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What are Microspheres?

Microspheres are spherical microparticles that are typically between 1 and 1,000 microns(1 mm) in diameter. By comparison, a human hair is approximately 75 microns in diameter. Microspheres are often referred to as spheres, balls, beads, microbeads or microballoons and are manufactured from a variety of raw materials. The most common types are solid and hollow glass microspheres, solid and hollow polymer microspheres, and ceramic microspheres. Microspheres can also be made from polymer, glass, cellulose, silica, metal, and other raw materials. To the naked eye, microspheres appear to be a fine powder or dust. Each type of microsphere offers unique material properties and functionality. Microspheres are manufactured in different grades depending on application requirements.

At Cospheric we are constantly discovering new exciting applications for our technologies. They have truly unlimited potential.

Our custom microspheres can be used as fillers, carriers, or active ingredients in paints, coatings, cosmetics, pharmaceuticals, and drug delivery. Our microcoatings enable us to create particles with dual-functionalities that can be manipulated externally by chemical reactions and electromagnetic forces, with many applications in diagnostic and medical devices. Our proprietary microstructures control fluid flow and position microparticles for proper operation in a device. Our unique encapsulation techniques and materials seal devices while maintaining the flexibility and optical clarity. Currently we are working on integrating our microtechnology solutions into electronic paper displays, solar cells, and diagnostic devices.

What is the History of the Microsphere Industry?

Solid glass microspheres, also known as glass beads, have been manufactured for at least 100 years. Brothers Rudolph and Paul Potters produced glass beads in New York as early as 1914. In 1922, large quantities of high-refractive-index glass beads were produced to coat movie screens.

Hollow glass microsphere technology was developed as an outgrowth of the manufacture of solid glass beads following the publication of the first patents in this area in the 1950s. Since that time, many companies have been involved in the development and manufacture of a variety of microspheres. Emerson and Cuming, Dow Chemical, Potters and 3M were some of the first companies manufacturing microspheres utilizing a variety of different manufacturing processes.

Microspheres were introduced as fillers for plastics in the mid-1960s and since then, their use has increased rapidly. First-generation microspheres have been used in applications in many areas, including aerospace and military materials, molded plastic components and retroreflective highway signs. Since their introduction, microspheres have been adopted into hundreds of applications in diverse industries, including oil and gas, recreation, paints and coatings, transportation, construction, mining explosives, and consumer products.

For the first 20 years after their introduction, hollow glass microspheres were not sufficiently robust to survive the high-shear forces and pressure involved in plastics compounding and injection molding. In the late 1980s, 3M introduced a hollow glass microsphere with isostatic crush strength of 10,000 psi, which is more than twice as strong as any microsphere that was previously available. This enhanced survivability meant that glass microspheres could be used as fillers in many high-shear processes. In recent years, microspheres have experienced excellent growth due to the emergence of new high-value, high-growth markets. These markets include biomedical, cosmetic, personal care and specialty applications, among others. Microspheres are increasingly found in many companies’ toolboxes.

How Much do Microspheres Cost?

The quality and prices of different types and grades of microspheres vary widely. The cost of microspheres depends on a variety of factors, including raw materials, density, strength, particle size and distribution, functionality, cleanliness and volume. Microsphere grades with large particle size distribution and poor uniformity that are used as low-cost, volumizing filler may cost less than $5 per pound. Monodisperse microspheres, used primarily for biomedical applications, are produced under very strict quality specifications and can cost more than $1,000 per gram.

The pricing of microspheres depends strongly on specifications such as the percentage of microspheres in a specified size range, particle size distribution and percentage of spherical particles. For example, glass microspheres that are >90% spherical and >90% in particle size range may cost $500 per pound, while the same microspheres that are >85% spherical and >80% in size range may cost $5 per pound. Monodisperse glass microspheres can cost as much as hudreds of dollars per gram. Monodisperse microspheres made from biodegradable polymers can cost as much as thousands of dollars per gram.

When comparing the cost of microspheres to resins and competing mineral fillers, it is critical to think in terms of cost per unit of volume rather than cost per pound as microspheres can displace a large volume of higher-density material at a very low weight. For example, hollow microspheres can have half or quarter the weight and proportionally more volume compared to solid fillers. Costs also depend on specialized surface treatments and coatings that add functionality beyond that of the raw materials and construction of microspheres and allow manufacturers to tailor their products for specific applications. Surface treatments can be added to make microspheres magnetic, fluorescent and/or conductive or to simply improve the bond between microspheres and the matrix.

What are Applications of Microspheres in Life Sciences?

The life sciences industry includes companies in the fields of biotechnology, pharmaceuticals, biomedical technologies, life systems technologies, nutraceuticals, environmental health and biomedical devices and organizations involved in the various stages of research, development, technology transfer and commercialization. Drug discovery, clinical diagnostics and biomedical research markets rely heavily on the use of microspheres.

Microspheres are used in the life sciences industry primarily in tools and as consumables in drug discovery and development, clinical diagnostics and biomedical research.

