An efficient method to synthesize carbonated nano hydroxyapatite assisted by poly (ethylene glycol) Huaifa Zhang a , Ming Liu b , Hongsong Fan a, ⁎, Xingdong Zhang a a National Engineering Research Center for Biomaterials, Sichuan University, Chengdu 610064, Sichuan, China b Analytical & Testing Center, Sichuan University, Chengdu 610064, Sichuan, China abstract article info Article history: Received 16 July 2011 Accepted 24 January 2012 Available online 31 January 2012 Keywords: Biomaterials Nanoparticles Nano hydroxyapatite Poly(ethylene glycol) A simple and efficient method to prepare carbonated nano hydroxyapatite (n-CHAp) powders with good dispersivity was developed. n-CHAp was synthesized using chemical precipitation method assisted by poly(ethylene glycol) (PEG), the PEG additive and reaction byproduct were excluded through calcination con- veniently. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscope (TEM) and dynamic lighting scattering (DLS), respectively. The results show that PEG can promote HAp formation, modulate the particle morphology and size, and effectively reduce the aggregation of n-CHAp powders. Both PEG and byproduct NH 4 NO 3 can be removed through calcination. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Hydroxyapatite (HAp) is chemically similar to the inorganic phase of natural bone [1] and has been widely used as biomaterials [2,3]. Due to their high surface energy and increased specific area, nano HAp (n-HAp) particles exhibit better biological and mechanical properties than normal HAp [4,5], and thus have gained extensive applications from bone grafts [3], metallic implants coatings [6] to drug delivery [7]. Actually, the minerals in natural bone are carbonated n-HAp (n-CHAp) [8]. Hence, n-CHAp may have better bioactivity than n-HAp [4] and is being more and more widely used as biomaterials. Therefore, it is meaningful to prepare large amounts of well-dispersed n-CHAp powders. Many methods have been used to synthesize n-CHAp [9]. However, those methods have some disadvantages, such as complex procedures, expensive raw materials (which are usually toxic), serious particle aggregation, and limited yield. The most critical challenge is how to obtain enough amounts of well dispersed n-CHAp powders. Poly(ethylene glycol) (PEG) can interact with calcium ions through ethylen oxygen groups (\CH 2 \CH 2 \O\) in the molecules and mediate the size and morphology of n-CHAp particles [10,11]. At the same time, PEG can enwrap the precipitations and reduce the aggregation among the nano particles [12]. In addition, PEG have large exclusion volume in aqueous solutions [13], and thus can provide additional steric hindrance among the nano particles, which can also inhibit particle aggregation. Moreover, PEG can decompose completely when heat-treated at high temperatures, so the added PEG can be removed easily from the products by calcination. Chemical precipitation method is cheap and simple to produce n- CHAp in high yield, making it a good candidate to synthesize n-CHAp in large scale. The problem is how to remove the contaminations, including the reaction additives and byproducts. Washing process is often used to remove the contaminations [14], but it is tedious and time consuming, and hard to remove them completely. Calcination method is convenient and fast to exclude the additives and bypro- ducts that can decompose into water and gases at high temperatures, however, it usually causes serious particle aggregation [15], so it is difficult to obtain well dispersed nano particles. Nevertheless, we try to solve this aggregation problem by adding dispersants with large steric hindrance. In this work, we developed a simple and efficient method to synthesize dispersive n-CHAp assisted by PEG. 2. Materials Poly(ethylene glycol) (MW6000, PEG6000) (AR), (NH 4 ) 2 HPO 4 (AR), Ca(NO 3 ) 2 ·4H 2 O (AR), HNO 3 (AR) and NH 3 ·H 2 O (AR) were acquired from Chengdu Kelong Chem Co. 3. Preparation and characterization of the samples Firstly, PEG6000 was dissolved in an aqueous solution of 0.1 mol/L Ca(NO 3 ) 2 with the concentration of 8.00 and 16.00 wt.%, respectively. Following the addition of 0.2 mL HNO 3 , equal volume of 0.06 mol/L (NH 4 ) 2 HPO 4 aqueous solution was added into the PEG-Ca(NO 3 ) 2 so- lution; Then the mixed liquid was stirred at 1 °C; When the solution Materials Letters 75 (2012) 26–28 ⁎ Corresponding author. Tel.: + 86 28 85410703; fax: + 86 28 85410246. E-mail address: hsfan@scu.edu.cn (H. Fan). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.01.110 Contents lists available at SciVerse ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet