Tuning the Properties of Poly(ethylene glycol) Films and Membranes by the Molecular Weight of the Precursors

Abstract

We show that ultrathin poly­(ethylene glycol) (PEG) films and freestanding membranes can be readily prepared by thermally activated cross-linking of amine/epoxy-decorated STAR-PEG compounds with the molecular weight (MW) varying from 2000 to 20,000 g/mol. The thickness of these objects, recorded in the 10–330 nm range, could be precisely controlled. They all exhibit characteristic hydrogel, biorepulsive, and elastic properties, with the exact parameters depending on the MW. This factor (MW) affects, in particular, the swelling behavior and biomolecule permeability of the PEG films as well as the elastic properties of the PEG membranes, which show an extreme elasticity with Young’s moduli of 2.1–5.2 MPa at 100 nm thickness. Contrary to intuitive expectations, the Young’s modulus does not decrease but increases with the increasing MW, which is explained by the progressive alignment of the PEG chains within the cross-linking network. The high stability, parameter tunability, and exceptional characteristics of the STAR-PEG-originated films and membranes make them promising candidates for application in biochemistry, medicine, and soft matter nanotechnology.

Elastic Properties of Poly(ethylene glycol) Nanomembranes and Respective Implications

“…This strategy has indeed been realized using amine- and epoxy-substituted, four-arm STAR-PEGs. Thermoactivated crosslinking of the respective STAR-NH 2 and STAR-EPX precursors allows for the fabrication of exceptionally stable ultrathin PEG films and coatings [ 15 , 16 ]. These films exhibit pronounced bioinert and hydrogel properties and their characteristics could be flexibly tuned by varying the parameters of the preparation procedure [ 15 ] and the molecular weight of the precursors [ 16 ].…”

“…Thermoactivated crosslinking of the respective STAR-NH 2 and STAR-EPX precursors allows for the fabrication of exceptionally stable ultrathin PEG films and coatings [ 15 , 16 ]. These films exhibit pronounced bioinert and hydrogel properties and their characteristics could be flexibly tuned by varying the parameters of the preparation procedure [ 15 ] and the molecular weight of the precursors [ 16 ]. Further options are provided by the creation of hybrid materials on the basis of these films [ 15 ], their decoration with bioreceptors [ 8 ], and their modification by electron irradiation and UV light [ 17 , 18 ], paving the way to a variety of lithographic applications.…”

“…In addition, PEG films can be separated from the substrate [ 19 ] and subsequently transferred to a secondary substrate in the context of a specific application [ 20 , 21 ] or even exist as a free-standing membrane [ 16 , 19 ]. These membranes are quite stable and possess an exceptional elasticity, emphasized by a very small Young’s modulus of 2.1–5.2 MPa at a thickness of ~100 nm [ 16 ].…”

“…In addition, PEG films can be separated from the substrate [ 19 ] and subsequently transferred to a secondary substrate in the context of a specific application [ 20 , 21 ] or even exist as a free-standing membrane [ 16 , 19 ]. These membranes are quite stable and possess an exceptional elasticity, emphasized by a very small Young’s modulus of 2.1–5.2 MPa at a thickness of ~100 nm [ 16 ]. The value of Young’s modulus depends on the molecular weight of the STAR-NH 2 and STAR-EPX precursors [ 16 ], but is most likely a function of the membrane thickness and its composition at a deviation from the standard 1:1 ratio between STAR-NH 2 and STAR-EPX, which is useful for some applications [ 8 ].…”

“…These membranes are quite stable and possess an exceptional elasticity, emphasized by a very small Young’s modulus of 2.1–5.2 MPa at a thickness of ~100 nm [ 16 ]. The value of Young’s modulus depends on the molecular weight of the STAR-NH 2 and STAR-EPX precursors [ 16 ], but is most likely a function of the membrane thickness and its composition at a deviation from the standard 1:1 ratio between STAR-NH 2 and STAR-EPX, which is useful for some applications [ 8 ]. It cannot also be excluded that the derived values of Young’s modulus are affected by the parameters of the experimental setup used for their measurement, which will strongly diminish their reliability.…”