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Biomedical subjects

K Urban

Publications and source records attributed to K Urban.

At least 19 recordsLinked to original sources
PubMed2006

Spontaneous 2D accumulation of charged Be dopants in GaAs p-n superlattices.

In a classical view, abrupt dopant profiles in semiconductors tend to be smoothed out by diffusion due to concentration gradients and repulsive screened Coulomb interactions between the charged dopants. We demonstrate, however, using cross-sectional scanning tunneling microscopy and secondary ion mass spectroscopy, that charged Be dopant atoms in GaAs p-n superlattices spontaneously accumulate and form two-dimensional dopant layers. These are stabilized by reduced repulsive screened Coulomb interactions between the charged dopants arising from the two-dimensional quantum mechanical confinement of charge carriers.

Journal Article↗
PubMed2006

[Scintigraphic detection of osteoblast activity after implantation of BAS-0 bioactive glass-ceramic material into long bone defects].

PURPOSE OF THE STUDY: The aim of the study was to demonstrate, by three-phase bone scintigraphy, radionuclide uptake at the site of defects in long bones filled with the non-resorbable bioactive glass-ceramic material BAS-0 at a long follow-up. MATERIAL: Twenty patients, 14 men and 6 women, operated on between 1990 and 2000 for benign bone tumors or tumor-like lesions localized in the femur, tibia or humerus were comprised in the study. Their average age at the time of operation was 14 years (range, 8 to 24). The diagnoses based on histological examination included juvenile bone cysts in 11, aneurysmal bone cyst in five, non-ossifying fibroma in two, and fibrous dysplasia in two patients. The lesions were localized in the femur, humerus and tibia in 11, five and four patients, respectively. The metaphysis was affected in eight and the diaphysis in 12 patients. METHODS: Clinical, radiological and scintigraphic examinations were carried out at 2 to 12 years (7 years on average) after surgery. The clinical evaluation included subjective complaints and objective findings. Radiographs were made in standard projections and the osteo-integration of glass-ceramic material was investigated. Three-phase bone scans were made and the healthy and the affected limbs in each patient were compared by means of an index. Radionuclide uptake was considered normal when the index value was equal to 1.0, mildly increased at an index value of 1.2, moderately increased at 1.2-1.5 and markedly increased at an index value higher than 1.5. RESULTS: The clinical evaluation showed that, in the patients with glass-ceramic filling of metaphyses, six had no subjective complaints and two reported transient pain. In the patients with implants in diaphyses, subjective complaints were recorded in nine and no complaints in three patients. No inflammatory changes in soft tissues were found. No restriction in weightbearing of the limb treated was reported by any of the patients. On radiography, 18 patients were free from any disease residue or recurrence. Two patients had a residual defect. The bioactive glass-ceramic material BAS-0 was completely incorporated in all patients. On three-phase bone scans, radionuclide distribution on the flow phase and soft tissue phase was symmetrical in both limbs of all patients. For the metaphyseal location of implants, the delayed images demonstrated physiological radionuclide distribution in one patient, mildly increased distribution (index up to 1.2) in four, increased uptake (index up to 1.5) in two patients, and highly increased uptake (index above 1.5) in one patient. For the diaphyseal location of implants, the delayed scans demonstrated slightly increased radionuclide distribution in two, markedly increased in two and highly increased uptake in eight patients. DISCUSSION: The tissue during incorporation of a non-resorbable synthetic material is influenced by stress-shielding. This changes local mechanical signals, which has a negative effect on the adjacent bone tissue. Stress accumulating at the interface of a rigid implant and bone tissue may result in pain, and is detected by scintigraphy as an increased nucleotide uptake, particularly in diaphyseal grafts. CONCLUSIONS: This paper presents problems associated with implantation of the non-resorbable bioactive glass-ceramic material BAS-0 in the treatment of diaphyseal defects of long bones. The results show that, for filling of the defects described herein, non-resorbable glass-ceramic materials are not suitable.

Adolescent↗
PubMed2005

Atomic-scale analysis of the oxygen configuration at a SrTiO3 dislocation core.

The atomic structure of a SrTiO3 dislocation is revealed directly by phase-retrieval electron microscopy. In particular, atomic columns of light oxygen are observed simultaneously with the columns of considerably heavier Sr and Ti. A distinct structural modification of the oxygen octahedra at the dislocation core as well as a significant nonstoichiometry, including a deficiency of oxygen, are observed. Deviations from the bulk chemical concentration are quantified column by column by means of structure modeling and quantum-mechanical simulations of the electron scattering process.

Journal Article↗
PubMed2005

Atomic-precision determination of the reconstruction of a 90 degree tilt boundary in YBa2Cu3O7-delta by aberration corrected HRTEM.

