Highly Selective Vertically Aligned Nanopores in Sustainably Derived Polymer Membranes by Molecular Templating

We describe a combination of molecular templating and directed self-assembly to realize highly selective vertically aligned nanopores in polymer membranes using sustainably derived materials. The approach exploits a structure-directing molecule to template the assembly of plant-derived fatty acids into highly ordered columnar mesophases. Directed self-assembly using physical confinement and magnetic fields provides vertical alignment of the columnar nanostructures in large area (several cm²) thin films. Chemically cross-linking the mesophase with added conventional vinyl comonomers and removing the molecular template results in a mechanically robust polymer film with vertically aligned 1.2–1.5 nm diameter nanopores with a large specific surface area of ∼670 m²/g. The nanoporous polymer films display exceptional size and charge selectivity as demonstrated by adsorption experiments using model penetrant molecules. These materials have significant potential to function as high-performance nanofiltration membranes and as nanoporous thin films for high-density lithographic pattern transfer. The scalability of the fabrication process suggests that practical applications can be reasonably anticipated

Photoresponsive and Magnetoresponsive Graphene Oxide Microcapsules Fabricated by Droplet Microfluidics

Fluid compartmentalization by microencapsulation is important in scenarios where protection or controlled release of encapsulated species, or isolation of chemical transformations is the central concern. Realizing responsive encapsulation systems by incorporating functional nanomaterials is of particular interest. We report here on the development of graphene oxide microcapsules enabled by a single-step microfluidic process. Interfacial reaction of epoxide-bearing graphene oxide sheets and an amine-functionalized macromolecular silicone fluid creates a chemically cross-linked film with micronscale thickness at the surface of water-in-oil droplets generated by microfluidic devices. The resulting microcapsules are monodisperse, mechanically resilient, and shape-tunable constructs. Ferrite nanoparticles are incorporated via the aqueous phase and enable microcapsule positioning by a magnetic field. We exploit the photothermal response of graphene oxide to realize microcapsules with photoresponsive release characteristics and show that the microcapsule permeability is significantly enhanced by near-IR illumination. The dual magnetic and photoresponsive characteristics, combined with the use of a single-step process employing biocompatible fluids, represent highly compelling aspects for practical applications

Photoresponsive and Magnetoresponsive Graphene Oxide Microcapsules Fabricated by Droplet Microfluidics

Fluid compartmentalization by microencapsulation is important in scenarios where protection or controlled release of encapsulated species, or isolation of chemical transformations is the central concern. Realizing responsive encapsulation systems by incorporating functional nanomaterials is of particular interest. We report here on the development of graphene oxide microcapsules enabled by a single-step microfluidic process. Interfacial reaction of epoxide-bearing graphene oxide sheets and an amine-functionalized macromolecular silicone fluid creates a chemically cross-linked film with micronscale thickness at the surface of water-in-oil droplets generated by microfluidic devices. The resulting microcapsules are monodisperse, mechanically resilient, and shape-tunable constructs. Ferrite nanoparticles are incorporated via the aqueous phase and enable microcapsule positioning by a magnetic field. We exploit the photothermal response of graphene oxide to realize microcapsules with photoresponsive release characteristics and show that the microcapsule permeability is significantly enhanced by near-IR illumination. The dual magnetic and photoresponsive characteristics, combined with the use of a single-step process employing biocompatible fluids, represent highly compelling aspects for practical applications

Facile Protein Immobilization Using Engineered Surface-Active Biofilm Proteins

Immobilization of enzymes and other biomolecules to surfaces is critically important for biotechnology, with important applications in sensing and controlled delivery of molecular species for analytical or biomedical purposes. The presentation of protein recognition elements in a way that avoids denaturation and nonspecific interactions while maintaining the accessibility of the active site is a challenge for which no general solution has been found. Here we present a robust, facile method for immobilization of any protein to a surface using engineered protein building blocks. By functionalizing an interfacial protein, BslA, with peptides (SpyTag and SnoopTag) that spontaneously react with their cognate protein partners (SpyCatcher and SnoopCatcher), we are able to create patterned surfaces of protein monolayers displaying reactive tags. We demonstrate that these surfaces can be functionalized rapidly, spontaneously, and specifically with proteins of interest attached to SpyCatcher or SnoopCatcher. This method both protects the surface from nonspecific adsorption and also presents the recognition element in a uniform, active conformation. We envision that this method will have widespread applications, including immobilization of therapeutically relevant proteins for diagnostic applications

Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA

Protein adsorption and assembly at interfaces provide a potentially versatile route to create useful constructs for fluid compartmentalization. In this context, we consider the interfacial assembly of a bacterial biofilm protein, BslA, at air–water and oil–water interfaces. Densely packed, high modulus monolayers form at air–water interfaces, leading to the formation of flattened sessile water drops. BslA forms elastic sheets at oil–water interfaces, leading to the production of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil microcapsules are unstable but display arrested rather than full coalescence on contact. The disparity in stability likely originates from a low areal density of BslA hydrophobic caps on the exterior surface of water-in-oil microcapsules, relative to the inverse case. In direct analogy with small molecule surfactants, the lack of stability of individual water-in-oil microcapsules is consistent with the large value of the hydrophilic–lipophilic balance (HLB number) calculated based on the BslA crystal structure. The occurrence of arrested coalescence indicates that the surface activity of BslA is similar to that of colloidal particles that produce Pickering emulsions, with the stability of partially coalesced structures ensured by interfacial jamming. Micropipette aspiration and flow in tapered capillaries experiments reveal intriguing reversible and nonreversible modes of mechanical deformation, respectively. The mechanical robustness of the microcapsules and the ability to engineer their shape and to design highly specific binding responses through protein engineering suggest that these microcapsules may be useful for biomedical applications

Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA

Protein adsorption and assembly at interfaces provide a potentially versatile route to create useful constructs for fluid compartmentalization. In this context, we consider the interfacial assembly of a bacterial biofilm protein, BslA, at air–water and oil–water interfaces. Densely packed, high modulus monolayers form at air–water interfaces, leading to the formation of flattened sessile water drops. BslA forms elastic sheets at oil–water interfaces, leading to the production of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil microcapsules are unstable but display arrested rather than full coalescence on contact. The disparity in stability likely originates from a low areal density of BslA hydrophobic caps on the exterior surface of water-in-oil microcapsules, relative to the inverse case. In direct analogy with small molecule surfactants, the lack of stability of individual water-in-oil microcapsules is consistent with the large value of the hydrophilic–lipophilic balance (HLB number) calculated based on the BslA crystal structure. The occurrence of arrested coalescence indicates that the surface activity of BslA is similar to that of colloidal particles that produce Pickering emulsions, with the stability of partially coalesced structures ensured by interfacial jamming. Micropipette aspiration and flow in tapered capillaries experiments reveal intriguing reversible and nonreversible modes of mechanical deformation, respectively. The mechanical robustness of the microcapsules and the ability to engineer their shape and to design highly specific binding responses through protein engineering suggest that these microcapsules may be useful for biomedical applications

Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA

Protein adsorption and assembly at interfaces provide a potentially versatile route to create useful constructs for fluid compartmentalization. In this context, we consider the interfacial assembly of a bacterial biofilm protein, BslA, at air–water and oil–water interfaces. Densely packed, high modulus monolayers form at air–water interfaces, leading to the formation of flattened sessile water drops. BslA forms elastic sheets at oil–water interfaces, leading to the production of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil microcapsules are unstable but display arrested rather than full coalescence on contact. The disparity in stability likely originates from a low areal density of BslA hydrophobic caps on the exterior surface of water-in-oil microcapsules, relative to the inverse case. In direct analogy with small molecule surfactants, the lack of stability of individual water-in-oil microcapsules is consistent with the large value of the hydrophilic–lipophilic balance (HLB number) calculated based on the BslA crystal structure. The occurrence of arrested coalescence indicates that the surface activity of BslA is similar to that of colloidal particles that produce Pickering emulsions, with the stability of partially coalesced structures ensured by interfacial jamming. Micropipette aspiration and flow in tapered capillaries experiments reveal intriguing reversible and nonreversible modes of mechanical deformation, respectively. The mechanical robustness of the microcapsules and the ability to engineer their shape and to design highly specific binding responses through protein engineering suggest that these microcapsules may be useful for biomedical applications

Fabrication of Modularly Functionalizable Microcapsules Using Protein-Based Technologies

Proteins are desirable building blocks to create self-assembled, spatially defined structures and interfaces on length-scales that are inaccessible by traditional methods. Here, we describe a novel approach to create functionalized monolayers using the proteins BslA and SpyCatcher/SpyTag. BslA is a bacterial hydrophobin whose amphiphilic character underlies its ability to assemble into a monolayer at both air/water and oil/water interfaces. We demonstrate that Bsa1A having the SpyTag peptide fused at the N- or C-terminus does not affect the formation of such monolayers. We establish the creation of stable oil-in-water microcapsules using BslA, and also show the fabrication of capsules outwardly displaying the reactive SpyTag peptide by fusing it to the C-terminus of BslA. Such capsules can be covalently labeled by reacting the surface-displayed SpyTag with SpyCatcher fused to any desired protein. We demonstrate this principle by labeling microcapsules using green fluorescent protein (GFP). All components are genetically encodable, the reagents can be readily prepared in large quantities, and all reactions occur at ambient temperature in aqueous solution. Thus, this straightforward, modular, scalable strategy has myriad potential applications in the creation of novel, functional materials, and interfaces