. Analysis of the short‐term frequency response of acoustic signals allows us to determine the origin of recorded noises and to consider their frequency variations. Results are compared with ancillary field data of water depth and bed load transport inferred from the signals of a geophone array. Hydrophone and geophone signals are well correlated. Thanks to the large network of deployed geophones, analysis of the spatial resolution of hydrophone measurements shows that the sensor is sensitive to bed load motion not only locally but over distances of 5–10 m (10–20% of river width). Our results are promising in terms of the potential use of hydrophones for monitoring bed load transport in large gravel bed rivers: acoustic signals represent a large river bed area, rather than being local; hydrophones can be installed in large floods; they can be deployed at a low cost and provide continuous monitoring at high temporal resolution. Hydrophone signals in a large gravel bed river are correlated to bed load discharge monitored by geophonesThe listening distance of a hydrophone is estimated at 5 to 10 mPassive acoustic signals recorded in a large gravel bed river are processed using short‐term frequency representations

Zusammenfassung Stammzellen haben mit ihrer hohen Proliferationsaktivität und Plastizität das Potenzial, eine zentrale Funktion in zelltherapeutischen Therapieansätzen zu übernehmen. Wenngleich die Erforschung der grundlegenden zellbiologischen Prozesse in Stammzellen unabdingbar ist, so reicht dieses alleine jedoch nicht aus, um Stammzellen als Bestandteil des therapeutischen Spektrums zu etablieren. Hierzu ist parallel auch die Weiterentwicklung entsprechender Technologien notwendig. Diese umfasst sowohl die Etablierung von geeigneten Verfahren zur Gewinnung und Differenzierung der Stammzellen, als auch die Entwicklung von geeigneten Zellträgersystemen und Bioreaktoren zur Kultivierung und Expansion der Zellen. Darüber hinaus stellt der Aufbau einer Logistik für die Gewinnung, den Transport und die Lagerung von Stammzellen als Grundlage eines breiten therapeutischen Einsatzes eine große organisatorische und technische Herausforderung dar.

Cartilage lacks the ability to regenerate structural defects. Therefore, autologous grafting has been used routinely to replace cartilaginous lesions. Because tissue engineering of human cartilage with the help of bioresorbable polymer scaffolds is possible in experimental models, the demand for the clinical application grows. In this study we present an analysis of the behavior of transplants made of human chondrocyte pools, agarose and the resorbable polymer scaffold Ethisorb and a preliminary comparison with transplants made of single patients' cells and Ethisorb but without the additional ingredient agarose. Chondrocytes were isolated from the matrix of human septal cartilage by enzymatic digestion. The pool cells were kept in monolayer culture for 2 weeks, the single patients' cells for 3–4 weeks. Chondrocyte pools were suspended in agarose and seeded into the resorbable polymer scaffold Ethisorb. Single patients' cells were seeded without agarose. All cell–polymer constructs were kept in perfusion culture for 10–14 days and transplanted subcutaneously into thymusaplastic nude mice. Additionally we implanted Ethisorb fleeces embedded in agarose without chondrocytes. After 6, 12 and 24 weeks the animals were sacrificed and the specimens were explanted and analyzed histochemically and immunohistochemically. Polymer scaffolds not seeded with chondrocytes did not show cartilage formation. Resorption was complete after 12 weeks in vivo. Transplants from cell pools remained mechanically stable over 24 weeks apart from four transplants that were resorbed completely. Cartilage formation was observed in all pool-specimens with the presence of chondronic structures and a homogeneous matrix containing hyaline cartilage-specific matrix molecules such as collagen type II. Single patients' transplants showed hyaline cartilage matrix synthesis and mechanical stability as well. Chondrocyte pools are a suitable method to study cartilage engineering of human cells in vitro and in vivo in experimental models. Under clinical conditions it is, however, necessary to study the generation of cartilage from single patients' cells. We showed that it is possible without additional ingredients such as agarose. However, variations in the preliminary results show that the clinical application with human cells is more difficult than one would expect when using human chondrocyte pools. Further studies need to be performed to find out which individual factors influence the in vitro engineered cartilage's fate in vivo. © 1999 Kluwer Academic Publishers

