Determining The Diffusion Rate Of Hydrogels For Topical
Drug Application
Jessica Fraley, Dr. Dore Meinholtz
Wilmington College, Wilmington, Ohio, 45177
Introduction:
Materials & Methods (cont.):
Results, Discussion, and Conclusion (cont):
0.14
Absorbance Vs. pH
biosynthesis. Obtaining Gentamicin was not possible; therefore the pH
indicator Acid Fucshin, which is similar in polarity to Gentamicin, was used as
a model. Acid Fucshin, like Gentamicin, is highly soluble in water and has a
pH range of 12(red)-pH14(colorless). This is important because it is not
desirable for the pH indicator to change color during the experiment.
0.12
0.1
Absorbane
Hydrogels are three dimensional cross linked polymers. They are
highly desired because of their flexibility, hydrophilic nature, and
because they are insoluble in water. Hydrogels are flexible, highly
absorbent and easy to manipulate. They are insoluble in water
because of cross linking, which is necessary in order to avoid the
dissolution of polymer chains (Figure 1). Cross linking can form
three different ways: interactions between two or more
monomers, hydrogen bonding, and Van der Waals interactions.
Hydrogen bonding occurs when water molecules are attracted to
negative charge on the hydrogel molecules which allows the
hydrogel to absorb over 500 times its own weight. Van der Waals
interactions work by attraction between short lived polarized areas
of the polymers.
0.08
0.06
0.04
0.02
0
5
6
7
8
pH
Figure 3. Absorbance vs. pH for the seven different solution samples ranging from
pH 5-8.
Figure 3 shows that there could be some correlation between pH and
diffusion rate. According to the data in Figure 3, as the pH increased the
absorbance decreased. The absorbance greatly decreases after a pH of
6.5. This could be due to partial deprotonation of Acid Fucshin at higher
pH values.
Figure 2. (Left) The expanded structure of Gentamicin and (right) the expanded structure
of Acid Fucshin.
Figure1. Three different ways hydrogels can cross link going from
most desirable (A) to least desirable (C).
Hydrogels have various applications including tissue engineering,
water conservation in soil, drug delivery systems, and topical
would healing which is the focus of this research. Healthy human
skin has a pH around 5. When a wound is infection the pH of
human skin rises to between 6.5-8 depending on the severity of
the infection. The more alkaline the wound site the more
complications occur during healing. The goal of this project is to
see if pH sensitive hydrogels can be created for topical drug
deleverly. Ideally, once infused with a drug its diffusion rate out of
the hydrogel will be inversely proportional to the alkalinity of the
wound.
Materials & Methods:
Research was carried out to find a typical drug used to treat
topical wounds, such a burns. The drug that was found is
Gentamicin. Gentamicin is an aminoglycoside that works by
binding to the 30s subunit of bacteria which stops protein
Conclusion:
Acid Fucshin, 0.0123g, was added to 1000mL of distilled water to make a
stock solution. 75mL of stock solution was added to a 500mL volumetric flask
and diluted with distilled water. This diluted solution was used for the
remainder of the experiment. Roughly 100 (0.1901g) Soil Moist crystals were
weighed and placed in a 50mL beaker along with 25mL of diluted Acid
Fucshin solution. This process was repeated for samples 2-7. The hydrogels
soaked in the diluted solution for 24 hours to ensure that maximum
absorbance was obtained. After soaking, each sample was weighed again.
The samples were then placed in another 50mL beaker with a 25mL of
solutions ranging from pH 5 to pH 8. The pH values were increased in 0.5
increments using 1.0M NaOH and measured using a pH meter that was
calibrated with a pH 4 and pH 7 buffers. Hydrogels, were soaked in their
respective pH solution for 10 minutes. The solution was decanted and the
absorbance of the solution obtained using UV-vis spectroscopy set to record
over the wavelength range of 400-600 nm.
The data support the idea that hydrogels are pH sensitive. It is not
conclusive if hydrogels could be used for timed drug release. The data
show that as the pH increased the diffusion rate decreased. This could
be useful because the more severe a wound is the longer the drug would
need to stay in the hydrogel for treatment. According to Figure 3 the data
show a large drop in absorbance at a pH of 7; it is not likely that this is
due to an interaction with Acid Fucshin because the pH range of the Acid
Fucshin color change is 12 to 14. Though it is unknown why this
happens, it is most likely due to an interaction of Acid Fucshin with the
hydrogel.
Results, Discussion, and Conclusion:
References:
The concentration of the solution was calculated by using Beer’s Law
(A=εBC), where A is the absorbance, ε is the extinction coefficient, B is the
path length, and C is concentration. The absorbance of the diluted standard
solution was 0.35 at a wavelength of 545.3 nm. From this point the equation
was solved for ε which was found to be 190 M-1cm-1. The extinction
coefficient and absorbance for each of the sample solutions was inserted into
the Beer’s Law equation, which was then solved for concentration.
1. "Drug Delivery Using PH-sensitive Semi-interpenetrating Network Hydrogels Northeastern University." Patent Searching and Invention Patenting Information.
Web. 25 Apr. 2012. <http://www.freepatentsonline.com/5904927.html>.
2. K. S. Kazanskii, S. A. Dubrovskii. Chemistry and Physics of “Agricultural”
Hydrogels. 1991, 1-37
3. Vijay Singh Jatav, Himmat Singh, Santosh Kumar Singh. Recent Trends on
Hydrogel in Human Body. 2011, Vol. 2, 1-6.
4. "Seattle Grace Hospital: Gentamicin." Web. 25 Apr. 2012.
<http://sitemaker.umich.edu/mc5/gentamicin>.
Acknowledgement:
This research was supported by the Wilmington College Chemistry Department
with guidance from Dore Meinholtz Ph.D.