Improved cytocompatibility and antibacterial properties of zinc-substituted brushite bone cement based on β-tricalcium phosphate

Abstract

For bone replacement materials, osteoconductive, osteoinductive, and osteogenic properties are desired. The bacterial resistance and the need for new antibacterial strategies stand among the most challenging tasks of the modern medicine. In this work, brushite cements based on powders of Zinc (Zn) (1.4 wt%) substituted tricalcium phosphate (β-TCP) and non-substituted β-TCP were prepared and investigated. Their initial and final phase composition, time of setting, morphology, pH evolution, and compressive strength are reported. After soaking for 60 days in physiological solution, the cements transformed into a mixture of brushite and hydroxyapatite. Antibacterial activity of the cements against Enterococcus faecium, Escherichia coli, and Pseudomonas aeruginosa bacteria strains was attested. The absence of cytotoxicity of cements was proved for murine fibroblast NCTC L929 cells. Moreover, the cell viability on the β-TCP cement containing Zn²⁺ ions was 10% higher compared to the β-TCP cement without zinc. The developed cements are perspective for applications in orthopedics and traumatology.

Fig. 1

Diffractograms of: TCP-based cement (A) before and (B) after soaking in physiological solution and Zn-substituted TCP cement (C) before and (D) after soaking in physiological solution. Labeled peaks relate to0 (*) β-Ca₃(PO₄)₂ (TCP) (card [09-169]), (□) CaHPO₄·2H₂O (DCPD) (card [72–713]), and (^) Ca₁₀(PO₄)₆(OH)₂ (HA) (card [72–1243])

Fig. 2

FTIR spectra of: A non-substituted and Zn-substituted TCP powders, B non-substituted and Zn-substituted TCP cements, and C non-substituted and Zn-substituted TCP cements after soaking in physiological solution

Fig. 3

Comparison of EPR spectra for Zn-TCP powder sample annealed at 900 °C before and after X-ray irradiation

Fig. 4

Central part of the X-Ray induced EPR for Zn-TCP powder sample annealed at 900 °C after 512 scans. The calculated values of g-factors are shown

Fig. 5

Cements’ morphology: A, B cement based on β-TCP; C, D cement based on Zn-β-TCP; E, F cement based on β-TCP after soaking in physiological solution; G, H cement based on Zn-β-TCP after soaking in physiological solution

Fig. 6

MTT test: NCTC L929 cells’ metabolic activity during 24 h of incubation with extracts from materials: 1-β-TCP, 2-Zn-β-TCP cement (*p < 0.01). Control sample (glass slide) is 100%. The error bars correspond to average ± standard deviation

Fig. 7

The inhibition of growth of: E. Coli for A Zn-TCP cement and B TCP cement; C E. faecium, and D P. aeruginosa for Zn-TCP cement (1) and TCP cement (2)