Nanoscale Surface Chemical Patterning of Soft Polyacrylamide with Elastic Modulus Similar to Soft Tissue

Nanometer-scale control over surface functionalization of soft gels is important for a variety of applications including controlling interactions with cells for in vitro cell culture and for regenerative medicine. Recently, we have shown that it is possible to transfer a nanometer-thick precision functional polymer layer to the surface of relatively stiff polyacrylamide gels. Here, we develop a fundamental understanding of the way in which the precision polymer backbone participates in the polyacrylamide radical polymerization and cross-linking process, which enables us to generate high-efficiency transfer to much softer hydrogels (down to 5 kPa) with stiffness similar to that of soft tissue. This approach creates hydrogel surfaces with exposed nanostructured functional arrays that open the door to controlled ligand presentation on soft hydrogel surfaces.

Sub-10 μm Soft Interlayers Integrating Patterned Multivalent Biomolecular Binding Environments

Designing surfaces that enable controlled presentation of multivalent ligand clusters (e.g., for rapid screening of biomolecular binding constants or design of artificial extracellular matrices) is a cross-cutting challenge in materials and interfacial chemistry. Existing approaches frequently rely on complex building blocks or scaffolds and are often specific to individual substrate chemistries. Thus, an interlayer chemistry that enabled efficient nanometer-scale patterning on a transferrable layer and subsequent integration with other classes of materials could substantially broaden the scope of surfaces available for sensors and wearable electronics. Recently, we have shown that it is possible to assemble nanometer-resolution chemical patterns on substrates including graphite, use diacetylene polymerization to lock the molecular pattern together, and then covalently transfer the pattern to amorphous materials (e.g., polydimethylsiloxane, PDMS), which would not natively enable high degrees of control over ligand presentation. Here, we develop a low-viscosity PDMS formulation that generates very thin films (<10 μm) with dense cross-linking, enabling high-efficiency surface functionalization with polydiacetylene arrays displaying carbohydrates and other functional groups (up to 10-fold greater than other soft materials we have used previously) on very thin films that can be integrated with other materials (e.g., glass and soft materials) to enable a highly controlled multivalent ligand display. We use swelling and other characterization methods to relate surface functionalization efficiency to the average distance between cross-links in the PDMS, developing design principles that can be used to create even thinner transfer layers. In the context of this work, we apply this approach using precision glycopolymers presenting structured arrays of N-acetyl glucosamine ligands for lectin binding assays. More broadly, this interlayer approach lays groundwork for designing surface layers for the presentation of ligand clusters on soft materials for applications including wearable electronics and artificial extracellular matrix.

Inkjet Printing of Nanoscale Functional Patterns on 2D Crystalline Materials and Transfer to Soft Materials

Nanometer-scale control over surface functionality is important in applications ranging from nanoscale electronics to regenerative medicine. However, approaches that provide precise control over surface chemistry at the nanometer scale are often challenging to use with higher throughput and in more heterogeneous environments (e.g., complex solutions, porous interfaces) common for many applications. Here, we demonstrate a scalable inkjet-based method to generate 1 nm-wide functional patterns on 2D materials such as graphite, which can then be transferred to soft materials such as hydrogels. We examine fluid dynamics associated with the inkjet printing process for low-viscosity amphiphile inks designed to maximize ordering with limited residue and show that microscale droplet fluid dynamics influence nanoscale molecular ordering. Additionally, we show that scalable patterns generated in this way can be transferred to hydrogel materials and used to create surface chemical patterns that induce adsorption of charged particles, with effects strong enough to overcome electrostatic repulsion between a charged hydrogel and a like-charged nanoparticle.

Surface-Templated Glycopolymer Nanopatterns Transferred to Hydrogels for Designed Multivalent Carbohydrate-Lectin Interactions across Length Scales

