SEARCH · PubMed Health

Results for “ARTIFICIAL ORGANS”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources

PubMed1992

Perspectives in diabetes. Islet transplantation with immunoisolation.

Immunoisolation is a potentially important approach to transplanting islets without need for immunosuppressive drugs. Immunoisolation systems have been conceived in which the transplanted tissue is separated from the immune system of the host by an artificial barrier. These systems offer a solution to the problem of human islet procurement by permitting use of islets isolated from animal pancreases. The devices used are referred to as biohybrid artificial organs because they combine synthetic, selectively permeable membranes that block immune rejection with living transplants. Three major types of biohybrid pancreas devices have been studied. These include devices anastomosed to the vascular system as AV shunts, diffusion chambers, and microcapsules. Results in diabetic rodents and dogs indicate that biohybrid pancreas devices significantly improve glucose homeostasis and can function for more than a year. Recent progress made with this approach is discussed, and some of the remaining problems that must be resolved to bring this technology to clinical reality are addressed.

Animals↗

PubMed2002

Phenotype of hepatocyte spheroids in Arg-GLY-Asp (RGD) containing a thermo-reversible extracellular matrix.

The spheroid of specific cells is often regarded as the better form in artificial organs and mammalian cell bioreactors for improved cell-specific functions. In this study, freshly harvested primary rat hepatocytes, which had been cultivated as spheroids and entrapped in a synthetic thermo-reversible extracellular matrix, were examined for differentiated morphology and enhanced liver-specific functions as compared to a control set (hepatocytes in single-cell form). A copolymer of N-isopropylacrylamide (98 mole % in the feed) and acrylic acid (poly(NiPAAm-co-AAc)), and the adhesion molecule, an Arg-Gly-Asp (RGD)-incorporated thermo-reversible matrix, were used to entrap hepatocytes in the form of either spheroids or single cells. In a 28-day culture period, the spheroids in the RGD-incorporated gel maintained higher viability and produced albumin and urea at constant rates, while there was lower cell viability and less albumin secretion by the spheroids in p(NiPAAm-co-AAc). Hepatocytes cultured as spheroids in the RGD-incorporated gel would constitute a potentially useful three-dimensional cell system for application in a bio-artificial liver device.

Acrylic Resins↗

PubMed2001

[Model fluids of blood for in vitro testing of artificial heart valves].

The increasing development and implantation of artificial organs subject to perfusion with human blood once implanted (grafts, heart-valve prostheses and assist systems) require extensive testing of hydrodynamic performance in mock circulation models. As human blood ist not always available in the necessary quantities, different fluids (water, saline or glycerine solutions) are employed for measurements of flow characteristics. However, these model fluids do not possess the non-Newtonian rheological properties of blood. In addition, they do not allow estimation of possible blood damage. Aqueous solutions of high molecular weight polyacrylamides (PAA) have rheological properties similar to blood, displaying also molecular degradation due to shear stress in the flow. Therefore, they were used as model fluid for blood. Different model solutions were compared to blood with regard to their influence on characteristic flow parameters of mechanical heart valves. Likewise, the shear damage of erythrocytes could be compared to flow-induced polymer degradation. It was shown that PAA solutions in definite concentrations are suitable models for blood, not only in terms of non-Newtonian rheology, but also in terms of estimation of hemolytic potential of artificial heart valves.

Acrylic Resins↗

PubMed1998

Shear stress related hemolysis and its modelling by mechanical degradation of polymer solutions.

Human or animal blood is normally used as a test fluid for in vitro evaluation of hemolysis by artificial organs. However, blood has some disadvantages (no transparence for visualization of the flow field, large biological variability and problems with cleaning the devices). For that reason, it would be of advantage to have a reproducibile transparent technical fluid with blood like flow characteristics and that exhibits similar shear depending destruction. We have shown that solutions of long-chaining polymer molecules are destroyed by heart valve prostheses in a similar manner as blood corpuscules. In the presented study, a direct comparison between erythrocyte destruction of bovine blood and degradation of Polyacrylamid molecules in a 300 ppm solution is given. A uniform shear field was applied to the fluid using a plate-plate geometry shear device. This device allows a variation of shear stress and shear time in the range of 15-500 N/m2 and 64-516 ms, respectively A correlation between the index of hemolysis (ratio of free plasma hemoglobin to total hemoglobin) and the percentage viscosity decrease (derived from low shear viscosity at a shear rate of 0.01/s) was found. Thus, PAA solutions are suitable model fluids for in vitro estimation of the damaging effects of artificial devices.

