Both nanoplatforms have diverse applications.Īn illustration of a representative multifunctional water-dispersible unimolecular micelle and a water-soluble unimolecular NP. For biomedical applications, the shells of the unimolecular NPs are commonly formed by poly(ethylene glycol) (PEG) or other types of hydrophilic polymers (e.g., polyzwitterions) to provide good water dispersity, reduce opsonization during circulation in the bloodstream, and improve biocompatibility. The cores of the water-soluble unimolecular NPs are usually polyelectrolytes (e.g., cationic or anionic polymers), which can be used to encapsulate hydrophilic payloads (e.g., nucleic acids, peptides, small proteins, metal-based drugs, etc.) via electrostatic interaction, hydrogen bonding, chelation, and/or ion–dipole interactions. Water-soluble unimolecular NPs are typically formed by single/individual dendritic multi-arm water-soluble block copolymers. Hydrophobic agents can be loaded into the hydrophobic core of the unimolecular micelles through hydrophobic interactions, hydrogen bonding, or covalent conjugation. Their unique hydrophobic core is of particular interest in delivering hydrophobic therapeutics or imaging probes. Water-dispersible unimolecular micelles are typically formed by single/individual dendritic multi-arm amphiphilic block copolymers, conferring excellent in vitro and in vivo stabilities. One way to classify unimolecular NPs is based on their chemical composition, which can be divided into two main categories: water-dispersible unimolecular micelles and water-soluble unimolecular NPs ( Figure 1). Polymeric unimolecular NPs can be made from a variety of polymers. In particular, polymeric unimolecular NPs formed by a single multi-arm polymer molecule containing only covalent bonds and exhibiting a core–shell structure are especially valuable for biomedical applications. Thereafter, development of the polymeric unimolecular NPs has been accelerated owing to their desirable characteristics as drug nanocarriers as well as versatile polymer chemistry. The concept of unimolecular NPs was introduced in the 1990s. Īmong all of the strategies that can be applied to address this instability issue, unimolecular NPs have received increasing attention because they are stable regardless of their concentration or the microenvironment. injection Moreover, a recent study also found that more than 80% of the self-assembled PEG-polyester micelles dissociated within 1 h after intravenous administration. For instance, a recent report attributed poor micelle stability to the failure of NK-911, a self-assembled polymeric micelle, at the early clinical stage as it bursts too rapidly after i.v.
Specifically, it is well-documented that dilution in the bloodstream, flow stress, environmental factors (e.g., pH and ionic strength), and interactions with serum proteins can lead to the disruption of the polymeric NPs before functioning. However, conventional polymeric NP systems, which mostly rely on relatively weak interactions as previously mentioned, often exhibit insufficient in vivo stability in terms of nanostructures. The stability of the NPs, or the ability to control NP stability, is of great importance for in vivo/human applications. A broad spectrum of payloads for therapeutic and diagnostic purposes have been delivered by polymeric NPs. Ĭertain types of polymers can form NPs with a core–shell structure in aqueous media owing to the various types of inter/intra-molecular interactions, including electrostatic interactions, hydrophobic interactions, and hydrogen bonding. The design of polymeric NPs can drastically impact the safety, pharmacokinetics, pharmacodynamics, and ultimate in vivo fate of their payloads. Polymer chemistry is also very versatile, thereby making it possible to precisely control the molecular structure, NP morphology, and surface characteristics (e.g., zeta potential and ligand conjugation) of polymeric NPs. Polymeric NPs are attractive for drug delivery applications because many polymers are biocompatible and biodegradable. Polymeric nanoparticle (NP)-based delivery systems have been extensively investigated to improve the diagnostic and treatment efficacy of a wide range of diseases, ranging from cancer and cardiovascular diseases, to bacterial and viral infections.
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