Can 1 gram hyaluronic acid really hold 6L of water?

According to this study (<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3970829/>), they make an (uncited) claim about hyaluronic acid: "One of its most important properties is that it can attach and hold large amounts of moisture; approximately 6L of water in just lg ."


Now, the MW of HA is $776.651$ g/[mol](https://pubchem.ncbi.nlm.nih.gov/compound/3084050), so there are about $\pu{0.00128865979}$ moles of HA in a gram. And about $\pu{7.757732e20}$ molecules.


Using google, 6L of water has $\pu{2.007e26}$ molecules. 


So this is essentially telling me that roughly 1 million water molecules are able to hydrogen bond with 1 molecule of HA...


Firstly, is this fact true? And if so, how is this possible??




Various figures can be found “on the internet”. E.g. *‘Hyaluronic Hydro Gel Has 1000 Times Water Holding Capacity Perfect for Hair to Heel’* (commercial link intentionally omitted).


Gel liquid phase absorption ability measure seems to be a ‘[swelling capacity](https://en.wikipedia.org/wiki/Swelling_capacity)’ (ratio).


For hyaluronic acid (HA), it can be increased by additional crosslinking. In one paper from 1992, usual swelling ratio was found to be in the order of magnitude 1 to 10, the maximum figure was 120 (for crosslinking ratio much higher than 2.1; 25–30 for the ratio 2.1).[1]


In another paper, another guys are using biphasic nanoparticles (some composite of crosslinked and non-crosslinked HA), they state they have achieved for two different particle types *‘… swelling ratio 1270, 1000 %, respectively’*[2] (note the percent sign). Which is, in both cases, approximately, not 1000× capacity, but rather 10× capacity, I'd say.


However, there are polymers with the claimed property – [superabsorbents](https://en.wikipedia.org/wiki/Superabsorbent_polymer):[3]



> 
> **3.27 superabsorbent polymer**
> 
> 
> Polymer that can absorb and retain extremely large amounts of a liquid relative to its own mass.
> 
> 
> Note 1: The liquid absorbed can be water or an organic liquid.  
> 
>  Note 2: The swelling ratio of a superabsorbent polymer can reach the order of 1000:1.  
> 
>  Note 3: Superabsorbent polymers for water are frequently polyelectrolytes.
> 
> 
> 


References:


1. Shah, Chirag B., and Stanley M. Barnett. "[Swelling behavior of hyaluronic acid gels.](https://doi.org/10.1002/app.1992.070450211)" *Journal of applied polymer science* 45.2 (1992): 293-298.
2. Chun, Cheolbyong, et al. "[Effect of molecular weight of hyaluronic acid (HA) on viscoelasticity and particle texturing feel of HA dermal biphasic fillers.](https://doi.org/10.1186/s40824-016-0073-3)" *Biomaterials research* 20.1 (2016): 24.
3. [Compendium of Polymer Terminology and Nomenclature (IUPAC Recommendations 2008)](https://doi.org/10.1515/ci.2009.31.4.32)


 3

Attach and Hold - a bit of a misnomer; it forms a 3 D Lattice matrix containing water; given its inherent viscosity and inherent elasticity, it can be compressed and upon release of pressure spring back to its original dimensions thus the visco-elastic/shock absorbing properties advantages medically (knees) and cosmetically (skin fulfillment/youthful appearance etc). 


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