Technical Note | ElastoSens™ Bio
Technical note: ElastoSens™ Bio
by Dr. Dimitria Camasão
Senior Application Specialist, Rheolution Inc.
Dr. Antoine Frayssinet
Senior Application Specialist, Rheolution Inc.
THE ELASTOSENS™ BIO SPECIFICATIONS AND TECHNOLOGY
The ElastoSens™ Bio is a compact analytical instrument that measures the viscoelastic properties of soft materials. The dimensions of one instrument are 26.8 cm (10.5 in), 23 cm (9 in), and 50.8 cm (20 in) for height, width, and length, respectively, and it weighs 17 kg.
ElastoSens™ Bio uses vibrations to obtain contactless viscoelastic measurements. Viscoelasticity Testing of Bilayered Materials (VeTBiM) is the patented technology behind the ElastoSens™ Bio . VeTBiM consists in measuring the free response of a bi-layered system to a vibrational impulse. The bi-layered system consists of (i) a sample over (ii) a flexible membrane located at the bottom of the patented sample holder (Figure 1). The sample holder is composed of a solid polycarbonate body with a PDMS elastomer-based membrane at its bottom.
Figure 1. Patented sample holder of the ElastoSens™ Bio.
During testing, this sample holder is firmly attached to a mechanical unit inside the instrument (Figure 2A). The mechanical unit applies at each measurement point a vertical pulse vibration into the bilayered structure (sample holder + sample) in the range of 0.1 to 0.2 mm in amplitude in order to gently induce its free linear resonance (Figure 3A). The spectrum of resonance of the bilayered structure is measured using the laser probe pointing to the center bottom of the sample holder and processed to extract its resonance frequency and amplitude. Sample height is measured using an ultrasonic probe located right at the center top of the sample holder (Figure 3B).
Knowing the geometrical properties of the bilayered structure (height is measured and diameter is known) and the mechanical properties of the flexible membrane, the resonance properties of the bilayered structure only depend on the unknown viscoelastic properties of the sample. An inverse problem is automatically applied by the instrument to obtain the viscoelastic properties of the sample including linear shear storage modulus (G’), linear shear loss modulus (G’’), shear complex modulus (G*) and the loss tangent tan(d). The viscoelastic data are stored and displayed in real time (Figure 3C).
Figure 2. Measuring chamber of the ElastoSens™ Bio. (A) Mechanical unit where the sample holder is placed. (B) Sensor of temperature.
Figure 3. Diagram of a testing in the ElastoSens™ Bio. (A) Single bilayered system (sample holder + sample) under stimulation in the measuring chamber of the ElastoSens™ Bio, (B) Resonance of the bilayered system, free of any constraint and monitored by a class 1 laser and an ultrasonic probe (for the height), (C) Data processing and display in the software of the ElastoSens™ Bio. 
In addition, the rate of G’ evolution (derivative of G’ as a function of time), the height of the sample (precision of ± 0.2 mm) and the temperature (precision of ± 0.1 °C) are also displayed at each measurement point. The sample height captures in real time any volume changes of the sample that may be caused by swelling, shrinking or degradation. Due to the non destructive nature of the technology, the sample can be removed from the instrument and the sample can be reused for other purposes or retested multiple times (Figure 4).
Figure 4. Sample holder can be removed after the test from the measuring chamber of the ElastoSens™ Bio. Sample can be kept in the sample holder for testing at later time points or reused for other purposes.
The ElastoSens™ Bio can measure the viscoelastic properties of a sample during the transition from liquid-to-solid, solid-to-liquid or directly at the solid state of the material. These measurements can be combined with environmental stimuli such as temperature, light or gases to study the behavior of materials in response to such stimuli.
In the ElastoSens™ Bio, a sensor of temperature is located inside the chamber and the thermoelectric peltier heating-cooling system is calibrated to go from 4 °C to 70 °C with a precision of ± 0.1 °C. The calibration is done using an external calibrated temperature probe inserted into a sample of 7 mL of water. The peltier heating-cooling system heats or cools down the air of the inner measuring chamber through an engineered ventilation system. Heating speed is approximately 10 °C/min and cooling speed is approximately 5 °C/min from 70 °C to room temperature, and lower as approaching 4 °C.
Bio mode and sterility
The bio mode of the ElastoSens™ Bio is an alternative to the peltier system for tests done at 37 °C. In this mode, both ventilation ports of the measurement chamber are closed (Figure 5) blocking the air circulation and deactivating the peltier system. Internal resistors embedded inside the measuring chamber are able to maintain the temperature at 37 °C. This mode is recommended when working with cells or bacteria to conserve a sterile environment limiting contamination from the air. This mode can also be chosen to avoid or reduce drying of the sample especially if long tests are conducted.
When a sterile environment is needed, the sample holder can be sterilized with ethanol 70% for up to 4 hours. The chamber can be cleaned with a clean cloth and an antiseptic liquid sprayer. The ElastoSens™ Bio can be placed inside a biological hood and the measuring chamber kept open for a few hours. The sample is kept in the sample holder which can be placed in a 6 well plate (or another sterile recipient) during incubation between tests.
Figure 5. The air circulation can also be blocked in the Bio Mode, by closing the vent at each side of the chamber
Figure 6. LEDs located at the lid of the ElastoSens™ Bio featuring three wavelengths (365 nm, 385 nm and 405 nm).
Figure 7. Lid of the ElastoSens™ Bio’s measuring chamber with the access channels. (A) Flexible tubes inserted in the access channels allowing the user to inject and aspire gases into and outside of the measuring chamber during testing. (B) Schematic example of a temperature probe installed in the access channels.
Testing duration and environment, as well as measurements duration and intervals can be fully customizable in the ElastoSens™ Bio through its user-friendly software. The ElastoSens™ Bio can measure samples with shear storage modulus (G’) from a few Pa to 1 MPa, with a volume varying between 300 µL and 7 mL depending on its final stiffness.
Testing configuration starts by selecting the mode of operation of the ElastoSens™ Bio known as soft and stiff modes (Figure 8). The soft mode is used for samples that have a final G’ (G’ in the final gel state) lower than 500 Pa. The stiff mode is used for samples that have a final G’ higher than 500 Pa. After creating a file for the sample, the user can start creating the measurement sequences.
Figure 8. Testing configuration window in the ElastoSens™ Bio App.
Figure 9. Measurement sequence configuration in the ElastoSens™ Bio App.
Testing of the empty sample holder
Once the sequence(s) is created, there is the step of testing the sample holder empty. This step is important because the viscoelastic properties of the membrane are included in the calculations to obtain the viscoelastic properties of the sample. The viscoelastic properties of the membrane can have slight differences according to its temperature. For a higher precision in the measurements, it is then recommended to pre-incubate the sample holder at the temperature of the testing before performing this step.
Finally, the test is ready to be started. The first measurement will start in less than a second after the play button is clicked. All the parameters mentioned above (G’, G’’, G*, rate, height, temperature) can be monitored in real time and exported from the tablet.
 Henni, A. R. H., & Schmitt, C. R. (2019). U.S. Patent No. 10,288,541. Washington, DC: U.S. Patent and Trademark Office.
 Ceccaldi, C., Strandman, S., Hui, E., Montagnon, E., Schmitt, C., Hadj Henni, A., Lerouge, S., (2017). Validation and application of a nondestructive and contactless method for rheological evaluation of biomaterials. J Biomed Mater Res B Appl Biomater, 105, 2565–2573.
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