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Biomedical subjects

B König

Publications and source records attributed to B König.

At least 37 records · Page 2Linked to original sources
PubMed2002

In vivo evaluation of hydroxyapatite foams.

Hydroxyapatite (HA) is widely applied as bone graft material due to its osteoconductive potential and well-established biocompatibility. In this work, macroporous hydroxyapatite structures made through foaming of aqueous suspensions and gelcasting were tested for in vivo osteointegration. These foams are composed of a three-dimensional array of spherical pores with diameters of approximately 100-500 microm, interconnected by windows of smaller size in the range of 30-120 microm. The HA foams were implanted in the tibia of albino New Zealand rabbits and removed after a period of 8 weeks. Histological analysis revealed that the pores in the foams were partially or completely filled progressively with mature new bone tissue and osteoid after the implanted period. No immune or inflammatory reactions were detected. The high osteoconductive potential of the HA foams provides a potential structure for use as bone substitute in orthopedic, oral, and cranio-maxillofacial reconstructive surgery, and as dento-alveolar implants.

Animals↗
PubMed2002

[Computer assisted pelvic and acetabular surgery. Clinical experiences and indications].

CT based navigation has been used in spine surgery since 1994. Several clinical studies could show an increase in precision compared to the conventional technique and thus nowadays the navigated pedicle screw placement is a routine procedure in many hospitals. Based upon the experience in spine surgery the CT based navigation module was used for percutaneous screw fixations in minimally displaced pelvic ring and acetabular fractures. After preclinical experimental trials the C-arm navigation was used for 19 screw fixations. The postoperative control of the screw position was performed with postop. X-ray and CT. Overall 23 of the 24 screws were placed correctly. In one SI screw the postoperative CT could reveal a ventral cortex perforation of the sacrum without any clinical symptoms. Based upon this limited clinical experience we see the indication for CT based navigation in minimally displaced acetabular fractures or in SI screw fixations in case of sacral dysplasia. The C-arm based navigation with adequate image quality is our method of choice for SI screw fixation in traumatic or degenerative instabilities, especially if reduction maneuvers are necessary.

Acetabulum↗
PubMed2001

Carbonyl- and carboxyl-substituted enediynes: synthesis, computations, and thermal reactivity.

The influence of electron-withdrawing groups (carbonyl and carboxyl) at the alkyne termini on the reactivity of enediynes was investigated by a combination of experimental and computational techniques. While the general chemical reactivity of such enediynes, especially if non-benzannelated, is increased markedly, the thermal cyclization, giving rise to Bergman cyclization products, is changed little relative to the parent enediyne system. This is evident from kinetic measurements and from density functional theory (DFT, BLYP/6-31G + thermal corrections) computations of the experimental systems which show that the Bergman cyclization barriers slightly (3-4 kcal/mol) increase, in contrast to earlier theoretical predictions. The effect on the endothermicities is large (DeltaDeltaH(r) = 7-12 kcal/mol). Hence, the increased reactivity of the substituted enediynes is entirely due to nucleophiles or radicals present in solution. This was demonstrated by quantitative experiments with diethylamine and tetramethyl piperidyl oxide (TEMPO) which both give fulvenes through 5-exo-dig cyclizations.

Journal Article↗
PubMed2001

In vitro and in vivo biocompatibility testing of Ti-6Al-7Nb alloy with and without plasma-sprayed hydroxyapatite coating.

The Ti-6Al-7Nb alloy has been recently developed for biomedical use, particularly for orthopedics and dental applications. Osteosynthesis has been used to analyze biocompatibility and osseoconduction properties. The interaction of the implant with its biological environment, the formation of the implant material/tissue interface, and the long-term success or failure of integration in the human body is strongly connected with the surface properties of the implant device. This study was undertaken to evaluate the processes involved in biological responses of the Ti-6Al-7Nb alloy with and without hydroxyapatite coatings with both in vitro and in vivo tests. The results were analyzed by scanning electron microscopy (SEM) and energy-dispersive x-ray (EDX) microanalysis. The morphology of the in vitro and in vivo testing results with hydroxyapatite coating was similar to those obtained on the uncoated samples. A mineralized extracellular matrix was formed on all materials. Observation of the interface between the cell layer and substrata showed the presence of calcium and phosphorous-rich globular deposits associated with collagen fibers on all materials in vitro and in vivo. A higher density of these globular deposits was observed in all samples.

