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At least 577 records · Page 32Linked to original sources

PubMed2007

Evaluation of the viability of cultured corneal endothelial cells by quantitative electron probe X-ray microanalysis.

Construction of artificial organs and tissues by tissue engineering is strongly dependent on the availability of viable cells. For that reason, the viability and the physiological status of cells kept in culture must be evaluated before the cells can be used for clinical purposes. In this work, we determined the viability of isolated rabbit corneal endothelial cells by trypan blue staining and quantitative electron probe X-ray microanalysis. Our results showed that the ionic content of potassium in cultured corneal endothelial cells tended to rise initially, but significantly decreased in cells in the fifth (and final) subculture, especially in comparison to cells in the fourth subculture (P < 0.001). However, the concentration of sulfur was higher in the fifth subculture than in the fourth subculture (P < 0.001), with a nonsignificant increase in sodium in the fifth subculture (P = 0.031). These data imply a remarkable decrease in the K/Na ratio from the fourth to the fifth subculture. Our microanalytical results, along with the morphological differences between cells in the last two subcultures, are compatible with an early phase of the preapoptotic process in the fifth subculture, and suggest that cells of the first four subcultures would be better candidates for tissue engineering.

Animals↗

PubMed1988

Comparison of different lasers in terms of thrombogenicity of the laser-treated vascular wall.

The thrombogenic properties of the laser-treated vascular wall are reported as quantitatively assessed on the basis of 33 experiments with peripheral canine vessel segments. Three types of surfaces, namely, 1) intact, 2) mechanically de-endothelized, and 3) postlaser, have been simultaneously exposed to platelet-enriched plasma in a sequentially organized artificial circulation system. Then the adherent platelets have been counted on the treated surfaces, and the relative thrombogenicity index has been calculated according to the equation T = (A1 - Aint)/(Ad - Aint), where Aint, Ad, A1 = the adherent platelet counts on intact, mechanically de-endothelized, and laser-treated surfaces, respectively. The following lasers have been evaluated: 1) Nd-YAG, 1,060 nm, continuous wave, 4W; 2) argon-ion, 480 and 514 nm and argon-ion, 350 nm, continuous-wave, 1 W and 400 mW [corrected], respectively; 3) excimer XeCl, 308 nm, pulsed, 30 mJ per pulse, repetition rate 10 Hz [corrected]; and also 4) the laser-heated metal probe (2 mm diameter, Trimedyne, Nd-YAG) 1,060 nm, 8 W. The thrombogenicity index values obtained were 83 +/- 7, 72 +/- 8, 57 +/- 9, 63 +/- 7, and 82 +/- 9%, respectively. The differences between these values were statistically insignificant. The data are suggestive of the essential requirement of, at least, anticoagulant therapy after laser angioplasty irrespective of the laser type.

Animals↗

PubMed1987

Recent advances in thromboresistant materials.

There are strong demands for innovative antithrombogenic materials, because of their necessity in fabricating artificial organs and progressive surgical prostheses. This paper reviews the recent advances in thromboresistant materials. Special emphasis is placed on the novel feature of the surface characterization of thromboresistant materials by X-ray photoelectron spectroscopy and its biomedical implications. Essential role of crystalline-amorphous microstructured surface in thromboresistant property of semicrystalline segmented copolymer is also discussed in detail.

Biocompatible Materials↗

PubMed1982

Pharmacokinetic characterization of extracorporeal therapy.

The efficiency of extracorporeal therapy with immobilized enzymes (reactive devices) and hemoperfusion cartridges (nonreactive devices) is evaluated in terms of a new pharmacokinetic parameter, the bioefficacy. A detailed analysis is provided in the former case, and it is shown how the bioefficacy can be calculated from a combined pharmacokinetic and reactor analysis. The theory is presented for evaluating bioefficacy in terms of linear pharmacokinetic models that view the reactor or other extracorporeal appliance as an artificial organ. Examples are drawn from recent work on methotrexate rescue with immobilized carboxypeptidase G1 and from literature data on the use of hemoperfusion to treat drug overdose to illustrate the calculations.

