Hemp-Based Sustainable Slippery Surfaces: Icephobic and Antithrombotic Properties.

With the passage of the 2018 Farm Bill that removed hemp from the Controlled Substances Act altogether, production of hemp is experiencing a renaissance. Building on this revival and re-emergence of hemp, we designed and fabricated hemp-based sustainable and robust slippery surfaces by coating hemp paper with beeswax and subsequently infusing it with hemp oil. A wide variety of aqueous liquids and beverages easily slide on our hemp-based sustainable slippery surfaces, without leaving a trace. We also fabricated hemp-based sustainable slippery surfaces using different textured metals. Our hemp-based sustainable slippery metal surfaces display good icephobic and antithrombotic properties. With these attributes, we envision that our hemp-based sustainable slippery surfaces will pave the path to more safe, non-toxic, and biodegradable or recyclable slippery surfaces for applications in food packaging, anti-icing or de-icing coatings, and antithrombotic medical devices.

Wettability-based ultrasensitive detection of amphiphiles through directed concentration at disordered regions in self-assembled monolayers.

Various forms of ecological monitoring and disease diagnosis rely upon the detection of amphiphiles, including lipids, lipopolysaccharides, and lipoproteins, at ultralow concentrations in small droplets. Although assays based on droplets' wettability provide promising options in some cases, their reliance on the measurements of surface and bulk properties of whole droplets (e.g., contact angles, surface tensions) makes it difficult to monitor trace amounts of these amphiphiles within small-volume samples. Here, we report a design principle in which self-assembled monolayer-functionalized microstructured surfaces coated with silicone oil create locally disordered regions within a droplet's contact lines to effectively concentrate amphiphiles within the areas that dominate the droplet static friction. Remarkably, such surfaces enable the ultrasensitive, naked-eye detection of amphiphiles through changes in the droplets' sliding angles, even when the concentration is four to five orders of magnitude below their critical micelle concentration. We develop a thermodynamic model to explain the partitioning of amphiphiles at the contact line by their cooperative association within the disordered, loosely packed regions of the self-assembled monolayer. Based on this local analyte concentrating effect, we showcase laboratory-on-a-chip surfaces with positionally dependent pinning forces capable of both detecting industrially and biologically relevant amphiphiles (e.g., bacterial endotoxins), as well as sorting aqueous droplets into discrete groups based on their amphiphile concentrations. Furthermore, we demonstrate that the sliding behavior of amphiphile-laden aqueous droplets provides insight into the amphiphile's effective length, thereby allowing these surfaces to discriminate between analytes with highly disparate molecular sizes.

Modularizable Liquid-Crystal-Based Open Surfaces Enable Programmable Chemical Transport and Feeding using Liquid Droplets.

Droplet-based miniature reactors have attracted interest in both fundamental studies, for the unique reaction kinetics they enable, and applications in bio-diagnosis and material synthesis. However, the precise and automatic feeding of chemicals, important for the delicate reactions in these miniaturized chemical reactors, either requires complex, high-cost microfluidic devices or lacks the capability to maintain a pinning-free droplet movement. Here, the design and synthesis of a new class of liquid crystal (LC)-based open surfaces, which enable a controlled chemical release via a programmable LC phase transition without sacrificing the free transport of the droplets, are reported. It is demonstrated that their intrinsic slipperiness and self-healing properties enable a modularizable assembly of LC surfaces that can be loaded with different chemicals to achieve a wide range of chemical reactions carried out within the droplets, including sequential and parallel chemical reactions, crystal growth, and polymer synthesis. Finally, an LC-based chemical feeding device is developed that can automatically control the release of chemicals to direct the simultaneous differentiation of human induced pluripotent stem cells into endothelial progenitor cells and cardiomyocytes. Overall, these LC surfaces exhibit desirable levels of automation, responsiveness, and controllability for use in miniature droplet carriers and reactors.

Liquid crystal-based open surface microfluidics manipulate liquid mobility and chemical composition on demand.

The ability to control both the mobility and chemical compositions of microliter-scale aqueous droplets is an essential prerequisite for next-generation open surface microfluidics. Independently manipulating the chemical compositions of aqueous droplets without altering their mobility, however, remains challenging. In this work, we address this challenge by designing a class of open surface microfluidic platforms based on thermotropic liquid crystals (LCs). We demonstrate, both experimentally and theoretically, that the unique positional and orientational order of LC molecules intrinsically decouple cargo release functionality from droplet mobility via selective phase transitions. Furthermore, we build sodium sulfide­loaded LC surfaces that can efficiently precipitate heavy metal ions in sliding water droplets to final concentration less than 1 part per million for more than 500 cycles without causing droplets to become pinned. Overall, our results reveal that LC surfaces offer unique possibilities for the design of novel open surface fluidic systems with orthogonal functionalities.

Design of a Waste Paper-Derived Chemically 'Reactive' and Durable Functional Material with Tailorable Mechanical Property Following an Ambient and Sustainable Chemical Approach.

Controlled tailoring of mechanical property and wettability is important for designing various functional materials. The integration of these characteristics with waste materials is immensely challenging to achieve, however, it can provide sustainable solutions to combat relevant environmental pollutions and other relevant challenges. Here, the strategic conversion of discarded and valueless waste paper into functional products has been introduced following a catalyst-free chemical approach to tailor both the mechanical property and water wettability at ambient conditions for sustainable waste management and controlling the relevant environmental pollution. In the current design, the controlled and appropriate silanization of waste paper allowed to modulate both the a) porosity and b) compressive modulus of the paper-derived sponges. Further, the association of 1,4-conjugate addition reaction between amine and acrylate groups allowed to obtain an unconventional waste paper-derived chemically 'reactive' sponge. The appropriate covalent modification of the residual reactive acrylate groups with selected alkylamines at ambient conditions provided a facile basis to tailor the water wettability from moderate hydrophobicity, adhesive superhydrophobicity to non-adhesive superhydrophobicity. The embedded superhydrophobicity in the waste paper-derived sponge was capable of sustaining large physical deformations, severe physical abrasions, prolonged exposure to harsh aqueous conditions, etc. Further, the waste paper-derived, extremely water-repellent sponges and membranes were successfully extended for proof-of-concept demonstration of a practically relevant outdoor application, where the repetitive remediation of oil spillages has been demonstrated following both selective absorption (25 times) of oils and gravity-driven filtration-based (50 times) separation of oils from oil/water mixtures at different harsh aqueous scenarios.

Unconventional and Facile Fabrication of Chemically Reactive Silk Fibroin Sponges for Environmental Remediation.

Silk fibroin and silk microfibers, both derived from silk cocoon, have been widely used for prospective biomedical, energy, and environmental applications. However, various complex and catalyst-based approaches have been adopted for chemical modification and integration of different functionalities in silk fibroin-based materials. Here, both tailored water wettability and mechanical property have been associated with silk microfiber reinforced silk fibroin sponges (SMFRSFSs) through the strategic introduction of ß-sheets and a facile and catalyst-free chemical reaction at ambient conditions. While the controlled tailoring of ß-sheets in the silk fibroin skeletal framework of the sponges allowed us to modulate the compressive modulus, the 1,4-conjugate addition reaction between amine residues of silk (fiber and fibroin) and acrylate groups of a multifunctional cross-linker provided residual chemical reactivity. Further, the chemically "reactive" sponge was postmodified with the selected alkylamines to introduce a wide range of water wettability (from 36 to 161°) without affecting the mechanical property. Thereafter, the silk cocoon-derived and extremely water-repellent sponge was used for environment-friendly cleaning of oil spillages through selective absorption-based and filtration-based oil/water separation at different and severe aqueous conditions. This silk cocoon-derived mechanically tailorable and chemically reactive sponge could also be useful for various biomedical and energy-related applications.

Ultrasensitive and Selective Detection of SARS-CoV-2 Using Thermotropic Liquid Crystals and Image-Based Machine Learning.

Rapid, robust virus-detection techniques with ultrahigh sensitivity and selectivity are required for the outbreak of the pandemic coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). Here, we report that the femtomolar concentrations of single-stranded ribonucleic acid (ssRNA) of SARS-CoV-2 trigger ordering transitions in liquid crystal (LC) films decorated with cationic surfactant and complementary 15-mer single-stranded deoxyribonucleic acid (ssDNA) probe. More importantly, the sensitivity of the LC to the SARS ssRNA, with a 3-bp mismatch compared to the SARS-CoV-2 ssRNA, is measured to decrease by seven orders of magnitude, suggesting that the LC ordering transitions depend strongly on the targeted oligonucleotide sequence. Finally, we design a LC-based diagnostic kit and a smartphone-based application (app) to enable automatic detection of SARS-CoV-2 ssRNA, which could be used for reliable self-test of SARS-CoV-2 at home without the need for complex equipment or procedures.

Correction: Simultaneous and controlled release of two different bioactive small molecules from nature inspired single material.

Correction for 'Simultaneous and controlled release of two different bioactive small molecules from nature inspired single material' by Adil M. Rather et al., J. Mater. Chem. B, 2018, 6, 7692-7702.

