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Tailoring cell–surface interactions is important for the of design medical implants as well as regenerative medicine and tissue engineering materials. Here the single parameter system is transcended via translating hard nanotopology into soft polymeric hydrogel structures via hydrogel imprinting lithography. The response of these cells to the nanotopology of the same dimensions but with different mechanical properties displays unexpected behavior between “hard” tissue cells and “soft” tissue cells.
Microstructured hydrogel allows for a new template-guided method to obtain conductive nanowire arrays on a large scale. To generate the template, an imprinting process is used in order to synthesize the hydrogel directly into the grooves of wrinkled polydimethylsiloxane (PDMS). The resulting poly(N-vinylimidazole)-based hydrogel is defined by the PDMS stamp in pattern and size. Subsequently, tetrachloroaurate(III) ions from aqueous solution are coordinated within the humps of the N-vinylimidazole-containing polymer template and reduced by air plasma. After reduction and development of the gold, to achieve conductive wires, the extension perpendicular to the long axis (width) of the gold strings is considerably reduced compared to the dimension of the parental hydrogel wrinkles (from approximate to 1 mu m down to 200-300 nm). At the same time, the wire-to-wire distance and the overall length of the wires is preserved. The PDMS templates and hydrogel structures are analyzed with scanning force microscopy (SFM) and the gold structures via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy. The conductivity measurements of the gold nanowires are performed in situ in the SEM, showing highly conductive gold leads. Hence, this method can be regarded as a facile nonlithographic top-down approach from micrometer-sized structures to nanometer-sized features.
Electrostatic attraction between charged nano particles and oppositely charged nanopatterned polymeric films enables tailored structuring of functional nanoscopic surfaces. The bottom-up fabrication of organic/inorganic composites for example bears promising potential toward cheap fabrication of catalysts, optical sensors, and the manufacture of miniaturized electric circuitry. However, only little is known about the time-dependent adsorption behavior and the electronic or ionic charge transfer in the film bulk and at interfaces during nanoparticle assembly via electrostatic interactions. In situ electrochemical impedance spectroscopy (EIS) in combination with a microfluidic system for fast and reproducible liquid delivery was thus applied to monitor the selective deposition of negatively charged gold nanoparticles on top of positively charged poly(2-vinylpyridinium) (qP2VP) domains of phase separated lamellar poly(styrene)-block-poly(2-vinylpyridinium) (PS-b-qP2VP) diblock copolymer thin films. The acquired impedance data delivered information with respect to interfacial charge alteration, ionic diffusion, and the charge dependent nanoparticle adsorption kinetics, considering this yet unexplored system. We demonstrate that the selective adsorption of negatively charged gold nanoparticles (AuNPs) on positively charged qP2VP domains of lamellar PS-b-qP2VP thin films can indeed be tracked by EIS. Moreover, we show that the nanoparticle adsorption kinetics and the nanoparticle packing density are functions of the charge density in the qP2VP domains.
It has long been appreciated that material chemistry and topology profoundly affect cell adhesion and migration. Here, aqueous poly(N- isopropyl acrylamide) nanogels are designed, synthesized and printed in form of colloidal arrays on glass substrates using wrinkled polydimethylsiloxane templates. Using low-temperature plasma treatment, nanogels are chemically grafted onto glass supports thus leading to highly stable nanogel layers in cell culture media. Liquid cell atomic force microscopy investigations show that surface-grafted nanogels retain their swelling behavior in aqueous media and that extracellular matrix protein coating do not alter their stability and topography. It is demonstrated that surface-grafted nanogels could serve as novel substrates for the analysis of cell adhesion and migration. Nanogels influence size, speed, and dynamics of focal adhesions and cell motility forcing cells to move along highly directional trajectories. Moreover, modulation of nanogel state or spacing serves as an effective tool for regulation of cell motility. It is suggested that nanogel arrays deposited on solid surfaces could be used to provide a precise and tunable system to understand and control cell migration. Additionally, such nanogel arrays will contribute to the development of implantable systems aimed at supporting and enhancing cell migration during, for instance, wound healing and tissue regeneration.
Due to the ability of microgels to rapidly contract and expand in response to external stimuli, assemblies of interconnected microgels are promising for actuation applications, e.g., as contracting fibers for artificial muscles. Among the properties determining the suitability of microgel assemblies for actuation are mechanical parameters such as bending stiffness and mobility. Here, we study the properties of linear, one-dimensional chains of poly(N-vinylcaprolactam) microgels dispersed in water. They were fabricated by utilizing wrinkled surfaces as templates and UV-cross-linking the microgels. We image the shapes of the chains on surfaces and in solution using atomic force microscopy (AFM) and fluorescence microscopy, respectively. In solution, the chains are observed to execute translational and rotational diffusive motions. Evaluation of the motions yields translational and rotational diffusion coefficients and, from the translational diffusion coefficient, the chain mobility. The microgel chains show no perceptible bending, which yields a lower limit on their bending stiffness.
A localized surface plasmon resonance biosensor in a flow-through configuration was applied for investigating kinetics of lectin binding to surface-grafted glycopolymer brushes. Polycarbonate filter membranes with pore sizes of 400 nm were coated with a 114-nm thick gold layer and used as substrate for surface-initiated atom-transfer radical polymerization of a glycomonomer. These grafted from glycopolymer brushes were further modified with two subsequent enzymatic reactions on the surface to yield an immobilized trisaccharide presenting brush. Specific binding of lectins including Clostridium difficile toxin A receptor domain to the glycopolymer brush surface could be investigated in a microfluidic setup with flow-through of the analytes and transmission surface plasmon resonance spectroscopy.
Hydrophobins are highly surface active proteins which self-assemble at hydrophilic-hydrophobic interfaces into amphipathic membranes. We investigate hydrophobin self-assembly at oil/water interfaces to deepen the understanding of protein behavior in order to improve our biomimetic synthesis. Therefore, we carried out pendant drop measurements of hydrophobin stabilized oil/water systems determining the time-dependent IFT and the dilatational rheology with additional adaptation to the Serrien protein model. We show that the class I hydrophobin H*Protein B adsorbs at an oil/water interface where it forms a densely-packed interfacial protein layer, which dissipates energy during droplet oscillation. Furthermore, the interfacial protein layer exhibits shear thinning behavior. (C) 2016 Elsevier Inc. All rights reserved.
Templates of complex nanopatterns in a form of hierarchically sequenced dots and stripes can be generated in block copolymer films on lithography-free 3D topographic substrates. The approach exploits thickness- and swelling-responsive morphological behavior of block copolymers, and demonstrates novel possibilities of topography-guided registration of nanopatterns due to periodic confinement and spontaneous orthogonal flow-fields.
We introduce a novel double-hydrophilic hydroxyethylmethacrylate (HEMA) based diblock glycopolymer which self-assembles into homogeneous spherical micellar structures in water. The micellar structure renders surface-oriented N-acetylglucocosamine (GlcNAc) sugar moieties for strong multivalent glycan-mediated lectin binding. Structural analysis and lectin binding is performed by microscopy methods, dynamic light scattering (DLS) and two-focus fluorescence correlation spectroscopy (2fFCS), revealing a novel micellar type of multivalent sugar binding scaffold with high potential for biomedical applications.