Acrylic Resins↗

PubMed2003

Tissue-culture surfaces with mixtures of aminated and fluorinated functional groups. Part 2. Growth and function of transgenic rat insulinoma cells (betaG I/17).

Interactions of transplantable cells with synthetic polymers can influence the function of biohybrid artificial organs. This study explored growth and secretion of human insulin by betaG I/17 cells cultured on surfaces bearing diamine groups (N2), trifluoropropyl groups (F3) and mixtures of the two. Cells cultured on high-F3 and high-N2 surfaces spread well, grew rapidly and produced >1.8 mol lactate per mol glucose consumed, closely resembling cells grown on the permissive control, glass. On one mixed surface, with a molar ratio of 33 N2 groups:67 F3 groups, cells had a lower lactate/glucose ratio, adopted a rounded form, grew slowly and were quick to form emergent aggregates, similar to cultures on the inhibitory control, untreated polystyrene. Cultures on surfaces with higher F3 content secreted the most insulin and, in the case of the highest-F3 surface, showed improved responsiveness to secretagogues. Hormone secretion was roughly 50% greater when cells were grown on F3 surfaces conditioned by earlier cultures of betaG I/17. Incubation of conditioned surfaces with high concentrations of a polyclonal anti-laminin serum prior to re-plating partially abolished this improvement in secretory function. Polymers bearing trifluoropropyl groups appear to be attractive candidates for use in the artificial endocrine pancreas. Surface coatings that include laminin might promote function of transgenic insulinoma cells in vitro and in vivo.

Animals↗

PubMed2006

Physical-chemical and biological characterization of silk fibroin-coated porous membranes for medical applications.

Membranes in artificial organs and scaffolds for tissue engineering are often coated with biomimetic molecules (e.g., collagen) to improve their biocompatibility and promote primary cell adhesion and differentiation. However, animal proteins are expensive and may be contaminated with prions. Silk fibroin (SF) made by Bombyx Mori silk worms, used as a scaffold or grafted to other polymers, reportedly promotes the adhesion and growth of many human cell types. This paper describes how commercial porous membranes were physically coated with SF, and their physical-chemical properties were characterized by SEM, AFM, tensile stress analysis and dynamic contact angle measurements. The effect of the SF coating on membrane biocompatibility and resistance to bacterial colonization is also examined. The proposed technique yields SF coats of different thickness that strengthen the membranes and make their surface remarkably more wettable. The SF coat is not cytotoxic, and promotes the adhesion and proliferation of an immortalized fibroblast cell line. Similarly to collagen, SF-coated membranes also exhibit a much better resistance to the adhesion of S. epidermidis bacteria than uncoated membranes. These preliminary results suggest that SF is a feasible alternative to collagen as a biomimetic coating for 3D scaffolds for tissue engineering or bioartificial (as well as artificial) prosthesis.

Chemical Phenomena↗

PubMed1997

Extracorporeal liver support: cell-based therapy for the failing liver.

It is perhaps self-evident to state that a liver support device is possible as long as the artificial organ provides liver function. This basic concept has received woefully little attention, mainly because "liver function" escapes precise definition. We have seen a variety of liver-assist devices that have little to do with liver function over the past 30 years. Recent work has focused on the liver as a biochemical reactor, rather than an excretory organ, and the paradigm has shifted away from blood purification and toward metabolic support. This new generation of devices includes viable liver cells, which provide the necessary biochemical function without needing to identify the numerous metabolic pathways necessary to support the patient with a failing liver. This approach is the most effective and least invasive method available with current technology, and it has yielded exciting data. Questions about the mass of cells required to provide adequate support, the timing and length of treatment, and the source of cellular material continue to be debated. Here we address theoretical and practical problems in developing an extracorporeal liver-assist device (ELAD) and suggest the future role of extracorporeal liver support in the management of liver failure.

