Effect of pore geometry and loading direction on deformation mechanism of rapid prototyped scaffolds

Rapid prototyping is a promising technique for producing tissue engineering scaffolds due to its capacity to generate predetermined forms and structures featuring distinct pore architectures. The objective of this study is to investigate the influences of different pore geometries and their orientation with respect to the compressive loading direction on mechanical responses of scaffolds. Plastic models of scaffolds with cubic and hexagonal unit cells were fabricated by three-dimensional (3-D) printing. An in situ imaging technique was utilized to study the progressive compressive deformation of the scaffold models. In both cubic and hexagonal geometries, organized buckling patterns relevant to each unit cell were observed at the onset of plastic deformation. These patterns were in good agreement with the elastic stress concentration patterns generated by finite element simulation. Uniaxial compression tests conducted on both geometries revealed that the stress-strain pattern may vary significantly by changing the loading direction. A secondary stress softening phenomenon was observed where limited pore deformation caused 3-D structure bending. However, when loading direction was adjusted such that deformation was localized on all pores simultaneously, a monotonically increasing stress was observed. These results accentuate the critical role of pore geometry and orientation with respect to the principal loading axis in designing functional tissue engineering scaffolds.