*2.3. Isolation and Culture of Chondrocytes*

Chondrocytes were isolated from macroscopically normal cartilage taken from four patients having arthroplasty and one cadaver (Table 1), as previously described [27]. In brief, cartilage tissues were minced and digested for 16 h with collagenase type II (250 IU/mg dry weight, Worthington, New Jersey, USA) at 37 ◦C. The extracted cells, were seeded at 5000 cell/cm<sup>2</sup> in complete culture media containing Dulbecco's Modified Eagle's Medium/F-12 (DMEM/F-12) with 1% (*v*/*v*) penicillin/streptomycin (P/S) and 10% (*v*/*v*) foetal calf serum (all Life Technologies, Loughborough, UK). Chondrocytes were passaged at 70–80% confluence and cultured to passage 2 (P2).
