Dear Researchers,
I am looking for ratios of sodium alginate (powder) and calcium chloride (flakes/ granulate) and processes to create calcium alginate in FabLab facilities.
PS: I am doing my PhD Research in Design. I'm not a chemistry student. I understand that the crosslinking can be made by spraying the sodium alginate hydrogel with 10% calcium chloride solution, but this limits the spraying/bath surface. Instead, calcium alginate would be mixed and applied in bio-based materials' fabrication.
Best regards,
Carolina Delgado
Hi Carolina,
Calcium alginate is itself the crosslinked form/hydrogel form of alginate. The calcium ions replace the sodium in sodium alginate. Because calcium has a plus two charge, it binds to two alginate domains at once, whereas sodium with a plus one charge can only bind one. This makes calcium the crossbridge between alginate strands.
As for quantities, most commonly used are sodium alginate percentages 0.5-3, with 1-2% being your standard hydrogel consistency and higher if you want a very firm gel. Dissolve your alginate in water, this will take a while even with physically mixing. I strongly recommend raising the temperatures a few tens of degrees Celsius, I believe I've even autoclaved alginate into solution if that is an option for you. At this point, dissolve your calcium chloride granules into ideally distilled (but tap can work for some applications) water. Give it a while to mix, but you shouldn't really need to use heat to dissolve the calcium. Finally, mix your solutions depending on your application. You can mix the solutions by pouring into one another, but crosslinking will likely occur quickly. You can also pour/inject your alginate solution into your calcium solution to induce hydrogelation. If you need to reverse crosslinking, using a calcium chelator like EDTA or sodium citrate solution will un-crosslink your calcium alginate, reverting it to sodium alginate.
Example quantities:
Hope this helps. Let me know if you have any more questions.
Dear Truman Roland ,
Thank you very much for your response! Should I pour the sodium alg. sol. into the calcium sol. slowly with a syringe (no needle) and then filtrate as a precipitation or it will all crosslink as gel bubble, to dry after? I will need the calcium alginate to make bio-based composites.
If you have any work on this or a reference to cite, I would be also very happy! Thank for your patience and for sharing your knowledge.
Best regards,
Carolina
You can certainly add your alginate with a blunt syringe. Cross-linking occurs swiftly, so whatever shape comes out will be what it solidifies as. So if you use a syringe, you'll basically get alginate "worms." If you don't want those, you could pour your alginate into a container of your desired hydrogel shape and add a small but concentrated calcium solution if you want a bulk construct. If you're looking to make very tiny particles, you could probably push out the alginate from the syringe very quickly or use an actual needle to shear the solution as it exists.
I don't have any published work on alginate hydrogels specifically, I'm just happy to share as is. Hope this helps.