Cellulose and Nanocellulose Emulsions in Biomedical Applications: From Fundamental Mechanisms to Therapeutic Translation

Poor aqueous solubility remains one of the most persistent challenges in pharmaceutical development, limiting clinical translation and requiring innovative formulation strategies; approximately 40% of newly discovered pharmaceutical compounds are affected, underscoring the scale of the problem. Emulsion-based delivery systems overcome this limitation by maintaining drugs in a dissolved state, increasing absorption surface area, and enabling controlled release; however, conventional emulsions face thermodynamic instability and coalescence challenges. Cellulose and nanocellulose—cellulose nanocrystals (CNCs), cellulose nanofibers (CNFs), and bacterial cellulose (BC)—have emerged as sustainable, biocompatible alternatives to synthetic surfactants for stabilizing emulsions via Pickering mechanisms involving irreversible adsorption of solid particles at the oil–water interface. This review synthesizes 142 references across eight application themes: fundamentals and history, emulsion templating, drug encapsulation, antimicrobial and pathogen applications, vaccine adjuvants, topical and transdermal delivery, commercial translation, and regulatory gaps. Rather than treating all sources equally, 37 primary studies are examined in depth through structured critical-appraisal tables organized by system type, goal, key result, and limitation; the remainder are synthesized at the pattern level. A key mechanistic distinction is identified between BC as a standalone biomedical material (used in wound dressings, tissue scaffolds, and drug delivery membranes) and BC as a source for Pickering-emulsion stabilizers after disintegration into nanocrystals or nanofibrils. The review’s overall assessment is that the fundamental materials science of cellulose Pickering emulsions is mature and consistent across sources, while the translational evidence, including in vivo confirmation of drug release performance, biofilm-relevant antimicrobial testing, standardized nanocellulose characterization, and up-to-date intellectual property mapping, remains the binding constraint on clinical and commercial adoption. Six specific, evidence-linked research priorities are identified to advance cellulose emulsions toward regulatory approval and clinical use.