"The isotopic effect of exchanging deuterium with hydrogen on the mechanical and surface properties of agar gel is examined. The elastic modulus of the D2O gels obtained by AFM nanoindentation is significantly higher (factor of ≈1.5–2) than the modulus found in H2O agar gels. Furthermore, the modulus is independent of loading rate. Surface imaging reveals that the surface roughness gets progressively smaller with increasing agar concentration. All these data suggest that the isotopic replacement of deuterium enhances the mechanical properties of the agar gel, with significant advantages in its use as a biphasic scaffold"I think it's a poorly written abstract, as on the one hand they refer to the deuterium from the heavy water exchanging for the hydrogens in the agar , but then they refer again to D2O gels as well. They don't seem to be isolating the results of the exchange reaction from the heavy water itself.
Maybe this dichotomy is addressed in the paper itself (it likely is), but I still am full of wonder as to why a deuteration of the water and/or the gel would alter the mechanical properties by a factor of 1.5 or 2. Deuteration and other isotopic changes are known to alter reaction kinetics , but to alter equilibrium interactions is a new one, at least for me, and I am having a hard time justifying the results in my mind. Anyone?
 A deuterium-hydrogen exchange is probably the only way to efficiently produced deuterated agar, although the thought of growing the red algae in a pool of heavy water is an intriguing one.
 It is known that heavy water is toxic to animals for just this reason.