Plastic Microspheres Research Articles

Experimental research on establishing chronic ischemic heart failure model of minipig with intracoronary perfusion of plastic microspheres by catheterization

To establish a stable chronic ischemic heart failure (CIHF) model of minipig caused by gradual myocardial ischemia and necrosis that was achieved with repetitive microspheres perfusion in left anterior descending artery (LAD). A total of fifteen Wuzhishan minipigs original in Hainan China (8 to 11 months old with body weight of 20 to 30 kg) were used. The 4F angiographic catheter was superselectively engaged in LAD, and 1 ml of suspending plastic microspheres fluid were given repeatedly at ten-minute intervals, which include microspheres 1.0 x 10(5)/ml, until LVEDP raising and maintaining from 15 mm Hg to 18 mm Hg and TIMI flow was less than or equal to grade 2. Electrocardiography, hemodynamic parameters, CK-MB and cTnT were monitored during the procedure. LVEF was repeatedly measured with ultracardiography at 10 d, 20 d, 30 d, 40 d, 50 d, 60 d after establishing chronic ischemic heart failure model. Meanwhile, hemodynamic indices including mRAP, mRVP, mPAP, PCWP and CO (thermo-dilution method) were measured before and two months after procedure. The success rate, stability and repetition of chronic ischemic heart failure model were identified and evaluated. Finally, myocardial infarcted area was measured and myocardial pathologic examination was investigated. Eleven minipigs survived two months after procedure. There were ten minipigs accorded with the criteria (LVEDP > 18 mm Hg CO reduced by 30%) of the CIHF model and the success rate was 66.7% with a mean of 3.2 +/- 0.9 times of microspheres injections and total doses of (3.2 +/- 0.9) x 10(5) microspheres. This resulted in 38.5% reduction in LVEF, 197.8% elevation in LVEDP and 46.8% declining in CO from baseline values (P < 0.01), while mRAP, mRVP, mPAP and PCWP increased significantly as compared with those before procedure. Cross myocardium pathology showed the ratio of necrosis area to left ventricle (LV) area was 25.4% - 34.9% (mean 28.6%) and light microscopy examination of LV myocardium revealed that intravascular semitransparent plastic microspheres distributed throughout subendocardium of left ventricular anterior and apical parts, with more numerous focal myofiber necrosis, which characterized by pathologic founding of ischemic necrosis of myocardium with fibre proliferation. A stable CIHF model could be established in Chinese Wuzhishan minipigs with intra-coronary microspheres perfusion via superselectively engaging in LAD, which was prior to those of drug-induced, tachycardia-pacing induced or coronary artery ligation-induced, and had the advantages of stability, closed chest, mild trauma higher success rate and easy for repetition. It might be suitable for using the research of CIHF as large reliable experimental animal model.

Shock melting of a two-dimensional complex (dusty) plasma.

Shock waves with a linear front were experimentally studied in a monolayer hexagonal Yukawa lattice which was formed from charged monodisperse plastic microspheres and levitated in the sheath of a radio-frequency discharge. It was found that the shock can cause phase transitions from a crystalline to gaslike and liquidlike states. Melting occurred in two stages. First, the lattice was compressed in the direction of shock propagation and second, the particle velocities were randomized a few lattice lines downstream. The Mach number of the shock reached 2.7.

India: Mahesh — plastic microspheres as functional fillers

India: Mahesh — plastic microspheres as functional fillers

Ion drag and thermophoretic forces acting on free falling charged particles in an rf-driven complex plasma

Monodisperse plastic microspheres have been dropped through a long radio-frequency discharge column. The trajectories of the falling particles have been measured. It was observed that the particles are driven out of the plasma. From the trajectory analysis and plasma measurements the forces on the particles have been derived. Special attention has been paid to the thermophoresis and ion drag forces which are also considered to be responsible for the void formation in microgravity experiments. Two experimental situations have been considered here: first a plasma characterized by its natural symmetric electric potential and temperature distribution and second, a plasma with an asymmetric temperature and electric potential profile. For both cases a good agreement has been found between the measured “trajectory force” obtained from the particle trajectory analysis and the sum of the ion drag, thermophoretic and electric field force.

Dissipative longitudinal solitons in a two-dimensional strongly coupled complex (dusty) plasma.

