An injectable and in situ gelable scaffold can fully fill the space of cartilaginous defects of complex shapes. The authors attempted to develop a novel injection-driven technique for cartilage repair using a thermoresponsive gelatin, poly(N-isopropylacrylamide)-grafted gelatin (PNIPAAm-gelatin). A mixed solution of chondrocytes was isolated from a Japanese white rabbit and PNIPAAm-gelatin was spontaneously solidified at 37 degrees C and cultured. The number of cells in the gel with a poly(N-isopropylacrylamide) (PNIPAAm) chain of high molecular weight (1.3 x 10(5) g/mol) and at low concentration (5 w/v%) remained unchanged irrespective of culture time, and minimal cell death and little cell proliferation were observed. A round-shaped morphology was dominantly restored even at 1 week of incubation. The cell population in the G(0)/G(1) phase was high (more than 90%), and this gradually increased with culture time. Type II collagen and sulfated glycosaminoglycan (s-GAG) were detected in the tissue-engineered cartilage, but a small amount of type I collagen was also detected. Total collagen and s-GAG increased in level close to those of native hyaline cartilage over 12 weeks of culture. Mechanical properties of the tissue-engineered cartilage responding to loading and unloading of compression force tend to approach those of native hyaline cartilage with culture time. These results suggest that PNIPAAm-gelatin may be a suitable in situ formable scaffold for cartilage repair.