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
Support of appositional bone ingrowth and resistance to bacterial adhesion and biofilm formation are preferred properties for biomaterials used in spinal fusion surgery. Although polyetheretherketone (PEEK) is a widely used interbody spacer material, it exhibits poor osteoconductive and bacteriostatic properties. In contrast, monolithic silicon nitride (Si3N4) has shown enhanced osteogenic and antimicrobial behavior. Therefore, it was hypothesized that incorporation of Si3N4 into a PEEK matrix might improve upon PEEK's inherently poor ability to bond with bone and also impart resistance to biofilm formation. A PEEK polymer was melted and compounded with three different silicon nitride powders at 15% (by volume, vol.%), including: (i) Introduction
Methods
Due to its remarkable stoichiometric flexibility and surface chemistry, hydroxyapatite (HAp) is the fundamental structural material in all vertebrates. Natural HAp's properties inspired an investigation into silicon nitride (Si3N4) to see if similar functionality could be engineered into this bioceramic. Biological and Four groups of Si3N4 discs, Ø12.7×1.0mm, (Amedica Corporation, Salt Lake City, UT USA) were subjected to surface treatments: (i) “As-fired;” (ii) HF-etched (5% HF solution for 45 s); (iii) Oxidized (1070°C for 7 h); and (iv) Nitrogen-annealed (1400°C for 30 min, 1.1 bar N2 gas).1 Titanium alloy discs (Ti6Al4V, ASTM F136) were used as a control group. SaOS-2 cells cultured for 24 h at 37°C were deposited (5×105 cells/ml) and incubated on the UV sterilized discs in an osteogenic medium for 7 days at 37°C. Cell proliferation was monitored using scanning electron and laser microscopy. The Receptor Activator of NF-kB Ligand (sRANKL) and the insulin growth factor 1 (IGF-1) were used to evaluate osteoclast formation and cell proliferation efficiency, respectively. Introduction
Materials and Methods
Periprosthetic infections are leading causes of revision surgery resulting in significant increased patient comorbidities and costs. Considerable research has targeted development of biomaterials that may eliminate implant-related infections.1 This Several surface treated silicon nitride (Si3N4, Introduction
Materials and Methods
Silicon nitride (Si3N4) is a ceramic material presently implanted during spine surgery. It has a fortunate combination of material properties such as high strength and fracture toughness, inherent phase stability, scratch resistance, low wear, biocompatibility, hydrophilic behavior, easier radiographic imaging and resistance to bacterial biofilm formation, all of which make it an attractive choice for orthopaedic applications beyond spine surgery. Unlike oxide ceramics, ( In the present study, a Si3N4 bioceramic formulation was exposed to thermal, chemical, and mechanical treatments in order to induce changes in surface composition and features. The treatments included grinding and polishing, etching in hydrofluoric acid solution, and heating in nitrogen or air. Resulting surfaces were characterized using a variety of microscopy techniques to assess morphology. Surface chemical and phase composition were determined using x-ray photoelectron and Raman spectroscopy, respectively. Streaming potential measurements evaluated surface charging, and sessile water drop techniques assessed wetting behavior.Introduction
Methods
Silicon nitride spinal fusion cages have been successfully used in the treatment or correction of stenosis, disc herniation, trauma, and other deformities of the spinal column since 2008. To date over 14,000 devices have been implanted with perioperative and postoperative complication rates of less than 0.2%. This remarkable achievement is due in part to the material itself. Silicon nitride is an ideal interbody material, possessing high strength and fracture toughness, inherent phase stability, biocompatibility, hydrophilicity, excellent radiographic imaging, and bacterial resistance. These characteristics can lead to implants that aid in prevention of nosocomial infections and achieve rapid osteointegration. In this paper, we will review the various
It has been seven years since silicon nitride (Si3N4) was first proposed as a new bearing material for total hip arthroplasty [1]. Although its introduction into this application has been hampered by regulatory and clinical hurdles, it remains a strong candidate for advancing the state of care in patients undergoing joint replacement. Si3N4 has a distinctive set of properties, such as high strength and fracture toughness, inherent phase stability, low wear, scratch resistance, biocompatibility, hydrophilicity, excellent radiographic imaging, and bacterial resistance, many of which are not fully realized with other bioceramics. This combination of properties is desirable for demanding structural implants in the hip, knee and other total joints. Of foremost concern to clinicians is the wear behavior of any new or novel bearing material. Minimization of wear debris and prevention of corresponding osteolytic lesions are essential regardless of whether the artificial implant is articulating against itself, a metallic or polymeric counterpart. In this regard, Si3N4 may have a unique advantage. Other bearing couples rely solely on the presence of a biologic lubricating film to minimize erosive wear. However, Si3N4 forms a tribochemical film between the articulation surfaces consisting of silicon diimide Si(NH)2, silicic acid Si(OH)4, and ammonia groups NH3, NH4OH. Depending upon the bearing couple, this tribochemical film generally produces low friction. It is self-replenishing and resorbable, leading to the minimization of wear debris within the joint capsule. In this paper, we will review the essential physical, mechanical, and surface chemistry of Si3N4, and contrast these properties with other available bioceramics. Results from hip simulator testing of Si3N4 femoral heads on conventional and highly cross-linked polyethylene will be presented and discussed. Data will demonstrate that various Si3N4 bearing couples have wear comparable to other bioceramics. Microscopy and spectroscopic examinations of surfaces will provide a view of the surface stoichiometry and chemical stability of Si3N4 in comparison to other bioceramics. Laboratory friction tests will be reported, which show that the tribochemistry of the lubricating film generated by Si3N4 favors the use of highly cross-linked polyethylene as a counterface material. Overall results will demonstrate that silicon nitride is poised to become a new generation biomaterial for total joint arthroplasty.
Common in vitro protocols for TGF-β driven chondrogenic differentiation of MSC lead to hypertrophic differentiation of cells. This might cause major problems for articular cartilage repair strategies based on tissue engineered cartilage constructs derived from these cells. BMPs have been described as alternate inductors of chondrogenesis while PTHrP and FGF-2 seem promising for modulation of chondrogenic hypertrophy. The aim of this study was to identify chondrogenic culture conditions avoiding cellular hypertrophy. We analyzed the effect of a broad panel of growth factors alone or in combination with TGF-β3 on MSC pellets cultured in vitro and after transplantation in SCID mice in vivo. Chondrogenic differentiation in vitro was successful after supplementation of the chondrogenic medium with TGF-β3 as confirmed by positive collagen type II and alcian blue staining. None of the other single growth factors (BMP-2, -4, -6, -7, FGF-1, IGF-1) led to sufficient chondrogenesis as indicated by negative collagen type II and alcian blue staining. Each of these factors, however, allowed chondrogenesis in combination with TGF-β without suppressing collagen type X expression. Combination of TGF-β with PTHrP or FGF-2 suppressed ALP activity, induced MMP13 expression, and prevented differentiation to chondrocyte-like cells when added from day 0. Delayed addition of PTHrP or FGF-2 stopped chondrogenesis at the reached level and repressed ALP activity. The treatment of MSC constructs with FGF-2 or PTHrP in the last 3 weeks before transplantation did not prevent hypertrophy and calcification in vivo. FGF-2 and PTHrP were potent inhibitors for early and late chondrogenic differentiation in contrast to BMPs. As soon as a developmental window of collagen type II positive and collagen type X negative pellet cultures can be created in this model, both seem to be potent factors to suppress hypertrophy and to generate stable chondrocytes for transplantation purposes.
