Single Step Process for Self-Assembled Block Copolymer Patterns via in Situ Annealing during Spin-Casting

We demonstrated a simple and time-efficient processing method for facilitating a microphase separation of block copolymers (BCPs) based on a single step of spin-casting with low volatile solvent and in situ annealing. Well-ordered lamellar patterns of poly­(styrene-<i>b</i>-methyl methacrylate) BCP films having wide range of molecular weights (51–235 kg/mol) were fabricated by a single 3 min process of spin-casting, even without the conventional pretreatment of substrate neutralization. The formation of this well-ordered lamellar structure is attributed to a synergetic effect between slow solvent evaporation and thermal energy that may provide an efficient cooling profile for the BCP film during the spin-casting process

Creating Opal-Templated Continuous Conducting Polymer Films with Ultralow Percolation Thresholds Using Thermally Stable Nanoparticles

We propose a novel and robust strategy for creating continuous conducting polymer films with ultralow percolation thresholds using polymer-coated gold nanoparticles (Au NPs) as surfactant. Continuous poly(triphenylamine) (PTPA) films of high internal phase polymeric emulsions were fabricated using an assembly of cross-linked polystyrene (PS) colloidal particles as template. Polymer-coated Au NPs were designed to be thermally stable even above 200 °C and neutral to both the PS and PTPA phases. Therefore, the Au NPs localize at the PS/PTPA interface and function as surfactant to efficiently produce a continuous conducting PTPA polymer film with very low percolation thresholds. The volume fraction threshold for percolation of the PTPA phase with insulating PS colloids (as measured by electron microscopy and conductivity measurements) was found to be 0.20. In contrast, with the addition of an extremely low volume fraction (ϕ_p = 0.35 vol %) of surfactant Au NPs, the volume fraction threshold for percolation of the PTPA phase was dramatically reduced to 0.05. The SEM and TEM measurements clearly demonstrated the formation of a continuous PTPA phase within the polyhedral phase of PS colloids. To elucidate the influence of the nanoparticle surfactant on the blend films, the morphology and conductivity of the blends at different PS colloid/PTPA volume ratios were carefully characterized as a function of the Au NP concentration. Our approach provides a methodology for a variety of applications that require a continuous phase for the transport of molecular species, ions, or electrons at low concentrations and a second phase for mechanical support or the conduction of a separate species

Nanopatterning Biomolecules by Block Copolymer Self-Assembly

The fabrication of sub-100 nm features with bioactive molecules is a laborious and expensive process. To overcome these limitations, we present a modular strategy to create nanostructured substrates (ca. 25 nm features) using functional block copolymers (BCPs) based on poly­(styrene-<i>b</i>-ethylene oxide) to controllably promote or inhibit cell adhesion. A single type of BCP was functionalized with a peptide, a perfluorinated moiety, and both compounds, to tune nanoscale phase separation and interactions with NIH3T3 fibroblast cells. The focal adhesion formation and morphology of the cells were observed to vary dramatically according to the functionality presented on the surface of the synthetic substrate. It is envisioned that these materials will be useful as substrates that mimic the extracellular matrix (ECM) given that the adhesion receptors of cells can recognize clustered motifs as small as 10 nm, and their spatial orientation can influence cellular responses

Multiscale, Hierarchically Patterned Topography for Directing Human Neural Stem Cells into Functional Neurons

Various biophysical and biochemical factors are important for determining the fate of neural stem cells (NSCs). Among biophysical signals, topographical stimulation by micro/nanopatterns has been applied to control NSC differentiation. In this study, we developed a hierarchically patterned substrate (HPS) platform that can synergistically enhance the differentiation of human NSCs (hNSCs) by simultaneously providing microscale and nanoscale spatial controls to facilitate the alignment of the cytoskeleton and the formation of focal adhesions. The multiscale HPS was fabricated by combining microgroove patterns (groove size: 1.5 μm), prepared by a conventional photolithographic process, and nanopore patterns (pore diameter: 10 nm), prepared from cylinder-forming block copolymer thin films. The hNSCs grown on the HPS exhibited not only a highly aligned, elongated morphology, but also a greatly enhanced differentiation into neuronal and astrocyte lineages, compared to hNSCs on a flat substrate (FS) or single-type patterned substrates [microgroove patterned substrate (MPS) and nanopore patterned substrate (NPS)]. Interestingly, the application of the HPS directed hNSC differentiation toward neurons rather than astrocytes. The expression of focal adhesion proteins in hNSCs was also significantly increased on the HPS compared to the FS, MPS, and NPS, likely a result of the presence of more focal contact points provided by nanopore structures. Inhibition of both β1 integrin-mediated binding and the intracellular Rho-associated protein kinase pathway of hNSCs eliminated the beneficial effects of the HPS on focal adhesion formation and actin filament alignment, which subsequently reduced hNSC differentiation. More importantly, hNSCs on the HPS differentiated into functional neurons exhibiting sodium currents and action potentials. The multiscale, hierarchically patterned topography would be useful for the design of functional biomaterial scaffolds to potentiate NSC therapeutic efficacy