Role of Hydrogen and Nitrogen on the Surface Chemical Structure of Bioactive Amorphous Silicon Oxynitride Films

Abstract

Silicon oxynitride (Si-O-N) is a new biomaterial in which its O/N ratio is tunable for variable Si release and its subsequent endocytotic incorporation into native hydroxyapatite for enhanced bone healing. However, the effect of nitrogen and hydrogen bonding on the formation and structure of hydroxyapatite is unclear. This study aims to uncover the roles of H and N in tuning Si-O-N surface bioactivity for hydroxyapatite formation. Conformal Si-O-N films were fabricated by plasma-enhanced chemical vapor deposition (PECVD) onto Ti/Si substrates. Fourier transform infrared spectroscopy (FTIR) and Rutherford backscattering spectrometry (RBS) analysis indicated increased Si-H and N-H bonding with increased N content. Surface energy decreased with increased N content. X-ray absorbance near edge structure (XANES) analysis showed tetrahedral coordination in O-rich films and trigonal coordination in N-rich films. O-rich films exhibited a 1:1 ratio of 2p to 2p electron absorbance, while this ratio was 1.73:1 for N-rich films. Both Si and N had a reduced partial charge for both O- and N-rich films, whereas O maintained its partial charge for either film. O-rich films were found to exhibit random bonding SiON, while N-rich films exhibited random mixing: [Si-Si]-[Si-O]-[Si-N]. Thus, hydrogen bonding limits random nitrogen bonding in Si-O-N films via surface Si-H and N-H bonding. Moreover, increased nitrogen content reduces the partial charge of constituent elements and changes the bonding structure from random bonding to random mixing.

Silicon nitride enhances osteoprogenitor cell growth and differentiation via increased surface energy and formation of amide and nanocrystalline HA for craniofacial reconstruction

“…For Ti or PEEK, nanocrystalline HA was confirmed with similar Ca/P ratio as that of as‐fired Si 3 N 4 . Furthermore, the formation of HA structures on the Si 3 N 4 surfaces was similar to that found in prior studies on amorphous silicon nitride (Varanasi et al, ). Combining the results from the SEM, EDS, XRD and Raman spectroscopy analyses, it is reasonable to attribute the enhanced osteoblast growth on the Si 3 N 4 surfaces to the presence of these surface functional groups, relatively dense nanocrystalline HA formation and relatively high surface energy (i.e., low wetting angles).…”

“…The fluorescence signal (FY) data for Si L2, 3 edge (Figure a) represent the absorption energy of the p core–shell electrons for Si. Peaks a and b at 105.7 and 106.3 represent 2p spin‐orbital splitting, which was described previously (Ilyas et al, ; Varanasi et al, ). These were observed in a shifted state in the as‐fired and polished samples possibly indicating a change in the near‐surface bonding of the Si atom.…”

“…The added N caused an increase in the carbonate/phosphate ratio and N‐H bond density prior to testing in cell culture. It was also observed that a large density of collagenous ECM formed on this silicon nitride surface, and it was speculated that the increased N‐H bonding could be integrated into the structure of the collagen via amine group bonding to the material's surface (Varanasi et al, ). In other investigations, it was found that N increased the expression of enzymes associated with collagen cross‐linking such as superoxide dismutase and lysyl oxidase (Ilyas et al, ).…”

“…In this study, evaluations of the Si L‐ edge and Y M‐edge were conducted at the National Synchrotron Light Source facility (Canadian Light Source, CLS, University of Saskatchewan, Saskatoon, Saskatchewan, Canada). Details of the beam energy for each studied element are given in previous publications (Ilyas et al, , ; Varanasi et al, ) and in the Results section below. XANES analysis was used to determine the presence of Si‐O, Si‐N and Si‐Si bonds and how the presence of Yttrium affects these coordination structures.…”

“…For each material, three samples were tested with 9 repetitive drops of DI water and diiodomethane at 25°C. Surface tensions, ( γ LV ), including polar ( γ d ) and dispersive ( γ p ) components, for water and diiodomethane were 72.8, 21.8, and 51.0 mJ/m 2 and 50.8, 50.4, and 0.4 mJ/m 2 , respectively (Amaral, Lopes, Santos, & Silva, ; Varanasi et al, ). The surface energy of each sample was calculated using the Owens–Wendt–Kaelble equation as described in prior work (Varanasi et al, ).…”