Table 1. Experimental Conditions of Box–Behnken Design for Preparation of PDGF-BB-Loaded Nanospheres by a Double-Emulsion Process (w/o/w).

			levels
			min	max
factors		coded units	–1	+1
#1	stirring rate (rpm)	X1	200	900
#2	stirring duration (min)	X2	30	150
#3	PVA concentration (%)	X3	0.4	1.0
#4	PDGF-BB concentration (ng/mL)	X4	200	300