Controlled loop and graft formations of water-soluble polymers on SAMs for the design of biomaterials surfaces

Abstract

We prepared four types of water-soluble polymers with anchoring group(s) at one or both terminals: poly(ethylene glycol) (PEG) with one or two anchoring groups and polyrotaxane with one or two anchoring groups. Each polymer was immobilized to successfully form a loop or graft structure on a gold substrate covered with a self-assembled monolayer (SAM) of a tri(ethylene glycol)-dodecanethiol conjugate. Controlled immobilization of the polymers onto a gold substrate was examined by an original two-step protocol and was confirmed by quartz crystal microbalance (QCM) measurement. We investigated the effects of the immobilization modes (loop and graft) of the polymers on the surface properties of biomaterials. Surface softness or rigidity of the hydrated polymers on a SAM was analyzed by QCM with dissipation monitoring measurements, by which we found smaller ratios of energy dissipation to frequency (DD/Df) for a loop structure than for a graft structure in an aqueous environment. With regard to surface wettability, substrates with PEG or polyrotaxane were similar in terms of static and dynamic contact angles and were also not influenced by the immobilization modes. We demonstrate that less fibrinogen was adsorbed on the polyrotaxane loop, making it a good platform for the design of biomaterials surfaces.

Hydrogen-Bonded Structure of Water in the Loop of Anchored Polyrotaxane Chain Controlled by Anchoring Density

“…These previous studies indicated that water molecules confined in a narrow space surrounded by polymers could have a relation to the biocompatibility. Indeed, Yamada et al (2012) reported that a polyrotaxane with looped PEG chains exhibited better biocompatibility than that with a linear one. We expect that the amount of water incorporated into the looped PEG, which may contribute to biocompatibility, could be controlled by changing the loop size according to the anchoring density.…”

“…Indeed, biocompatibility can also be improved by the morphology of the polymer in addition to its constituents. For example, an excellent anti-fouling property [hereafter referred to as biocompatibility because this is often linked to nonbiofouling ( Schlenoff, 2014 )] has been reported for looped polymers ( Yamada et al, 2012 ; Kang et al, 2016 ; Benetti et al, 2017 ). Articular joints of mammalians are coated with a lubricating protein, which adopts the looped conformation, has also exhibited outstanding biocompatibility ( Greene et al, 2015 ).…”

“…The looped shape is more rigid and provides stronger resistance against compression than a linear one. The higher resistance of the looped chains towards external compression translated into an excellent biocompatibility, a protein repellent behavior ( Yamada et al, 2012 ; Benetti et al, 2017 ). The looped shape also accommodates water molecules inside loops having a size of a few nanometers ( Ostaci et al, 2011 ).…”

Interactions of hyaluronan grafted on protein surfaces studied using a quartz crystal microbalance and a surface force balance

“…3(b). [28][29][30] A low Dd/Df value often indicates mass addition without a significant dissipation increase, 24 which is characteristic of a fairly stiff layer; while in contrast, a large Dd/Df implies a soft and dissipative layer. In this study for all layers, Dd always appears to be in a linear relationship with Df, but the Dd/Df ratio of bHA (8.8 Â 10 À2 Hz À1 ) is nearly 20 times that of bBSA or Neut (4.6 Â 10 À3 Hz À1 ).…”

Synthesis of Loop Poly(Methyl Methacrylate) Brushes via Chain-End Postpolymerization Modification

“…In contrast to their linear counterparts, loop-type polymer brushes have received only relatively limited attention . Loop brushes in recent reports, however, were shown to better resist nonspecific protein adsorption compared to their linear analogues. , Furthermore, loop poly­(2-ethyl-2-oxazoline) (PEOXA) brushes grafted onto TiO 2 substrates showed lower friction coefficients compared to single-chain end-tethered PEOXA brushes . Loop polymer brushes can form Velcro-type interactions with linear polymer chains, which may be exploited to generate large scale adhesive interfaces .…”