Fabrication of 3D Hybrid Scaffolds with high Strength using Micro-stereolithography technology and Sintering process

Abstract

The scaffolds, which were implanted in articular cartilage defects, were in mechanically unstable environment and could not integrate with surrounding cartilage tissue and regenerate the articular cartilage effectively. Thus, to regenerate the articular cartilage, it was advantageous to regeneration bone and cartilage tissue simultaneously in a connected form. That was hybrid scaffolds for osteochondral tissue regeneration. The goal of this research therefore was to develop hybrid scaffolds consisting ceramic for bone tissue and hydrogel for cartilage tissue to regenerate osteochondral tissue. To achieve this goal, development of ceramic scaffolds for bone tissue must be a priority because bone tissue has outstanding healing ability and provide mechanical stability for articular cartilage in osteochondral tissue regeneration. Projection-based microstereolithography (pMSTL) system, which is a solid freeform fabrication method, was applied to fabricate scaffolds for bone tissue, and modified to solve the problems associated with misaligned UV light, and system setting time.In this research, hydroxyapatite (HA) and tricalcium phosphate (TCP) were used as a material for ceramic scaffold fabrication. To fabricate 3D scaffolds using ceramic powders, the sintering behavior of ceramic powders was evaluated by dilatometry, and the densification according to maximum sintering temperatures was observed. Throughout these experiments, sintering conditions were determined. Moreover, solidification characteristics of ceramic slurry were evaluated, and fabrication conditions for desired line width and depth were determined. After ceramic scaffolds fabrication, proliferation of cells on the ceramic scaffolds was examined to determine their usefulness for tissue regeneration. To improve the capacity of ceramic scaffolds for bone tissue regeneration, ceramic scaffolds having osteoinductivity were developed. Because calcium ions released from ceramic materials play a role in inducing bone formation, we controlled the degradation rate of ceramic scaffolds by changing the weight fraction of HA and TCP. The effects of calcium ions on osteogenic differentiation and bone regeneration were evaluated in vitro and in vivo. In the in vivo experiments, ceramic scaffolds were implanted into rat calvarial defect of 8 in diameter. These results showed that HA/TCP scaffolds had a greater capacity of bone regeneration than HA scaffolds. Throughout these experiments, we successfully developed the ceramic scaffolds enhancing their capacity for bone tissue regeneration.Finally, using developed ceramic scaffolds for bone tissue and hydrogel scaffolds for cartilage tissue, hybrid scaffolds for osteochondral tissue regeneration were developed. Alginate hydrogel with chondrocytes and growth factor was used for cartilage tissue, and function of chondrocytes in alginate hydrogel was evaluated in the in vitro. These two scaffolds, ceramic and hydrogel scaffolds, were assembled together in the process hydrogel crosslinking, and the depth of integration region was controlled to be about 1 to prevent dislocation and delamination of hydrogel after implantation. After fabricating, in vivo experiments were performed, and osteochondral tissue regeneration was evaluated using histological and immunohistochemical analyses. Throughout these results, we confirmed that osteochondral tissue, especially articular cartilage tissue regeneration was much better in hydrogel/ceramic (hybrid) scaffolds than in hydrogel scaffolds.From this research, it can be seen that hybrid scaffolds to improve the osteochondral tissue regeneration were successfully developed, and we expect that these results will give the direction of scaffold fabrication for osteochondral tissue regeneration.