Physical characterization of acrylic bone cement cured with new accelerator systems

The Effect of TBB, as an Initiator, on the Biological Compatibility of PMMA/MMA Bone Cement

Acrylic bone cement is widely used in orthopedic surgery for treating various conditions of the bone and joints. Bone cement consists of methyl methacrylate (MMA), polymethyl methacrylate (PMMA), and benzoyl peroxide (BPO), functioning as a liquid monomer, solid phase, and polymerization initiator, respectively. However, cell and tissue toxicity caused by bone cement has been a concern. This study aimed to determine the effect of tri-n-butyl borane (TBB) as an initiator on the biocompatibility of bone cement. Rat spine bone marrow-derived osteoblasts were cultured on two commercially available PMMA-BPO bone cements and a PMMA-TBB experimental material. After a 24-h incubation, more cells survived on PMMA-TBB than on PMMA-BPO. Cytomorphometry showed that the area of cell spread was greater on PMMA-TBB than on PMMA-BPO. Analysis of alkaline phosphatase activity, gene expression, and matrix mineralization showed that the osteoblastic differentiation was substantially advanced on the PMMA-TBB. Electron spin resonance (ESR) spectroscopy revealed that polymerization radical production within the PMMA-TBB was 1/15–1/20 of that within the PMMA-BPO. Thus, the use of TBB as an initiator, improved the biocompatibility and physicochemical properties of the PMMA-based material.

Physicochemical, Mechanical, and Biological Properties of Bone Cements Prepared with Functionalized Methacrylates

Bone cements prepared with methyl methacrylate (MMA) as a base monomer and either methacrylic acid (MAA) or diethyl amino ethyl methacrylate (DEAEMA) as comonomers were characterized in terms of curing behavior, mechanical properties, and their in vitro biocompatibility.

The curing time and setting temperature were found to be composition dependent while the residual monomer was not greatly affected by the presence of either acidic or alkaline comonomers in the bone cements. For samples with MAA comonomer, a faster curing time and higher setting temperature were observed when compared to the cement with DEAEMA comonomer.

In terms of mechanical properties, the highest compressive strength was exhibited by formulations containing MAA, while the highest impact strength was shown by the formulations prepared with DEAEMA. There were no differences observed between the two formulations for tensile, shear, and bending strength values. Similarly, fatigue crack propagation studies did not reveal differences with the addition of either DEAEMA or MAA.

No differences were observed in the initial number of attached primary rat femur osteoblasts on the different bone cements and positive controls. However, after 48 h there was a reduced proliferation in the cells grown on bone cements containing MAA.

Bone cements and their potential use in a mandibular endoprosthesis

Bone cement was first used in the 1950s. Since then many modifications have been made and alternatives developed to the original polymethylmethacrylate (PMMA) cement. In view of the use of bone cement in a novel mandibular endoprosthetic system, we performed a review of the current literature on this material. Different cements are described and their potential use in a mandibular endoprosthetic system discussed. The PMMA-based cements are currently the most suitable choice. Plain PMMA has the longest track record and is the default choice for the initial development phase of this system. If there is a significant risk of infection, then an antibiotic-loaded PMMA cement can be selected. However, modified PMMA cements, composite resin cements, osteoinductive calcium phosphate compounds, and cementless fixation are options that offer advantages over PMMA cements, and further research should be conducted to study their suitability.

Alternative acrylic bone cement formulations for cemented arthroplasties: present status, key issues, and future prospects

All the commercially available plain acrylic bone cement brands that are used in cemented arthroplasties are based on poly (methyl methacrylate) and, with a few exceptions, have the same constituents. It is well known that these brands are beset with many drawbacks, such as high maximum exotherm temperature, lack of bioactivity, and volumetric shrinkage upon curing. Furthermore, concerns have been raised about a number of the constituents, such as toxicity of the activator (N,N,dimethyl-p-toluidine) and possible involvement of the radiopacifier (BaSO(4) or ZrO(2) particles) in third-body wear. Thus, over the years, many research efforts have been expended to address these drawbacks, culminating in a large number of alternative formulations, which may be grouped into 16 categories. Although there are a number of reviews of the large literature that now exists on these formulations, each covers only some of the categories and none contains a detailed discussion of the germane issues. The objective of the present work, therefore, was to present a comprehensive and critical review of the whole field. In addition to succinct descriptions of the cements in each category, there are explicative summaries of literature reports, a detailed discussion of several key issues surrounding the potential for use of these cements in cemented arthroplasties, and a presentation of numerous ideas for future studies.

