A Review of Polymeric Micelles and Their Applications

Abstract

Self-assembly of amphiphilic polymers with hydrophilic and hydrophobic units results in micelles (polymeric nanoparticles), where polymer concentrations are above critical micelle concentrations (CMCs). Recently, micelles with metal nanoparticles (MNPs) have been utilized in many bio-applications because of their excellent biocompatibility, pharmacokinetics, adhesion to biosurfaces, targetability, and longevity. The size of the micelles is in the range of 10 to 100 nm, and different shapes of micelles have been developed for applications. Micelles have been focused recently on bio-applications because of their unique properties, size, shape, and biocompatibility, which enhance drug loading and target release in a controlled manner. This review focused on how CMC has been calculated using various techniques. Further, micelle importance is explained briefly, different types and shapes of micelles are discussed, and further extensions for the application of micelles are addressed. In the summary and outlook, points that need focus in future research on micelles are discussed. This will help researchers in the development of micelles for different applications.

Keywords: critical micelle concentration; drug delivery; imaging; micelles; polymers.

Figure 1

CMC determination of HePC with 50 µM of cavitand and without cavitand via the filter paper method (a), the capillary height method (b), the dye micellization method (c), and the Wilhelmy plate method (d,e). Reprinted from ref. [12].

Figure 2

CMC measurement of CPB using absorbance (a), fluorescence (b), and conductivity (c) as related to concentration of CPB. Reprinted from [36], Copyright (2019) with permission from Elsevier.

Scheme 1

Illustration of the self-assembly of the polymer or surfactant into a spherical micelle.

Figure 3

(a) schematic representation of topological constraints on the micelle using linear diblock (A-B), linear triblock (A-B-A), and cyclic diblock (A-B) polymers. AFM topographic images of PS-PI micelles in heptane at concentrations (b) 0.1 mg/mL, (c) 1 mg/mL, and (d) 5 mg/mL. Reprinted with permission from [53]. Copyright 2003 American Chemical Society.

Figure 4

The fit of the SAXS intensity profile of Pluronic (F127) (1%) and linalool (0.2%) solutions in D₂O at 37 °C. Reprinted with permission from [65]. Copyright 2018 American Chemical Society.

Figure 5

Synthesis of POEGMA-b-PBzA-b-PVP and self-assembly characterization. (A) reaction scheme involved in the preparation of the polymer and (B) step-wise formation of micelles and multi-compartment micelles. TEM and DLS measurements of polymers in (C) methanol and (D) in water at pH 7. Reprinted from ref. [66].

Scheme 2

Illustration of self-assembly of a polymer or surfactant into an inverse micelle.

Figure 6

Inverse micelles were prepared in a (left) simulation study and (right) using the water/oil microemulsion method. Reprinted with permission from [81]. Copyright 2017 American Chemical Society.

Figure 7

(a) Schematic illustration of the preparation of homo-micelles and block co-micelles in isopropanol and water using (PFS₂₅-b-P2VP₅₀₀)-b-(PFS-b-(PEO-g-TEG))-b-(PFS₂₅-b-P2VP₅₀₀). TEM images of a monodispersed cylindrical micelle of addition of (b) 10 µg, (c) 20 µg, (d) 40 µg of PFS₂₅-b-P2VP₅₀₀ unimer to 20 µg of PFS-b-(PEO-g-TEG) cylinders in isopropanol. (e–g) TEM images of triblock co-micelles (shown in (b–d) after adding Me₂SO₄ and dialysis against water. Reprinted with permission from [95]. Copyright 2016 American Chemical Society.

Figure 8

MRI imaging of iron-stabilized micelles in mouse (A) MRI of HCT16 mouse xenograft (1–72 h) and (B) (24–168 h). The red circles indicate tumors. Reprinted from [101], Copyright (2017) with permission from Elsevier.

Figure 9

Fluorescence imaging of rat organs using DiR solution and DiR-loaded PNIPAM-b-PCL, reprinted from ref. [106].

Figure 10

IT-147 clusters of inverse micelles produced by the simulation study: empty RM (without antioxidant), HT-loaded RM, and GA-loaded RM are antioxidant-loaded RMs. Reprinted with permission from [81]. Copyright 2016 American Chemical Society.

Figure 11

SEM images of PLA-b-PEG-b-PLA inverse micelle membrane with heparin in different magnifications (A) higher magnification and (B) lower magnification. Reprinted from [83], Copyright (2015) with permission from Elsevier.