Abstract
The repair of severe bone defects is still a formidable clinical
challenge, requiring the implantation of bone grafts or bone substitute
materials. The development of three-dimensional (3D) bioprinting has
received considerable attention in bone tissue engineering over the past
decade. But 3D printing has a limitation. It only takes into account the
original form of the printed scaffold, which is inanimate and static,
and is not suitable for dynamic organisms. With the emergence of
stimuli-responsive materials, four-dimensional (4D) printing has become
the next generation solution for biological tissue engineering. It
combines the concept of time with three-dimensional printing. Over time,
4D printed scaffolds change their appearance or function in response to
environmental stimuli (physical, chemical and biological). In
conclusion, 4D printing is the change of the fourth dimension (time) in
3D printing, which provides an unprecedented potential for bone tissue
repair. In this review, we will discuss the latest research on shape
memory materials and 4D printing in bone tissue repair.