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U Meyer

Publications and source records attributed to U Meyer.

At least 37 records · Page 2Linked to original sources
PubMed2004

Biological and biophysical principles in extracorporal bone tissue engineering. Part II.

The aim of this review is to characterise the biological and biophysical background of in vitro bone tissue engineering. The paper focuses on basic principles in extracorporal engineering of bone-like tissues, considering parameters such as scaffold design, tissue construction, bioreactors, and cell stimulation in vivo and in vitro. Scaffolds have a key function concerning cellular invasion and bone formation. The intra-architectural scaffold geometry, as well as the scaffold material, play an important role in the process of bone regeneration. Various types of bioreactors have been tested for their utility in bone substitute fabrication that is clinically effective and reproducible. Sophisticated bioreactor systems are those that mimic the three-dimensional morphology and the mechanical situation of bones. Mechanical stimulation as well as other biophysical stimuli appear to be critical factors for proliferation and differentiation of bone cells and for bone mineral and structure formation. Furthermore an enhancement of bone regeneration by application of chemical stimulation factors is discussed.

Animals↗
PubMed2004

Biological and biophysical principles in extracorporal bone tissue engineering. Part III.

Over the last decade extracorporal bone tissue engineering has moved from laboratory to clinical application. The restoration of maxillofacial bones from cell harvesting through product manufacture and end-use has benefited from innovations in the fields of biomechanical engineering, product marketing and transplant research. Cell/scaffold bone substitutes face a variety of unique clinical challenges which must be addressed. This overview summarises the recent state of the art and future anticipations in the transplantation of extracorporally fabricated bone tissues.

Animals↗
PubMed2004

Biological and biophysical principles in extracorporal bone tissue engineering. Part I.

Advances in the field of bone tissue engineering have encouraged physicians to introduce these techniques into clinical practice. Bone tissue engineering is the construction, repair or replacement of damaged or missing bone in humans or animals. Engineering of bone can take place within the animal body or extracorporal in a bioreactor for later grafting into the body. Appropriate cell types and non-living substrata are minimal requirements for an extracorporal tissue engineering approach. This review discusses the biological and biophysical background of in vitro bone tissue engineering. Biochemical and biophysical stimuli of cell growth and differentiation are regarded as potent tools to improve bone formation in vitro. The paper focuses on basic principles in extracorporal engineering of bone-like tissues, intended to be implanted in animal experiments and clinical studies. Particular attention is given in this part to the contributions of cell and material science to the development of bone-like tissues. Several approaches are at the level of clinical applicability and it can be expected that widespread use of engineered bone constructs will change the surgeon's work in the near future.

Animals↗
PubMed2004

Dissemination of the entomopathogenic fungus verticillium lecanii (Zimmermann) Viégas (Hyphomycetales: Moniliaceae) in a population of Frankliniella occidentalis (Pergande, 1895) (Thysanoptera: Thripidae).

Tests were carried out to investigate the dissemination of the entomopathogenic fungus Verticillium lecanii (Zimmermann) Viégas in a population of Frankliniella occidentalis. The tested factors, which influence the efficacy of the fungus against the pest insect, have been the population density of the thrips at the application moment as well as the temperature. The population density influenced the dissemination of the fungal spores in the population. The higher the density has been, the higher the insetting control effect has been as well. The temperature influenced the speed of the fungal effect, too. The higher the temperature has been, the earlier the control effect started. However, an increase of the natural mortality was found as well.

Animals↗
PubMed2003

[Primary implant stability with different bone surgery techniques. An in vitro study of the mandible of the minipig].

The treatment concept of osseointegration is based on a stable embodiment of implants in bone and the maintenance of stability during functional load. A goal of the surgical preparation technique is therefore to obtain a stable and firm implant anchorage. The aim of this study was to evaluate implant stability after different surgical treatment of the bony implantation bed. Thirty cylindrical solid-screw-shaped implants with standard SLA ITI configuration were implanted into the explanted mandibles of five minipigs. The implant sites were prepared either by a conventional burr technique (group A), by burr technique with additional thread cutting (group B), or by the osteotome technique (group C). Primary implant stability was evaluated by resonance frequency analysis and removal torque test. The average value of the resonance frequency analysis (RFA) was 6000+/-469 cycles/s in group A, 5700+/-557 cycles/s in group B, and 5540+/-527 cycles/s in group C. Removal torque values of group A (507+/-57 Nmm) were significantly higher than those of group B (466+/-45 Nmm) and group C (240+/-31 Nmm) (between group A and C p<0.05, group A to B p=0.39, and B to C p<0.05). It can be concluded from this study that the conventional burr technique achieves a statistically significantly better primary bone anchorage than the osteotome technique.

