During the development of fertilized eggs into mature individuals, some types of cells usually form along a "one-way street". With the continuous development, these cells will gradually lose plasticity and become specific types of irreversible cells. For example, skin cells do not automatically become brain cells, and small intestine cells do not become heart cells. However, there are some experimental methods that can make the transformation between different types of cells possible. These methods all make use of the principle of nuclear reprogramming, that is, transforming the nuclear gene expression of one type of cells into embryonic cells or other types of cells. This mechanism has aroused widespread interest in the scientific community.

The "natural cross-linking theory of biological molecules" of aging points out that the fundamental cause of biological growth, development and aging is cell proliferation and differentiation, which is the progressive molecular cross-linking caused by the interaction of chemical active groups in various biological macromolecules. When demonstrating the molecular mechanism of organism aging, this theory points out that organism is an unstable chemical system and belongs to dissipative structure. All kinds of biomolecules in the system have a large number of active groups, and they must interact with each other to produce chemical reactions, so that biomolecules can be slowly crosslinked to stabilize their chemical activities. With the passage of time, the degree of crosslinking increases, the consumption of active groups of biomolecules decreases, and the original molecular structure changes gradually. The accumulation of these changes will lead to the gradual aging of biological tissues.

An aging cell, its division and proliferation have stopped, its DNA and other biomolecules are mostly in a cross-linking state, and the cross-linking reaction of biomolecules tends to be aging with the decrease of active molecules; However, if the aging cells can re-enter the track of division and proliferation or make them produce active biomolecules at a faster rate than the cross-linking inactivation rate by other means, the aging balance of the decreasing active molecules can be broken and the cells can be restored to a younger or even omnipotent state.