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4D printing can be defined as the evolution of 3D printing structure in terms of shape, performance and function. It has time dependence, printer independence and predictability, and its smart dynamic performance creates promising capabilities and broad potential applications. On the basis of a brief review of the status of 4D printing at home and abroad, the concept and components of 4D printing were given firstly. Then the 4D printing was classified from the dimension of printing structure shape change. Furthermore, the key technologies such as printing materials, incentive mechanism and mathematical modeling method in 4D printing elements were analyzed. Finally, it was pointed out that the development direction of 4D printing technology is to combine intelligent materials with 3D printing, simplify the manufacture of complex structures, and realize the automation, intellectualization and personalization applications in special service environments and fields such as aerospace, deep sea and precise medical treatment by using its unique characteristics of self-assembly, self-adaption and self-repairing.

The resistance and the surface morphology of the graphene films were studied after atomic oxygen exposure. The graphene films can be etched away during atomic oxygen exposure, the resistance of graphene films decreases at first and then increases. It shows that the adsorption of oxygen atom may play an important role in the change of the resistance of graphene films at the beginning of the exposure and then the change of the resistance conforms to the law of resistance. The atomic oxygen erosion rate which is about 1.2×10-25cm3/atom to 1.3×10-25cm3/atom can be obtained. A kind of new atomic oxygen detector was put forward based on the relationship between the resistance of graphene films and atomic oxygen fluence.