Patent 6,929,950

The invention relates to a particulate product comprising at least one microprojectile; characterized in that the or at least one of the microprojectiles comprises silicon. The invention also relates to devices and components used in the microprojectile implantation of the particulate product to a target of cells or target tissue.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide products that better satisfy the requirements associated with microprojectile delivery of an active substance to cells or tissue. It is a further object of the present invention to provide components and devices that also better satisfy the requirements associated with microprojectile delivery of an active substance to a cells or tissue. It is a yet further object of the invention to provide methods of fabricating said products, components, and devices.

According to a first aspect the invention provides a particulate product comprising at least one silicon particle.

The or each silicon particle comprises silicon.

The or at least one of the silicon particles may comprise one or more of: porous silicon, polycrystalline silicon, resorbable silicon, bioactive silicon, bulk crystalline silicon, biocompatible silicon, and amorphous silicon.

If the particulate product comprises more than one silicon particle, then the silicon particles from which the product is formed need not all comprise the same type of silicon. For example some of the particles may comprise porous silicon and others may comprise bulk crystalline silicon.

Advantageously the or at least one of the silcon particles is a microprojectile.

For the avoidance of doubt a microprojectile is a particle having a composition, size, shape, and mass such that it is suitable for microprojectile implanation into a target tissue or cell, or into the blood stream of a patient.

Preferably the microprojectile has a composition, size, shape and mass such that it is suitable for microprojectile implantation into a human or animal.

Advantageously the or at least one of the microprojectiles has an elongated shape. More advantageously the or at least one of the microprojectiles has a pointed tip. Yet more advantageously the or at least one of the microprojectiles comprises a microneedle.

The or at least one of the microprojectiles may comprise a microbarb and/or a microdart.

Preferably the or at least one of the microprojectiles comprises porous and/or polycrystalline silicon.

Advantageously the or at least one of the microprojectiles has a composition, size, shape, and mass such that they are suitable for use in one or more of the devices disclosed in U.S. Pat. Nos. 5,204,253; 5,219,746; 5,506,125; 5,584,807; 5,865,796; 5,877,023; 5,919,159; 6,004,287; and 6,013,050, which are hereby incorporated by reference.

The particulate product may comprise a multiplicity of microprojectiles, the microprojectiles forming a powder. The powder may have a substantially uniform particle size distribution.

A number of advantages are associated with the use of silicon, particularly porous and/or polycrystalline silicon, in the fabrication of microprojectiles.

Porous and polycrystalline materials, if they have suitable nanostructure, exhibit visible-near infrared fluorescence. The fluorescence of the porous and polycrystalline silicon may be of value in monitoring drug concentrations in the blood of a patient, as well as the presence and quality of the implanted microprojectile. This is of particular value silicon devices comprising resorbable silicon. Where the blood of a patient contains microprojectiles with which a drug has been combined, analysis of a blood sample containing the microprojectiles could yield information about the drug and microprojectile concentration. The fluorescence allows the microprojectiles to be identified and their numbers to be determined with relative ease.

The fabrication of microprojectiles from silicon allows the use of silicon processing technologies. These silicon processing techniques, in turn, open the way for exquisite control over microprojectile shape and size, coupled with high yields and high purity products. Better control over not only the size, but also the shape of an assembly of microprojectiles will result in better control of the depth of penetration of tissue or their incorporation within target cells. The use of porous silicon microprojectiles is also advantageaous since the presence of pores allows a greater dose, and flexibility of loading of, active substance to be delivered for a given microprojectile size.

The or at least one of the microprojectiles may further comprise a high density material having a density greater than that of bulk crystalline silicon. The high density material may comprise one or more of: gold, tungsten, platinum, iron, nickel, molybdenum, silver, palladium, erbium, iridium, rhenium, and cobalt. The microprojectile may comprise a silicide. The silicon, from which the microprojectile is formed, may be located at the surface of the high density material.

The use of a material having a density greater than that of bulk crystalline silicon may be of particular value in intercellular microprojectile delivery.

The or at least one of the microprojectiles may comprise bulk crystalline silicon.

The or at least one of the microprojectiles may have a mass in the range 0.001 ng to 5 ng. The or at least one of the microprojectiles may have a mass in the range 1 ng to 1 μg. The or at least one of the microprojectiles may have a mass in the range 1 ng to 5 ng.

