Controlled release of amitriptyline via the transdermal route using SmartReservoirs and hydrogel-forming microneedles

SmartReservoirs (SRs) are novel drug reservoirs made from a cellulose-based matrix for hydrogel-forming microneedles (HF-MNs). SRs can incorporate drug molecules within a cellulose-based matrix in amorphous form. This significantly improves the solubility of poorly soluble drugs, which enhances drug delivery by allowing for rapid dissolution and absorption once the dosage form is administered. In contrast to improving the solubility of hydrophobic drugs, SRs might be used to modify the amorphous/crystalline properties of hydrophilic drugs, thus leading to a controlled release profile. Hence, SRs hold a promise as drug reservoirs for hydrophilic drugs and has not yet been investigated for such drugs; this study explores the transdermal delivery of the hydrophilic model drug amitriptyline hydrochloride (AMT) using SRs. Furthermore, the effect of the cellulose-based matrix on drug loading and release profile was also tested using tissue paper-based (SR-T) and copier paper-based (SR-P) SmartReservoirs. The current research involves the fabrication of HF-MNs and two types of AMT-SRs. Subsequently, a comprehensive characterisation of the HF-MNs and SRs was conducted regarding their morphological features, mechanical and physicochemical properties, amorphous/crystallinity state, interaction with the cellulose matrix, drug distribution, drug loading capacity, and transdermal permeation efficiency. The findings of the study demonstrated that the active pharmaceutical ingredient (API) remained intact within the cellulose matrices of both SRs. The type of cellulose matrix employed had a major influence on the loading and release of the drug. The SR-P demonstrated a significantly enhanced drug loading and release profile compared to the SR-T. The drug content analysis of the SRs revealed that SR-T had approximately 4 mg/cm² of AMT, in comparison to SR-P, which had a concentration nearly double that amount. The results of the skin deposition and permeation studies were also consistent, indicating that SR-T combined with HF-MNs deposited approximately 75 μg and permeated <150 μg (~5 % delivered), while SR-P combined with HF-MNs deposited approximately 128 μg and permeated >500 μg of AMT into the skin (~9 % delivered). Ultimately, this work provides substantial evidence to support the use of SRs as a hydrophilic drug reservoir for HF-MNs.