PubMed · 16355964
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J Hockey. 2005. Material selection: the moulder's view.. https://pubmed.ncbi.nlm.nih.gov/16355964/
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PURPOSE: The purpose of the present study was to develop mathematical relationships that allow obtaining equilibrium water content and refractive index of conventional and silicone hydrogel soft contact lenses from refractive index measures obtained with automated refractometry or equilibrium water content measures derived from manual refractometry, respectively. METHODS: Twelve HEMA-based hydrogels of different hydration and four siloxane-based polymers were assayed. A manual refractometer and a digital refractometer were used. Polynomial models obtained from the sucrose curves of equilibrium water content against refractive index and vice-versa were used either considering the whole range of sucrose concentrations (16-100% equilibrium water content) or a range confined to the equilibrium water content of current soft contact lenses (approximately 20-80% equilibrium water content). RESULTS: Values of equilibrium water content measured with the Atago N-2E and those derived from the refractive index measurement with CLR 12-70 by the applications of sucrose-based models displayed a strong linear correlation (r2 = 0.978). The same correlations were obtained when the models are applied to obtain refractive index values from the Atago N-2E and compared with those (values) given by the CLR 12-70 (r2 = 0.978). No significantly different results are obtained between models derived from the whole range of the sucrose solution or the model limited to the normal range of soft contact lens hydration. CONCLUSIONS: Present results will have implications for future experimental and clinical research regarding normal hydration and dehydration experiments with hydrogel polymers, and particularly in the field of contact lenses.
Chitosan is functionalized with poly(ethylene glycol) methyl ether (mPEG) at the amino and hydroxyl groups via a single step reaction in a homogeneous aqueous system. A chitosan aqueous solution obtained from the mixture of chitosan and hydroxybenzotriazole (HOBt) in water is a key factor in providing mild conditions to conjugate mPEG by using a carbodiimide conjugating agent. The reaction at ambient temperature for 24 h gives chitosan-g-mPEG with water solubility with mPEG content as high as 42%. This work demonstrates that a water-soluble chitosan-HOBt complex is an effective system for the preparation of chitosan derivatives via the aqueous system without the use of acids or organic solvents.
Poly(propylene carbonate)/starch (PPC/starch) composites with different starch contents were prepared by melt compounding. The biodegradability of the composites was studied by soil burial for a period of 6 months. FTIR study, thermal analysis and morphology observation indicated clearly the changes of the buried specimens. The weight loss curves and the molecular weight changes of the specimens revealed a three-stage biodegradation, corresponding to the propagation of microorganisms, the degradation of starch and the degradation of PPC. The experimental results showed that the addition of starch accelerated the degradation of PPC. Specimens with higher starch content exhibited greater weight loss in the second stage and smaller weight loss in the third stage.