Measurement of the dynamic behavior of thin poly(N-isopropylacrylamide) hydrogels and their phase transition temperatures measured using reflectometric interference spectroscopy

• Published in: Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology 2015-03, Vol.17 (3), p.1-10, Article 148
• Main Authors: Okada, Fuminori, Akiyama, Yoshikatsu, Kobayashi, Jun, Ninomiya, Hidetaka, Kanazawa, Hideko, Yamato, Masayuki, Okano, Teruo
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Dynamic tests; Dynamical systems; Dynamics; Engineered Bioinspired Nanomaterials; Fabrication; Hydrogels; Inorganic Chemistry; Lasers; Materials Science; Microfluidics; Nanoparticles; Nanostructure; Nanotechnology; Optical Devices; Optics; Phase transformations; Photonics; Physical Chemistry; Reflectance; Research Paper; Spectroscopy; Transition temperatures
• ISSN: 1388-0764; 1572-896X
• DOI: 10.1007/s11051-015-2951-3

Temperature-responsive cell culture surfaces prepared by modifying tissue-culture polystyrene with nanoscale poly( N -isopropylacrylamide) (PIPAAm) hydrogels are widely used as intelligent surfaces for the fabrication of various cell sheets that change with temperature. In this work, the characteristics of nanoscale PIPAAm hydrogels were phenomenologically elucidated on the basis of time-dependent surface evaluations under conditions of changing temperature. Because the dynamic characteristics of the nanoscale hydrogel did not exhibit good performance, the nanoscale PIPAAm hydrogel was analyzed by monitoring its temperature-dependent dynamic swelling/deswelling changes using reflectometric interference spectroscopy (RIfS) on an instrument equipped with a microfluidic system. RIfS measurements under ambient atmosphere provided the precise physical thickness of the dry PIPAAm hydrogel (6.7 nm), which agreed with the atomic force microscopy results (6.6 nm). Simulations of the reflectance spectra revealed that changes in the wavelength of the minimum reflectance (Δ λ ) were attributable to the changes in the refractive index of the thin PIPAAm hydrogel induced by a temperature-dependent volume phase transition. The temperature-dependent Δ λ change was used to monitor the swelling/deswelling behavior of the nanoscale PIPAAm hydrogel. In addition, the phase transition temperature of the thin PIPAAm hydrogel under aqueous conditions was also determined to be the inflection point of the plot of the change in Δ λ as a function of temperature. The dynamic behavior of a thin PIPAAm hydrogel chemically deposited on a surface was readily analyzed using a new analytical system with RIfS and microfluidic devices.