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At least 1,729 records · Page 96Linked to original sources
PubMed2005

Adsorption of poly(acrylic acid) onto the surface of titanium dioxide and the colloidal stability of aqueous suspension.

The adsorption of poly(acrylic acid) (PAA) in aqueous suspension onto the surface of TiO(2) nanoparticles was investigated. FTIR spectroscopic data provided evidence in support of hydrogen bonding and chemical interaction in the case of the PAA-TiO(2) system. Adsorption isotherms demonstrated that part of the PAA initially added to the suspension was adsorbed onto the TiO(2) surface, after which there was a gradual attainment of an adsorption plateau. The adsorption density of PAA was found to increase with an increase of PAA molecular weight, while it decreased with an increase of pH. The thickness of the PAA adsorption layer was calculated based on measurements of suspension viscosities in the absence and presence of PAA. It was shown that the thickness of the adsorption layer increased with the increase of pH, PAA molecular weight, and its concentration. The surface charge density, the diffuse charge density, and the zeta potential of TiO(2) varied distinctly after PAA adsorption. The shift of pH(iep) toward a lower pH value was observed in the presence of PAA. PAA was found to stabilize the suspension of TiO(2) nanoparticles through electrosteric repulsion. The influence of factors such as PAA molecular weight and its concentration on the colloidal stability of the aqueous suspension was also investigated.

Journal Article↗
PubMed2005

Assessing the effect of latex particle size and distribution on the rheological and adhesive properties of model waterborne acrylic pressure-sensitive adhesives films.

The adhesive and rheological properties of model acrylic pressure-sensitive adhesive (PSA) films prepared from high solid emulsions with different particle sizes and distributions have been investigated with a customized probe tack apparatus. For each emulsion, the monomer composition and gel content were kept constant but different average particle sizes and distributions were used. Adhesive films 100 microm thick were then prepared from these emulsions and their rheological properties in the linear regime and adhesive properties were systematically characterized. Surprisingly, both the rheological and adhesive properties were found to be very dependent on the initial latex particle size distribution. A series of experiments were carried out to assess the adhesive properties of films made from blends of small- and large-particle-size latexes. Using the probe tack test, a maximum in adhesion energy of the dry films was found for 60% of small particles in the blend, a composition clearly different from that giving a minimum viscosity of the latex implying that optimizing for properties may not be equivalent to optimizing for processing in these adhesive applications. Finally, the adhesive properties of two multimodal latexes with different particle size distributions were investigated. Both gave significantly higher adhesion energies and clear evidence of a fibrillar detachment process. This important result suggests that the spatial distribution of gel domains in the dry film and the molecular connectivity between those gel domains also play an important role in controlling its adhesive properties.

Journal Article↗
PubMed2005

Film formation from monodisperse acrylic lattices 1. Influence of concentration and layer thickness on particle ordering.

The influence of concentration and layer thickness on particle ordering in polymer latex films, both open and closed, has been studied by means of rheology, microscopy and turbidimetry. Monodisperse acrylic lattices were synthesized by semicontinuous emulsion polymerization. The lattices exhibited a distinct thixotropy above a certain concentration, which is attributed to crystallization. Microscopy revealed a three-layer structure and a dependence of crystal size and crystal packing on layer thickness and layer concentration. Turbidimetry (i.e., analysis of light transmission and interference) was used to study the progress of ordering in open and closed systems. In closed films crystallization proceeds faster at higher concentrations and in thinner films. Above a sufficiently high concentration no crystallization was observed. Furthermore, an induction time was found below certain concentrations. The drying of open latex films at temperatures below the minimum film formation temperature (MFFT) was shown to proceed through five distinct stages. The drying of open films at temperatures below the MFFT was studied by analysis of the turbidity of rewetted films. A more compact structure was found in thinner films. The structure in lattices is discussed as a result of long-range and short-range ordering.

Journal Article↗
PubMed2005

Preparation and properties of poly(acrylic acid) oligomer stabilized superparamagnetic ferrofluid.

Ferrofluids, which are stable dispersions of magnetic particles, behave as liquids that have strong magnetic properties. Nanoparticles of magnetite with a mean diameter of 10-15 nm, which are in the range of superparamagnetism, are usually prepared by the traditional method of co-precipitation from ferrous and ferric electrolyte solution. When diluted, the ferrofluid dispersions are not stable if anionic or cationic surfactants are used as the stabilizer. This work presents an efficient way to prepare a stable aqueous nanomagnetite dispersion. A stable ferrofluid containing Fe3O4 nanoparticles was synthesized via co-precipitation in the presence of poly(acrylic acid) oligomer. The mechanism, microstructure, and properties of the ferrofluid were investigated. The results indicate that the PAA oligomers promoted the nucleation and inhibited the growth of the magnetic iron oxide, and the average diameter of each individual Fe3O4 particle was smaller than 10 nm. In addition, the PAA oligomers provided both electrostatic and steric repulsion against particle aggregation, and the stability of dispersions could be controlled by adjusting the pH value of solution. A small amount of Fe2O3 was found in the nanoparticles but the superparamagnetic behavior of the nanoparticles was not affected.