Aberration corrected high-resolution transmission electron microscopy is used to determine the reconstruction of atomic bonds of a 90 degree [100] grain boundary in YBa(2)Cu(3)O(7-delta). A precise measurement of atom positions within the grain boundary and the assessment of the oxygen stoichiometry require at the same time a high control of residual lens aberrations of the electron microscope and a good signal-to-noise ratio. This goal is achieved by the combination of spherical-aberration correction in the microscope with the numerical exit-plane wave function reconstruction from focal series. Atomic column positions for individual cations and anions are determined by the regression analysis of peak maxima in the phase image of the retrieved exit-plane wave function. The measurement accuracy is quantitatively assessed, including the statistical error related to residual noise. Changes in bondlengths between copper atoms and the apical oxygen are measured, indicating the distortion of the square pyramidal oxygen coordination of plane copper sites and the square coordination of chain copper sites in the grain boundary.

Journal Article↗
PubMed2005

[Juvenile unstable severe slip of the proximal femoral epiphysis: case report and review of treatment options].

The authors present the case of a severe unstable slip of the proximal femoral epiphysis in a 14-year-old boy. A serious metabolic disorder diagnosed in the boy led to postponement of necessary surgical intervention. The primary development of necrosis of the proximal femoral epiphysis during the 6 months following the slip is reported here. A good outcome was eventually achieved by three-plane valgus, flexion and derotational osteotomy of the femur at second-stage surgery. The authors emphasize the prognostic importance of stability assessment in the displaced epiphysis.

Adolescent↗
PubMed2004

Atomic-resolution measurement of oxygen concentration in oxide materials.

Using high-resolution imaging at negative spherical aberration of the objective lens in an aberration-corrected transmission electron microscope, we measure the concentration of oxygen in Sigma3[111] twin boundaries in BaTiO3 thin films at atomic resolution. On average, 68% of the boundary oxygen sites are occupied, and the others are left vacant. The modified Ti2O9 group unit thus formed reduces the grain boundary energy and provides a way of accommodating oxygen vacancies occurring in oxygen-deficient material by the formation of a nanotwin lamellae structure. The atomically resolved measurement technique offers the potential for studies on oxide materials in which the electronic properties sensitively depend on the local oxygen content.

Journal Article↗
PubMed2004

Differentiated adamantinoma of the fibula: a rhabdoid variant.

A benign- appearing osteolytic lesion surrounded by a sclerotic rim was found in the upper fibula of a 25-year-old man. Based on histological features the definitive diagnosis of osteofibrous dysplasia-differentiated adamantinoma was made. The correct histological diagnosis of differentiated adamantinoma depends on factors such as the uniform predominance of an osteofibrous dysplasia-like pattern, and scattered epithelial elements positive for cytokeratin and vimentin. In this case the scattered epithelial cells had abundant eosinophilic cytoplasm and resembled rhabdoid elements, but immunohistochemistry proved their epithelial origin.

Adult↗
PubMed2004

Spherical aberration correction in tandem with exit-plane wave function reconstruction: interlocking tools for the atomic scale imaging of lattice defects in GaAs.

With the availability of resolution boosting and delocalization minimizing techniques, for example, spherical aberration correction and exit-plane wave function reconstruction, high-resolution transmission electron microscopy is drawing to a breakthrough with respect to the atomic-scale imaging of common semiconductor materials. In the present study, we apply a combination of these two state-of-the-art techniques to investigate lattice defects in GaAs-based heterostructures at atomic resolution. Focusing on the direct imaging of stacking faults as well as the core structure of edge and partial dislocations, the practical capabilities of both techniques are illustrated. For the first time, we apply the technique of bright-atom contrast imaging at negative spherical aberration together with an appropriate overfocus setting for the investigation of lattice defects in a semiconductor material. For these purposes, the elastic displacements associated with lattice defects in GaAs viewed along the 110 zone axis are measured from experimental images using reciprocal space strain map algorithms. Moreover, we demonstrate the benefits of the retrieval of the exit-plane wave function not only for the elimination of residual imaging artefacts but also for the proper on-line alignment of specimens during operation of the electron microscope--a basic prerequisite to obtain a fair agreement between simulated images and experimental micrographs.

Arsenicals↗
PubMed2004

[Treatment of juvenile bone cysts by curettage and filling of the cavity with BAS-0 bioactive glass-ceramic material].

