Rapid and Selective Deposition of Patterned Thin Films on Heterogeneous Substrates via Spin Coating

Silanization Strategies for Tailoring Peptide Functionalization on Silicon Surfaces: Implications for Enhancing Stem Cell Adhesion

Biomaterial surface engineering and the integration of cell-adhesive ligands are crucial in biological research and biotechnological applications. The interplay between cells and their microenvironment, influenced by chemical and physical cues, impacts cellular behavior. Surface modification of biomaterials profoundly affects cellular responses, especially at the cell-surface interface. This work focuses on enhancing cellular activities through material manipulation, emphasizing silanization for further functionalization with bioactive molecules such as RGD peptides to improve cell adhesion. The grafting of three distinct silanes onto silicon wafers using both spin coating and immersion methods was investigated. This study sheds light on the effects of different alkyl chain lengths and protecting groups on cellular behavior, providing valuable insights into optimizing silane-based self-assembled monolayers (SAMs) before peptide or protein grafting for the first time. Specifically, it challenges the common use of APTES molecules in this context. These findings advance our understanding of surface modification strategies, paving the way for tailoring biomaterial surfaces to modulate the cellular behavior for diverse biotechnological applications.

Empowering ultrathin polyamide membranes at the water-energy nexus: strategies, limitations, and future perspectives

Membrane-based separation is one of the most energy-efficient methods to meet the growing need for a significant amount of fresh water. It is also well-known for its applications in water treatment, desalination, solvent recycling, and environmental remediation. Most typical membranes used for separation-based applications are thin-film composite membranes created using polymers, featuring a top selective layer generated by employing the interfacial polymerization technique at an aqueous-organic interface. In the last decade, various manufacturing techniques have been developed in order to create high-specification membranes. Among them, the creation of ultrathin polyamide membranes has shown enormous potential for achieving a significant increase in the water permeation rate, translating into major energy savings in various applications. However, this great potential of ultrathin membranes is greatly hindered by undesired transport phenomena such as the geometry-induced "funnel effect" arising from the substrate membrane, severely limiting the actual permeation rate. As a result, the separation capability of ultrathin membranes is still not fully unleashed or understood, and a critical assessment of their limitations and potential solutions for future studies is still lacking. Here, we provide a summary of the latest developments in the design of ultrathin polyamide membranes, which have been achieved by controlling the interfacial polymerization process and utilizing a number of novel manufacturing processes for ionic and molecular separations. Next, an overview of the in-depth assessment of their limitations resulting from the substrate membrane, along with potential solutions and future perspectives will be covered in this review.

Selective Spin Dewetting for Perovskite Solar Modules Fabricated on Engineered Au/ITO Substrates

We introduce a novel method for fabricating perovskite solar modules using selective spin-coating on various Au/ITO patterned substrates. These patterns were engineered for two purposes: (1) to enhance selectivity of monolayers primarily self-assembling on the Au electrode, and (2) to enable seamless interconnection between cells through direct contact of the top electrode and the hydrophobic Au connection electrode. Utilizing SAMs-treated Au/ITO, we achieved sequential selective deposition of the electron transport layer (ETL) and the perovskite layer on the hydrophilic amino-terminated ITO, while the hole transport layer (HTL) was deposited on the hydrophobic CH3-terminated Au connection electrodes. Importantly, our approach had a negligible impact on the series resistance of the solar cells, as evidenced by the measured specific contact resistivity of the multilayers. A significant outcome was the production of a six-cell series-connected solar module with a notable average PCE of 8.32%, providing a viable alternative to the conventional laser scribing technique.

