Table 4.

Evaluation of tetanus toxoid (TT) active self-healing microencapsulation in PLGA microspheres as a function of initial concentration of vaccine antigen in loading solution (ASM-1), and type of the plasticizer (ASM-24) and porosigen (ASM-27) incorporated.

Formulation	TT massa		TT loading based on			Encapsulation efficiency (%)*
			Mass loss from loading solution (μg)*	Polymer content
	Initial (μg)	Remaining (μg)*		(μg)*	(wt%)*
ASM-1	400	70 ± 3	330 ± 3	308 ± 43b	1.38 ± 0.2b	77 ± 11b,c
ASM-1	320	6 ± 2	314 ± 2	309 ± 10b	1.38 ± 0.1b	97 ± 3b,c
ASM-24	320	38 ± 4	282 ± 4	ND	1.35 ± 0.03d	88 ± 1d
ASM-27	320	81 ± 3	239 ± 3	ND	1.11 ± 0.02d	75 ± 1d

^a: volume = 0.5 mL;

^*: Mean ± SEM, n = 3;

^b: TT content in the polymer was determined by amino acid analysis;

^c: based on the antigen content in the polymer;

^d: based on the TT mass loss from loading solution

ASM-1: 3.2 wt% Al(OH)₃/3.5 wt% trehalose/5 wt% DEP/PLGA microspheres; ND: Not determined

ASM-24: 3.2 wt% Al(OH)₃/3 wt% trehalose/5 wt% TBAC/PLGA microspheres

ASM-27: 3.2 wt% Al(OH)₃/1.5 wt% trehalose/1.5 wt% MgCO₃/5 wt% TBAC/PLGA microspheres

Active self-healing encapsulation of TT was performed by incubating ~20 mg microspheres (20-63 μm in size) with 0.5 mL of 0.64-0.8 mg/mL TT in normal saline (pH 6.8) under mild agitation at 10, 25 and 38 °C respectively for 24, 24, and 40 h.