Fabrication of patterned high-density polymer graft surfaces. II. Amplification of EB-patterned initiator monolayer by surface-initiated atom transfer radical polymerization

Coordinated Responsive Arrays of Surface-Linked Polymer Islands-CORALs

The concept of co-ordinated responsive arrays of surface-linked islands (polymer CORALs) is introduced. This study targets a responsive system capable of revealing or covering the substrate surface in response to environmental changes in a reversible way. A convenient method of fabrication of polymer CORALs is proposed. It is based on microphase separation that occurs in thin films of supramolecular assemblies of block copolymers with reactive blocks. Such blocks form nanometer-size domains that may serve as anchors for surface-linked polymer islands. Two characteristics of the islands are critically important for the switching function: high grafting density within the islands and small lateral separation that allows interactions between polymer chains grafted to the neighboring islands. This combination permits complete coverage of the substrate surface upon exposure to a good solvent (relaxed state). In a weak solvent, the chains collapse within the islands, thus revealing the substrate (compact state). The morphology of the CORALs in both states and some details of the switching process were studied with atomic force microscopy, grazing incidence small-angle scattering, and coarse-grained molecular dynamic simulations.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Nanopatterned polymer brushes: conformation, fabrication and applications

Surfaces with end-grafted, nanopatterned polymer brushes that exhibit well-defined feature dimensions and controlled chemical and physical properties provide versatile platforms not only for investigation of nanoscale phenomena at biointerfaces, but also for the development of advanced devices relevant to biotechnology and electronics applications. In this review, we first give a brief introduction of scaling behavior of nanopatterned polymer brushes and then summarize recent progress in fabrication and application of nanopatterned polymer brushes. Specifically, we highlight applications of nanopatterned stimuli-responsive polymer brushes in the areas of biomedicine and biotechnology.

Patterning of polymer brushes made easy using titanium dioxide: direct and remote photocatalytic lithography

Titanium dioxide photocatalytic lithography of initiator functionalized surfaces is proved for the realization of micropatterned polymer brushes.

Cell membrane-inspired phospholipid polymers for developing medical devices with excellent biointerfaces

This review article describes fundamental aspects of cell membrane-inspired phospholipid polymers and their usefulness in the development of medical devices. Since the early 1990s, polymers composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) units have been considered in the preparation of biomaterials. MPC polymers can provide an artificial cell membrane structure at the surface and serve as excellent biointerfaces between artificial and biological systems. They have also been applied in the surface modification of some medical devices including long-term implantable artificial organs. An MPC polymer biointerface can suppress unfavorable biological reactions such as protein adsorption and cell adhesion - in other words, specific biomolecules immobilized on an MPC polymer surface retain their original functions. MPC polymers are also being increasingly used for creating biointerfaces with artificial cell membrane structures.

Nanostructured bio-functional polymer brushes

Structured poly(glycidyl methracrylate) (poly-GMA) brushes have been grafted onto flexible fluoro-polymer films using a radiation grafting process. The reactive epoxide of poly-GMA provides the basis for a versatile biofunctionalization of the grafted brushes. Structure definition by extreme ultraviolet (EUV) exposure allowed nanometer-scale resolution of periodic patterns. By variation of the exposure dose the height of the grafted structures can be adapted in a wide range. Derivatization of the grafted brushes included reaction with various amines with different side chains, hydrolysis of the epoxide to diols to increase protein resistance and introduction of ionic groups to yield poly-electrolytes. As an example for biofunctionalization, biotin was linked to the grafted brush and biofunctionality was demonstrated in a competitive biotin-streptavidin assay. In this article we also present a brief review of other approaches to obtain structured biofunctional polymer brushes.

Patterning of polymer brushes. A direct approach to complex, sub-surface structures

We report a unique method to directly fabricate complex polymer brush structures with nanometer scale features by means of electron beam lithography. Polymer brushes for direct patterning were grown from surface-anchored initiator sites using atom transfer radical polymerization. Selected monomers (poly(2-hydroxyethyl methacrylate) and poly(methyl methacrylate)) were used based on their ability to readily scission when exposed to radiation. Single step direct patterning of polymer brushes is attractive as this eliminates many process steps, reducing the possibility of contamination and possibly improving resolution. In addition, we report a method to form subsurface polymer brush channels with nanometer-scale features. With the chains tethered to a surface, a diblock copolymer brush with a negative tone upper layer (polystyrene) and a positive tone under layer (poly(methyl methacrylate)) or (poly(2-hydroxyethyl methacrylate) were patterned to create channels. In the work presented, the direct electron beam patterning behavior of the brushes was studied and fabrication of nanochannels was demonstrated. Imaging of the nanopatterned surfaces was carried out using atomic force microscopy and fluorescence microscopy.

Effect of nanoconfinement on the collapse transition of responsive polymer brushes

Nanopatterned brushes of a thermo-responsive polymer, poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMEO2MA), displaying a collapse temperature in the physiological range were synthesized for grafting diameters from a few micrometers down to 35 nm. The reversible collapse transition of the nanobrushes was studied in water as a function of their lateral confinement, down to ensembles of brushes containing only approximately 300 chains. The confinement results in a considerable broadening of the collapse transition and in an increase of the degree of vertical swelling, which can be explained by the internal structure of the nanodroplets derived from a theoretical model of dry nanobrushes. These results enable the rational design of responsive surfaces having a tunable topography engineered at the nanometer scale, which is of direct interest for the development of soft nanoactuators and new substrates for cell adhesion studies.

Control of Nanobiointerfaces Generated from Well-Defined Biomimetic Polymer Brushes for Protein and Cell Manipulations

To better understand protein/material and cell/material interactions at the submolecular level, well-defined polymer brushes consisting of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) on silicon wafers were prepared by atom transfer radical polymerization (ATRP). Silicon wafers were treated with 3-(2-bromoisobutyryl)propyl dimethylchlorosilane (BDCS) to form a monolayer that acts as initiators for ATRP. Silicon-supported BDCS monolayers were soaked in a methanol/water mixture solution containing Cu(I)Br, bipyridine, and a sacrificial initiator. After MPC was added to the solution, ATRP was carried out for 18 h. The molecular weight and thickness of the PMPC brush layer on the silicon surface increased with an increase in the polymerization time. The dense polymer brushes were obtained by the "grafting from" system. By selective decomposition of the BDCS monolayer by UV light-irradiation, the PMPC brush region and the sizes were well controlled, resulting in fabricating micropatterns of the PMPC brushes. When the thickness of the PMPC brush layer was greater than 5.5 +/- 1.0 nm (3 h polymerization), serum protein adsorption and fibroblast adhesion were effectively reduced, i.e., proteins and cells could recognize such thin polymer brushes on the surface. In addition, the density of the adherent cells on the patterned PMPC brush surface could be controlled by changing the size of the pattern.