Impact of Membrane Modification and Surface Immobilization Techniques on the Hemocompatibility of Hemodialysis Membranes: A Critical Review

Despite significant research efforts, hemodialysis patients have poor survival rates and low quality of life. Ultrafiltration (UF) membranes are the core of hemodialysis treatment, acting as a barrier for metabolic waste removal and supplying vital nutrients. So, developing a durable and suitable membrane that may be employed for therapeutic purposes is crucial. Surface modificationis a useful solution to boostmembrane characteristics like roughness, charge neutrality, wettability, hemocompatibility, and functionality, which are important in dialysis efficiency. The modification techniques can be classified as follows: (i) physical modification techniques (thermal treatment, polishing and grinding, blending, and coating), (ii) chemical modification (chemical methods, ozone treatment, ultraviolet-induced grafting, plasma treatment, high energy radiation, and enzymatic treatment); and (iii) combination methods (physicochemical). Despite the fact that each strategy has its own set of benefits and drawbacks, all of these methods yielded noteworthy outcomes, even if quantifying the enhanced performance is difficult. A hemodialysis membrane with outstanding hydrophilicity and hemocompatibility can be achieved by employing the right surface modification and immobilization technique. Modified membranes pave the way for more advancement in hemodialysis membrane hemocompatibility. Therefore, this critical review focused on the impact of the modification method used on the hemocompatibility of dialysis membranes while covering some possible modifications and basic research beyond clinical applications.

Role of nanostructured materials in hard tissue engineering

The rise in the use of biomaterials in bone regeneration in the last decade has exponentially multiplied the number of publications, methods, and approaches to improve and optimize their functionalities and applications. In particular, biomimetic strategies based on the self-assembly of molecules to design, create and characterize nanostructured materials have played a very relevant role. We address this idea on four different but related points: self-setting bone cements based on calcium phosphate, as stable tissue support and regeneration induction; metallic prosthesis coatings for cell adhesion optimization and prevention of inflammatory response exacerbation; bio-adhesive hybrid materials as multiple drug delivery localized platforms and finally bio-inks. The effect of the physical, chemical, and biological properties of the newest biomedical devices on their bone tissue regenerative capacity are summarized, described, and analyzed in detail. The roles of experimental conditions, characterization methods and synthesis routes are emphasized. Finally, the future opportunities and challenges of nanostructured biomaterials with their advantages and shortcomings are proposed in order to forecast the future directions of this field of research.

Stretchable Conductors Fabricated by Stencil Lithography and Centrifugal Force-Assisted Patterning of Liquid Metal

Embedding liquid metals (LMs) into an elastomer is emerging as a promising strategy for stretchable conductors. Existing manufacturing techniques are struggling between spatial resolution and process complexity and are limited to chemically resistant substrates. Here, we report on a hybrid process combining stencil lithography and centrifugal force-assisted patterning of liquid metal for the development of LM-based stretchable conductors. The selective wetting behavior of oxide-removed eutectic gallium-indium (EGaIn) on metal patterns defined by stencil lithography enables micrometer scale LM patterns on an elastomeric substrate. Stencil lithography allows for defining metal regions without harsh chemical treatments, making it suitable for a wide range of substrates. Microscale LM patterns are achieved by efficiently removing the excess material by the centrifugal forces experienced from spinning the substrate. The proposed approach allows for the creation of LM patterns with a line width as small as 2 μm on a stretchable poly(dimethylsiloxane) (PDMS) substrate. The electrical measurement results show that the fabricated EGaIn devices can endure 40% mechanical strain over several thousands of cycles. Furthermore, a stencil design using microbridges is proposed to address the mechanical stability issue in stencil lithography. An EGaIn conductor with a serpentine structure and an interdigitated capacitor are fabricated and characterized. The results demonstrate that the patterned serpentine conductors retain their functionality with applied mechanical strain up to 80%. The performance of the interdigitated capacitors upon applied strain is in good agreement with the theoretical estimation. Finally, we demonstrate our approach also on poly(octamethylene maleate (anhydride) citrate) (POMaC) substrates to broaden the use of the proposed method to not only flexible and stretchable but also biodegradable substrates, opening a way for in vivo transient microsystem engineering. The work presented here provides a versatile and reliable approach for manufacturing stretchable conductors.