Journal Article↗
PubMed2004

Single-piece hydrophobic acrylic intraocular lens explanted within the capsular bag: case report with clinicopathological correlation.

A 74-year-old woman had uneventful phacoemulsification with implantation of a single-piece hydrophobic acrylic intraocular lens (IOL) (SA30AL) in her left eye. Two weeks after the surgery, the patient presented for ophthalmological consultation reporting pseudophakic dysphotopsia, which she had subjectively noted since surgery. Explantation/exchange of the IOL was performed 3 months after the surgery. The IOL was strongly attached to the capsule, which was fibrotic and contracted; explantation of the capsular bag complex in toto was done. To our knowledge, this is the first case of explantation of this IOL design with clinicopathological correlation.

Aged↗
PubMed2006

Postoperative opacification of the peripheral optic region and haptics of a hydrophilic acrylic intraocular lens: case report and clinicopathologic correlation.

We report the first case of opacification of the BioComFold 92S (Morcher GmbH) intraocular lens. The opacification pattern is unique, presenting mainly in the periphery of the optic and the haptics of the lens, leaving the central portion of the optic clear. The clinical course of this opacification pattern is not observed typically with other hydrophilic acrylic lens designs and requires further study.

Aged↗
PubMed2005

Acrylic bone cement: clinical development and current status in North America.

This article discusses issues surrounding acrylic bone cement and covers functional results, mechanism and definition of failure, design issues, wear and alternate bearing surfaces, revision, and evolution of concepts regarding infection, dislocation, thromboembolic issues, surgical approach, bone loss and bone grafts, and finally a couple of problems the author sees for the future.

Arthroplasty, Replacement↗
PubMed2005

The genesis and evolution of acrylic bone cement.

In 1957 John Chamley and I began to discuss the question of cement fixation of femoral prostheses. This was an independent development, because we had no knowledge of any other work in this area. Our conclusion was to grout in the prosthesis with a suitable cement. I selected a cold-curing acrylic denture repair material called Nu-Life as most appropriate. This material proved satisfactory in laboratory and clinical trials, and in 1958 Chamley undertook hip replacement using a cemented femoral prosthesis in six patients. This clinical success aroused great interest and some skepticism, because it was not always appreciated that Charnley and I had a substantial body of scientific data that justified this new approach to arthroplasty. Not surprisingly,the clinical aspects received most emphasis in the next decade. The scientific data were published mostly in the dental literature and were forgotten by the time cementation arthroplasty was generally accepted and so were rediscovered in subsequent years.

History, 20th Century↗
PubMed2006

Applications of a polymeric microgel template/ultrasonic degradation method: preparation of poly(sodium acrylate)/La(OH)3 nano-composites.

A polymeric microgel template/ultrasonic degradation method for the preparation of organic-inorganic nano-composites is proposed and successfully used in the preparation of poly(sodium acrylate) (PAANa) and lanthanium hydroxide nano-composites (PAANa/La(OH)(3)). The nano-composites were prepared via three steps. La(NO(3))(3) was trapped within the PAANa microgels first, and then the metal ions within the microgels were hydrolyzed by slow introduction of ammonia. Finally, the composites of the micro-particles were degraded by ultrasonic treatment. The product was characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The average diameter of the composites prepared in this way is about 50 nm and the size distribution of them is narrow. TGA analysis shows that the content of La(OH)(3) in the composites is about 20%.

Gels↗
PubMed1989

Effect of metal fillers on some physical properties of acrylic resin.

Thermal conductivity of poly(methylmethacrylate) is low. Fillers of silver, aluminum, and copper particles at 25% concentration, increased thermal conductivity of poly(methylmethacrylate) by 4.53, 4.43, and 4.04 times, respectively. Although the compressive strength of poly(methylmethacrylate) increased with the addition of these fillers, tensile strength decreased. Silver and copper particles made the material radiopaque. Advantages of metal-filled acrylic resin denture bases are described.

Aluminum↗
PubMed2002

Mechanical performance of acrylic bone cements containing different radiopacifying agents.

