Book excerpt: Stimuli sensitive hydrogels resemble to living tissues more than any other class of synthetic biomaterials, thanks to the soft and elastic consistency. They are described as "intelligent" and "smart" gels because they have the ability to change one or more of its properties in a reversible manner. This book presents a new procedure for synthesis of thermo-sensitive copolymer hydrogels poly(N-isopropylacrylamide-co-2-hydroxypropyl methacrylate). The amounts of residual reactants in synthesized hydrogels were determined. The synthesized hydrogels were characterized by FTIR spectrometry, scanning electron microscopy, differential scanning calorimetry and by X-ray diffraction. The scientific contribution is intended to research swelling kinetics for synthesized hydrogels depending on temperature, definition of a mathematical model for swelling process and the swelling reaction order determination. These results present the research of intelligent material with good swelling properties, interesting for absorbtion and releasing molecules of different sizes. They can be used in formulations as carriers for modified release of drugs/active ingredient for different applications.