Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Osmotic pressure
Reexamination Certificate
2000-05-10
2001-10-09
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Osmotic pressure
Reexamination Certificate
active
06298713
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to commonly-assigned applications U.S. Ser. Nos. 09/567931 and 09/567991 filed on even date herewith.
BACKGROUND
Water transport has been identified as a factor in the selection of biocompatible materials for medical applications, including ophthalmic lenses such as contact lenses. It would therefore be desirable to quantify in-vitro flux and diffusion coefficients of water, through biocompatible materials such as hydrogels.
U.S. Pat. No. 5,776,999 to Nicolson et al. discloses a method for screening materials for use as extended-wear ophthalmic lenses. The Nicolson et al. patent also discloses various methods for measuring the diffusivity of hydrogel materials.
Prior art methods for determining water transport require the preparation and use of buffered solutions. It would be desirable to provide a simpler laboratory technique that does not require the preparation and use of buffered solutions. It would also be desirable to provide a method that does not require the use of radio-labeled materials. Further, it would be desirable to provide a method that produces reliable results using readily available laboratory equipment.
SUMMARY OF THE INVENTION
The present invention provides a method for measuring the water diffusion coefficient across a sample of a water-permeable material, for example a biocompatiblc material such as hydrogel. The present invention provides a method for determining the water diffusion coefficient of a hydrogel material comprising the steps of:
(a) defining a calibration algorithm to relate the NMR spectra of at least three known concentrations of water in solution with D
2
O, wherein the concentration of D
2
O is greater than the concentration of water;
(b) providing a first cell containing a first aqueous solution;
(c) providing a second cell containing a second solution comprising D
2
O;
(d) equilibrating a sample of said biocompatible material in D
2
O and positioning said equilibrated sample of said biocompatible material at an interface between said first cell and said second cell to permit diffusion across said equilibrated sample of said biocompatible material;
(e) withdrawing a sample of said second solution;
(f) measuring the NMR spectrum of said withdrawn sample of said second solution;
(g) calculating the concentration of hydrogen ions in said second cell by applying the calibration algorithm of step (a) to said NMR spectrum of said second solution; and
(h) calculating the water diffusion coefficient of said biocompatible material using the hydrogen ion concentration calculated in step (g).
The method of the invention may further comprise replacing a volume of solution in the second cell that is substantially equal to the volume of the withdrawn sample. In a preferred embodiment, the solution used to replace the withdrawn volume is substantially pure D
2
O.
REFERENCES:
patent: 5156041 (1992-10-01), Schaper et al.
patent: 5211055 (1993-05-01), Steudle et al.
patent: 5612222 (1997-03-01), Gordon et al.
patent: 5776999 (1998-07-01), Nicolson et al.
Leibenguth Eric J.
Nandu Mahendra P.
Bausch & Lomb Incorporated
Cygan Michael
Furr, Jr. Robert B.
Polyn Denis A.
Williams Hezron
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