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At least 883 records · Page 49Linked to original sources
PubMed1989

Fluorescent latex microspheres as a retrograde tracer in the peripheral nervous system.

Rhodamine labeled latex microspheres were used as a fluorescent retrograde tracer in the peripheral nervous system. Examination of rabbit trigeminal ganglia following application of microspheres to crushed or intact inferior alveolar nerve revealed that: (1) microspheres were taken up by only damaged axons; (2) microspheres remained in trigeminal cell bodies for up to 3 months without degradation or diffusion to extracellular structures; and (3) cells containing microspheres were capable of regenerating axons as evidenced by the return of evoked sensory action potentials and the retrograde axonal transport of True blue. Thus, fluorescent microspheres may be useful tools for in vivo survival studies of peripheral nervous system regeneration and development.

Action Potentials↗
PubMed1993

Effects of naftidrofuryl oxalate on microsphere embolism-induced changes in tricarboxylic acid cycle intermediates of rats.

The present study was undertaken to determine whether naftidrofuryl oxalate, a cerebral vasodilator, may improve or attenuate microsphere embolism-induced damage to the mitochondrial tricarboxylic acid cycle. For this purpose, the intermediates in the tricarboxylic acid cycle were determined using cerebral cortex isolated from microsphere-injected rats with and without naftidrofuryl oxalate treatment. Seven-hundred microspheres, with a diameter of 48 microns were injected into the right hemisphere through the right common carotid artery. The presence of cerebral infarction on the 3rd day after the operation was confirmed by the development of triphenyltetrazolium chloride-unstained areas in brain sections. Succinate, fumarate, malate, citrate and alpha-ketoglutarate, but not oxaloacetate, contents were significantly decreased in the right hemisphere of rats on the 3rd day following microsphere embolism. In the left hemisphere, a similar but smaller decrease in these intermediates was seen. The rats, which showed typical stroke-like symptoms, were treated with 15 mg/kg naftidrofuryl oxalate i.p., twice daily for 2.5 days, resulting in a significant reversal of the intermediate content of both hemispheres toward the control and an increased in the triphenyltetrazolium-stained area of a coronal section of the right hemisphere relative to the untreated animals. The results suggest that naftidrofuryl oxalate attenuates the development of microsphere embolism-induced cerebral infarction and improves microsphere-induced impairment of the mitochondrial tricarboxylic acid cycle. The observed effects provided evidence for a possible site of action of the agent on ischemic brain energy metabolism.

Animals↗
PubMed1982

The preparation of dry, monodisperse microspheres of [99mTc]albumin for lung ventilation imaging.

2 micron microspheres of albumin were prepared and labelled with 99mTc according to published methods. However, when the labelling technique was repeated without the inclusion of microspheres, apparent labelling, which was attributed to the formation of a 99mTc tin colloid, was still observed. It was not possible to identify 99mTc tin colloid in the presence of 99mTc microspheres. To establish conditions under which there was no 99mTc tin colloid formation, labelling, with and without microspheres, was studied at low pH for a range of SnCl2 X 2H2O concentrations. A "kit" containing 0.4 mg of microspheres and 1 microgram of SnCl2 X 2H2O in 1 ml of 25 mM HCl gave optimum labelling of 88.3% (SD 3.9, n = 38). Unlabelled and labelled kits were stable for 1 and 3 h respectively. Before administration, the microspheres were resuspended in ethanol, in which they were stable for 6 h. None of the preparations contained 99mTc tin colloid.

Drug Stability↗
PubMed1983

Polyacrolein microspheres as immunoreagents.

Polyacrolein microspheres were prepared by radiation polymerization of acrolein in the absence of emulsifying or stabilizing agent. The microspheres had functional surface aldehyde groups permitting covalent binding with antibody in 1 step. The particle size of the microspheres varied with polymerization conditions, especially irradiation temperature. The microsphere antibody conjugates obtained by binding immunoglobulins to polyacrolein microspheres were used to label cells. The reactivity of microsphere antibody conjugates was shown by specific aggregation by antigen.

Acrolein↗
PubMed1989

Development of a microsphere-based fluorescent immunoassay and its comparison to an enzyme immunoassay for the detection of antibodies to three antigen preparations from Candida albicans.

