Table 2.

Summary of main synthesis methods for CaP.

Method	CaP phase	Size	Shape	Advantages	Disadvantages	Ref.
sol-gel chemistry	ACP, β-TCP, HAp, DCPA	Nano/micron	Particle/sheet	narrow size distribution, comparatively low synthesis temperature	high cost, serious aggregation, usually needs special regents	[[27], [28], [29]], [37,38,40]
flame spray pyrolysis	β-TCP, HAp	submicron to hundreds of microns	particle	rapid synthesis, large-scale, usually resulted in spheic structure	difficult to obtain nano-size product, high energy consumption	[[42], [43], [44]]
solid-state reactions	β-TCP, α-TCP, HAp	micron	diverse	low cost, large-scale	serious aggregation, poor redispersability	[45,46]
wet-chemical precipitation in room temperature	Mainly HAp	nano	diverse	bulk synthesis, low cost, incorporation of compounds, often only water as solvent	upscaling can be difficult and requires a continuous process	[[47], [48], [49], [50], [51]]
wet-chemical precipitation under heating conditions	ACP, HAp	nano	Controllable shape	high reaction rate and efficiency	energy consumption; cannot load drugs (nucleic acids or proteins)	[[52], [53], [54], [55]]