In reconstructive surgery there is increasing demand for cartilage transplants to fill defects, especially nose and/or outer ear defects. Tissue engineering is one of the most modern pathways to generate autologous cartilage transplants. Isolated chondrocytes obtained from a tiny patient's biopsy were seeded on bioresorbable preshaped cell carriers to provide a 3-dimensional cell arrangement as in vivo. The combined use of these cell carriers in form of a non-woven mesh and a constant medium perfusion was performed to generate a cartilage-like cell-polymer-construct, which was finally subcutanously implanted in nude mice for full maturation. After explantation of 6 months, expression of cartilage specific extracellular matrix molecules was obvious by using histochemical and immunohistochemical methods. These data show that tissue engineering with isolated multiplied human chondrocytes from a tiny biopsy seeded on bioresorbable polymer is a promising system to generate autologous cartilage transplants for replacements in reconstructive surgery.

Our first target on the way towards the synthesis of enantiomerically pure chatancin is the preparation of the title compound. The cycloadduct of 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene and thymoquinone is stereo- and regioselectively reduced to the tricyclic ketoalcohol4, which by nucleophilic cyclisation and reductive removal of the keto group as well as the chlorine atoms yielded a tetracyclic dimethoxyketal. Acidic hydrolysis freed the keto group, which now was treated with a chiral lithium alkyl compound derived from methyl (R)-2-methyl-3-hydroxypropionate in few steps. The resulting stereomeric tertiary alkohols were fragmented and the decalinones thus obtained separated. X-ray analysis permitted the determination of the absolute configuration of these decalinone derivatives.

If cells or tissues are taken out of an organ and put in culture, normally they lose morphological, physiological and biochemical features. This dedifferentiation process starts during the isolation procedure and continues during the whole culture period. It is caused by the stagnant liquid condition and the inadequate anchorage of cells at the bottom of tissue culture plasticware. The use of filters as basement membrane substitutes and the coating of cultureware with extracellular matrix proteins improve the environmental factors for cultured cells but do not consider the paracrine influence of cytokines or the nutritional needs of individual cell types. To limit cellular dedifferentiation in culture, we constructed a new system, which adapts, as far as possible, cell and tissue cultures to an organo-typical environment. The system is based on a compatible cell carrier arrangement, which allows individual selection of supports for optimal cell anchorage and differentiation. The cell carriers are placed in a newly constructed container, which is permanently perfused with fresh culture medium. The system runs outside an incubator with simple laboratory tools; only a peristaltic pump, a warming table and pH-stabilized media are necessary. Without any subculturing, acute and chronic influences of drugs or the quality of medical implantation grafts can be studied over months.

The aim of this study was to investigate the possibility of using the benzyl ester of hyaluronic acid (HYAFF® 11), a recently developed semisynthetic resorbable material, as a scaffold for the culture of human nasoseptal chondrocytes in tissue-engineering procedures of cartilage reconstruction. Different techniques such as immunohistochemistry, scanning electron microscopy, and confocal laser scanning microscopy were used to study the behavior, morphology, and phenotype expression of the chondrocytes, which were initially expanded and then seeded on the material. The nonwoven cell carrier allowed good viability and adhesivity of the cells without any surface treatment with additional substances. Furthermore, the cultured cells expressed cartilage-specific collagen type II, indicating that they were able to redifferentiate within the scaffold of HYAFF® 11 and were able to retain a chondrocyte phenotype even after a long period of in vitroconditions. Nevertheless, the expression of collagen type I, which was produced by dedifferentiated or incompletely redifferentiated chondrocytes, was noticeable. Additional data were obtained by subcutaneous implantation of samples seeded with human cells in the in vivomodel of the athymic nude mouse. The results after 1 month revealed the development of tissue similar to hyaline cartilage. This study is promising for the use of this scaffold for tissue engineering of cartilage replacements. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 172–181, 1998.

