What Are Block Copolymer Micelles?
Block copolymer micelles are generally formed by the self-assembly of either amphiphilic or oppositely charged copolymers in aqueous medium. The hydrophilic and hydrophobic blocks form the corona and the core of the micelles, respectively.
Block copolymer micelles can be classified according to the type of intermolecular forces driving the segregation of the core segment from the aqueous milieu. In the past few decades, at least three main categories were identified, viz. amphiphilic micelles (formed by hydrophobic interactions), polyion complex micelles (PICM; resulting from electrostatic interactions), and micelles stemming from metal
complexation. Generally, when the hydrophilic segment is longer than the core block, the shape of the resulting micelles is spherical. Conversely, increasing the length of the core segment beyond that of the corona-forming chains may generate various non-spherical structures, including rods and lamellae.
- What Is Block Polymer?
Block copolymers consist of two or more chemically distinct polymer blocks covalently bonded together. These blocks may be thermodynamically incompatible with each other because the entropy of mixing per unit volume is small and varies inversely with molecular weight. In the bulk, block copolymers (BCPs), achieved simply by joining polymer chains together, microphase separate on the molecular scale (5–100 nm), producing complex nanostructures with various morphologies.
- What Are Polymeric Micelles?
Polymeric micelles are nanoscopic core/shell structures formed by amphiphilic block copolymers. Both the inherent and modifiable properties of polymeric micelles make them particularly well suited for drug delivery purposes. The three most widely studied block copolymer classes are characterized by their hydrophobic blocks, and are poly(propylene oxide), poly(L-amino acid)s and poly(ester)s.
- What Is Copolymer Used for?
Copolymerization is used to modify the properties of manufactured plastics to meet specific needs, for example to reduce crystallinity, modify glass transition temperature, control wetting properties or to improve solubility. It is a way of improving mechanical properties, in a technique known as rubber toughening.
4. Block Copolymer Micellesfor Drug Delivery?
Micelles, nanosized colloidal particles with a hydrophobic core and hydrophilic shell, can be successfully used for the solubilisation of various poorly soluble pharmaceuticals, and demonstrate a series of attractive properties as drug carriers. Polymeric micelles, such as micelles formed by amphiphilic block copolymers, are of a special interest as they possess high stability both invitro and invivo, and good biocompatibility. Drug-loaded micelles can spontaneously accumulate in body areas with compromised vasculature (tumours, infarcts) via the enhanced permeability and retention (EPR) effect. Micelles made of stimuli-responsive (pH- or temperature-sensitive) amphiphilic block copolymers can release their contents in pathological areas demonstrating hyperthermia or acidosis. Various specific targeting ligand molecules, such as antibodies, can be attached to the micelle surface and bring drug-loaded micelles to, and into, target cells (cancer cells being a primary target). Micelles carrying various reporter (contrast) groups may become the imaging agents of choice in different imaging modalities.
References
- Gaucher, Geneviève, et al. Block copolymer micelles: preparation, characterization and application in drug delivery. Journal of controlled release. 2005, 109(1-3):169-88.
- Rodríguez-Hernández J. Micro-/nanostructured polymer blends containing block copolymers. Recent Developments in Polymer Macro, Micro and Nano Blends. 2017, (pp. 131-161). Woodhead Publishing.
- Kataoka K, Harada A, Nagasaki Y. Block copolymer micelles for drug delivery: design, characterization and biological significance.Advanced drug delivery reviews. 2001, 47(1):113-31.
- Cabral, Horacio, et al. Block copolymer micelles in nanomedicine applications. Chemical reviews. 2018, 118(14):6844-92.