Manipulation of Silicon Nitride Biomaterial Surfaces for Enhanced Osteoconductivity and Bacteriostasis

骨伝導性および静菌性を高めるための窒化ケイ素生体材料における表面処理

2017-03-24

2017-03-24

Silicon nitride (Si3N4) has a distinctive combination of material properties desirable for orthopaedic implants, such as high strength and fracture toughness, phase stability, biocompatibility, hydrophilicity, radiotranslucency and resistance to biofilm formation. Its unique oxynitride surface, populated by native amino- and hydroxyl-terminated functional groups, lends itself to easy tuning via simple thermal, chemical, and mechanical treatments. In this thesis, Si3N4 surfaces subjected to various treatments, such as grinding and polishing, chemical etching, and annealing in nitrogen or air, were characterized using a variety of microscopic and spectroscopic techniques, streaming potential measurements, and static contact angle measurements. Significant differences in surface properties were observed with isoelectric points ranging from 2 to 5.6, and moderate to extremely hydrophilic water contact angles varying from ~65° to ~8°. With promising surface properties observed, in vitro tests using cells from the SaOS-2 line were employed for an assessment of the modified surfaces’ osteoconductive potential. While all Si3N4-derived surfaces were found to encourage osteoid production and mineralization, samples annealed in N2 exhibited by far the greatest volume of deposited hydroxyapatite. Further observation revealed that the cells preferentially clustered on islands of SiYAlON phase at the surface of these samples. Motivated by this result, a synthetic glaze designed to mimic the composition of the SiYAlON islands was applied to Si3N4 substrates and subjected to a similar battery of tests. As hypothesized, the glazed surfaces induced even more osteoid formation and mineralization than their N2-annealed precursors. In vitro testing was also employed to observe potential inhibition to biofilm formation by Staphylococcus epidermidis and Escherichia coli, both commonly responsible for post-surgical infection, due to changes in surface chemistry. It was found that treated surfaces retained all or most of as-fabricated Si3N4’s inherent resistance to biofilm formation. Further understanding was gleaned when Raman spectroscopy was employed to probe interactions between the samples and living cells, both SaOS-2 and the bacterium Porphyromonas gingivalis. Shifts in bands associated with metabolic indicators illuminated some of the mechanisms at play during these interactions. This work demonstrates that modification of Si3N4’s surface can enhance its native osteoconductivty without compromising its bacteriostatic character. Novel SiYAlON formulations show promise not just as a surface enhancement for silicon nitride, but also as a novel bioactive material that can be infused into or coated onto existing products to enable desirable biologic interactions.

博士（工学）

京都工芸繊維大学

14303乙第206号

http://hdl.handle.net/10212/2398

eng

ETD

Thesis or Dissertation

Thesis