LF-NMR water self-diffusion and relaxation time measurements of hydrogel contact lenses interacting with artificial tears

Physico-Chemical Changes of Composite Whey Protein Hydrogels in Simulated Gastric Fluid Conditions

Polysaccharide blended whey protein isolate (WPI) hydrogels were developed for the delivery of black carrot ( Daucus carota) concentrate as bioactive agent in simulated gastric fluid (SGF). Pectin (PC), gum tragacanth (GT), and xanthan gum (XG) were blended as additional polymers to modulate the release characteristics of the WPI hydrogels. Experiments showed that sole whey protein (C), XG, and GT blended hydrogels possessed restricted release profiles 67%, 61%, and 67%, respectively, whereas PC samples attained higher release rates (83%) ( p < 0.05). Interactions between polymers and aqueous medium were analyzed by nuclear magnetic resonance relaxometry. C (82 ms) and GT (84 ms) hydrogels attained higher T₂ values than PC (74 ms) and XG (73 ms) samples in SGF. Hardness of only XG hydrogels increased from 1.9 to 4.1 N after gastric treatment. Physicochemical changes within hydrogels during release were also investigated, and hydrogels were proved to be appropriate for desired delivery purposes.

1D Measurement of Sodium Ion Flow in Hydrogel After a Bath Concentration Jump

NMR is used to measure sodium flow driven by a 1D concentration gradient inside poly-acrylamid (pAA) hydrogel. A sodium concentration jump from 0.5 M NaCl to 0 M NaCl is applied at the bottom of a cylindrical pAA sample. The sodium level and hydrogen level are measured as a function of time and position inside the sample for 5 days. Then a reversed step is applied, and ion flow is measured for another 5 days. During the measurement, the cylindrical sample is radially confined and allowed to swell in the axial direction. At the same time, sodium and moisture in the sample are measured on a 1D spatial grid in the axial direction. A quadriphasic mixture model (Huyghe and Janssen in Int J Eng Sci 35:793, 1997) is used to simulate the results and estimate the diffusion coefficient of sodium and chloride. The best fit results were obtained for D\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{Na^+} = 1.15\times 10^{-5}$$\end{document}Na+=1.15×10-5 cm²/s and D\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{Cl^-} = 2.15\times 10^{-5}$$\end{document}Cl-=2.15×10-5 cm²/s, at 25 degrees centigrade. Different time constants were observed for swelling and deswelling.

Application of hydrophobic resin adhesives to acid-etched dentin with an alternative wet bonding technique

Hydrophilic dentin adhesives are prone to water sorption that adversely affects the durability of resin-dentin bonds. This study examined the feasibility of bonding to dentin with hydrophobic resins via the adaptation of electron microscopy tissue processing techniques. Hydrophobic primers were prepared by diluting 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] pro- pane/triethyleneglycol dimethacrylate resins with known ethanol concentrations. They were applied to acid-etched moist dentin using an ethanol wet bonding technique that involved: (1) stepwise replacement of water with a series of increasing ethanol concentrations to prevent the demineralized collagen matrix from collapsing; (2) stepwise replacement of the ethanol with different concentrations of hydrophobic primers and subsequently with neat hydrophobic resin. Using the ethanol wet bonding technique, the experimental primer versions with 40, 50, and 75% resin exhibited tensile strengths which were not significantly different from commercially available hydrophilic three-step adhesives that were bonded with water wet bonding technique. The concept of ethanol wet bonding may be explained in terms of solubility parameter theory. This technique is sensitive to water contamination, as depicted by the lower tensile strength results from partial dehydration protocols. The technique has to be further improved by incorporating elements of dentin permeability reduction to avoid water from dentinal tubules contaminating water-free resin blends during bonding.

LF-NMR and multivariate data analysis: compression of data to classify hydrogel contact lenses

Hydrogel contact lenses swollen in viscoelastic artificial tears solution have been studied, measuring transversal relaxation times of water molecules using LF-NMR techniques. Data were processed by classical multiexponential fitting, by principal component analysis and by SLICING, a multi-way analysis method. The reason for using multivariate data analysis was not to obtain a better fitting, but rather more effective data description. The single-sample relaxation curves were projected in a space spanned by the loading curves, and in this space it was simpler to compare data. In particular, it contributed to the description of the variability of motion characteristics of the water molecule 'families' contained in the studied samples. Applying multivariate techniques, we were able to group lenses with different Equilibrium Water Content (EWC) and with the same water content but different compositions. Accordingly, we were able to point out that, if the lenses are swollen first in physiological solution and then in viscoelastic artificial tears solution, hydration characteristics remained unchanged in all the studied samples, except for 38% EWC lenses.