Evaluation of Diammonium hydrogen phosphate and Ca(OH)2 nanoparticles for consolidation of ancient bones

The development of innovative conservation strategies for the restoration and conservation of bone finds of historical and archaeological interest is crucial to warrantee the fruition of the relics and, most important, to maintain the long-term access to the biological information recorded in the bones. The approach purposed in this study is based on smart nanostructured inorganic materials with both high physical and chemical compatibility with the treated support. In particular, an aqueous solution of diammonium hydrogen phosphate (DAP), which is a precursor agent for the growth of a 3D crystalline network of hydroxyapatite (HAP) has been used for the consolidation of degraded ancient bones of historical and archaeological interest to restore a continuous crystalline HAP network in the regions of the bone relics affected by degradation phenomena. The consolidation performance of the HAP has been evaluated also after a pre-treatment with Ca(OH)2 nanoparticles (NPs), successfully used in the last years for the consolidation of both carbonatic matrixes of artistic interest and of bone relics. The treated bone relics have been characterized in terms of porosity and surface area through gas porosimetry measurements: the in-situ precipitation of hydroxyapatite with or without pre-treatment with Ca(OH)2 NPs affects the overall porosity and the adsorption-desorption isotherms obtained through the Brunauer Emmet and Teller (BET) theory indicate a decrease of surface area and pore volume of 45% and 64% respectively. X-ray microtomography images clearly show, after the treatment, the formation of a homogeneous dense phase, confirming the consolidating effect on the bone relics. Moreover, it has been also observed that the consolidation treatment induces an increase of the Vickers microhardness higher than the 40%. Additionally, by means of a paleogenetic analysis we showed that authentic genetic data could be retrieved from bones even after the consolidating treatments.