TABLE 2.

Some commonly used approaches for designing different microstructures of bone scaffolds.

Formation method	Representative microstructure	Advantages and disadvantages	References
Linearly functionally graded scaffold	Relative density grading	Advantages: The overall performance of the structure can be easily optimized	Al-Ketan et al. (2020)
	Cell size grading
Exponentially functionally graded scaffold	One structure	Disadvantages: Some special properties cannot be achieved and there is still room for improvement	Al-Ketan and Abu (2019)
	Different structure
Hybrid scaffold		Advantages: The advantages of various structures can be combined	Chen et al. (2019)
		Disadvantages: The design and optimization are challenging