Thickness Dependence of Bovine Serum Albumin Adsorption on Thin Thermoresponsive Poly(diethylene glycol) Methyl Ether Methacrylate Brushes by Surface Plasmon Resonance Measurements

Abstract

This study reports on the dependence of the temperature-induced changes in the properties of thin thermoresponsive poly(diethylene glycol) methyl ether methacrylate (PDEGMA) layers of end-tethered chains on polymer thickness and grafting density. PDEGMA layers with a dry ellipsometric thickness of 5-40 nm were synthesized by surface-initiated atom transfer radical polymerization on gold. To assess the temperature-induced changes, the adsorption of bovine serum albumin (BSA) was investigated systematically as a function of film thickness, temperature, and grafting density by surface plasmon resonance (SPR), complemented by wettability and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. BSA adsorption on PDEGMA brushes is shown to differ significantly above and below an apparent transition temperature. This surface transition temperature was found to depend linearly on the PDEGMA thickness and changed from 35 °C at 5 nm thickness to 48 °C at 23 nm. Similarly, a change of the grafting density enables the adjustment of this transition temperature presumably via a transition from the mushroom to the brush regime. Finally, BSA that adsorbed irreversibly on polymer brushes at temperatures above the transition temperature can be desorbed by reducing the temperature to 25 °C, underlining the reversibly switchable properties of PDEGMA brushes in response to temperature changes.

Thin Poly(Di(Ethylene Glycol)Methyl Ether Methacrylate) Homopolymer Brushes Allow Controlled Adsorption and Desorption of PaTu 8988t Cells

“…For PaTu 8998T cell culture medium qualitatively similar observations were made (Figure b,d). The dependence of the angle shift due to irreversibly adsorbed proteins and molecules in the cell medium versus temperature can be described in both cases by a sigmoid function, in analogy to the previously reported BSA experiments . The inflection points of 32 ± 2 °C for fibronectin (Figure c) and 29 ± 2 °C for cell culture medium are close to each other and to the LCST of PDEGMA brushes (32 °C) .…”

“…From the data, the angle shift attributed to irreversibly adsorbed protein was determined to be 10.1 ± 0.7 m° at 20 °C (Figure c). This value corresponds to ≈10 ng cm −2 of adsorbed protein . The adsorption at temperature of 37 °C led to an irreversible angle shift of 29 ± 2 m°.…”

“…PDEGMA brushes were prepared via SI‐ATRP on gold surfaces covered with a neat monolayer of the initiator MUBiB, resulting in a maximum of grafting density (Scheme ) for all experiments, except of the experiment shown in Figure . There, polymer brushes were synthesized with different fractions of MUBiB and MHDA on the surface (Figure S1, Supporting Information), resulting in different grafting densities of the brushes . The PDEGMA layers were characterized by ellipsometry, XPS and grazing angle FTIR spectroscopy (Figure a–c).…”

“…Fibronectin was used at a concentration of 10 μg mL −1 in PBS or PaTu 8988t cell culture medium (see Section ). 96 regions of interest were selected and analyzed in each measurement according to the previously published protocol …”

“…Key to the development of new thermoresponsive coatings for cell release applications is the temperature‐switchable protein desorption and adsorption, which is generally of utmost importance for the adhesion of biological cells to biomaterial surfaces . Expanding on the previous discovery that bovine serum albumine (BSA) adsorption on PDEGMA brushes, which are known to be protein resistant, increases with decreasing brush thickness and can be precisely and reversibly modulated by changes in temperature around an apparent transition temperature (from 35 °C at 5 nm to 48 °C at 23 nm brush thickness), these brushes were characterized, as reported here, in more detail to assess their potential as thermoresponsive cell release coating . On the basis of this study and independent atomic force microscopy (AFM) investigations, it was hypothesized that very thin PDEGMA homopolymer brushes will change from an extended to a collapsed state and thereby switch the passivating character of PDEGMA, known for thick brushes, into a cell attractive and adherent state above the LCST (Scheme ) …”