Bioinspired superhydrophobic surfaces with silver and nitric oxide-releasing capabilities to prevent device-associated infections and thrombosis.

Bacteria-associated infections and thrombus formation are the two major complications plaguing the application of blood-contacting medical devices. Therefore, functionalized surfaces and drug delivery for passive and active antifouling strategies have been employed. Herein, we report the novel integration of bio-inspired superhydrophobicity with nitric oxide release to obtain a functional polymeric material with anti-thrombogenic and antimicrobial characteristics. The nitric oxide release acts as an antimicrobial agent and platelet inhibitor, while the superhydrophobic components prevent non-specific biofouling. Widely used medical-grade silicone rubber (SR) substrates that are known to be susceptible to biofilm and thrombus formation were dip-coated with fluorinated silicon dioxide (SiO2) and silver (Ag) nanoparticles (NPs) using an adhesive polymer as a binder. Thereafter, the resulting superhydrophobic (SH) SR substrates were impregnated with S-nitroso-N-acetylpenicillamine (SNAP, an NO donor) to obtain a superhydrophobic, Ag-bound, NO-releasing (SH-SiAgNO) surface. The SH-SiAgNO surfaces had the lowest amount of viable adhered E. coli (> 99.9 % reduction), S. aureus (> 99.8 % reduction), and platelets (> 96.1 % reduction) as compared to controls while demonstrating no cytotoxic effects on fibroblast cells. Thus, this innovative approach is the first to combine SNAP with an antifouling SH polymer surface that possesses the immense potential to minimize medical device-associated complications without using conventional systemic anticoagulation and antibiotic treatments.

Chemical Modification of Tiopronin for Dual Management of Cystinuria and Associated Bacterial Infections.

Cystinuria is an inherited autosomal recessive disease of the kidneys of recurring nature that contributes to frequent urinary tract infections due to bacterial growth and biofilm formation surrounding the stone microenvironment. In the past, commonly used strategies for managing cystinuria involved the use of (a) cystine crystal growth inhibitors such as l-cystine dimethyl ester and lipoic acid, and (b) thiol-based small molecules such as N-(2-mercaptopropionyl) glycine, commonly known as tiopronin, that reduce the formation of cystine crystals by reacting with excess cystine and generating more soluble disulfide compounds. However, there is a dearth of simplistic chemical approaches that have focused on the dual treatment of cystinuria and the associated microbial infections. This work strategically exploited a single chemical approach to develop a nitric oxide (NO)-releasing therapeutic compound, S-nitroso-2-mercaptopropionyl glycine (tiopronin-NO), for the dual management of cystine stone formation and the related bacterial infections. The results successfully demonstrated that (a) the antibacterial activity of NO rendered tiopronin-NO effective against the stone microenvironment inhabitants, Escherichia coli and Pseudomonas aeruginosa, and (b) tiopronin-NO retained the ability to undergo disulfide exchange with cystine while being reported to be safe against canine kidney and mouse fibroblast cells. Thus, the synthesis of such a facile molecule aimed at the dual management of cystinuria and related infections is unprecedented in the literature.

Role of chemistry in bio-inspired liquid wettability.

Chemistry and topography are the two distinct available tools for customizing different bio-inspired liquid wettability including superhydrophobicity, superamphiphobicity, underwater superoleophobicity, underwater superoleophilicity, and liquid infused slippery property. In nature, various living species possessing super and special liquid wettability inherently comprises of distinctly patterned surface topography decorated with low/high surface energy. Inspired from the topographically diverse natural species, the variation in surface topography has been the dominant approach for constructing bio-inspired antiwetting interfaces. However, recently, the modulation of chemistry has emerged as a facile route for the controlled tailoring of a wide range of bio-inspired liquid wettability. This review article aims to summarize the various reports published over the years that has elaborated the distinctive importance of both chemistry and topography in imparting and modulating various bio-inspired wettability. Moreover, this article outlines some obvious advantages of chemical modulation approach over topographical variation. For example, the strategic use of the chemical approach has allowed the facile, simultaneous, and independent tailoring of both liquid wettability and other relevant physical properties. We have also discussed the design of different antiwetting patterned and stimuli-responsive interfaces following the strategic and precise alteration of chemistry for various prospective applications.

Design of 'tolerant and hard' superhydrophobic coatings to freeze physical deformation.

