Engineered delivery systems for vaccine adjuvants

Vaccine adjuvants are essential for eliciting robust adaptive immunity, yet conventional formulations are limited by insufficient targeting precision, uncontrolled release profiles, and suboptimal immune polarization. In response, adjuvant development progressively shifts toward advanced materials-engineered delivery systems, such as lipid nanoparticles (LNPs), liposomes, polymeric architectures, and metal-organic frameworks (MOFs), which enable localized targeting, programmed release, and enhanced biocompatibility. To guide the rational design of these technologies, this review systematically categorizes contemporary adjuvant delivery strategies across three interdependent dimensions: spatial precision, temporal control, and immunological precision. Through this multidimensional framework, the ways in which material physicochemical properties, stimuli-responsive architectures, and surface engineering regulate the location of adjuvants, the timing of immune stimulation, and the polarization of responses are examined. Furthermore, the interdependence of these dimensions is highlighted, demonstrating that their coordinated optimization is critical for maximizing overall vaccine efficacy. Finally, recent progress in clinical translation is evaluated, with particular emphasis on bio-manufacturing scalability, formulation stability, and regulatory challenges. Collectively, this review provides a practical, materials-centric roadmap for the design, evaluation, and clinical advancement of next-generation precision adjuvants.