The 1 ng to 1 μg mass range may be of particular value in the delivery vaccines to cells. The 0.001 ng to 1 ng mass range may be of particular value in drug delivery to target tissues.

Advantageously the or at least one of the silicon particles further comprises an active substance.

The active substance may comprise one or more of: a pharmaceutical material, a biological material, a genetic material, a radioactive material, an antibacterial agent, and luminescent agent.

The active substance may comprise one or more of: insulin, lidocaine, anaesthetic, alprostadil, calcitonin, DNA, RNA, peptide, cytokine, hormone, antibody, cytotoxic agent, adjuvant, steroid, and protein.

The active substance may comprise one or more of: GnRH, Goserilin, Leuprordin Acetate, Triptordin, Buserelin, a GnRH agonist, a GnRH superagonist, a GnRH antagonist, a GnRH homologue, a GnRH analogue, and a GnRH mimic.

For the purposes of this specification the term active substance means any substance to be transferred into a target cell or tissue or into a patient.

Advantageously the active substance comprises DNA or RNA.

The active substance may be disposed, at least partly, in the interior of the or at least one of the silicon particles. The or at least one of the silicon particles may comprise porous silicon and the active substance may be disposed, at least partly, in the pores of the porous silicon. Alternatively the or at least one of the silicon particles may comprise a cavity that is bounded, at least partly, by the silicon. The active substance may be disposed in said cavity.

If the silicon particle comprises an active substance that is disposed in a cavity at least partly bounded by the silicon, or that is disposed in the pores of porous silicon; then the active substance will be protected from the effect of implantation into the cells or tissue. For example if the active substance comprises DNA, then the DNA will be protected from shearing forces as it passes through the tissue or cell walls.

Preferably the or at least one of the microprojectiles comprises resorbable silicon.

Advantageously the silicon comprises derivatised silicon. More advantageously the silicon comprises derivatised porous and/or polycrystalline silicon. Yet more advantageously the derivatised silicon comprises one or both of: Si-C bonding, and Si-O-C bonding.

As is well known in the art, the term "derivatised porous and/or polycrystalline silicon" means porous and/or polycrystalline silicon that has been derivatised predominantly or exclusively at the surface of the silicon.

By selecting appropriate derivatisation, the surface functionality of the microprojectile may be tailored to meet the requirements of the active substance.

The use of resorbable silicon is of value since resorbable silicon is known to dissolve or corrode in biological environments. The use of an active substance associated with resorbable silicon therefore opens the way for the controlled release of the active substance as a result of the corrosion/dissolution of the resorbable silicon. If the resorbable silicon is porous then the active substance may be disposed in the pores of the porous silicon; corrosion of the silicon may then release the substance from the pores. If the microprojectile comprises a cavity, in which an active substance is disposed and which is bounded by resorbable silicon, then corrosion of the silicon may also result in release of the substance.

The use of resorbable silicon microprojectiles potentially allows the delivery of large quantities of an active substance, relative to prior art microprojectiles. For example gold microprojectiles are only able to deliver active substances from the surface of the microprojectile. The use of resorbable silicon allows delivery of the whole active substance payload, throughout the volume of the microprojectile.

Advantageously the or at least one of the silicon particles comprises porous silicon having a porosity between 1% and 90%. More advantageously the porous silicon has a porosity between 10% and 80%.

Preferably the or at least one of the silicon particles may have a size in the range 100 nm to 500 μm. More preferably the or at least one of the silicon particles has a size in the range 100 nm to 250 μm.

The or at least one of the silicon particles may have a size in the range 10 μm to 100 μm. The or at least one of the silicon particles may have a size in the range 10 μm to 70 μm. The or at least one of the silicon particles may have a size in the range 1 μm to 15 μm.

The size range 10 μm to 100 μm may be of particular value for extracellular drug microprojectile delivery. The size range 1 μm to 15 μm may be of particular value for intracellular microprojectile delivery.

Advantageously the particulate product comprises at least five substantially single sized silicon particles, each single sized silicon particle having a volume that is substantially identical to the volume of the other single sized particles. More advantageously the particulate product comprises at least ten substantially single sized silicon particles, each single sized silicon particle having a volume that is substantially identical to the volume of the other single sized particles. Yet more advantageously the particulate product comprises at least twenty substantially single sized silicon particles, each single sized silicon particle having a volume that is substantially identical to the volume of the other single sized particles.

