Superhydrophilicity Regulation of Carbon Nanotubes Boosting Electrochemical Biosensing for Real-time Monitoring of H2O2 Released from Living Cells

Dynamic and accurate monitoring of cell-released electroactive signaling biomolecules through electrochemical techniques has drawn significant research interest for clinical applications. Herein, the functionalized carbon nanotubes (f-CNTs) featuring with gradient surface wettability from hydrophobicity to hydrophilicity, and even to superhydrophilicity, were regulated by thermolysis of an ionic liquid for exploration of the dependence of surface wettability on electrochemical biosensing performance to a cell secretion model of hydrogen peroxide (H2O2). The superhydrophilic f-CNTs demonstrated boosting electrocatalytic reduction activity for H2O2. Additionally, the molecular dynamic (MD) simulations confirmed the more cumulative number density distribution of H2O2 molecules closer to the superhydrophilic surface (0.20 vs 0.37 nm), which would provide a faster diffusional channel compared with the hydrophobic surface. Thereafter, a superhydrophilic biosensing platform with a lower detectable limit reduced by 200 times (0.5 vs 100 μM) and a higher sensitivity over 56 times (0.112 vs 0.002 μA μM cm-2) than that of the hydrophobic one was achieved. Given its excellent cytocompatibility, the superhydrophilic f-CNTs was successfully applied to determine H2O2 released from HeLa cells which were maintained alive after a 30 min real-time monitoring test. The surface hydrophilicity regulation of electrode materials presents a facile approach for real-time monitoring of H2O2 released from living cells and would provide new insights for other electroactive signaling targets at the cellular level.

Biopolymer Honeycomb Microstructures: A Review

In this review, we present a comprehensive summary of the formation of honeycomb microstructures and their applications, which include tissue engineering, antibacterial materials, replication processes or sensors. The history of the honeycomb pattern, the first experiments, which mostly involved the breath figure procedure and the improved phase separation, the most recent approach to honeycomb pattern formation, are described in detail. Subsequent surface modifications of the pattern, which involve physical and chemical modifications and further enhancement of the surface properties, are also introduced. Different aspects influencing the polymer formation, such as the substrate influence, a particular polymer or solvent, which may significantly contribute to pattern formation, and thus influence the target structural properties, are also discussed.

Honeycomb-Structured Porous Films from Poly(3-hydroxybutyrate) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Physicochemical Characterization and Mesenchymal Stem Cells Behavior

Surface morphology affects cell attachment and proliferation. In this research, different films made of biodegradable polymers, poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-HV), containing different molecular weights, with microstructured surfaces were investigated. Two methods were used to obtain patterned films—water-assisted self-assembly (“breath figure”) and spin-coating techniques. The water-assisted technique made it possible to obtain porous films with a self-assembled pore structure, which is dependent on the monomer composition of a polymer along with its molecular weight and the technique parameters (distance from the nozzle, volume, and polymer concentration in working solution). Their pore morphologies were evaluated and their hydrophobicity was examined. Mesenchymal stem cells (MSCs) isolated from bone marrow were cultivated on a porous film surface. MSCs’ attachment differed markedly depending on surface morphology. On strip-formed stamp films, MSCs elongated along the structure, however, they interacted with a larger area of film surface. The honeycomb films and column type films did not set the direction of extrusion, but cell flattening depended on structure topography. Thus, stem cells can “feel” the various surface morphologies of self-assembled honeycomb films and change their behavior depending on it.

Hierarchically Structured Surfaces Prepared by Phase Separation: Tissue Mimicking Culture Substrate

The pseudo 3D hierarchical structure mimicking in vivo microenvironment was prepared by phase separation on tissue culture plastic. For surface treatment, time-sequenced dosing of the solvent mixture with various concentrations of polymer component was used. The experiments showed that hierarchically structured surfaces with macro, meso and micro pores can be prepared with multi-step phase separation processes. Changes in polystyrene surface topography were characterized by atomic force microscopy, scanning electron microscopy and contact profilometry. The cell proliferation and changes in cell morphology were tested on the prepared structured surfaces. Four types of cell lines were used for the determination of impact of the 3D architecture on the cell behavior, namely the mouse embryonic fibroblast, human lung carcinoma, primary human keratinocyte and mouse embryonic stem cells. The increase of proliferation of embryonic stem cells and mouse fibroblasts was the most remarkable. Moreover, the embryonic stem cells express different morphology when cultured on the structured surface. The acquired findings expand the current state of knowledge in the field of cell behavior on structured surfaces and bring new technological procedures leading to their preparation without the use of problematic temporary templates or additives.

