Evaluating Initial Content of the Slurry and Cooling Rate on the Microstructural and Mechanical Characteristics of Freeze casted Hydroxyapatite Macroporous Scaffolds Sajad Farhangdoust a , Sayed Mahmood Rabiee b , Ali Zamanian c , Mana Yasaei d , Mina Khorami e , Masoud Hafezi-Ardakani f , Nanotechnology and Advanced Materials Department, Materials and Energy Research Center, Karaj, Iran a s.farhangdoust@yahoo.com, b rabiee@nit.ac.ir, c a-zamanian@merc.ac.ir, d yasaei.m@gmail.com, e khorami_m@merc.ac.ir, f mhafezi@merc.ac.ir Keywords: scaffold; freeze-casting; cooling rate; concentration; hydroxyapatite; unidirectional; mechanical properties; Abstract. Scaffolds have to meet exacting physical, chemical, and biological criteria to function successfully, and those criteria vary with the type of tissue being repaired. In the present work, slurry with different initial content of 7.5-22.5 vol% HA prepared from calcinated hydroxyapatite. The prepared slurries freeze casted unidirectionally with the different cooling rate of 2-14°C/min with intervals of 3°C/min from the ambient temperature. Then, green bodies freeze-dried for 72h following with sintering at temperatures of 1350°C. The results showed that compressive strength goes up with cooling rate and initial content. Total porosity has a range of 66-88% while has a compressive strength of ~0.4-18 MPa. Porosity size has a value of 20-200 µm by initial content and cooling rate. Based on strength and porosity, the specimen with initial content and cooling rate of 15 vol% and 5°C/min, respectively, chose to be the optimum. This specimen has a compressive strength and porosity size of 5.26 MPa and 88 µm, respectively. The compressive strength value of the mentioned lamellar HA scaffolds was in the range of the values reported for human proximal tibia. Introduction Fabrication of materials with homogeneous and well defined architectures has received increasing research interest owing to their broad applications such as tissue engineering, delivery matrices, green packaging, nanocomposites, and automotive industry. Several methods including solvent casting/particulate leaching, gas foaming , rapid prototyping, and freeze-casting has been utilized to organize micron/nano size particles to obtain ordered structures. Among the different techniques used, freeze casting has been shown as a versatile, easily implemented, and promising technique to build structures such as scaffolds, porous nanocomposites, and microwire networks with well aligned and controlled porosity [1-3]. Porous hydroxyapatite (HA) bioceramics with open porestructures are of particular interest and importance, since they have excellent permeability and a large surface area, as well as excellent biocompatibility. These properties allow them to be used in biomedical engineering applications, such as bone scaffolds and drug carriers [4]. However, the low mechanical strength of normal HA ceramics restricts its use mainly to low load-bearing applications [5]. The preferred method of fabricating such bioceramics should be capable of tailoring their porosity, offering perfect and large interconnections, and achieving dense ceramic networks. During recent years, unidirectional freeze- casting has been emerged to solve this problem. Deville et al. prepared highly porous HA material that exhibited extraordinarily high compressive strengths, up to 145 MPa, with a porosity that reached 47% [2]. They suggested that these HA-based materials could be used in load-bearing Key Engineering Materials Vols. 529-530 (2013) pp 147-152 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.529-530.147 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 2.146.19.36-21/09/12,13:19:53)