Table 2.

Differences between implantable scaffolds and injectable biomaterials.

	Implantable scaffold	Injectable biomaterial
Advantages	Enable sustained release	Avoid surgery-related complications
	Preload with biological factors, therapeutic agents, or even cells	Require less technical expertise
Disadvantages	Require invasive surgery	Limit material types
	Limit the desired implanted place
	Cause fibrosis and compromise normal organ function
Material type	Drug delivery chips; osmosis pumps; polymer conduits for nerve regeneration, etc.	Self-assembling peptide hydrogels; macroporous cryogel sponges; liposome, etc.
Applications	Drug delivery system [210]	Drug delivery system [218]
	Deliver adoptive T cells and activated dendritic cells [212]	Deliver tumor-specific CD8+ T lymphocytes [219]
	Provide an optimal stem cell niche [220]	Serve as an injectable vaccine platform [221]
		Re-establish tolerance to treat autoimmune diseases [222]