A sensitive assay for the simultaneous detection of multiple serum antibodies by flow cytometry was developed. Polystyrene microspheres of 5, 7 and 9.3 micron in diameter were used as solid supports for the attachment of three different antigen preparations from Candida albicans. These antigens were a whole cell extract; a cytoplasmic protein extract and a cell wall polysaccharide. Microsphere-associated fluorescence was quantitated by flow cytometry, with the different sized microspheres analyzed separately using electronic volume gating. This procedure allowed for different antigen-coated microspheres with discrete sizes to be analyzed independently for immunofluorescence. The assay detected antibody levels in human serum at dilutions up to 10(-6) and provided complete discrimination, using all three antigen preparations, between antibody levels seen in healthy subjects and those seen in patients suspected of having a systemic Candida infection. A standard enzyme immunoassay (EIA) failed to provide complete discrimination between healthy subjects and patient samples: at least 17% of patient values fell within the healthy subject range using all three antigen preparations. The microsphere assay which allowed for the simultaneous detection of multiple antibodies, has increased dynamic range over EIA and provides for better discrimination of patients from healthy subjects in comparison to EIA. Precise quantitation of antibodies is possible and the rapid analysis of thousands of microspheres markedly enhances the statistical accuracy of the assay. We suggest this assay is likely to have many other important applications in immunologic testing.

Antibodies, Fungal↗
PubMed1990

Microvascular hemodynamics in experimental arthritis: disparity between the distribution of microspheres and plasma flow in bone.

The microcirculation in normal and arthritic juxtaarticular bone was studied in 16 young dogs with carragheenan-induced arthritis of one knee. The regional blood flow was determined by the tissue uptake of intracardially injected 15-microns 141Ce-labeled microspheres, and the microvascular plasma volume was determined by the distribution space of circulating 125I-fibrinogen. Disparities between the distribution of plasma flow and microspheres, introduced by plasma skimming or nonentrapment of spheres in the intraosseous circulation, were estimated by 59Fe-transferrin, a third intravascular tracer, injected as a bolus intracardially and trapped peripherally after 15 sec by prompt circulatory arrest. The tissue uptake of the plasma flow tracer was compared to that of microspheres by the ratio between observed and expected activity of 59Fe-transferrin, the expected activity being calculated from the microsphere distribution. The transferrin and microsphere uptake agreed well in patella, marginal epiphyseal bone, and cortical bone, whereas observed activity of transferrin was twice the expected in central epiphyseal bone, three times higher in marrow, and up to eightfold higher in metaphyses adjacent to growth plates. This discrepancy was significantly greater in arthritic bone when the metaphyses were examined in toto. The microsphere method thus appears to underestimate blood flow to cancellous bone and marrow due to uneven distribution of plasma and formed elements from profound plasma skimming and perhaps also by AV shunting.

Animals↗
PubMed1993

Ultrasound scattering properties of Albunex microspheres.

Albunex is an ultrasound contrast agent used in echocardiography and in other areas, it consists of microspheres of which more than 95% have a diameter in the range 1-10 microns. The scattering properties of this agent as functions of ultrasound frequency and microsphere diameter and concentration are investigated. A model of the Albunex microspheres has been previously described, considering the individual microspheres as air bubbles surrounded by a thin elastic shell. In the present study this model is extended by including into it the internal friction in the shell when the microsphere vibrates. Acoustic scattering and transmission are measured in the frequency range from 700 kHz to 12.5 MHz. The measured transmitted power is used to estimate the two parameters in the theoretical model: the shell elasticity parameter, Sp and the shell friction, Sf. Introduction of the shell friction into the model improves the agreement between theory and measurements. For the scattered power, differences between measured and calculated values lie within 3 dB. It is concluded that for the frequencies 2.5 and 5 MHz, microspheres with a diameter between 5 and 12 microns are preferred as these deliver the most significant contribution to the total scattered power and cause relatively little attenuation.

Albumins↗
PubMed1987

Treatment of a syngeneic rat tumor with magnetically responsive albumin microspheres labeled with doxorubicin or protein A.

The tumoricidal activity of magnetically responsive albumin microspheres tagged with either doxorubicin or Staphylococcal protein A was tested against an induced mammary adenocarcinoma, 13762, implanted subcutaneously in the tail of female Fischer-344 rats. Magnetically responsive albumin microspheres containing Fe3O4 particles were prepared by an emulsion polymerization method incorporating either doxorubicin or protein A into the albumin matrix. Microspheres were produced with an average diameter of 1 micron (0.2 to 1.5 micron) in a concentration of 10(9) microspheres/mg. Microspheres were injected either directly into the tail artery and localized to the implanted tumor using a permanent bipolar adjustable gap magnet with a field strength of 8000 Oe, or directly into the femoral vein with no magnetic localization. Control groups consisted of animals treated with intravenously or intraarterially administered microspheres containing no active agent, and a no-treatment group. Survival was significantly greater in both the doxorubicin- and protein A-treated animals than in the control groups. First appearance of local metastases was prolonged in only the intraarterial magnetically localized doxorubicin-treated group of animals. Tumor growth rate was significantly depressed in both intraarterially magnetically localized treatment groups when compared to intravenously administered nonlocalized treatment groups. Magnetically responsive albumin microspheres appear to be an effective delivery system for cytotoxic agents and biologic response modifiers. Significant tumoricidal activity can be produced with a one-time administration of these agents utilizing this drug delivery system.