Alloys↗
PubMed2001

[Navigation assisted by image conversion. An experimental study on pelvic screw fixation].

Within an experimental trial the new method of fluoroscopy based navigation was tested for percutaneous pelvic screw fixations. A regular C-arm was used and the navigation system developed by Medivision. In a first step appropriate C-arm projections were defined for five standardized screw positions. Then precision and fluoroscopy time of 60 screws in 6 artificial pelves were evaluated. For the sacroliacal screw in S1, S1 screw in S2, anterior column screw, posterior column screw and the supraacetabular ilium screw three to four appropriate projections were defined. These were all combinations of the known special pelvic views inlet/outlet and iliac/obturator. Using these standardized views the average fluoroscopy time was 6 seconds per screw. 51 screws (85%) were inserted correctly. In five cases there was a slight deviation without perforating the cortex, four times the cortex was perforated.

Acetabulum↗
PubMed2001

Sensitivity and specificity of carbohydrate-deficient transferrin in drinking experiments and different patients.

Information provided by patients about the amounts of alcohol they drink may often be too subjective and therefore unreliable. Because of the possible serious consequences of interactions between alcohol and medication, reliable laboratory test markers for alcohol consumption are needed. Carbohydrate-deficient transferrin (CDT) is at present the best available objective measure of drinking behavior. During a withdrawal trial, 92 alcohol-dependent patients who had been admitted to a hospital in an ethanol-intoxicated state were monitored over the following 28 days by using the percent carbohydrate-deficient transferrin (%CDT of total transferrin) (%CDT) method. At the time of admission, 63% showed elevated %CDT levels. After a subsequent period of abstinence, a decrease in %CDT levels was apparent in four different groups of patients, whereas in two groups, comprising the greatest number of patients, normal %CDT levels were evident after 14 days of abstinence. In patients whose CDT levels were very high at study initiation, it took at least 21 to 28 days--and sometimes longer--for CDT to decrease to the radioimmunoassay (RIA) %CDT test cutoff point of 2.5. In a further study of 56 male alcohol-dependent patients, we measured liver enzyme concentrations, mean corpuscular volume (MCV), and four CDT variants on the first day of evidence of withdrawal syndrome. We found a significant correlation between results on the Munich Alcoholism Test (MALT) and MCV levels; among gamma-glutamyltransferase (GGT), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels; and among all four CDT variants. A cluster analysis yielded three clusters: (1) GGT, AST, and ALT levels; (2) MCV levels and MALT results; and (3) all CDT measurement variants. We conclude that these three clusters measure different detriments to the patient and that all available CDT variants are commensurate.

Alcohol Drinking↗
PubMed2001

A study of histological responses from Ti-6Al-7Nb alloy dental implants with and without plasma-sprayed hydroxyapatite coating in dogs.

Titanium alloys are hoped to be used much more for applications as implant materials in the medical and dental fields because of their basic properties, such as biocompatibility, corrosion resistance and specific strength compared with other metallic implant materials. Thus, the Ti-6Al-7Nb alloy that has recently been developed for biomedical use, that is, primarily developed for orthopaedic use, is to be studied in this paper, for application in dental implants. The biocompatibility test in vivo was carried out in dogs and the osseointegration was verified through histological analysis of the samples of the Ti-6Al-7Nb alloy with and without hydroxyapatite coating that were inserted in the alveoli. Within the controlled conditions the samples did not show any toxic effects on the cells.

Journal Article↗
PubMed2001

Crystal structure of Mip, a prolylisomerase from Legionella pneumophila.

The human pathogen Legionella pneumophila, the etiological agent of the severe and often fatal Legionnaires' disease, produces a major virulence factor, termed 'macrophage infectivity potentiator protein' (Mip), that is necessary for optimal multiplication of the bacteria within human alveolar macrophages. Mip exhibits a peptidyl prolyl cis-trans isomerase (PPIase) activity, which appears to be important for infection. Here we report the 2.4 A crystal structure of the Mip protein from L. pneumophila Philadelphia 1 and the 3.2 A crystal structure of its complex with the drug FK506. Each monomer of the homodimeric protein consists of an N-terminal dimerization module, a long (65 A) connecting alpha-helix and a C-terminal PPIase domain exhibiting similarity to human FK506-binding protein. In view of the recent significant increase in the number of reported cases of Legionnaires' disease and other intracellular infections, these structural results are of prime interest for the design of new drugs directed against Mip proteins of intracellular pathogens.

