A quantitative approach for studying the bioactivity of nanohydroxyapatite/gold composites Amany A. Mostafa, 1,2,3 Hassane Oudadesse, 1 Mayyada M. H. El-Sayed 3,4,5 1 Solid-State Chemistry, Universit e de Rennes 1, UMR CNRS 6226, 263 av. du g en eral leclerc, 35042 Rennes Cedex, France 2 Biomaterials Department, National Research Centre NRC, Cairo, Egypt 3 Nanomedicine & Tissue Engineering Lab, Medical Research Center of Excellence (MRCE), NRC, Cairo, Egypt 4 Chemical Engineering Department, National Research Centre, Al Bohooth St., Cairo, Egypt 5 Chemistry Department, American University in Cairo, New Cairo, Egypt Received 12 January 2015; revised 25 April 2015; accepted 29 April 2015 Published online 19 May 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.a.35494 ABSTRACT: This work describes a quantitative kinetic approach to assess the in vitro bioactivity of gold-doped hydroxyapatite-polyvinyl alcohol nanocomposites. The sur- face morphology of the in situ prepared nanocomposites as characterized by transmission electron microscopy (TEM) revealed a rod-like shape. Differential thermal analysis- thermogravimetric (DTA–TG), and fourier transformed infra- red spectroscopy (FTIR) as well as zeta potential measure- ments of the prepared nanocomposites were carried out. Uptake profiles of Ca and P were studied onto nanocompo- sites of different gold concentrations after their soaking in simulated body fluid and they best followed the pseudo second-order kinetic model. The highest uptakes of both Ca and P were obtained using the nanocomposite with the low- est concentration of gold. Furthermore, sorption mechanism was described by the intraparticle diffusion model where pore diffusion was found to be the rate limiting step. The prepared nanocomposites have promising potential in ortho- pedic and tissue engineering applications because of their high capacity and fast uptake for Ca and P, which form apa- tite. V C 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 3483–3492, 2015. Key Words: gold nanoparticles, kinetics, bioactivity, nano- composites, hydroxyapatite How to cite this article: Mostafa AA, Oudadesse H, El-Sayed MMH. 2015. A quantitative approach for studying the bioactivity of nanohydroxyapatite/gold composites. J Biomed Mater Res Part A 2015:103A:3483–3492. INTRODUCTION The structure of ceramic biomaterials can be configured to attain favorable chemical, surface, and mechanical proper- ties similar to that of physiological bone. 1,2 They could hence be utilized in orthopedic and dental formulations with enhanced biological and mechanical properties that promote osteoblast adhesion and decrease osteoclasts. How- ever, biocompatibility of these materials remains an issue that has to be considered in the synthesis and design pro- cess. Biomineralization of bone has been investigated in pre- vious work where calcium phosphate was deposited on a matrix of collagen fibrils. 3,4 The hydrophilicity of these mac- romolecules allowed for enhanced growth of calcium and phosphorous in vitro 5 and in vivo 6 and regulated nucleation, polymorphism, and growth of the crystals. 7 The osteoconductivity and biocompatibility of hydroxy- apatite (HA) crystals has attracted many researchers to uti- lize them as appropriate implant materials and drug delivery agents. For implant applications, the capability to control the morphology and size of HA crystal is crucial since it permits modifying the mechanical properties of the implant. 8–12 However, bone is considered as an example of a composite with multiple levels of hierarchical organization, which makes it difficult to be completely mimicked. 13 Metal nanoparticles, especially gold nanoparticles (Au NPs), have been widely used in biosensor fabrication and as efficient materials for protein immobilization. 14,15 Gold and silver nanoparticles have been used as templates for the growth of HA crystals. 16,17 Gold nanoparticles, mostly with dimension less than 10 nm, reveal highly catalytic activities in different kinds of reactions, a property not shown in bulk gold. 18–21 Gold nanoparticles were used to prepare biocon- jugates with proteins, 22 for example gold bioconjugated with collagen forms an efficient matrix for HA growth. 23–25 As has been reported, polymer-conjugated HA is an effective formulation for intelligent artificial bone materi- als. 26–28 Several workers have adopted the biomimetic approach in the synthesis of HA-polymer composites. Some of the most recently employed polymers are gelatin, colla- gen, poly (lactic acid) (PLA) and poly (acrylic acid) (PAAc) and these have been utilized due to their calcium binding ability. 29–33 Other polar polymers with potential biomedical applications are polyvinyl alcohol (PVA) and polyvinyl pyr- rolidone (PVP). 34–36 Designing novel experimental processes Correspondence to: Amany Mostafa; e-mail: amany.mostafa@univ-rennes1.fr, amani.mostafa@gmail.com V C 2015 WILEY PERIODICALS, INC. 3483