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.     

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.     

Analysis of mortality time trend using generalized linear models

In this work it is shown how generalized linear models allow one to describe different patterns of temporary evolution of mortality data, while at the same time allow for an easy interpretation. As a practical application, the evolution of the female breast cancer mortality in Catalonia from 1986 to 2000 is analyzed. Remarkably, the mortality from breast cancer first increases and then decreases for all age groups. Moreover, the year in which the cancer rate starts decreasing is more recent in the older age groups.     

New macroporous calcium phosphate glass ceramic for guided bone regeneration

This work describes a method to obtain macroporous resorbable glass and glass ceramic scaffolds with controlled biodegradability for tissue engineering applications. The constructs consisted of glass and glass ceramics in the system P(2)O(5)-CaO-Na(2)O-TiO(2) and they were prepared by foaming a slurry of glass particles by addition of a H(2)O(2) solution, and subsequent sintering of the porous structures obtained. Different thermal treatments were applied to control the degree of devitrification of the glass. The resultant materials showed a porosity percentage between 40% and 55% with a wide variety of pores ranging from 20 to 500 microm in diameter as determined by SEM and Image Analysis. The resulting constructs were predominantly formed by a vitreous phase, although small amounts of calcium metaphosphate and pyrophosphates were detected by X-ray diffraction and Raman spectroscopy after the sintering process. The biological response was also evaluated by means of the MTT test, the material showed a non-cytotoxic effect.     

Wear behaviour of the pair Ti-6Al-4V-UHMWPE of acrylic bone cements containing different radiopaque agents

The objective of this study was to improve the wear behaviour of acrylic bone cements by substituting the conventional inorganic radiopaque agents (BaSO(4), ZrO(2)) for different iodinated radiopaque monomers which can co-polymerize with the methyl methacrylate monomer, MMA. To this aim, the wear behaviour of the pair Ti-6Al-4V-UHMWPE (ultra high molecular weight polyethylene) was studied in the absence and in the presence of cement particles (the third body).     

Relevance of microstructure for the early antibiotic release of fresh and pre-set calcium phosphate cements

Calcium phosphate cements (CPCs) have great potential as carriers for controlled release and vectoring of drugs in the skeletal system. However, a lot of work still has to be done in order to obtain reproducible and predictable release kinetics. A particular aspect that adds complexity to these materials is that they cannot be considered as stable matrices, since their microstructure evolves during the setting reaction. The aims of the present work were to analyze the effect of the microstructural evolution of the CPC during the setting reaction on the release kinetics of the antibiotic doxycycline hyclate and to assess the effect of the antibiotic on the microstructural development of the CPC. The incorporation of the drug in the CPC modified the textural and microstructural properties of the cements by acting as a nucleating agent for the heterogeneous precipitation of hydroxyapatite crystals, but did not affect its antibacterial activity. In vitro release experiments were carried out on readily prepared cements (fresh CPCs), and compared to those of pre-set CPCs. No burst release was found in any formulation. A marked difference in release kinetics was found at the initial stages; the evolving microstructure of fresh CPCs led to a two-step release. Initially, when the carrier was merely a suspension of α-TCP particles in water, a faster release was recorded, which rapidly evolved to a zero-order release. In contrast, pre-set CPCs released doxycycline following non-Fickian diffusion. The final release percentage was related to the total porosity and entrance pore size of each biomaterial.     

Calcium phosphate cements as bone drug delivery systems: a review.

Since calcium phosphate cements were proposed, several formulations have been developed, some of them commercialised, and they have proven to be very efficient bone substitutes in different applications. Some of their properties, such as the injectability, or the low-temperature setting, which allows the incorporation of different drugs, make them very attractive candidates as drug carriers. In this article, the performance of calcium phosphate cements as carriers of different types of drugs, such as antibiotics, analgesics, anticancer, anti-inflammatory, as well as growth factors is reviewed.     

In vitro degradation behavior of a novel bioresorbable composite material based on PLA and a soluble CaP glass

Poly(alpha-hydroxy acids), and in particular polylactic acid (PLA), are nowadays amongst the most used bioabsorbable materials. However, this polymer may not meet some application requirements due to inadequate mechanical properties and or its degradation characteristics. A possible strategy to tackle this problem is the incorporation of an inorganic phase into the polymeric matrix. In this work a new fully biodegradable composite material made with PLA and calcium phosphate soluble glass particles has been developed. The behaviour of the PLA/glass composite has been analysed during its degradation in simulated physiological conditions by means of weight loss, molecular weight and thermal properties analysis and electron microscopy observation. The results showed that the incorporation of phosphate glass particles into the polymer significantly accelerated the degradation of the PLA and induced the formation of calcium phosphate precipitates at the composite surface.     

Electrochemical microelectrodes for improved spatial and temporal characterization of aqueous environments around calcium phosphate cements

Calcium phosphate compounds can potentially influence cellular fate through ionic substitutions. However, to be able to turn such solution-mediated processes into successful directors of cellular response, a perfect understanding of the material-induced chemical reactions in situ is required. We therefore report on the application of home-made electrochemical microelectrodes, tested as pH and chloride sensors, for precise spatial and temporal characterization of different aqueous environments around calcium phosphate-based biomaterials prepared from α-tricalcium phosphate using clinically relevant liquid to powder ratios. The small size of the electrodes allowed for online measurements in traditionally inaccessible in vitro environments, such as the immediate material-liquid interface and the interior of curing bone cement. The kinetic data obtained has been compared to theoretical sorption models, confirming that the proposed setup can provide key information for improved understanding of the biochemical environment imposed by chemically reactive biomaterials.     

Of the in vivo behavior of calcium phosphate cements and glasses as bone substitutes

The use of injectable self-setting calcium phosphate cements or soluble glass granules represent two different strategies for bone regeneration, each with distinct advantages and potential applications. This study compares the in vivo behavior of two calcium phosphate cements and two phosphate glasses with different composition, microstructure and solubility, using autologous bone as a control, in a rabbit model. The implanted materials were alpha-tricalcium phosphate cement (cement H), calcium sodium potassium phosphate cement (cement R), and two phosphate glasses in the P(2)O(5)-CaO-Na(2)O and P(2)O(5)-CaO-Na(2)O-TiO(2) systems. The four materials were osteoconductive, biocompatible and biodegradable. Radiological and histological studies demonstrated correct osteointegration and substitution of the implants by new bone. The reactivity of the different materials, which depends on their solubility, porosity and specific surface area, affected the resorption rate and bone formation mainly during the early stages of implantation, although this effect was weak. Thus, at 4 weeks the degradation was slightly higher in cements than in glasses, especially for cement R. However, after 12 weeks of implantation all materials showed a similar degradation degree and promoted bone neoformation equivalent to that of the control group.