Anti-Bacterial Agents↗
PubMed2000

[Cast immobilization versus vacuum stabilizing system. Early functional results after osteosynthesis of ankle joint fractures].

In a prospective randomized trial the early functional results after immobilisation in a cast were compared to those after using a vacuum stabilizing system. The vacuum stabilizing system Vacoped offers equivalent stability compared to a plaster cast. In contrast to the cast the Vacoped can be removed for body care and physical therapy. Additionally the range of motion for dorsal flexion/extention in the upper ankle joint can be adjusted. From 9/1996 to 7/1997 there were 40 patients included in the study with an operated ankle fracture as monotrauma. Six weeks postoperatively the patients with cast treatment showed significantly higher functional deficits for the upper ankle joint (20%), the lower ankle joint (40%) and muscle atrophy (2.1 cm side difference) than the group with the vacuum stabilizing system (upper ankle joint 15%, lower ankle joint 25%, 1.4 cm muscle atrophy). Five patients out of the group with the vacuum system were already at work three weeks postoperatively. Three months postoperatively the functional results for both groups were approximating. The vacuum stabilizing system Vacoped offers better early functional results than conventional cast treatment after osteosynthesis of ankle fractures. Because of the increased patient comfort and the early ability for physical therapy the vacuum stabilizing system is preferable to cast treatment.

Adult↗
PubMed2000

[Dorsal oblique pelvic fixator: development and biomechanical testing].

In haemodynamically unstable patients with an unstable pelvic ring injury the primary stabilisation of the pelvis and thus reduction of pelvic volume is important for the success of the treatment. The pelvic C-clamp is an approved emergency device for these unstable pelvic ring injuries. A secondary procedure though is necessary in most of the cases with a hig rate of wound problems in already traumatized soft tissue areas. The ventrally placed external fixator is a simple and quick procedure with little soft tissue damage. Though primary stability is sufficient even for C-type injuries, biomechanic stability of the posterior pelvic ring is often insufficient for mobilization. Based on biomechanic considerations, a new dorsal oblique pelvic external fixator was developed for pelvic C-type injuries. With the advantages of the supraacetabular fixator and two additional Schanz screws the ventral fixator should stabilize the posterior pelvic ring with comparable stability to the pelvic C-clamp. A primary and already definitive minimal invasive stabilization of the posterior pelvic ring was the aim. In the first series several variations of this asymmetric fixator with two different Schanz screw applications were tested biomechanically. In a second series the favorite version was tested versus the supraacetabular fixator and the pelvic C-clamp. Both of the biomechanic test series were performed with artificial pelves in the one leg stance model in the material testing machine. SI disruption and sacral fracture were the posterior instability types in 6 pelves each. There was no statistically significant difference between the dorsal oblique fixator and the pelvic C-clamp. But the new fixator was significantly more stable than the supraacetabular fixator or the new fixator without pretension.

Biomechanical Phenomena↗
PubMed2000

Mitochondrial DNA (mtDNA) reveals that female Bechstein's bats live in closed societies.

We present a microgeographic analysis of mitochondrial DNA (mtDNA) in Bechstein's bats using three sources of control region sequence variability, including a novel mtDNA microsatellite, to assess individual relatedness both within and among 10 maternity colonies. Comparison of marker variability among 268 adult females revealed little genetic variability within each colony. However, most colonies were clearly distinguished by colony-specific mitochondrial haplotypes (total n = 28). Low intracolony variability and strong haplotype segregation among colonies, was reflected by an extraordinary high FST of 0.68, indicating a very low intercolony dispersal rate of approximately one female in five generations. Haplotype distribution among 18 solitary males showed that males frequently disperse between colony locations, indicating the absence of dispersal barriers. Bechstein's bat maternity colonies are thus closed groups that comprise 20-40 females probably belonging to only one or, at most, two matrilines. The genetic population structure of Bechstein's bats is in agreement with the hypothesis that females seek familiar and, at least, partially related cooperation partners for raising their young. Alternatively strong philopatry might reflect the importance of profound roost or habitat knowledge for successful reproduction in female Bechstein's bats.

Animals↗
PubMed2000

Histomorphometric evaluation of titanium implants in osteoporotic rabbits.