Influence of the activator in an acrylic bone cement on an array of cement properties

In all but one of the acrylic bone cement brands used in cemented arthroplasties, N,N-dimethyl-4-toluidine (DMPT) serves as the activator of the polymerization reaction. However, many concerns have been raised about this activator, all related to its toxicity. Thus, various workers have assessed a number of alternative activators, with two examples being N,N-dimethylamino-4-benzyl laurate (DMAL) and N,N-dimethylamino-4-benzyl oleate (DMAO). The results of limited characterization of cements that contain DMAL or DMAO have been reported in the literature. The present work is a comprehensive comparison of cements that contain one of these three activators, in which the values of a large array of their properties were determined. These properties range from the setting time and maximum exotherm temperature of the curing cement to the variation of the loss elastic modulus of the cured cement with frequency of the applied indenting force in dynamic nanoindentation tests. The present results, taken in conjunction with those presented in previous reports by the present authors and co-workers on other properties of these cements, indicate that both DMAL and DMPT are suitable alternatives to DMPT.

Fatigue testing and performance of acrylic bone-cement materials: state-of-the-art review

Over the past three decades or so, a very large volume of literature has been generated on the impact of an assortment of variables on the fatigue lifetimes of a large number of acrylic bone-cement formulations. In the present article, this literature is examined critically to reveal areas of agreement, areas of disagreement, as well as a welter of underexplored and unexplored topics. For example, there is unanimity of support for the notion that an increase in the molecular weight of the powder constituents or the fully cured cement leads to an increase in the cement's fatigue life, whereas there is disagreement as to whether vacuum mixing the cement constituents leads to an increase in the fatigue life of the fully cured cement (relative to the hand-mixed counterpart). Among the underexplored topics is systematic study of the effect of test frequency on the fatigue results, whereas determination of the optimal concentration of the antibiotic in an antibiotic-loaded cement is an example of the unexplored topics. It is pointed out that resolving the controversies, addressing the underexplored topics, and filling the lacunae will allow comprehensive evaluations of acrylic bone-cement materials to be made. This enhanced body of knowledge will prove invaluable in the continued use of acrylic bone cement as the anchoring agent in cemented arthroplasties.

Comparative study of bone cements prepared with either HA or alpha-TCP and functionalized methacrylates

The properties of bone cements prepared with both hydroxyapatite (HA) and alpha-tricalcium phosphate (alpha-TCP) and methacrylates containing acidic or basic groups are the main interest of this article. The presence of methacrylic acid or diethyl amino ethyl methacrylate as comonomers in the bone cement and both ceramic types as filler were found not to affect the amount of residual monomer, which was generally less than 4.5 wt%. In contrast, setting times, maximum temperature, and glass transition temperature were found to be composition dependent. For samples with acidic comonomer, a faster setting time, a higher maximum temperature, and higher glass transition temperatures were observed compared to those with the basic comonomer. The presence of the fillers slightly increased the setting time but did not affect the other parameters. The mechanical properties of the filled bone cements depended mainly on composition and type of testing. Both HA or alpha-TCP filled systems fulfilled the minimum compressive strength required for bone cement application, although a significantly lower value was observed for the alkaline comonomer systems. The minimum bending strength was not satisfied by any of these formulations. The tensile and shear strength of these composites ranged from 20 to 37.9 and from 18 to 27 MPa, respectively. In all cases it was higher for bone cements containing methacrylic acid. The results of this study suggest that the properties of dry unfilled bone cements prepared with MAA are comparable to CMW 3 in mechanical terms but inferior in their setting properties.

