Mucoadhesive Mini-Containers with Unidirectional Drug Release Capacity for Macromolecular Therapeutics

Abstract

Purpose: Peptide-based therapeutics have gained widespread attention for their high specificity and efficacy. However, their oral delivery remains challenging owing to their poor stability and bioavailability in the gastrointestinal environment and limited membrane permeability. To address these barriers, we have designed a novel mini-container system with unidirectional drug release and enhanced mucoadhesion capacities.

Methods: Mini-containers composed of ethyl cellulose shells of varying degrees of viscosity were fabricated using a simple molding process and integrated with catechol-conjugated chitosan (CC) to improve their mucosal adhesion capacity and structural stability.

Results: The catechol substitution levels were optimized (CC-A, CC-B, and CC-C), with the CC-C formulation exhibiting the highest degree of substitution (20.93%) and superior adhesion capacity, maintaining 80% attachment on porcine small intestinal mucosa after 72 h. Insulin, a model peptide drug, was successfully loaded into the CC-C mini-containers, and circular dichroism spectroscopy analysis confirmed that its secondary structure remained intact. The insulin content in the mini-containers, as determined by HPLC-UV analysis, demonstrated consistency across formulations: 101.1 ± 2.4% for 1% CC-C, 95.4 ± 3.8% for 2% CC-C, and 100.0 ± 1.8% for 3% CC-C, while in-vitro dissolution and Franz diffusion cell studies demonstrated its sustained and unidirectional release. After 12 hours of dissolution, the 3% CC-C formulation showed a release rate of 26.22 ± 2.23%, while the 1% CC-C formulation exhibited a release rate of 53.11 ± 0.25%. Catechol-mediated crosslinking significantly slowed the release rate relative to that of controls. The robust structure of the mini-containers fabricated with high-viscosity ethyl cellulose exhibited a mechanical strength of 13.21 ± 0.50 N, comparable to that of commercial enteric capsules (10 N), ensuring durability under gastrointestinal conditions.

Conclusion: This study shows the potential of mini-container technology for the stable and prolonged oral delivery of macromolecular therapeutics. However, further investigation is required to confirm its effectiveness in-vivo.

Keywords: catechol-conjugated chitosan; mini-container shell; mold; mucoadhesion; unidirectional.

Graphical abstract

Figure 1

Mini-container shell fabrication schematic diagram and photos PLA template, silicon mold, and mini-container.

Figure 2

SEM images of the bottom and side surfaces of mini-container shells prepared with EC of different viscosities using stripe and non-stripe molds: (A) Mini-container shells manufactured using a stripe mold, (B) Mini-container shells manufactured using a non-stripe mold.

Figure 3

Hardness of mini-container shells with striped and non-striped surfaces prepared using EC of different viscosities (n=3).

Figure 4

H-NMR results of CC-A, CC-B, and CC-C with different degrees of substitution: (A) H-NMR spectrum and (B) Degree of catechol substitution.

Figure 5

Ex-vivo attachment duration of mini-containers on porcine small intestine depending on catechol conjugation and polymer concentration: (A) Representative images from the mucoadhesive shear test; (B) Mini-containers with 1% concentration of chitosan, CC-A, CC-B, and CC-C; (C) with 2% concentration; and (D) with 3% concentration.

Figure 6

Correlation of CC concentration and catechol substitution degree with the number of remaining containers: (A) Effect of CC concentration on remaining containers for CC-A, CC-B, and CC-C formulations and (B) Effect of catechol substitution degree on remaining containers at CC concentrations (1%, 2%, and 3%).

Figure 7

The mean residue ellipticity (MRE) spectra calculated from circular dichroism (CD) measurements of insulin in HCl solution (pH 2.0) and in catechol-conjugated chitosan (CC) solutions. The spectra demonstrate the preservation of insulin’s secondary structure upon interaction with CC formulations, as indicated by comparable MRE profiles.

Figure 8

Dissolution profiles of mini-container formulations composed of chitosan (CS) and catechol-conjugated chitosan C (CC-C) at polymer concentrations of 1%, 2%, and 3%, conducted in a water bath at 37 °C with agitation at 100 rpm (n = 3).

Figure 9

Evaluation of unidirectional release of mini-container using the Franz diffusion cell: (A) Insulin-containing solutions of distilled water (DW), 3% chitosan (CS), and 3% catechol-conjugated chitosan C (CC-C) and (B) Mini-containers prepared with 3% CS (normal and reverse direction) and 3% CC-C (normal and reverse direction) (n = 3).