In situ Synthesis and Characterizations of Bio-ceramic Based Hydroxyapatite in the Re-mineralization of Calcium-rich Matrices:

• The research develops hydroxyapatite (HAP) based, inorganic mineral system with improved properties for the consolidation – providing the binding mechanism to reestablish the loss of cohesion – of powdery porous building materials (calcareous stone, marble, cement) and decorated architectural surfaces (rock-art, wall paintings and mosaics) of archaeological, historic and artistic value. The interdisciplinary nature of this research focused at the interface of materials science, biotechnology and conservation science develops tailored sustainable conservation treatments, which consider fundamental aspects of substrate chemistry and structure to prescribe and metricate treatment protocols. The scientific approach exploits biomimetic principles to induce the formation of HAP crystals by triggering reactions between the Ca-rich substrates of wall paintings and ammonium phosphate precursors such as diammonium hydrogen phosphate (DAP, (NH₄)₂HPO₄), and ammonium dihydrogen also known as monoammonium dihydrogen phosphate (MAP, NH₄H₂PO₄).

  From a purely scientific perspective, the research develops new information to relate: (1) the chemical interactions, thermodynamics and kinetics of reactions between the phosphate reactants and CaCO₃, the main component in the stone, plaster or mortar, at various pH levels to the formation of orthophosphates such as HAP and rate/extent of consolidation (2) the impact of HAP formation within the decohesive layers in terms of microstructure-linked, fluid-transport, mechanical, durability and optical properties and (3) the chemical interactions of the reactant precursors with different pigments present in the surface paint layers. Acquired data show the potential of this treatment for the consolidation of powdery calcium carbonate-based surfaces and their protection from weathering and deterioration induced by passage-of-time and environmental action linked effects. These efforts develop quantitative materials science-based structure/property relations to engineer practical, prescriptive consolidation solutions in relation to the reactant chemistry, the substrate properties and the treatment application method relevant to the materials.

  

  Figure shows the application of ammnium phosphate to do the evaluation of hydroxyapatite effects for the consolidation of a Hellenistic-Roman rock-cut chamber tomb at Athienou-Malloura in Cyprus

  My group have carried out research work in the consolidation of excavated deteriorated ivories from Sanxingdui site.  The ivories, unearthed from the Sanxingdui site, have been buried underground for thousands of years. Over time, the organic matter within them has decomposed, and a substantial amount of clay has permeated, leaving the ivory relics fragile and severely deteriorated. Traditional consolidants, such as resins, are no longer sufficient to meet the conservation requirements. Hence, there is an urgent need to explore innovative materials for safeguarding these invaluable cultural heritage objects.  

  

  We have employed a range of analytical techniques to gain insights into the phase composition, microstructure, and the deterioration mechanism of the waterlogged ivory. Building upon this knowledge, we have implemented novel materials and methods for consolidation. A three-dimensional networked structure of hydroxyapatite can be synthesized in-situ within the ivory, resulting in a consolidation effect. This treatment has significantly enhanced the mechanical properties of the ivory samples.

  Selected Publications:

  1. Xiao Ma* (corresponding author), Magdalena Balonis, Hélène Pasco, Michael Toumazou, Derek Counts, Ioanna Kakoulli, “Evaluation of hydroxyapatite effects for the consolidation of a Hellenistic-Roman rock-cut chamber tomb at Athienou-Malloura in Cyprus”, Construction and Building Materials, 150 (2017), 333-344.

  2. Xiao Ma* (corresponding author), Hélène Pasco, Magdalena Balonis, Ioanna Kakoulli, “Investigation of the Optical, Physical, and Chemical Interactions between Diammonium Hydrogen Phosphate (DAP) and Pigments”, Sustainability 11 (2019), 3803.

  3. Magdalena Balonis, Xiao Ma, Ioanna Kakoulli, “Phase relations in the system calcium carbonate/ammonium phosphate under aqueous conditions and 25°C”, Journal of the American Ceramic Society 103 (2020), 3837-3850.

  4. Chao Wang, Siyi Xue, Yufeng Huang, Yangyang Li, Xiao Ma*(corresponding author), “Synthesis, characterization, and biological evaluation of “Bamboo lamellar” biomimetic hydroxyapatite”, Accepted, Ceramics International. DOI: 10.1016/j.ceramint.2025.01.285.

  More Publications are currently under way…