The osteogenic capability of any biomaterial is governed by a number of critical surface properties such as surface energy, surface potential, and topography. Prior work suggested that the Si-Y-O-N phase(s) present in the form of a thin (<150 nm), interrupted film at the surface of an annealed silicon nitride bioceramic may be responsible for an observed upregulation of osteoblastic activity due to passive surface properties and dissolution of chemical species. In this study high- resolution analytical electron microscopy was utilized to identify the Si-Y-O-N phase present on the annealed silicon nitride surface, and dissolution studies were employed to elucidate mechanisms of the material's favorable cell interactions. Si3N4 discs (12.7 mm diameter × 1 mm thick) containing Y2O3 and Al2O3 sintering aids were processed using conventional techniques and subsequently subjected to annealing in a nitrogen atmosphere. Pre-cultured SaOS-2 osteosarcoma cells at a concentration of 5 × 105 cells/ml were seeded onto sterile polished nitrogen-annealed Si3N4 discs in an osteogenic medium consisting of DMEM supplemented with about 50 µg/mL ascorbic acid, 10 mM β-glycerol phosphate, 100 mM hydrocortisone, and 10% fetal bovine calf serum. The samples were incubated for up to 7 days at 37°C with two medium replenishments. Transmission electron microscopy (TEM) images were acquired from focused ion beam (FIB)-prepared samples using a Hitachi HF-3300 TEM (300 kV). Scanning transmission electron microscopy (STEM) images were recorded using a Nion UltraSTEM 100 (60 kV). STEM high-angle annular dark-field (HAADF) imaging and energy dispersive X-ray spectroscopy (EDS) analyses were performed on a JEOL JEM2200FS (200 kV) equipped with a third-order CEOS aberration corrector and a Bruker XFlash silicon drift detector.Introduction
Materials and Methods
A secure bone/cement interface at the bone cement junction is an important requirement for the long-term success in the cemented hip arthroplasty. Cementing techniques have evolved and now involve pressurisation of the acetabulum and femur. It can be difficult to get a complete rim seal and hence adequate pressurisation due to the unique anatomy of the acetabulum and the contyloid notch. Several acetabular pressurisers are commercially available. We have developed an instrument for controlled and reproducible cement pressurisation in the acetabulum before socket insertion. It is a T-bar incorporating a central plunger, which protrudes from an outer sleeve when force is applied. The protrusion of the central plunger and hence the amount of force applied can be limited by a stop-sleeve. A laboratory saw bone model was designed to assess this system and compare it with two existing pressurisers. A polypropylene model of the acetabulum was used. Included in the model were two 1.3mm diameter capillary outlets, one at its pole and one at a point close to its rim opposite the cotyloid notch. Water was free to flow through the capillaries at a pressure of 13.5” WG to represent blood flow. 5 test per pressuriser were performed. CMW 1 Gentamicin bone cement was mixed as per manufacturers instruction in a Vacuum Mix system. The cement was then pressurised using one of three systems; the Depuy T handle pressuriser, the Exeter pressuriser and our new instrument. The cement mantle produced with the Depuy T-handle and the Exeter pressuriser was thicker at the pole than the rim and the cement intrusion was not consistent nor reproducible. The new pressurizer produced a cement mantle equal at the pole and the rim to within 1mm. A reproducible cement mantle compatible to the shape of the socket and with cement intrusion of 5mm (+/− 1mm) could be achieved. We recommend the use of this pressuriser.
