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

Abstract

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 N2 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 (VN 3+) and nitrogen N–N bonds (N4 +) formed during annealing in N2 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 VN 3+/N4 + and SiO– defective sites, is proposed as a mechanism to explain the attractive forces between transmembrane proteins and the COO– and NH2+ 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 (PO4 2–).

Bioactive silicon nitride: A new therapeutic material for osteoarthropathy

“…It showed a large number of areas with pronounced hydroxyapatite formation, which preferentially occurred at locations corresponding to the mixture of Si-Y-Al-O-N phases. While this observation confirmed previous findings89, it was newly revealed that there were surface depressions in the vicinity of the apatite deposits. We have interpreted this finding as evidence that the SaOS-2 cells actually scavenged molecules from the Si-Y-Al-O-N phases and apparently consumed them to produce bony apatite.…”

Development of a SiYAlON glaze for improved osteoconductivity of implantable medical devices

“…Regarding the mechanism of Saos‐2 cell adsorption, proliferation, and HAp mineralization, it has been previously shown that SiYAlON possesses a zwitterionic‐like surface at physiologic pH due to intermixing of surface moieties exhibiting negative (Si–O ‐ ) and positive (Y , Al , Si ) charges . Surfaces engineered to exhibit zwitterionic character through grafting of polymers containing this functionality have also previously demonstrated extreme hydrophilicity due to their high degree of surface polarization .…”

“…These control discs consisted of both as‐fabricated (AFSN) and nitrogen‐annealed (N 2 ASN) Si 3 N 4 . They were selected because they had previously demonstrated enhanced osteoconductive behavior using living Saos‐2 osteosarcoma cells . When not being evaluated, all samples were stored in a desiccating cabinet to minimize inadvertent surface contamination.…”

“…First, the glaze's affinity for apatite formation and deposition was determined using an in vitro acellular ISO protocol . Second, Saos‐2 osteosarcoma cell adsorption, proliferation, osteoid deposition, and HAp formation were examined using a previously validated procedure …”

Incorporating Si3N4 into PEEK to Produce Antibacterial, Osteocondutive, and Radiolucent Spinal Implants

“…With this twofold purpose in mind, a minor fraction of Si 3 N 4 particles was incorporated into a PEEK matrix. Si 3 N 4 was selected because the surface chemistry of this nonoxide bioceramic has previously demonstrated both bacterial lysis and enhanced bone formation . These properties resulted from its biologically friendly silicon/nitrogen surface chemistry and its slow elution rate which was suitable for implant applications.…”