CO2-Triggered ON/OFF Wettability Switching on Bioinspired Polylactic Acid Porous Films for Controllable Bioadhesion

Bioinspired honeycomb-like porous films with switchable properties have drawn much attention recently owing to their potential application in scenarios in which the conversion between two opposite properties is required. Herein, the CO₂-gas-triggered ON/OFF switching wettability of biocompatible polylactic acid (PLA) honeycomb porous films is fabricated. Highly ordered porous films with diameters between 2.0 and 2.8 μm are separately prepared from complexes of nonresponsive PLA and a CO₂-sensitive melamine derivative [N²,N⁴,N⁶-tris(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine, MET] via the breath figure method. The hydrophilic CO₂-sensitive groups can be precisely arranged in the pore's inner surface and/or top surface of the films by simply changing the PLA/MET ratio. The sensitive groups in the pore's inner surface act as a switch triggered by CO₂ gas controlling water to enter the pores or not, thus resulting in ON/OFF switching wettability. The largest response of the water contact angle of honeycomb films reaches 35°, from 100 to 65°, leading to an obvious hydrophobic-hydrophilic conversion. The improved surface wettability enhances the interaction between the cell and honeycomb film surface, thus resulting in a better cell attachment. Such smart properties accompanying the biocompatible polymer and biological gas trigger facilitate possible biomedical and bioengineering applications in the future for these films.

Cell-friendly photo-functionalized TiO2 nano-micro-honeycombs for selectively preventing bacteria and platelet adhesion

Titanium dioxide (TiO₂) is a widely used biomaterial. It is a great challenge to confer antibacterial and antithrombotic properties to TiO₂ while maintaining its cell affinity. Here, we developed a new strategy to achieve the above goal by comprehensively controlling the chemical cues and geometrical cues of the surface of TiO₂. Using colloidal etching technology and UV irradiation treatment, we obtained the photofunctionalized nano-micro-honeycomb structured TiO₂. The honeycomb structured increased the photocatalytic activity of TiO₂, which endowed TiO₂ with photo-induced superhydrophilicity to inhibit bacterial adhesion. The high photocatalytic activity also induced the strong photocatalytic oxidation of TiO₂ surface organic adsorbates to suppress fibrinogen and platelet attachment. In addition, owing to the micropore trapping-isolation effect on the bacteria and the nano-frames' contact guidance effect on the growth and spreading of platelet pseudopods, the honeycomb structure also shows a considerable inhibiting effect on bacterial and platelet adhesion. Therefore, due to the controlled chemical and geometrical cues' synergistic effect, the photo-functionalized TiO₂ honeycomb structure shows excellent bacterial-adhesion resistance and antithrombotic properties. More importantly, the photo-functionalized TiO₂ honeycomb did not inhibit the adhesion and growth of endothelial cells (ECs) after culturing for 3 d, indicating a good cell affinity that the traditional antifouling surfaces do not possess.

Fabrication and characterization of ultrathin spin-coated poly(L-lactic acid) films suitable for cell attachment and curcumin loading

In the present study, ultrathin poly(L-lactic acid) (PLLA) films were fabricated using the spin-coating technique. Physicochemical properties of the formed materials, including their morphology, thickness, transparency, and contact angle, have been studied. We determined that the morphology of PLLA films could be regulated by changing the polymer concentration and humidity. By altering the humidity, microporous and flat PLLA films can be fabricated. The obtained samples were subsequently used for culturing mesenchymal stem cells and fibroblasts. It has been determined that cells effectively adhered to prepared films and formed on them a monolayer culture with high viability. It has been shown that PLLA films are suitable for the entrapment of curcumin (up to 12.1 μm cm^-2) and provide its sustained release in solutions isotonic to blood plasma. The obtained PLLA films appear to be prospective materials for potential application in regenerative medicine as part of cell-containing tissue engineered dressings for chronic wound treatment.

In Vivo Restoration of Myocardial Conduction With Carbon Nanotube Fibers

BACKGROUND

Impaired myocardial conduction is the underlying mechanism for re-entrant arrhythmias. Carbon nanotube fibers (CNTfs) combine the mechanical properties of suture materials with the conductive properties of metals and may form a restorative solution to impaired myocardial conduction.

METHODS

Acute open chest electrophysiology studies were performed in sheep (n=3). Radiofrequency ablation was used to create epicardial conduction delay after which CNTf and then silk suture controls were applied. CNTfs were surgically sewn across the right atrioventricular junction in rodents, and acute (n=3) and chronic (4-week, n=6) electrophysiology studies were performed. Rodent toxicity studies (n=10) were performed. Electrical analysis of the CNTf-myocardial interface was performed.

