Enhancing cell penetration and proliferation in chitosan hydrogels for tissue engineering applications

The aim of this study was to develop a process to create highly porous three-dimensional (3D) chitosan hydrogels suitable for tissue engineering applications. Chitosan was crosslinked by glutaraldehyde (0.5 vol %) under high pressure CO(2) at 60 bar and 4 °C for a period of 90 min. A gradient-depressurisation strategy was developed, which was efficient in increasing pore size and the overall porosity of resultant hydrogels. The average pore diameter increased two fold (59 μm) compared with the sample that was depressurised after complete crosslinking and hydrogel formation (32 μm). It was feasible to achieve a pore diameter of 140 μm and the porosity of hydrogels to 87% by addition of Acacia gum (AG) as a surfactant to the media. The enhancement in porosity resulted in an increased swelling ratio and decreased mechanical strength. On hydrogels with large pores (>90 μm) and high porosities (>85%), fibroblasts were able to penetrate up to 400 μm into the hydrogels with reasonable viabilities (~80%) upon static seeding. MTS assays showed that fibroblasts proliferated over 14 days. Furthermore, aligned microchannels were produced within porous hydrogels to further promote cell proliferation. The developed process can be easily used to generate homogenous pores of controlled sizes in 3D chitosan hydrogels and may be of use for a broad range of tissue engineering applications.