Animals↗
PubMed2003

[Experimental and clinical study of the stability of an osteosynthesis plate for the atrophic mandible].

BACKGROUND: The high rate of complications led us to develop a new osteosynthesis plate for the treatment of the fractured atrophied mandible. The development of the new so-called pencil-bone plate is based on the 2.0 mini-plate system manufactured by the Medartis Company. MATERIAL AND METHODS: Finite elements (FE) analysis of the new plate as well as flexibility experiments were undertaken, and 14 patients with 16 fractures of the atrophied mandible were treated with the pencil-bone plate between October 2000 and November 2001. RESULTS: The results clearly show that the pencil-bone plate reacted in both the FE model and the static flexibility experiment in a more stable way than a standard 2.0 plate. In 13 patients, healing proceeded without serious complications; all of the patients showed subjective, nearly unchanged chewing, speaking, and swallowing abilities and no complications occurred when wearing dentures. One patient underwent surgical intervention after a new trauma. CONCLUSION: The clinical outcome of the treated fractures confirmed the experimental results, which proved the high stability of the plate in the area of the fracture site. Due to the mini-plate format the intraoral application of the plate is possible without problems. The intraoral access allows rapid operation followed by a minimum of morbidity. A great advantage of the small dimension system is the unrestricted wearing of dentures after the application.

Aged↗
PubMed2003

Incidence of tumor lysis syndrome in children with advanced stage Burkitt's lymphoma/leukemia before and after introduction of prophylactic use of urate oxidase.

To evaluate the clinical benefit of the prophylactic use of urate oxidase in children with non-Hodgkin's lymphoma (NHL), we analyzed the incidence and complications of tumor lysis syndrome (TLS) in children with B-cell acute lymphoblastic leukemia (B-ALL) or stage III/IV Burkitt's lymphoma and a lactate dehydrogenase (LDH) level > or =500 U/l before and after the introduction of a protocol amendment to use urate oxidase for the prophylaxis of TLS. Data from 1791 children with NHL enrolled in the two subsequent multicenter studies NHL-BFM 90 and 95 were evaluated. The presence of the side effects TLS, anuria, sepsis, and other complications during the first 2 weeks after admission were registered. Until March 1996, no urate oxidase was used (period 1). From November 1997 all children with B-ALL or stage III and IV B-NHL and LDH > or =500 U/l should receive urate oxidase prophylactically (period 3). In between (period 2), urate oxidase was given in a minority of hospitals therapeutically. Initial chemotherapy was identical. Altogether, 78 children (4.4%) developed a TLS. Patients with B-ALL had the highest risk to develop a TLS (26.4%) followed by B-ALL/Burkitt's lymphoma and a LDH > or =500 U/l (14.9%). In period 1, 16.1% and 9.2% of the latter children developed a TLS or anuria, respectively, compared to 12.3% and 6.2% in period 3 ( p=NS). The incidence of sepsis remained unchanged (5.0% vs 4.6%). In children with B-ALL the differences in the incidence of TLS and anuria between period 3 and period 1 were more pronounced, reaching significance for anuria (15.4% vs 3.8%, p=0.03). Our results suggest that patients with the highest risk to develop a TLS might benefit from the prophylactic use of urate oxidase.

Adolescent↗
PubMed2003

Evaluation of accuracy of insertion of dental implants and prosthetic treatment by computer-aided navigation in minipigs.

The survival of loaded implants is critically dependent on their biomechanical stability. We have used a computer-guided navigation technique to evaluate the accuracy of computer-assisted insertion for immediately-loaded implants in minipigs. On the basis of computed tomographical data, the Robodent system was used for preoperative planning and guidance of inserting the implant. An optical tracking system allowed positioning of the implant and immediate prosthetic rehabilitation by inserting it in a plaster model and during the operation. Postoperative computed tomograms (CT) showed that the implants were placed precisely in the preoperatively planned position. The accuracy achieved corresponded well with the spatial resolution of the CT used. Immediate placement of the prefabricated crowns resulted in favourable occlusal positioning. Histological cross-sections showed that the implants were biomechanically stable. The accuracy of insertion of oral implants illustrated here suggests that insertion and prosthetic modelling of implants may benefit from computer-assisted navigation.

Animals↗
PubMed2003

Intraoral sebaceous carcinoma.

Sebaceous carcinoma in the oral cavity is extremely rare, and we have found only four previously reported cases. We describe a fifth case. A wide surgical excision seems to be the correct treatment and estimation of serum carcinoembryonic antigen (CEA) may be a useful tumour marker in the follow-up of intraoral sebaceous carcinomas.

Adenocarcinoma, Sebaceous↗
PubMed2003

Are collimated low-dose digital radiographs valid for performing Delaire's architectural analysis?