A New Hybrid Sensitive PANI/SWCNT/Ferrocene-Based Layer for a Wearable CO Sensor

Developing a sensing layer with high electroactive properties is an important aspect for proper functionality of a wearable sensor. The polymeric nanocomposite material obtained by a simple electropolymerization on gold interdigitated electrodes (IDEs) can be optimized to have suitable conductive properties to be used with direct current (DC) measurements. A new layer based on polyaniline:poly(4-styrenesulfonate) (PANI:PSS)/single-walled carbon nanotubes (SWCNT)/ferrocene (Fc) was electrosynthesized and deposed on interdigital transducers (IDT) and was characterized in detail using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), and X-ray diffraction (XRD). The sensor characteristics of the material towards carbon monoxide (CO) in the concentration range of 10–300 ppm were examined, showing a minimal relative humidity interference of only 1% and an increase of sensitivity with the increase of CO concentration. Humidity interference could be controlled by the number of CV cycles when a compact layer was formed and the addition of Fc played an important role in the decrease of humidity. The results for CO detection can be substantially improved by optimizing the number of deposition cycles and enhancing the Fc concentration. The material was developed for selective detection of CO in real environmental conditions and shows good potential for use in a wearable sensor.

Impact of the process conditions on polymer pattern morphology during spin coating over topological surfaces

Micro and nanofabrication techniques depend on the technology of polymer film casting. Spin coating is a relatively robust method to develop uniform polymer films over the substrate surface. However, polymer casting over a topographically prepatterned surface using the spin coating technique is challenging because of the complex transport phenomena involved in the process. Apart from the substrate wettability and the polymer composition, the geometry of the substrate prepatterns affects the polymer phase separation characteristics and thus the morphology of the polymer pattern. In this work the phase separation dynamics during the spinodal decomposition of a polymer-solvent system in a spin coating process is mathematically investigated. The effect of the prepattern topography, substrate wettability, spin-coating rotational speed, and polymer composition on the phase separation dynamics is investigated. The results reveal that the periodicity and phase difference of the polymer peaks with the topography are dependent on the geometric parameters and substrate wettability. The impact of the rotational motion, on the polymer film, is restricted by the surface roughness (due to the topological prepatterns). On reducing the polymer fraction in the solution, the transition from a uniform coating to film defects to isolated patches (wetting to dewetting) occurs. The surface wettability plays a crucial role in topology directed dewetting, which is not observed in flat substrates.

Precise Definition of a "Monolayer Point" in Polymer Brush Films for Fabricating Highly Coherent TiO2 Thin Films by Vapor-Phase Infiltration

In this work, we show that in order to fabricate coherent titania (TiO₂) films with precise thickness control, it is critical to generate a complete polymer brush monolayer. To date, demonstrations of such dense polymer monolayer formation that can be utilized for inorganic infiltration have been elusive. We describe a versatile bottom-up approach to covalently and rapidly (60 s processing) graft hydroxyl-terminated poly(2-vinyl pyridine) (P2VP-OH) polymers on silicon substrates. P2VP-OH monolayer films of varying thicknesses can subsequently be used to fabricate high-quality TiO₂ films. Our innovative strategy is based upon room-temperature titanium vapor-phase infiltration of the grafted P2VP-OH polymer brushes that can produce TiO₂ nanofilms of 2-4 nm thicknesses. Crucial parameters are explored, including molecular weight and solution concentration for grafting dense P2VP-OH monolayers from the liquid phase with high coverage and uniformity across wafer-scale areas (>2 cm²). Additionally, we compare the P2VP-OH polymer systems with another reactive polymer, poly(methyl methacrylate)-OH, and a relatively nonreactive polymer, poly(styrene)-OH. Furthermore, we prove the latter to be effective for surface blocking and deactivation. We show a simple process to graft monolayers for polymers that are weakly interacting with one another but more challenging for reactive systems. Our methodology provides new insight into the rapid grafting of polymer brushes and their ability to form TiO₂ films. We believe that the results described herein are important for further expanding the use of reactive and unreactive polymers for fields including area-selective deposition, solar cell absorber layers, and antimicrobial surface coatings.

