Manufacturing polymeric porous capsules

Abstract

Polymeric porous capsules represent hugely promising systems that allow a size-selective through-shell material exchange with their surroundings. They have vast potential in applications ranging from drug delivery and chemical microreactors to artificial cell science and synthetic biology. Due to their porous core-shell structure, polymeric porous capsules possess an enhanced permeability that enables the exchange of small molecules while retaining larger compounds and macromolecules. The cross-capsule transfer of material is regulated by their pore size cut-off, which depends on the molecular composition and adopted fabrication method. This review outlines the main strategies for manufacturing polymeric porous capsules and provides some practical guidance for designing polymeric capsules with controlled pore size.

Fig. 1. Schematic illustration of different copolymer and supramolecular structures at increasing packing parameter values. (A) Using diverse synthesis approaches, it is possible to obtain several copolymer architectures. (B) Three parameters (a₀, l, V) define the packing parameter p of an amphiphilic copolymer (left). The hydrophilic block is represented in blue, while the hydrophobic is in red. Based on the p value, amphiphilic copolymer can self-assemble in spherical and cylindrical micelles and vesicles (right).

Fig. 2. Schematic overview of different techniques for the generation of polymeric porous capsules. Polymeric porous capsules can be prepared using different strategies: variation of packing factor, copolymers’ mixtures, templated self-assembly, perturbating stimuli and insertion of transmembrane channels.

Fig. 3. Microscopy characterisation of porous capsules made with a packing parameter variation and copolymers mixture strategy. The variation of the copolymer packing parameter leads to the generation of pores during (A) PISA and (B) PIPS. Scale bar = 50 μm. (C) Pores are also produced by mixing different curvature-forming copolymers in the same formulation. Scale bar = 100 nm. (Di–iii) The hydrolysis of one of the copolymers in the formulations leads to the formation of pores which causes an increase of the polymeric vesicle permeability (from Di to Dii) and a morphological change (Diii) over time. In this case, the nano-pores are below the resolution of the microscopy characterisation and pore size was inferred by other means. Scale bars = 5 μm. Figure adapted with permission from ref. 20,28,38 and 40 with permission from The Royal Society of Chemistry, copyright 2017, 2021 American Chemical Society and Elsevier respectively.

Fig. 4. Electron microscopy characterisation of porous capsules made with templated self-assembly, stimuli-responsive and membrane channel insertion strategies. Examples of porous polymeric capsules made with (A) solid and (B) soft templates, (C) external stimuli and (D) protein channel insertion. Figure adapted with permission from ref. Royal Society of Chemistry, copyright 2006 and 2019 American Chemical Society, 2020 Springer Nature and 2007 National Academy of Sciences, respectively.

Claudia Contini

Wenyi Hu

Yuval Elani