Abstract
We recently reported that the water holding capacity of myofibrillar protein hydrogels could be increased upon addition of small amounts of microparticles, particularly glass microspheres. Glass microspheres were found to decrease the spin-spin relaxation time (T2) of water protons in the gels, which was interpreted as enhanced water binding by the glass. We were thus interested in determining whether the observed effects on water proton relaxation were a direct consequence of water-glass interactions. Here we show how glass microspheres reduce the mobility of pure water, reflected in large decreases in the T2 of water protons, decreases in the self-diffusion coefficient of water molecules, a lower water activity, and strengthening of O-H bonds. Even though glass is considered an inert material, glass microspheres were shown to inhibit the growth of human embryonic kidney cells, and stimulate or inhibit the growth of leukemia and monocytic lymphoma cells in vitro, depending on dose and time. The germination of alfalfa seeds and the growth of E.coli cells were also inhibited upon exposure to glass microspheres. This work indicates that the properties and behavior of materials, even ones considered inert, can be affected by their size. These observations suggest possible toxicological consequences of exposure to microparticles, but also open us possibilities to affect cellular/organism function via modulation of macromolecular hydration.
Highlights
We recently reported that the water holding capacity of myofibrillar protein hydrogels could be increased upon addition of small amounts of microparticles[1], glass microspheres[2,3]
Assuming that the exchange between free and bound water is fast on the timescale of the diffusion experiments (50 msec), and that the addition of the glass particles does not affect the local viscosity of free water molecules, the observed diffusion coefficients are a population-weighted average of the free and bound water diffusion coefficients (i.e., D = pfree∙Dfree + pbound∙Dbound)
The population of total bound water may be calculated assuming Dfree is equal to that of water in a xanthan gum solution, while Dbound values are estimated via the Stokes-Einstein relation assuming 4, 8.5 and 40 μm particle diameters
Summary
Maybe the presence of this surface charge explains the apparent lack of aggregation of these glass microspheres at the low concentrations used, as determined by static light scattering (Figure S9) Since water is such an integral part of living biological matter, subtle changes in its dynamics could possibly have significant effects on structure and function of biological systems. The germination of alfalfa seeds was strongly affected by the presence of 4 μm and 50 μm glass microspheres in the water, both in terms of the number of sprouts (Fig. 3B and the number of leaf pairs (Figures S11) (P < 0.001) This effect was concentration dependent, with saturation reached at 0.5% (v/v) addition levels (Figure S12).
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