Preparation, characterisation and comparison of glabridin-loaded hydrogel-forming microneedles by chemical and physical cross-linking

Poly(vinyl alcohol) (PVA) and carbomer were used as the hydrogel system to fabricate glabridin-loaded hydrogel-forming microneedles (HFMNs) by chemical cross-linking (CCMNs) and physical cross-linking (PCMNs). The properties and drug permeation effects of glabridin-loaded HFMNs with different methods were compared. They both owned excellent shapes, mechanical and insertion properties. PCMNs showed collapsed shapes during swelling due to the low cross-linking rate and high porosity, which probably results in resealing of skin pores during transdermal drug delivery. However, CCMNs could rapidly swell within 2 h with slightly bending. The infrared spectra indicate that CCMNs and PCMNs might form the hydrogel network by generating hydrogen and covalent bonds, respectively. The in vitro release studies showed that cumulative permeation amount within 24 h (1654 μg/cm²) of CCMNs significantly higher than that (372 μg/cm²) achieved by PCMNs and that (118 μg/cm²) achieved by glabridin-loaded gel. The skin barrier recovery test suggests the desirable security of both microneedles (MNs), notwithstanding the presence of mild erythema in the mouse skin applied CCMNs. These results indicate that CCMNs were more desirable for glabridin delivery using PVA and carbomer as a skeleton of the hydrogel network.