Adenocarcinoma↗
PubMed1988

Effect of the size and surface charge of polymer microspheres on their phagocytosis by macrophage.

Polystyrene and phenylated polyacrolein microspheres of different diameters, as well as modified cellulose microspheres with different surface charges, were prepared in order to study the size and surface charge effect on their phagocytosis by mouse peritoneal macrophages. It was found that the maximal phagocytosis of polystyrene and phenylated polyacrolein microspheres took place when their size was in the range 1.0-2.0 microns. Microspheres with hydrophobic surfaces were more readily phagocytosed than those with hydrophilic surfaces. There was no significant difference in phagocytosis between cationic and the anionic surfaces when compared at a zeta potential of the same absolute value. The least phagocytosis was observed for cellulose microspheres with non-ionic hydrophilic surfaces. Addition of fetal calf serum to the culture medium resulted in decrease in phagocytosis for all microspheres.

Acrolein↗
PubMed1994

Preparation and characterization of albumin-heparin microspheres.

Albumin-heparin microspheres were prepared by a two-step process which involved the preparation of a soluble albumin-heparin conjugate, followed by formation of microspheres from this conjugate or by a double cross-linking technique involving both coupling of soluble albumin and heparin and microsphere stabilization in one step. The first technique was superior since it allowed better control over the composition and the homogeneity of the microspheres. Microspheres could be prepared with a diameter of 5-35 microns. The size could be controlled by adjusting the emulsification conditions. The degree of swelling of the microspheres was sensitive to external stimuli, and increased with increasing pH and decreasing ionic strength of the medium.

Albumins↗
PubMed1987

Regional hyperthermia combined with blockade of the hepatic arterial blood flow by degradable starch microspheres in pigs.

The benefit of hepatic arterial microembolization by degradable starch microspheres (DSM) was investigated in regional hyperthermia of the liver. Hyperthermia with and without blood flow blockade of the hepatic artery using degradable starch microspheres was performed on six pigs. Heat was given for 30 min in each treatment by 8 MHz radiofrequency capacitive heating equipment. To maintain blood flow blockade during hyperthermia, 10 mg/kg of degradable starch microspheres was administered into the hepatic artery as an initial dose and 5 mg/kg of the drug was added periodically under the measurement of hepatic arterial blood flow by an electromagnetic flowmeter. To evaluate the effect of degradable starch microspheres, the temperature increase in the liver and rectum was compared between the treatment with and without DSM. All pigs showed a larger increase in intrahepatic temperature when heated in combination with degradable starch microspheres than without. On the other hand, temperature increase in the rectum as a result of hyperthermia to the liver was suppressed by DSM as compared with hyperthermia alone. These results indicate that hepatic arterial embolization by degradable starch microspheres potentiates radiofrequency capacitive heating of the liver. Although this study was not made with liver tumors, regional hyperthermia may be effective in the control of liver tumors when heat is given after the blockade of the hepatic artery by DSM.

Animals↗
PubMed1988

Cell-sized microspheres in the hippocampus show cleavage planes and passive displacement.

Fluorescent microspheres (6 or 10 micron in average diameter) dispersed in fluid were injected into the hippocampus, neocortex or striatum. In the hippocampus the microspheres were located in one of three cleavage planes. Cleavage planes were found above the alveus, in the obliterated hippocampal fissure and on the hilar side of the dentate granule cells. When the injections were made into the infragranular cleavage plane, the adjacent granule cells degenerated, presumably because the cavity separated the axons from their cell bodies. Some microspheres were passively displaced beyond the boundary of the injection site. If the microspheres gained access to the subarachnoid space, some of the displaced microspheres were found at considerable distances from the injection site. There were no cleavage planes in neocortex or striatum but there was passive displacement of microspheres into the host parenchyma. In cell suspension transplants, the passive displacement of cells should be distinguished from migration and the possibility of a widespread distribution of transplanted cells needs to be considered.