Enzymes, Immobilized↗

PubMed1989

Acute induction of sustained ventricular tachycardia: a new porcine model.

In this study we evaluated the possibility of initiating long-lasting ventricular tachycardias acutely, using isolated porcine hearts and thus avoiding an open-chest operation model. This set-up was designed especially to investigate defibrillating or antitachycardiac pacing devices, which terminate these malignant arrhythmias if medical treatment fails. The experiments were performed on 42 pigs, weighing 20-25 kg. After thoracotomy their hearts were removed and adapted to a Langendorff perfusion system. Supplied with their own blood, beating hearts were manipulated in three different ways: direct current impulses (4.5 V, 750 ms) or programmed ventricular stimulation, creation of a small myocardial infarction, and application of antiarrhythmic drugs (ajmalin, lidocaine, sotalol). Out of all possibilities the combination of ajmalin (mean concentration 0.041 micrograms/ml) and a small anteroapical myocardial infarction (3-6 cm2) along with direct current impulses (4.5 V), led to sustained ventricular tachycardias in the highest proportion (93%) of trials (P less than 0.001). The heart rate was 251 beats per minute on average. Lidocaine trials were less successful (53%), while programmed ventricular stimulation and sotalol failed to induce ventricular tachycardias. This study supports the evidence that the combination of ajmalin and a small myocardial infarction with direct current impulses is a reliable model for sustained ventricular tachycardias in isolated pig hearts. Although it is a rather artificial organ model, tachycardias can be induced acutely without any long-term pretreatment. Animal models based on chronic myocardial infarctions will therefore be unnecessary for the investigation of defibrillating systems and antitachycardiac pacing devices.

Animals↗

PubMed2005

Drug targeting with nano-sized carrier systems.

This paper discusses the present status of, and future perspectives on, drug targeting through the bloodstream by describing the drug targeting concept, its methodologies, types of drug carriers, and recent clinical examples. This explanation and discussion is made from the viewpoint of possible correlations with studies on artificial organs, implants, and biomaterials. Two targeting methodologies (active and passive targeting), two targeting strategies (the magic bullet and the enhanced permeability and retention effect), and five types of drug carriers are explained. In addition, the clinical status of the five carrier systems is discussed.

Drug Carriers↗

PubMed2004

Transformation of Spirulina platensis strain C1 (Arthrospira sp. PCC9438) with Tn5 transposase-transposon DNA-cation liposome complex.

Spirulina platensis is one of the most commercially important species of microalgae. Thus, it is an attractive candidate for genetic manipulation and the development of novel practical applications. However, this process is hampered by the absence of a stable gene transfer system, specifically the limited number of suitable vectors and transformation methods available for this organism. Artificial transposon systems developed by extracting the essential elements from natural transposons have been extensively studied, and recently a mutated transposase and transposon system was reported to improve transformation efficiency by electroporation. We applied a modified transformation strategy using a natural Tn5 transposon, transposase, and cation liposome complex by electroporation to improve the transformation efficiency for Spirulina platensis strain C1 (Arthrospira sp. PCC9438). Aggregation of cells became visible after 3 weeks during 2.0 microg/ml chloramphenicol selection, and growth continued for more than 12 months. Transfected chloramphenicol acetyltransferase (CAT) genes were detected in the genomic DNA by Southern hybridization. Transformed cells demonstrated CAT activity, but non-transformed cells did not.

Base Sequence↗

PubMed1984

Role of red cells in preventing the growth of platelet aggregation.

Using high-resolution real-time two-dimensional ultrasound, we have investigated the role of red cells in the growth of already established platelet aggregates under controlled flow conditions. Platelet rich plasma (PRP) was circulated in vitro in horizontally and vertically arranged tubing at mean shear rate ranging from 60 to 0 sec-1, and adenosine diphosphate (ADP) was used to induce platelet aggregation. ADP-induced platelet aggregates grew in size and tended to sediment as shear rate decreased, in particular, below 10 sec-1. At 0 sec-1 (stasis), large clusters of platelet aggregates formed. The addition of washed red cells to produce a hematocrit of only 2% significantly interfered with the growth and sedimentation of platelet aggregates as shear rate was reduced. Formaldehyde-hardened erythrocytes had a similar effect in preventing the growth of platelet aggregates, suggesting that mechanical collision of red cells with platelet aggregates may be the cause of growth inhibition. Therefore, the thrombotic process may be enhanced in red cell poor zones in circulation resulting from flow disturbances associated with vascular stenosis or within artificial organs and extracorporeal systems. The present study also suggested that red cell free PRP should be carefully administered therapeutically.