Animals↗

PubMed1994

The status of pacemaker implantations in Japan.

It has been over 40 years since the initial clinical application of a cardiac pacemaker. Currently, approximately 300 per million patients in the United States and Europe are kept alive owing to the benefit of implantable pacemakers. Recently, the Japanese Cardiac Pacing Society and the Japanese Society of Artificial Organs performed pacemaker registry studies for 1989 and 1990. In this paper, results of this survey are described. Currently, implantable cardiac pacemakers are utilized only on the level of 120 per million patients in Japan. Surprisingly, all implantations were performed using foreign manufactured pacemakers. Despite the high level of electronic technologies available in Japan, no Japanese-made implantable cardiac pacemakers are utilized in Japan. One could speculate that a major reason for the low level of clinical application of cardiac pacemakers is that these devices are quite expensive because of the import duties imposed on them. It is necessary and strongly recommended that implantable cardiac pacemakers be manufactured in Japan in order for them to be utilized as fully as they are in the United States and Europe.

Adolescent↗

PubMed2005

Modelling brain emergent behaviours through coevolution of neural agents.

Recently, many research efforts focus on modelling partial brain areas with the long-term goal to support cognitive abilities of artificial organisms. Existing models usually suffer from heterogeneity, which constitutes their integration very difficult. The present work introduces a computational framework to address brain modelling tasks, emphasizing on the integrative performance of substructures. Moreover, implemented models are embedded in a robotic platform to support its behavioural capabilities. We follow an agent-based approach in the design of substructures to support the autonomy of partial brain structures. Agents are formulated to allow the emergence of a desired behaviour after a certain amount of interaction with the environment. An appropriate collaborative coevolutionary algorithm, able to emphasize both the speciality of brain areas and their cooperative performance, is employed to support design specification of agent structures. The effectiveness of the proposed approach is illustrated through the implementation of computational models for motor cortex and hippocampus, which are successfully tested on a simulated mobile robot.

Animals↗

PubMed1986

[Problems of biocompatibility in hemodialysis treatment].

Although hemodialysis is one of the best examined, and clinically best established, methods of patient treatment with artificial organs, a number of biocompatibility problems remain. This review discusses the problem of water quality. Recently, much concern has been focused on potential longterm risks from patients exposure to subthreshold concentrations of endotoxin in dialysate. Further problems comprise inorganic and organic contaminants, some of which with potential carcinogenetic hazards. Complement activation by, and thrombogenicity of, dialysis membranes have not been eliminated. Presumably, the hazards of complement activation are less acute shortterm reactions (which according to more recent studies appear to be ETO-related anaphylactoid reactions) but rather potential longterm hazards, e.g. beta 2 m related amyloid. However, the issue is not settled since we have recently found cell activation by dialysis membranes even in the absence of complement. Apart from membranes, dialysis tubing presents hazards, e.g. leakage of plasticizers and release of oligomers or radicals. The recognition of ETO as a potent immunogen, inducing antibodies detectable in approximately 40% of the dialysis population, will require to replace ETO as a sterilisant for dialysis devices. This demand is even more urgent in view of the recognized carcinogenicity of this alkylating agent.

Biocompatible Materials↗

PubMed2006

Morphology of spheroidal hepatocytes within injectable, biodegradable, and thermosensitive poly(organophosphazene) hydrogel as cell delivery vehicle.

An aggregate of specific cells is often regarded as a better form of single-cell in artificial organs and mammalian cell bioreactors for improved cell-specific functions. In this study, freshly harvested primary rat hepatocytes, cultivated as spheroids and entrapped in a synthetic thermoreversible extracellular matrix, were examined for differentiation morphology and enhanced liver-specific functions and compared with a control set (single-cell hepatocytes). A copolymer of poly(organophsophazene) hydrogel, an injectable, biodegradable, and thermosensitive matrix, was used to entrap hepatocytes as spheroids or single cells. In a 28-d culture period, the spheroidal hepatocytes maintained a higher viability and produced albumin and urea at constant rates, whereas the single hepatocytes showed a reduction in the level of albumin secretion in the hydrogel. The culturing of spheroidal hepatocytes is a potentially useful three-dimensional cell system for application in bioartificial liver devices and bioreactors.

