In Vitro Study of Octacalcium Phosphate Behavior in Different Model Solutions

Abstract

Octacalcium phosphate (OCP), a new-generation bone substitute material, is a considered precursor of the biological bone apatite. The two-layered structure of OCP contains the apatitic and hydrated layers and is intensively involved in ion-exchange surface reactions, which results in OCP hydrolysis to hydroxyapatite and adsorption of ions or molecular groups presented in the environment. During various in vitro procedures, such as biomaterial solubility, additive release studies, or the functionalization technique, several model solutions are applied. The composition of the environmental solution affects the degree and rate of OCP hydrolysis, its surface reactivity, and further in vitro and in vivo properties. The performed study was aimed to track the structural changes of OCP-based materials while treating in the most popular model solutions of pH values 7.2−7.4: simulated body fluid (SBF), Dulbecco's phosphate-buffered saline (DPBS), supersaturated calcification solution (SCS), normal saline (NS), and Dulbecco's modified Eagle's medium (DMEM). Various degrees of OCP hydrolysis and/or precipitate formation were achieved through soaking initial OCP granules in the model solutions. Detailed data of X-ray diffraction, Fourier-transform infrared spectroscopy, atomic emission spectrometry with inductively coupled plasma, and scanning electron microscopy are presented. Cultivation of osteosarcoma cells was implemented on OCP pre-treated in DMEM for 1−28 days. It was shown that NS mostly degraded the OCP structure. DPBS slightly changed the OCP structure during the first treatment term, and during further terms, the crystals got thinner and OCP hydrolysis took place. Treatment in SBF and SCS caused the precipitate formation along with OCP hydrolysis, with a larger contribution of SCS solution to precipitation. Pre-treating in DMEM enhanced the cytocompatibility of materials. As a result, on performing the in vitro procedures, careful selection of the contact solution should be made to avoid the changes in materials structure and properties and get adequate results.

Thermodynamics and Kinetics of Struvite Crystallization from Hydrothermal Liquefaction Aqueous-Phase Considering Hydroxyapatite and Organics Coprecipitation

“…The empirically fitted reaction orders obtained for the crystallization of struvite and hydroxyapatite were 0.6 and 0.13, respectively (see Table ). The fractional order of reaction indicated that both reactions were nonelementary and suggested the involvement of a series of multiple steps rather than one single step, in agreement with the three steps reported earlier for struvite − and the five steps reported for hydroxyapatite crystallization in previous studies. − …”

“…Hydroxyapatite crystallization starts with the formation of unstable amorphous calcium phosphate, followed by the hydration, dissolution, and recrystallization steps to form octacalcium phosphate . The formed octacalcium phosphate may experience rapid hydrolysis to yield thermodynamically stable hydroxyapatite crystal nuclei via a topotactic reaction, followed by the crystal growth. ,, The stoichiometry of hydroxyapatite formation is shown in Scheme B.…”

“…76 The formed octacalcium phosphate may experience rapid hydrolysis to yield thermodynamically stable hydroxyapatite crystal nuclei via a topotactic reaction, followed by the crystal growth. 74,75,78 The stoichiometry of hydroxyapatite formation is shown in Scheme 1 B.…”

Acceleration of bone formation by octacalcium phosphate composite in a rat tibia critical-sized defect

“…Studies have shown that the use of OCP as a bone substitute material is of interest from the point of view of osteogenesis in intramembranous ossification [ 36 , 37 ]; however, its clinical utility is still unclear and there is a lack of evidence compared to β-TCP or calcium sulfate, which are widely used in orthopedics. Regarding the phase composition, OCP has a two-layered structure of hydrate and apatite layers, and the apatite layers are involved in ion–exchange reactions at the phase boundary between the material and given environment [ 38 ]. Moreover, OCP has been proposed as a precursor of biological apatite in bones and OCP was reabsorbed by osteoclasts in addition to dissolution by pH in the body [ 36 ].…”

Periodontal Disease Monitoring by Raman Spectroscopy of Phosphates: New Insights into Pyrophosphate Activity

“…The two-layered structure of OCP contains the apatitic and hydrated layers and is intensively involved in ion-exchange surface reactions, which results in OCP hydrolysis to hydroxyapatite (HA) and adsorption of ions or molecular groups presented in the environment as motion species ((HPO 4 ) 2− , Ca 2+ , OH 1− ). The composition of the solution and environmental structure (collagen matrix) affects the degree and rate of OCP hydrolysis, its surface reactivity and further in vitro and in vivo properties [ 13 ].…”