Optical projection tomography technique for image texture and mass transport studies in hydrogels based on gellan gum

The microstructure and permeability are crucial factors for the development of hydrogels for tissue engineering, since they influence cell nutrition, penetration and proliferation. The currently available imaging methods able to characterize hydrogels have many limitations. They often require sample drying and other destructive processing, which can change hydrogel structure, or they have limited imaging penetration depth. In this work, we show for the first time an alternative non-destructive method, based on optical projection tomography (OPT) imaging, to characterize hydrated hydrogels without the need of sample processing. As proof of concept we used gellan gum (GG) hydrogels obtained by several crosslinking methods. Transmission mode OPT was used to analyse image microtextures and emission mode OPT to study mass transport. Differences in hydrogels structure related to different types of crosslinking and between modified and native GG were found through the acquired Haralickâ s image texture features followed by multiple discriminant analysis (MDA). In mass transport studies, the mobility of FITC-dextran (MW 20, 150, 2000 kDa) was analysed through the macroscopic hydrogel. The FITC-dextran velocities were found to be inversely proportional to the size of the dextran as expected. Furthermore, the threshold size in which the transport is affected by the hydrogel mesh was found to be 150 kDa (Stokesâ radii between 69 à and 95 à ). On the other hand, the mass transport study allowed us to define an index of homogeneity to assess the crosslinking distribution, structure inside the hydrogel and repeatability of hydrogel production. As a conclusion,  we showed that  the set of OPT imaging based material characterization methods presented here are useful for screening many characteristics of hydrogel compositions in relatively short time in an inexpensive manner, providing  tools for improving the process of designing hydrogels for tissue engineering and drugs/cells delivery applications.Portuguese Foundation for Science and Technology (FCT) - Grant No. SFRH/BPD/100590/201

Optical projection tomography as a tool for 3D imaging of hydrogels

An Optical Projection Tomography (OPT) system was developed and optimized to image 3D tissue engineered products based in hydrogels. We develop pre-reconstruction algorithms to get the best result from the reconstruction procedure, which include correction of the illumination and determination of sample center of rotation (CoR). Existing methods for CoR determination based on the detection of the maximum variance of reconstructed slices failed, so we develop a new CoR search method based in the detection of the variance sharpest local maximum. We show the capabilities of the system to give quantitative information of different types of hydrogels that may be useful in its characterization.The authors thank to Tekes, Finnish Cultural Foundation, CIMO, Jane and Aatos Erkko Foundation and EXTREMA COST Action MP1207 for supporting this work