Preferably the particulate product comprises a multiplicity of single shaped silicon particles, each single shaped silicon particle having the substantially same shape as the other single shaped silicon particles. More advantageously each single shaped silicon particle has the substantially the same volume as the other single shaped silicon particles. Yet more advantageously each single shaped silicon particle is substantially symmetric.

The total mass of the single shaped silicon particles, from which the particulate product is at least partly formed, may be greater than 10% of the total mass of the particulate product. The total mass of the single shaped silicon particles, from which the particulate product is at least partly formed, may be greater than 50% of the total mass of the particulate product.

The particulate product may comprise a multiplicity of silicon particles and at least some of said silicon particles may be monodispersed.

Advantageously the or at least one of the silicon particles is substantially symmetric. More advantageously the particualte product comprises a multiplicity of substantially symmetric silicon particles, each substantially symmetric silicon particle being substantially symmetric.

The or at least one of the silicon particles may be substantially cubic. The or at least one of the silicon particles may be substantially spherical.

For the purposes of this specification the term "symmetric", when used to describe an object, means that the object comprises at least one plane of symmetry and/or at least one axis of symmetry.

According to a second aspect the invention provides a carrier component, for use in microprojectile implantation, comprising a carrier body and at least one microprojectile, the carrier body having a shape and being arranged such that the carrier body retains the or at least one of the microprojectiles, characterised in that the or at least one of the microprojectiles comprises silicon.

Carrier components (and hence the carrier body) are usually used in microprojectile delivery devices. They are designed to facilitate removal and replacement of the component in the device.

The carrier body may have a shape and be arranged such that it forms a cartridge, the or at least one of the microprojectiles being disposed within the cartridge. The carrier body may comprise a carrier wall, the or at least one of the microprojectiles being adhered to, or integral with, said carrier wall.

Advantageously the microprojectile comprises porous and/or polycrystalline silicon.

According to a third aspect, the invention provides a delivery device comprising at least one microprojectile and an activatable gas source; the gas source being arranged such that, when activated, it causes gas to impart kinetic energy to the or at least one of the microprojectiles; characterised in that the or at least one of the microprojectiles comprises silicon.

The gas may impart kinetic energy to the microprojectiles by direct impact of the gas with the microprojectiles. Alternatively the microprojectiles may be adhered to one side of a disc; in which case the microprojectiles may be accelerated by impact of the gas with the disc surface opposite to that on which the particles are adhered.

When the device is arranged appropriately, impact of the gas with the microprojectiles (or a body to which the microprojectiles are adhered) causes them to accelerate towards the target cells or tissue.

The gas source may comprise a reservoir, containing gas held under pressure and having a reservoir wall that encloses the gas. The gas source may be activated by rupturing the wall, thereby causing the gas to flow from the interior to the exterior of the reservoir.

The microprojectile delivery device need not comprise a reservoir of gas. The gas source may, for example, simply comprise a gas conduit attached by a tube to a cylinder; the cylinder being separate from the device. In this case the gas source may be activated by opening a valve between the tubing and the conduit.

The gas source may comprise an explosive, such as gunpowder; the gas source being activated by ignition of the explosive.

The microprojectile delivery device may further comprise a carrier body the carrier body having a shape and being arranged such that the carrier body retains the or at least one of the microprojectiles.

Preferably the microprojectile comprises porous and/or polycrystalline silicon.

According to a fourth aspect, the invention provides a method of fabricating a particulate product comprising the steps: (a) taking a sample of silicon and (b) forming at least one silicon product particle from the sample of silicon.

The silicon sample comprises silicon and the or each of the silicon product particles comprises silicon.

The sample of silicon may comprise one or more of: porous silicon, polycrystalline silicon, resorbable silicon, bioactive silicon, bulk crystalline silicon, biocompatible silicon, and amorphous silicon.

The or at least one of the silicon product particles may comprise one or more of: porous silicon, polycrystalline silicon, resorbable silicon, bioactive silicon, bulk crystalline silicon, biocompatible silicon, and amorphous silicon.

Preferably step (b) is performed in such a manner that at least one of the silicon product particles is a microprojectile.

Advantageously step (b) is performed in such a manner that at least one of the silicon product particles is symmetric. Yet more advantageously step (b) is performed in such a manner that a multiplicity of symmetric silicon product particles.

Step (b) may be performed in such a manner that at least five single sized silicon product particles are formed, each single sized silicon particle having a volume that is substantially identical to the other single sized product silicon particles.

