Separation of copolymers using high-performance liquid chromatography with polymeric stationary phase and liquefied carbon dioxide as adsorption promoting solvent.

Chromatographic separation of copolymers depending on the chemical composition was studied by a solvent gradient method using liquefied carbon dioxide (CO2) as an adsorption promoting solvent. As the high polar stationary phase, non-bonded silica gel, crosslinked acrylamide (AA) gel and crosslinked acrylonitrile (AN) gel were utilized. All columns showed the typical normal phase type of adsorption. Polymeric stationary phases showed the higher sample recovery for styrene-methyl methacrylate (St-MMAs) copolymers, indicating suitability for quantitative analyses. The separations of butyl methacrylate (BMA)-methyl methacrylate, and 2,2,3,3,4,4,4-heptafluorobutyl methacrylate (FBMA)-methy methacrylate copolymers were also carried out, and the latter copolymers were separated based on the CO2-philicity with acrylonitrile column.

Ridley intraocular lens revisited: chemical analysis of residuals in the original lens material.

Two original Ridley intraocular lenses, made of poly(methyl methacrylate) (PMMA) at least 35 years ago, were extracted in two different media, diethyl ether and water. The extracts were suitably processed and analyzed by high resolution capillary gas chromatography. Residual monomer (MMA) was detected in both extracts. The amount of MMA in the aqueous extract was significantly lower than that in the ether extract. It is postulated that the residual monomer in lenses originated from an incomplete polymerization at the time of the polymer production. However, the MMA content found in one lens (0.147%) is comparable to that currently detected in modern IOLs, and probably does not cause toxic reaction in the eye because it is leached out by aqueous fluid action to a very low extent.

[Free methyl-methacrylate content of some dental acrylates]. / Egyes fogászati akrilátok szabad metil-metakrilát tartalma.

The authors have proved the presence of free monomer content in 0,26% with Superacryl Special, 0,29% with Superpont C-B, 0,8% with Kallocryl C and the Duracryl O from a metanol solution of samples taken by cutting. By means of soaking in water for three months the most dissolved free monomer was 0.002% from Superpont C-B and Kallocryl C, and 0.004% from Duracryl O. From Superacryl Special no MNA was dissolved in determinable quantity.

[The porosity, microhardness, roughness and internal stresses of PMMA base materials in relation to their isolation. 1. Porosity and microhardness]. / Porositäten, Mikrohärte, Rauheit und Eigenspannungen von PMMA-Basismaterialien in Abhängigkeit von der Isolierung. 1. Mitteilung: Porositäten und Mikrohärte.

Selected material properties of hot and cold polymerized denture basic materials (polymethylmethacrylate) were investigated after different methods of isolation: alginate, tin foil and silicone. Both tin foil and silicone isolation the handling of which is much easier result in a decreased portion of porosities and an increased microhardness in the PMMA.

Influence of mixing technique on some properties of PMMA bone cement.

PMMA bone cements (Refobacin-Palacos R, Sulfix 6, AKZ, and CMW bone cement, types I and II), from six different clinics, were investigated in three stages. In the first stage, studies of density, hardness, flexural strength, and compressive strength were made, as well as molecular weight measurements and microscopic investigations. These studies reflected the current state of techniques of application used in operating theaters. They revealed wide variations in the properties of the materials studied. Secondly, a comprehensive study of the process-technology in the laboratory was performed. The following variables were investigated or discussed: mixing vessel, order of the individual components, mixing time, rate of mixing, pressure application on the mixed bone cement, kneading, cement thickness, pouring into the syringe, contact force during polymerization, and preparation quantity. The third stage involved the development and clinical testing of an improved mixing technique. Using this improved mixing technique, all three selected clinics achieved far better results with reduced variability. A comparison between a centrifuging technique after mixing and our improved, but conventional, mixing technique, displays advantages for the latter. The question regarding a correlation between cement specimens of high porosity and early implant loosening could not be answered on the basis of the 43 PMMA bone cement explants investigated (implanted 6 months to 15 years). In some cases, the studies revealed that the bone cement manufacturers should be required to revise and quantify existing instructions for use. The users, on the other hand, should give more consideration to the mixing technique and its consequences.

The penetration of the embedding medium methyl methacrylate in undecalcified bone.

Cutting artifacts in microtome sections prepared from undemineralized methyl methacrylate embedded bone are due to the almost complete absence of methacrylate in the intercellular compartment of the bone tissue, the soft tissues being fully impregnated with the polymer. The osteocyte system is only partially penetrated by methacrylate.