Solitary waves are experimentally studied in a monolayer hexagonal dust lattice which is formed from monodisperse plastic microspheres and levitated in the sheath of an rf discharge. It is found that the product of the soliton amplitude and the square of the soliton width is constant as the soliton propagates. The analytical theory describing the experiment is based on the equations of motion written for a linear chain. It takes into account damping, dispersion, and nonlinearity. The numerical simulation of a linear chain produces double solitons like those observed in the experiment.

Role of particle cavitation in rubber-toughened epoxies: II. Inter-particle distance

Two types of conventional rubber modifiers and a series of hollow plastic micro-spheres were employed as toughening agents in a diglycidyl ether of bisphenol A (DGEBA) epoxy in Part I (Bagheri R, Pearson RA. Polymer 1996;37:4529) of this study. It was found that the rubber modifiers with different cavitation resistance and hollow plastic micro-spheres which act as pre-existing microvoids toughen epoxies in the same manner. The current study is composed to further examine the previous results in terms of the role inter-particle distance in rubber/microvoid toughened epoxies. It is shown that the fracture toughness in toughened blends goes through a ductile-to-brittle transition with inter-particle distance. The source of this transition is found to be a stress state change provided by voided particles. The ligament between neighboring particles, thus, experiences a transition from plane strain to plane stress state by decreasing the inter-particle distance. Interestingly, it is shown that the transition in toughened blends does not occur at a specific inter-particle distance as frequently proposed in literature, but varies with the size of the modifier. Therefore, there is an influence of particle size on yielding of the toughened epoxies that is responsible for the shift in transition.

Resonator frequency shift due to ultrasonically induced microparticle migration in an aqueous suspension: Observations and model for the maximum frequency shift

Aqueous suspensions of plastic and hollow-glass microspheres are subjected to the radiation pressure of an ultrasonic standing wave. It is well known that the particles are attracted to the pressure nodes of the standing wave for the particle and host properties considered. We demonstrated that the radiation pressure induced migration of particles leads to a significant shift in the resonant frequency of a suitably designed chamber. This shift is easily resolved with a phase-locked loop even if the particle volume fraction is as small as 0.001. For sufficient ultrasonic amplitudes, the shift is found to saturate at a limiting value. To approximate the limiting frequency shift, the principle of adiabatic invariance is first applied to the case of a single compressible sphere in a standing wave and then superposition is used to give the collective shift for the suspension. The measured limiting shifts are typically within 25% of the calculated value and this method may have application to the characterization of dilute suspensions since the shift is proportional to the volume fraction and to a material contrast factor. The applicability of adiabatic invariance is confirmed by comparing frequency shifts for certain cases of idealized particle spatial distributions with results based on transfer matrix eigenvalues combined with an effective-medium approximation.

Competing effects of collisional ionization and radiative cooling in inertially confined plasmas

We describe an experimental investigation, a detailed analysis of the Ar XVII ${1s}^{2}{}^{1}S--1s3p{}^{1}P$ (He\ensuremath{\beta}) line shape formed in a high-energy-density implosion, and report on one-dimensional radiation-hydrodynamics simulation of the implosion. In this experiment trace quantities of argon are doped into a lower-$Z$ gas-filled core of a plastic microsphere. The dopant level is controlled to ensure that the He\ensuremath{\beta} transition is optically thin and easily observable. Then the observed line shape is used to derive electron temperatures ${(T}_{e})$ and electron densities ${(n}_{e}).$ The high-energy density plasma, with ${T}_{e}$ approaching 1 keV and ${n}_{e}{=10}^{24}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3},$ is created by placing the microsphere in a gold cylindrical enclosure, the interior of which is directly irradiated by a high-energy laser; the x rays produced by this laser-gold interaction indirectly implode the microsphere. Central to the interpretation of the hydrodynamics of the implosions is the characterization and understanding of the formation of these plasmas. To develop an understanding of the plasma and its temporal evolution, time-resolved ${T}_{e}$ and ${n}_{e}$ measurements are extracted using techniques that are independent of the plasma hydrodynamics. Comparing spectroscopic diagnostics with measurements derived from other diagnostic methods, we find the spectroscopic measurements to be reliable and further we find that the experiment-to-experiment comparison shows that these implosions are reproducible.

Perfusion-induced changes in cardiac contractility depend on capillary perfusion.

