Definitions of Microspheres: What are they?

What are Microspheres?

Microspheres are engineered materials defined as spherical particles with dimensions on the micro scale. Micro scale is typically used to describe measurements between 1 micron (1um) and 1000 micron (1 millimeter or 1 mm). Dimensions of microspheres are typically specified as average diameter in micron. As a reference, human hair is about 75 micron in diameter, pollen particles are about 50 micron, a red blood cell is about 25 micron, and a white blood cell is about 8 micron. Often microspheres appear to be a dry free-flowing powder. However, sometimes they are provided suspended in a solution at a specified concentration.

Microspheres are both round and spherical, which gives them unique shape and unique properties. This feature offers multiple advantages in a variety of applications, such as bond-line spacers, precision optical instruments, syringes and medical devices, tracer particles, and many others where it is critical that a particle has the same footprint and dimensions regardless of its physical orientation. Spherical shape also offers a ball-bearing effect that allows microspheres to flow freely and easily past each other and on top of surfaces. Microspheres can typically be observed and measured with an optical microscope which has a limitation of about 2 micron.

Are microspheres and microparticles the same materials? No, these two terms are quite different and cannot be used interchangeably. The term microparticle only refers to the size but the not the shape of the material. The best way to think about it is that microspheres are a unique and special type of microparticles.

In conversation with scientists and engineers, the answer to the question “exactly what are microspheres?” we would say that microspheres are precision spherical microparticles. In conversation with a non-technical person who asks “what are microspheres,” we often say that we are working with precision dust, small spherical particles that are often not even visible to the human eye with diameters sometimes smaller than a human hair.

What are Microspheres vs. Microparticles?

Microparticles are micro-scale materials that have the same dimensions as microspheres (greater than 1 micron and less than 1000 micron in equivalent diameter, where equivalent diameter is calculated as the theoretical diameter of a sphere of equivalent volume).

Unlike microspheres, microparticles can have a wide variety of shapes including rough edges and sharp points. Examples of microparticles in our daily life are salt, sugar, flour, detergent, baking soda and basically every powdered substance that we come across. Sand is a great example of a microparticle that comes in a variety of shapes, sizes, and colors.

Surface texture of microparticles can make them quite abrasive and cause undesired friction in many applications. Surface roughness is even known to alter the viscosity of suspensions. In addition, irregular shape of non-spherical microparticles creates challenges in R&D and process control due to the limitations of accurate commercially available tools that reliably quantify 3D shape of a large population of small particles.

What are Microspheres vs. Nanospheres?

Microspheres are different from nanospheres. The reason for this distinction is that nanosphere dimensions are best defined on a nano scale, which typically refers to particles smaller than 1 micron (1um) or 1,000 nanometers (1000nm) in diameter. Some scientists narrow this definition down further by classifying nanospheres are particles with diameters between 10 and 200 nanometers.

A strand of DNA is about 2.5 nanometers wide, a virus may be 100 nanometers in diameter, and a bacteria about 1000 nanometers (1 micron). Atoms are even smaller at 0.1 nanometers in diameter. Nanospheres will not be visible with optical microscopy and will require larger magnification, such as Scanning Electron Microscope (SEM).

Even though there are many advantages to working with nanospheres when the material needs to be ingested or injected, as well as working with nanoscale devices and technologies, there are safety precautions that need to be taken in the laboratory when working with such small particles due to the risk of potential inhalation hazard. Health and safely limits of occupational exposure to nanospheres has not been sufficiently studies and documented.

What are Microspheres vs. Microcapsules?

Microspheres should not be confused with microcapsules, because they have different structures, properties, and applications. Microspheres are solid or hollow, but they are always made of rigid materials, either solid material throughout or, in the case of hollow particles, a solid shell.  Even though microspheres can be produced to incorporate a wide variety of additive and active ingredients, they don’t typically contain any liquid inside.

Microcapsules, in contrast, typically consist of a flexible or frangible shell encapsulating a liquid inside. Microcapsules are frequently used in personal care, pharmaceutical, and food industry. Often the capsule acts a delivery mechanism for the active ingredient inside. The capsule will usually dissolve inside a human body (in food or pharmaceutical applications) or break when rubbed on the skin (when used in skin care and cosmetics products).

What are Microspheres vs. Microballoons?

Microballoons are a specific type of microspheres. They have the same high sphericity and dimensions as microspheres and can be made from a variety of materials. The reason they are called microballoons is because they are hollow inside, surrounded by a solid shell.

Microballoons have unique properties of extremely low density and light-weight while preserving the volume, which have many advantages and special application as a weight-reducing filler in composites and flotation devices. Microballoons add volume and buoyancy to the part or the material they are incorporated into.

For extra functionality, hollow glass microspheres (or microballoons) can be metal-coated on the outside to achieve a low-density conductive surface or material.

What are Microspheres vs. Microbeads?

Microbeads and microspheres are terms that often used interchangeably, but that is not accurate. Microbeads is actually a completely different grade of materials with alternate quality specifications and characteristics, which are manufactured and used for a different purpose.

Even though microbeads can have roughly the same dimensions as microspheres, they are not nearly as spherical or round as precision microparticles that we would categorize as microspheres.

Microbeads can be most accurately be referred to as plastic beads or pellets that typically sold in bulk at low cost for cosmetics and personal care applications.

There has been a big push from activists, followed by legislation in several countries, to completely ban the use of microbeads in personal care products due to the potential risk of plastic particles being washed down the drain and into the waterways, risking ingestion by wildlife, from insect larvae, small fish, amphibians and turtles to birds and larger mammals, who can potentially mistake microbeads for their food source.

There have been numerous, often conflicting, studies on exactly how much effect do these microbeads have. Unfortunately negative publicity of microbeads have created negative bias against some microsphere manufacturing companies who are not even serving personal care industry and are producing spherical particles for research and development applications supporting scientists in numerous fields of study.

What are Microspheres vs. Spheres?

Spherical particles that are larger than microspheres, with average diameters over 1mm (equivalent to 1,000 micron or 1,000,000 nm) are simply called spheres, beads, or balls. An ant is about 4 millimeters long, so it would be considered a macro scale object. A tennis ball is about 100 millimeters across.

Large, highly-spherical and colorful particles that are easily visible to the naked eye are a useful tool as reference particles in simulation experiments and are successfully used in vision systems and as flow tracers in fluidized bed applications, as well as reference particles or verification/calibration beads for instruments and applications that require tight tolerances. Opaqueness and bright coloration of the precision spheres increases their visibility in experimental set-up. Depending on the density of the material and the media, spheres can be selected to float or sink in the solution.

Microspheres Online website is a digital library and a compilation of resources for scientists and engineers working with microspheres. We are here for you.

Do you still have a question on what are microspheres? Do you agree with our definition of microspheres or do you use a different one? Do you need assistance finding additional information or an answer to a specific question? Have research you would like to be included on this website?

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