736 J. Indian Chem. Soc., Vol. 92, May 2015, pp. 736-738 Sodium calcium silicate/chitosan composites for hard tissue applications Aviral Srivastava, Sivasankar Koppala, Madhusudhana Rao Nasina and Sasikumar Swamiappan* School of Advanced Sciences, VIT University, Vellore-632 014, Tamilnadu, India E-mail : ssasikumar@vit.ac.in Abstract : In this study, we have prepared bioactive sodium calcium silicate (SCS) powders from sodium carbonate, calcium nitrate, tetraethyl orthosilicate (TEOS) by sol-gel combustion method using citric acid as a fuel. Phase forma- tion of the synthesized SCS powders was characterized by powder X-ray diffraction (XRD). Composites were prepared by adding different ratios of sodium calcium silicate powder to chitosan and their in vitro bioactivity was analyzed by immersing the composites in simulated body fluid (SBF) solution. Results show that more chitosan contain composite shows greater bioactivity when compared to the composites contains lesser chitosan. Estimation of calcium ion concen- tration in the SBF solution indicates that the calcium content present in the composite influences bioactivity. Keywords : Sol-gel combustion, sodium calcium silicate, chitosan, bioactivity. Introduction Hydroxyapatite (HAP) is well studied for several years for biomedical applications because of its excellent bio- activity and osteoconductivity. However the poor me- chanical properties (such as low fracture toughness) limit the scope of HAP in clinical applications. Recently, ex- tensive research interest has been shown in development of silicon (Si) containing biomaterials for biomedical com- mitments particularly hard tissue regeneration applica- tions. The advantage of silicates materials is their ability to release Si ions at concentrations that stimulates osteo- blast cell growth and differentiation. These osteoblast cells are responsible for the extracellular matrix formation in bone 1–3 . Calcium silicate ceramics such as larnite and wollastonite were already known for its bioactivity and biocompatibility characteristics. Similarly bioactive glasses are also studied intensively for hard tissue repair, due to their ability to form a chemical bond via apatite layer between bioactive glasses and natural tissues. In bioactive glasses silicon plays a major role in bioactivity and con- sidered as a potential candidate for hard tissue repair. Moreover, alkali metal containing calcium silicates such as sodium calcium silicate having similar composition of bioactive glasses possess good bioactivity with basic Na 2 O, CaO and SiO 2 components. Further, these sodium cal- cium silicates possess excellent mechanical properties 4–6 . HAP/chitosan bioceramic composites show better biomedical applications, since chitosan has hydrophilic surface, which helps in cell adhesion, proliferation and differentiation. Moreover, chitosan has cationic behavior along with good biocompatibility as well as better host response 7–9 . But sodium calcium silicate/chitosan (SCSC) composites are not well studied, which is expected to possess excellent bioactivity. In this study we prepared SCS powders by sol-gel combustion method and evalu- ated the HAP formation ability of their composites with chitosan. Results and discussion Synthesis and characterization : In this sol-gel process the H + ions from acid and OH – ions from silanes combines and condensation reaction takes place through which gel was formed via polymeric net- work. The evolved high temperature during combustion helps for SCS phase formation. The dried gel was cal- cined at 700 ºC and grinded, used for characterization. Fig. 1 shows the XRD pattern (obtained using Cu K, Ni filtered radiation in powder-XRD instrument, Bruker, D8 Advance, Germany) of the synthesized SCS powders cal- cined at 700 ºC for 4 h and resultant pattern was com- pared with reported pattern of the SCS powders with cubic crystal system (Na 2 CaSiO 4 , JCPDS file number : 096-101-0112). Particle size (D) of Na 2 CaSiO 4 phase was calculated to be in the nano regime using Scherrer’s for-