IOP PUBLISHING BIOMEDICAL MATERIALS Biomed. Mater. 5 (2010) 015005 (6pp) doi:10.1088/1748-6041/5/1/015005 Conversion of borate-based glass scaffold to hydroxyapatite in a dilute phosphate solution * Xin Liu 1,2, 4 , Haobo Pan 3 , Hailuo Fu 2 , Qiang Fu 2 , Mohamed N Rahaman 2 and Wenhai Huang 1, 4 1 Institute of Bioengineering and Information Technology Materials, Tongji University, Shanghai 200092, People’s Republic of China 2 Department of Materials Science and Engineering, and Center for Bone and Tissue Repair and Regeneration, Missouri University of Science and Technology, MO 65409, USA 3 Department of Orthopaedics and Traumatology, University of Hong Kong, Hong Kong 999077, People’s Republic of China E-mail: tsliuxin@hotmail.com and whhuang@tongji.edu.cn Received 1 September 2009 Accepted for publication 2 December 2009 Published 7 January 2010 Online at stacks.iop.org/BMM/5/015005 Abstract Porous scaffolds of a borate-based glass (composition in mol%: 6Na 2 O, 8K 2 O, 8MgO, 22CaO, 36B 2 O 3 , 18SiO 2 , 2P 2 O 5 ), with interconnected porosity of ∼70% and pores of size 200–500 μm, were prepared by a polymer foam replication technique. The degradation of the scaffolds and conversion to a hydroxyapatite-type material in a 0.02 M K 2 HPO 4 solution (starting pH = 7.0) at 37 ◦ C were studied by measuring the weight loss of the scaffolds, as well as the pH and the boron concentration of the solution. X-ray diffraction, scanning electronic microscopy and energy dispersive x-ray analysis showed that a hydroxyapatite-type material was formed on the glass surface within 7 days of immersion in the phosphate solution. Cellular response to the scaffolds was assessed using murine MLO-A5 cells, an osteogenic cell line. Scanning electron microscopy showed that the scaffolds supported cell attachment and proliferation during the 6 day incubation. The results indicate that this borate-based glass could provide a promising degradable scaffold material for bone tissue engineering applications. 1. Introduction Tissue engineering provides an alternative way to regenerate diseased or damaged tissues back to their original state and function. In the bone tissue engineering approach, a porous material or scaffold serves as a substrate for cell attachment, proliferation and differentiation. Ideally, the scaffold should be biocompatible and biodegradable, and have a porous three-dimensional structure with the requisite mechanical properties [1]. Bioactive glasses have attractive properties for bone tissue engineering. They react with the body fluids to form a hydroxyapatite-type surface layer which is responsible for ∗ This work was presented at the Materials Science and Technology (MS&T’09) Conference Symposium: Next Generation Biomaterials, Pittsburgh, PA, 25–29 October 2009. 4 Authors to whom any correspondence should be addressed. forming a strong bond with bone [2]. Since the discovery of 45S5 glass by Hench [3], most bioactive glass materials have been based on the silicate 45S5 composition. The conversion of silicate bioactive glass to hydroxyapatite (HA) in an aqueous phosphate solution involves a series of reactions, such as ion exchange reactions between the glass and the solution, leading to the formation of a SiO 2 -rich layer on the glass surface, followed by the precipitation of an amorphous calcium phosphate layer on the SiO 2 -rich layer, which eventually crystallizes to HA [4–6]. The formation of this HA layer is responsible for the strong bonding between the bioactive glass and surrounding bone and soft tissue, so the rate at which the bioactive glass converts to HA provides a criterion for evaluating the in vitro bioactivity of a material. There has been growing interest in the use of bioactive glass as scaffolds for bone tissue engineering [7–11]. However, despite their excellent bioactivity, the silicate-based bioactive glasses such 1748-6041/10/015005+06$30.00 1 © 2010 IOP Publishing Ltd Printed in the UK