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Biomedical subjects

A Steinbach

Publications and source records attributed to A Steinbach.

14 recordsLinked to original sources
PubMed2005

Surviving high-intensity field pulses: strategies for improving robustness and performance of electrotransfection and electrofusion.

Electrotransfection and electrofusion, both widely used in research and medical applications, still have to face a range of problems, including the existence of electroporation-resistant cell types, cell mortality and also great batch-to-batch variations of the transfection and fusion yields. In the present study, a systematic analysis of the parameters critical for the efficiency and robustness of electromanipulation protocols was performed on five mammalian cell types. Factors examined included the sugar composition of hypotonic pulse media (trehalose, sorbitol or inositol), the kinetics of cell volume changes prior to electropulsing, as well as the growth medium additives used for post-pulse cell cultivation. Whereas the disaccharide trehalose generally allowed regulatory volume decrease (RVD), the monomeric sugar alcohols sorbitol and inositol inhibited RVD or even induced secondary swelling. The different volume responses could be explained by the sugar selectivity of volume-sensitive channels (VSC) in the plasma membrane of all tested cell types. Based on the volumetric data, highest transfection and fusion yields were mostly achieved when the target cells were exposed to hypotonicity for about 2 min prior to electropulsing. Longer hypotonic treatment (10-20 min) decreased the yields of viable transfected and hybrid cells due to (1) the cell size reduction upon RVD (trehalose) or (2) the excessive losses of cytosolic electrolytes through VSC (inositol/sorbitol). Doping the plasma membrane with lipophilic anions prevented both cell shrinkage and ion losses (probably due to VSC inhibition), which in turn resulted in increased transfection and fusion efficiencies.

Animals↗
PubMed2005

Towards a medically approved technology for alginate-based microcapsules allowing long-term immunoisolated transplantation.

The concept of encapsulated-cell therapy is very appealing, but in practice a great deal of technology and know-how is needed for the production of long-term functional transplants. Alginate is one of the most promising biomaterials for immunoisolation of allogeneic and xenogeneic cells and tissues (such as Langerhans islets). Although great advances in alginate-based cell encapsulation have been reported, several improvements need to be made before routine clinical applications can be considered. Among these is the production of purified alginates with consistently high transplantation-grade quality. This depends to a great extent on the purity of the input algal source as well as on the development of alginate extraction and purification processes that can be validated. A key engineering challenge in designing immunoisolating alginate-based microcapsules is that of maintaining unimpeded exchange of nutrients, oxygen and therapeutic factors (released by the encapsulated cells), while simultaneously avoiding swelling and subsequent rupture of the microcapsules. This requires the development of efficient, validated and well-documented technology for cross-linking alginates with divalent cations. Clinical applications also require validated technology for long-term cryopreservation of encapsulated cells to maintaining a product inventory in order to meet end-user demands. As shown here these demands could be met by the development of novel, validated technologies for production of transplantation-grade alginate and microcapsule engineering and storage. The advances in alginate-based therapy are demonstrated by transplantation of encapsulated rat and human islet grafts that functioned properly for about 1 year in diabetic mice.

Alginates↗
PubMed2005

Real-time 3-D dark-field microscopy for the validation of the cross-linking process of alginate microcapsules.

Alginate-based microencapsulation is a promising method for long-term maintenance of cellular and membrane function of the cells and tissue fragments required for in vitro and in vivo biosensors, for tissue engineering and particularly for immunoisolation of non-autologous transplants. Microcapsules of high mechanical strength and optimum permeability can be produced by injection of BaCl2 crystals into alginate droplets before they come into contact with external Ba2+. A key requirement is that the system parameters (number of crystals, speed of the crystal stream etc.) are properly adjusted according to the mannuronic and guluronic acid ratio and the average molecular mass of the alginate as well as to the diameter of the microcapsules. Robust, reliable, rapid and low-cost validation tools are, therefore, needed for assurance of the microcapsule quality. Here, we describe a novel three-dimensional (3-D) dark-field microscopy that allows the real-time measurement of the number and spatial distribution of the injected Ba2+ ions throughout the microcapsules after treatment with sulphate. This novel method requires only a conventional microscope equipped with three polarising filters and a double aperture stop. In contrast to confocal laser scanning microscopy images, peripherally attached BaSO4 precipitates can clearly be distinguished from internal ones. The data also demonstrate that several steps of the alginate gelling process must be improved before such immunoisolation can be used in patients.

Alginates↗
PubMed2004

Assessing microbial degradation of o-xylene at field-scale from the reduction in mass flow rate combined with compound-specific isotope analyses.