RESULTS

In all cases, the large animal studies demonstrated improvement in conduction velocity using CNTf. The acute rodent model demonstrated ventricular preexcitation during sinus rhythm. All chronic cases demonstrated resumption of atrioventricular conduction, but these required atrial pacing. There was no gross or histopathologic evidence of toxicity. Ex vivo studies demonstrated contact impedance significantly lower than platinum iridium.

CONCLUSIONS

Here, we show that in sheep, CNTfs sewn across epicardial scar acutely improve conduction. In addition, CNTf maintain conduction for 1 month after atrioventricular nodal ablation in the absence of inflammatory or toxic responses in rats but only in the paced condition. The CNTf/myocardial interface has such low impedance that CNTf can facilitate local, downstream myocardial activation. CNTf are conductive, biocompatible materials that restore electrical conduction in diseased myocardium, offering potential long-term restorative solutions in pathologies interrupting efficient electrical transduction in electrically excitable tissues.

Direct formation of hydrophilic honeycomb film by self-assembly in breath figure templating of hydrophobic polylacticacid/ionic surfactant complexes

Honeycomb-patterned porous films with good surface wettability have great potential applications in various areas. However, hydrophilic honeycomb films are difficult to obtain using the direct self-assembly of pure (co)polymers. Thus, additional and special treatments are required to improve film wettability, which makes the procedure complicated and difficult to access. In this study, a facile way to prepare hydrophilic honeycomb-structured porous films is proposed that uses the direct self-assembly of complexes of biocompatible hydrophobic poly(l-lactic acid) and dodecyltrimethylammonium chloride by breath figure templating. The addition of ionic surfactant not only improves film quality but also confers good wettability. The obtained hydrophilic pore arrays were found to effectively promote cell attachment. Such a hydrophilic honeycomb-patterned porous film could find potential applications where pore wetting is required, including tissue engineering, lithography, and nanoparticle embedding.

CO2-Driven reversible wettability in a reactive hierarchically patterned bio-inspired honeycomb film

A triple structured honeycomb film is fabricated through block copolymer directed self-assembly in “Breath Figure” templating as a clickable patterned platform to enhance its reversible surface wettability between hydrophobicity and hydrophilicity upon a biological CO₂ trigger.

Designing 3D Biological Surfaces via the Breath-Figure Method

The fabrication of biointerfaces that mimic cellular physiological environments is critical to understanding cell behaviors in vitro and for the design of tissue engineering. Breath figure is a self-assemble method that uses water droplets condensed from moisture as template and ends up with a highly ordered hexagonal pore array; this approach is used to fabricate various biological substrates. This progress report provides an overview of strategies to achieve topographical modifications and chemical-patterned arrays, such as modulation of the pore size, shape and selective decoration of the honeycomb holes. Using recent results in the biological fields, potential future applications and developments of honeycomb structures are commented upon.

Breath figures in tissue engineering and drug delivery: State-of-the-art and future perspectives

The breath figure (BF) method is an easy, low-cost method to prepare films with a highly organized honeycomb-like porous surface. The particular surface topography and porous nature of these materials makes them valuable substrates for studying the complex effects of topography on cell fate, and to produce biomimetic materials with high performance in tissue engineering. Numerous researchers over the last two decades have studied the effects of the honeycomb topography on a variety of primary and immortalized cell lines, and drew important conclusions that can be translated to the construction of optimal biomaterials for cell culture. The literature also encouragingly shows the potential of honeycomb films to induce differentiation of stem cells down a specific lineage without the need for biochemical stimuli. Here, we review the main studies where BF honeycomb films are used as substrates for tissue engineering applications. Furthermore, we highlight the numerous advantages of the porous nature of the films, such as the enhanced, spatially controlled adsorption of proteins, the topographical cues influencing cellular behavior, and the enhanced permeability which is essential both in vitro and in vivo. Finally, this review highlights the elegant use of honeycomb films as drug-eluting biomaterials or as reservoirs for distinct drug delivery systems.

STATEMENT OF SIGNIFICANCE

Combining biocompatible surfaces and 3D nano/microscale topographies, such as pores or grooves, is an effective strategy for manufacturing tissue engineering scaffolds. The breath figure (BF) method is an easy technique to prepare cell culture substrates with an organized, honeycomb-like porous surface. These surface features make these scaffolds valuable for studying how the cells interact with the biomaterials. Their unique surface topography can also resemble the natural environment of the tissues in the human body. For that reason, numerous studies, using different cell types, have shown that honeycomb films can constitute high performance substrates for cell culture. Here, we review those studies, we highlight the advantages of honeycomb films in tissue engineering and we discuss their potential as unique drug-eluting systems.

