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There has been a growing interest in RNA therapeutics globally, and much progress has been made in this area, which has been further accelerated by the clinical applications of RNA-based vaccines against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Following these successful clinical trials, various technologies have been developed to improve the efficacy of RNA-based drugs. Multimerization of RNA therapeutics is one of the most attractive approaches to ensure high stability, high efficacy, and prolonged action of RNA-based drugs. In this review, we offer an overview of the representative approaches for generating repetitive functional RNAs by chemical conjugation, structural self-assembly, enzymatic elongation, and self-amplification. The therapeutic and vaccine applications of engineered multimeric RNAs in various diseases have also been summarized. By outlining the current status of multimeric RNAs, the potential of multimeric RNA as a promising treatment strategy is highlighted.

Advances in the DNA nanotechnology have enabled the fabrication of DNA-based hydrogels with precisely controlled structures and tunable mechanical and biological properties. Compared to DNA hydrogel, preparation of RNA-based hydrogel remains challenging due to the inherent instability of naked RNA. To overcome these limitations, we fabricated a DNA-RNA hybrid hydrogel via stepwise dual enzymatic polymerization. Multimeric short hairpin RNAs (shRNAs) were hybridized with functional DNA aptamers for targeting and mechanical properties of the hydrogel. The obtained DNA-RNA hybrid hydrogel was ultrasoft, robust, and injectable hence reconfigurable into any confined structures. As a model system, the hydrogel was able to mimic microtubule structures under physiological conditions and designed to release the functional small interfering RNA (siRNA)-aptamer complex (SAC) sequentially. In addition, we encoded restriction enzyme-responsive sites in DNA-RNA hybrid hydrogel to boost the release of SAC. This novel strategy provides an excellent platform for systematic RNA delivery through double-controlled release, SAC release from hydrogel, and subsequent release of siRNA from the SAC, which has promising potential in RNA therapy.

Cells secrete extracellular vesicles (EVs) to external environments to achieve cellular homeostasis and cell-to-cell communication. Their therapeutic potential has been constantly spotlighted since they mirror both cytoplasmic and membranous components of parental cells. Meanwhile, growing evidence suggests that EV engineering could further promote EVs with a maximized capacity. In this review, a range of engineering techniques as well as upscaling approaches to exploit EVs and their mimetics are introduced. By laying out the pros and cons of each technique from different perspectives, we sought to provide an overview potentially helpful for understanding the current state of the art EV engineering and a guideline for choosing a suitable technique for engineering EVs. Furthermore, we envision that the advances in each technique will give rise to the combinatorial engineering of EVs, taking us a step closer to a clinical translation of EV-based therapeutics.

A novel fabrication method for RNA particles (RPs) was developed based on enzymatic polymerization, and the size of the RPs was controlled intentionally by adjusting the RNA polymerase concentration for a variety of potential applications.