Design and characterization of pectin-starch/organoclay-tea tree essential oil composite hydrogel beads as a gastrointestinal-specific sustained release system.

The therapeutic potential of essential oils in feed and medicine is limited by their volatility, degradation, and poor bioavailability. To overcome these challenges, a novel colon-targeted microsphere was engineered for the controlled delivery of tea tree essential oil (TEO), as illustrated in Scheme 1. A critical component of this system is a pH-responsive coating composed of pectin and starch, which acts as a colon-specific polymeric barrier. This coating demonstrated precise pH-responsive release, with minimal leakage in simulated gastric fluid (SGF) (only 10.87 % release over 4 h) and sustained, colon-specific release in simulated intestinal fluid (SIF) (79.77 % over 14 h). The core of the system, designated TEOCMT, was fabricated through the modification of montmorillonite (MMT) with cetyltrimethylammonium bromide (CTAB), resulting in organo-montmorillonite (CMT). Tea tree essential oil was then encapsulated within the interlayer spaces of CMT, forming an effective sustained-release system (TEOCMT). Compared to raw MMT (5.63 %), the TEO loading capacity of CMT increased 8.3-fold, reaching 46.79 %. Furthermore, the antibacterial activity of PS/TEOCMT microspheres was triggered in alkaline media, where they dissolved and released the TEOCMT core. This resulted in enhanced efficacy, particularly against S. aureus (MIC = 1.25 mg mL-1), which was superior to that of pure TEO (MIC = 2.5 mg mL-1). The PS/TEOCMT microspheres also exhibited excellent biocompatibility. This work presents a robust and effective strategy for unlocking the full potential of essential oils in colon-specific applications.