Photoreaction of a Hydroxyalkyphenone with the Membrane of Polymersomes: A Versatile Method To Generate Semipermeable Nanoreactors

Abstract

Block copolymer vesicles can be turned into nanoreactors when a catalyst is encapsulated in these hollow nanostructures. However the membranes of these polymersomes are most often impermeable to small organic molecules, while applications as nanoreactor, as artificial organelles, or as drug-delivery devices require an exchange of substances between the outside and the inside of polymersomes. Here, a simple and versatile method is presented to render polymersomes semipermeable. It does not require complex membrane proteins or pose requirements on the chemical nature of the polymers. Vesicles made from three different amphiphilic block copolymers (α,ω-hydroxy-end-capped poly(2-methyl-2-oxazoline)-block-poly(dimethylsiloxane)-block-poly(2-methyl-2-oxazoline) (PMOXA-b-PDMS-b-PMOXA), α,ω-acrylate-end-capped PMOXA-b-PDMS-b-PMOXA, and poly(ethylene oxide)-block-poly(butadiene) (PEO-b-PB)) were reacted with externally added 2-hydroxy-4'-2-(hydroxyethoxy)-2-methylpropiophenone under UV-irradiation. The photoreactive compound incorporated into the block copolymer membranes independently of their chemical nature or the presence of double bonds. This treatment of polymersomes resulted in substantial increase in permeability for organic compounds while not disturbing the size and the shape of the vesicles. Permeability was assessed by encapsulating horseradish peroxidase into vesicles and measuring the accessibility of substrates to the enzyme. The permeability of photoreacted polymersomes for ABTS, AEC, pyrogallol, and TMB was determined to be between 1.9 and 38.2 nm s(-1). It correlated with the hydrophobicity of the compounds. Moreover, fluorescent dyes were released at higher rates from permeabilized polymersomes compared to unmodified ones. The permeabilized nanoreactors retained their ability to protect encapsulated biocatalysts from degradation by proteases.

Stimuli-Triggered Activity of Nanoreactors by Biomimetic Engineering Polymer Membranes

“…8 An essential molecular parameter for an in situ reaction inside the cavity of a nanoreactor is membrane permeability to allow transport of the substrates required for the reaction, and the 4 products generated by the reaction. Various approaches have been used to produce permeable membranes, including: (i) selection of a copolymer, which forms an intrinsic permeable membrane, 15 (ii) chemical modification of membranes to create pores, 16,17 (iii) incorporation of stimuli responsive polymer chains to induce membrane permeability in the presence of a stimulus, 18 and (iv) reconstitution of channel porins. 3,9,19 However, none of these approaches To maximize their effectiveness, especially when they are intended to serve as artificial organelles or simple mimics of cells, an additional step in nanoreactor design should be triggered activity of encapsulated enzymes to respond in a controlled manner or to produce and release molecules "on demand".…”

Polyester Dendrimers: Smart Carriers for Drug Delivery

“…Polymer vesicles commonly referred to as polymersomes have recently received significant attention for biological applications [213][214][215][216][217][218][219][220][221]. Polymersomes can be readily accessed from a wide range of block copolymers and they typically exhibit much lower critical aggregation concentrations and enhanced thermodynamic and kinetic stabilities [222,223].…”

Stimuli-responsive polymersomes and nanoreactors

“…139 Bruns and co-workers developed a simple and versatile method to generate UV-responsive nanoreactors by encapsulating a hydroxyalkylphenone within a polymersome membrane. 140 They used α,ω-hydroxy-endcapped PMOXA-b-PDMS-b-PMOXA, α,ω-acrylate-endcapped PMOXA-b-PDMS-b-PMOXA, and PEO-b-PB polymer mixtures to prepare polymersomes. The two latter polymers, containing double bonds at the chain ends or in the PB block, are prone to be attacked by radicals and could potentially undergo cross-linking reactions.…”