While the development of mechanically durable and abrasion tolerant superhydrophobicity on a rigid substrates itself remains a highly challenging task, the design of superhydrophobic coatings that can restrict both the tensile and compressive deformations of soft and deformable substrates is unprecedented-and such an approach would be of potential interest in various applied and fundamental contexts. In this communication, a reaction mixture was developed following a simple 1,4-conjugate addition reaction between selected small molecules and appropriate crosslinkers for achieving 'tolerant and hard' superhydrophobicity-which is not just capable of surviving under severe conditions-but also restricts both the tensile and compressive deformations of the selected soft substrates. The compressive and tensile moduli of the selected soft substrates increased by 2.2 × 104% and 1.8 × 104%, respectively, after the deposition of the appropriate reaction mixtures. Moreover, the integration of the crosslinkers in the reaction mixture provided a facile basis to resist the physical erosion/rupture of the selected soft substrates under severe abrasive conditions. Thus, a simple and elegant chemical approach not only controlled the mechanical properties of the porous and fibrous soft substrates under ambient conditions-but also provided highly tolerant superhydrophobicity-which likely leads to various outdoor applications.

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.

Metal-Organic Framework (MOF) Derived Recyclable, Superhydrophobic Composite of Cotton Fabrics for the Facile Removal of Oil Spills.

Marine oil spill cleanup is one of the major challenges in recent years due to its detrimental effect on our ecosystem. Hence, the development of new superhydrophobic oil absorbent materials is in high demand. The third-generation porous materials, namely metal-organic frameworks (MOFs), have drawn great attention due to their fascinating properties. In this work, a superhydrophobic MOF with UiO-66 (SH-UiO-66) topology was synthesized strategically with a new fluorinated dicarboxylate linker to absorb oil selectively from water. The fully characterized superhydrophobic MOF showed extreme water repellency with an advancing water contact angle (WCA) of 160° with a contact angle hysteresis (CAH) of 8°. The newly synthesized porous MOF (SBET = 873 m2 g-1) material with high WCA found its promising application in oil/water separation. The superhydrophobic SH-UiO-66 MOF was further used for the in-situ coating on naturally abundant cotton fiber to make a superhydrophobic MOF@cotton composite material. The MOF-coated cotton fiber composite (SH-UiO-66@CFs) showed water repellency with a WCA of 163° and a low CAH of 4°. The flexible superhydrophobic SH-UiO-66@CFs showed an oil absorption capacity more than 2500 wt % for both heavy and light oils at room temperature. The superoleophilicity of SH-UiO-66@CFs was further exploited to separate light floating oil as well as sedimentary heavy oil from water. SH-UiO-66@CFs material can also separate oil from the oil/water mixture by gravity-directed active filtration. Hence, the newly developed MOF-based composite material has high potential as an oil absorbent material for marine oil spill cleanup.

A Scalable Chemical Approach for the Synthesis of a Highly Tolerant and Efficient Oil Absorbent.

In the past, bio-inspired extreme water repellent property has been strategically embedded on commercially available sponges for developing selective oil absorbents. However, most of the reported materials lack physical and chemical durability, limiting their applicability at practically harsh settings. Herein, a stable dispersion of polymeric nanocomplexes was exploited to achieve a chemically reactive coating on the highly compressible melamine foam. A superhydrophobic melamine foam (SMF) was achieved after post-covalent modification of the reactive coating through 1,4-conjugate addition reaction at ambient conditions. The durability of the embedded extreme water repellent property in the as-modified melamine foam has been elaborately demonstrated through exposing it to severe physical manipulations, chemically harsh aqueous media including pH 1, pH 12, surfactant contaminated water, river water, seawater and prolonged UV irradiation. Thus, the highly tolerant SMF was utilized as an efficient oil absorbent wherein oils of varying densities could be selectively recovered from an oil/water interface with high (e.g., 137 g g-1 for chloroform and 83 g g-1 for diesel) oil absorption capacity. Moreover, the selective oil absorption capacity of the as-synthesized material remained unaffected at practically relevant severe chemical and physical settings, and the extreme water repellency of the material remained unaltered even after repetitive (at least 50 cycles) use for oil/water separation.

Chemically reactive protein nanoparticles for synthesis of a durable and deformable superhydrophobic material.

The past few decades have witnessed significant development in the field of artificially biomimicking extremely water repellent interfaces, developed mostly through tedious synthetic processes using synthetic/non-biodegradable polymers and fluorinated derivatives rendering health and environment related hazards. Only a few approaches furnish superhydrophobic materials that can withstand different harsh environments. Here, in this current design, naturally abundant and biodegradable bovine serum albumin (BSA) protein nanoparticles and cotton fibers are rationally selected for environment-friendly green synthesis of a highly sustainable and deformable artificial superhydrophobic material through strategic association of facile and rapid Michael addition reactions between amine and acrylate moieties under ambient conditions without the aid of any catalyst. This protein based nature-inspired interface can endure severe repetitive physical manipulations, abrasions and prolonged (30 days) chemical exposure i.e. extremes of pH, artificial sea water, river water and surfactant contaminated water. This highly durable and compressible superhydrophobic material was successfully exploited for efficient (above 2000 wt%), selective and repetitive removal of contaminating oils from aqueous phases under harsh chemical conditions. Such a durable biomimicking interface derived directly from serum protein following a facile synthetic approach would be useful for developing various other functional materials.

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.

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.