Step (b) may be performed in such a manner that a multiplicity of single shaped product silicon particles are formed, each single shaped silicon product particle having a shape that is substantially identical to the other single shaped silicon product particles.

The method of fabricating a particulate product may comprise the further step (c) of porosifying said sample of silicon and/or porosifying the or at least one of the silicon product particles formed from the sample of silicon.

If the porosification step (c) involves the porosification of the or at least one of the silicon product particles, then the porosification may be performed in such a manner that it does not substantially alter the size and/or shape of the silicon product particle.

The method of fabricating a particulate product may comprise the further step (d), performed prior to steps (b) and (c), of forming the sample of silicon by depositing a layer of polycrystalline silicon on a substrate.

The particle forming step (b) may be performed prior to or after step (c). In other words the silicon product particles may be formed from porous or non-porous silicon.

Advantageously the particle forming step (b) is performed after step (c) and comprises the step of mechanically crushing said porous silicon.

Preferably the sample of silicon comprises a silicon wafer and step (b) comprises the step of etching the wafer. The step of etching the wafer may performed in such a manner that a multiplicity of monodispersed silicon product particles are formed; said monodispersed silicon product particles having a uniform size and/or shape.

The step (b) may comprise the step of photolithographically etching the wafer.

Advantageously step (b) is performed in such a manner that the or at least one of the silicon product particles has a size in the range 1 nm to 500 μm. More advantageously the or at least one of the silicon product particles has a size in the range 1 nm to 250 μm.

Step (b) may be performed in such a manner that the or at least one of the silicon product particles has a size in the range 10 μm to 100 μm. Step (b) may be performed in such a manner that the or at least one of the silicon product particles has a size in the range 10 μm to 70 μm. Step (b) may be performed in such a manner that the or at least one of the silicon product particles has a size in the range 1 μm to 15 μm.

Step (c) may comprise the step of anodising said sample of silicon. Step (c) may comprise the step of electrochemical etching said sample of silicon.

Preferably the step (c) comprises the step of applying a stain etch solution to the or at least one of the silicon product particles and/or applying a stain etch solution to the sample of silicon. More preferably the stain etch solution comprises hydrofluoric acid and an oxidising agent. Yet more preferably the stain etch solution comprises hydrofluoric acid and one or more of: nitric acid, sodium nitrite, and chromium trioxide. Even more preferably the stain etch solution comprises hydrofluoric acid and nitric acid; wherein the concentration of hydrofluoric acid, in the stain etch solution, is in the range 10 to 30 mol per litre and the concentration of nitric acid, in the stain etch solution, is in the range 0.0016 to 0.32 mol per litre.

Advantageously the process for fabricating a particulate product comprises the step of bombarding the or at least one of the silicon product particles, and/or bombarding the sample of silicon, with one or more of: ions, neutrons, and electrons; and further comprises the step of porosifying the silicon contained in the or at least one of the silicon product particles, and/or contained in the sample of silicon, that has been so bombarded.

Preferably the step of porosifying the silicon contained in the or at least one of the silicon product particles, and/or the silicon contained in the sample of silicon, comprises the step of light assisted porosification.

Preferably step (d) comprises the step of reacting a silicon containing gas in the region of the substrate. More preferably step (d) comprises the step of pyrolysing a silane and/or halogen substituted silane in the region of the substrate. Yet more preferably step (d) comprises the step of pyrolising SiH₄ in the region of the substrate.

Preferably step (b) comprises the steps: (i) mechanically processing the sample of silicon in such a manner that at least one intermediate silicon particle, is/are formed, the or each intermediate particle having a volume that is less than that of the sample of silicon from which it was formed; and (ii) applying a size reduction etch to the or at least one of the intermediate silicon particles, the etch being performed in such a manner that it reduces the size of the or at least one of the intermediate silicon particles.

The size reduction etch (ii) may be performed in such a manner that it does not substantially alter the shape of the or at least one of the intermediate silicon particles.

Preferably the step (i) of mechanically processing the sample of silicon comprises the step of dicing and/or sawing and/or milling and/or crushing and/or polishing and/or grinding the sample of silicon.

Advantageously the step (ii) of mechanically processing the sample of silicon is performed in such a manner that a multiplicity of monodispersed intermediate silicon particles are formed, each monodispersed intermediate silicon particle having substantially the same size and/or shape.