Adenosine Diphosphate↗

PubMed1987

Inhibitory effect of immobilized microsomal proteins on platelet aggregation.

Bovine aorta microsome was solubilized by 0.5% Triton X-100, and then immobilized on agarose gel (Sepharose 4B). Immobilized microsomal proteins (I-MP) inhibited platelet aggregations induced by ADP, arachidonic acid, collagen, and thrombin. The decrease of free platelet count in sheared whole blood was suppressed by I-MP. The anti-aggregatory activity of I-MP on arachidonic acid-induced aggregation was inhibited by 15-HPETE. This result suggests that I-MP contains PGI2 synthetase activity. It is considered that immobilization of enzymatic systems in aorta microsome which limited platelet aggregation is effective to provide an antithrombogenicity to the artificial polymers for artificial organs, especially used under the conditions which frequently induced platelet aggregation.

Animals↗

PubMed1987

Microencapsulation of CHO cells in a hydroxyethyl methacrylate-methyl methacrylate copolymer.

Chinese hamster ovary fibroblasts, as model cells, have been microencapsulated in a hydroxyethyl methacrylate-methyl methacrylate copolymer (HEMA-MMA) by interfacial precipitation. The polymer containing approximately equal to 75 mol% HEMA, dissolved in polyethylene glycol 200 (PEG 200) was coextruded with the cell suspension (4-6 X 10(5) cells/ml in the alpha-MEM with 10% foetal calf serum +/- Ficoll 400/PBS) through a concentric needle assembly. Polymer solution droplets, containing cells, were blown off the end of the needle assembly by a coaxial filtered air stream into a nonsolvent bath containing phosphate buffered saline (PBS) with 5 ppm Pluronic L101, overlaid with hexadecane. The nascent capsules hang at the hexadecane/PBS interface while the solvent is extracted into the aqueous nonsolvent, to precipitate the polymer around the cells. The resultant capsules were 500 microns-1 mm in diam. with a microporous sponge-like interior, and also very tough and flexible. The cells survived encapsulation based on subculture ability, retention of some fluorescein diacetate (FDA) activity over 5 d and direct light microscopic evidence of cell growth over 10 d after histological sectioning and staining. However, cell growth was not uniformly observed (especially in the FDA assay) and this was attributed to space limitations for growth within the microporous interior. Continued development of this process and adaptation to cells such as pancreatic islets is expected to lead to hybrid artificial organs which are capable of ameliorating metabolic disorders such as diabetes.

Acrylates↗

PubMed1990

Alginate as immobilization matrix for cells.

In recent years, entrapment of cells within spheres of Ca2+ alginate has become the most widely used technique for immobilizing living cells. This versatile method includes applications ranging from immobilization of living or dead cells in bioreactors, immobilization of plant protoplasts for micropropagation and immobilization of hybridoma cells for production of monoclonal antibodies, to entrapment of animal cells for implantation of artificial organs. This review evaluates the potential of this method on the basis of the current knowledge of structural and functional relationships in alginate gels.

Alginates↗

PubMed2004

Prediction of diagnosis in patients with early arthritis using a combined Kohonen mapping and instance-based evaluation criterion.