In this study, the osteointegration of two kinds of titanium implants were analyzed (cylindrical and screw-type) inserted in the tibiae of control (n = 8) and osteoporotic (n = 12) female rabbits. Osteoporosis was induced by the surgical removal of the ovaries (oophorectomy). Bone mass density of all animals was evaluated by densitometry of the tibiae and vertebrae. Densitometry was carried out at the beginning of the study and 4 months after oophorectomy. Mass loss in the tibia was not observed, however, in the vertebrae there was an 11% loss compared with the initial value. The implants remained for 8 weeks, after which the animals were then sacrificed and bone segments were analyzed by histomorphometry. The trabecular volume and mineral apposition rate was significantly greater in control animals than in osteoporotic animals, independent of which type of implant was used. In the osteoporotic animals, the area and osteoid perimeter were greater than in the control animals. By measuring the thickness of the compact layer in the tibia, it was observed that in the control animals, it was 28% thicker than in the osteoporotic animals. This study leads to the conclusion that bone formation was greater in the control animals than in the osteoporotic animals. The screw-type implants yielded the greatest formation of bone both in the control and in the osteoporotic animals.

Absorptiometry, Photon↗
PubMed2000

Living together, feeding apart: how to measure individual food consumption in social house mice.

In many studies with animals kept in groups, scientists need information about each individual's food access without disturbance or separation of the animals. We developed an automatic feeding device that allows measurement of individual food consumption and experimental manipulation of individual food availability in small social mammals, such as house mice. The feeding device is based on radio frequency identification that triggers access to a motor-driven metal arm filled with food pellets and is mediated with the help of subcutaneously implanted transponders.

Animals↗
PubMed1999

Improved automatic separation of renal parenchyma and pelvis in dynamic renal scintigraphy using fuzzy regions of interest.

The aim of the study was to examine the physiological relevance of factors produced by a modified procedure for factor analysis of dynamic renal studies. Factor analysis has been applied locally to subsets of dynamic renal data which were well defined in both space and time domains. Optimised factor images resulting from different subsets were used as fuzzy regions of interest (ROIs) for the extraction of time-activity curves corresponding to renal parenchyma, renal pelvis, vascular and spatially homogeneous background. The original procedure employed the factor images of renal parenchyma and pelvis resulting from an analysis of the interval between the peaks of parenchymal and pelvic curves. In an attempt to improve the separation of renal parenchyma and pelvis, new fuzzy ROIs were used. They correspond to the factor image of renal uptake obtained from the analysis of the early phase of the study, and to the factor image of the renal pelvis obtained from the outflow phase. The curves generated with the new fuzzy ROIs were compared with those of the original procedure and tested for the presence of known artefacts inconsistent with the expected physiological behaviour. Unlike with the original procedure, no such artefacts were found. The most striking difference was that the pelvic factor curves did not start from zero time of the study but exhibited a physiologically correct initial horizontal zero segment the length of which correlated closely with the minimum parenchymal transit time (r=0.79, n=46, P<0.001). The new method permits easy and reliable application of factor analysis to dynamic renal studies. Problems which remain to be solved are user-independent identification of the optimum factors and suboptimal performance of the method under extreme conditions. Our results provide additional evidence that factor analysis can extract physiologically relevant information quantitatively from dynamic scintigraphic data.

Algorithms↗
PubMed1999

The microangioarchitecture of the conducting system in cattle.

Macroscopic researches on heart vascularization have indicated that the angioarchitecture of the conducting system differs from that of the normal myocardium. In order to observe this variance, eight cow hearts were dissected for perfusion through the Ramus ventricularis dexter and Ramus septalis of the A. coronaria dextra with Ringer's solution, and then injected with Mercox. After corrosion in KOH the casts were prepared for observation in a SEM. In the region of the sinoatrial node no special capillary arrangement was observed, but only valves on the venous side. At the atrioventricular node and the bundle of His, the arterioles showed a diffuse formation, filling this area with a regular caliber, without any special capillary orientation. The arteries that reach the right bundle dichotomized and ran collateral to the opposite extremity of this structure, lying parallel. The vessels with the biggest caliber were deeply positioned. In the left bundle the arterioles showed a net like figure, mainly in one plane. Following the form of the bundle, and below the conducting tissue a big anastomotic venous arrangement is observable.

Animals↗