The size reduction etch (ii) may comprise a wet etch. The size reduction etch (ii) may comprise an isotropic etch. The size reduction etch (ii) may comprise a planar etch.

Advantageously the step (ii) of applying a size reduction etch comprises the step of applying a size reduction etch solution to the or at least one of the intermediate silicon particles, the etch solution comprising hydrofluoric acid and nitric acid. More advantageously the size reduction etch (ii) solution comprises hydrofluoric acid, nitric acid, and ethanoic acid, the concentration of the hydrofluoric acid, in the size reduction etch solution, being in the range 1.1 to 7.7 mol per litre, the concentration of nitric acid, in the size reduction etch solution, being in the range 10.4 to 14.2 mol per litre, and the concentration of ethanoic acid, in the size reduction etch solution, being in the range 0.0 to 1.74 mol litre.

According to a fifth aspect, the invention provides a method of fabricating a carrier component, suitable for use in a microprojectile delivery device, comprising the steps: (a) taking a sample of silicon and (b) forming particles from the silicon, step (b) being performed in such a manner that a particulate product comprising at least one microprojectile is formed, and (e) assembling the particulate product with a carrier body in such a manner that the product is retained by the body to form a carrier component.

The silicon may comprise bulk crystalline silicon and/or polycrystalline and/or porous silicon.

The method of fabricating a carrier component may comprise the further step (c) of porosifying said sample of silicon.

Step (c) may be performed before or after step (b).

The method of fabricating a carrier component may comprise the step (d), performed prior to steps (b) and (c), of forming the sample of silicon by depositing a layer of polycrystalline silicon on a substrate.

Advantageously step (b) is performed in such a manner that the or at least one of the microprojectiles has a size in the range 1 nm to 500 μm. More advantageously the or at least one of the microprojectiles has a size in the range 1 nm to 250 μm.

Step (b) may be performed in such a manner that the or at least one of the microprojectiles has a size in the range 10 μm to 100 μm. Step (b) may be performed in such a manner that the or at least one of the microprojectiles has a size in the range 10 μm to 70 μm. Step (b) may be performed in such a manner that the or at least one of the microprojectiles has a size in the range 1 μm to 15 μm.

Preferably step (d) comprises the step of reacting a silicon containing gas in the region of the substrate. More preferably step (d) comprises the step of pyrolysing a silane and/or halogen substituted silane in the region of the substrate. Yet more preferably step (d) comprises the step of pyrolising SiH₄ in the region of the substrate.

According to a sixth aspect, the invention provides a method of fabricating a delivery device comprising the steps: (a) taking a sample of silicon, and (b) forming particles from the silicon, step (b) being performed in such a manner that at least one microprojectile is formed, and (f) assembling an activatable gas source and the microprojectile(s) to form a microprojectile delivery device, the gas source and microprojectile(s) being arranged in such manner that, when activated, the gas source causes gas to impart kinetic energy to the microprojectile(s).

The method of fabricating a microprojectile delivery device may comprise the further step (c) of porosifying said sample of silicon.

The silicon may comprise bulk crystalline silicon and/or polycrystalline and/or porous silicon.

Step (b) may be performed before or after step (c).

The method of fabricating a microprojectile delivery device may comprise the step (d), performed prior to steps (b) and (c), of depositing a layer of polycrystalline silicon on a substrate.

Preferably step (d) comprises the step of reacting a silicon containing gas in the region of the substrate. More preferably step (d) comprises the step of pyrolysing a silane and/or halogen substituted silane in the region of the substrate. Yet more preferably step (d) comprises the step of pyrolising SiH₄ in the region of the substrate.

Advantageously step (b) is performed in such a manner that the or at least one of the microprojectiles has a size in the range 1 nm to 500 μm. More advantageously the or at least one of the microprojectiles has a size in the range 1 nm to 250 μm.

Step (b) may be performed in such a manner that the or at least one of the microprojectiles has a size in the range 10 μm to 100 μm. Step (b) may be performed in such a manner that the or at least one of the microprojectiles has a size in the range 10 μm to 70 μm. Step (b) may be performed in such a manner that the or at least one of the microprojectiles has a size in the range 1 μm to 15 μm.

According to an seventh aspect the invention provides a method of transfecting at least one cell, the method comprising the steps: (a) taking a microprojectile comprising silicon, (b) combining the particle with a sample of DNA, and (c) implanting the microprojectile in the or at least one of said cells by microprojectile implantation.