PURPOSE OF THE STUDY: The aim of the study was to evaluate the long-term results of using the bioactive, glass-ceramic material BAS-0 for bone tissue replacement after removal of juvenile bone cysts by curettage. MATERIAL: Between 1990 and 2000, BAS-0 material was used to fill the cavity after removal of a juvenile bone cyst in 21 patients, 15 males and 6 females, with an average age of 15 years (range 4 to 44 years). Surgical treatment was indicated only in juvenile bone cysts meeting the following criteria: 1) subjective complaints, i. e., pain at activity; 2) X-ray findings of either a) thinning cortical layer with a potential for pathological fracture, particularly in the proximal femur, b) recurrent pathological fractures without apparent healing of the cyst or c) increase in cyst size by 25% within 6 months. In all patients, the diagnosis of a juvenile bone cyst was confirmed by histological examination. Cyst localization was as follows: eight in the humerus, eight in the femur, two in the fibula and one in the ulna, iliac bone and tibia each. METHODS: After careful curettage of a soft tissue lining from the inner surface of the cystic cavity, the space was filled completely with 2- to 4-mm BAS-0 granules in 15 patients; in the rest granules were applied in a mixture with cancellous bone graft, which was either autologous or allogenic. The former was implanted in one patient, the latter, taken from either the mother or father, was used in four and one patients, respectively. All patients were clinically and radiologically examined during the follow-up period of 3 to 12 years, with an average of 7 years. The clinical evaluation was based on subjective complaints, and on the state of soft tissues in the region of lesion, range of motion in the adjacent joints and the loading capacity of the limb treated. Radiological evaluation was based on standard X-ray images assessed according to the classification system of Neer. RESULTS: The clinical examination showed that 10 patients were free from subjective complaints, one patient had rest pain, three patients experienced pain when using the limb, four patients reported mild and intermittent pain, two patients were in pain when the whether changed and one patient complained of pain during pregnancy. Objectively, no inflammatory changes of soft tissues were found. Both passive and active motion of the adjacent joints was possible in the full range and the treated limb retained its complete function in all patients. X-ray examination showed excellent results, i. e., no residuum or cysts recurrence, in 16 patients. A residual lesion was present in one patient and cyst recurrence was recorded in four patients. DISCUSSION: The currently used methods of treatment include corticoid instillation in the cyst, injection of autologous bone marrow, multiple drilling and drainage of the cyst and removal of the cyst with subsequent filling of the cavity with bone graft. In our patients, the bioactive, glass-ceramic material BAS-0 was used to replace either autogenous or allogenic bone grafts. Complete healing of the cyst was achieved in 76% of our patients, which is the result comparable with the literature data. CONCLUSIONS: Although the therapy of juvenile bone cysts has changed from extensive surgical procedures to less invasive techniques, the curettage of a cyst with subsequent filling of the residual cavity still remains the method of choice in selected patients. Instead of autogenous cancellous bone grafts or allogenic grafts predominantly used for this procedure, the bioactive, glass-ceramic material BAS-0 can be recommended, particularly when the cavity to be filled is located in the metaphysis of a long bone, i. e., in the region subject to great compression.

Adolescent↗
PubMed2003

Atomic-resolution imaging of oxygen in perovskite ceramics.

Using an imaging mode based on the adjustment of a negative value of the spherical-aberration coefficient of the objective lens of a transmission electron microscope, we successfully imaged all types of atomic columns in the dielectric SrTiO3 and the superconductor YBa2Cu3O7. In particular, we were able to view the oxygen atoms which, due to their low scattering power, were not previously accessible, and this allowed us to detect local nonstoichiometries or the degree of oxygen-vacancy ordering. This technique offers interesting opportunities for research into oxides, minerals, and ceramics. In particular, this holds for the huge group of perovskite-derived electroceramic materials in which the local oxygen content sensitively controls the electronic properties.

Journal Article↗
PubMed2003

Analysis of gene transfer and expression in skeletal muscle using enhanced EIAV lentivirus vectors.

Skeletal muscle is an attractive target tissue for gene therapy involving both muscle and nonmuscle disorders. HIV-1-based vectors transduce mature skeletal muscle; however, the use of these vectors for human gene therapy may be limited by biosafety concerns. In this study, we investigated gene transfer using lentivirus vectors based on the equine infectious anemia virus (EIAV) in skeletal muscle in vitro and in vivo. EIAV vectors transduce proliferating and differentiating C2C12 mouse muscle cells; furthermore, the addition of the woodchuck hepatitis posttranscriptional element to EIAV vectors markedly increases gene expression in these cells. A single injection of EIAV vectors into skeletal muscle of adult mice led to detectable gene marking and gene expression for the duration of the 3-month study. Use of a second-generation EIAV self-inactivating vector (E-SIN) increased transduction in muscle cells in vitro, and injection of E-SIN vectors into skeletal muscle resulted in increased gene marking and gene expression compared to first-generation EIAV vectors.

Animals↗
PubMed2002

High-resolution imaging with an aberration-corrected transmission electron microscope.