The perfusion-induced increase in cardiac contractility (Gregg phenomenon) is especially found in heart preparations that lack adequate coronary autoregulation and thus protection of changes in capillary pressure. We determined in the isolated perfused papillary muscle of the rat whether cardiac muscle contractility is related to capillary perfusion. Oxygen availability of this muscle is independent of internal perfusion, and perfusion may be varied or even stopped without loss of function. Muscles contracted isometrically at 27 degrees C (n = 7). During the control state stepwise increases in perfusion pressure resulted in all muscles in a significant increase in active tension. Muscle diameter always increased with increased perfusion pressure, but muscle segment length was unaffected. Capillary perfusion was then obstructed by plastic microspheres (15 microns). Flow, at a perfusion pressure of 66.6 +/- 26.2 cmH2O, reduced from 17.6 +/- 5.4 microliters/min in the control state to 3.2 +/- 1.3 microliters/min after microspheres. Active tension developed by the muscle in the unperfused condition before microspheres and after microspheres did not differ significantly (-12.8 +/- 29.4% change). After microspheres similar perfusion pressure steps as in control never resulted in an increase in active tension. Even at the two highest perfusion pressures (89.1 +/- 28.4 and 106.5 +/- 31.7 cmH2O) that were applied a significant decrease in active tension was found. We conclude that the Gregg phenomenon is related to capillary perfusion.

Cardiac secretion of atrial and brain natriuretic peptides in acuteischaemic heart failure in pigs: effect of angiotensin II receptor antagonism

In a model of acute ischaemic left ventricular failure in pigs, we compared the plasma levels and cardiac secretion of the three atrial peptides, atrial natriuretic factor (ANF), N-terminal proatrial natriuretic factor (N-terminal proANF) and brain natriuretic peptide (BNP). Acute ischaemic left ventricular failure was induced by embolization of the left coronary artery with plastic microspheres. Thereafter, treatment was given by an intravenous injection of the angiotensin II receptor (AT1) antagonist losartan. Effects of failure induction and treatment were documented by measurement of haemodynamic parameters and plasma concentrations of catecholamines, plasma renin activity, angiotensin II and aldosterone. Acute left ventricular failure was accompanied by significant increases in cardiac secretion and plasma levels of all three atrial peptides, which was considerably more pronounced for ANF and N-terminal proANF than for BNP. Treatment with losartan resulted in significant decreases in plasma ANF and N-terminal proANF, whereas BNP did not change. These findings indicate that ANF and N-terminal proANF may be better suited than BNP as markers of cardiac preload during the development and treatment of acute heart failure.

Development of moulded pulp materials for the packaging of electronic equipment

A new shredded pulp–plastic microsphere composite with modified starch binder which is applicable to the packaging of electronic equipment has been developed. This composite with a 3 wt% microsphere content has almost the same compressive stress at 50% compressive strain as that of (poly)styrene foam, which has a specific gravity of 0.025. A moulded sample of the above composites can be released from a mould after 1.5 minutes of steam heating, the same cycle time as that of styrene foam. © 1997 John Wiley & Sons, Ltd.

使用材料および配合が吹付けコンクリートの品質に及ぼす影響

The quality of shotcrete is lower than that of cast-in-place concrete because of its materials used and its construction process. Objectives of this study are to improve several properties of shotcrete and to enable us to manufacture high-quality shotcrete. The results obtained within the scope of this study may be summarized as follows :High-quality shotcrete can be economically manufactured by using a water reducing agent, not increasing unit water content, because a dosage of a set accelerating agent can be decreased. Compressive strength and the resistance to carbonation of shotcrete can be improved by using a set accelerating agent whose principal ingredient is calcium sulfoaluminate. The resistance to freezing and thawing of shotcrete can also be improved by incorporating plastic hollow microspheres that act as an air entraining agent, however the shotcrete does not necessarily possess sufficient durability due to the existence of large pores like honeycomb induced by shotcreting.

The AMPA Antagonist LY293558 Improves Functional Neurological Outcome following Reversible Spinal Cord Ischemia in Rabbits

Glutamate (Glu) neurotoxicity is an important element of a number of neurological disorders including central nervous system (CNS) ischemia. We evaluated the effects of the novel AMPA Glu antagonist LY293558 on functional neurological outcome in two rabbit stroke models. In the reversible spinal cord ischemia model, ischemia of the caudal lumbar spinal cord was produced by temporary occlusion of the abdominal aorta. LY293558 was administered 5 min after recirculation as a 16 mg/kg i.v. bolus followed by 2.2 mg/kg infused over 1 h. Control animals received saline. LY293558 significantly increased the duration of ischemia required to produce paraplegia, from 30.5 +/- 15.8 min (mean +/- SD) controls to 50.1 +/- 11.5 in treated animals (p < 0.01). In an irreversible model of cerebral ischemia, 50 microns plastic microspheres were injected into the carotid artery and lodged in the cerebral microvasculature. LY293558 did not significantly reduce neurological damage in this model. These data suggest that LY293558 may have therapeutic benefit following some types of ischemic injury.