The effect that three different radiopacifying agents, two of them inorganic (BaSO4, ZrO2) and one organic (an iodine containing monomer, IHQM) have on the static and dynamic mechanical properties of acrylic bone cements was studied. Compressive and tensile strength, fracture toughness and fatigue crack propagation were evaluated. The effect of the inorganic fillers depends on their size and morphology. In relation to the radiolucent cement, the addition of zirconium dioxide improved significantly the tensile strength, the fracture toughness and the fatigue crack propagation resistance. In contrast, the addition of barium sulphate produced a decrease of the tensile strength, but did not affect the fracture toughness and improved the crack propagation resistance. When the iodine containing monomer was used, although the tensile strength and the fracture toughness increased, the fatigue crack propagation resistance remained as low as it was for the radiolucent cement.

Barium Sulfate↗
PubMed2003

Mechanical properties of oligomer-modified acrylic bone cement.

The aim of this study was to determine the mechanical properties of acrylic bone cement modified with an experimental oligomer filler, based on an amino acid of trans-4-hydroxy-L-proline synthesized in the laboratory. The test specimens were tested either dry, or after being stored in distilled water or in simulated body fluid (SBF) for 1 week and then tested in distilled water. The three-point bending test was used to measure the flexural strength and flexural modulus of the cement, and the compression tests were used to measure the compression strength and modulus. One test specimen from each group was examined under a scanning electron microscope (SEM) to determine the nature of the oligomer filler in the polymethylmethacrylate-polymethylacrylate copolymer-based (PMMA-PMA/PMMA) polymer blend. In dry conditions, the flexural strength of the test specimens tested in air was 66 MPa, and the compression strength was 93 GPa (p<0.001) for the plain bone cement. For the test specimens including 20 wt% of oligomer filler, the flexural strength was 37 MPa, and the compression strength was 102 MPa(p<0.001) in dry conditions. The storage in wet conditions (in distilled water and the SBF) decreased the flexural strength of the test specimens with 20 wt% of oligomer filler (p<0.001) by 60% and the flexural modulus by 44% compared to the plain bone cement specimens stored in the same conditions. The reduction in compression strength in wet conditions was 32%, and that of the compression modulus was 30% (p<0.001). No significant differences were found between test specimens stored in distilled water or SBF (ANOVA, p<0.001). In the SEM examinations, random voids were observed in the oligomer-PMMA-PMA/PMMA polymer blend after water or SBF storage. The results suggest that both water and SBF storage decrease the mechanical properties of the PMMA-PMA/PMMA bone cement modified with oligomer, while at the same time, there was porous formation in the bone cement structure.

Analysis of Variance↗
PubMedDate not supplied

Effect of fabrication pressure on the fatigue performance of Cemex XL acrylic bone cement.

During a cemented arthroplasty, the prepared polymerizing dough of acrylic bone cement is subjected to pressurization in a number of ways; first, during delivery into the freshly prepared bone bed, second, during packing in that bed (either digitally or with the aid of a mechanical device), and, third, during the insertion of the prosthesis. Only a few studies have reported on the influence of the level of pressurization experienced during these events (which, depending on the cementing technique used, has been put at between 8 and 273 kPa) on various properties of the cement. That was the focus of the present study, in which the fully reversed tension-compression (+/-15 MPa; 5 Hz) fatigue lives (expressed as number of cycles to fracture, N(f)) of rectangular cross-sectioned "dog-bone" specimens (Type V, per ASTM D 638) fabricated from Cemex XL cement, at pressure applied continuously to the cement dough during curing in the specimen mold, p=75,150, and 300 kPa, were determined. The N(f) results were analyzed using the linearized transformation of the three-parameter Weibull relationship to obtain estimates of the Weibull mean, N(WM), which was taken to be the index of fatigue performance of the specimen set. Over the range of p studied, N(WM) increased as p increased (for example, from 329,118 cycles when p was 75 kPa to 388,496 cycles when p was 300 kPa); however, the increase was not significant over any pair of p increment steps (Mann-Whitney U-test; alpha<0.05).

Compressive Strength↗
PubMed1999

Apparent fracture toughness of acrylic bone cement: effect of test specimen configuration and sterilization method.

