Bioscience Engineering involves the production of a variety of new materials for use in the human body. Just a few of the examples include ophthalmic fluids, dental adhesives, and bone joint fillers. Thus, in order to qualify the performance of these materials, both in terms of their handling as well as final application within the body, it is important to conduct physical property testing.
One of the main instruments increasingly being used in this field is the texture analyzer. Determining the force resistance as changes occur, this device functions as an axial load tester applying deformation to a sample material. In this regard, a specially designed probe that penetrates into the material causes deformation and displacement at a defined rate of travel.
Selection of the right probe is critical to mimic the type of action under study. For instance, the objective in the above examples may be to study the force needed to syringe the material into position during application by medical staff.
Figure 1 shows a texture analyzer that has an accessory device, i.e. a cylindrical cup which contains the sample material. Attached to the texture analyzer is a cylindrical disc, with a diameter small enough to fit inside the sample cup. At the cup’s base is a disc with a circular aperture in the center, which allows the material to drain out when the probe travels downward. Figure 2 shows the complete kit for the accessory device.
Figure 1. Brookfield CT3 Texture Analyzer with Extrusion Cell
Figure 2. Dual Extrusion Cell Fixture
The equipment includes:
- Texture Analyzer with load cell Compression Disc (Extrusion Plunger)
- Extrusion Cell with aperture in disc at bottom
- Optional: Texture Pro CT software
The settings are shown in Table 1.
The test procedure is shown in Figure 3, consisting of the following steps:
Figure 3. Sample ready for testing
- First, the disc or the extrusion plunger is attached to the load cell
- Second, the table is fixed onto the instrument while the thumb screws are loosened to facilitate some degree of mobility
- Third, the sample cup is positioned with 4 mm diameter aperture in the bottom end filled with test sample on the table
- The probe is then lowered, positioned just a few centimeters above the sample surface
- Next, the sample cup is positioned to be at the center under the extrusion plunger
- This is done by re-positioning the table such that the probe can penetrate the cup fully without touching its rim
- On completing the above alignment, the table is secured to prevent further movement
- Finally, a start position is selected 10 mm above the top of the container or sample surface
- The test is started as shown in Figure 4
Figure 5 depicts the textural consistency and firmness for two different types of sample materials. This extrusion test was conducted at room temperature, where sample hardness is depicted by the maximum peak on the graph. The area under each curve from the start of the test to the maximum load is a measure of hardness work done.
However, it is important to note that data value fluctuations can result from the compression of air pockets in the sample. Also noteworthy is the fact that the target distance for penetration of the disc should not deform the sample to more than 75% of sample depth. If this is more than 75%, base effects related to the bottom of the sample cup may affect the test data values.
The extrusion plunger can compress the sample over the specified distance of 15 mm. During this period, the sample is deformed and compressed, which enables it to be packed more tightly into the space that remains below the descending plunger.
Once the sample condenses with limited air pockets, the force rapidly increases. This causes material to be extruded from the aperture at the base of the cup. And on reaching the specified distance, the plunger withdraws from the sample cup.
Since the maximum force on the graph measures the sample firmness over the specified distance, it can be concluded that the higher this value, the firmer the sample. Moreover, since the area below the curve is an indication of the sample consistency, the higher this value, the thicker the sample consistency.
The right instrument for studying the extrusion force needed to expel the sample materials from a syringe is the Texture Analyzer. This instrument also allows samples to be tested for physical properties such as stickiness or adhesiveness and adhesive force. These values are obtained when the plunger probe retracts from the sample and returns to its starting position.
In contrast, the negative section of graph’s curve, where the force load values are below zero, results from back extrusion. This is an indication of the sample’s resistance and cohesiveness when separating from the disc. Finally, the sample adhesive force is indicated by the maximum negative force on the graph; concluding that the more negative the value, the more “sticky” the sample.
About AMETEK Brookfield
Brookfield, a business unit of AMETEK Inc, is the world leader in viscosity measurement and control of liquids and semi-solids for 80+ years!
We manufacture and distribute globally viscometers the AST 100 for advance sensor technology for simple, direct in-line viscosity measurement, DV2T Touch Screen with temperature measurement, rheometers DV3T for measuring yield stress and viscosity, RST Controlled Stress for challenging rheological measurements, CT3 Texture Analyzers which features compression and tension mode for measuring firmness, springiness and chewiness and PFT Powder Flow Testers which measure yield stress and viscosity flow index and arching dimension used in R&D, QC and inline applications for rheological fluid analysis, tension and compression and powder flow analysis.
Markets include: food cosmetics, pharmaceuticals, oil & gas, personal care products, adhesives, printing, inks & coatings, paper coatings, chemicals, packaging, plastics, construction materials, and asphalt.
Brookfield AMETEK manufacturers and services a full range of viscometers and rheometers, texture analyzers, and powder flow testers. Additional services include: testing for viscosity, texture and powder properties, calibration and certification program, custom fixture development, free technical papers, seminars, videos, application notes, manuals, and educational and training programs.
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