Rheumatoid arthritis (RA) and spondyloarthropathy (SpA) are the two most frequent forms of chronic autoimmune arthritis. These diseases lead to important inflammatory symptoms resulting in an important functional impairment. This paper introduces a self-organizing artificial neural network combined with a case-based reasoning evaluation criterion to predict diagnosis in patients with early arthritis. Results show that 47.2% of the sample space can be predicted with an accuracy of 84.0% and attaining a high confidence level. 37.7% of the sample space is classified with an overall accuracy of 65.0%. The remaining group was labeled as "undetermined". A general prediction accuracy of 75.6% is reached, exceeding the performance of other approaches such as a backpropagation neural network and the Quest decision tree program. Furthermore, by using this new method, more specifically case-based reasoning, as a helpful tool to classify patients with early arthritis, the possibility of a confidence measure is given, indicating a degree of "belief" of the system in its results. This is often an important feature when dealing with diagnosis in human patients.

Algorithms↗

PubMed2006

Characterizing short-term release and neovascularization potential of multi-protein growth supplement delivered via alginate hollow fiber devices.

Multi-protein (10-250 kDa) endothelial cell growth supplement (ECGS) contains growth factors of varying sizes resulting in advanced release rates from diffusion-based drug delivery devices. As a result, the biochemical stimulus provided by ECGS for neovascularization in the critical initial stages of cell transplantation in artificial organs may differ from that for single growth factor delivery. In this study, both in vitro and in vivo studies were conducted with ECGS to correlate in vitro release of multiple angiogenic growth factors to vascularization potential in vivo. The short-term release of ECGS from calcium alginate gels supported in the lumen of polypropylene (PP) hollow fibers was investigated in vitro for up to 142 h. The overall time constant increased from 2, 2.2 and 6.3 h as the alginate concentration was increased from 1.5%, 2% and 3%, respectively. However, time constants for individual species ranged from 1.5 to 77 h. The in vivo bioactivity of released ECGS was assessed for up to 21 days using a Lewis rat model implanted with 1.5% calcium alginate gels supported in PP and polysulfone hollow fibers. For the ECGS-releasing PP hollow fiber system, a two-fold increase in neovascularization with respect to the control was observed for the period between 7 and 17 days post-implantation at the device-tissue interface (p<0.05).

Alginates↗

PubMed2005

Prosthetic heart valves' mechanical loading of red blood cells in patients with hereditary membrane defects.

Implantable cardiovascular devices such as prosthetic heart valves (PHVs) are widely applied clinical tools. Upon implantation, the patient can suffer from anemia as a result of red cell destruction and hemolysis can be more relevant whenever the patient is also affected by red cell disorders in which erythrocytes are more susceptible to mechanical stress such as hereditary spherocytosis (HS) and hereditary elliptocytosis (HE). Considering the typical morphological alterations observed in HS and HE, a study of the influence of cell geometry on the distribution of the shear stress on red cells in biological fluids was carried out. A numerical simulation of the loading caused by Reynolds shear stresses on a prolate spheroid was performed, with the ellipticity of the particle as the independent parameter. The average shear stress on a particle in the blood stream was found to depend on the particle's geometry, besides the stress field produced by the prosthetic device. The relevance of an increasing particle ellipticity on the global load is discussed. The model was applied to erythrocytes from implanted patients with HE or HS, enabling to explain the occurrence of moderate or severe anemia, respectively. The clinical data support the relevance of the proposed global parameter as erythrocyte trauma predictor with regard to the fluid dynamics of artificial organs.

Adult↗

PubMed2006

Counteracting apoptosis and necrosis with hypoxia responsive expression of Bcl-2Delta.

In the encapsulated environment of biohybrid artificial organs, cells often encounter a deficiency in oxygen, which lead to apoptosis, necrosis, and lost of productivity. Two vectors with constitutive CMV promoters were constructed to examine the ability of Bcl-2Delta to help C2C12 mouse myoblasts maintain exogenous protein production under hypoxia. Two additional vectors with hypoxia-inducible promoters (5HRE) that switched on Bcl-2Delta expression based on low oxygen levels (0.0%, 0.5%, 1.0%, 2.0%, 5.0%, or 21.0%) were tested for protein productivity and protection against hypoxic stresses. A yellow fluorescent protein was used as a model protein in all vector constructs. C2C12 cells with Bcl-2Delta consistently produced more protein regardless of the oxygen level or promoter used. Cells utilizing the 5HRE rather than the CMV promoter showed an increased level of protein production as the oxygen was decreased. Among the cells with 5HRE promoters, the presence of Bcl-2Delta also increased viability and decreased apoptosis.

