The Effect of Ultraviolet Light on Biorepulsive Hydrogel Poly(ethylene glycol) Films

Abstract

We studied the effect of ultraviolet (UV) light (254 nm) on porous poly(ethylene glycol) (PEG) films, formed by cross-linking of the epoxide-and amino-terminated four-arm STAR-PEG compounds. The major effect of irradiation is progressive decomposition of the PEG material followed by immediate desorption of the released fragments. The removal of the PEG material can be coarsely described by zero-order kinetics with a rate constant of 0.32 ± 0.05 nm/(J/cm 2 ). Surprisingly, this process does not affect the chemical composition of the residual film, which preserves all the useful properties of the original PEG material, including its hydrogel character and biorepulsion behavior, which is in striking contrast to the effect of electron irradiation on the PEG films and the effect of UV irradiation on oligo(ethylene glycol) (OEG)-substituted self-assembled monolayers, for which the removal of the PEG/OEG material is accompanied by substantial chemical modification of the residual part, losing its original properties. The behavior of the PEG films under UV irradiation is not only an interesting and unexpected phenomenon but can also be applied to three-dimensional patterning of PEG materials, with the preservation of biorepulsive properties over the entire patterns, which can be potentially useful for applications.

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

“…In contrast to electron irradiation, the exposure of the PEG films to UV light does not result in their modification but only in a partial loss of material [ 18 ]. However, the mechanism behind the respective decomposition of the PEG network, which follows zero-order kinetics [ 18 ], is still unclear.…”

“…In contrast to electron irradiation, the exposure of the PEG films to UV light does not result in their modification but only in a partial loss of material [ 18 ]. However, the mechanism behind the respective decomposition of the PEG network, which follows zero-order kinetics [ 18 ], is still unclear. Interestingly, the exposure of closely related, PEG-substituted self-assembled monolayers (SAMs) to UV light results in the same effect as their exposure to electrons, viz.…”

“…Representative ∆ p vs. h plots for the pristine and exposed-to-UV-light PEG membranes are shown in Figure 9 a; the decrease in the membrane thickness, given in the legend, manifests the expected effect of UV light [ 18 ]. The experimental points for all the samples lie quite close to each other, which suggests a similarity of the elastic properties.…”

“…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.…”

“…These issues are specifically addressed in the present study in which we also explore the possibility of tuning the elastic properties of the PEG membranes by the modification of the parent films by electron irradiation and UV light. The latter experiments, in combination with additional measurements, also shed some light onto the effect of UV light on PEG materials, which is still controversially discussed in the community [ 18 ].…”