New cell culture techniques raise the possibility of creating cartilage in vitrowith the help of tissue engineering. In this study, we compared two resorbable nonwoven cell scaffolds, a polyglycolic acid/poly-L-lactic acid (PGA/PLLA) (90/10) copolymer (Ethisorb) and pure PLLA (V 7-2), with different degradation characteristics in their aptitude for cartilage reconstruction. Chondrocytes were isolated enzymatically from human septal cartilage. The single cells were resuspended in agarose and transferred into the polymer scaffolds to create mechanical stability and retain the chondrocyte-specific phenotype. The cell–polymer constructs were then kept in perfusion culture for 1 week prior to subcutaneous transplantation into thymusaplastic nude mice. After 6, 12, and 24 weeks, the specimens were explanted and analyzed histochemically on the presence of collagen (azan staining), proteoglycans (Alcian blue staining), and calcification areas (von Kossa staining). Furthermore, different collagen types (collagen type I, which is found in most tissues, but not in hyaline cartilage matrix; and collagen type II, which is cartilage specific) were differentiated immunohistochemically by the indirect immunoperoxidase technique. Vascular ingrowth was investigated by a factor VIII antibody, which is a endothelial marker. Quantification of several matrix components was performed using the software Photoshop. Significant differences were found between both nonwoven structures concerning matrix synthesis and matrix quality as well as vascular ingrowth. Ethisorb, with a degradation time of approximately 3 weeks in vitro, showed no significant differences from normal human septal cartilage in the amount of collagen types I and II 24 weeks after transplantation. Thin fibrous tissue layers containing blood vessels encapsulated the transplants. V 7-2 constructs, which did not show strong signs of degradation even 24 weeks after transplantation, contained remarkably smaller amounts of cartilage-specific matrix components. At the same time, there was vascular ingrowth even in central parts of the transplants. In conclusion, polymer scaffolds with a short degradation time are suitable materials for the development of cartilage matrix products, while longer stability seems to inhibit matrix synthesis. Thus, in vitroengineering of human cartilage can result in a cartilage-like tissue when appropriate nonwovens are used. Therefore, this method could be the ideal cartilage replacement method without the risk of infection and with the possibility of reconstructing large defects with different configurations. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 347–356, 1998.

The new Ford Escort is a front–wheel driven vehicle with a 3/5–door semi fast back Sedan body style, with Wagon/Van derivatives. Its new aluminium head OHC engines of 1100cc, 1300cc and 1600cc displacement feature hemispherical combustion chambers and hydraulic tappets. To allow for optimum and flexible use of Ford's engine plant capacities the new Escort is also marketed in some European countries with the well known 1100cc Valencia engine of the Fiesta (Aigner and Franz, 1978). The Sedan and Wagon models have independent rear suspensions, and the Van derivative has a beam rear axle with leaf springs on an extended wheel base. The front suspension is based on the reliable McPherson strut concept with offset springs; the 1100cc model has a tie bar, and the 1300cc and 1600cc models have stabilizer antiroll bars to hold and support the front axle. The 4–speed, all synchro–mesh gear box is of the same design as the Fiesta's, which permits multi model usage and manufacturing rationalisation. An automatic 3–speed transmission option is in development and will be launched soon. Similar to other Ford models the new Escort series range from Base and 'L' to 'GL' and Ghia with additional 'S' pack versions and a Super 'S' for sporty driving. Local customer needs and preferences, together with national legal requirements made it necessary to combine and optimise body styles, engines and series for 15 different markets. The summary of technical data and features at the end of this report gives an impression of the many combinations possible.

Vehicle evaluation is an important tool for the development engineer, whether as a means of interpreting measured results or of analysing and understanding customer preferences and criticism. However, like any other measuring instrument, the evaluator has to calibrate this data output and analyse error sources. The student's t–test shows at a glance how accurately a group of evaluators can do the job. To cater for product quality variation the student's t–test formula is extended by a correction factor. Thus a relatively quick method of analysing evaluation data with respect to accuracy range and reliability is now available.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.