Heat build-up during homogenization can be a significant challenge, especially when working with temperature-sensitive samples. As the sample temperature increases, irreversible changes, such as protein and nucleic acid denaturation, become increasingly more likely.
During homogenization of biological samples, such as this cardiac tissue, care needs to be taken to prevent heat damage to proteins, nucleic acids, and other heat-sensitive components of the sample.
So how can you prevent heat damage to your sample during homogenization?
In this article, we provide specific tips on how to deal with sample overheating in four popular types of homogenizer:
- Rotor–stator (high-shear) homogenizers
- Ultrasonic (sonicator) homogenizers
- Bead mill homogenizers
- High-pressure homogenizers
With these practical tips, we hope that you can find a suitable approach to working with even the most temperature-sensitive of samples.
If you’re in a hurry, then check out the handy summary table at the end of the article, which outlines the key approaches in brief.
Rotor–stator (high-shear) homogenizers
How much heat do they generate?
At most, rotor–stator homogenization generates a low to moderate level of heating. If your sample is heat sensitive, then you should consider using one of the cooling methods described below.
POLYTRON Ecoline PT Stand Dispersers can be attached to a stand during rotor–stator homogenization, giving the option to place the sample in an ice bath (not shown).
Why does this heating occur?
Heating is mostly caused by friction generated by the rotating parts, which lead to fluid shear forces and mechanical tearing.
How can sample overheating be prevented?
Ice cooling
One simple and effective method of cooling your sample is to set up a clamp stand to hold the sample container in an ice bath during homogenization.
For example, the POLYTRON Ecoline PT Stand Dispersers can be bought as part of a bundle that includes a stand, while optional stands can be purchased for other models such as the Scilogex D160 and D500 Homogenizers or the IKA T 25 Easy Clean.
The PRO Scientific DPS-20 Homogenizing System contains an integrated cooling system that can cool samples using ice, ice-water, or cold beads.
Integrated cooling system
Certain rotor–stator homogenizer models provide integrated cooling systems — the Cooling Carousel Racks available for the PRO Scientific DPS-20 Homogenizing System, for example, are able to cool sample tubes using ice, ice-water, or cold beads.
Temperature sensor
Overheating can also be monitored using a temperature sensor — for example, the IKA T 25 Easy Clean “Control” model can be fitted with a dispersing element that provides a continuous readout of the temperature of your sample, enabling to key the temperature below the required threshold.
Ultrasonic homogenizers (sonicators)
How much heat do they generate?
Ultrasonic homogenizers (also known as sonicators) generate a very high level of sample heating. Therefore, if your sample is heat sensitive, you need to pay special attention to your heat mitigation methods or should consider using an alternative homogenization strategy.
If your sample has some degree of heat tolerance or you require a sonicator for your application, then we recommend using one of the cooling methods outlined below.
The Benchmark Pulse 150 Ultrasonic Homogenizer offers a pulsed sonication program that can be configured via the touch-screen interface to limit sample heating.
Why does this heating occur?
This heating is generated by the rapid vibration of the tip of the sonicator, which transmits large amounts of kinetic energy to the sample via cavitation and fluid shear forces.
How can sample overheating be prevented?
Pulsed homogenization
Heat build-up can be limited by using a pulsed homogenization program, in which periods of active homogenization alternate with periods of inactivity that allow the heat to dissipate.
For example, the Benchmark Pulse 150 Ultrasonic Homogenizer includes a programmable touch-screen control for configuring the pulse program to limit the heating of your sample.
Ice cooling
Ice cooling can be performed between the sonication steps of a pulsed program, or alternatively the sample can be immersed continuously in an ice bath. The temperature of the ice bath can be monitored independently using a thermometer, if desired.
To hold the sample in ice during sonication, clamps and stands are available for specific models of sonicator, including the Sonifier SFX150, S-250/450 and SFX250/550, the Ultra-Turrax T 18 and T 25, and the Qsonica Q500 & Q700 Sonicators.
The Continuous Flow Attachment for Sonifier homogenizers, such as the Sonifier SFX250 / SFX550, incorporates a cooling jacket that helps to prevent heat build-up during sonication.
Integrated water cooling
Accessories that provide integrated cooling during high-volume sample processing are available for some models of sonicator.
For example, the High Volume Flocells for the Q2000 sonicator are water jacketed for cooling. The temperature of the water jacket can be reliably maintained at a low temperature using a High Capacity Recirculating Chiller.
The Continuous Flow Attachment offers the same cooling jacket functionality for Sonifier homogenizers, such as the Sonifier SFX250 / SFX550.
Temperature sensor
A temperature probe can be used to monitor and limit the sample temperature during homogenization.
For example, the Sonifier SFX series can be fitted with an SFX Temperature Probe, which maintains the sample temperature within user-specified limits. The Qsonica Q2000 sonicator also has a temperature probe option, enabling you to limit sample heating.