Computed radiography (CR) provides the dynamic exposure range to reveal objects in film areas exposed by very low X-ray exposure. Conventional cephalometric radiographs are normally beam limited to the facial skeleton. The cranial vault and cervical vertebra are collimated and only exposed by extra-focal radiation and scatter. We hypothesize that, on conventional cephalometric radiographs obtained with CR, image data of collimated film areas can be enhanced for reliable performance of Delaire's cephalometric analysis of the entire skull. Therefore the aim of the present study was to compare the reproducibility of landmark placement on normal and underexposed film areas of CR images. Intra- and inter-observer reproducibility of landmark identification was evaluated on 200 randomly selected radiographs by calculating the error radius of repeated landmark placements. A paired-samples t-test revealed differences (P< 0.001) between intra- and inter-observer reproducibility. Intra-observer accuracy was influenced (P< 0.001) by variability of suture obliteration (bregma). Identification of landmarks in areas of extra-focal radiation showed no difference (P> 0.05) from that of landmarks inside the normally exposed area. CR offers the opportunity to perform of a full cranial analysis on a cephalometric radiograph collimated to the facial region.

Cephalometry↗
PubMed2003

Fuzzy-control for improved nitrogen removal and energy saving in WWT-plants with pre-denitrification.

In the last few years, numerous studies were carried out, dealing with the application of fuzzy-logic to improve the control of the activated sludge process. In this paper, fuzzy-logic based control strategies for wastewater treatment plants with pre-denitrification are presented that should lead to better effluent quality and, in parallel, to a reduction of energy consumption. Extensive experimental investigations on a large scale pilot plant as well as simulation studies (ASM1 with SIMBA) were carried out in order to design, evaluate and compare different fuzzy-controllers with each other and with comparable conventional control systems. The fuzzy-controllers were designed as high-level controllers that determine the DO-setpoints in the aerated zones and the ratio between aerated and non-aerated zones. Conventional PI-controllers were used to maintain the DO-concentration at the set-point levels. The ammonia and nitrate concentration in the effluent and the ammonia load in the influent were considered as input variables for the different fuzzy-controllers. Compared to the operation with fixed nitrification/denitrification zones and constant DO concentrations, the required air-flow could be reduced up to 24% by using fuzzy-logic based control strategies. In comparison with a more advanced conventional control strategy (relay controller with two thresholds and the NH4-N concentration in the effluent as single control variable) a reduction of air-flow-rate up to 14% could be achieved. At the same time, NH4-N peaks in the effluent that are normally caused by peak flow conditions could be reduced significantly. The large scale experiments show that the fuzzy-controllers can be easily implemented in modern control and supervision systems and that the control characteristics can be followed and modified during operation. It therefore can be expected that the developed fuzzy-control systems will be accepted by the operating personnel in wastewater treatment plants.

Automation↗
PubMed2003

Factors affecting constancy of acetate concentration and correct determination of methanogenic activity in pH-stat experiments.

The determination of methanogenic activity with a pH-stat titration bioassay is evaluated utilising a mathematical model of this system. For given kinetic parameters and experimental conditions the model calculates the development of titrant flow and acetate concentration during experiments. Simulations of experiments under various conditions are compared. They show that the original method inherently causes a strong drift of acetate concentration during the experiments and a misestimation of methanogenic activity. As a solution to these disadvantages the addition of sodium hydroxide to the titrant and a careful control of pH during flushing the reactor with gas prior to the experiment are recommended. In this way a better constancy of acetate concentration and a more accurate determination of methanogenic activity should be achievable. The accuracy of this method is limited by the stability of pH-electrode calibration parameters.

Acetates↗
PubMed2003

A new method for the fast determination of kinetic parameters in anaerobic digestion processes and application to textile wet processing wastewater.

A new method for the fast and efficient determination of the anaerobic degradability and for the calculation of kinetic parameters is proposed. It is based on the idea that monitoring of the acidification step in the anaerobic degradation cascade is sufficient, as the subsequent steps (acetogenesis, methanogenesis) are well known processes dependent on the intermediate concentrations and not on the original substrate used. The investigation of the acidification is subdivided into two steps. In the first step, biomass is adapted to the new substrate in a continuously operated bioreactor. The second step, the only step monitored, is the acidification of the substrate (or wastewater) in a batch experiment. Three different methods to monitor the acidification were tested: gas chromatography (offline), on-line titration and monitoring of the base consumption (direct titration). The results of these methods were compared to "traditional" batch tests. It is shown that the simplest method (direct titration) revealed the most important information. The investigated substrates were selected pollutants of textile wet processing wastewater.

