Mesenchymal stem cells (MSCs) and osteoblasts respond to the surface electrical charge and topography of biomaterials. This work focuses on the connection between the roughness of calcium phosphate (CP) surfaces and their electrical potential (EP) at the micro- and nanoscales and the possible role of these parameters in jointly affecting human MSC osteogenic differentiation and maturation in vitro. A microarc CP coating was deposited on titanium substrates and characterized at the micro- and nanoscale. Human adult adipose-derived MSCs (hAMSCs) or prenatal stromal cells from the human lung (HLPSCs) were cultured on the CP surface to estimate MSC behavior. The roughness, nonuniform charge polarity, and EP of CP microarc coatings on a titanium substrate were shown to affect the osteogenic differentiation and maturation of hAMSCs and HLPSCs in vitro. The surface EP induced by the negative charge increased with increasing surface roughness at the microscale. The surface relief at the nanoscale had an impact on the sign of the EP. Negative electrical charges were mainly located within the micro- and nanosockets of the coating surface, whereas positive charges were detected predominantly at the nanorelief peaks. HLPSCs located in the sockets of the CP surface expressed the osteoblastic markers osteocalcin and alkaline phosphatase. The CP multilevel topography induced charge polarity and an EP and overall promoted the osteoblast phenotype of HLPSCs. The negative sign of the EP and its magnitude at the micro- and nanosockets might be sensitive factors that can trigger osteoblastic differentiation and maturation of human stromal cells.

Correlation analysis demonstrated the role of inorganic parameters of the surfaces of calcium phosphate materials in the regulation of osteogenic differentiation of mesenchymal precursors. The progenitor stromal cells were isolated from syngeneic bone marrow immobilized in vitro on calcium phosphate surfaces with different structure, phasic, and elemental composition. After 45 days of subcutaneous ectopic osteogenesis in BALB/c mice, the tissues grown on these matrixes were characterized histologically. It was found that adhesion of bone marrow cells is the initial stage determining their future proliferation (conduction) over the artificial surface and the area of formed tissue plate. The success of histogenesis depends on surface roughness. The optimal roughness class was 4-5 (Russian State Standards), which enables differentiation of progenitor stromal cells under the specific microenvironmental conditions into the connective and adipose tissue cells. Differentiation of the progenitor cells into the stromal cells producing the hemopoiesis-inducing microenvironment also takes place in the foci of active hemopoiesis. Induction of osteogenic potential of the stromal precursors (osteoinduction) is determined by the ratio between calcium and phosphate atoms in surface coatings. In our experimental system, osteogenic differentiation of stromal mechanocytes was blocked only at Ca/P<0.5.

Metallic implants have been successfully used in medicine for the past 60–70 years. Historically, implants were designed only as mechanical devices, whereas the biological aspects of their application were beyond the researchers’ interest. The improvement of living conditions and the increase of the average life span have changed the situation. The clinical requirements for medical implants rise up substantially. Presently, it seems impossible to imagine the use of metallic implants in the human body without preliminary surface modification to modulate the interaction between the surrounding biological environment and the implant. The review highlights the most recent advances in the field of functional coatings formed on implants by the plasma electrolytic oxidation technology. Special attention is dedicated to the principles of surface modification of the commercially pure titanium, titanium nickelide, and Mg-Mn-Ce magnesium alloy. The advantages and disadvantages of the method and the characteristics of these materials are discussed from this point of view. Some aspects of this review are aimed at corrosion protection of implants with application of polymer materials.

The aim of this research is experimental investigation of the topography and evaluation of some parameters of artifi cial microterritories promoting osteogenic differentiation of stromal stem cells. A technique of short-term culturing of prenatal human lung stromal cells with fi broblastoid morphology on calcium phosphate substrates with known topography was used. Judging from secretory activity of the cell culture (osteocalcin, alkaline phosphatase), stromal stem cells directly interacting with calcium phosphate discs have advantage in manifestation of osteoblast-like functional activity in comparison with cells cultured on plastic. Rough surfaces of calcium phosphate discs stimulate the formation of spatial human fi broblastoid cell culture. The cells with positive reaction to acid phosphatase are located on spheroliths forming the relief of calcium phosphate coatings. The cells with positive reaction to alkaline phosphatase (marker of osteoblasts) populate hollows (niches) of the artifi cial surface. The niche for induction of osteogenic differentiation of human multipotent mesenchymal stem cells is apparently a structural and functional formation. It can be characterized by an index calculated as the ratio of the total area occupied by alkaline phosphatase-positive cells to the area of artifi cial surface occupied by one stained cell.

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A comparative investigation of the physical, chemical and biological properties of micro‐arc deposited calcium phosphate coatings on titanium and zirconium‐niobium substrates was performed. Calcium phosphate coatings on titanium have a higher surface density, porosity and pore size, and a more homogeneous surface topography. Under the same conditions, calcium phosphate coatings on zirconium‐niobium have a relief topography, but their surface density, porosity and pore size were all smaller. X‐ray diffraction of the coatings showed that the coatings on titanium were X‐ray amorphous whereas the coatings on zirconium‐niobium consisted of a mixture of crystalline CaZr4(PO4)6, ZrP2O7, and ZrO2. These differences are due to different electrical and thermophysical characteristics of substrates and passivating films on their surfaces. The coatings were shown to be biocompatible by in‐vitro cell culture experiments.

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