In Situ Spectroscopic Screening of Osteosarcoma Living Cells on Stoichiometry-Modulated Silicon Nitride Bioceramic Surfaces.

Osteosarcoma cell viability, proliferation, and differentiation into osteoblasts on a silicon nitride bioceramic were examined as a function of chemical modifications of its as-fired surface. Biological and spectroscopic analyses showed that (i) postsintering annealing in N gas significantly improved apatite formation from human osteosarcoma (SaOS-2) cells; (ii) in situ Raman spectroscopic monitoring revealed new metabolic details of the SaOS-2 cells, including fine differences in intracellular RNA and membrane phospholipids; and (iii) the enhanced apatite formation originated from a high density of positively charged surface groups, including both nitrogen vacancies (V) and nitrogen N-N bonds (N) formed during annealing in N gas. At homeostatic pH, these positive surface charges promoted binding of proteins onto an otherwise negatively charged surface of deprotonated silanols (SiO). A dipole-like electric-charge, which includes V/N and SiO defective sites, is proposed as a mechanism to explain the attractive forces between transmembrane proteins and the COO and NH termini, respectively. This is analogous to the mechanism occurring in mineral hydroxyapatite where protein groups are specifically displaced by the presence of positively charged calcium loci (Ca) and off-stoichiometry phosphorus sites (PO).