Figure 4. HR-TEM images and FFTs after 50 cycles under 3.0-4.8 V conditions. a) Lattice image of the surface region where (b-e) correspond to the FFTs of Regions 1-4, respectively. (11-1) c is the diffraction spot of the rock salt phase of the metal monoxide.

The ability of surface coatings containing poly(ethylene glycol) (PEG) to prevent nonspecific protein adsorption and cell adhesion has been recognized for decades and has resulted in many biomedical applications of this class of materials.[1] Selfassembled monolayers of oligo(ethylene glycol)-terminated alkanethiols [(EG) n ±SH self-assembled monolayers (SAMs)] present a dense ªnon-foulingº brush that confers protein resistance to gold, and are arguably the best non-fouling systems that are currently available, but they have limited robustness. [2,3] We believe that methods to synthesize non-fouling coatings that combine the advantages of SAMs, namely their high surface density and ease of formation, with those of polymersÐthicker, more robust films and versatile architecture and chemistryÐare of significant interest for a variety of applications. We demonstrate in this paper that (EG) n -functionalized polymer brushes of tunable thickness in the 5±50 nm range, a thickness inaccessible to SAMs or polymer grafts, can be easily synthesized by surface-initiated polymerization (SIP), [4] that these polymer brushes exhibit no detectable adsorption of proteins, and are cell-resistant for up to a month under typical cell culture conditions. We also show that the synthesis method is compatible with a range of patterning techniques from the nano-to the microscale, which enables the patterning of cells in a biologically relevant milieu over extended periods of time. [20,21] These factors contribute to the loss of cell resistance after a week in culture.[2]Surface-initiated polymerization of an (EG) n -functionalized polymer brush was carried out from an alkanethiol SAM on gold, as follows ( Fig. 1A): x-mercaptoundecyl bromoisobutyrate (1) was synthesized as previously described [22] and a SAM of 1 was formed by immersion of a freshly prepared gold substrate in an ethanol solution of 1; [23] in some experiments mixed SAMs were also prepared, where 1 was diluted with 1-undecanethiol (2) to vary the polymer brush density. (2), and a repeat unit of a tethered ªbottleº brush of poly(OEGMA) grown from a mixed SAM of 1 and 2. B) Ellipsometric thickness of the poly(OEGMA) brush, grown from a pure SAM of 1, as a function of polymerization time. The standard deviation (sd) for each data point is < 3 (n = 3). C) Poly(OEGMA) brushes were grown from mixed SAMs of 1 and 2 for a polymerization time of 40 min, and a saturation point in thickness of the polymer brush was observed at a bulk mole fraction of 1 of 0.6 v 1 ; the sd for each data point is < 4 . The lower panel in the figure shows the thickness of the mixed SAM as a function of v 1 . The curves in B and C are simply a guide to the eye.

No abstract

We describe the molecular recognition-mediated, stepwise fabrication of patterned protein nanostructures with feature sizes on the order of 200 nm. First, a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHA) is patterned onto gold by dip-pen nanolithography (DPN), and the unpatterned regions are passivated with a protein-resistant oligoethylene glycol-terminated alkanethiol SAM. Next, an amine-terminated biotin derivative is covalently conjugated with the chemically activated MHA SAM nanopattern. The surface is then incubated with streptavidin to form streptavidin nanostructures, mediated by molecular recognition between biotin and streptavidin. Finally, protein nanopatterns are fabricated by molecular recognition-mediated immobilization of biotinylated protein from solution. Our fabrication methodology is generically applicable because of the ubiquity of biotin-tagged molecules.

Previously reported syngas conversion experiments on silica-supported Rh nanoparticles show that CO conversion and oxygenate selectivity vary as a function of nanoparticle size. Theoretical studies in the literature have examined the effect of steps on CO dissociation, but structure sensitivity for C1 and C2 oxygenates has not been systematically investigated. In this study, density functional theory-based reaction energetics and kinetics for C−H, C−C, C−O, and O−H bond formation on flat Rh(111) and stepped Rh(211) surfaces are reported and compared. Multiple paths for methanol and ethanol formation are considered to ascertain the lowest energy pathways. Nearly an identical methanol formation route via CO → CHO → CH2O → CH3O → CH3OH is found to be favored on both Rh terrace and (211) sites. CO insertion into CH2 is deduced to be the precursor for C2 oxygenate formation irrespective of site structure. Ethanol formation pathways, however, are determined to be markedly different on flat and stepped Rh surfaces in terms of barriers and intermediates. Our results show that reaction pathways are typically preferred on Rh step sites irrespective of the bond-breaking and -making (C−H, C−C, and C−O) reactions considered.

