Something Old and Something New

Hi everyone!

This past week, I started another release study using the same polymers I have used before mixed with a drug and salt/acid solution. I intended to begin the study on Monday, but something unexpected happen: when I mixed the polymer and drug phases together, the following mixture turned white! (they're usually clear after mixing). This occured for each of my samples (acid mixtues, salt mixtures, and neither). This is problematic because this means one of two things: 1) the mixture became a gel or 2) there was simply a very high concentration of salt or drug that could not be dissolved. 1) is problematic because it prevents the gel from being placed into vials where the release studies take place. 2) is problematic because that means that maybe not all the drug or salt can dissolve with that much gel.

To test which of these hypotheses are true, I simply placed the mixtures back into the refrigerator. After a couple of hours, the mixtures became clear again. Thus, 1) was shown true as a decrease in temperature caused the mixture to transition back to liquid. After the mixtures became completely clear, I began the release study and took time points throughout the week.

One possibility for this is the high concentration of the drug (I doubled the drug concentration from previous release studies). The drug may react with the polymer in some way that causes the polymer to become a gel. However, this is just speculation. Furthermore, in the past, this has happened in several cases with different molecules, and cooling the "gel-ed" mixture does not affect results. However, it does affect how I plan release studies for the future as I may need an extra day, or I may need to stay very late some days (it can take around 4-6 hours for the gel to transition back).

With that extra time though, I can analyze how much drug was released by using the plate reader. Furthermore, I will help out another project in the lab.

This project I am helping on concerns the degradation time of the polymer. The degradation time is the time it takes for the polymer to break down to a certain point. This is measured by seeing the temperature at which the gel transitions from liquid to solid (that temperature is called the Lower Critical Solution Temperature or LCST). The higher the LCST, the more the polymer has degraded (this is true because of the properties of the molecules that compose of the polymer).

To find the LCST of a gel, I have to run a cloud point test. This test is actually the first test I learned when I went to lab over the summer. Simply, I heat a water bath to a certain temperature. Place the gels in the water bath at that temperature for a minute. Then dry of the container and place it in a spectrophotometer. This time, I measure the absorbance for the color white. Thus, if the gel is clear, the spectrophotometer will read 0. At multiple temperatures,  I measure the absorbance. With this data, I can approximately determine where the LCST is.

Hopefully this week I can attain lots of data. If I do, I will share them with you next week.

See you then!

Russell