Effects of the cooling mode on the structure and strength of porous scaffolds made of chitosan, alginate, and carboxymethyl cellulose by the freeze-gelation method

A freeze-gelation method was utilized to prepare porous scaffolds made of chitosan, alginate, and carboxymethyl cellulose because of their usefulness in tissue engineering applications. These polysaccharide solutions were cooled down to freezing using either a fast-cooling (FC) mode (>20 °C/min) or a slow-cooling (SC) mode (0.83 °C/min). Then the frozen polysaccharide solutions were immersed in their respective non-solvents to form porous scaffolds. Based on the SEM and optical microscope images of the scaffolds, the FC mode induced non-simultaneous nucleation and generated directional pore structures. In contrast, simultaneous nucleation and uniform and isotropic pore structures (mean pore size: 60–100 μm) were obtained by using the SC mode. Moreover, the tensile strength of the scaffolds prepared by the SC mode (about 60 N/g) was three times higher than that of scaffolds prepared by the FC mode (about 20 N/g). This study reveals that when using the freeze-gelation method, the cooling rate (mode) is a crucial factor which controls the pore structure and strength of porous scaffolds. Therefore, our results suggest that polysaccharide scaffolds with pore structures suitable for tissue engineering applications can be obtained via an appropriate cooling mode.