Design and evaluation of mesoporous silica nanoparticles for the targeted co-delivery of essential oils

Abstract

Bromodosis, characterised by excessive foot odour, affects many individuals, particularly those who wear closed-toe shoes for extended periods of time. Current treatment options for bromodosis include zinc oxide powder, antibacterial agents, antiperspirants, botulinum toxin, laser therapy, or surgery. However, these treatments often manage symptoms rather than addressing the underlying causes. Additionally, they may require long-term use, which can be inconvenient and costly. Targeting and reducing the population of Brevibacterium spp. and Staphylococcus aureus, key culprits in bromodosis, could be an effective strategy for combating foot odour. Mesoporous Silica Nanoparticles (MSNs) are favoured over other nanoparticles for delivering essential oils due to their high drug loading capacity, controlled release capabilities, biocompatibility, stability, and ease of customisation, offering a versatile and effective approach for managing foot odour. Developing an essential oil-loaded MSNs formulation offers a promising solution against bromodosis. This research aimed to synthesise MSNs (~100-200 nm) encapsulating Styrax benzoin and Juniperus virginiana essential oil for targeted bromodosis treatment. A sol-gel method using two surfactants ensured precise particle size control and uniform pores within the nanoparticles for effective encapsulation. The MSNs suitability for essential oil encapsulation was confirmed, followed by essential oil loading via adsorption. Encapsulation efficacy (EE), loading capacity (LC), release, antibacterial and toxicity studies were conducted. Nanoparticles were primarily spherical with mesopores, confirmed by SEM and TEM images. The MSNs size was 182.27 ± 6.50 nm with a PDI of 0.14 ± 0.02 and a zeta potential of -19.8 ± 8.53 mV, confirming their nano-size, homogeneity and stability, facilitating successful encapsulation. Higher %EE was observed for 2:1 S. benzoin oil:MSNs (BEN-MSNs) and J. virginiana oil:MSNs (JUN-MSNs) ratio compared to a 1:1 ratio. Cumulative release at pH 5.2 and pH 6.5 ranged from 48.43% to 78.23%, catering to pH variations of foot perspiration. Antibacterial studies demonstrated a large reduction in S. aureus and B. linens, while B. agri and B. epidermidis showed lower colony forming unit reductions. The 1:1 ratio of BEN-MSNs with JUN-MSNs exhibited non-toxicity at both pH levels, indicating safety for topical use. This study underscores MSNs’ potential as effective essential oil carrier into the mesopores. Loading efficiency varies with essential oil type and compounds present but can be optimised through MSNs modification. These results support the development of pharmaceutical formulations utilising MSNs and essential oils for targeted antimicrobial activity against bromodosis pathogens while ensuring safety for topical use.