Multivalent interactions between carbohydrates and proteins enable a broad range of selective chemical processes of critical biological importance. Such interactions can extend from the macromolecular scale (1-10 nm) up to much larger scales across a cell or tissue, placing substantial demands on chemically patterned materials aiming to leverage similar interactions in vitro. Here, we show that diyne amphiphiles with carbohydrate headgroups can be assembled on highly oriented pyrolytic graphite (HOPG) to generate nanometer-resolution carbohydrate patterns, with individual linear carbohydrate assemblies up to nearly 1 μm, and microscale geometric patterns. These are then photopolymerized and covalently transferred to the surfaces of hydrogels. This strategy suspends carbohydrate patterns on a relatively rigid polydiacetylene (persistence length ∼ 16 nm), exposed at the top surface of the hydrogel above the bulk pore structure. Transferred patterns of appropriate carbohydrates (e.g., N-acetyl-d-glucosamine, GlcNAc) enable selective, multivalent interactions (K_D ∼ 40 nM) with wheat germ agglutinin (WGA), a model lectin that exhibits multivalent binding with appropriately spaced GlcNAc moieties. WGA binding affinity can be further improved (K_D ∼ 10 nM) using diacetylenes that shift the polymer backbone closer to the displayed carbohydrate, suggesting that this strategy can be used to modulate carbohydrate presentation at interfaces. Conversely, GlcNAc-patterned surfaces do not induce specific binding of concanavalin A, and surfaces patterned with glucuronic acid, or with simple carboxylic acid or hydroxyl groups, do not induce WGA binding. More broadly, this approach may have utility in designing synthetic glycan-mimetic interfaces with features from molecular to mesoscopic scales, including soft scaffolds for cells.

Halogen bond-directed self-assembly in bicomponent blends at the solid/liquid interface: Effect of the alkyl chain substitution position

The fabrication of well-organised molecular assemblies on surfaces is fundamental for the creation of functional molecular systems applicable to nanoelectronics and molecular devices. In this study, we investigated the effect...

Lipids: An Atomic Toolkit for the Endless Frontier

The evolution of lipids in nanoscience exemplifies the powerful coupling of advances in science and technology. Here, we describe two waves of discovery and innovation in lipid materials: one historical and one still building. The first wave leveraged the relatively simple capability for lipids to orient at interfaces, building layers of functional groups. This simple form of building with atoms yielded a stunning range of technologies: lubricant additives that dramatically extended machine lifetimes, molecules that enabled selective ore extraction in mining, and soaps that improved human health. It also set the stage for many areas of modern nanoscience. The second wave of lipid materials, still growing, uses the more complex toolkits lipids offer for building with atoms, including controlling atomic environment to control function (e.g., pK_a tuning) and the generation of more arbitrary two-dimensional and three-dimensional structures, including lipid nanoparticles for COVID-19 mRNA vaccines.

Large-Scale Noncovalent Functionalization of 2D Materials through Thermally Controlled Rotary Langmuir-Schaefer Conversion

As two-dimensional (2D) materials are more broadly utilized as components of hybrid materials, controlling their surface chemistry over large areas through noncovalent functionalization becomes increasingly important. Here, we demonstrate a thermally controlled rotary transfer stage that allows areas of a 2D material to be continuously cycled into contact with a Langmuir film. This approach enables functionalization of large areas of the 2D material and simultaneously improves long-range ordering, achieving ordered domain areas up to nearly 10 000 μm². To highlight the layer-by-layer processing capability of the rotary transfer stage, large-area noncovalently adsorbed monolayer films from an initial rotary cycle were used as templates to assemble ultranarrow gold nanowires from solution. The process we demonstrate would be readily extensible to roll-to-roll processing, addressing a longstanding challenge in scaling Langmuir-Schaefer transfer for practical applications.

Hierarchically patterned striped phases of polymerized lipids: toward controlled carbohydrate presentation at interfaces

Microcontact printing can be used to generate well-defined microscopic areas of striped phases of both single-chain and dual-chain amphiphiles.

Probing functional self-assembled molecular architectures with solution/solid scanning tunnelling microscopy

Over the past two decades, solution/solid STM has made clear contributions to our fundamental understanding of the thermodynamic and kinetic processes that occur in molecular self-assembly at surfaces. As the field matures, we provide an overview of how solution/solid STM is emerging as a tool to elucidate and guide the use of self-assembled molecular systems in practical applications, focusing on small molecule device engineering, molecular recognition and sensing and electronic modification of 2D materials.

Edge-on adsorption of multi-chain functional alkanes stabilizes noncovalent monolayers on MoS2

Diyne phospholipids adsorb edge-on on MoS₂, producing stable monolayers with large, ordered domains, despite low alkane adsorption enthalpies on MoS₂.