Igor Valerievich Smirnov

A method for creating bioactive coatings for implants is proposed. These coatings consist of a plasma-coated hydroxyapatite layer and a dicalcium phosphate dihydrate transition layer deposited on top. This layer is then hydrolyzed to produce octacalcium phosphate (where Me = Mg²⁺, Sr²⁺, Ba²⁺) doped with divalent metal ions. X-ray diffraction analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy revealed that strontium cations isomorphically replace calcium in the octacalcium phosphate structure, while magnesium and barium ions inhibit the phase transformation of dicalcium phosphate dihydrate into octacalcium phosphate, forming amorphous phases. An in vitro study in a simulated physiological environment of SBF demonstrated the ability of coatings based on octacalcium phosphate doped with magnesium, barium and strontium cations to biomineralize, indicating their increased bioactive potential compared to bioinert hydroxyapatite.

The development of modern osteoplastic materials with controlled immunomodulatory properties represents a critical objective in bone tissue engineering. Octacalcium phosphate (OCP) serves as a promising precursor to bone apatite; however, its clinical application is limited by inconsistent biological response for recipients with similar nosology. Ionic doping presents a prospective approach for enhancing the functional characteristics of calcium phosphates. This study is dedicated to the synthesis and in vitro investigation of the immunomodulatory effects of low-temperature OCP co-doped with Sr²⁺/Mg²⁺ and Sr²⁺/Ba²⁺. The developed materials were characterized using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The incorporation of strontium during OCP synthesis was shown to destabilize the crystal lattice and reduce crystallite size. In vitro studies utilizing monocyte-like (THP-1 ATRA) and macrophage-like (THP-1 PMA) cell models demonstrated that the doped OCP materials did not induce cytotoxic effects and effectively modulated the functional activity of immune cells. Specifically, in monocyte-like cells, both OCP materials enhanced phagocytic activity and significantly increased the secretion of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6). In macrophage-like cells, the materials reduced phagocytic activity and exerted dual ion-dependent effects on reactive oxygen species (ROS) production. Furthermore, they stimulated cytokine secretion predominantly under non-inflammatory conditions. Notably, OCP_Sr20_Mg1 induced a comparatively milder proinflammatory response compared to OCP_Sr20_Ba1, specifically reducing ROS formation and cytokine secretion by monocyte-like and macrophage-like cells under standard conditions. These results suggest that Sr/Mg co-doping may provide a more balanced immunomodulatory profile favorable for osteoplastic applications. The findings indicate that the immunomodulatory effect is likely mediated through direct particle-cell interactions influencing intracellular processes such as phagocytosis and lysosomal activity, rather than being solely attributable to soluble ion release.

The clinical success of calcium phosphate bone grafts (CPs) largely depends on the body’s immune response. However, traditional biocompatibility tests use healthy organisms and cannot predict effectiveness in patients with common chronic inflammatory diseases. This study examines how inflammation modulates the immune response, in vitro and in vivo, to low-temperature biomimetic CPs: dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP), and hydroxyapatite (HAp). In vitro studies involved human monocytes, macrophages, lymphocytes, and mesenchymal stromal cells (MSCs), with or without pro-inflammatory activation. In vivo biocompatibility was assessed via subcutaneous implantation in rats, with or without Complete Freund’s Adjuvant (CFA)-induced inflammation. Under normal conditions, all CP caused minimal immune reactivity. Inflammation-activated macrophages, however, triggered an acute reaction with significantly increased TNF-α and IL-1β secretion. Healthy and inflamed animals showed sharp contrasts. Although all materials exhibited thickened fibrous capsules during inflammation, biocompatibility varied markedly: DCPD performed best by promoting angiogenesis with minimal inflammation; HAp provoked the most severes response, including tissue necrosis and signs of rejection; OCP showed intermediate effects, with angiogenesis but notable fibrosis. Inflammatory processes critically influence CP biocompatibility; materials biocompatible in healthy organisms can induce fibrosis or rejection under inflammation. Disease-relevant, immune-challenged models are essential to predict clinical efficacy and safety.

This paper presents the concept of formation of low-temperature ceramics—octacalcium phosphate and dicalcium phosphate dihydrate in the presence of directed magnetic fields. The phase composition and formation of the structure of the materials obtained during recrystallization were studied. It was found that the formation of calcium phosphate structures under the influence of a directed magnetic field leads to an increase in strength characteristics owing to the reorientation of the crystal growth plane during the transformation process.

