Engineering, 2011, 3, ***-*** doi:10.4236/eng.2011.380** Published Online August 2011 (http://www.SciRP.org/journal/eng) Copyright © 2011 SciRes. ENG A Study on Mechanical Properties of PMMA/Hydroxyapatite Nanocomposite S. M. Zebarjad, S. A. Sajjadi, T. Ebrahimi Sdrabadi, A. Yaghmaei, B. Naderi Department of Materials Science and Metallurgical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran E-mail: zebarjad@um.ac.ir Received 2011 Abstract This study is focused on the role of nano hydroxyapatite particles on the mechanical properties of PMMA/HA nanocomposites. In order to achieve a proper and homogeneous distribution of HA particles in the polymer matrix, mixer milling process was applied. Wear, compression and three-point bending tests were conducted. It was observed that wear rate decreased by increasing in HA content in both atmosphere and artificial saliva. The results of compression tests showed that the addition of 2.5 percent HA to PMMA promoted ultimate compressive strength, yield strength and modulus while caused to decrease elongation at break. Also it was elucidated that addition of HA more than 2.5 wt.% caused a decrease in both ultimate compressive strength and compression yield strength and an increase in elongation at break. The results of three-point bending tests on the PMMA cements containing 2.5 percent HA demonstrated the maximum bending strength value and modulus among all the HA containing formulations. However there was no direct proportionality between the results of bending tests and the HA content and the addition of HA to PMMA (up to 10 wt.%) did not change the bending properties significantly. Keywords: PMMA, Nano Hydroxyapatite, Mechanical Properties 1. Introduction Polymethylmethacrylate (PMMA) is widely used as bone cement to secure orthopedic implants to the skeleton [1]. Because of its limited mechanical properties and poor compatibility with bone, the clinical use of this cement is accompanied by complications. Some examples of these limitations are brittleness and shrinkage of PMMA, void production in processing [2,3,4], lack of adherence to the bone [5,6] and exothermic reaction of polymerization which can damage bone tissue [7,8]. To improve the noted deficiencies several investigators have studied bioceramic-reinforced polymer composite materials [9-12]. Hydroxyapatite (HA)-reinforced polymer com- posites are instances of these materials that can be used as bone cement, filling bone defects, coating of joint re- placement prosthesis and dental implants [13]. Several investigators have studied HA-reinforced PMMA (PM- MA/HA) as a potential bone cement [10, 14-16]. In fact addition of HA to the bone cement can improve bio- compatibility and also enhance the mechanical properties of the cement because of its both biocompatibility and osteoconductivity [17–20]. Depending on HA amount added, mechanical and thermal properties of the cement can differ [21]. It is also reported that size and surface properties of the particles can increase or decrease the mechanical properties of the bone cement [12, 22]. Vallo et al. [23] indicated that addition of up to 15 wt% HA to a commercially available PMMA-based bone cement can improve the flexural modulus but with this amount of HA, the tensile and compressive strengths have been observed to remain constant in PMMA base cement. The fracture toughness of HA-reinforced PMMA has been observed to be increased by addition of 40wt% HA [24]. Moursi et al. [25] have used three point bending test to investigate the effect of addition of HA on mechanical properties of PMMA cement. It is indicated that the presence of HA can increase the ultimate stress of PMMA from 4-44 MPa to 11-83 MPa. Kim et al. [11] produced a new bioactive bone cement that consists of HA, PMMA and chitosan. It was indicated that compres- sive strength of the cement was lower than the pure PMMA. Mechanical properties of acrylic base cements reinforced with HA have been studied by Serbetci et al.