High-resolution soft lithography: enabling materials for nanotechnologies

Integrating microfluidic and bioprinting technologies: advanced strategies for tissue vascularization

Tissue engineering offers immense potential for addressing the unmet needs in repairing tissue damage and organ failure. Vascularization, the development of intricate blood vessel networks, is crucial for the survival and functions of engineered tissues. Nevertheless, the persistent challenge of ensuring an ample nutrient supply within implanted tissues remains, primarily due to the inadequate formation of blood vessels. This issue underscores the vital role of the human vascular system in sustaining cellular functions, facilitating nutrient exchange, and removing metabolic waste products. In response to this challenge, new approaches have been explored. Microfluidic devices, emulating natural blood vessels, serve as valuable tools for investigating angiogenesis and allowing the formation of microvascular networks. In parallel, bioprinting technologies enable precise placement of cells and biomaterials, culminating in vascular structures that closely resemble the native vessels. To this end, the synergy of microfluidics and bioprinting has further opened up exciting possibilities in vascularization, encompassing innovations such as microfluidic bioprinting. These advancements hold great promise in regenerative medicine, facilitating the creation of functional tissues for applications ranging from transplantation to disease modeling and drug testing. This review explores the potentially transformative impact of microfluidic and bioprinting technologies on vascularization strategies within the scope of tissue engineering.

Mesoscale Filamentous Polyelectrolytes: Chemical Functionalization and Fluidic Structure

The preparation and study of synthetic mesoscale structures opens opportunities to understand soft materials properties at length scales that are intermediate between that of the molecular and bulk, often referred to as the mesoscale. This paper details the preparation of mesoscale polymer filaments, prepared by flow coating and evaporative deposition from solution to yield filamentous versions of charged polymers. Using thiol-ene reactions on olefin-containing mesoscale polymer ribbons, anionic character in the form of carboxylates is introduced to the filamentous structures. The resultant mesoscale ribbons exhibit morphological changes as a function of their aqueous solution environment, based on their neutral versus anionic character, offering insights into the structure and morphology of small, multi-length scale, soft structures comprised of macromolecular materials.

An Alternative Micro-Milling Fabrication Process for Rapid and Low-Cost Microfluidics

Microfluidics is an important technology for the biomedical industry and is often utilised in our daily lives. Recent advances in micro-milling technology have allowed for rapid fabrication of smaller and more complex structures, at lower costs, making it a viable alternative to other fabrication methods. The microfluidic chip fabrication developed in this research is a step-by-step process with a self-contained wet milling chamber. Additionally, ethanol solvent bonding is used to allow microfluidic chips to be fully fabricated within approximately an hour. The effect of using this process is tested with quantitative contact profileometery data to determine the expected surface roughness in the microchannels. The effect of surface roughness on the controllability of microparticles is tested in functional microfluidic chips using image processing to calculate particle velocity. This process can produce high-quality channels when compared with similar studies in the literature and surface roughness affects the control of microparticles. Lastly, we discuss how the outcomes of this research can produce rapid and higher-quality microfluidic devices, leading to improvement in the research and development process within the fields of science that utilise microfluidic technology. Such as medicine, biology, chemistry, ecology, and aerospace.

Grafting Block Copolymer Nanoparticles to a Surface via Aqueous Photoinduced Polymerization-induced Self-Assembly at Room Temperature

The creation of well-defined surface nanostructures is important for a diverse set of applications such as cell adhesion, superhydrophobic coating, and lithography. In this study, we describe a robust bottom-up method for surface functionalization that involves surface-initiated reversible deactivation radical polymerization (RDRP) and the grafting of block copolymer nanoparticles to material surfaces via aqueous photoinduced polymerization-induced self-assembly (photo-PISA) at room temperature. Using silica nanoparticles as a model substrate, colloidal mesoscale hybrid assemblies with various morphologies were successfully prepared. The morphologies can be easily tuned by changing the lengths of macromolecular chain transfer agents and parameters of the silica nanoparticles. The surface-initiated photo-PISA approach can also be employed for other large-scale substrates such as silicon wafer. Taking advantage of mild reaction conditions of this method (room temperature, aqueous medium, and visible light), enzymatic deoxygenation was introduced to develop oxygen-tolerant surface-initiated photo-PISA that can fabricate well-defined nanostructures on large-scale substrates under open-to-air conditions.

