Sic Parvis Magna: Manganese-Substituted Tricalcium Phosphate and Its Biophysical Properties

Abstract

Succeeding in the substitution of pharmaceutical compounds with ions deliverable with the use of resorbable biomaterials could have far-reaching benefits for medicine and economy. Calcium phosphates are known as excellent accommodators of foreign ions. Manganese, the fifth most abundant metal on Earth was studied here as an ionic dopant in β-tricalcium phosphate (β-TCP) ceramics. β-TCP containing different amounts of Mn2+ ions per Mn x Ca3–x (PO4)2 formula (x = 0, 0.001, 0.01, and 0.1) was investigated for a range of physicochemical and biological properties. The results suggested the role of Mn2+ as a structure booster, not breaker. Mn2+ ions increased the size of coherent X-ray scattering regions averaged across all crystallographic directions and also lowered the temperature of transformation of the hydroxyapatite precursor to β-TCP. The particle size increased fivefold, from 20 to 100 nm, in the 650–750 °C region, indicating that the reaction of formation of β-TCP was accompanied by a considerable degree of grain growth. The splitting of the antisymmetric stretching mode of the phosphate tetrahedron occurred proportionally to the Mn2+ content in the material, while electron paramagnetic resonance spectra suggested that Mn2+ might substitute for three out of five possible calcium ion positions in the unit cell of β-TCP. The biological effects of Mn-free β-TCP and Mn-doped β-TCP were selective: moderately proliferative to mammalian cells, moderately inhibitory to bacteria, and insignificant to fungi. Unlike pure β-TCP, β-TCP doped with the highest concentration of Mn2+ ions significantly inhibited the growth of all bacterial species tested: Staphylococcus aureus, Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, and Enterococcus faecalis. The overall effect against the Gram-positive bacteria was more intense than against the Gram-negative microorganisms. Meanwhile, β-TCP alone had an augmentative effect of the viability of adipose-derived mesenchymal stem cells (ADMSCs) and the addition of Mn2+ tended to reduce the extent of this augmentative effect, but without imparting any toxicity. For all Mn-doped β-TCP concentrations except the highest, the cell viability after 72 h incubation was significantly higher than that of the negative control. Assays evaluating the effect of Mn2+-containing β-TCP formulations on the differentiation of ADMSCs into three different lineagesosteogenic, adipogenic, and chondrogenicdemonstrated no inhibitory or adverse effects compared to pure β-TCP and powder-free positive controls. Still, β-TCP delivering the lowest amount of Mn2+ seemed most effective in sustaining the differentiation process toward all three phenotypes, indicating that the dose of Mn2+ in β-TCP need not be excessive to be effective.

In Vitro Properties of Manganese-Substituted Tricalcium Phosphate Coatings for Titanium Biomedical Implants Deposited by Arc Plasma

“…The growth of cell mass on the surface of the Mn-TCP coating occurs faster compared to the TCP coating’s surface, which is likely due to the influence of the manganese. This observation is confirmed by our previous studies regarding the Mn-TCP powders with different concentrations of Mn [ 12 ]. It was found that Mn ions have a positive effect on adipose-derived mesenchymal stem cells’ viability and proliferation, demonstrating no inhibitory or adverse effects, and on cells differentiation into osteogenic, adipogenic, and chondrogenic lineages.…”

“…Further increase of manganese amount is followed by the EPR spectrum narrowing, due to the exchange interaction. From the comparison of the obtained EPR pattern ( Figure 3 ) with the results presented in [ 12 ], one can give the estimation of the Mn 2+ amount in the investigated powder as higher than 2 wt%, which is in good agreement with the results obtained by the EDX analysis.…”

“…Our results ( Figure 3 ) can be satisfactorily described by g ≈ 2.003, D = 42(5) mT, Е = 9(2) mT, and A ≈ 9.5(5) mT. From the analysis of the high-frequency (W-band, 94 GHz) EPR results, it was concluded that even at low manganese concentrations, Mn 2+ ions substitute not only Ca(5) site, as it was predicted by calculations [ 32 ], but at least three of the five possible calcium sites, presumably Ca(5), Ca(4), and Ca(2), in TCP structure, and both possible sites in the HA structure [ 12 ].…”

“…The antibacterial activity of Mn-TCP powders, containing various amount of Mn, was studied in our previous work [ 12 ]. According to the results obtained in [ 12 ], TCP doped with the highest concentration of Mn, corresponding to the one used in this work, inhibited the growth of the tested bacterial species: Staphylococcus aureus , Salmonella typhi , E. coli , E. faecalis , and P. aeruginosa . In this work, we tested the antibacterial activity of the prepared TCP and Mn-TCP coatings on Ti against E. coli , E. faecalis , and P. aeruginosa strains, and the results are presented in Figure 14 .…”

“…According to authors [ 19 ], Mn 2+ ions exhibit antibacterial activity in concentrations not less than 12.5 µg/mL. Mn ions incorporated in bulk and coating materials are known to inhibit the growth of various bacterial species [ 11 , 12 , 20 ]. It was found that Mn stimulated the bactericidal activity of polymorphonuclear leukocytes [ 21 ].…”