JOURNAL OF MATERIALS SCIENCE: MATERIALS IN MEDICINE 9 (1998) 679 — 685 Acrylic bone cements incorporating polymeric active components derived from salicylic acid: curing parameters and properties C. ELVIRA, B. VAZQUEZ, J. SAN ROMA  N Instituto de Cy T de Polimeros, CSIC, c/ Juan de la Cierva 3, E-28006 Madrid, Spain B. LEVENFELD, EPS, U. Carlos III, Leganes, Madrid, Spain P. GINEBRA, X. GIL, J. A. PLANELL ETSII, UPC, Av. Diagonal 647, 08028 Barcelona, Spain E-mail: ictsr04@fresno.csic.es A methacrylic monomer derived from salicylic acid, 5-hydroxy-2-methacrylamido benzoic acid, 5-HMA, was incorporated with 2-hydroxyethyl methacrylate, (HEMA), in different proportions to the liquid phase of classical bone cement formulations. The monomer 5-HMA shows the ability to form molecular complexes with calcium atoms in order to improve osteointegration in the application of bone cement formulations used for the fixation of joint prostheses such as knee and hip. Kinetic parameters, peak temperature and setting time of the bone cement formulations prepared were determined, obtaining lower peak temperature values when 5-HMA was incorporated, with respect to classical acrylic bone cements based on PMMA. Mechanical and thermal properties as well as surface energy values, have been determined for all cured bone cement formulations.  1998 Kluwer Academic Publishers 1. Introduction Self-curing acrylic bone cements have been widely used in dentistry and orthopaedic surgery as filling agents and for the fixation of prostheses, due to their biostability and good adaptation [1—5]. They are gen- erally obtained by free-radical polymerization of methyl methacrylate monomer (MMA) mixed with a solid phase containing beads of poly (methyl methac- rylate) (PMMA) [3]. The polymerization is initiated in the presence of benzoyl peroxide (BPO) which is incorporated in the solid polymer phase. N,N- dimethyl-p-toluidine (DMT) is constituted in the liquid phase which acts as an activator of the reaction. The major function of acrylic bone cement is the stress distribution on the contact area between the bone and the prostheses, therefore their mechanical properties are very important in these applications. One of the major problems of these materials is the fixation into bony structure, so that the most frequent long- term complication is loosening of the prosthetic components, caused by both mechanical and biolo- gical factors. In this sense, some research groups have proposed the incorporation of biodegradable compo- nents to acrylic bone cement formulations such as carboxymethyl cellulose [6] in order to create a por- ous cement which could facilitate bone regeneration. Other authors have incorporated bone particles in acrylic bone cements promoting a decrease in the porous number but a better osteointegration [7—9]. Another component which has been added to acrylic bone cement formulations, is hydroxyapatite. It has been incorporated as microparticles, maintaining the mechanical properties, decreasing the maximum cur- ing temperature and accelerating the bone tissue formation in the implant surroundings with respect to classical formulations of PMMA [10—14]. The present work is a study on curing parameters and the most important properties of acrylic bone cement formulations in which the liquid phase has been modified by the incorporation of methacrylic monomers, one derived from salicylic acid, 5-hydroxy- 2-methacrylamido benzoic acid, 5-HMA, and 2-hy- droxyethyl methacrylate (HEMA). HEMA was also incorporated on its own in order to carry out com- parative studies with formulations in which 5-HMA was incorporated into the liquid phase with HEMA. The monomer 5-HMA has the ability to form molecu- lar complexes with calcium atoms [15] and could facilitate osteointegration in the application of these materials. 2. Materials and methods The experimental solid phase of acrylic bone cements was prepared from commercial PMMA beads ob- tained by suspension polymerization, kindly supplied 0957—4530  1998 Kluwer Academic Publishers 679