Theoretical Insights into the Solubility Polarity Switch of Metal-Organic Nanoclusters for Nanoscale Patterning

Metal-organic nanoclusters(MOCs) are being increasingly used as prospective photoresist candidates for advanced nanoscale lithography technologies. However, insight into the irradiation-induced solubility switching process remains unclear. Hereby, the theoretical study employing density functional theory (DFT) calculations of the alkene-containing zirconium oxide MOC photoresists is reported, which is rationally synthesized accordingly, to disclose the mechanism of the nanoscale patterning driven by the switch of solubility from the acid-catalyzed or electron-triggered ligand dissociation. By evaluating the dependence of MOCs' imaging process on photoacid, lithographies of photoresists with and without photoacid generators after exposure to ultraviolet (UV), electron beam, and soft X-ray, it is revealed that photoacid is essential in UV lithography, but it demonstrates little effect on exposure dose in high-energy lithography. Furthermore, theoretical studies using DFT simulations to investigate the plausible photoacid-catalyzed, electron-triggered dissociation, and accompanying radical reaction are performed, and a mechanism is demonstrated that the nanoscale patterning of this type of MOCs is driven by the solubility switch resulting from dissociation-induced strong electrostatic interaction and low-energy barrier radical polymerization with other species. This study can give insights into the chemical mechanisms of patterning, and guide the rational design of photoresists to realize high resolution and high sensitivity.

Exploring the Evolution of Organofluorine-Containing Compounds during Simulated Photolithography Experiments

One potential source of per- and polyfluoroalkyl substances (PFASs) in electronics fabrication wastewater are the organofluorine-containing compounds used in photolithography materials such as photoresists and top antireflective coatings (TARCs). However, the exact identities of these constituents are unknown and transformation reactions that may occur during photolithography may result in the formation of unknown or unexpected PFASs. To address this knowledge gap, we acquired five commercially relevant photolithography materials, characterized the occurrence of organofluorine-containing compounds in each material, and performed simulated photolithography experiments to stimulate any potential transformation reactions. We found that photoresists and TARCs have total fluorine (TF) concentrations in the g L-1 range, similar to the levels of other industrial and commercial products. However, the target and suspect PFASs present in these materials can only explain up to 20% of the TF in a material. We evaluated wastewater samples collected after simulated photolithography experiments and used a mass balance approach to assess the extent of transformations. Although a number of target, suspect, and nontarget PFASs were identified in the wastewater samples, the extent of transformation was limited and the fluorine contained in the PFASs could not explain more than an additional 1% of the TF in the photolithography materials.

Fast-Embeddable Grooved Microneedles by Shear Actuation for Accurate Transdermal Drug Delivery

Percutaneous drug delivery using microneedles (MNs) has been extensively exploited to increase the transdermal permeability of therapeutic drugs. However, it is difficult to control the precise dosage with existing MNs and they need to be attached for a long time, so a more simple and scalable method is required for accurate transdermal drug delivery. In this study, we developed grooved MNs that can be embedded into the skin by mechanical fracture following simple shear actuation. Grooved MNs are prepared from hyaluronic acid (HA), which is a highly biocompatible and biodegradable biopolymer. By adjusting the aspect ratio (length:diameter) of the MN and the position of the groove, the MN tip inserted into the skin can be easily broken by shear force. In addition, it was demonstrated that it is possible to deliver the desired amount of triamcinolone acetonide (TCA) for alopecia areata by controlling the position of the groove structure and the concentration of TCA loaded in the MN. It was also confirmed that the tip of the TCA MN can be accurately delivered into the skin with a high probability (98% or more) by fabricating an easy-to-operate applicator to provide adequate shear force. The grooved MN platform has proven to be able to load the desired amount of a drug and deliver it at the correct dose.

