Pre-assembled nanospheres in mucoadhesive microneedle patch for sustained release of triamcinolone in the treatment of oral submucous fibrosis.

Abstract

Objectives: Drug-loaded mucoadhesive silk fibroin (SF) microneedle patch can overcome the limitations of low bioavailability and significant pain associated with traditional treatment methods, such as topical application or injection of triamcinolone for oral submucous fibrosis (OSF). However, these systems release the drug too quickly, failing to meet the clinical requirements. This study aims to construct a mucoadhesive SF microneedle patch pre-assembled with silk fibroin nanospheres (SFN) and explore its ability to sustain the release of triamcinolone in the treatment of OSF.

Methods: SFN was pre-assembled via precipitation reaction and characterized by scanning electron microscope (SEM) for the morphology. The particle size and ζ-potential were measured by dynamic light scattering (DLS). Triamcinolone was loaded onto SFN using a diffusional post-loading method. The effective loading of triamcinolone was confirmed using Fourier-transform infrared spectroscopy (FTIR). The concentration of unloaded triamcinolone was quantified by high-performance liquid chromatography. Drug encapsulation efficiency and loading capacity of SFN were then calculated to determine the optimal amount of drug loading. The SFN suspension was pre-mixed with SF solution to prepare the microneedle under-layer. The microneedle morphology was observed by SEM. Compression mechanical tests were performed to evaluate the fracture force of microneedles at different nanosphere contents (5%, 10%, and 20%), determining the optimal pre-mixing ratio. Ex-vivo mouse oral mucosa permeation studies were performed to ascertain the insertion depth of the microneedles via histological sections. The adhesive top layer was synthesized using SF and tannic acid, with FTIR confirming its successful synthesis. Its viscoelasticity was characterized by a rheometer, and differential scanning calorimetry analyzed thermal properties. Tensile tests evaluated the interfacial bonding strength between the adhesive layer and microneedle base to ensure no detachment during use. Adhesion to wet oral mucosal tissues was tested and compared to commercial oral patches.Under the optimized conditions, the double-layered mucoadhesive microneedle patch with pre-assembled nanospheres was prepared. Its cell compatibility was evaluated by cell counting kit-8 (CCK-8), live/dead staining, and phalloidin staining after co-culturing with fibroblasts. The drug release experiment was conducted to demonstrate its sustained release efficacy.

Results: SFN (mean diameter 46.25 nm) was successfully prepared. The maximum drug encapsulation efficiency was (63.88±1.09)% (corresponding loading capacity of SFN was (27.41±3.06)% when the weight ratio of triamcinolone/SFN was 0.5. The corporation of SFN did not affect microneedle morphology. The mechanical properties of microneedles decreased with increasing nanosphere amount. Only the fracture force of the group with 5% SFN [(0.07±0.01) N/needle] exceeded the minimum force required for mucosal penetration, thus selected as the optimal pre-mixing ratio. Histological sections confirmed that the SFN microneedles could penetrate the epithelial layer and deliver drugs to OSF-affected areas. Adhesion strength between the microneedle base and top layer was (94.8±6.89) kPa, confirming strong bonding with no detachment during use. The wet adhesive strength of the double-layered mucoadhesive microneedle patch [(41.28±7.43) kPa] was significantly enhanced compared to commercial oral patches (4.5 kPa, P<0.01). CCK-8 and live/dead staining results confirmed no significant cytotoxicity. Drug release experiment showed the double-layered mucoadhesive microneedle patch with pre-assembled SFN enabled sustained release time of triamcinolone from 4 days to 14 days.

Conclusions: Pre-assembling nanospheres in mucoadhesive SF microneedle patches can extend triamcinolone release time, meeting clinical requirements for sustained drug delivery.