The plane strain fracture toughness of Palacos R bone cement was determined using linear elastic fracture mechanics (LEFM) principles and three different test specimen configurations: single edge notched three-point (SENB), rectangular compact tension (RCT), and chevron notched short rod (CNSR). Another aspect of the study was an investigation of the effect of three methods used to sterilize the powder constituents of the cement-none, gamma irradiation and ethylene oxide--on the fracture toughness of the fully polymerized material. A detailed justification is provided for using LEFM. The fracture toughness results obtained using the CNSR specimens were, on average, 14 and 16% higher than those obtained using the SENB and RCT types, respectively. These differences are accounted for in terms of differences in four aspects of these specimen configuration (namely, residual stress effects, loading rate, material inhomogeneity, and the nature of the test). For a given specimen configuration, gamma irradiation produced a statistically significant decrease in fracture toughness which, it is suggested, is due to the concomitant depreciation in molecular weight. For a given cement type, there is no statistically significant difference in fracture toughness results obtained using SENB and RCT specimens. It is thus suggested that either of these configurations can be used to determine the fracture toughness of acrylic bone cement.

Bone Cements↗
PubMed1998

Stability of alpha-amylase immobilized on poly(methyl methacrylate-acrylic acid) microspheres.

Poly(methyl methacrylate-acrylic acid) microspheres were prepared and the acid groups were activated by using either carbodiimide (CDI) or thionyl chloride (SOCl2). alpha-Amylase was covalently bound on these activated microspheres. The properties of the immobilized enzyme were investigated and compared with those of the free enzyme. The relative activities were found to be 80.4 and 67.5% for carbodiimide and thionyl chloride bound enzymes, respectively. Maximum activities were obtained at lower pHs and higher temperatures upon immobilization compared to free enzyme. No change in Vmax and approximately 12-fold increase in K(m) were observed for immobilized enzymes. The enzyme activities, after storage for 1 month, were found to be 24.5 and 52.5% of the initial activity values for CDI and SOCl2 activated matrices, respectively. On the other hand the free enzyme lost its activity completely in 20 days. Immobilization, storage stability and repeated use capability experiments carried out in the presence of Ca2+ ions demonstrated higher stability, such as SOCl2 immobilized enzyme retained 83.7% and CDI immobilized enzyme retained 90.3% of the original activity of the enzyme. The immobilized enzymes that were used 20 times in 3 days in repeated batch experiments demonstrated that, in the absence of Ca2+ ions about 75% and in the presence of Ca2+ ions greater than 90% of the original enzyme activity was retained.

Calcium↗
PubMed2000

Comparison of poly(acryl starch) and poly(lactide-co-glycolide) microspheres as drug delivery system for a rotavirus vaccine.

Drug delivery systems allowing controlled release of antigen are of particular interest in the development of vaccines. We have compared poly(acrylic starch) microspheres (PAS) and poly(lactide-co-glycolide) microspheres (PLG) as drug delivery systems for a rotavirus vaccine. The polymers are both biodegradable but have different degradation mechanisms and antigen release profiles. PAS are enzymatically degraded and have a continuous fast antigen release rate compared to the hydrolytically degraded PLG which release the incorporated antigen in a pulsatile manner. In this study mice were immunised intramuscularly and orally on three occasions with formalin-inactivated rotavirus (FRRV) incorporated in PAS and PLG and with FFRV alone. Serum and faeces samples were collected and analysed by ELISA for rotavirus specific IgG and IgA antibodies. A neutralising assay was also conducted on both serum and faeces antibodies. The two different polymer drug delivery systems induced different immune responses depending on administration route. PAS elicited significant antibody levels and neutralising effect after oral administration while PLG showed high antibody levels after intramuscular administration. The immune response appears to be dependent on the differences in antigen release and degradation mechanism for the two polymer systems.

Animals↗
PubMed2001

Acrylic microspheres for oral controlled release of the biguanide buformin.

Spherical microparticles based on methacrylic acid-methyl methacrylate copolymer have been developed. The method chosen for the preparation of such microparticles was suspension radical copolymerization of acrylic comonomers in the presence of the ethyleneglycol dimethacrylate as crosslinking agent. The microparticles obtained were characterised by inverse size exclusion chromatography, scanning electron microscopy, swelling degree and exchange capacity. The porous volume of the microspheres ranged from 0.086 ml/g for the microparticles produced by a methacrylic acid/methyl methacrylate ratio of 1/3 and a 10% degree of crosslinking, to 8.57 ml/g for the microparticles produced by a methacrylic acid/methyl methacrylate ratio of 3/1 and 2% degree of crosslinking (in 0.1 N NaCl in phosphate buffer pH 7.4). Also the pore diameter of the swollen microparticles ranged from a few to 120 A. Buformin tosylate - a classical hypoglycaemic drug - was included in the polymer network of the microparticles during the polymerization process. Due to the water solubility of the drug and its low solubility in the organic phase, the entrapment yield did not exceed 15%. However the amount of encapsulated drug as well as the drug released from the microparticles, was dependent on the methacrylic acid/methyl methacrylate ratio, the degree of crosslinking and solvent/comonomers ratio.

Administration, Oral↗