BACKGROUND: Synthetic materials based on calcium phosphate compounds (CPCs) are increasingly used in modern regenerative medicine to stimulate bone tissue regeneration. AIM: The work aimed to assess key parameters of biocompatibility in vitro, including the content of acidic compartments and reactive oxygen species production, during the interaction of human macrophages with low-temperature-synthesized barium doped dicalcium phosphate dihydrate under normal and lipopolysaccharide (LPS)-induced inflammatory conditions. METHODS: Morphology and qualitative and quantitative elemental composition of dicalcium phosphate dihydrate (DCPD) powder and its barium-doped form (DCPD-Ba) were evaluated using scanning electron microscopy, infrared spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. Cell viability, lysosomal content, and reactive oxygen species production were assessed by flow cytometry after co-culturing primary human macrophages with DCPD and DCPD-Ba under both normal and LPS-stimulated conditions. RESULTS: Barium-doped DCPD samples were synthesized using a low-temperature method at Ba²⁺ concentrations of 1%, 5%, and 10% of the theoretically possible substitution level (theor.%). For each variant, the calculated actual substitution percentage amounted to 0.62, 1.43, and 6.43 atomic %, respectively. X-ray diffraction analysis confirmed complete transformation of the initial α-tricalcium phosphate into DCPD at all Ba2+ concentrations. The infrared spectroscopy data validated the conformity of DCPD structure to the reference standard across all Ba2+ doping levels. Doping with Ba2+ ions has been found to enhance the hydration activity of DCPD and cause deformation of its crystal structure. The results of in vitro studies indicate that substitution of Ca2+ with Ba2+ in the DCPD structure does not affect the cytotoxic properties of the material. Furthermore, DCPD-Ba did not suppress lysosomal biogenesis and promoted reactive oxygen species production in non-activated macrophages, whereas suppressing reactive oxygen species production under LPS-induced inflammatory conditions. CONCLUSION: Thus, both DCPD and its Ba substituted variants represent promising candidates for incorporation into materials intended for regenerative medicine. The proposed low temperature synthesis of Ba2+-substituted DCPD is of considerable interest for the development of specialized osteoplastic CPC based materials. The most effective DCPD variant, with the highest Ca2+-to-Ba2+ substitution level (6.43 atomic %), demonstrated potential regulatory activity on activated macrophages (i.e., under inflammatory conditions). This property may be of critical importance for modulating the immune response and promoting effective osteointegration of the material in the recipient’s body.

One of the key factors of the interaction ‘osteoplastic material—organism’ is the state of the implant surface. Taking into account the fact that the equilibrium in regeneration conditions is reached only after the reparative histogenesis process is completed, the implant surface is constantly modified. This work is devoted to the numerical description of the dynamic bilateral material–medium interaction under close to physiological conditions, as well as to the assessment of the comparability of the model with in vitro and in vivo experimental results. The semi-empirical model obtained on the basis of chemical kinetics allows us to describe numerically the processes occurring in the in vitro systems and extrapolates well to assess the behavior of dicalcium phosphate dihydrate (DCPD) material under conditions of ectopic (subcutaneous) implantation in Wistar rats. It is shown that an experiment conducted using a perfusion–diffusion bioreactor in a cell culture medium with the addition of fetal bovine serum (FBS) allows for achieving morphologically and chemically identical changes in the surface of the material in comparison with the real organism. This fact opens up wide possibilities for the creation of an analog of a ‘laboratory-on-a-chip’ and the transition from classical in vivo models to more controlled and mathematically based in vitro systems.

Creating bioactive materials for bone tissue regeneration and augmentation remains a pertinent challenge. One of the most promising and rapidly advancing approaches involves the use of low-temperature ceramics that closely mimic the natural composition of the extracellular matrix of native bone tissue, such as Hydroxyapatite (HAp) and its phase precursors (Dicalcium Phosphate Dihydrate—DCPD, Octacalcium Phosphate—OCP, etc.). However, despite significant scientific interest, the current knowledge and understanding remain limited regarding the impact of these ceramics not only on reparative histogenesis processes but also on the immunostimulation and initiation of local aseptic inflammation leading to material rejection. Using the stable cell models of monocyte-like (THP-1ATRA) and macrophage-like (THP-1PMA) cells under the conditions of LPS-induced model inflammation in vitro, the influence of DCPD, OCP, and HAp on cell viability, ROS and intracellular NO production, phagocytosis, and the secretion of pro-inflammatory cytokines was assessed. The results demonstrate that all investigated ceramic particles exhibit biological activity toward human macrophage and monocyte cells in vitro, potentially providing conditions necessary for bone tissue restoration/regeneration in the peri-implant environment in vivo. Among the studied ceramics, DCPD appears to be the most preferable for implantation in patients with latent inflammation or unpredictable immune status, as this ceramic had the most favorable overall impact on the investigated cellular models.

This study examined the effectiveness of coating demineralized bone matrix (DBM) with amorphous calcium phosphate (DBM + CaP), as well as a composite of DBM, calcium phosphate, and serum albumin (DBM + CaP + BSA). The intact structure of DBM promotes the transformation of amorphous calcium phosphate (CaP) into dicalcium phosphate dihydrate (DCPD) with a characteristic plate shape and particle size of 5–35 µm. The inclusion of BSA in the coating resulted in a better and more uniform distribution of CaP on the surface of DBM trabeculae. MG63 cells showed that both the obtained forms of CaP and its complex with BSA did not exhibit cytotoxicity up to a concentration of 10 mg/mL in vitro. Ectopic (subcutaneous) implantation in rats revealed pronounced biocompatibility, as well as strong osteoconductive, osteoinductive, and osteogenic effects for both DBM + CaP and DBM + CaP + BSA, but more pronounced effects for DBM + CaP + BSA. In addition, for the DBM + CaP + BSA samples, there was a pronounced full physiological intrafibrillar biomineralization and proangiogenic effect with the formation of bone-morrow-like niches, accompanied by pronounced processes of intramedullary hematopoiesis, indicating a powerful osteogenic effect of this composite.

В настоящей работе представлена концепция образования низкотемпературной керамики - октакальцийфосфата и дикальцийфосфата дигидрата в присутствии направленных магнитных полей. Исследованы фазовый состав и формирование структуры полученных материалов в процессе перекристаллизации. Установлено, что формирование структур фосфатов кальция при воздействии направленного магнитного поля приводит к увеличению прочностных характеристик за счет переориентации плоскости роста кристаллов в процессе трансформации.