Green and Rapid Synthesis of Durable and Super-Oil (under Water) and Water (in Air) Repellent Interfaces.

In this letter, a single polymer is rapidly and covalently transformed into a chemically reactive and functional bulk polymeric coatings through a catalyst-free mutual chemical reaction between acrylates and amine groups at ambient condition-in the absence of any external reaction solvent, which is unprecedented in the literature. This facile and green chemical approach provided a common basis for achieving two distinct biomimicked wettabilities-that are superhydrophobicity (lotus-leaf mimicked) in air and superoleophobicity (fish-scale inspired) under water. The essential chemistry that conferred bioinspired wettability was optimized in the hierarchically featured polymeric material by postcovalent modulation of chemically reactive polymeric material with primary-amine-containing small moleculess, glucamine and octadecylamine. The inherently sticky and "chemically reactive" polymeric material having appropriate hierarchical topography is highly capable of providing substrate-independent (irrespective of chemical compositions and mechanical strength of the substrates) stable coatings with robust bioinspired (i.e., lotus leaf and fish scale) wettability.

Simultaneous and controlled release of two different bioactive small molecules from nature inspired single material.

Extended and controlled release of more than a single bioactive molecule, simultaneously, from the same biocompatible matrix is challenging to achieve. However, this is important for combating various severe challenges (drug resistance, improved efficacy, etc.) related to drug delivery. In the recent past, the meta-stable trapped air (in the lotus leaf inspired artificial interfaces), which attributed to the extreme water repellency in biomimicked heirarchical (consisted of micro/nano features) interfaces, was unprecedentedly exploited for addressing multiple relevant aspects related to drug delivery (e.g., multiple drug release, tunable drug release, dose control through post-loading of drug molecules, etc.). A biocompatible polymeric material that is (a) synthesized using a one-step covalent and featured gelation of a single polymer and (b) capable of tailoring with a wide range of water wettabilities, was exploited for post loading both hydrophilic and hydrophobic small molecules from a wide variety (less polar, more polar, nonpolar) of organic solvents. Such small molecules loaded polymeric materials continued to display durable nature-inspired bulk wettability and provided simultaneous co-release of two different bioactive drug molecules (i.e., doxorubicin (DOX, anticancer drug) and tetracycline (TC, antibacterial drug)), over 6 months. Moreover, the release extent (from hours to months) of these small molecules was successfully tuned by controlling the water wettability of the single porous polymeric material. The released drug molecules remained bioactive and capable of inhibiting the proliferation of cancer cells (MG-63 (human osteosarcoma) and MDA-MB-231 (human breast adenocarcinoma)) and microorganisms (S. aureus and E. coli). These results provide a facile basis for developing a more potent and multifunctional drug release system for prospective biomedical applications.

Strategic Formulation of Graphene Oxide Sheets for Flexible Monoliths and Robust Polymeric Coatings Embedded with Durable Bioinspired Wettability †.

Artificial bioinspired superhydrophobicity, which is generally developed through appropriate optimization of chemistry and hierarchical topography, is being recognized for its immense prospective applications related to environment and healthcare. Nevertheless, the weak interfacial interactions that are associated with the fabrication of such special interfaces often provide delicate biomimicked wettability, and the embedded antifouling property collapses on exposure to harsh and complex aqueous phases and also after regular physical deformations, including bending, creasing, etc. Eventually, such materials with potential antifouling property became less relevant for practical applications. Here, a facile, catalyst-free, and robust 1,4-conjugate addition reaction has been strategically exploited for appropriate covalent integration of modified graphene oxide to developing polymeric materials with (1) tunable mechanical properties and (2) durable antifouling property, which are capable of performing both in air and under oil. Furthermore, this approach provided a facile basis for (3) engineering a superhydrophobic monolith into arbitrary free-standing shapes and (4) decorating various flexible (metal, synthetic plastic, etc.) and rigid (glass, wood, etc.) substrates with thick and durable three-dimensional superhydrophobic coatings. The synthesized superhydrophobic monoliths and polymeric coatings with controlled mechanical properties are appropriate to withstand different physical insults, including twisting, creasing, and even physical erosion of the material, without compromising the embedded antiwetting property. The materials are also equally resistant to various harsh chemical environments, and the embedded antifouling property remained unperturbed even after continuous exposure to extremes of pH (pH 1 and pH 11), artificial sea water for a minimum of 30 days. These flexible and formable free-standing monoliths and stable polymeric coatings that are extremely water-repellent both in air and under oil, are of utmost importance owing to their suitability in practical circumstances and robust nature.