Abstract <p>The paper considers the possibility of cationic isomorphic substitutions for controlling and changing the properties of hydroxyapatite (HA). HA was synthesized by changing the concentration of Mg²⁺, Ca²⁺ ions and adding Zn²⁺ ions at physiological pH 7.45 ± 0.05 from a model solution of synovia. It was found that the synthesis carried out with an increase in the concentration of magnesium ions leads to the appearance of a new phase—whitlockite. A large volume of the unit cell and a variety of different structural positions determine the ability of whitlockite to a variety of isomorphism. This largely serves as a source of a wide range of functional properties inherent in compounds with this structural type. Synthesis carried out with a simultaneous increase in the concentration of Mg² ions and a decrease in the concentration of Ca²⁺ ions has a huge destabilizing effect on the formation of HA and leads to the formation of new phases: whitlockite, phosphate, oxide and hydroxide of magnesium. It has been established that synthesis with the introduction of small amounts of Zn²⁺ ions (up to 12 mg/L inclusive) does not affect the phase composition of the obtained samples, the amorphousness of the solid phase and the mass of the resulting sediments increase slightly, and the size of the crystallites decreases. Synthesis of new compounds with specified physical properties and chemical composition is a relevant and practical task.</p>