Depends... if this is primarily for storage until use: more brittle coatings like waxes would work and

polymers like polyethylene could also be used ..

if you want something flexible - silicone is probably the best.

I suggest to add glycerol from 1 to 5%

Thanks for the suggestion James E Hanson, we'll try to work out on this. We'd also like to utilize biodegradable coating for our material to make it 100% biomaterial.

Hi Dmitriy Berillo

Our material is incorporated with ~50% w/w Glycerol as plasticizer making it somehow flexible and gummier, however, most of the water content evaporated that's why we had the idea to come up with a biodegradable coating for the purpose.

if you want all bioderived etc then waxes are your best bet. Can add a little bit of an oil to reduce the brittleness.

think waxy rind they put on cheeses!

PS one other option ... if your gel is derived from say Alginate or you can coat with Alginate around it. If you then immerse in concentrated Ca ion solution the Alginate will become cross linked by the +2 ions. It makes a pretty tough skin - but can be removed with Na ion solution.

people make "artificial caviar" by dropping flavored alginate gel/solution into CaCl2 solution. Forms a shell around the soft interior. They call it "molecular gastronomy ".

This sounds interesting James E Hanson ! Our gel is derived from Carrageenan. We'lll look onto the possibility of soaking it with salt solutions.

Most Carrageenans will do the same thing with Ca ions. The SO3- groups cross link instead of the CO2- in alginate. since it takes two to counteract each Ca+2 ion they are held together.

so you could put foil on one side then pour Ca solution over to seal the other - when ready to apply to skin remove foil.

or seal the whole thing with Ca solution and use a Na solution on the skin when you apply - the Na replaces the Ca and cuts the cross links.