CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 39 (2013) 6533–6542 Micro-porous calcium phosphate coatings on load-bearing zirconia substrate: Processing, property and application Jing-Zhou Yang a,b , Rumana Sultana a , Paul Ichim c , Xiao-Zhi Hu a,n , Zhao-Hui Huang b , Wei Yi a , Bin Jiang a , Youguo Xu b a School of Mechanical and Chemical Engineering, University of Western Australia, Perth, WA 6009, Australia b School of Materials Science and Technology, China University of Geosciences (Beijing), Beijing 100083, PR China c School of Dentistry, University of Western Australia, Perth, WA 6009, Australia Received 7 October 2012; received in revised form 25 January 2013; accepted 25 January 2013 Available online 8 February 2013 Abstract This study presents the design, processing, properties and potential applications of a novel layered bio-ceramic composites consisting of three different micro-porous calcium phosphate coatings on strong zirconia cores manufactured using a recently developed slip coating-deposition and coating-substrate co-sintering technique. Detailed microstructures of the three graded micro-porous calcium phosphate coatings, and the coating/substrate interface have been investigated. Also, the flexural strength of the bio-ceramic composite and the bonding state between the coatings and zirconia substrate have been characterized. A preliminary and limited in vitro cell test indicates that the new scaffold composite has no cytotoxicity to the fibroblasts which can attach, proliferate and grow on the coating surfaces. Because of the combination of bio-function and strength, such layered load-bearing bio-ceramic composites are a potential candidate for large-scale head bone repairs. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Sintering; B. Microstructure; C. Strength; E. Biomedical application; Apatite-zirconia composite 1. Introduction The intended use of artificial bio-functional bone scaf- folds is for implantation in critical size hard tissue defects which in some cases need to sustain mechanical loading [1]. The ceramic scaffolds have drawn significant interest in the past years and experimental data shows that hydroxyapa- tite/tri-calcium phosphate (HA/TCP) scaffolds structures with open pores larger than 100 mm are bio-resorbable and osteoconductive [2–5]. However, such scaffolds can be used as implants/spacers mostly for small bone defect and light-load-bearing bone defect repairs, because of their inadequate mechanical performance, with a compressive strength in the range of 2–36 MPa [6]. Even the fully dense hydroxyapatite ceramic only exhibits a bending strength of 100 MPa. A load bearing device provides mechanical stability at the time of implantation and, by gradually transferring the load to the bone, stimulates bone healing [1]. Significant efforts have been made to build load bearing scaffolds. Cesarano et al. [7] used a robocasting technique to produce a load bearing HA lattice scaffold with hierarchical porosity and the compressive strength similar to the cortical bone. Using double slip-casting method, Zhang et al. manufactured a strong HA scaffold with a bending strength of 73.3 MPa [8]. Because the bending strength of compact bones ranges from 50 MPa to 300 MPa [9] the immediate or heavy load- bearing capacity of calcium phosphate based scaffolds for large scale bone defects such as cranioplasty or mandibular recosntructions is obviously limited. In addition to carrying the motion generated by muscle contractions, some clinical applications of rigid scaffolds require for these to provide physical protection of the organs they cover, as is the case of titanium plates (Fig. 1a) and scaffold-like meshes [10,11] used for cranioplasty defect repair as it is essential to preserve the brain safety. www.elsevier.com/locate/ceramint 0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.01.086 n Corresponding author. Tel.: þ 61 8 6488 2812; fax: þ 61 8 6488 1024. E-mail addresses: xhu@mech.uwa.edu.au, xiao.zhi.hu@uwa.edu.au (X.-Z. Hu).