Whitlockite can be a substrate for apatite growth in simulated body fluid

Calcium phosphates are the predominant type of mineral in humans. They are essential for the formation of bones and teeth but can also deposit in diseased tissues. Whitlockite, a calcium phosphate mineral, is almost exclusively found in diseased calcified lesions. Despite its significance, the crystal growth mechanisms of whitlockite under physiological conditions are poorly understood. To investigate this, we conducted a constant composition experiment and applied a growth kinetics model to study the growth of whitlockite and hydroxyapatite nanoparticles in simulated body fluid. Contrary to our expectations, whitlockite did not dissolve in the undersaturated simulated body fluid. Instead, whitlockite nanoparticles served as a substrate for the formation of poorly-crystalline apatite, resulting in increased particle size. Our findings may help explain the colocalisation of whitlockite particles and large poorly-crystalline apatite lesions in human diseases.