Porous silicon finds numerous applications in the areas of bio-technology, drug delivery, energetic materials and catalysis. Recent studies by Vesta Sciences have led to the development of porous silicon nanosponge particles from metallurgical grade silicon powder through their own patented chemical etching process (Irish patent no. IE20060360). This discovery paves the way for a more economical production method for porous silicon. The work presented here studies the structural morphology of the porous silicon nanosponge particles using high resolution electron microscopy techniques combined with porisometry type measurements where appropriate. The related surface pore structure is examined in detail using Scanning Electron Microscopy and Transmission Electron Microscopy techniques while the internal pore structure is explored using Focused Ion Beam milling and ultramicrotomed cross-sections. Three samples of the silicon particles were analysed for this study which include the starting metallurgical grade silicon powder and two samples that have been chemically etched. Analysis of the etched samples indicates a disordered pore structure with pore diameters ranging up to 15nm on porous silicon particles ranging up to 5µm in size. Crystallographic orientation did not appear to affect the surface pore opening diameter. Internal pore data indicated pore depths of up to 1 µm dependant on the particle size and etching conditions applied.
Studies into bone-like apatite or hydroxyapatite (HA) growth on potential biomaterials when in contact with simulated body fluid (SBF) not only establish a general method for determining bioactivity but coincidently lead to the design of new bioactive materials in biomedical and tissue engineering fields. Previous studies of HA growth on porous silicon have examined electrochemically etched silicon substrates after immersion in a simulated body fluid. This study differs from previous work in that it focuses on characterising HA growth on chemically etched metallurgical grade nanoporous silicon particles. The porous silicon (PS) used in this study is comprised of nanosponge particles with disordered pore structures with pore sizes ranging up to 10nm on micron sized particles.The silicon particles are analysed before and after immersion into SBF using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray (EDX) analysis and x-ray photoelectron spectroscopy (XPS). Results indicate that a HA layer forms on the surface of the nanosponge particles. Experimental analysis indicates that the morphology and calcium-tophosphorus ratio (Ca/P) verify the formation of crystalline HA on the nanoporous silicon particles.2
Porous silicon is generally achieved through electro-chemical etching or chemical etching of bulk silicon in hydrofluoric acid based solutions. The work presented here explores the effect of a chemical etching process on a metallurgical grade silicon powder. It is found that the metallurgical grade silicon particles contain surface bound impurities that induce a porous structure formation upon reaction with the chemical etchant applied. The correlation between the resultant porous structure formed due to the material composition is examined in detail. The elemental composition is determined using a combination of X-ray Photoelectron Spectroscopy and Time of Flight Secondary Ion Mass Spectroscopy. The porous structure is analysed using Transmission Electron Microscopy and Scanning Electron Microscopy. Three samples of the silicon particles analysed for this study include an un-etched bulk silicon powder sample and two samples of chemically etched powder. Pore formation within the particles is found to be dependent on the presence, dispersion, and local concentration of surface bound impurities within the starting powder.
The properties of porous silicon make it a promising material for a host of applications including drug delivery, molecular and cell-based biosensing, and tissue engineering. Porous silicon has previously shown its potential for the controlled release of pharmacological agents and in assisting bone healing. Hydroxyapatite, the principle constituent of bone, allows osteointegration in vivo, due to its chemical and physical similarities to bone. Synthetic hydroxyapatite is currently applied as a surface coating to medical devices and prosthetics, encouraging bone in-growth at their surface and improving osseointegration. This paper examines the potential for the use of an economically produced porous silicon particulate-polytetrafluoroethylene sheet for use as a guided bone regeneration device in periodontal and orthopaedic applications. The particulate sheet is comprised of a series of microparticles in a polytetrafluoroethylene matrix and is shown to produce a stable hydroxyapatite on its surface under simulated physiological conditions. The microstructure of the material is examined both before and after simulated body fluid experiments for a period of 1, 7, 14 and 30 days using Scanning Electron Microscopy. The composition is examined using a combination of Energy Dispersive X-ray Spectroscopy, Thin film X-ray diffraction, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy and the uptake/release of constituents at the fluid-solid interface is explored using Inductively Coupled Plasma-Optical Emission Spectroscopy. Microstructural and compositional analysis reveals progressive growth of crystalline, 'bone-like' apatite on the surface of the material, indicating the likelihood of close bony apposition in vivo.
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