PubMed Health⌕ Search

Biomedical subjects

R Born

Publications and source records attributed to R Born.

At least 19 recordsLinked to original sources
PubMed2003

Electrochemically assisted deposition of thin calcium phosphate coatings at near-physiological pH and temperature.

An electrochemical method for the deposition of calcium phosphate phases on titanium surfaces using the galvanostatic mode is presented. Deposition was performed in a (Ca(2+) / H(x)PO(4) ((3-x)-))-containing electrolyte near physiological conditions with regard to pH (6.4) and temperature (36 degrees C). Cathodic alkalization leads first to the formation of a thin homogeneous layer that shows a nanoscale surface topography of alternating wall-like elevations and channels. It is thought that these channels in the calcium phosphate prelayer are formed as pathways for hydroxyl ions and hydrogen. Upon this layer, spheres of amorphous calcium phosphate (ACP) are formed as indicated by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy. According to transmission electron microscopy images, these spheres consist of small clusters of calcium phosphate (approximately 30 nm) and can grow up to 300 nm in diameter. Characteristic for this ACP is a high water content as seen by FTIR. As a function of current density, the ACP is then transformed into crystalline hydroxyapatite (HAP), which was identified using FTIR and X-ray diffraction. The morphology of the HAP crystals can be described as needles with dimensions of <500-nm length and <60-nm width. By choice of different electrochemical parameters, a homogeneous coating of either ACP, HAP, or the intermediate phase can be achieved, as shown in a kinetic phase diagram, thus allowing the formation of coatings with different properties in solubility and morphology.

Alloys↗
PubMed1995

The proliferative capacity of mouse fibrosarcoma cells that survived x-irradiation.

Delayed reproductive death, the appearance of colonies with a reduced cell density (impaired colonies) and the number of giant cells per colony were investigated in murine fibrosarcoma cells after irradiation with 3 to 9 Gy of x-rays. Radiation survivors were replated after reaching confluence, which occurred after 13 to 15 doublings; this procedure was repeated three times. The replating efficiency decreased in a dose-dependent manner, the survivors of 9 Gy achieving only 30% of the plating efficiency of unirradiated cells. After the third replating, i.e. after 40 to 45 doublings, the plating efficiency of the survivors approached that of the controls. The median colony size of the survivors showed a similar dose-dependent decrease, which was pronounced after the first replating but still remained significant after the third replating. The fraction of impaired colonies was increased to more than 30% in 9-Gy survivors, and though abating, the increase was still significant even after the third replating. Evidence of residual damage was also provided by the presence of giant cells. For instance, after 6 Gy irradiation and 13 to 15 doublings, the proportion of colonies with giant cells was 60%, decreasing only to 45% after 40 to 45 doublings. The number of giant cells per colony was 1.4 in colonies arising immediately after 6 Gy, decreasing to 0.9 after the third replating. These results suggest that the proliferative capacity of surviving cells is depressed even longer than their clonogenic capacity.

Animals↗
PubMed1993

Transient cisplatin-resistant murine fibrosarcoma cell characterized by increased metallothionein content.

Cisplatin-resistant mouse fibrosarcoma cells, SSK-R, were isolated after short and low-dose drug treatment of the sensitive SSK cells in vitro. These SSK-R sublines exhibit up to sevenfold cisplatin resistance and are characterized mainly by an increased metallothionein content. Loss of drug resistance after about 140-180 cell divisions in drug-free medium coincides with loss of metallothionein content. The glutathione level is the same in the sensitive and resistant sublines; inhibition of glutathione synthesis by buthionine sulphoximine enhances the sensitivity in both cells lines by a factor of 2.7. The resistant sublines are not cross-resistant to radiation; a radiation exposure followed immediately by cisplatin treatment results in an additive effect. The cellular cisplatin content is slightly reduced in SSK-R2 cells and it remains at this level also upon loss of drug sensitivity.

Animals↗
PubMed1989

[Ultrasonically-guided transvaginal puncture under local anesthesia for oocyte recovery].

We practised 17 cases of oocyte retrieval between January and June 1988 in our programme of IVF using a vaginal sound and local analgesia in order to retrieve oocytes using a transvaginal ultrasonic guide. The method is described. The recent literature has been reviewed and our results are given: 7.9 oocytes retrieved on an average from each patient, 4.4 oocytes fertilized per patient and 18% of clinical pregnancies. In view of the results that have been obtained and the lessening of risk by avoiding general anaesthesia and the lower cost for each case, as well as the fact that the patients tolerate the method very well, we are now recommending its application routinely and reserve laparoscopy for rare cases.

Adult↗
PubMed1988

Clonogenicity of the progeny of surviving cells after irradiation.

The clonogenic potential of the progeny of irradiated cells was tested in vitro by replating irradiated cultures after various times, allowing between five and over 25 subsequent divisions to take place after irradiation. Whereas the plating efficiency of surviving Chinese hamster cells was not decreased, in C3H10T1/2 cells a dose-dependent but slight decrease in plating efficiency was observed even after the longest follow-up period. These data do not contradict the prevalent hypothesis in radiobiology that the proliferation potential of a clonogenic cell surviving after irradiation is not significantly different from that of a non-irradiated cell.

Animals↗
PubMed1981

Effect of different physiological conditions on the action of adriamycin on Chinese hamster cells in vitro.

