An osteochondral scaffold (MaioRegen, Fin-Ceramica, Faenza, Italy) has a porous 3D tri-layer composite structure to mimic the osteochondral tissue. The top layer (the red C) is for the cartilage tissue and made from type-I collagen, the transition layer (the red T) is for the transition zone, subchondral bone, and is 60% from type-I collagen and 40% from magnesium-hydroxyapatite, and the bottom layer (the red B) is for the bone tissue and is 30% from type-I collagen and 70% from magnesium-hydroxyapatite (a), a bilayer osteochondral scaffold (Agili-C; CartiHeal, Israel) that is currently in clinical trial and made from aragonite and hyaluronic acid shape of cylinders, with a similar surgical technique as the mosaic-like osteochondral transplantation. The top layer is for the cartilage tissue and is from aragonite and hyaluronic acid, and the bottom layer is for bone tissue phase and is from calcium carbonate in the aragonite crystalline form (b), a bilayer scaffold (TruFit CB; Smith & Nephew, Andover, Massachusetts) is from poly(lactic-co-glycolic acid), poly(glycolic acid) fibres, and calcium sulphate (c). Adapted with a minor modification from (Kon et al. 2014)