State of the Art on Tannin-Based Micro-/Nano-Carriers as Drug Delivery Systems: A Comprehensive Review

Introduction: Tannins are structurally diverse plant polyphenols increasingly recognized as sustainable building blocks for advanced drug delivery systems. Their capacity for hydrogen bonding, electronic interactions between aromatic moieties (“π-π stacking”), and metal coordination enables the formation of versatile nano- and micro-carriers with intrinsic antioxidant, anti-inflammatory, antimicrobial, and anticancer activities. This review synthesizes current evidence on tannin-based delivery platforms and evaluates their pharmaceutical relevance. Methods: A structured narrative review was conducted using major scientific databases, focusing on peer-reviewed studies (2010-2025) reporting clearly identified hydrolysable, condensed, or complex tannins formulated as nano- or micro-carriers. Data were extracted on fabrication strategies, physicochemical properties, drug-loading performance, release behavior, biocompatibility, and in vitro/in vivo outcomes. The current situation was analyzed qualitatively due to methodological heterogeneity across studies. Results: Tannin-based carriers, including metal-phenolic networks, self-assembled nanoparticles, nanogels, microcapsules, and layer-by-layer systems, consistently exhibit high encapsulation efficiencies (60% - 95%) and drug-loading capacities (5% - 30%). Particle sizes typically range from 50 - 400 nm, with negative surface charges ensuring colloidal stability. Many systems demonstrate pH- and redox-responsive release, enhanced muco-adhesion, and synergistic bioactivity. Preclinical studies in cell lines, zebrafish, and rodent models report favorable biocompatibility, low toxicity, and improved therapeutic efficacy in wound healing, infection control, and oncology. Discussion: Compared with synthetic polymers, tannin-based carriers offer multifunctionality, biocompatibility, biodegradability, and compatibility with green chemistry principles. However, variability in tannin composition, lack of standardized characterization, and limited pharmacokinetic data constrain reproducibility and translation. Conclusion: Tannin-based micro-/nano-carriers represent promising, sustainable drug delivery platforms. Advances in standardization, mechanistic understanding, and GMP-oriented manufacturing are essential to unlock their full clinical and industrial potential.