Variations of Polymer Porous Surface Structures via the Time-Sequenced Dosing of Mixed Solvents

A new approach to polystyrene surface treatment via the time-sequenced dispensing of good and poor solvent mixtures on the rotating surface of treated substrate is presented in this study. It is demonstrated that the variation of the sequencing together with other variables (e.g., temperature and solvent concentration) affects the size and depth of pores evolving on the polystyrene surface. A model of the surface pore creation, associated with the viscoelastic phase separation, surface tension, and secondary flows caused by temperature variations and the rapid evaporation of the good solvent is proposed. Experimental results of profilometric, goniometric, and optical measurements show that this approach enables the simple and quick preparation of surfaces with various numbers, diameters, and depths of individual pores, which ultimately affects not only the wetting characteristics of the surfaces but also the fate of cells cultivated there. The presented method allows the easy preparation of a large number of structured substrates for effective cell cultivation and proliferation.

Combined use of breath figures process and microphase separation of PS-b-P4VP to produce stable porous nanomaterials

Among various templating strategies available for the preparation of porous polymer films, Breath Figures (BFs) as a fast, low-cost and versatile method has aroused extensive interest.

Phase Separation of Silicon-Containing Polymer/Polystyrene Blends in Spin-Coated Films

In this Article, two readily available polymers that contain silicon and have different surface tensions, polydimethylsiloxane (PDMS) and polyphenylsilsequioxane (PPSQ), were used to produce polymer blends with polystyrene (PS). Spin-coated thin films of the polymer blends were treated by O2 reactive-ion etching (RIE). The PS constituent was selectively removed by O2 RIE, whereas the silicon-containing phase remained because of the high etching resistance of silicon. This selective removal of PS substantially enhanced the contrast of the phase separation morphologies for better scanning electron microscope (SEM) and atomic force microscope (AFM) measurements. We investigated the effects of the silicon-containing constituents, polymer blend composition, concentration of the polymer blend solution, surface tension of the substrate, and the spin-coating speed on the ultimate morphologies of phase separation. The average domain size, ranging from 100 nm to 10 μm, was tuned through an interplay of these factors. In addition, the polymer blend film was formed on a pure organic layer, through which the aspect ratio of the phase separation morphologies was further amplified by a selective etching process. The formed nanostructures are compatible with existing nanofabrication techniques for pattern transfer onto substrates.

Phase Behavior of Ternary Polymer Brushes

Ternary polymer brushes consisting of polystyrene, poly(methyl methacrylate), and poly(4-vinylpyridine) have been synthesized. These brushes laterally phase separate into several distinct phases and can be tailored by altering the relative polymer composition. Self-consistent field theory has been used to predict the phase diagram and model both the horizontal and vertical phase behavior of the polymer brushes. All phase behaviors observed experimentally correlate well with the theoretical model.

Tailor-made dimensions of diblock copolymer truncated micelles on a solid by UV irradiation

We investigated the structural evolution of truncated micelles in ultrathin films of polystyrene-block-poly(2-vinylpyridine), PS-b-P2VP, of monolayer thickness on bare silicon substrates (SiOx/Si) upon UV irradiation in air- (UVIA) and nitrogen-rich (UVIN) environments. The structural evolution of micelles upon UV irradiation was monitored using GISAXS measurements in situ, while the surface morphology was probed using atomic force microscopy ex situ and the chemical composition using X-ray photoelectron spectroscopy (XPS). This work provides clear evidence for the interpretation of the relationship between the structural evolution and photochemical reactions in PS-b-P2VP truncated micelles upon UVIA and UVIN. Under UVIA treatment, photolysis and cross-linking reactions coexisted within the micelles; photolysis occurred mainly at the top of the micelles, whereas cross-linking occurred preferentially at the bottom. The shape and size of UVIA-treated truncated micelles were controlled predominantly by oxidative photolysis reactions, which depended on the concentration gradient of free radicals and oxygen along the micelle height. Because of an interplay between photolysis and photo-crosslinking, the scattering length densities (SLD) of PS and P2VP remained constant. In contrast, UVIN treatments enhanced the contrast in SLD between the PS shell and the P2VP core as cross-linking dominated over photolysis in the presence of nitrogen. The enhancement of the SLD contrast was due to the various degrees of cross-linking under UVIN for the PS and P2VP blocks.

