Osteoblast bone cells. Coloured scanning electron micrograph (SEM) of osteoblasts (blue) amongst collagen fibres (thread-like). Osteoblasts are primarily found in regions of new bone growth. They produce and secrete osteoid, a matrix of new bone tissue composed of collagen fibrils and other structural proteins. As soon as osteoid is formed, calcium salts crystallise inside it to form hard, mineralised bone. Magnification: x27,000 when printed 10 centimetres wide.