This article describes the fabrication and characterization of stimulus-responsive elastin-like polypeptide (ELP) nanostructures grafted onto omega-substituted thiolates that were patterned onto gold surfaces by dip-pen nanolithography (DPN). In response to external stimuli such as changes in temperature or ionic strength, ELPs undergo a switchable and reversible, hydrophilic-hydrophobic phase transition at a lower critical solution temperature (LCST). We exploited this phase transition behavior to reversibly immobilize a thioredoxin-ELP (Trx-ELP) fusion protein onto the ELP nanopattern above the LCST. Subsequent binding of an anti-thioredoxin monoclonal antibody (anti-Trx) to the surface-captured thioredoxin showed the presentation of the immobilized protein in a sterically accessible orientation in the nanoarray. We also showed that the resulting Trx-ELP/anti-Trx complex formed above the LCST could be reversibly dissociated below the LCST. These results demonstrate the intriguing potential of ELP nanostructures as generic, reversible, biomolecular switches for on-chip capture and release of a small number (order 100-200) of protein molecules in integrated, nanoscale bioanalytical devices. We also investigated the molecular mechanism underlying this switch by measuring the height changes that accompany the binding and desorption steps and by adhesion force spectroscopy using atomic force microscopy.

Microstamping on an activated polymer surface (MAPS) is a methodology that enables biomolecules to be patterned on polymers with micrometer spatial resolution. MAPS combines homogeneous surface derivatization of a polymer to introduce a reactive functional group followed by reactive microcontact printing (µCP) of a biological ligand of interest, linked to an appropriate reactive group. We demonstrate here that polyethylene, polystyrene, poly(methyl methacrylate), and poly(ethylene terephthalate) films can be successfully modified to introduce COOH groups on their surfaces, which can be subsequently patterned by reactive µCP of amine-terminated biotin after derivatization of the COOH groups with pentafluorophenol. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (TOF-SIMS) confirmed the chemistry of MAPS at each stage of the derivatization of the polymer surfaces and reactive µCP of biotin. Micropatterned biotin surfaces fabricated by MAPS were patterned with streptavidin by exploiting molecular recognition between biotin and streptavidin. The formation of streptavidin patterns was examined by fluorescence microscopy of Alexa488-labeled streptavidin and by TOF-SIMS imaging of 15 N-labeled recombinant streptavidin, bound to biotin patterns. The contrast in the streptavidin micropatterns was optimized by examining the effect of blocking agents and streptavidin incubation time. Maximum contrast was obtained for binding of 0.1 µM streptavidin from a buffer containing 0.02% (v/v) Tween 20 detergent for an incubation time of 1 min.

Inadequate rheological properties of gelatin methacrylamide (GelMA) were successfully improved by incorporating cellulose nanofibers (CNFs), such that the printed scaffolds could maintain their structural fidelity during the three-dimensional (3D) bio-printing process. The CNFs provided an outstanding shear thinning property, and the GelMA/CNF inks exhibited high zero shear viscosity and structural fidelity under a low dispensing pressure. After evaluating the printability, composite inks containing 2% w/v CNF were observed to have an optimal concentration of CNF to prepare 3D print stable constructs. Therefore, these inks were used to manufacture human nose and ear structures, producing highly porous structures in the printed composite hydrogels. Furthermore, the mechanical stability of the GelMA/CNF composite hydrogel was increased when CNFs were incorporated, which indicated that CNFs played an important role in enhancing the structural properties of the composite hydrogels. Additionally, the biocompatibility of CNF-reinforced hydrogels was evaluated using a fibroblast cell line.