Preparation of highly permeable BPPO microfiltration membrane with binary porous structures on a colloidal crystal substrate by the breath figure method

A highly permeable brominated poly(phenylene oxide) (BPPO) microfiltration membrane with binary porous structures was fabricated by combination of the breath figure and colloidal crystal template methods. The pore size in the bottom layer of the membrane was adjusted by the diameter of SiO2 microspheres in the colloidal crystal template, while the pore size in the top layer of the membrane was adjusted by varying the BPPO concentration in the casting solution. The permeability of the membrane cast on the colloidal crystal substrate was much higher than that of the membrane cast on a bare silicon wafer. The binary porous BPPO membrane with high permeability and antifouling property was used for microfiltration applications.

Synthesis of well-defined α-fluorinated alkyl ester, ω-carboxyltelechelic polystyrenes and fabrication of their hydrophobic highly ordered porous films and microspheres

Porous films and microspheres of α-fluorinated alkyl ester, ω-carboxyl telechelic polystyrenes synthesized via combining aminolysis of RAFT-polystyrene with thiol–ene “click” reaction.

Single-step fabrication of large-scale patterned honeycomb structures via self-assembly of a small organic molecule

A schematic diagram of honeycomb structure formation from AOB-t8.

Functional porous membranes from amorphous linear dendritic polyester hybrids

Non-toxic and functional linear dendritic hybrids were synthesized and exploited to generate reactive porous membranes for straightforward functionalization in aqueous media.

Particle-assisted semidirect breath figure method: a facile way to endow the honeycomb-structured petri dish with molecular recognition capability

Recently, we have developed a semidirect breath figure (sDBF) method for direct fabrication of large-area and ordered honeycomb structures on commercial polystyrene (PS) Petri dishes without the use of an external polymer solution. In this work, we showed that both the pore size and the pore uniformity of the breath figure patterns were controllable by solvent amount. The cross-sectional image shows that only one layer of pores was formed on the BF figure patterns. By combing the sDBF method and Pickering emulsion and using the modular building blocks, we endowed the honeycomb-structured Petri dish with molecular recognition capability via the decoration of molecularly imprinted polymer (MIP) nanoparticles into the honeycomb pores. The radioligand binding experiments show that the MIP nanoparticles on the resultant honeycomb structures maintained high molecular binding selectivity. The reusability study indicates that MIP-BF patterns had excellent mechanical stability during the radioligand binding process. We believe that the modular approach demonstrated in this work will open up further opportunities for honeycomb structure-based chemical sensors for drug analysis, substrates for catalysts, and scaffold for cell growth.

Breath figure patterns made easy

In this work, a simple breath figure method was proposed to directly fabricate large-area and ordered honeycomb structures on commercial PMMA substrates or PS Petri dishes without the use of an external polymer solution. The obtained honeycomb structure is indeed part of the substrate, providing the honeycomb layer with enough mechanical stability. The breath figure method in this work for the synthesis of honeycomb structure is extremely simple with scale-up capability to large-area production, which offers new insights into surface engineering with great potential in commercial technologies. For example, using the honeycomb-patterned Petri dishes prepared via this method, cells can be easily separated into divided aggregation, which favors understanding of naturally occurring networks in higher organisms and cell-cell and cell-matrix interactions, and the therapeutic control of genetic circuits.

Synthesis of core cross-linked star polystyrene with functional end groups and self-assemblies templated by breath figures

We report the synthesis of core cross-linked star (CCS) polymers with functional end groups for self-assembled films, which show mono-layer and multi-layer transition, depending on arm numbers, arm length, and end groups.

Multiple interfaces in self-assembled breath figures

Progress in the breath figure method is reviewed by emphasizing the role of the multiple interfaces and the applications of honeycomb films in separation, biocatalysis, biosensing, templating, stimuli-responsive surfaces and adhesive surfaces.

Porous surface structure fabricated by breath figures that suppresses Pseudomonas aeruginosa biofilm formation

As colonizers of medical-device surfaces, Pseudomonas aeruginosa strains present a serious source of infection and are of major concern. In this study, we fabricated films with porous surfaces by breath figures that disturb mergence by bacterial attachment, thereby impeding biofilm development. Previous studies have shown that microtopography prevents the development of P. aeruginosa biofilms. Accordingly we indented surfaces with patterns of micrometer-sized pores using breath figures at ordinary temperatures and pressures. The antimicrobial effect of surface figures was experimentally investigated by controlling the surface structure. The results suggested that pores of 5-11 μm in diameter effectively inhibit bacterial activity. It appears that biofilm development is precluded by the decreased contact area between the films and bacteria.