Addition Of Polymethylmethacrylate Research Articles

Radio-opaque agents in bone cement increase bone resorption.

A heavy infiltrate of foreign-body macrophages is commonly seen in the fibrous membrane which surrounds an aseptically loose cemented implant. This is in response to particles of polymethylmethacrylate (PMMA) bone cement and other biomaterials. We have previously shown that monocytes and macrophages responding to particles of bone cement are capable of differentiating into osteoclastic cells which resorb bone. To determine whether the radio-opaque additives barium sulphate (BaSO4) and zirconium dioxide (ZrO2) influence this process, particles of PMMA with and without these agents were added to mouse monocytes and cocultured with osteoblast-like cells on bone slices. Osteoclast differentiation, as shown by the presence of the osteoclast-associated enzyme tartrate-resistant acid phosphatase (TRAP) and lacunar bone resorption, was observed in all cocultures. The addition of PMMA alone to these cocultures caused no increase in TRAP expression or bone resorption relative to control cocultures. Adding PMMA particles containing BaSO4 or ZrO2, however, caused an increase in TRAP expression and a highly significant increase in bone resorption. Particles containing BaSO4 were associated with 50% more bone resorption than those containing ZrO2. Our results suggest that radio-opaque agents in bone cement may contribute to the bone resorption of aseptic loosening by enhancing macrophage-osteoclast differentiation, and that PMMA containing BaSO4 is likely to be associated with more osteolysis than that containing ZrO2.

Pyro-piezoelectrics polymers materials—I. Effect of addition of PVA and/or PMMA on overall crystallization kinetics of PVDF from isothermal and non-isothermal data

Since electrical properties such as pyroelectricity, piezoelectricity and ferroelectricity strongly depend on the structural parameters, an important role is played by molecular orientation and crystal structures. So, the overall isothermal and non-isothermal kinetics for different polyvinylidene fluoride (PVDF), polyvinyl acetate (PVA) and polymethyl methacrylate (PMMA) was investigated in order to characterize them from a microstructural point of view.

The formation of stain on acrylic surfaces by the interaction of cationic antiseptic mouthwashes and tea.

Clinical and in vitro studies have implicated dietary components as major aetiological factors in staining of teeth and acrylic materials associated with chlorhexidine use, a local side effect not unique to this antiseptic. These experiments studied the precipitation and surface staining reactions of the cationic antiseptics alexidine, cetyl pyridinium chloride (CPC), chlorhexidine, and hexetidine, with the beverage tea. All of the antiseptics precipitated a standard tea solution and for alexidine and chlorhexidine acetate and gluconate, this was at concentrations greater than 100 mumol/L, for hexetidine greater than 200 mumol/L, and for CPC greater than 400 mumol/L. With the exception of CPC precipitation was reduced with decreasing pH and for chlorhexidine was inhibited below pH 3. The addition of polymethylmethacrylate (PMMA) to the antiseptic solutions increased the precipitation concentrations by an amount calculated to be adsorbed by polymer. Acrylic blocks treated with equimolar solutions of the antiseptics became progressively and significantly more stained by tea than control specimens over a 5-day period. Alexidine induced significantly greater staining and hexetidine significantly less than the other antiseptics. Staining was pH dependent and significantly reduced as the pH decreased. Both stain and precipitates were insoluble in strong acids and alkalis. It is concluded that staining observed clinically may represent a precipitation reaction with the complexing of antiseptics with dietary chromogenic material.

Thermal degradation of polymethacrylonitrile. IV. Formation and decomposition of ketene‐imine structures

AbstractThe reaction of ketene‐imine structures in polymethacrylonitrile is most conveniently followed by observing the disappearance of the 2012 cm.−1 peak in the infrared spectrum. These structures are stable to 120°C. in the bulk material but disappear rapidly in solution at lower temperatures. Like simple ketene‐imines they are destroyed by addition of water, chlorine, methanol, and hydrogen sulfide. Thermal decomposition in cyclohexanone solution in the temperature range 65–90°C. is a second‐order process. The second‐order rate constant decreases with increasing polymer concentration although, within experimental error, it is independent of the ketene‐imine concentration. The rate constant can also be depressed by addition of polymethyl methacrylate. These observations have been interpreted in terms of diffusion (viscosity) control of the reaction rate. Ketene‐imine structures are formed during polymerization by reaction of the growing polymer radical in the form magnified image By preparing a series of polymers at the same temperature (30°C.) but with different initiator concentrations and determining their ketene‐imine contents, it has been possible to show that the ketene‐imine structures are formed predominantly in the termination step. The ketene‐imine form of the radical appears not to be reactive enough to add monomer readily in a propagation process. The mechanism of the thermal disappearance of ketene‐imine structures is not clear. In particular it is difficult to correlate the second‐order kinetics with the chain‐scission process which is associated with the reaction. There is some evidence, however, that the extent of this chain scission is a measure of ketene‐imine concentration.