Gold is for the mistress, silver for the maid: Enhanced mechanical properties, osteoinduction and antibacterial activity due to iron doping of tricalcium phosphate bone cements

• Published in: Materials Science & Engineering C 2019-01, Vol.94, p.798-810
• Main Authors: Uskoković, Vuk, Graziani, Valerio, Wu, Victoria M., Fadeeva, Inna V., Fomin, Alexander S., Presniakov, Igor A., Fosca, Marco, Ortenzi, Marzo, Caminiti, Ruggero, Rau, Julietta V.
• Format: Article
• Language: English
• Subjects: Air hardening; Animals; Anti-Bacterial Agents - pharmacology; Antibacterial activity; Antibacterial materials; Background noise; Biocompatibility; Biological activity; Biomedical materials; Bone cancer; Bone cement; Bone cements; Bone Cements - pharmacology; Bone growth; Calcium; Calcium phosphates; Calcium Phosphates - chemistry; Cancer; Cbfa-1 protein; Cell Line; Cell morphology; Cement; Compressive strength; Core Binding Factor Alpha 1 Subunit - metabolism; Crystallography; Crystals; Cytology; Dopants; E coli; Escherichia coli; Gene expression; Genetic transformation; Glioblastoma; Glioblastoma cells; Gold; Gold - pharmacology; Growth factors; Hardening behaviour; Hardening rate; Humans; Hyperthermia; Intermediates; Ions; Iron; Iron - chemistry; Iron 57; Iron-doped tricalcium phosphate; Kinetics; Magnetic fields; Materials science; Mechanical properties; Mice; Morphology; Osseointegration - drug effects; Osteoblastic MC3T3-E1; Osteoblasts; Osteoblasts - cytology; Osteoblasts - metabolism; Osteocalcin; Osteocalcin - genetics; Osteocalcin - metabolism; Osteogenesis; Phase transitions; Porosity; Powders; Prophylaxis; Pseudomonas aeruginosa; RNA, Messenger - genetics; RNA, Messenger - metabolism; Salmonella enteritidis; Side effects; Silver; Silver - pharmacology; Spectrometry; Spectroscopy, Mossbauer; Spectrum Analysis, Raman; Staphylococcus aureus; Temperature; X-Ray Diffraction
• ISSN: 0928-4931; 1873-0191
• DOI: 10.1016/j.msec.2018.10.028

Self-hardening calcium phosphate cements present ideal bone tissue substitutes from the standpoints of bioactivity and biocompatibility, yet they suffer from (a) weak mechanical properties, (b) negligible osteoinduction without the use of exogenous growth factors, and (c) a lack of intrinsic antibacterial activity. Here we attempt to improve on these deficiencies by studying the properties of self-setting Fe-doped bone-integrative cements containing two different concentrations of the dopant: 0.49 and 1.09 wt% Fe. The hardening process, which involved the transformation of Fe-doped β-tricalcium phosphate (Fe-TCP) to nanocrystalline brushite, was investigated in situ by continuously monitoring the cements using the Energy Dispersive X-Ray Diffraction technique. The setting time was 20 min and the hardening time 2 h, but it took 50 h for the cement to completely stabilize compositionally and mechanically. Still, compared to other similar systems, the phase transformation during hardening was relatively fast and it also followed a relatively simple reaction path, virtually free of complex intermediates and noisy background. Mössbauer spectrometry demonstrated that 57Fe atoms in Fe-TCP were located in two non-equivalent crystallographic sites and distributed over positions with a strong crystal distortion. The pronounced presence of ultrafine crystals in the final, brushite phase contributed to the reduction of the porosity and thereby to the enhancement of the mechanical properties. The compressive strength of the hardened TCP cements increased by more than twofold when Fe was added as a dopant, i.e., from 11.5 ± 0.5 to 24.5 ± 2.0 MPa. The amount of iron released from the cements in physiological media steadied after 10 days and was by an order of magnitude lower than the clinical threshold that triggers the toxic response. The cements exhibited osteoinductive activity, as observed from the elevated levels of expression of genes encoding for osteocalcin and Runx2 in both undifferentiated and differentiated MC3T3-E1 cells challenged with the cements. The osteoinductive effect was inversely proportional to the content of Fe ions in the cements, indicating that an excessive amount of iron can have a detrimental effect on the induction of bone growth by osteoblasts in contact with the cement. In contrast, the antibacterial activity of the cement in the agar assay increased against all four bacterial species analysed (E. coli, S. enteritidis, P. aeruginosa, S. aur