Switchable wettability on cooperative dual-responsive poly-L-lysine surface

Cell adhesion molecule immobilized gold surfaces for enhanced neuron-electrode interfaces

To provide a long-term solution for increasing the biocompatibility of neuroprosthetics, approaches to reduce the side effects of invasive neuro-implantable devices are still in need of improvement. Physical, chemical, and bioactive design aspects of the biomaterials are proven to be important for providing proper cell-to-cell, cell-to-material interactions. Particularly, modification of implant surfaces with bioactive cues, especially cell adhesion molecules (CAMs) that capitalize on native neural adhesion mechanisms, are promising candidates in favor of providing efficient interfaces. Within this concept, this study utilized specific CAMs, namely N-Cadherin (Neural cadherin, N-Cad) and neural cell adhesion molecule (NCAM), to enhance neuron-electrode contact by mimicking the cell-to-ECM interactions for improving the survival of cells and promoting neurite outgrowth. For this purpose, representative gold electrode surfaces were modified with N-Cadherin, NCAM, and the mixture (1:1) of these molecules. Modifications were characterized, and the effect of surface modification on both differentiated and undifferentiated neuroblastoma SH-SY5Y cell lines were compared. The findings demonstrated the successful modification of these molecules which subsequently exhibited biocompatible properties as evidenced by the cell viability results. In cell culture experiments, the CAMs displayed promising results in promoting neurite outgrowth compared to conventional poly-l-lysine coated surfaces, especially NCAM and N-Cad/NCAM modified surfaces clearly showed significant improvement. Overall, this optimized approach is expected to provide an insight into the action mechanisms of cells against the local environment and advance processes for the fabrication of alternative neural interfaces.

Surface Modification, Topographic Design and Applications of Superhydrophobic Systems

Superhydrophobic surfaces with expanded wetting behaviors, like tunable adhesion, hybrid surface hydrophobicity and smart hydrophobic switching have attracted increasing attention due to their broad applications. Herein, the construction methods, mechanisms and advanced applications of special superhydrophobicity are reviewed, and hydro/superhydrophobic modifications are categorized and discussed based on their surface chemistry, and topographic design. The formation and maintenance of special superhydrophobicity in the metastable state are also examined and explored. In addition, particular attention is paid to the use of special wettability in various applications, such as membrane distillation, droplet-based electricity generators and anti-fogging surfaces. Finally, the challenges for practical applications and future research directions are discussed.

Adhesion behaviors on four special wettable surfaces: natural sources, mechanisms, fabrications and applications

The study of adhesion behaviors on solid-liquid surfaces plays an important role in scientific research and development in various fields, such as medicine, biology and agriculture. The contact angle and sliding angle of the liquid on the solid surface are commonly used to characterize and measure the wettability of a particular surface. They have a wide range of values, which results in different wettability. It boils down to the adhesion of solid surfaces to liquids. This feature article is aimed at revealing the essence of the adhesion behavior from the aspects of controlling the chemical composition or changing the geometrical microstructure of the surface, and reviewing the natural sources, wetting models, preparation methods and applications of four kinds of typical solid-liquid surfaces (low-adhesion superhydrophobic surfaces, high-adhesion superhydrophobic surfaces, slippery liquid-infused porous surfaces (SLIPS) and hydrophilic/superhydrophilic surfaces). Last, a summary and outlook on this field are given to point out the current challenges and the potential research directions of surface adhesion in the coming future.

Bioinspired Dual-Responsive Nanofluidic Diodes by Poly-l-lysine Modification

A smart nanofluidic device attracts attention as it enables to control the physicochemical properties and transportation phenomena, by using stimuli-responsive materials. This work reports a bioinspired modification of a conical ion track-etched polyethylene terephthalate nanopore surface by coating a layer of poly-l-lysine (PLL), which is a commonly used coating in biotechnology to achieve a dual-responsive nanofluidic channel by pH or temperature. The rectification of ionic transportation can be reversed by assembling PLL because of the change of surface bonds from the carboxyl to amine group. The PLL-modified nanopore becomes nonconductive as an "OFF" state at pH 11.5 and at a temperature of 70 °C in solution. The ionic transport in nanopores can be switched to the "ON" (conductive) state, by either decreasing pH or temperature. The transitions between "ON" and "OFF" states present excellent reversibility, which make the PLL-modified nanopores a promising smart nanofluidic device that can be used for drug delivery or biomimic ion/mass transport in future, besides the good biocompatibility and ease of use of PLL modification.

Switchable and Obedient Interfacial Properties That Grant New Biomedical Applications

Toward imitating the natural smartness and responsivity of biological systems, surface interfacial properties are considered to be responsive and tunable if they show a reactive behavior to an environmental stimulus. This is still quite different from many contemporary biomaterials that lack responsiveness to interact with blood and different body tissues in a physiological manner. Meanwhile it is possible to even go one step further from responsiveness to dual-mode switchability and explore "switchable" or "reversible" responses of synthetic materials. We understand "switchable biomaterials" as materials undergoing a stepwise, structural transformation coupled with considerable changes of interfacial and other surface properties as a response to a stimulus. Therewith, a survey on stimuli-induced dynamic changes of charge, wettability, stiffness, topography, porosity, and thickness/swelling is presented here, as potentially powerful new technologies especially for future biomaterial development. Since living cells constantly sense their environment through a variety of surface receptors and other mechanisms, these obedient interfacial properties were particularly discussed regarding their advantageous multifunctionality for protein adsorption and cell adhesion signaling, which may alter in time and with environmental conditions.