Chronically hypoxic cells were 5 times more resistant to Adriamycin (ADR) than exponentially growing oxic cells. On reoxygenation, resistance decreased slowly to reach the ADR sensitivity of oxic cells after 24 h. With increasing pH, ADR efficiency increased more in oxic than in chronically hypoxic cells. With increasing cell density, ADR efficiency decreased linearly. The differences in ADR efficiency under the various conditions were accompanied by differences in intracellular ADR uptake. Chronically hypoxic cells incorporated 1.6 times less than oxic cells; the incorporation rate at pH 6.5 was half that at pH 7.4; and at a cell density of 5 X 10(5)/bottle the intracellular uptake was 6 times that at 5 X 10(6)/bottle. The observed differences in uptake of ADR were not, however, sufficient to explain the differences in cytotoxicity.

Animals↗
PubMed1978

[Relationship between dose rate and oxygen effect (author's transl)].

Chinese hamster cells were exposed to 60Co gamma-rays using dose rates between 3.64 and 0,01 Gy/min under euoxic or chronically hypoxic conditions of growth in order to clarify the relationship of the oxygen enhancement ratio (OER) to the dose rate. It turned out that the D0 of dose-effect curves from cells irradiated under euoxic conditions was increasing from 1.35 to 4.5 Gy with decreasing dose rates, whereas the curves from cells irradiated under chronically hypoxic conditions were not much influenced by the dose rate. The oxygen enhancement ratio decreased from 3.9 with 1.35 Gy/min to 1.8 with 0.07 Gy/min.

Animals↗
PubMed1975

Rate and time of DNA synthesis of individual Chinese hamster cells.

The duration of DNA synthesis of a diploid cell line of Chinese hamster fibroblasts was determined in a comparative study by the FLM technique, and also by a new technique for measuring the rate of DNA synthesis of individual cells. These methods produced comparable results when applied during exponential growth of the cells. The rate of DNA synthesis was measured by means of quantitative autoradiography following a short-term incubation of the cells with 5 X 10(-6) M FUdR and 10(-5) M 14C-TdR. The choice of the medium for this purpose did not seem to be critical. The autoradiographic silver grains over cells and 14C-standard sources are counted by microphotometry using incident light bright-field. The direct measurements of DNA synthesis rate are 'compartment' statistics which have been converted into 'flux' parameters for comparison with the FLM method and applicability in cell-kinetic calculations. Frequency distributions of the rate of DNA synthesis of individual cells thus obtained may resemble normal distributions quite closely. They result from several factors: differences in the rate of synthesis in different parts of the S-phase, the density distribution of cells within the S-phase, the variation in the time of DNA synthesis among individual cells, and the experimental error. In the case of a pronounced partial synchronization as probably has been present in one experiment performed in the lag phase, an incorrect time of DNA synthesis may result from the rate values. Due to the variation in DNA synthesis rate in different parts of the S-phase it is not possible to determine the duration of DNA synthesis of an individual cell. However, the mean values of DNA synthesis time are reliable. The new method will be preferentially applied for determining the duration of DNA synthesis of human cells in as far as difficulties are encountered with the classical methods. In addition, it may be used to advantage for studying cells which make up low percentages in mixed populations. It finally permits a safer morphological classification of the cells under study than is possible with the classical methods.

Autoradiography↗
PubMedDate not supplied

Biomimetic coatings functionalized with adhesion peptides for dental implants.

A complete biological integration into the surrounding tissues (bone, gingiva) is a critical step for clinical success of a dental implant. In this work biomimetic coatings consisting either of collagen type I (for the gingiva region) and hydroxyapatite (HAP) or mineralized collagen (for the bone interface) have been developed as suitable surfaces regarding the interfaces. Additionally, using these biomimetic coatings as a matrix, adhesion peptides were bound to further increase the specificity of titanium implant surfaces. To enhance cell attachment in the gingiva region, a linear adhesion peptide developed from a laminin sequence (TWYKIAFQRNRK) was bound to collagen, whereas for the bone interface, a cyclic RGD peptide was bound to HAP and mineralized collagen using adequate anchor systems. The biological potential of these coatings deduced from cell attachment experiments with HaCaT human keratinocytes and MC3T3-E1 mouse osteoblasts showed the best results for collagen and laminin sequence coating for the gingiva region and mineralized collagen and RGD peptide coatings for regions with bone contact. Our concept opens promising approaches to improve the biological integration of dental implants.

Journal Article↗
PubMedDate not supplied

[Hodgkin's disease in children. Modified COPP combined treatment and radiotherapy in advanced stages].

Twenty two children, under 15 years of age, from southern Chile's Tenth Region, with advanced stages of Hodgkin's disease (8 III-A, 6 III-B and 8 IV-B) were treated with chemotherapy (modified COPP protocol) and radiotherapy between 1976 and 1985 at Valdivia's Regional Hospital. Overall survival rate was 77.3% and disease-free survival rate was 64.5% after a follow-up period from 3 to 13 years (median 70 months). Five patients died during the first two years. One relapsed 10 years after beginning of therapy, but achieved a second complete remission. The survival rate in patients with lymphocytic depletion type (5 cases) was 20.0%, whereas that of the mixed cellularity type (14 cases) was 92.9% (p less than 0.01). No cases of second neoplasms related to chemotherapy and radiotherapy were seen in this series.

Adolescent↗
PubMedDate not supplied

[Neonatal necrotizing enterocolitis: surgical treatment].

Since December 1984 to July 1987, 18 patients with NEC were studied. Vásquez-Estévez's protocol, was applied in order to define the surgical indication, taking in to account ten different clinical and laboratory parameters, each one scored 0 to 3 points. Only patients with score 15 or more should be operated and this was the case in 30% of our NEC. In all surgically treated patients intestinal necrosis was a constant finding, two of them had also bowel perforations. No patients died in the conservative management group (score under 15). Lethality among operated subjects was 16%.

Enterocolitis, Pseudomembranous↗