Biomimetic nanocomposites of carboxymethyl cellulose-hydroxyapatite: novel three dimensional load bearing bone grafts

An innovative biomimetic synthesis of novel three dimensional micro/macro porous carboxymethyl cellulose (CMC)-hydroxyapatite (HA) nanocomposites having four systematically different compositions has been established for its possible application as a load bearing synthetic bone graft. Our process, being in situ, involves a simple and cost effective route akin to a matrix mediated biomineralization process. Developed synthesis route not only controls the size of HA particles in the range of 15-50 nm, embedded in CMC matrix, but also assists in the formation of a mechanically strong three dimensional nanocomposite structures due to physical cross linking of HA impregnated CMC matrix. The process does not involve any toxic cross linker and works at near ambient conditions. The nanocomposites are systematically structurally and mechanically characterized using various techniques like scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform IR (FTIR), solid state (13)C nuclear magnetic resonance ((13)C NMR), thermo-gravimetric analysis (TGA) and Universal mechanical test. It reveals that the ionic/polar or electrostatic interactions are the main driving force for formation of load bearing three dimensional nanocomposites via a process similar to matrix mediated biomineralization. Compressive strength and compressive modulus of nanocomposites, being in the range of 1.74-12 MPa and 157-330 MPa, respectively, meet the desired range of compressive strength for the synthetic grafts used in cancellous bone. An increase in the compressive strength with increase in the porosity has been an interesting observation in the present study. In vitro cytotoxicity of the synthesized nanocomposites has been evaluated using bone marrow mesenchymal stem cells (BMSC) isolated from Wistar rat.