Tissue engineering can be classified into two strategic approaches with or without cell transplantation to induce tissue regeneration. Cell transplantation involves problems to be improved, such as low rates of cell survival and the consequently low therapeutic efficacy, and the shortage of cell source. As one trial of regenerative therapy, it is
practically possible to make use of host cells present in the body. For example, efficient manipulation of in vivo local environment necessary for recruitment of host cells and their functioning will enhance the cell-induced natural healing of tissues. Peripheral blood contains several types of primitive cells with high potentials for natural healing. The in vivo recruitment of these circulating cells is being tried with biomaterials to assist and enhance the cell recruitment and retention as well as release chemoattractants. In situ tissue regeneration based on the natural self-healing potential of the body may be possible by making use of biomaterial technologies to regulate cell recruitment and their functions.