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ParaMagnetic Microspheres
Paramagnetic microspheres have the ability to increase in magnetization with an applied magnetic field and loose their magnetism when the field is removed. Neither hysteresis nor residual magnetization is observed and that provides the end use two very practical advantages:
- When the filed is removed, the microspheres demagnetize and re-disperse easily. This property allows efficient washing steps, low background and good reproducibility.
- The behavior of the microspheres is always the same whatever the magnetization cycles may be. Such behavior is a key point for automated instrument.
106-125um Magnetic Microspheres
Recently black paramagnetic microspheres have been produced in larger sizes of 10 micron to 1mm (1000um) and in dry form enabling scientists to leverage the benefits of paramagnetic particles in new applications. These highly spherical polyethylene microspheres offer the flow-ability of standard microspheres, with the ability to be separated from other materials for re-use and cleanup.
One use of paramagnetic microspheres as large as 1mm in diameter to simulate salmon eggs, Scientists are able to place them in a natural habitat, observe how they move with the water currents and then use their magnetic properties to clean them up.
SuperParamagnetic microspheres, sometimes just called magnetic microspheres or paramagnetic microspheres have become widely used in the life sciences industry (<10um diameters) for applications such as:- Solid Phase Immunoassays
- Bacteria Detection
- High Throughput screening
- Rapid Tests
- Cell Sorting
- Biosensors
- Nucleic Acids Technology
- Microfluidics1
Super paramagnetic microspheres used in the life science industry are supplied in solution form.
1. Merck Estapor Super Paramagnetic Microspheres Brochure
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Technical Characteristics of PMMA Microspheres
PMMA microspheres - Cospheric LLC
PMMA micropsheres or polymethylmethacrylate microspheres are often referred as acrylic microspheres. PMMA polymer is an amorphous, transparent and colorless thermoplastic that is hard and stiff. It has good abrasion and UV resistance and excellent optical clarity. It has somewhat poor solvent resistance. PMMA spheres are soluble in organic solvents such as acetone, benzene, or halogenated hydrocarbons. Though flammable, PMMA material has low smoke emission.
Poly(methyl methacrylate) or PMMA is less hydrophobic than polystyrene and reported to show reduced nonspecific protein and peptide binding. The density of these beads, 1.19 g/cc, is considerably heavier than polystyrene particles, allowing more rapid separation and making them easier to concentrate by centrifugation. The particles typically have a hydrophilic anionic surface with refractive index of 1.48.
PMMA micropsheres have good biocompatibility which allows the particles to be used in many medical and biochemical applications. Diameter and monodispersity specifications for the micropsheres are dictated by the requirements of each application.
PMMA micropsheres are used in such a wide variety of industries as investigations in the colloidal crystal field, toners for copying machines, biomedical devices and injectable dermal fillers.
Research quantities of PMMA microspheres can be obtained from several suppliers depending on the desired particle size.
Bangs Labs offers PMMA microspheres 0.5 micron – 5 micron in diameter. Cospheric LLC sells research samples of PMMA spheres in several tight size ranges from 10 micron to 150 micron. Goodfellow offers polymethylmethacrylate spheres in two diameters of 1.5mm and 3.18mm.
Below is some detailed technical information on material properties of PMMA:
(source: Goodfellow)Electrical Properties
Dielectric constant @1MHz 2.6
Dielectric strength ( kV mm-1 ) 15
Dissipation factor @ 1MHz 0.014
Surface resistivity ( Ohm/sq ) 1014
Volume resistivity ( Ohmcm ) 2-14 x 1015Mechanical Properties
Elongation at break ( % ) 2.5-4
Hardness – Rockwell M 92-100
Izod impact strength ( J m-1 ) 16-32
Poisson’s ratio 0.35 – 0.4
Tensile modulus ( GPa ) 2.4-3.3
Tensile strength ( MPa ) 80Physical Properties
Abbe number 57.2
Density ( g cm-3 ) 1.19
Flammability HB
Limiting oxygen index ( % ) 17-20
Radiation resistance Fair
Refractive index 1.49
Resistance to Ultra-violet Good
Water absorption – over 24 hours ( % ) 0.2Thermal Properties
Coefficient of thermal expansion ( x10-6 K-1 ) 70-77
Heat-deflection temperature – 0.45MPa ( C ) 105
Heat-deflection temperature – 1.8MPa ( C ) 95
Lower working temperature ( C ) -40
Specific heat ( J K-1 kg-1 ) 1400 – 1500
Thermal conductivity @23C ( W m-1 K-1 ) 0.17-0.19
Upper working temperature ( C ) 50 to 90 -
Cosmetic Applications of Injectable Polymer Microspheres
Polymer microspheres, in particular injectable polymer particles with a diameter in the range of 30−300 μm, are becoming widely used as a biomaterial in different clinical fields, such as cosmetic surgery, reconstructive surgery, and urology. Injectable skin fillers offer many benefits in cosmetic dermatology, allowing new forms of facial rejuvenation and wrinkle treatment without surgery. Injectable skin and wrinkle fillers are used to increase tissue volume, reduce wrinkles, and improve skin’s overall contour.
According to The American Society for Aesthetic Plastic Surgery, two formulations of fillers that are based on microsphere technology are FDA approved for use, differing in design and expected longevity of results. These injectable microspheres products are used for volume replacement and for deep facial wrinkles (such as the nasolabial folds.) They are not approved for use in the lips.
One of cosmetic dermatology products using injectable microspheres is ArteFill® – a new breed of dermal filler that offers longer lasting results than other cosmetic filler injections. ArteFill® (known as Artecoll® outside of the United States) is made of polymethylmethacrylate (PMMA) microspheres (miniature beads) that are suspended in bovine collagen. Tiny microspheres are made of non-resorbable polymethylmethacrylate – a biocompatable compound that has been used for years. PMMA has been used since the early 1930s in such common procedures as dental prostheses, eye lenses, bone repair, orthopedics and in pacemakers. PMMA microspheres are well tolerated by human tissue (no rejection). Continue reading “Cosmetic Applications of Injectable Polymer Microspheres” »
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Motivations for Using Biodegradable Microspheres in Drug Delivery
In recent years there is significant interest in using biodegradable polymeric microspheres for drug delivery. Delivering drugs through biodegradable microspheres has numerous advantages compared to conventional delivery systems. While in conventional systems the drug is usually released shortly after delivery and stops working after a brief period of time, biodegradable polymer offers a way to provide sustained release over a longer time, thus eliminating the need for multiple doses and ensuring sustained and controlled drug delivery over weeks or months. Continue reading “Motivations for Using Biodegradable Microspheres in Drug Delivery” »
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Electrostatic-based DNA Microarray Offers Medical Diagnostics Capabilities
The uses for microspheres continue to grow, a recent article published by UC-Berkley shows how DNA sequencing can be achieved through the use of statically charged microspheres. The key breakthrough is that they have been able to achieve a visible result through using the electrostatic repulsion of the microspheres. A copy of their announcement follows:
Groves, and members of his research group Nathan Clack and Khalid Salaita, have published a paper on their technique in the journal Nature Biotechnology, which is now available online. The paper is entitled “Electrostatic readout of DNA microarrays with charged microspheres.” Continue reading “Electrostatic-based DNA Microarray Offers Medical Diagnostics Capabilities” »