Animals↗

PubMed1999

Development of the Nimbus/University of Pittsburgh innovative ventricular assist system.

BACKGROUND: Nimbus Inc, and the University of Pittsburgh's McGowan Center for Artificial Organ Development have been collaborators on rotary blood pump technology initiatives since 1992. Currently, a major focus is an innovative ventricular assist system (IVAS) that features an implantable, electrically powered axial flow blood pump. In addition to the blood pump, a major development item is the electronic controller and the control algorithm for modulating pump speed in response to varying physical demand. METHODS: Methods used in developing the IVAS include computational fluid dynamic modeling of the pump's interior flow field, flow visualization of the flow field using laser-based imaging, computer simulation of blood pump-physiological interactions, vibroaccoustic monitoring, and an extensive in vivo test program. RESULTS: Results to date, which are presented below, include successful in vivo tests of blood pumps with blood-immersed bearings, and feasibility demonstration of vibroacoustic monitoring in this application. CONCLUSIONS: This unique blend of industrial experience and technologies with the University-based Research and Development Center has greatly enhanced the progress made on this IVAS project.

Animals↗

PubMed1999

The development of microfabricated biocatalytic fuel cells.

The production of electricity by biocatalytic fuel cells has been feasible for almost two decades and can produce electric power at a practical level. These fuel cells use immobilized microorganisms or enzymes as catalysts, and glucose as a fuel. A microfabricated enzyme battery has recently been made that is designed to function as a power supply for microsurgery robots or artificial organs.

Animals↗

PubMed1993

Leukodepletion blood filters: filter design and mechanisms of leukocyte removal.

Modern leukocyte removal filters have been developed after years of refinement in design. Current filters are composite filters in which synthetic microfiber material is prepared as a nonwoven web. The filter material may be surface modified to alter surface tension or charge to improve performance. The housing design promotes effective contact of blood with the filter material and decreases shear forces. The exact mechanisms by which these filters remove leukocytes from blood components are uncertain, but likely represent a combination of both physical and biological processes whose contributions to leukocyte removal are interdependent. Small-pore microfiber webs result in barrier phenomena that permit retention of individual cells and increase the total adsorptive area of the filter. Modifications in surface charge can increase or decrease cell attraction to the fibers. Optimum interfacial surface tensions between blood cells, plasma, and filter fibers not only permit effective blood flow through small fiber pores, but also facilitate cell contact with the material. Barrier retention is a common mechanism for all modern leukocyte-removal filters and applies to all leukocyte subtypes. Because barrier retention does not depend on cell viability, it is operative for cells of any age and will retain any nondeformable cell, including whole nuclei from lymphocytes or monocytes. Barrier retention is supplemented by retention by adhesion. RBCs, lymphocytes, monocytes, granulocytes, and platelets differ in their relative adhesiveness to filter fibers. Different adhesive mechanisms are used in filters designed for RBCs compared with filters designed for platelets. Although lymphocytes, monocytes, and granulocytes can adhere directly to filter fibers, the biological mechanisms underlying cell adhesion may differ for these cell types. These differences may depend on expression of cell adhesion molecules. In the case of filtration of fresh RBCs, platelet-leukocyte interaction seems to supplement other mechanisms of leukocyte retention. The interactions of cells with biomaterials is an area of important research for implantable medical devices, artificial organs, and orthopedic, vascular, and dental prosthetics. Research in these areas is likely to contribute to improved biomaterials for blood filters. Improved techniques for the preparation of hybrid polymers and new techniques for surface modification of existing polymers will increase the technical opportunities for the development of synthetic surfaces ideally designed for leukocyte removal. It is therefore likely that the performance of leukocyte-removal filters will continue to improve. The development of cost-effective leukocyte removal filters specifically designed for use during component preparation would permit leukocyte depletion of all cellular blood components.

Biomechanical Phenomena↗