How a living creature could produce "bio" aerogel?

Question

In base to my question about How could a dragon develop blue fire breath?, one of the most interesting solutions is that the dragon could be able to produce aerogel for resist its own fire, so why not?, aerogel have a lot of more interesting characteristics, in addition to the high temperature resistance is extremly light and resistant compared with its weight and density.

And compared with other strange biological features this looks easy to develop, with the different types of aerogel. Inorganic based on metalic oxides, organic based on carbon polymers and the two which I thought are more helpful for this question, the silica and graphite aerogels.

Currently the stingging nettle can synthetize silica spines and marine sponges use silica en their skeletons. And carbon, practically the life is based in carbon and carbon dioxide is extremely abundant.

Although it has a limit of resistance to heat, which is very high of 500-2000 ° C, if a dragon could produce this material in its body, it could regenerate it when it wears out. Thing that is useful too for other kind or fire manipulators, How would a "flaming collar" work in an animal and how could it be useful?

And apparently the raw materials are the easy part, but I don't know how aerogel is produced and how a living creature could produce it in its body, neither I know if this could be product of natural evolution or obligatory genetic engineering product.

By the way, if aerographite (aerographene) is other problem already exist a question about Could a living creature produce graphene? and I thought by myself I can solve that probkem

Answer 1

Aerogels are usually made by removing the water from a gel, leaving a porous matrix which was once present in the gel.

The closest resemblance to an aerogel in living creature I can think of is cork. Cork is the bark of some trees, which have developed this type of bark to, guess what, get protection from fire.

The main obstacle you will face is that, both for cork and sponges, the size of the "holes" you can leave in the matrix is dictated by the size of the cell/organism producing it. To go smaller than that you would need some trick.

One of this trick would be to have the cell assemble an internal proteic structure, not water soluble, and then die. The structure, remaining after the cell, would sum up with those of the neighbors and produce the very fine structure of an aerogel.

Answer 2

First off what is an aerogel.

A gel is mostly liquid with some dilute linked solids holding it together. Biology produces lots of gels (mucus, the vitreous humor of the eye, cartilage, tendons and blood clots) so no problem there.

Aerogel is what happens when the liquid in a gel is removed in such a way that the diffuse cross linked solid is left behind. This is the hard part. Normal drying won't work as evaporation happens at the edges of a gel producing a flow of the liquid that destroys the delicate linking of solids and causes them to shrink and crumble. To get aerogel you need the liquid to leave the gel as a gas throughout the gel simultaneously so as not to damage the remaining solid matrix. This usually involves precisely changing the pressure and temperature of the materials to reach the supercritical point, where there is no distinction between a liquid and a gas, and thus no evaporation liquid gas boundary. Then replace the liquid/gas binder with another gas and lower the pressure. These reaction tend to happen at fairly high pressures, most current aerogel production uses liquid CO2 at around 73x atmospheric pressure, other liquids use even higher pressure than that, and making a gel with liquid CO2 is a complex process.

But wait, you said a DRAGON! Normal biology probably won't produce the pressures necessary, but fire can! If your dragon's fire ignition method is internal it could likely produce a high pressure region in that fire gland/orifice/bladder/whatever. And it would likely be coated with a mucus gel. It could then theoretically (given some specific mucus chemistry) produce a thin layering of aerogel from the mucus using the temperature and pressure of the flame. If this layering of aerogel was retained and built up over time it might be comparable to a very solid fire resistant type of scar tissue building up from repeated breathing of fire.

This type of buildup of aerogel would mean that young dragons would be less able to breath fire without injury, but older dragons would have developed a nice aerogel liner allowing them to burninate with impunity.

Answer 3

I'm going to go with direct extrusion. Basically, you want to 3D print the entire aerogel using specialized protein channels in the cell membrane as the extruders. The gel is prevented from collapsing due to its electrical charge, which repels the outer strands of the gel from the equivalently charged outer layer of the cell membrane. The inner layer is oppositely charged, but the cell pays the energy cost, at the channel, to push these charges apart.

The cells that secrete aerogel adjoin on a very dry space, but they have well maintained lipid membranes. In those membranes are channels, through which fibers can be moved. The fibers are assembled in the cytosol and are as durable as is feasible. Ordinarily, the aerogel simply is moved outward by myosin-like motors at the same rate as it is produced. However, the aerogel needs to be cross-linked, so every now and then the cell starts extruding a batch of new fibers through previously untapped channels. These channels each start off joined to an existing channel, and the fibers are solidly cross-linked at a three-way junction to start. But then the channels separate, remaining within the membrane, and the halves are moved around by the cytoskeleton. After a short time, they meet up with another channel and splice their fibers together, after which one channel becomes again temporarily inactive.