Animals↗
PubMed1993

Intracoronary air-filled albumin microspheres for myocardial blood flow measurement.

OBJECTIVES: The aim of this study was to explore the possibility of quantifying coronary blood flow by myocardial contrast echocardiography with air-filled serum albumin microspheres (Albunex). BACKGROUND: Air-filled albumin microspheres have been proposed as an intravascular tracer for the study of myocardial perfusion by contrast echocardiography. METHODS: In six anesthetized open chest dogs, the left circumflex coronary artery was cannulated and perfused by a roller pump with blood from the femoral artery. Both air-filled albumin microspheres (0.4 ml, 2 x 10(8) spheres/ml) and technetium-99m-labeled albumin were injected as a bolus into the coronary cannula at baseline and after treatment with dipyridamole (0.56 mg/kg body weight intravenously for 4 min). Two-dimensional echographic images of the left ventricular short axis were digitized to generate myocardial time-intensity curves; myocardial radioactivity was measured by an external detector to generate radionuclide time-activity curves. RESULTS: After dipyridamole, left circumflex coronary artery blood flow (as measured by both the pump and an electromagnetic flow meter) significantly increased (from 1.06 +/- 0.28 to 3.61 +/- 1.43 ml/min per g of myocardium). Peak intensity and rise time of contrast echo curves were able to differentiate baseline myocardial perfusion from coronary hyperemia but did not show any significant correlation with coronary blood flow. A weak inverse correlation with coronary blood flow was provided by myocardial mean transit time of air-filled albumin microspheres (r = 0.33). Conversely, a close inverse correlation with coronary blood flow was obtained by myocardial mean transit time of technetium-99m-labeled albumin (r = 0.95). Myocardial transit time of air-filled albumin microspheres (1.95 +/- 0.60 s) was also markedly shorter than that of labeled albumin (5.35 +/- 3.43 s, p < 0.001) and the measurements were less reproducible. CONCLUSIONS: In this experimental study, coronary blood flow was not adequately quantified by myocardial contrast echocardiography with intracoronary injection of air-filled albumin microspheres.

Albumins↗
PubMed2004

A protein delivery system: biodegradable alginate-chitosan-poly(lactic-co-glycolic acid) composite microspheres.

In the present study we developed alginate-chitosan-poly(lactic-co-glycolic acid) (PLGA) composite microspheres to elevate protein entrapment efficiency and decrease its burst release. Bovine serum albumin (BSA), which used as the model protein, was entrapped into the alginate microcapsules by a modified emulsification method in an isopropyl alcohol-washed way. The rapid drug releases were sustained by chitosan coating. To obtain the desired release properties, the alginate-chitosan microcapsules were further incorporated in the PLGA to form the composite microspheres. The average diameter of the composite microcapsules was 31+/-9microm and the encapsulation efficiency was 81-87%, while that of conventional PLGA microspheres was just 61-65%. Furthermore, the burst releases at 1h of BSA entrapped in composite microspheres which containing PLGA (50:50) and PLGA (70:30) decreased to 24% and 8% in PBS, and further decreased to 5% and 2% in saline. On the contrary, the burst releases of conventional PLGA microspheres were 48% and 52% in PBS, respectively. Moreover, the release profiles could be manipulated by regulating the ratios of poly(lactic acid) to poly(glycolic acid) in the composite microspheres.

Alginates↗
PubMed2004

Calcium phosphate-alginate microspheres as enzyme delivery matrices.

The present study concerns the preparation and initial characterisation of novel calcium titanium phosphate-alginate (CTP-alginate) and hydroxyapatite-alginate (HAp-alginate) microspheres, which are intended to be used as enzyme delivery matrices and bone regeneration templates. Microspheres were prepared using different concentrations of polymer solution (1% and 3% w/v) and different ceramic-to-polymer solution ratios (0.1, 0.2 and 0.4 w/w). Ceramic powders were characterised using X-ray diffraction, laser granulometry, Brunauer, Emmel and Teller (BET) method for the determination of surface area, zeta potential and Fourier transform infrared spectroscopy (FT-IR). Alginate was characterised using high performance size exclusion chromatography. The methodology followed in this investigation enabled the preparation of homogeneous microspheres with a uniform size. Studies on the immobilisation and release of the therapeutic enzyme glucocerebrosidase, employed in the treatment of Gaucher disease, were also performed. The enzyme was incorporated into the ceramic-alginate matrix before gel formation in two different ways: pre-adsorbed onto the ceramic particles or dispersed in the polymeric matrix. The two strategies resulted in distinct release profiles. Slow release was obtained after adsorption of the enzyme to the ceramic powders, prior to preparation of the microspheres. An initial fast release was achieved when the enzyme and the ceramic particles were dispersed in the alginate solution before producing the microspheres. The latter profile is very similar to that of alginate microspheres. The different patterns of enzyme release increase the range of possible applications of the system investigated in this work.

