Mechanism of Water Dynamics in Hyaluronic Dermal Fillers Revealed by Nuclear Magnetic Resonance Relaxometry

Abstract

1H spin−lattice nuclear magnetic resonance relaxation experiments were performed for five kinds of dermal fillers based on hyaluronic acid. The relaxation data were collected over a broad frequency range between 4 kHz and 40 MHz, at body temperature. Thanks to the frequency range encompassing four orders of magnitude, the dynamics of water confined in the polymeric matrix was revealed. It is demonstrated that translation diffusion of the confined water molecules exhibits a two‐dimensional character and the diffusion process is slower than diffusion in bulk water by 3–4 orders of magnitude. As far as rotational dynamics of the confined water is concerned, it is shown that in all cases there is a water pool characterized by a rotational correlation time of about 4×10−9 s. In some of the dermal fillers a fraction of the confined water (about 10 %) forms a pool that exhibits considerably slower (by an order of magnitude) rotational dynamics. In addition, the water binding capacity of the dermal fillers was quantitatively compared.

Dynamics of Ionic Liquids in Confinement by Means of NMR Relaxometry—EMIM-FSI in a Silica Matrix as an Example

“…The correlation time is defined as: = , where denotes the distance of the closest approach between the molecules (ions) carrying the I -nuclei, while denotes their translation diffusion coefficient; denotes the gyromagnetic factor of the I -nucleus, while is the number of the I -nuclei ( 1 H or 19 F in this case) per unit volume. The expression of Equation (2) can be expanded into the Taylor series in the limit (i.e., in the low frequency range), leading to the relationship [ 23 , 24 , 25 ]: …”

“…The expression not only allows to straightforwardly determine the translation diffusion coefficient from the low frequency slope of the relaxation rate versus the squared root of the resonance frequency [ 23 ], but also enables to unambiguously identify the mechanism of the translation diffusion—the linear dependence of on is a fingerprint of the 3D character of the translation motion [ 19 , 20 , 23 , 24 , 25 , 28 , 29 ]. In the case of two-dimensional (2D) diffusion, expected for liquids in confinement in the vicinity of the confining walls, the form of the corresponding spectral density changes, leading to the expression [ 21 , 24 ]: where denotes a dipolar relaxation constant associated with the translation dynamics. In the low frequency range, , Equation (4) can be approximated as indicating a linear dependence of the relaxation rate on [ 21 , 24 ].…”

“…In the case of two-dimensional (2D) diffusion, expected for liquids in confinement in the vicinity of the confining walls, the form of the corresponding spectral density changes, leading to the expression [ 21 , 24 ]: where denotes a dipolar relaxation constant associated with the translation dynamics. In the low frequency range, , Equation (4) can be approximated as indicating a linear dependence of the relaxation rate on [ 21 , 24 ].…”

“…This implies that one is able to probe, in a single experiment, dynamical processes on the time scales from ms tons [ 10 , 12 , 13 ]. Moreover, the shape of the relaxation dispersion profile (spin–lattice relaxation rate versus the resonance frequency) unambiguously reveals the mechanism of motion [ 14 , 15 , 16 , 17 ], also allowing to differentiate between the translation diffusion pathways of different dimensionality: 3D, 2D, 1D [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. Relaxation rates are given as linear combinations of spectral density functions being Fourier transforms of the corresponding time correlation functions, characterising the motion associated with the relaxation process [ 3 , 4 , 5 , 6 , 7 ].…”

Anisotropic Dynamics of Binary Particles in Confined Geometries

“…There has been a great deal of endeavors to study the long‐time diffusions occurring across the confined boundaries by means of experimental methods . Nowadays accurate experiments allow us to measure the structure factors of confined particle mixtures from the intermediate scattering functions via X‐ray scattering technology .…”