Bead mill homogenizers
How much heat do they generate?
Bead mill homogenizers generate a low to moderate level of heating.
The temperature increase is affected by the sample volume and type, the bead quantity and type, the speed of agitation, and the procedure duration. As a general rule of thumb, there is a 10°C increase for every minute of homogenization.
The BioSpec BeadBeater comes with an ice-water cooling jacket to limit heating during homogenization.
Why does this heating occur?
The heating of the sample is mostly due to the impact of the moving beads imparting kinetic energy to the sample, which increases its temperature. In addition, fluid shear forces contribute to sample heating.
How can sample overheating be prevented?
Ice cooling
Sample temperatures can be kept within acceptable limits by cooling them on ice between periods of bead-mill homogenization. Cycles of alternating homogenization and ice cooling can be repeated until the full homogenization procedure is complete.
The BioSpec BeadBeater includes an ice-water jacket that similarly limits sample temperature increases, without the need to remove the samples from the homogenizer. Cooling can be improved further by using the Aluminum Sample Chamber or the Stainless Steel Chamber accessories for the BeadBeater homogenizer.
Air cooling
Some models of bead mill homogenizer come with a built-in cooling system — for example, the Bullet Blender® 5E Pro provides air cooling to samples by driving ambient air through vents in the top of the device to remove heat from the sample chamber.
The Cryolys® Evolution cooling unit maintains the Precellys® Evolution tissue homogenizer between 0°C–10°C during homogenization via dry ice sublimation.
Dry ice cooling
Meanwhile, the Bullet Blender® 50 Gold uses dry ice to keep samples close to 4°C, making it suitable for homogenization applications with temperature-sensitive refrigerated samples.
Similarly, the Cryolys® Evolution, which is compatible with the Precellys® Evolution tissue homogenizer, uses dry ice sublimation to maintain the sample temperature between 0°C–10°C before and during the homogenization procedure.
Electronic cooling
Some newer bead mill homogenizer designs have a built-in refrigeration system which does not require dry ice, such as the BeadBlaster 24-R.
High-pressure homogenizers
How much heat do they generate?
High-pressure homogenizers can generate a high level of heating — as much as 1.5°C–3.0°C for every 10 MPa (1.45 Kpsi) of pressure. As laboratory high-pressure homogenizers are often run at pressures ranging from 20 kpsi to 45 kpsi, this can add up to a lot of heating!
The Nano DeBEE High Pressure Homogenizer can be fitted with a cooling heat exchanger to keep sample heating low, even when homogenizing samples at pressures of up to 45 kpsi.
Why does this heating occur?
As the sample is forced at high pressure through a narrow valve or membrane, it undergoes powerful fluid shear forces, along with cavitation and turbulence, which increase its temperature considerably. In addition, the sample may impact surfaces at high speed, imparting further kinetic energy and heating.
How can sample overheating be prevented?
Cooling heat exchanger
High-pressure homogenizers such as the ShearJet HL60 Electric Hydraulic High Shear Homogenizer come with a water-jacketed heat exchanger that actively cools the sample during homogenization. Similarly, an optional cooling heat exchanger is available for the Nano DeBEE High Pressure Homogenizer.
The ShearJet HL60 Electric Hydraulic High Shear Homogenizer can additionally be fitted with an optional chiller that maintains the low temperature of the heat exchanger during prolonged homogenization procedures.
To limit sample heating, the piston and cylinder of French press homogenizers, such as the Glen Mills French Press G-M, can be pre-cooled, along with the sample.
Pre-cooling
For French press homogenizers, such as the Glen Mills French Press G-M, pre-cooling of the sample, piston, and cylinder are recommended to counteract the heating effect of high-pressure homogenization within the cylinder.
Summary
This table summarizes the different types of homogenizer, how much sample heating to expect from each, and strategies for dealing with overheating:
|
Homogenizer type |
Heating level |
Mechanisms of action/heating |
Solutions to prevent overheating |
|
Rotor–stator |
Low to moderate |
Fluid shear forces; Mechanical tearing |
Ice cooling; Integrated cooling system; |
|
Ultrasonic (sonicators) |
Very high |
Cavitation; Fluid shear forces |
Ice cooling; Integrated water cooling; Pulsed homogenization; Temperature sensor |
|
Bead mill |
Low to moderate |
Fluid shear forces; Impact with beads |
Air cooling; Dry ice cooling; Electronic cooling; Ice cooling |
|
High-pressure |
High |
Cavitation; Fluid shear forces; Impact with surfaces; Turbulence |
Cooling heat exchanger; Pre-cooling |
We hope that the practical advice offered in this article can help you to develop suitable procedures for working with temperature-sensitive samples in your lab.
Don’t forget to check out our Application Center for additional detailed information on homogenization technologies, applications, and specific protocols for different sample types and homogenizers.
If you have any further questions about the homogenizers or cooling accessories mentioned here, then please contact us for assistance!