Preferably the microprojectile comprises porous and/or polycrystalline silicon.

According to an ninth aspect the invention provides the use of porous and/or polycrystalline silicon, in the preparation of a microprojectile for the delivery of a physiologically active substance to a subject.

Whilst many countries do not, yet, permit the patenting of methods of treatment of the human or animal body by surgery or therapy, there are some (e.g. USA) who do. In order for there to be no doubt about the Paris Convention priority entitlement to such an invention in those countries that do permit it, the invention also comprises the treatment, therapeutic or prophylactic, of a disorder of the human or animal body by microprojectile implantation of at least one microprojectile comprising porous and/or polycrystalline silicon; and allowing the release of an beneficial substance which helps to alleviate or ameliorate the disorder, or to prevent the disorder from occurring.

A "beneficial substance" is something beneficial overall: it could be a toxin, toxic to undesirable cells or to interfere with an undesirable physiological process. For example, anti-cancer substances would be considered "beneficial", even though their aim is to kill cancer cells.

According to an eleventh aspect, the invention provides a use of a particulate product comprising at least one silicon particle for the manufacture of a medicament for the treatment of a patient by microprojectile injection.

Advantageously the or at least one of the silcon particles is a microprojectile.

Advantageously the or at least one of the silicon particles further comprises an active substance.

The active substance may comprise one or more of: a pharmaceutical material, a biological material, a genetic material, a radioactive material, an antibacterial agent, and luminescent agent.

The active substance may comprise one or more of: insulin, lidocaine, anaesthetic, alprostadil, calcitonin, DNA, RNA, peptide, cytokine, hormone, antibody, cytotoxic agent, adjuvant, steroid, and protein.

The active substance may comprise one or more of: GnRH, Goserilin, Leuprordin Acetate, Triptordin, Buserelin, a GnRH agonist, a GnRH superagonist, a GnRH antagonist, a GnRH homologue, a GnRH analogue, and a GnRH mimic.

For the purposes of this specification the term active substance means any substance to be transferred into a target cell or tissue or into a patient.

Advantageously the active substance comprises DNA or RNA.

Advantageously the or at least one of the silicon particles comprises porous silicon having a porosity between 1% and 90%. More advantageously the porous silicon has a porosity between 10% and 80%.

Preferably the or at least one of the silicon particles may have a size in the range 100 nm to 500 μm. More preferably the or at least one of the silicon particles has a size in the range 100 nm to 250 μm.

The or at least one of the silicon particles may have a size in the range 10 μm to 100 μm. The or at least one of the silicon particles may have a size in the range 10 μm to 70 μm. The or at least one of the silicon particles may have a size in the range 1 μm to 15 μm.

Advantageously the particulate product comprises at least five substantially single sized silicon particles, each single sized silicon particle having a volume that is substantially identical to the volume of the other single sized particles. More advantageously the particulate product comprises at least ten substantially single sized silicon particles, each single sized silicon particle having a volume that is substantially identical to the volume of the other single sized particles. Yet more advantageously the particulate product comprises at least twenty substantially single sized silicon particles, each single sized silicon particle having a volume that is substantially identical to the volume of the other single sized particles.

Preferably the particulate product comprises a multiplicity of single shaped silicon particles, each single shaped silicon particle having the substantially same shape as the other single shaped silicon particles. More advantageously each single shaped silicon particle has the substantially the same volume as the other single shaped silicon particles. Yet more advantageously each single shaped silicon particle is substantially symmetric.

The total mass of the single shaped silicon particles, from which the particulate product is at least partly formed, may be greater than 10% of the total mass of the particulate product. The total mass of the single shaped silicon particles, from which the particulate product is at least partly formed, may be greater than 50% of the total mass of the particulate product.

The particulate product may comprise a multiplicity of silicon particles and at least some of said silicon particles may be monodispersed.

Advantageously the or at least one of the silicon particles is substantially symmetric. More advantageously the particualte product comprises a multiplicity of substantially symmetric silicon particles, each substantially symmetric silicon particle being substantially symmetric.

The or at least one of the silicon particles may be substantially cubic. The or at least one of the silicon particles may be substantially spherical.

Claim 1 of 10 Claims

1. A particulate product comprising monodispersed porous silicon particles, at least one of the porous silicon particles comprising porous silicon obtainable from a sample of silicon by one or more of: stain etching, anodization, and electrochemical etching.

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