Spectroscopy of compressed high energy density matter.

A theoretical and experimental time-resolved spectroscopic investigation of indirectly driven microsphere implosions is described. The plasma dynamics is studied for several fill gases with a trace amount of argon. Through an analysis of the line profile of Ar XVII 1${\mathit{s}}^{2}$--1s3p${\mathrm{}}^{1}$P, with a line center position at ${\mathit{E}}_{\mathrm{\ensuremath{\upsilon}}}$=3684 eV, the evolution of the plasma density and temperature as a function of fill gas is examined. The theoretical calculations are performed with a fast computer code, which has been previously benchmarked through the analysis of specific complex ionic spectra in hot dense plasmas. The experimental aspect of the work utilizes the Lawrence Livermore National Laboratory Nova 10 beam laser facility to indirectly drive the implosion of a gas filled plastic microsphere contained in a gold Holhraum target. The dynamical density measurement is derived from a streak camera linewidth measurement and a comparison with the computed profile. Calculations demonstrate that in certain cases there can be a substantial ion dynamics effect on the line shape. The frequency fluctuation model is used to compute the effect on the line profile and a comparison with the experimental spectra provides evidence that ion dynamics may be affecting the line shape. This study provides a method for obtaining an improved understanding of the basic processes dominating the underlying plasma physics of matter compressed to a state of high energy density. \textcopyright{} 1996 The American Physical Society.

Coronary arteriography with an oxygenated contrast medium: Cardiac effects in dogs with and without acute ischemic heart failure

We investigated the possible cardiac effects of oxygen addition to contrast media (CM) during coronary arteriography in dogs that did and did not have ischemic heart failure. Acute ischemic heart failure was induced by injecting small plastic microspheres into the left coronary artery of 18 dogs. Hemodynamic and electrophysiologic measurements were performed during a single injection before and during heart failure and during a single injection and five rapidly repeated CM injections during heart failure. Iohexol supplemented with electrolytes (iohexol + electrolytes = IPE), oxygenated IPE (IPE+O), Ringer acetate, and oxygenated Ringer acetate were injected into the left coronary artery. Single injections of IPE and IPE+O induced small hemodynamic and electrophysiologic effects. However, repeated injections of IPE and IPE+O increased left ventricular inotropy (maximum value of the first derivative of the left ventricular pressure) by 36% and 39%, reduced heart rate by 7% (for both), and lengthened QTc time (corrected QT interval) by 39 and 38 msec, respectively. A comparison of IPE and IPE+O revealed no statistically significant differences. Although electrolyte addition to nonionic CM may reduce the risk of cardiac complications during coronary arteriography, oxygenation does not seem to significantly further reduce this risk.

Additive hemodynamic and electrophysiologic effects of repeated intracoronary contrast media injections in dogs with heart failure

We investigated the cardiac effects of single and repeated contrast media injections in dogs with heart failure and compared the effects of iohexol with iohexol supplemented with electrolytes (30 mmol/l NaCl, 0.15 mmol/l CaCl2, 0.9 mmol/l KCl, and 0.1 mmol/l MgCl2; iohexol + electrolytes [IPE]). Although it has a higher osmolality than iohexol, IPE appears to be safer when injected through a wedged catheter. Acute ischemic heart failure was induced by injections of small plastic microspheres into the left coronary artery of 16 anesthetized dogs. Iohexol, IPE, and Ringer acetate were injected into the left coronary artery either as a 5-ml single injection or repeatedly five times, once every 10th second. Single injections of iohexol and IPE induced small hemodynamic and electrophysiologic effects. However, repeated injections of iohexol and IPE increased the maximum rate of isovolumetric contraction by 46% and 36%, reduced heart rate by 8% and 7%, and lengthened QTc (the Q-T interval corrected for heart rate) time by 44 and 39 msec, respectively. No statistically significant differences were found in a comparison of IPE and iohexol. During heart failure, repeated injections of iohexol and IPE induced similar additive hemodynamic and electrophysiologic effects without inducing arrhythmias or serious hemodynamic changes.