Bacteria, Anaerobic↗
PubMed2002

[Experimental study on the biomechanical stability of different internal fixators for use in the mandible].

BACKGROUND: Comparative studies of different forms of osteosynthesis require that biomechanical and biological criteria be observed. The conditions in experimental studies should be as close as possible to the in vivo situation. The aim of our study was to develop a fracture model that would allow determination of the micromovements in the gap tissue following different forms of internal fixation in fractured human mandibles. METHODS: Micromovements in the gap tissue of five human mandibles treated with different osteosynthetic systems (DCP, EDCP, Miniplates, 3-D systems) following osteotomy or fracture in the region of the corpus and median region were investigated by means of strain gauges. By fitting the human mandibles in plaster according to a method of our own it was possible to create fractures at predictable and comparable localizations. RESULTS: Our investigations show that the micromovements in the gap tissue of osteotomied and fractured mandibles are different and not dependent on the form of osteosynthesis applied. Physiological micromovements in the gap tissue were found under strain for all osteosynthetic systems used in fractured and congruently reset mandibles. DISCUSSION: Our fracture and osteosynthesis model allows the quantitative determination of micromovements in the gap tissue and shows the importance of ideal realignment, which has a decisive influence on micromovements in the gap tissue.

Biomechanical Phenomena↗
PubMed2002

[Possibilities and limitations in evaluating treatment concepts in lip-jaw-palate clefts].

BACKGROUND: Recently, government and medical practitioners have shown considerable interest in the discipline of evidence-based medicine. LITERATURE RESEARCH AND RESULTS: In this study, we investigated the literature concerning treatment concepts in cleft surgery according to criteria of evidence-based medicine. Over the last decade 996 articles on cleft patients were published, 181 of which were studies evaluating the clinical outcome of distinct treatment options. Only 57 studies proved to be classifiable due to a well-described study protocol. One treatment study of cleft patients reached the strength of evidence grade I and strength of recommendation grade A, whereas all other studies had a lower evidence rating. DISCUSSION: The reasons behind these findings seem to be due to problems faced by the specialty of this disease.

Child, Preschool↗
PubMed2002

Toxicity of linear alkylbenzene sulfonate in anaerobic digestion: influence of exposure time.

The inhibition of anaerobic digestion by the anionic surfactant linear alkylbenzene sulfonate was studied. The development of bacterial activity during several weeks was monitored by performing batch degradation tests with acetate and propionate. In the first phase the decay of activity without surfactant addition was studied. After the addition of the surfactant an immediate inhibition was detected. Subsequently, the degradation activity continued to decrease with increasing exposure time. Both, the immediate inhibition and the rate of the subsequent decrease of activity were dependent on the surfactant concentration. A kinetic model is presented that describes this behavior. A surfactant concentration of 14 mg L(-1) causes a 50% immediate inhibition of acetate degradation (27 mg L(-1) in the case of propionate degradation). Additionally, each 12 mg L(-1) of surfactant increases the decay rate of acetate degradation activity by a factor 10 (23 mg L(-1) for propionate degradation). A deviation from this model occurs at low surfactant concentrations (<3 mg L(-1)), where a slight stimulation of bacterial activity was observed. The above-mentioned concentrations refer to measured surfactant concentrations. These were substantially lower than the nominal concentrations (added surfactant per volume). This discrepancy is explained by adsorption of the surfactant to the biomass. Finally, the importance of the presented kinetic model and the significance of surfactant toxicity for anaerobic digestion are discussed.

Alkanesulfonic Acids↗
PubMed2002

Anaerobic digestion of alcohol sulfate (anionic surfactant) rich wastewater--batch experiments. Part I: influence of the surfactant concentration.

Textile wet processing wastewater (e.g., from cotton desizing) contains high concentrations of surfactants as well as readily biodegradable compounds like starch and other carbohydrates. Decyl sulfate (DS, surfactant) and soluble starch were used as model pollutants for biodegradation batch experiments. Very high loadings of the biomass were applied (DS: 21.7-217 g/kg cell dry weight (CDW); starch: 910 g/kg cell dry weight) to study inhibitory effects of the surfactant on the degradation cascade of the biopolymer. The starch hydrolysis was inhibited above sludge loadings of 65 g DS/kg CDW. Acidogenesis was the degradation step with the highest resistance towards inhibitory effects of the surfactant, whereas methanogenesis proved to be the most sensitive. The effects of the surfactant were described by the change of the methane evolution, which was reduced by 50% in 87 days with an addition of 58 g DS/kg CDW. The surfactant caused a high temporary accumulation of intermediates like volatile fatty acids. At the highest loading (217 g DS/kg CDW) the conversion of the substrate to methane was only minor.

Alcohols↗