Characterization of bone cements prepared with functionalized methacrylates and hydroxyapatite

Bone cements prepared with methyl methacrylate and either methacrylic acid or diethyl amino ethyl methacrylate as comonomers were characterized by infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, dynamic mechanical thermal analysis, and mechanical testing. Selected formulations containing these functionalized methacrylates were filled with hydroxyapatite and studied in terms of their properties in tension, compression and bending, and X-ray diffraction. It was found that residual monomer was not greatly affected by the presence of either acid or basic comonomers in the unfilled bone cements. In contrast, molecular weight, curing times, and glass transition temperature were composition dependent. For samples with acidic comonomer, a faster curing time, higher molecular weight, and higher glass transition temperatures were observed with respect to those with the basic comonomer. X-ray diffraction revealed that the crystalline structure was not affected by the nature of comonomer in the bone cement while scanning electron microscopy showed that hydroxyapatite remained as clusters in the bone cement. The mechanical properties of filled bone cements depended mainly on composition and type of testing. Hydroxyapatite-filled bone cements fullfilled the minimum compressive strength (70 MPa) required for bone cement use. However, the minimum tensile strength (30 MPa) was only fullfilled by cements prepared without comonomer and those containing methacrylic acid. The minimum bending strength requirement (50 MPa) was not satisfied by any of the formulations studied.

Relative roles of cement molecular weight and mixing method on the fatigue performance of acrylic bone cement: Simplex P versus Osteopal

The weight-average molecular weight (MW(w)) of a cement and the method used to mix its powder and liquid monomer constituents have been identified in the literature as key variables that affect mechanical properties of the fully polymerized cement that are relevant to its performance as a grouting agent in cemented arthroplasties. The goal of the present work was to identify which of these two variables exerts the greater effect in the case of fully reversed tension-compression fatigue performance. A judicious choice of cement brands, Surgical Simplex P and Osteopal, and the use of hand versus vacuum mixing, permitted this identification to be achieved. Three key observations were made in this work. First, for a given cement, the fatigue performance of vacuum-mixed specimens is far superior to that of hand-mixed ones, which may be a consequence of the substantially lower percentage areal porosity of the former specimens. Second, regardless of the mixing method, the fatigue performance of Osteopal outstrips that of Simplex P, a result that is attributed to the much higher MW(w) of the former cement. Third, hand-mixed Osteopal outperforms vacuum-mixed Simplex P (especially at low alternating stress levels), indicating that MW(w) of a bone cement is more influential than mixing method on its fatigue performance.

Properties of acrylic bone cement: state of the art review

Acrylic bone cement occupies a distinctive place in the hierarchy of synthetic biomaterials, because it is the only material currently used for anchoring the prosthesis to the contiguous bone in a cemented arthroplasty. However, the cement is not without its drawbacks. The main one is the role that it has been postulated to play in the aseptic loosening and, hence, clinical life of the arthroplasty. In turn, this role is directly related to the mechanical properties of the cement, especially the resistance to fracture of the cement in the mantle at the cement-prosthesis interface or the cement-bone interface. The present work is a detailed critical review of the recent literature on the properties of bone cement that are considered germane to its use in the stated application. The relevant properties are identified and a case is made for including each of them. Compilations of the values of these properties, obtained under clearly identified conditions, are presented for the six commercial formulations of bone cement in current popular orthopedic use. The gaps and unresolved questions in the current data base, efforts that should be made to address these issues, and research directions are covered.

Application of long chain amine activator in conventional acrylic bone cement

A long chain acid derivative bearing an aromatic tertiary amine group, 4-N,N-dimethylaminobenzyl laurate (DML), which acts as an activator for the curing of acrylic cements at low temperature, has been synthesized and characterized to reduce the biological adverse effects usually associated with the classical activator N,N-dimethyl-4-toluidine (DMT). The effectiveness of the activator was tested on commercial formulations (e.g., Palacos R) and on experimental bone cements based on poly (methyl methacrylate) by using different benzoyl peroxide/amine molar ratios. The exotherms of polymerization were followed at three different temperatures: 25, 30, and 37 degrees C. The DML activator was found to be more sensitive to temperature than the corresponding DMT. DML provided exotherms of polymerization with decreasing peak temperatures and increasing setting times without impairing the mechanical properties. Residual monomer content was analyzed in a range of activator concentrations by keeping the benzoyl peroxide concentration constant. In all cases the residual monomer content was lower than 5%, indicating its good efficiency in the benzoyl peroxide initiated polymerization.