Microparticle
This article needs additional citations for verification. (August 2013) |
Particle with dimensions between 1 × 10−7 and 1 × 10−4 m.
Note 1: The lower limit between micro- and nano-sizing is still a matter of debate.
Note 2: To be consistent with the prefix “micro” and the range imposed by the definition,
dimensions of microparticles should be expressed in μm.[1]
Microparticles are particles between 0.1 and 100 μm in size. Commercially available microparticles are available in a wide variety of materials, including
, sand, dust, flour, and powdered sugar.Microparticles have a much larger surface-to-volume ratio than at the macroscale, and thus their behavior can be quite different. For example, metal microparticles can be explosive in air.
In biological systems, a microparticle is synonymous with a
Alternative definitions for size
Mathematical: as the term "micro" refers to , the range for micro would then be to , or roughly 31.6 nm to 31.6 micrometers. However, general acceptance considers particles smaller than 100 nm nanoparticles.
Rounding: rules of rounding in mathematics provide an alternative for the definition. Anything larger than 0.5 μm and anything smaller than 0.5 mm is considered microparticles.
Convenient/popular: Very often particles with dimensions more than 100 nm are still called nanoparticles. The upper range may be between 300 and 700 nm, so this would give a size definition for microparticles of 0.3 to 300 μm or 0.7 to 700 micrometers.
Applications
Home pregnancy tests make use of gold microparticles. Many applications are also listed in the
A recent study showed that infused, negatively charged, immune-modifying microparticles could have therapeutic use in diseases caused or potentiated by inflammatory monocytes.[4]
Microspheres
Microspheres are small spherical particles, with diameters in the micrometer range (typically 1 μm to 1000 μm (1 mm). Microspheres are sometimes referred to as spherical microparticles. In general microspheres are solid or hollow and do not have a fluid inside, as opposed to microcapsules.
Microspheres can be made from various natural and
Polyethylene, polystyrene and expandable microspheres are the most common types of polymer microspheres.
Microparticle of spherical shape without membrane or any distinct outer layer.
Note: The absence of outer layer forming a distinct phase is important to distinguish
microspheres from microcapsules because it leads to first-order diffusion phenomena,
whereas diffusion is zero order in the case of microcapsules.[6]
Polystyrene microspheres are typically used in
Expandable microspheres are polymer microspheres that are used as a blowing agent in e.g. puff ink, automotive underbody coatings and injection molding of thermoplastics. They can also be used as a lightweight filler in e.g. cultured marble, waterborne paints and crack fillers/joint compound. Expandable polymer microspheres can expand to more than 50 times their original size when heat is applied to them. The exterior wall of each sphere is a thermoplastic shell that encapsulates a low boiling point hydrocarbon. When heated, this outside shell softens and expands as the hydrocarbon exerts a pressure on the internal shell wall.
Microspheres made from highly transparent glass can perform as very high quality optical microcavities or optical microresonators.
Ceramic microspheres are used primarily as grinding media.
Hollow microspheres loaded with drug in their outer polymer shell were prepared by a novel emulsion solvent diffusion method and spray drying technique.
Microspheres vary widely in quality, sphericity, uniformity, particle size and particle size distribution. The appropriate microsphere needs to be chosen for each unique application.
Applications
New applications for microspheres are discovered every day. Below are just a few:
- Assay - Coated microspheres provide measuring tool in biology and drug research
- Buoyancy - Hollow microspheres are used to decrease material density in plastics (glass and polymer), neutrally-buoyant microspheres are frequently used for fluid flow visualization.
