Electrotherapy is the use of electrical energy as a medical treatment. In medicine, the term electrotherapy can apply to a variety of treatments, including the use of electrical devices such as deep brain stimulators for neurological disease. The term has also been applied specifically to the use of electric current to speed wound healing. Additionally, the term "electro-therapy" or "electromagnetic therapy" has also been applied to a range of alternative medical devices and treatments. Finally, it has not been found to be effective in increasing bone healing. Tissue engineering is the use of a combination of cells, engineering and materials methods, and suitable biochemical and physicochemical factors to improve or replace biological tissues. Tissue engineering involves the use of a tissue scaffold for the formation of new viable tissue for a medical purpose. While it was once categorized as a sub-field of biomaterials, having grown in scope and importance it can be considered as a field in its own. In biology, the term phoresis, also called phoresy, is an inter-species biological interaction in ecology and refers to a form of symbiosis.