Animals↗

PubMed2005

Phenotype of hepatocyte spheroids behavior within thermo-sensitive poly(NiPAAm-co-PEG-g-GRGDS) hydrogel as a cell delivery vehicle.

Aggregates (spheroids) of specific cells are often regarded as a better form in artificial organs and mammalian cell bioreactors for improved cell-specific functions. Freshly harvested primary rat hepatocytes, cultivated as spheroids and entrapped in an adhesion molecules of Arg-Gly-Asp (RGD)-conjugated extracellular matrix, have been examined for differentiated morphology and enhanced liver-specific functions. A copolymer of RGD conjugated p(NiPAAm-co-PEG) hydrogel was used to entrap hepatocytes in the forms of spheroids. Over 28 days, entrapped the spheroids had a higher viability and produced albumin and urea at constant rates, while there was slight increase in cell numbers and reduction of albumin secretion in single cell culture in the hydrogel. Hepatocytes cultured in this way are a potentially useful three-dimensional cell system for application in a bioartificial liver device and bioreactor.

Acrylamides↗

PubMed2004

"He knows that machine is his mortality": old and new social and cultural patterns in the clinical trial of the AbioCor artificial heart.

The clinical trial of the AbioCor artificial heart, initiated in July 2001 and still in process, has taken place within a matrix of social and cultural patterns that are both "old" and new. The old patterns--those that have accompanied previous clinical trials of other vital artificial organs and transplantation in the United States--include "experiment perilous," and courage, heroism, and pioneering themes; "right stuff" motifs; "Americana" symbols; allusions to the meaning of the human heart; connections with a for-profit corporation; and the occurrence of moratoriums. New patterns--those more particular and distinctive to the AbioCor trial--involve the restrictions imposed on releasing information about the post-operative clinical status of the implant recipients; the quasi-institutionalization of a patient advocacy system to represent patient-subjects and their families; and the "crises of success" that were encountered when several of the AbioCor recipients survived longer than expected. In certain instances, old and new patterns have been combined--for example, in some of the idiosyncratic features of the AbioCor-associated lawsuit that has resulted in part from the problem of the "therapeutic misconception," the belief that an experimental intervention is actually intended to be a treatment.

Attitude to Health↗

PubMed1990

Biomedical and clinical applications of automated single cell electrophoresis.

The automated single cell electrophoresis microscope Parmoquant has been used for the discrimination of lymphocytes and the study of the interaction of substances with cells and synthetic particles. Electrophoretic histograms allowed the determination of changes in the proportion of lymphocyte populations after kidney transplantation, during dialysis treatment, open heart surgery and during pregnancy. Discrimination of leukemic cells on the basis of electrophoresis was used as an additional parameter in diagnosis. In a mouse tumor model, histogram determination enabled the in vivo effect of the tumor necrosis factor on immune cells to be evaluated. Cell electrophoresis was shown to be suitable to detect the influence of antibodies, lectins and bacteria on the cell surface. Protein adsorption was studied on synthetic particles using cell electrophoresis. This method was applied to investigate the phenomena of blood interaction with biomaterials used in artificial organs and to determine differences in the protein composition of serum or other body fluids connected with diseases.

Animals↗

PubMed1981

The in vitro and in vivo behavior of urokinase immobilized onto collagen-synthetic polymer composite material.

