Development of tissue-simulating optical phantoms: poly-N-isopropylacrylamide solution entrapped inside a hydrogel

The average turbid optical properties of the N-isopropylacrylamide (NIPA) polymer solution entrapped inside a polyacrylamide hydrogel (called an NIPA/PAAM gel system) were studied using a multiwavelength oblique-incidence reflectometer. The turbidity of such a system can be drastically changed by simply switching the temperature from below the low critical solution temperature of the NIPA, around 33°C, to above. The absorption coefficient and the reduced scattering coefficient were obtained as a function of wavelength for samples with selected NIPA and blue dextran concentrations. It is found that the scattering of the optical phantom comes from the NIPA polymer chains and the absorption from the blue dextran. The turbid optical properties of an NIPA/PAAM gel system can be tuned to simulate biological tissues at a specific wavelength by varying compositions of NIPA and blue dextran and further modified by controlling the temperature.