First Results

This week, I processed the data from my previous release study, and after seeing the results, I planned for how to go forward with my project.

As mentioned in my previous post, the way I measure the amount of drug released from the gel, I take aliquots of the solvent in the vial into tubes at different times. Each time I place some solvent in a tube, I replace the solvent in the vial. After a certain time, I place a small sample of each tube onto a plate reader. The plate reader is then placed into a spectrometer which measures the absorbance of the sample of a particular wavelength of light. The results from the spectrometer transferred to an excel document look like this
  

The bottom line of the results does not have samples from the release study. Rather, they are standards I created. Standards are samples in which the concentration of a particular drug is known (because I made them). They are necessary because they show the relationship between absorbance and concentration. When I plotted the absorbance of the standards against their calculated concentrations, I created the following graph



Firstly, as shown by the high R2 value, a linear approximation is appropriate, and so the equation listed in the graph is used to calculate the concentration of each of the samples from the absorbance in the plate reader. After a series of unit conversions, I was able to calculate the mass released from each gel at each time point. Furthermore, a calculated the cumulative release of each gel. To calculate this, I add the mass of a particular time point with the masses of all the time points before it. This is done because the solvent is replaced at each time point.  Then, I calculated the theoretical amount of drug within each gel. This can be calculated because the percentage of drug in the gel is known by how I created the gels.

After all of these calculations, I created two graphs. The first graph shows the cumulative amount of drug divided by the total amount of drug for each gel at each time point. The second graph shows the mass at each time point divided by the cumulative release of that gel. “Average” is used because for each type of gel, there were three samples for repetition. In the graph, rather than having twenty-seven different lines, I averaged each sample of each gel. “Control” is a gel without a salt or acid.




One trend shown in these graphs is that a higher concentration of a specific salt/acid has a faster release than the lower concentration of the same salt/acid. Furthermore, the salt/acid mostly had slower releases then the control group. However, my data suggests that the gels were not mixed very well. When I mixed the gels, I connected two syringes and pushed the contents of one syringe into another multiple times. If the gel in the syringe was not mixed well, then some parts of the syringe will have large concentrations of drug, while other parts would have lower concentrations of drug. As one syringe is used for three samples of a gel (for example, one syringe has ~800 mg of gel and so ~200 mg of gel is placed into each vial), the release would be different between the samples. This is shown in the table below.



In addition to this bad mixing, the gels also finished releasing relatively quickly then previous studies done in the lab. Usually, it takes approximately 4-5 days for the gel to finish releasing, while my gels finished in about 1-2 days. A gel is finished releasing when the lines become horizontal in the graph. This may not be a mistake in procedure, but possibly because I used smaller gels and smaller vials, which no one has really used before.

And so, next week, I plan to start a new release study with one control and another compound. In addition to seeing the drug release from these new drugs, I will test another variable: size, specifically surface area and volume. To do this, for each gel, I will have samples of different masses. With this, I can my technique (particularly mixing), see if my variability in results was caused by size of my gels, and hopefully find a relationship between size and release.

Thanks for reading!

Russell Llave