With a view to developing biomaterials for semipermanent substitution, we have studied a composite material constituted with collagen and a synthetic polymer which possesses high tissue compatibility. This collagen-synthetic polymer composite was applied as a support for immobilization of enzymes for the purpose of providing a material surface with biological function. The enzymes, urokinase and trypsin, were successfully bound to the collagen membrane layer which had been activated by acyl azide formation of its carboxyl groups. The enzyme-bearing composite material showed excellent catalytic activity toward a protein substrate as well as a low-molecular-weight synthetic substrate. The immobilized urokinase was characterized enzymatically and compared with native urokinase. The apparent affinity of immobilized urokinase for the substrate was slightly decreased, but its intrinsic kinetic properties were not significantly affected. No decrease in its esterase activity was observed both on repeated use and on long-term storage, and its fibrinolytic activity was stable on heat or disinfection treatment. When this urokinase-bearing composite material was applied into rabbit blood vessels, its in vivo fibrinolytic activity was maintained. Thus, enzyme-collagen-synthetic polymer composites may find wide application for biomaterials and artificial organs as functional biomaterials.

Animals↗

PubMed1986

A simple method to heparinize biological materials.

A new method was developed inducing antithrombogenicity to biologic materials. A basic protein, protamine, was used to increase heparin binding to collagenous materials. Protamine sulfate solution was poured into a collagen-rich material (porcine ureter). The protamine adsorbed to the collagen was then cross-linked to the material by glutaraldehyde. The collagen-protamine complex was then interacted with a heparin solution to ionically bind heparin to the material. The amount and the distribution of the bound heparin can be controlled by changing the protamine fixation to the material. A heparinized porcine ureter as a vascular substitute showed excellent antithrombogenicity in experimental animal studies. This method is expected to be used as method for developing antithrombogenic artificial organs, and as a method for the development of antiadhesive membranes.

Animals↗

PubMed1994

Antithrombogenicity of lumbrokinase-immobilized polyurethane.

Lumbrokinase is a potent fibrinolytic enzyme purified from the earthworm, Lumbricus rubellus. We immobilized 18 IU/cm2 of lumbrokinase to polyurethane using maleic anhydride methylvinyl ether copolymer (MAMEC) as an enzyme carrier, and the proteolytic and fibrinolytic activities of immobilized lumbrokinase were assayed. Immobilized lumbrokinase retained about 34% of its activity, compared with soluble lumbrokinase activity. Immobilized lumbrokinase showed stability against thermal inactivation and degradation and within a various pH range. The optimal pH of immobilized lumbrokinase shifted 1.0 pH unit upward compared with soluble enzyme. Upon exposure to the human whole blood, less amount of 125I-fibrinogen was adsorbed to lumbrokinase-immobilized surface than to the polyurethane control surface. The lumbrokinase-immobilized surface showed less platelet adhesion than did the MAMEC-grafted surface. At the early stage of platelet adhesion, the number of adhered platelets increased on the lumbrokinase-immobilized surface with increasing time; yet, the platelet number drastically decreased on the lumbrokinase-immobilized surface after 80 min incubation. This suggests that lumbrokinase-immobilized polyurethane digested the adsorbed fibrinogen and inhibited platelet adhesion on the surface, probably by inhibiting fibrinogen adsorption to be highly antithrombogenic. Clinical applications of this material to artificial organs should be developed in the near future.

Adsorption↗

PubMed1995

Surface microarchitectural design in biomedical applications: preparation of microporous polymer surfaces by an excimer laser ablation technique.

In this report we demonstrate a microprocessing method to prepare microporous polymer films by an excimer laser ablation technique, which may enable the fabrication of functional biomedical devices such as advanced artificial organs. The irradiation of a KrF excimer laser pulses (wave-length 248 nm; fluence 1 J/cm2 pulse) onto several polymer films was achieved by passing a laser pulse through an optical microscope, resulting in the formation of an etched pit on the irradiated surface due to ablative photodecomposition. The number of pulses and the micropositioning of the irradiation were precisely controlled by a computer-aided control unit. Minimal ablation was observed for polyethylene with very small absorption coefficient (alpha) at 248 nm. For polymers which absorbed the laser photons, the etch depth increased linearly with number of pulses. The etch depth per pulse decreased with an increase in alpha values. An excellent structural quality, with micron-order precision of an etched pit, was found for those polymers with larger alpha values, such as polyimide, segmented polyurethane, and polycarbonate.

Biocompatible Materials↗