Synthesis and characterization of nanoscale biomimetic polymer vesicles and polymermembranes for bioelectronic applications

Abstract

An amphiphilic ABA triblock copolymer was synthesized using poly(2-ethyl-2-oxazoline)(PEtOz) as hydrophilic block [A] and poly(dimethylsiloxane) (PDMS) as hydrophobicblock [B]. The cationic ring-opening polymerization of 2-ethyl-2-oxazoline was initiated bybenzyl chloride in the presence of NaI. PEtOz–PDMS–PEtOz was characterized in aqueoussolution using transmission electron microscopy (TEM). The block copolymers formedvesicles with a [B] block hydrophobic component thickness of 4 nm, which is thinenough for successful reconstitution of proteins. The mean diameters of the vesicleswere measured to be in the range of 150–250 nm, with a narrow distribution. Theelectrochemical properties of planar PEtOz–PDMS–PEtOz membrane films spread across aTeflon aperture were investigated by electrochemical impedance spectroscopy(EIS). The impedance data showed an increase of planar membrane capacitance(CMEM) from2.58 × 10−7 to2.71 × 10−7 F cm−2 and a decrease ofmembrane resistance (RMEM) from 12 to 10.8 Ω cm2.The increase of CMEM over time in buffer solution can be explained by an increase of the dielectric constant as aresult of membrane electrolyte incorporation and/or by the formation and growth of defectin the free-standing films. In contrast to the formation of thin-walled vesicles, thespread triblock copolymer formed a free-standing membrane with a 9 nm thickness.Based on the two possible conformations (bridge midblock conformation and loopmidblock conformation) that the triblock copolymer can have, we can conclude thatPEtOz–PDMS–PEtOz formed 4 nm thick polymer vesicles with intercalated loop midblockstructure in aqueous solution, while 9 nm thick free-standing polymer films with bilayerloop midblock conformation or with bridge midblock conformation were formed by aperturespreading.