Recently an electromagnetic hexapole system for the correction of the spherical aberration of the objective lens of a 200 kV transmission electron microscope has been constructed by Haider and coworkers. By appropriately exciting the hexapole elements it is possible to adjust specific values of the spherical aberration coefficient ranging from the value of the original uncorrected instrument over zero even to negative values. In the first part of the paper the consequences of the tunable spherical aberration are investigated. New imaging modes are available: By adjustment of an optimum value for the spherical-aberration coefficient, the point resolution of phase-contrast imaging can be extended to the information limit. Phase-contrast imaging can be improved by a reduced level of contrast delocalisation. For zero aberration contrast delocalisation does not occur. In this case high-resolution investigations are carried out under amplitude-contrast conditions, where the local image intensity of crystalline objects is controlled by electron diffraction channelling. The defocus and spherical aberration values related to the new imaging modes are given. In the second part novel applications of the instrument to semiconductor heterostructures and ceramic grain boundaries are examined.

Journal Article↗
PubMed2002

[Use of bioactive glass ceramics in the treatment of tibial plateau fractures].

PURPOSE OF THE STUDY: The surgical treatment of proximal tibia fractures requires a reduction and fixation of the split condyle, elevation of the depressed interfragment of articular surface. The golden standard is the application of autogenous bone grafts for filling in the defect in the cancellous bone of the tibial condyle. Bioactive glass-ceramics material may be successfully used for the filling. Gass-ceramics BAS-O is biocompatible and bioactive and has also suitable mechanical properties and therefore it was used in combination with autogenous bone marrow in order to speed up osteogenesis. MATERIAL: The study covered 12 patients, 4 men and 8 women, with a fracture of the proximal tibia classified according to AO as type B3.1, B3.2 and C3.2. The average follow-up period was 5.5 years (range, 2 to 8 years). METHOD: After the assessment of the type of fracture and revision of soft tissues the depressed interfragment of articular surface was elevated and the defect was completely filled with BAS-O granules in combination with 10 ml of autogenous bone marrow. The broken condyle was fixed by screws or buttress plate. During the first year the process of healing was checked by radiographs at 3-month intervals. All 12 patients were invited for a follow-up examination where the radiograph of the proximal tibia was assessed in two projections and the clinical condition was evaluated using Rasmussen criteria. RESULTS: According to the Rasmussen criteria 12 patients achieved the value of 21-29 points with the average of 26.4 of 30 possible points. The volume of the BAS-O filling was 7.1-44.3 ccm and did not change throughout the whole period of the follow-up. The depression of an interfragment of articular surface prior to operation was 3-17 mm, average 6.3 mm. The residual depression after the operation was 0-4 mm, average 1.7 mm. No symptoms of loosening, extrusion or surrounding of the BAS-O material by fibrous tissue was found. The integration with the surrounding bone occurred during the first 3 months. DISCUSSION: The bioactive coral hydroxyapatite has been successfully used to fill similar defects by a number of authors. Among the benefits of BAS-O granular system is an easy handling and a fast integration with the bone tissue of the recipient due to the development of a hydroxyapatite layer on its surface after the contact with tissue fluid. Autologous bone marrow was added to the system in order to initiate osteogenesis and a faster healing of the defect. The mentioned material is suitable also from the mechanical viewpoint as neither deformation nor resorption was found in the followed-up patients. We reduced the surgery duration and morbidity and improved the patients comfort. CONCLUSIONS: Part of the surgical management of the fracture of the tibial plateau with a depressed segment of subchondral bone is its elevation. For filling in of the traumatic defect in the cancellous bone of the proximal tibia the bioactive, glass-ceramics, granular material BAS-O may be successfully used. Mechanical and chemical properties (compression strength, non-resorption) ensure its stable position in the filling as well as a constant volume. Osteointegration was accelerated by adding 10 ml of autologous bone marrow. The use of the glass-ceramics material reduces the surgery duration, improves the patient's comfort and decreases the probability of incidence of complications.

Adult↗
PubMed2002

[Giant cell angiofibroma of the lower eyelids].

The authors present a rare case of giant cell angiofibroma (GCAF) of the lower eyelids and the possibility of its surgical treatment. They emphasize the basic morphological indicators for assessment of GCAF and its difference from similar entities.

Adult↗
PubMed2002

Types of vascular reconstructions in replantations of distal parts of the fingers.

The authors present the case of a 17-year-old patient with amputation of the distal portions of three-phalangeal fingers. During replantation of each finger a different method of revascularization of the amputate was used. In one finger the classical replantation pattern was used: anastomosis of the digital artery and dorsal vein. Inthe second finger anastomosis of the digital artery and volar vein was made, while in the third finger a method of nontraditional revascularization was used, i.e. by using an arteriovenous shunt: transposition of the second digital artery with adequate back-flow to the dorsum and anastomosis with the dorsal vein.

Adolescent↗