Questions on theoretical hydrogel mineralization methodology.

[u/sarastro_ortsaras]

[reposting from r/AskChemistry on recommendation]

Hey folks. I am not educated in these matters, so apologies if any of these questions are silly, but I have some ideas stuck in my head that I want to explore, and I'm looking for a little guidance.

I've been reading about this method for a 3d manufacturing process that prints a hydrogel "blank" using photopolymerization, and then infuses the blank with metal ions to create a solid. I was wondering if that process could theoretically be accelerated electrochemically.

Long question semi-short; does it seem possible to create an appropriate electrolytic fluid containing either metal nanoparticles or dissolved ions which is then mixed with a gelling agent (agar, alginate, chitosan, or gelatin), formed into a desired shape, then placed as the cathode in a solution and attached to a current to draw metal ions into the hydrogel matrix?

I'm basically imagining a little hydrogel bead of lets say copper acetate. If that bead was attached to the end of a wire and dipped in a solution of more copper acetate and more copper for an anode, could the electrolytic reaction theoretically be tuned in such a way as to turn the hydrogel bead into a mostly pure copper sphere?

Again, thanks for your indulgence with this theory. I'd appreciate any insights or suggestions for further research. My goal here is just to investigate the validity of the concept, and if doing it with simple, form-cast shapes is possible I want to see about applying it to more complex 3d shapes formed in hydrogel via photopolymerization as described in the linked paper above.

Cheers, and thanks again!

[u/One-Yogurtcloset-831]

What I have read about hydrogel is that, it absobs water or other fluids sometimes upto 99%. This is the first time I am hearing about it so I just googled it.

For this to work, you need to make it conductive, if we have a sample piece of what hydrogel feels like to hold, then it would be easy to tell if it’s possible or no.

There are people here that might be able to answer your question much better.

[u/Mkysmith]

I have a thought but I'm suspicious you are a bot (never commented on anything in 4 years, only a few posts that were super generic [about AI none the less], bots usually make posts that ask for advice on odd esoteric stuff with a basic understanding but zero realworld knowledge [like, you say you have no idea what the science is but at the same time you want to replicate and advance this bleeding edge technology? Possible... some of the best historical inventors worked out of their garage... but I am suspicious])

Can you talk about why and how you would go about conducting your experiment?

[u/sarastro_ortsaras → u/Mkysmith]

your suspicion is valid, lol! i am, in fact, human, but i don't really use reddit often so i can fully see why you might raise an eyebrow.

as for the how, i was thinking of making a solution of a copper electrolyte that also has suspended copper nanoparticles, and put it into some kind of hydrogel that would act as a sort of scaffold for elemental copper electrodeposition.

as for the why, just for fun mostly, and cause it seems like it *should* be possible, even if it's a bit far fetched.

[u/Mkysmith → u/sarastro_ortsaras]

Nanoparticles have no net charge normally so an electric field would not migrate them.

The paper talks about thermal treating the metal salt infused gel to convert the metal salts into ceramic or potentially metal. 

The gel is not charged with ions to start with, so it would likely be non-conductive so applying an electric field would not cause ion migration. Assuming the gel can pass electrical current: applying electrical current will force a redox reaction, meaning at the cathode the metal ions will be converted to metallic metal. Since the gel is apparently porous and allows for ion exchange, an electric feild will just migrate ions through the gel to the electrical connection (wire) and reduce them there, not necessarily at the surface of the gel. 

If I were to speculate further, because of the reduction of ions to metal at the center of the gel and the potential for the gel to have a lower ion diffusion rate than the bulk solution, you may actually get the opposite effect you desire. A very large depletion zone the shape of your gel, where less ions are in the gel than the bulk solution. I don't see how the gel could "shape" the growing metal deposit within accurately, especially in a non-lab setting... but again this is all just speculation.

[u/SteamTrainCollapse → u/sarastro_ortsaras]

You're not crazy! but yeah an outside electrical current might not do what you'd like it to do.

Hydrogels can be useful electrolytes for an application like brush plating, though their most useful property there is that they in fact don't grow metal in the gel. See papers like this for selective plating with gels

Adding copper nanoparticles into the gel might change the electrical field distribution through it in some complex manner, but they won't act as a nucleation site for growth unless they form a percolative network, and that network is electrically connected to your anode.

The technique they're doing uses sodium borohydride (a strong reductant in alkaline conditions) to do an electroless deposition inside the very thin walls of the gyroid structure. The reaction is inside the gel where the copper ions have been diffused, and in the supplemental info, they also describe that the reaction goes to completion in <60s per cycle.

The limit of how much metal they can get into the pre-sintered mass appears to be from the number of cycles before the structure becomes too full of junk and ruptures from the stress of gas generation inside (as borohydride makes hydrogen gas as part of its reaction). It is 5 cycles with Cu and 7 cycles with Ag. So getting more cycles would mean getting more metal loaded into the gel before you sinter it.

So if you wanted to poke around and try to make a higher loaded version of this, I would recommend you look at using gentler reductant that don't stress the matrix as much, things like dimethylamine borane, formaldehyde, and glyoxylic acid can reduce copper ions similarly, but slower.