Localized Crystallization of Calcium Phosphates by Light‐Induced Processes

Medical treatment options for bones and teeth can be significantly enhanced by taking control over the crystallization of biomaterials like hydroxyapatite in the healing process. Light-induced techniques are particularly interesting for this approach as they offer tremendous accuracy in spatial resolution. However, in the field of calcium phosphates, light-induced crystallization has not been investigated so far. Here, we establish a proof of principle to successfully induce carbonate-hydroxyapatite precipitation by light irradiation. Phosphoric acid is released by a photolabile molecule exclusively after irradiation, combining with calcium ions to form a calcium phosphate in the crystallization medium. 4-Nitrophenylphosphate (4NPP) is established as the photolabile molecule and the system is optimized and fully characterized. We successfully crystallize a calcium phosphate by irradiation in aqueous solution and identify it as carbonate apatite. Control over the localization and stabilization of the carbonate apatite is achieved by a pulsed laser, triggering precipitation in calcium and 4NPP-containing gel matrices. We anticipate that the results of this communication will open up a wide range of new opportunities; both, in the field of chemistry for more sophisticated reaction control in localized crystallization processes, as well as in the field of medicine for enhanced treatment of calcium phosphate containing biomaterials.