3 - Cleaning Franz Cells
Prior to using the cells, clean the stirbars and donor chambers shown in Figure 3 by rinsing them with methanol (MeOH) and deionized water several times. Let them dry. Also fill the receptor chambers with methanol. Keep stirring for one hour. Then use a disposable plastic pipette to suck and release methanol from the receptor several times to clean the receptor chambers as well as the upper surfaces of the receptors and the sampling ports. Replace methanol with deionized water. Stir for another hour and repeat the previous cleaning step. Finally turn off the stirring and replace the used deionized water with fresh water. Keep the receptor chambers filled with water until testing. Repeat the cleaning procedures after use.
4 - In vitro release testing
Before testing, the medium in the receptor, membrane (polymeric or skin), the temperature of the receptor medium, sampling volume and time points of sampling should be determined based on the project.
Prior to starting, the temperature on the water bath/circulator is set to a predetermined value and a stir bar is put into each cell. The specific receiving medium is filled to the level somewhat higher than the receptor surface to avoid creating bubbles when the membrane is mounted. Then a membrane is slowly mounted from the top of the receptor medium, pushing the excessive medium to the side until the membrane touches the joint surface. If there is still some air trapped beneath the membrane, remove the membrane and add more medium to the receptor chamber to make it overflow slightly. Repeat previous mounting step until no air bubbles appear beneath the membrane. Also make sure the membrane completely covers the surface of the medium.
Next the donor chamber is placed on top of the membrane and secured by the clamp. A certain amount, usually 0.3gm or ml of the subject product such as a gel, lotion, or suspension is applied to each membrane. Cover the donor chamber with triple layers of Parafilm®. Cover the sampling arm with double layers of Parafilm® as well.
At each predetermined sampling time, by removing the Parafilm covering the sampling port, a specific amount (such as 200l, 300l) of receptor medium is sucked out from the sampling port by a long needle-shaped pipette (e.g., Fisher band, 9” Pasteur Pipets, Cat. #: 13-678-6B). The same amount of fresh medium is refilled into the cell through the sampling port by a regular pipette and the sampling port is covered by the same Parafilm temporarily removed.
If bubbles are created during the sampling process, carefully lift the cell up out of the Cell Holder. Quickly reverse the cell to turn it upside down so that bubbles would be released out through the sampling port. Be cautious to prevent the testing product leaking out of the donor chamber.
5 - Cleaning
After the testing is completed, turn off the stirring of each cell and water bath. Remove the donor chamber and membrane. Empty the receptor. Fill in the receptor with methanol. Turn on stirring for an hour. Use the methanol in the receptor to clean the joint surface of the receptor and the sampling arm as described in Section 3. Replace methanol with deionized water. Stir for another hour and repeat the previous cleaning step. Finally replace the used deionized water with fresh water. Keep the receptor chambers filled with water until next testing. The donor chamber should be washed by methanol as well, rinse first in tap water and then by deionized water.