Samples are homogenised in rotor-stator homogenizers by mechanical tearing, shear fluid forces, and/or cavitation, with the rotor spinning rapidly inside a stationary outer sheath (stator) (the rapid forming and collapsing of bubbles). However, particularly tough tissue can be a challenge for rotor-stators when trying to homogenise cells or tissues. Although some high-throughput models and continuous / in-line models are available, most rotor-stators homogenise a single sample at a time.

Bear in mind that not all rotor-stators are equipped with a probe, which is necessary for operating a rotor-stator homogenizer.

Although the phrase “high-shear homogenizer” is commonly used to describe rotor-stator homogenizers, this can be misleading because other types of homogenizers, such as high-pressure homogenizers, also function in whole or in part by causing high shear.

What is the purpose of homogenization?

Homogenization is a procedure used to reduce the size of particles or droplets in a liquid, resulting in a more stable and homogeneous combination. The aim of homogenization might vary based on the specific application, however some frequent reasons include:

1. Emulsification: Homogenization is typically used to make emulsions, which are mixes of two or more immiscible liquids, such as oil and water. By lowering the size of the droplets, the emulsion becomes more stable and less likely to split.
2. Suspension Stabilization: Homogenization is also used to stabilise suspensions, which are combinations of solid particles in a liquid. By lowering the size of the particles, the suspension becomes more stable and less likely to settle.
3. Dispersing: Homogenization is used to disperse particles, liquids or gases in a liquid. This is widely employed in the food, cosmetic and pharmaceutical industries where materials need to be well blended.
4. Cell lysis: Homogenization is employed to break down cells in a sample for further investigation. This is often used in the biotechnology business.
5. Deagglomeration: Homogenization is used to break down clumps of particles or droplets that have accumulated in a liquid.
6. Increasing the surface area: By lowering the size of particles or droplets, homogenization improves the surface area available for chemical reactions or absorption.

Overall, the objective of homogenization is to generate a more stable and homogenous mixture, increase product quality, and make the product more easily processable.

What is Rotor-Stator Homogenization?

Rotor-stator homogenization is a mechanical method used to homogenise or emulsify liquids. It employs a rotor (a spinning disc or impeller) and a stator (a stationary ring) to create high-pressure and high-shear forces that break down particles or droplets in the liquid, resulting in a homogenised or emulsified combination. This technology is extensively utilised in the food, cosmetic, and pharmaceutical industries, among others.

Principle of Rotor-Stator Homogenization (How does a rotor stator homogenizer work?)

Rotor-stator homogenization employs a revolving metal shaft (the rotor) contained within a stationary metal housing (the stator) (the stator). The rotation of the rotor causes a suction effect that sucks the sample into the gap between the rotor and stator, where it is subjected to extremely high shear stresses as a result of a rapid velocity shift in the narrow region between the rotor and stator. (According to the rules of fluid physics, the velocity of the fluid close to the rotor is the same as the rotor’s velocity, whereas the velocity of the fluid near to the stationary stator is zero.) The material is subsequently expelled via slots in the stator by centrifugal forces, and the rapid velocity of the fluid induced by the rotor-stator guarantees that the process is repeated as the liquid and sample cycle through it.

Parts of Rotor-Stator Homogenization

Rotor-stator homogenization normally consists of the following parts:

• Rotor: This is the spinning disc or impeller that provides high-velocity flow in the liquid. It can be built of different materials, such as stainless steel or ceramic, and have varied geometries, such as a flat disc or a slanted disc.
• Stator: This is the stationary ring that surrounds the rotor. It has a succession of closely spaced, precision-machined, orifices or slots that create high-pressure and high-shear forces when the liquid travels through them.
• Shaft: This is the rod that connects the rotor to the motor, which provides the power to spin the rotor.
• Motor: This is the power source that drives the rotor. It might be electric, pneumatic, or hydraulic.
• Housing: This is the housing that encloses the rotor, stator, shaft, and motor. It provides a sealed atmosphere for the homogenization process and can be made of different materials, such as stainless steel or plastic.
• Inlet and Outlet ports: These are the ports that allow the liquid to enter and exit the homogenizer. Some homogenizers also contain a pressure gauge, thermometer or temperature controller.
• Adjustable gap : The distance between the rotor and stator is adjustable, and it is used to alter the level of shear given to the liquid.

Operating Procedure of rotor stator homogenizers

• These specifications apply to rotor stator homogenizers used for industrial, pilot plant laboratory, or pharmaceutical applications. The rotor stator homogenizers are simple to assemble; the shafts are prefabricated and simple to attach to the motor.
• The instruction manuals for these devices contain information about their specs and unique features. All units must include a dial or other type of control to precisely adjust the rotor speed.
• Once the unit has been constructed, ready to combine the solution and, if necessary, heat it. Place the end of the homogenizer into the vessel.
• Enough solution must cover the homogenizer’s rotor and stator, or dispersion will be insufficient. To initiate the process, turn the device on at a low rpm. The solution will be drawn into the shaft and submerge the rotor; the inert solution will be sheared, and there should be a visible change.
• If at all possible, avoid forming a vortex in your solution by keeping the vessel at an angle. In less than one minute, a high-speed homogenizer may completely emulsify its solution. Slowly increase the rpms as everything begins to blend.

Differences Between Rotor-Stator Homogenizers and High-pressure Homogenizers

Rotor-Stator Homogenizers

• Rotor-stator homogenizers, sometimes referred to as high-shear mixers or colloid mills, are meant to reduce particle size by hydraulic and mechanical shear and cavitation. Originally designed to make dispersions and emulsions, this type of homogenizer works through the movement of a rotor inside a stator, which causes a suction effect.
• Mixing happens when a sample is pulled in through one of the mixing heads as the blades rotate and is subsequently discharged at a high velocity through a hole in the stator. The combination of high rpm from the rotor and egress through tiny apertures allows the sample to be mechanically shredded into very fine particles.
• This sort of homogenizer is best utilised for biological (plant and animal) tissue and processes liquid samples in the 0.01 ml-20-liter range.
• It is most often utilised in the chemical, cosmetic, pharmaceutical and food industries to create suspensions, emulsions, lyosols and other products through solid-liquid suspension, liquid-liquid emulsification and homogenization, particle size reduction, power-liquid dispersion and other applications.
• Though high pressure-homogenizers utilise significant quantities of energy to produce pressure differentials to homogenise food, their rotor-stator equivalents manipulate substances though a shearing action.
• They emit low heat during operation and are able to homogenise reasonably delicate tissue. However, working with aerosols and foams might be challenging with this sort of homogenizer.

High-pressure Homogenizers

• In a manner similar to that of liquid mixers, high-pressure homogenizers force cell suspensions through a very narrow channel under pressure. They use pressure and force (such as turbulence and cavitation) to obtain a consistent and uniform sample.
• High-pressure homogenizers are mostly utilised for cell lysis or generating emulsions when huge volumes are being processed, and they can be used for many types of bacteria, yeast, and mycelia. Following are some of the numerous advantages offered by high-pressure homogenizers:
  • Capability to process enormous amounts of liquid in an orderly and reproducible manner.
  • Consistency in product composition.
  • Cavitation and turbulent flow under control.
  • increased disintegration rate
  • Low product contamination risk.
  • Particle size decrease uniformly.
  • Improved stability of the finished product.
  • Forces that can be modified to maximise results.
  • Fewer passes are needed to achieve consistent outcomes.
  • Allow for a wide variety of sample sizes.
  • Reduced cost.
• Clearly, high-pressure homogenizers offer numerous advantages to businesses. It is crucial to note, however, that they cannot manage large particles or materials with a high fibre content and are not ideal for high-temperature materials. In addition, they can be exceedingly huge and hefty.

Advantages of Rotor-Stator Homogenization

• Due to the ability to swap between probes, a broader volume range may be handled than with other approaches.
• Using various probes, rotor-stator homogenizers can homogenise contents ranging from 30 microliters to 30 litres.
• For single samples, rotor-stator homogenizers are particularly quick and effective.
• A number of automated, higher-throughput rotor-stator homogenizers are also available. In general, these are more expensive than a bead mill with an identical throughput, but they can process larger samples.
• There are also a variety of rotor-stator homogenizers that permit semi-continuous in-line processing and are hence capable of handling extremely high volumes. At addition to high-pressure homogenizers, these are the only homogenizers available in real industrial scale.

Disadvantages of Rotor-Stator Homogenization

• In addition, there is no volume limitation; rotor-stator homogenizers are available for laboratory, pilot, and industrial size applications.
• Due to the usage of probes, rotor-stator homogenizers are less appropriate for high-throughput, multiple-sample applications. If the risk of cross-contamination is a concern, the probe must be cleaned after each use.
• Some manufacturers offer packs of inexpensive probes or disposable, limited-use probes that are intended to allow you to process many samples with a clean probe each time (such as the PRO Multi-Gen Generator Probes).

Precautions

• Rotor-stator homogenizers are ideally suited for liquid applications like mixing and emulsification. Additionally, they are excellent at rupturing cells and homogenising relatively soft tissue. Keep in mind, when homogenising solids, that the particles must fit between the rotor and stator in order to be homogenised. While the suction action can somewhat overcome the form of soft solids (such as most soft tissue), for tougher solids (such as tablets or fibrous tissue), the sample may need to be pre-processed so that the particle size is sufficiently tiny. Probes with sawtoothed heads can assist in tearing apart fibrous samples and a variety of other materials.
• During use of a rotor-stator, the probe should be moved within the sample for optimal results. This ensures that the sample is completely and uniformly homogenised. It can also help reduce the required runtime, especially when working near the instrument’s maximum volume.
• During operation, Rotor-Stators transfer a considerable amount of heat to the sample, due primarily to frictional forces. If your application is susceptible to heat, investigate ways for cooling the sample. Attaching the sample container to a clamp and immersing it in an ice bath is suitable for the vast majority of laboratory-scale applications.
• To increase the longevity of your probes, ensure that they are cleaned after each usage. Using a volatile cleaner, such as 70% ethanol, to clean the probes will expedite their drying time.

FAQ

References

• https://homogenizers.net/collections/rotor-stator-homogenizers
• https://homogenizers.net/pages/ac-rotor-stator-homogenization
• https://www.omni-inc.com/high-shear-lab-homogenizers.html
• https://arxiv.org/ftp/arxiv/papers/1912/1912.07861.pdf
• https://www.labconsult.be/catalog/lab-equipment-tools/homogenizing-disrupting-grinding/rotor-stator-homogenizers/
• https://www.labindiainstruments.com/rotor-stator-homogenizers.html
• https://www.labindiainstruments.com/pdf/rotor-stator-homogenizers.pdf
• https://www.proscientific.com/rotor-stator-homogenizers/
• https://www.beei.com/blog/rotor-stator-vs.-high-pressure-homogenizers-what-you-need-to-know
• https://adilabtech.com/rotor-stator-homogenizers.php
• https://catscientific.com/principles-of-rotor-stator-homogenization/
• http://gingerscience.co.in/index.php?option=com_content&view=article&id=108&Itemid=212
• https://www.misceo-cosmetics.com/en/emulsifier-homogenizer/77-misceo-300f.html
• https://www.goldleaflabs.com/blogs/blog/rotor-stator-homogenizers-guide-to-industrial-and/