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Objectives
- Prepare PVA-clay microspheres.
- Run diffusion tests on hydrogels prepared on 2013/01/30 with Rhodamine 6G dye added on 2013/02/08.
Microsphere Preparation
- Due to the relatively unsuccessful preparation of PVA/clay microspheres(the prepared spheres were either larger than a micrometer or did not appear at all), a new method was used for the preparation of PVA/clay microspheres.
General Protocol:
- The desired ratio of PVA and clay was measured out. The total mass was ~1g.
- The PVA/clay was placed in a 50mL beaker with a magnetic stir bar. 25mL distilled H2O were added to the beaker and the solution was heated to ~100°C and allowed to stir until complete dissolution of PVA/clay.
- The magnetic stir bar was removed and 25mL of mineral oil was added to the beaker.
- The contents of the beaker were poured into a blender to homogenize the solution and create an emulsion of the aqueous and organic layer in the attempt to create a suspension of microspheres.
- The blender was turned on a low setting for 7 minutes.
- The contents of the blender were poured into a beaker and the appropriate amount of DMSO/Rhodamine 6G solution was added.
- The microsphere solution was placed in a freezer at -20°C for 24 hours and then removed and allowed to thaw for 24 hours.
- Repeat this freeze-thaw cycle three times.
This procedure was adapted from [1]
Preparation of Microspheres:
- New calculations for the amount of DMSO/Rhodamine 6G to be added:
For a 90:10 ratio:
(25mL)(1μM)/(92μM)=0.272mL
For a 50:50 ratio:
(25mL)(1μM)/(165μM)=0.152mL
- Information about prepared microspheres:
| Prepared Clay-PVA(MW 146,000-186,000) microspheres
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| Composition of hydrogel(ratio of PVA to clay) |
Amount of PVA added(g) |
Amount of clay added(g) |
Concencentration of DMSO/dye stock solution added(μM) |
Amount of DMSO/dye added(mL)
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| 90:10 PVA:110% NaMT |
0.9099 |
0.1045 |
92 |
0.272
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| 50:50 PVA:110% NaMT |
0.5076 |
0.4913 |
165 |
0.152
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| 90:10 PVA:110% Lamponite |
0.9010 |
0.0998 |
92 |
0.272
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Observations:
- After the addition of dye/DMSO to the 110% Lamponite, the dye appeared to stick to very small spheres at the bottom of the beaker. Bright pink spheres immediately formed. This did not occur for the samples containing 110% NaMT.
Fluorescence
- The six hydrogel samples that were allowed to soak in Rhodamine 6G were tested for the rate of diffusion of Rhodamine 6G from the samples.
General Protocol:
- Excess Rhodamine 6G sample still present in the beaker was removed.
- Hydrogel samples were removed from the beakers, pat dry with a paper towel, and placed in a new, clean beaker.
- 25mL distilled H2O were added to each beaker sample.
- A timer was started, and every 15 minutes, a sample of distilled H2O was removed from the beaker and placed in an unfrosted cuvette.
- The sample was discarded into a waste beaker.
- This process was repeated for 2 hours.
Spectra:
Observations:
- Each of the samples had a very fast diffusion rate. If the spectra are viewed additively for each hydrogel sample, a significant amount of dye leaked out of the hydrogel sample in only 2 hours, in comparison to the hydrogels which remained in distilled H2O for one week and had minimal dye diffusion. This indicates that the dye must be added prior to the freeze-thaw crosslinking method.
- Due to the fact that the dye did not immediately, completely diffuse out, the crosslinking of PVA/clay hydrogels slowed the diffusion rate of the dye.
- Comparing the 50:50 ratio of PVA:clay and the 90:10 ratio, the hydrogels with 50:50 ratio had more dye leak out of the hydrogel than the 90:10 ratio. Perhaps indicates a more effective pressure stimuli.
- In the future, when performing the diffusion tests, after taking a sample every fifteen minutes, the sample will be readded to the test beaker rather than discarded.
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