Biomedical subjects

M Gurruchaga

Publications and source records attributed to M Gurruchaga.

6 recordsLinked to original sources

PubMed1999

Characterization of new acrylic bone cement based on methyl methacrylate/1-hydroxypropyl methacrylate monomer.

New formulations of acrylic bone cement based on methyl methacrylate/1-hydroxypropyl methacrylate (MMA/HPMA) monomers were developed with the purpose of obtaining more ductile materials with reduced polymerization shrinkage. In this way, the ductility of such materials increased, but the introduction of high percentages of the hydrophilic component produced an important decrease in Young's modulus and strength. To ascertain the reason for the deterioration of the tensile parameters, an analysis by scanning electron microscopy of these formulations was carried out; it revealed poor adhesion between the matrix and poly(MMA) beads. We also observed that the polymerization shrinkage increased as the amount of hydrophilic monomer in the formulation decreased, and the 50% (v/v) HPMA modified bone cement compensated for this volume reduction with its water uptake swelling. Measurements taken on the setting time and polymerization exotherm showed a decrease in the former and an increase in the latter, because of the introduction of a more reactive monomer in the bone cement formulation.

Bone Cements↗

PubMed1999

Modified acrylic bone cement with high amounts of ethoxytriethyleneglycol methacrylate.

One cause of arthroplasty failure is the brittle mechanical behavior of bone cements. However, the improvement of cement formulations must also be accompanied by the maintenance of a wide variety of characteristics. New bone cements were obtained by the substitution of high percentages, up to 60% (v/v), of methyl methacrylate (MMA) by a higher molecular weight and more hydrophilic monomer, ethoxytriethyleneglycol methacrylate (TEG). The essential advantages of these materials were the decrease of maximum temperature together with a decrease in the residual monomer content with respect to conventional cement formulations. The water absorption process obeyed diffusion laws and the equilibrium water content increased by the introduction of higher percentages of the hydrophilic component. This characteristic had an appreciable effect on the viscoelastic behavior analyzed by DMTA. These modified bone cements had reduced polymerization shrinkage and similar levels of porosity. Tensile test revealed that the introduction of TEGMA gave rise to an important modification of the mechanical behavior, with a noticeable increase in the fracture strain. This fact was also confirmed by means of the analysis of the fracture surfaces by SEM.

Absorption↗

PubMed1999

Influence of the modification of P/L ratio on a new formulation of acrylic bone cement.

The use of smaller powder/liquid (P/L) ratio favours the handling and wetting of poly(methyl methacrylate) (PMMA) beads in bone cement formulations. In this paper a P/L ratio of 1.86 is tested to overcome adhesion problems found in hydroxypropyl methacrylate (HPMA) modified bone cements and the influence on bone cement characteristics was analysed. The reduction of the P/L ratio leads to higher temperature peaks and shorter setting times, whereas the residual monomer content increases slightly. Water uptake obeys the diffusion laws, and the introduction of a more hydrophilic monomer gives rise to an increase of this parameter, which does not present significant changes with modification of the P/L ratio. Polymerization shrinkage is slightly greater because of the introduction of higher proportions of monomer in the formulation. Mechanical properties are similar to those obtained with conventional P/L ratios. The analysis of scanning electron microscopy (SEM) reveals an improvement of the adhesion between phases with respect to P/L = 2 formulations.

Acrylic Resins↗

PubMed1997

Application of tertiary amines with reduced toxicity to the curing process of acrylic bone cements.

4-Dimethylaminobenzyl alcohol (DMOH) and 4-dimethylaminobenzyl methacrylate (DMMO) were used as the activators in the benzoyl peroxide initiated redox polymerization for the preparation of acrylic bone cement based on poly(methylmethacrylate) beads of different particle size. The residual monomer content of the cured cements was about 2 wt %, independent of the redox system used in the polymerization, indicating that the activating effect of the tertiary aromatic amines DMOH or DMMO was sufficient to reach a polymerization conversion similar to that obtained with the benzoyl peroxide (BPO) N,N-dimethyl-4-toluidine (DMT) system. The BPO/DMOH and BPO/DMMO redox systems provided exotherms of decreasing peak temperature and increasing setting time, and the cured materials presented higher average molecular weight and similar glass transition temperatures in comparison with those obtained when DMT was used as the activator. In addition, these activators are three times less toxic than the classical DMT.

Acrylates↗

PubMed1997

pH-sensitive hydrogels based on non-ionic acrylic copolymers.

Hydrogels based on ethoxytriethyleneglycol monomethacrylate/methyl methacrylate copolymers were prepared by free radical polymerization at 70 degrees C in bulk with 2,2'-azobisisobutyronitrile as initiator. The swelling behaviour of the hydrogels was studied by immersion of the films in water and in buffered solutions at various pHs. The hydration process was followed gravimetrically measuring the water uptake of the films with the time of treatment. The kinetics fit adequately a Fickian law for reduced sorption coefficients, Mt/M infinity, lower than 0.6. The values of the diffusion coefficient were lower at neutral pH than at acidic or alkaline pHs, and they seemed to be independent of the copolymer composition. The results obtained were consistent with the stress relaxation model of polymer chains predicted for a relatively fast hydration process. The swelling process is reversible and the polymeric films are stable after repeating cycles of hydration and desorption promoted by the change of pH in appropriate buffered solutions.

Biopolymers↗

PubMed1996

New aspects of the effect of size and size distribution on the setting parameters and mechanical properties of acrylic bone cements.

The effect of the size and the size distribution of poly(methyl methacrylate) (PMMA) beads on the classical kinetic parameters, peak temperature and setting time, for acrylic bone cement formulations prepared with PMMA particles in the range 10-60 microns of average diameter and a relatively wide size distribution is analysed. In addition, the combined effects of the concentration of the free radical initiator benzoyl peroxide and the activator N, N-dimethyl-4-toluidine for the different particle sizes are studied and compared with those commercially available formulations like CMW or Rostal. The results obtained indicated that the use of PMMA particles with average diameter of 50-60 microns, and a relatively wide size distribution (10-140 microns diameter), significantly changes the curing parameters (peak temperature and setting time) of the cement formulations in comparison with the classical behaviour of the commercial systems of CMW and Rostal, without any noticeable loss in the mechanical properties, such as tensile strength, elastic moduli, and compressive strength and plastic strain.

Benzoyl Peroxide↗