Dynamic Porous Pattern through Controlling Noncovalent Interactions in Polyelectrolyte Film for Sequential and Regional Encapsulation

Inspired by nature, many functional surfaces have been developed with special structures in biology, chemistry, and materials. Many research studies have been focused on the preparation of surfaces with static structure. Achieving dynamical manipulation of surface structure is desired but still a great challenge. Herein, a polyelectrolyte film capable of regional and reversible changes in the microporous structure is presented. Our proposal is based on the combination of azobenzene (Azo) π-π stacking and electrostatic interaction, which could be affected respectively by ultraviolet (UV) irradiation and water plasticization, to tune the mobility of polyelectrolyte chains. The porous patterns can be obtained after regional ultraviolet irradiation and acid treatment. Owing to the reversibility of Azo π-π stacking and electrostatic interaction, the patterns can be repeatedly created and erased in the polyelectrolyte film made by layer-by-layer (LbL) self-assembly of poly(ethyleneimine)-azo and poly(acrylic acid). Furthermore, through two rounds of porous pattern formation and erasure, different functional species can be loaded separately and confined regionally within the film, showing potential applications in the functional surface. This work highlights the coordination of two noncovalent interactions in thin films for regional and reversible controlling its structure, opening a window for more in-depth development of functional surfaces.

Hierarchical 3D Patterns with Dynamic Wrinkles Produced by a Photocontrolled Diels-Alder Reaction on the Surface

Three-dimensional (3D) reconfigurable patterns with dynamic morphologies enable the on-demand control of surface properties, such as optical, wetting, and adhesive properties, to achieve smart surfaces. Here, a simple yet general strategy is developed for fabricating 3D patterns with reversible wrinkles on the surface, in which a Diels-Alder (D-A) reaction in the top layer, which consists of a reversible cross-linked polymer network composed of a furan-containing copolymer (PSFB) and bismaleimide (BMI), can be spatially controlled by the photodimerization of BMI. When a photomask is used during irradiation with ultraviolet (UV) light, selective photodimerization of the maleimide leads to the diffusion of maleimide from the unexposed region to the exposed region, resulting in the generation of a diffused relief pattern. By controlling the reversible D-A reaction at different temperatures, orthogonal wrinkles can be sequentially and reversibly generated or erased in both the exposed and unexposed regions on the surface. Theoretical modeling with boundary effects reveals that the orientation of the wrinkle in the exposed region is perpendicular to the boundary, whereas the wrinkle in the unexposed region is parallel to the boundary. This strategy, based on a photocontrolled D-A reaction, provides an important and robust alternative for fabricating 3D patterned surfaces with dynamic topographies.

Reusable Chemically-Micropatterned Substrates via Sequential Photoinitiated Thiol-Ene Reactions as Template for Perovskite Thin-Film Microarrays

Patterning semiconducting materials are important for many applications such as microelectronics, displays, and photodetectors. Lead halide perovskites are an emerging class of semiconducting materials that can be patterned via solution-based methods. Here we report an all-benchtop patterning strategy by first generating a patterned surface with contrasting wettabilities to organic solvents that have been used in the perovskite precursor solution then spin-coating the solution onto the patterned surface. The precursor solution only stays in the area with higher affinity (wettability). We applied sequential sunlight-initiated thiol-ene reactions to functionalize (and pattern) both glass and conductive fluorine-doped tin oxide (FTO) transparent glass surfaces. The functionalized surfaces were measured with the solvent contact angles of water and different organic solvents and were further characterized by XPS, selective fluorescence staining, and selective DNA adsorption. By simply spin-coating and baking the perovskite precursor solution on the patterned substrates, we obtained perovskite thin-film microarrays. The spin-coated perovskite arrays were characterized by XRD, AFM, and SEM. We concluded that patterned substrate prepared via sequential sunlight-initiated thiol-ene click reactions is suitable to fabricate perovskite arrays via the benchtop process. In addition, the same patterned substrates can be reused several times until a favorable perovskite microarray is acquired. Among a few conditions we have tested, DMSO solvent and modified FTO surfaces with alternatively carboxylic acid and alkane is the best combination to obtain high-quality perovskite microarrays. The solvent contact angle of DMSO on carboxylic acid-modified FTO surface is nearly zero and 65±3° on octadecane modified FTO surface.