Gold Nanoparticles Grafted with PLL-b-PNIPAM: Interplay on Thermal/pH Dual-Response and Optical Properties

Narrowly distributed poly(l-lysine-b-N-isopropylacrylamide) (PLL-b-PNIPAM) was prepared through ring-opening polymerization of ε-benzyloxycarbonyl-l-lysine N-carboxy-α-amino anhydride and atom transfer radical polymerization of NIPAM, followed with the removal of ε-benzyloxycarbonyl group. Then gold nanoparticles (AuNPs) grafted with PLL-b-PNIPAM (PNIPAM-PLL-AuNPs) were obtained by the reduction of chloroauric acid with sodium citrate in the presence of PLL-b-PNIPAM. PNIPAM-PLL-AuNPs and its precursors were thoroughly characterized by proton magnetic resonance spectroscope, Fourier transform infrared spectroscope, UV-vis spectroscope, transmission electron microscopy, dynamic light scattering, thermogravimetric analysis, and circular dichroism. The obtained PNIPAM-PLL-AuNPs exhibited high colloid stability even at strong alkaline (pH = 12) and acidic (pH = 2) conditions. The thermal and pH dual-responsive behaviors of the grafting PLL-b-PNIPAM chains was observed to be affected by AuNPs, while not for the secondary structure of PLL chains. Correspondingly, the surface plasmon resonance (SPR) of AuNPs was found to be sensitive to both pH value and temperature. A blue shift in the SPR happened both with increasing pH value and increasing temperature. The stimuli-response was reversible in heating-cooling cycles. The gold nanoparticles with both pH and temperature response may have potential applications in biomedical areas and biosensors.

Temperature- and/or pH-Responsive Surfaces with Controllable Wettability: From Parahydrophobicity to Superhydrophilicity

Multifunctional surfaces with reversible wetting characteristics are fabricated utilizing end-anchored polymer chains on hierarchically roughened surfaces. Temperature- and/or pH-responsive surfaces are developed that exhibit reversible and controllable wettability, from the "parahydrophobic" behavior of natural plant leaves all the way to superhydrophilic properties in response to the external stimuli. For this purpose, dual scale micro/nanoroughened surfaces were prepared by laser irradiation of inorganic surfaces (Si wafers) utilizing ultrafast (femtosecond) laser pulses under a reactive gas atmosphere. End-functionalized polymer chains were anchored onto those surfaces utilizing the "grafting to" method; poly(N-isopropylacrylamide), PNIPAM, and poly(2-vinylpyridine), P2VP, were used for the formation of monofunctional as well as mixed brushes. The surfaces exhibit "parahydrophobic" behavior in the hydrophobic state (high temperature and/or high pH), with high static contact angles (∼120°) and high water adhesion (∼30° contact angle hysteresis), whereas they show superhydrophilic behavior in the hydrophilic state (low temperature and/or low pH). The surfaces were tested for their wettability under repetitive cycles and found to be stable and reproducible.

Fabrication of "Plug and Play" Channels with Dual Responses by Host-Guest Interactions

The "Plug and Play" template can be individually or successively grafted by dual-responsive molecules on the α-CD modified channels by host-guest interactions and can be peeled off by UV irradiation. The artificial channels present six kinds of responses cycling among four states responding to three environment stimuli, as light, pH, and temperature.

Multi-Stimuli-Responsive Polymeric Materials

Stimuli-responsive materials are of immense importance because of their ability to undergo alteration of their properties in response to their environment. The properties of such materials can be tuned by subtle adjustments in temperature, pH, light, and so forth. Among such smart materials, multi-stimuli-responsive polymeric materials are of pronounced significance as they offer a wide range of applications and their properties can be tuned through several mechanisms. Here, we aim to highlight some recent studies showcasing the multi-stimuli-responsive character of these polymers, which are still relatively little known compared to their single-stimuli-responsive counterpart.

Learning from nature: binary cooperative complementary nanomaterials

In this Review, nature-inspired binary cooperative complementary nanomaterials (BCCNMs), consisting of two components with entirely opposite physiochemical properties at the nanoscale, are presented as a novel concept for the building of promising materials. Once the distance between the two nanoscopic components is comparable to the characteristic length of some physical interactions, the cooperation between these complementary building blocks becomes dominant and endows the macroscopic materials with novel and superior properties. The first implementation of the BCCNMs is the design of bio-inspired smart materials with superwettability and their reversible switching between different wetting states in response to various kinds of external stimuli. Coincidentally, recent studies on other types of functional nanomaterials contribute more examples to support the idea of BCCNMs, which suggests a potential yet comprehensive range of future applications in both materials science and engineering.