- Particle image velocimetry - Solid or hollow microspheres used for flow visualization, density of the particle has to match that of the fluid.[9]
- Ceramics - Used to create porous ceramics used for filters (microspheres melt out during firing, Polyethylene Microspheres) or used to prepare highstrength lightweight concrete.[10]
- Cosmetics - Opaque microspheres used to hide wrinkles and give color, Clear microspheres provide "smooth ball bearing" texture during application (Polyethylene Microspheres)
- Deconvolution - Small fluorescent microspheres (<200 nanometers) are required to obtain an experimental Point spread function to characterise microscopes and perform image deconvolution
- Drug delivery - As miniature time release drug capsule made of, for example, polymers. A similar use is as outer shells of microbubble contrast agents used in contrast-enhanced ultrasound.
- Electronic paper - Dual Functional microspheres used in Gyricon electronic paper
- Insulation – expandable polymer microspheres are used for thermal insulation and sound dampening.
- Personal Care- Added to Scrubs as an exfoliating agent (Polyethylene Microspheres)
- Spacers - Used in LCD screens to provide a precision spacing between glass panels (glass)
- Standards - monodispere microspheres are used to calibrate particle sieves, and particle counting apparatus.
- Retroreflective- added on top of paint used on roads and signs to increase night visibility of road stripes and signs (glass)
- Thickening Agent - Added to paints and epoxies to modify viscosity and buoyancy
- Drugs can be formulated as HBS floating microsphere. Following are list of drugs which can formulated as microsphere: L-Dopaand beneseragide, Fluorouracil.
Biological protocells
Some refer to microspheres or protein protocells as small spherical units postulated by some scientists as a key stage in the
In 1953,
In 1957, Sidney Fox demonstrated that dry mixtures of amino acids could be encouraged to polymerize upon exposure to moderate heat. When the resulting polypeptides, or proteinoids, were dissolved in hot water and the solution allowed to cool, they formed small spherical shells about 2 μm in diameter—microspheres. Under appropriate conditions, microspheres will bud new spheres at their surfaces.
Although roughly cellular in appearance, microspheres in and of themselves are not alive. Although they do reproduce asexually by budding, they do not pass on any type of genetic material. However they may have been important in the development of life, providing a membrane-enclosed volume which is similar to that of a cell. Microspheres, like cells, can grow and contain a double membrane which undergoes diffusion of materials and osmosis. Sidney Fox postulated that as these microspheres became more complex, they would carry on more lifelike functions. They would become heterotrophs, organisms with the ability to absorb nutrients from the environment for energy and growth. As the amount of nutrients in the environment decreased at that period, competition for those precious resources increased. Heterotrophs with more complex biochemical reactions would have an advantage in this competition. Over time, organisms would evolve that used photosynthesis to produce energy.
Cancer research
One useful discovery made from the research of microspheres is a way to fight
Extracellular vesicles
See also
- Coacervate
- Luminescent
- Proteinoid
- Micro-encapsulation
- Microbeads
- Nanoparticle
References
- S2CID 98107080.
- ^ "Solid Metal Microspheres - Stainless Steel and Titanium Spheres". www.cospheric.com. Retrieved 2019-05-07.
- ^ "Microspheres Online". Microspheres Online. Retrieved 2019-05-07.
- PMID 24431111.
- ^ "Microspheres, Spherical Particles, Microbeads, Custom Density, Fluorescent, Conductive". www.cospheric.com. Retrieved 2019-05-07.
- S2CID 98107080.
- ^ Paint and Coatings Industry Magazine, January 1st, 2010 : Opaque Polyethylene Microspheres for the coatings applications
- ^ Cosmetics and Toiletries, April 2010 Issue: Solid Polyethylene Microspheres for effects in color cosmetics Archived 2012-03-04 at the Wayback Machine
- ^ http://microspheres.us/fluorescent-microspheres/piv-seeding-microparticle-flow-visualization/599.html PIV seeding particle recommendations
- S2CID 137481918.
- ^ Mithun Singh Rajput, Purti Agrawal. Microspheres in Cancer Therapy. Indian Journal of Cancer. 2010;47(4):458-468. http://www.indianjcancer.com/text.asp?2010/47/4/458/73547
- PMID 30637094.