Absorption↗
PubMed2004

Poly(D,L lactic-co-glycolic acid) microspheres as biodegradable microcarriers for pluripotent stem cells.

The pluripotent nature and proliferative capacity of embryonic stem cells makes them an attractive cell source for tissue engineering and regeneration. In our study we investigated the use of poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres as biodegradable microcarriers of pluripotent cells and as delivery systems of bioactive factors, which influence cell differentiation. The pluripotent P19 embryonal carcinoma cell line was used as a model to study cell attachment, growth and differentiation of pluripotent stem cells on PLGA microspheres. Retinoic acid (RA) was encapsulated in the PLGA microcarriers to influence cell differentiation-more specifically, to induce P19 cell differentiation into neurons. The results revealed that P19 cells attach and grow on the surface of the RA loaded PLGA microspheres. Moreover, the RA loaded PLGA microspheres were shown to be as effective as soluble RA at inducing P19 cell differentiation into neurons. Hence, the results of these ex vivo studies clearly demonstrate the capacity of PLGA microspheres to serve a dual role as both delivery systems of bioactive factors and as scaffolds for pluripotent cells. More importantly, our study demonstrates the potential use of PLGA microspheres as transplantation matrices of pluripotent stem cells for tissue engineering and regeneration.

Absorbable Implants↗
PubMed2006

The brain tissue response to biodegradable poly(methylidene malonate 2.1.2)-based microspheres in the rat.

The aim of this study was to follow the in vivo biodegradation as well as to appreciate the brain tissue response to poly(methylidene malonate 2.1.2) (PMM 2.1.2)-based microspheres implanted into the rat brain. Ninety-three adult Sprague-Dawley female rats were engaged in the study in which 54 underwent stereotactic implantation of blank gamma-sterilized PMM 2.1.2-based microspheres, prepared by an emulsion-extraction method. Twelve rats were implanted with the same 5-fluorouracil (5-FU)-loaded microspheres. Seventeen controls received the suspension medium alone (carboxymethylcellulose aqueous solution). The animals were sacrificed on post-operative days 1, 2, 8 and months 1, 2, 3, 6, 9, 12, 15 and 18. The brains were dissected, frozen, cut in a freezing microtome, and the slides were processed for immunohistological evaluation and scanning electron microscopy. During the first few days, the moderate inflammatory response to blank or loaded PMM 2.1.2 microspheres was largely a consequence of the mechanical trauma that occurs during surgery. The macrophagous-microglial reaction was similar to the one typically found following any damage in the CNS. There were also no differences in GFAP reactivity between the implanted animals and the controls. Blank microspheres began to degrade between 3 and 6 months, while 5-FU microspheres degraded between 8 days and 1 month. The polymer degradation generated in both cases a pronounced inflammatory and immunological reaction, leading to an important cell loss, a cerebral atrophy and to the death of several animals. PMM 2.1.2 was thus shown to be inadequate for intracerebral drug delivery.

Absorbable Implants↗
PubMed2005

Effects of pulmonary surfactant system on rifampicin release from rifampicin-loaded PLGA microspheres.

Pulmonary surfactants little affected the release ratio of rifampicin from rifampicin-loaded poly(lactide-co-glycolide) PLGA microspheres. The release ratio of rifampicin was depending on pH of pulmonary surfactant solution, showing that rifampicin-loaded PLGA microspheres have an ideal property to deliver rifampicin into alveolar macrophages inside of which Mycobacterium tuberculosis bacilli reside and to kill them. That is, little amount of rifampicin is released in alveolar lining liquid before the microspheres are phagocytosed by alveolar macrophages, then rifampicin is released in phagosome or cytoplasm, but little amount of rifampicin is released in lysosome of alveolar macrophages after the microspheres are internalized. Pulmonary surfactants also little affected the changes in molecular weight of residual PLGA during its hydrolytic degradation process. From the electrophoretic mobility measurements of PLGA microspheres, it was shown that pulmonary surfactants changed the surface charge density of PLGA microspheres by adsorbing on their surfaces.

Lactic Acid↗