Key applications of microspheres in life sciences applications include the following:

  • Fluorescent, colored or luminescent labels for detection
  • Capture reagents for lateral flow immunoassays
  • Calibrators for flow cytometry, microarray analysis, microscopy, automated imaging and other instruments or assays
  • Platform for monitoring coagulation by light scattering
  • Surfaces for immunoprecipitation
  • Tracers for fluid flow (including blood flow) or air flow
  • Tools for automated sample preparation
  • Fluorescence immunoassay
  • Enzyme immunoassay (EIA)
  • Fluorescence microscopy
  • Confocal fluorescence microscopy
  • Flow cytometry/image cytometry
  • Magnetic cell separation
  • Magnetic particle EIA
  • Microfluidics
  • Cell separation
  • Magnetic particle assay development
  • Agglutination tests
  • Molecular diagnostics
  • Nucleic-acid separation
  • Lateral flow tests
  • Diagnostic assays
  • Bacteria isolation
  • Sample preparation for polymerase chain reaction (PCR)
  • Enzyme immunoassay
  • Immunopurification
  • Particle-size standards
  • Respiratory or drug delivery models for the pharmaceutical industry
  • Other research and industrial applications

Several microsphere companies offer a wide selection of colored and unstained, functionalized and non-functionalized microspheres for research, clinical and diagnostic applications, water- and air-flow testing and other bead-based applications. Several companies offer precision microspheres for use as a reference standard for size measurements, as flow tracing devices, for molecular biology and nucleic-acid isolation applications, and as reactive surfaces for transport diagnostic reagents. Microspheres used in life sciences are generally made of polymer or silica (ceramic). Polymer microspheres made from polystyrene or PMMA are generally hydrophobic with high protein binding abilities. Silica microspheres are inherently hydrophilic and negatively charged.

What are the Benefits of Using Microspheres?

The advantage of microspheres is that their ability to be customized with respect to diameter, density (very small microspheres below 1 micron in diameter can be designed to remain in suspension indefinitely), surface charge density, type of surface group, color and fluorescent response, among other properties. Microspheres can be monodisperse with very tight particle-size distribution.

Depending on the raw materials used, each type of microsphere offers unique advantages suitable for particular applications. Due to their small, spherical structure, all types of microspheres share some advantages. The sphere is nature’s most efficient shape, with the least surface area compared to volume. It is this shape that gives microspheres such unique properties.

Ball-Bearing Effect

Microspheres can act as mini ball bearings as they roll over each another easily. This contributes to lower viscosity and better flow. In the composite industry, the ball-bearing effect enables resins to more easily infiltrate mold geometries, resulting in faster cycle times. In cosmetics and personal care formulations, the ball-bearing effect is used to enhance the sensory properties of products by creating a luxury feel and ensuring good spreadability. The free-flowing nature of microspheres lends itself to easy handling in a factory environment. Spherical powders are easy to spray or pump, can be easily fed by gravity without blockage, and can be pumped in dry form. Microspheres improve workability and ease of use in a wide variety of applications.

High Filler Loading

The sphere has the lowest surface area to volume ratio of any shape. The spherical shape of microspheres means that it takes less binder to wet out the surface of microspheres than filler of any other shape. This results in low resin or binder demand, which, in turn, increases volume-loading capacity, allows high solid formulation, lowers shrinkage and reduces costs. Smaller spheres fill voids between larger spheres to enhance packing efficiency.

Surface Quality

Microspheres do not orient and obstruct the directional orientation of reinforcing fibers and matrix. As a result, stresses are more evenly distributed, enhancing both reinforcement and dimensional stability. Their high packing efficiency and spherical shape improve burnish resistance and hardness, which means that surfaces look new longer, and the time and costs associated with touch-ups and repainting are reduced. The inherent bonding of spheres with the base resin prevents the filler from scarring or separating from the surface of the composite. With ordinary fillers, soft or jagged particles on the surface often break or wear away.

Weight Reduction

The low density of hollow microspheres helps reduce the weight of finished products. Many grades of microspheres, although lightweight, have high mechanical strength.

Does Particle Shape Matter?

The answer is: Absolutely.

Particle shape is a critical component in the behavior of the particles. For particles greater than 500 micron or 0.5mm shape is easy to determine with a naked eye. For smaller particles, down to about 1-2 micron, particle shape or morphology is easily determined by observation under optical microscope. Smaller, submicron particles, require more specialized higher-magnification equipment, such as Scanning Electron Microscopy. Shape is often classified as spherical, spheroidal, granular, or flake.

To start, it influences flow characteristics of a powder. Spheres and microspheres are well-known for their ball-bearing effect. If you spill spheres on the ground, the floor will turn into a skating rink. The same spherical particles can give silky, flowing and luxurious feel to creams and lotions in cosmetics applications. They smoothly glide past each other with minimal effort and friction, so much unlike the non-round granular or flake particles.

Shape plays a large role in reactivity of any material, because it controls how much surface area is available for the reaction to occur. For example, various powder shapes can be used to create pyrotechnic effects in fireworks. Spherical powders with smallest surface area and high roundness are slow to ignite, compared to flakes which have a large surface area and sharp edges which ignite more easily.

Most mathematical models are based on the assumption that the particle is a sphere. Until particle shape becomes an adjustable design parameter, scientists and engineers will have to rely on precision spherical particles to test their models and simulations.