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Tissue engineering approaches have been clinically tried to repair damaged articular cartilages. It is an essential step to uniformly seed chondrocytes into 3D scaffolds in order to reconstruct tissue-engineered cartilages in vitro, but the tissue engineering could not have been provided with efficient cell seeding methods. Type I collagen is clinically used and known as a cytocompatible material, having recognition sites for integrins. Collagen gel encapsulating chondrocytes has been tried for making regenerated cartilages, but it is found difficult to have the gel keep its original shape after long-term culture, because of shrinking. On the other hand, 3D scaffolds, either of a nonwoven structure or a sponge-like structure, involve difficulty in that chondrocytes could not be uniformly seeded, although they have adequate initial mechanical properties. In this study, by combining collagen gelation with a nonwoven PLLA scaffold, we achieved uniform cell seeding into the 3D scaffold. Bovine articular chondrocytes were mixed with type I collagen solution, and the solution was poured into the nonwoven PLLA scaffold (1.5 mm thick, f 15 mm). The collagen–chondrocyte mixture was made into gel at 37°C for 1 h. The 0.39% collagen mixture was viscous enough to prevent cells from precipitating during gelation. Almost all chondrocytes were able to be incorporated into the PLLA scaffolds by mixing with collagen solution and subsequently making into gel, while 30–40% of the chondrocytes seeded as a cell suspension were not trapped into the PLLA scaffolds. The method presented, where chondrocytes were mixed with collagen solution, and the mixture was incorporated into a 3D scaffold, then made into gel in the scaffold, could serve as an alternative for in vitro cartilage regeneration, also simultaneously having the advantages of both materials.

Although rapid formation of a smooth inner surface is important in constructing an artificial vascular graft, a conventional model that uses a biodegradable polymer such as polyglycolic acid needs long-term culture to form it. In another model, which uses collagen gel, it is reported that prompt formation of the smooth inner surface was achieved. But the mechanical properties were not suitable, resulting in rupture under high pressure at the arterial level. Therefore, we propose a new artificial vascular graft model made of biodegradable polymer, gel, and cells. At first we manufactured an artificial vascular graft (i.d. 5 mm, o.d.7 mm) consisting of poly-l-lactic acid (PLLA) with open pore structures by using gas-forming methods. After mixing human normal aortic smooth muscle cells (SMCs) with type I collagen solution, pores of the PLLA scaffold were filled with the mixture. The collagen mixture was made into gel in the pores of the PLLA scaffold, incubating at 37°C. WET-SEM analysis showed that the prompt formation of a smooth inner surface was achieved in the new model. The ratio of incorporation of SMCs into the artificial vascular graft became approximately 100% by using the cell–collagen mixture, whereas only 40% of SMCs were trapped in the conventional model where SMCs were inoculated as a cell–medium suspension. Therefore, it was suggested that the new artificial vascular graft model was superior in smooth inner surface formation and cell inoculation, compared with conventional models using either biodegradable polymer or gel.