Independent versus cooperative binding in polyethylenimine-DNA and Poly(L-lysine)-DNA polyplexes

The mechanism of polyethylenimine-DNA and poly(L-lysine)-DNA complex formation at pH 5.2 and 7.4 was studied by a time-resolved spectroscopic method. The formation of a polyplex core was observed to be complete at approximately N/P = 2, at which point nearly all DNA phosphate groups were bound by polymer amine groups. The data were analyzed further both by an independent binding model and by a cooperative model for multivalent ligand binding to multisubunit substrate. At pH 5.2, the polyplex formation was cooperative at all N/P ratios, whereas for pH 7.4 at N/P < 0.6 the polyplex formation followed independent binding changing to cooperative binding at higher N/Ps.

Grafting of poly-L-lysine dendrigrafts onto polypropylene surface using plasma activation for ATP immobilization - Nanomaterial for potential applications in biotechnology

The present work describes a new environmental friendly strategy for the development of surfaces with high amine density via the grafting of native or modified poly-L-lysine dendrigraft (DGL G3) onto plasma activated polypropylene (PP), polystyrene (PS), polyimide, and polytetrafluoroethylene (PTFE) surface. Modified DGL G3 was prepared by replacement of few peripheral amines by various functionalities. Grafting efficiency was determined by wettability measurements, IRTF, XPS, AFM, and by colorimetry using optimized Coomassie Brilliant Blue method tailored for surface analysis. It was shown that a 4-7nm DGL G3 monolayer with 4×10(14)aminecm(-)(2) was covalently grafted onto various surfaces. Immobilization of adenosine triphosphate on the DGL-g-PP material from dilute solution was studied by bioluminescence and proved the ability of the material to interact with polyanionic biological compounds: 1 ATP complex with 5 amine groups. So, this material has a potential use in diagnostic and more widely for biotechnology due to its high capacity for biomolecule immobilization.

Printable superhydrophilic-superhydrophobic micropatterns based on supported lipid layers

A new and simple method for creating superhydrophilic micropatterns on a superhydrophobic surface is demonstrated. The method is based on printing an "ink", an ethanol solution of a phospholipid, onto a porous superhydrophobic surface and, thus, is compatible with a variety of commonly available printing techniques.

Characterisation of surface wettability based on nanoparticles

Nanoparticles are becoming frequently used in the research area of creating functional surfaces because they can be more versatile than just making dimensions smaller. Particularly, a variety of nanoparticles have been applied for the construction of superhydrophobic and superhydrophilic surfaces with micro- and nano-scaled structures. As nanoparticles can also be fashioned and modified, their effects will be of great importance to the formed surface structures. In the present paper, we review the recent research progress in the utilization of nanoparticles to form extremely wettable/non-wettable surface structures and their influence on surface wettability. This report manifests an apparent inclination of nanoparticle structured surfaces using the multidisciplinary approaches, from the viewpoint of engineer/scientist. Therefore, the typical methodologies with regard to the use of nanoparticles, including the preparation and functionalisation processes, for the realization of surface wettabilities are discussed in this work. The discussions also represent some of the size-determined phenomena that are related to wettable/non-wettable surfaces. This Review thus provides an insight into the connection between nanoparticles and surface wettability.

Reversible photocontrol of surface wettability between hydrophilic and superhydrophobic surfaces on an asymmetric diarylethene solid surface

By alternate UV and visible light irradiation, reversible topographical changes were observed on a newly synthesized diarylethene microcrystalline surface between the rough crystalline surface of an open-ring isomer and flat eutectic surfaces. The contact angle changes of a water droplet between 80° and 150° and peak intensities changes of the open-ring isomer in XRD patterns within 2 h of repeating cycle were observed. The results indicated that reversibly photogenerated rod-shaped crystals on the surface were produced based on the lattice of the open-ring isomer crystals in the subphase.

Low power, biologically benign NIR light triggers polymer disassembly

Near infrared (NIR) irradiation can penetrate up to 10 cm deep into tissues and be remotely applied with high spatial and temporal precision. Despite its potential for various medical and biological applications, there is a dearth of biomaterials that are responsive at this wavelength region. Herein we report a polymeric material that is able to disassemble in response to biologically benign levels of NIR irradiation upon two-photon absorption. The design relies on the photolysis of the multiple pendant 4-bromo7-hydroxycoumarin protecting groups to trigger a cascade of cyclization and rearrangement reactions leading to the degradation of the polymer backbone. The new material undergoes a 50% Mw loss after 25 sec of ultraviolet (UV) irradiation by single photon absorption and 21 min of NIR irradiation via two-photon absorption. Most importantly, even NIR irradiation at biologically benign laser power is sufficient to cause significant polymer disassembly. Furthermore, this material is well tolerated by cells both before and after degradation. These results demonstrate for the first time a NIR sensitive material with potential to be used for in vivo applications.