Showing papers by "Leigh T. Canham published in 2011"

Extremely High Surface Area Metallurgical-Grade Porous Silicon Powder Prepared by Metal-Assisted Etching

Abstract: Nanostructured mesoporous silicon powders are being developed for a diverse range of applications including drug delivery, therapeutics, biosensors, and explosives. Such powders are easily produced through mechanical milling of membranes taken from electrochemically anodized silicon wafers. Where applications require highvolume, low-cost production, however, wafer feedstock is not viable and alternative feedstocks such as metallurgical-grade silicon powders become more attractive. Porosification of powders can be achieved using electro-less processing such as stain etching. Although much of the stain-etch literature has been developed around silicon wafers, the process, involving immersion of the silicon in an aqueous solution of hydrofluoric and nitric acids, has been readily transferred to powders. 1,2 Scalable synthesis methodologies have been reported for powders, 3 albeit with limitations on achievable surface area (143 m 2 /g), pore volume (0.3 ml/g), and yield (5%). Encouraging results have been reported 4 on the use of alternative oxidants, containing transition metals, for porosification of wafers, thus avoiding issues such as quiescence periods, inhomogeneity and irreproducibility usually associated with hydrofluoric-nitric acid processing. Metal-assisted chemical etching of silicon wafers has been the subject of two reviews. 5,6 For the first time, to our knowledge, we have applied metal-assisted etching using the hydrofluoric acid (HF)-ferric chloride (FeCl3) process, 7,8 in modified form, to metallurgical-grade silicon powders. The metal-assisted etch reaction can be described as

The role of nanostructured mesoporous silicon in discriminating in vitro calcification for electrospun composite tissue engineering scaffolds

Abstract: The impact of mesoporous silicon (PSi) particles—embedded either on the surface, or totally encapsulated within electrospun poly (e-caprolactone) (PCL) fibers—on its properties as a tissue engineering scaffold is assessed. Our findings suggest that the resorbable porous silicon component can sensitively accelerate the necessary calcification process in such composites. Calcium phosphate deposition on the scaffolds was measured via in vitro calcification assays both at acellular and cellular levels. Extensive attachment of fibroblasts, human adult mesenchymal stem cells, and mouse stromal cells to the scaffold were observed. Complementary cell differentiation assays and ultrastructural measurements were also carried out; the levels of alkaline phosphatase expression, a specific biomarker for mesenchymal stem cell differentiation, show that the scaffolds have the ability to mediate such processes, and that the location of the Si plays a key role in levels of expression.

Medically Biodegradable Hydrogenated Amorphous Silicon Microspheres

Abstract: Hydrogenated amorphous silicon colloids of low surface area (<5 m 2 /g) are shown to exhibit complete in- vitro biodegradation into orthosilicic acid within 10-15 days at 37°C. When converted into polycrystalline silicon colloids, by high temperature annealing in an inert atmosphere, microparticle solubility is dramatically re- duced. The data suggests that amorphous silicon does not require nanoscale porosification for full in-vivo biodegrad- ability. This has significant implications for using a-Si:H coatings for medical implants in general, and orthopedic implants in particular. The high sphericity and biodegrad- ability of submicron particles may also confer advantages with regards to contrast agents for medical imaging.

Bioerodible silicon-based devices for delivery of therapeutic agents

Abstract: This invention discloses bioerodible devices, such as implants for delivering therapeutic agents, particularly large molecules such as proteins and antibodies, in a controlled manner The devices comprise a porous silicon-based carrier material impregnated with the therapeutic agent The device may be used in vitro or in vivo to deliver the therapeutic agent, preferably in a controlled fashion over an intended period of time such as over multiple days, weeks or months The device may be used for treating or preventing conditions of a patient such as chronic diseases

Dispositifs à base de silicium pouvant être biologiquement érodés pour administration d'agents thérapeutiques

Abstract: La presente invention porte sur des dispositifs pouvant etre biologiquement erodes, tels que des implants, pour l'administration d'une maniere controlee d'agents therapeutiques, en particulier des molecules de grande dimension, telles que des proteines et des anticorps. Les dispositifs comportent un materiau support a base de silicium poreux impregne de l'agent therapeutique. Le dispositif peut etre utilise in vitro ou in vivo pour administrer l'agent therapeutique, de preference d'une maniere controlee au cours d'un laps de temps prevu, telle qu'au cours de plusieurs jours, de plusieurs semaines ou de plusieurs mois. Le dispositif peut etre utilise pour traiter ou prevenir des etats d'un patient, tels que des maladies chroniques.