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Brookfield AMETEK

Transdermal Delivery System

Test Principle

Evaluating the adhesiveness of a transdermal delivery patch using a 1-inch ball probe..

Background

Transdermal Drug Delivery Systems (TDDS) are a fundamental part of novel drug delivery systems. They are polymeric formulations applied to the skin to deliver the drug at pre-determined rates in order to achieve their systemic effect. There are several important advantages to TDDS such as the limitation of hepatic first pass metabolism. This is particularly useful to drugs that would normally undergo extensive first pass metabolism, drugs with a narrow therapeutic window, or even drugs with a short half-life causing non-compliance due to frequent dosing. Other advantages include maintenance of a steady plasma level, reduced side effects and enhanced therapeutic efficiency.

The use of adhesive patches for controlled release in applications, such as nicotine patches, appetite suppressants, contraceptive and hormone replacement therapy, has become popular worldwide. Adhesives on a patch generally help maintain contact between the transdermal system and skin surface. The adhesiveness of the patches is critical in the drug delivery mechanism, its safety, product quality, and efficacy. As such, a good adhesive should easily adhere to the skin with an applied finger pressure and be tacky enough to maintain a strong holding force. The adhesive should also be easily removed from the skin without leaving a residue.

The CT3 Texture Analyser can be used to quantify the tack performance of a transdermal delivery patch, seen as the adhesive force required to break contact between the probe surface and adhesive of the patch using a ball probe. The use of the ball probe ensures contact consistency.

Method

Equipment

  • CT3 with 4.5 kg load cell
  • Fixture Base table (TA-BT_KIT)
  • 0.5 inch Ball Probe (TA 18)
  • Texture Pro CT Software

Settings

  • Test Type: Compression
  • Pre-Test Speed:°.1 mm/s
  • Test Speed:°.05 mm/s
  • Post-Test Speed:°.05 mm/s
  • Target Type: Force
  • Force Value: 200 g
  • Trigger Force: 60.0 g
  • Hold Time: 2 s
  • Temperature: 21°C

Materials

  • Sample
  • Protective gloves
  • Double-sided adhesive tape
  • Scissors

Sample Preperation

Remove the adhesive tape from its pack at the time of testing. Care must be taken not to touch the adhesive test surface that contains the active ingredients.

Procedure

  1. Attach the ball probe to the CT3.
  2. Place the fixture base table on the base of the instrument and loosely tighten with the thumbscrews to enable some degree of mobility for the alignment stage.
  3. Fit the plate to the base table and tighten with the side screws.
  4. Place two strips of double-sided tape (sticky side down) onto the plate.
  5. Remove the surface backing of the double-sided adhesive using a scalpel and bond the sample (adhesive side up) onto the tape.
  6. Centrally align the ball probe to the sample then tighten the screws of the base table to prevent further movement.
  7. Position the probe a few millimetres (less than a centimetre) from the sample surface.
  8. Commence the test.
  9. Clean the probe after every test to remove all traces of adhesive, grease or moisture from the previous sample.
    • Note: If a long contact time between probe and sample is required before withdrawal, a hold time may be used before probe withdrawal. The force value can also be increased. These adjustments will ultimately increase both adhesiveness and work done values.
    • A force of 200 g has been initially selected for the test as being the most suitable force to generate full contact between sample and probe. Firmer samples may require higher force values to ensure full sample/probe contact.
    • All adhesive measurements are relative to specified contact force. The post-test speed will also directly affect the adhesive values. Consequently, the test has been set such that the probe returns at the test speed.
    • When optimizing test settings, the hardest sample is best tested first in order to predict the maximum testing range for subsequent samples.

Results

Figure 1 shows the adhesiveness of a transdermal adhesive patch tested at room temperature. Three samples of the same batch have been tested and plotted.

Figure 2 shows the force vs. distance for the adhesiveness of the transdermal patch. At the probe/sample surface, an increasing force is observed until a load of 200 g has been attained. At this point the probe begins to withdraw from the sample (negative part of graph). The negative peak represents the adhesive force required for the adhesive filaments on the sample to detach from the probe. Once the probe is detached from the sample surface, the probe returns to its starting position above the sample (seen by the flat line).

Observations

When a trigger force of 60 g has been detected on the sample surface, the probe proceeds to apply a force of 200 g at a test-speed of°.05 mm/s. Once a force of 200 g has been attained, a hold time of 2 seconds is applied after which the probe withdraws from the sample at a test-speed of°.05 mm/s. The resistance to withdrawal exerted by the sample on the probe is indicated by a negative peak force, a measure of sample stickiness, tackiness, or adhesive force. The area under the negative peak represents sample adhesiveness. The more adhesive the patch, the more negative the peak and the larger the area under the curve.

Results from 3 Transdermal patches give the following mean values: