Imaging the Structure of Macroporous Hydrogels by Two-Photon Fluorescence Microscopy

Two-photon fluorescence microscopy (TPFM) usually used to get 3-D pictures of biological systems has been applied here for the first time to macroporous hydrogels prepared by cryogelation ("cryogels"). Unlike environmental scanning electron microscopy (ESEM) which analyzes the Surface of swollen samples, TPFM delivers images of successive planes in the depth of the material allowing a 3-D imaging of its structure. The macroporous hydrogels studied were poly(N-isopropylacrylamide) (pNIPA), poly(hydroxyethyl methacrylate-L-lactide-dextran) (pHEMA-LLA-D) and various copolymeric gels of these two ones. A quantification of the macropore size distribution and the wall thickness and their modification with respect to the ratio NIPA/HEMA-LLA-D or to the temperature, in the case of pNIPA, was readily obtained.