I am currently working with hydrogels formed from gellan gum, a plant-derived polysaccharide which can be gelated using divalent cations such as Ca2+. An alternative method of gelation, which I am investigating, involves the use of polyamines, such as spermine, as the crosslinker. In both cases, the crosslinkers induce gelation instantaneously upon mixing with the GG. This rapid gelation time makes it very difficult to mix the gel homogeneously and also to measure gelation time via rheometry.
A disaccharide is included in both the GG and crosslinker solutions in order to reduce osmotic pressure. Increasing disaccharide concentration to up to 60 wt% reportedly strengthens the gel; however, the substantial increase in viscosity of the GG solution makes it almost impossible to mix the gel. At 10 wt% disaccharide, the gel can be mixed but it is difficult to make homogeneous and impossible to measure by rheometry.
I mix the GG with crosslinker at 37ºC. Bringing the temperature down to 4ºC may slow the speed at which the polyamine crosslinks the gel, but conversely, this low temperature makes the GG extremely viscous and difficult to mix.
I would appreciate any advice that could help me overcome this catch-22 situation!
HI! I use GG as well. is it Phytagel perhaps? Why are you mixing it at 37 degrees? that is the exact temperature where gelation starts. Have you tried with higher temperatures while mixing? this should favourite mixing and lower viscosity. Good luck!
Hi Antonio, thanks for your response. I'm working with Gelzan and am making hydrogels for biomedical applications, which is why I work at physiological temperature. The gel can be injected into the body and so it needs to gelate at body temperature. Also, the polyamine crosslinker is of biological origin and may degrade at high temperatures.
A colleague of mine working with hydrogels suggests using a Glucono-delta-lactone and Calcium Carbonate system, wherein the GDL releases the Ca2+ ions from the carbonate over time to slow the cross-linking process. I'm not too familiar with this myself but he's happy to provide a paper and protocol if it's something that sounds like it might be of use to you?
Hi Merlin, thanks very much for the suggestion. This particular project is focused on the use of polyamines for crosslinking the gels, as opposed to divalent cations such as Ca2+. The reason for focusing on this is that certain polyamines have have been shown to have anti-inflammatory effects, protection against oxidative stress and to play a positive role in several regenerative processes. By incorporating them as part of the physical structure of the gel, it is possible to control the physical properties of the gel and to control the release of these and other incorporated molecules.
I am not looking to incorporate Ca2+, since it would compete with the polyamine, making gelation even more rapid and also potentially preventing some of the polyamine from binding and causing it to be released more rapidly.
GDL appears to act as a chelating agent. Do you or your colleague think it is possible that this would act on the polyamine in a similar way to how it acts on the CaCO3, delaying gelation via the polyamine crosslinker?
- Badges
- Science topic
- Similar topics
- Chemistry