In recent years, natural attenuation (NA) has evolved into a possible remediation alternative, especially in the case of BTEX spills. In order to be approved by the regulators, biodegradation needs to be demonstrated which requires efficient site investigation and monitoring tools. Three methods--the Integral Groundwater Investigation method, the compound-specific isotope analysis (CSIA) and a newly developed combination of both--were used in this work to quantify at field scale the biodegradation of o-xylene at a former gasworks site which is heavily contaminated with BTEX and PAHs. First, the Integral Groundwater Investigation method [Schwarz, R., Ptak, T., Holder, T., Teutsch, G., 1998. Groundwater risk assessment at contaminated sites: a new investigation approach. In: Herbert, M. and Kovar, K. (Editors), GQ'98 Groundwater Quality: Remediation and Protection. IAHS Publication 250, pp. 68-71; COH 4 (2000) 170] was applied, which allows the determination of mass flow rates of o-xylene by integral pumping tests. Concentration time series obtained during pumping at two wells were used to calculate inversely contaminant mass flow rates at the two control planes that are defined by the diameter of the maximum isochrone. A reactive transport model was used within a Monte Carlo approach to identify biodegradation as the dominant process for reduction in the contaminant mass flow rate between the two consecutive control planes. Secondly, compound-specific carbon isotope analyses of o-xylene were performed on the basis of point-scale samples from the same two wells. The Rayleigh equation was used to quantify the degree of biodegradation that occurred between the wells. Thirdly, a combination of the Integral Groundwater Investigation method and the compound-specific isotope analysis was developed and applied. It comprises isotope measurements during the integral pumping tests and the evaluation of delta13C time series by an inversion algorithm to obtain spatially integrated mean isotope values at the control planes. It was shown that the Rayleigh equation is applicable to spatially integrated mean isotope values in order to obtain the mean biodegradation between the consecutive control planes. All three approaches yielded consistently a 98-99% degradation of o-xylene.

Biodegradation, Environmental↗
PubMed2001

Direct measurement of the Josephson supercurrent in an ultrasmall Josephson junction.

We have measured the supercurrent flowing through a nonhysteretic, ultrasmall, voltage-biased Josephson junction. In contrast with experiments performed so far on hysteretic Josephson junctions, we find a supercurrent peak whose maximum I(s max) increases as the temperature T decreases. The asymptotic T = 0 value of I(s max) agrees with the junction Ambegaokar-Baratoff critical current, as predicted by theory.

Journal Article↗
PubMed1993

The role of staging bronchoscopy in the preoperative assessment of a solitary pulmonary nodule.

In order to assess the role of a staging fiberoptic bronchoscopy in the preoperative assessment of an indeterminate solitary pulmonary nodule (SPN), we reviewed our experience in 33 SPNs identified among 1,269 bronchoscopies performed at the Albert Einstein Medical Center between 1985 and 1989. All lesions were less than 4 cm in greatest diameter and were not associated with symptoms of weight loss, chest pain, hemoptysis, localized wheezing, or hoarseness. A tissue diagnosis was established in 25 patients, 23 of whom had a malignant SPN. This study failed to detect a single case in which a fiberoptic bronchoscopic examination of the airway discovered a lesion that would preclude surgery and potentially curative resection. We recommend the abandonment of a staging bronchoscopy in the evaluation of a patient with an indeterminant SPN in whom history, physical examination, laboratory, and imaging studies fail to document contraindications to surgery. No additional useful information is derived and a substantial cost savings to the patient can be realized if the procedure is eliminated.

Adenocarcinoma↗
PubMed1986

Effect of hyperbaric oxygen exposure on oxygen tension within the medullary canal in the rabbit tibial osteomyelitis model.

The effect on intramedullary oxygen tension of 100% oxygen exposure at 1, 2, 2.4, and 3 atm pressure was studied in 12 New Zealand white rabbits with chronic right tibial osteomyelitis. The model, modified from that described by others, incorporates a multipuncture silastic closure plug placed transcortically in the proximal tibial metaphysis through which platinum needle, polarographic electrode oxygen tension determinations can be made without repeat surgical exposure. In 40% of the control, left, noninfected tibial metaphyses the baseline oxygen tension with the animals breathing room air at sea level was suboptimal for leukocyte bacterial killing. This oxygen tension was depressed further in the infected right tibia. Medullary canal oxygen tension increased in response to hyperbaric oxygen exposure in both the infected and noninfected tibiae. Whereas the amount of the oxygen tension increase varied with the presence of infection and depth of dive, neither the time for oxygen tension to plateau nor the time required for return to baseline tension after completion of hyperbaric oxygen exposure varied with the presence of infection or depth of dive. After completion of hyperbaric oxygen exposure, the oxygen tension within the medullary canal returned to baseline within 15 min.

Animals↗
PubMed1985

Neutron microscopy. The low-damage imaging of specialized organic materials.

It is shown that, insofar as radiation damage is concerned, transmission neutron microscopy using neutrons in the energy range approximately 0.0001-1.0 eV is extremely attractive for the imaging of specialized organic materials. By "specialized organic materials" is meant organic specimens composed entirely of specific isotopes that have been selected on the basis of their favorable properties with regard to radiation damage. In connection with such specimens, it is demonstrated that at a resolution of, for example, 100 A, neutrons will have an advantage over soft X-rays in terms of radiation damage, provided that the inherent (neutron) bright field image contrast turns out to be greater than 10(-5). Suggestions relating to (a) the comprehensive calculation of the radiation damage sustained by specialized organic specimens under slow neutron irradiation, (b) the construction of a theory of image formation in the neutron microscope, (c) the development of neutron lenses/focusing devices, and (d) the development of a brighter neutron source (essential for neutron microscopy) are outlined in some detail. The paper concludes with two appendices, which provide important background material.

Animals↗
PubMedDate not supplied

Pap smear adequacy.

Explore the source record for details and available documents.

Female↗