The use of microvoids to toughen polymers

The concept of microvoid toughening of polymers has been proposed by several investigators. This investigation illustrates the similarities between the function of rubber particles in rubber-toughened plastics with that of microvoids. While previous researchers created microvoids within polymeric materials by means of non-adhering particles, our novel approach is based on using hollow plastic micro-spheres to generate holes. An epoxy polymer is used as a model polymer matrix. The results of this investigation show that hollow plastic particles toughen the epoxy resin in the same manner as rubber particles. Surprisingly, mechanical characterization of modified blends revealed that the use of hollow plastic micro-spheres provides greater yield strength than that of similar blends with equivalent rubber content.

The use of microvoids to toughen polymers

The concept of microvoid toughening of polymers has been proposed by several investigators. This investigation illustrates the similarities between the function of rubber particles in rubber-toughened plastics with that of microvoids. While previous researchers created microvoids within polymeric materials by means of non-adhering particles, our novel approach is based on using hollow plastic micro-spheres to generate holes. An epoxy polymer is used as a model polymer matrix. The results of this investigation show that hollow plastic particles toughen the epoxy resin in the same manner as rubber particles. Surprisingly, mechanical characterization of modified blends revealed that the use of hollow plastic micro-spheres provides greater yield strength than that of similar blends with equivalent rubber content.

Diaspirin cross-linked hemoglobin improves neurological outcome following reversible but not irreversible CNS ischemia in rabbits.

Hemodilution using modified hemoglobin solutions may reduce ischemic central nervous system injury. Purified diaspirin cross-linked hemoglobin (DCLHb) is a cell-free hemoglobin that is intramolecularly cross-linked between the two alpha subunits, resulting in enhanced oxygen offloading to tissues and increased half-life. In the present experiments, we evaluated the ability of DCLHb to reduce neurological damage in two rabbit stroke models. In a reversible spinal cord ischemia model, ischemia of the caudal lumbar spinal cord was produced by temporary occlusion of the abdominal aorta. In an irreversible model of cerebral ischemia, plastic microspheres (50 microns) were injected into the internal carotid artery and lodged in the cerebral microvasculature. DCLHb was administered 5 minutes after initiation of ischemia as either a 10-mL/kg infusion, 10-mL/kg exchange transfusion, or a 20-mL/kg infusion. Control animals received human serum albumin that was oncotically matched to the DCLHb. In the spinal cord model, DCLHb significantly increased the duration of ischemia required to produce permanent paralysis from 27.33 +/- 8.71 minutes (mean +/- SD) in controls to 42.59 +/- 10.10 minutes in the 10-mL/kg exchange transfusion group and to 40.82 +/- 18.16 minutes in the 20-mL/kg infusion condition (P < .05). DCLHb did not significantly reduce neurological damage in the microsphere embolization model. These data suggest that cross-linked hemoglobin reduces neurological damage after reversible central nervous system ischemia and that this is not attributable to hemodilution or hypervolemia only.

Histochemical demonstration of free radicals (H2O2) in ischemic brain edema and protective effects of human recombinant superoxide dismutase on ischemic neuronal damage.

A new histofluorescence method by HPAA (p-hydroxyphenyl acetic acid) for free radicals in the brain tissue was devised to study neuronal damage induced by ischemia. Cerebral ischemia was produced in rats by injection of plastic microspheres and arachidonic acid (AA) into the right carotid artery. The concentration of malondialdehyde (MDA; free radical) in cerebral cortex of aminotriazol (an H2O2-dependent inhibitor of catalase) treated rats 2 h after stroke was 6.33 times the level before infarction, while the concentration of MDA in h-r SOD (free radical-scavenging enzyme) treated rats 2 h after stroke was significantly lower than in untreated rats. The histochemical findings demonstrated marked H2O2 production around blood vessels occluded by microspheres in the cerebral cortex of the aminotriazole treated rats 2 h after stroke together with disruption of the BBB. Light microscopical findings demonstrated extensive edematous changes in the aminotriazole treated rats 2 h after stroke, while pathological damage in SOD treated rat brains was absent or minimal. We conclude that free radicals are formed during ischemia, and that AA appears to be a major source of activated oxygen radicals. The findings indicate that SOD is protective against ischemia-induced neuronal damage.