Journal of Applied Solution Chemistry and Modeling, 2016, 5, 21-29 21 E-ISSN: 1929-5030/16 © 2016 Lifescience Global Colloidal Hydroxyapatite/Poly(Acrylic Acid) Hybrids Using Calcium Sucrate and Ammoniumdihydrogen Orthophosphate W.P.S.L. Wijesinghe 1,2 , M.M.M.G.P.G. Mantilaka 1,2 , A.M.C.P. Weerasinghe 3 , K.M. Nalin de Silva 4 , T.P. Gamagedara 1,2 and R.M.G. Rajapakse 1,2,* 1 Department of Chemistry, Faculty of Science, University of Peradeniya, 20400 Peradeniya, Sri Lanka 2 Postgraduate Institute of Science, University of Peradeniya, 20400 Peradeniya, Sri Lanka 3 Department of Botany, Faculty of Science, University of Peradeniya, 20400 Peradeniya, Sri Lanka 4 Sri Lanka Institute of Nanotechnology, Nanotechnology and Science Park, Mahenwatta, Pitipana, Homagama, Sri Lanka Abstract: This manuscript is concerned with a simple and novel method to synthesize hydroxyapatite-poly(acylic acid) hybrid materials for broad range of applications. In this method, hydroxyapatite nanoparticles are synthesized using calcium sucrate and ammoniumdihydrogen orthophosphate in the presence of poly(acrylic acid). Increase in poly(acrylic acid) concentration in the synthesis medium results in the increase in the hydrodynamic radius of particle size allowing increased hydration. Poly(acylic acid) tends to control both crystallite size and colloidal stability. Increase in poly(acrylic acid) concentration decreases the crystallite size of the products but considerably increases their shelf life as stable colloidal solutions. Thermo gravimetric analysis shows that there are no combustible or volatile impurities present in these samples. This is further supported by FT-IR studies, which show three types of interactions between hydroxyapatite nanoparticles and poly(acrylic acid). Keywords: Hydroxyapatite, Poly(acrylic acid), Stable colloids, Hybrid materials, Calcium sucrate. 1. INTRODUCTION Stable dispersions of colloidal hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] (HA) nanoparticles are very useful in biomedical fields. Therefore, it is essential to preserve HA nanoparticles as dispersions for a prolonged period in order to use them in wide-range of biomedical applications [1]. Well-stabilized HA colloids are mainly used in the preparation of HA-coated, biocompatible metal prostheses which are prepared by electro- deposition and dip-coating techniques [2]. Furthermore, colloidal HA nanoparticles are used as delivery systems of peptides, proteins, and DNA therapeutics and as a dental adhesive [3, 4]. Water-soluble, biocompatible polymers are used in the stabilization of HA nanoparticles in their colloidal forms. The resulting material is a polymer/HA hybrid. Furthermore, the phase, morphology and particle size of HA in the composite are controlled by the polymer [5]. Therefore, preparation of such hybrid materials is very important to prepare HA for specific applications. Bone is an excellent example for an organic/HA nanohybrid which is made up of HA nanoparticles and collagen protein fibers [6, 7]. Collagen fibers provide a structural framework for the bone and HA nanoparticles *Address correspondence to this author at the Department of Chemistry, Faculty of Science, University of Peradeniya, 20400 Peradeniya, Sri Lanka; Tel: +94 81 2394442; E-mail: rmgr@pdn.ac.lk are dispersed in collagen matrix [8, 9]. Therefore, HA nanoparticles are synthesized to use in biomedical applications with structurally and compositionally similar characteristics to natural HA in bones [10]. However, it is not possible to produce artificial bones with synthetic HA alone to mimic natural bones, for them to be used in biomedical applications such as bone remodeling, mechanical stability and carrier for drugs/growth factors [11]. Therefore, synthetic HA nanoparticles are combined with biocompatible and biodegradable organic polymers such as poly(acrylic acid) (PAA) [12, 13], poly(lactic acid) [14], poly(caprolactone) [15], and gelatin [16-18] in order to prepare hybrid materials to suit different biomedical applications [19]. These hybrid materials containing biodegradable polymers are degraded after introducing to the body as bone fillers [11]. Mechanical properties of HA can also be enhanced by combining with the polymers [18, 20]. Therefore, HA-polymer hybrid materials play a vital role in biomedical applications [18, 21]. Hybrid materials should be homogenously dispersed when they are used as bone cements and drug delivery agents. Most of the researchers have re- dispersed HA hybrid materials in different solvents [22, 23]. Generally, PAA is used to deliver drugs individually and also by combining with the other polymers. As such, PAA-HA hybrids also can deliver drugs or growth factors when they are applied in biomedical devices