Regenerative medicine involves processes of replacing, engineering or regenerating human cells, tissues or organs to restore or establish normal function. A major technology of regenerative medicine is tissue engineering, which has variously been defined as "an interdisciplinary field that applies the principles of engineering and the life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function", or "the creation of new tissue by the deliberate and controlled stimulation of selected target cells through a systematic combination of molecular and mechanical signals".