Osteoblasts are bone cells that are responsible for the formation of new bone.Unlike the much larger osteoclasts, osteoblasts are much smaller; they only have one nucleus. Osteoblasts also work in groups to form new bone.he osteoblasts come from the differentiation of osteogenic cells in the tissue that covers the outside of the bone, or the periosteum and the bone marrow. The osteoblast creates and repairs new bone by actually building around itself. First, the osteoblast puts up collagen fibers.