Synthesis and characterization of xanthan–hydroxyapatite nanocomposites for cellular uptake

• Hydroxyapatites with or without strontium were prepared in xanthan solution.
• Xanthan chains enriched the surface of hydroxyapatite nanoparticles (HAp).
• Xanthan modified HAp and xanthan hydrogels formed compatible nanocomposites.
• Nanocomposites are suitable for bone mineralization, particularly those with Sr.

In this work xanthan–nanohydroxyapatite (XnHAp) and its equivalent strontium substituted (XnHApSr) were synthesized by the precipitation of nanohydroxyapatite in xanthan aqueous solution, characterized and compared to conventional hydroxyapatite particles (HAp). XnHAp and XnHApSr were less crystalline than HAp, as revealed by X-ray diffraction. Xanthan chains enriched the surface of XnHAp and XnHApSr particles, increasing the zeta potential values from −(7 ± 1) mV, determined for HAp, to −(17 ± 3) mV and −(25 ± 3) mV, respectively. This effect led to high colloidal stability of XnHAp and XnHApSr dispersions and acicular particles (140 ± 10) nm long and (8 ± 2) nm wide, as determined by scanning electron microscopy and atomic force microscopy. XnHAp and XnHApSr particles were added to xanthan hydrogels to produce compatible nanocomposites (XCA/XnHAp and XCA/XnHApSr). Dried nanocomposites presented surface energy, Young's modulus and stress at break values comparable to those determined for bare xanthan matrix. Moreover, adding XnHAp or XnHApSr nanoparticles to xanthan hydrogel did not influence its porous morphology, gel content and swelling ratio. XCA/XnHAp and XCA/XnHApSr composites proved to be suitable for osteoblast growth and particularly XCA/XnHapSr composites induced higher alkaline phosphatase activity.

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