Sensors-integrated organ-on-a-chip for biomedical applications

As a promising new micro-physiological system, organ-on-a-chip has been widely utilized for in vitro pharmaceutical study and tissues engineering based on the three-dimensional constructions of tissues/organs and delicate replication of in vivo-like microenvironment. To better observe the biological processes, a variety of sensors have been integrated to realize in-situ, real-time, and sensitive monitoring of critical signals for organs development and disease modeling. Herein, we discuss the recent research advances made with respect to sensors-integrated organ-on-a-chip in this overall review. Firstly, we briefly explore the underlying fabrication procedures of sensors within microfluidic platforms and several classifications of sensory principles. Then, emphasis is put on the highlighted applications of different types of organ-on-a-chip incorporated with various sensors. Last but not least, perspective on the remaining challenges and future development of sensors-integrated organ-on-a-chip are presented.

A Sensitive and Flexible Capacitive Pressure Sensor Based on a Porous Hollow Hemisphere Dielectric Layer

Capacitive pressure sensors based on porous structures have been widely researched and applied to a variety of practical applications. To date, it remains a big challenge to develop a capacitive pressure sensor with a high sensitivity and good linearity over a wide pressure range. In this paper, a sensitive, flexible, porous capacitive pressure sensor was designed and manufactured by means of the "salt template method" and man-made grooves. To this aim, the size of the salt particles used for forming pores/air voids, time taken for thorough dissolution of salt particles, and the depth of the man-made groove by a pin were taken into consideration to achieve a better effect. With pores and the groove, the sensor is more liable be compressed, which will result in a dramatic decrease in distance between the two electrodes and a conspicuous increase of the effective dielectric constant. The optimize-designed sensor represents a sensitivity 6-8 times more than the sensor without the groove in the pressure range of 0-10 kPa, not to mention the sensor without pores or the groove, and it can keep good linearity within the measurement range (0-50 kPa). Besides, the sensor shows a low detection limit of 3.5 Pa and a fast response speed (≈50 ms), which makes it possible to detect a tiny applied pressure immediately. The fabricated sensor can be applied to wearable devices to monitor finger and wrist bending, and it can be used in the object identification of mechanical claws and object cutting of mechanical arms, and so on.

Progress of Microfluidic Hydrogel-Based Scaffolds and Organ-on-Chips for the Cartilage Tissue Engineering

Cartilage degeneration is among the fundamental reasons behind disability and pain across the globe. Numerous approaches have been employed to treat cartilage diseases. Nevertheless, none have shown acceptable outcomes in the long run. In this regard, the convergence of tissue engineering and microfabrication principles can allow developing more advanced microfluidic technologies, thus offering attractive alternatives to current treatments and traditional constructs used in tissue engineering applications. Herein, the current developments involving microfluidic hydrogel-based scaffolds, promising structures for cartilage regeneration, ranging from hydrogels with microfluidic channels to hydrogels prepared by the microfluidic devices, that enable therapeutic delivery of cells, drugs, and growth factors, as well as cartilage-related organ-on-chips are reviewed. Thereafter, cartilage anatomy and types of damages, and present treatment options are briefly overviewed. Various hydrogels are introduced, and the advantages of microfluidic hydrogel-based scaffolds over traditional hydrogels are thoroughly discussed. Furthermore, available technologies for fabricating microfluidic hydrogel-based scaffolds and microfluidic chips are presented. The preclinical and clinical applications of microfluidic hydrogel-based scaffolds in cartilage regeneration and the development of cartilage-related microfluidic chips over time are further explained. The current developments, recent key challenges, and attractive prospects that should be considered so as to develop microfluidic systems in cartilage repair are highlighted.

Micromolding of Thermoplastic Polymers for Direct Fabrication of Discrete, Multilayered Microparticles

Soft lithography provides a convenient and effective method for the fabrication of microdevices with uniform size and shape. However, formation of an embossed, connective film as opposed to discrete features has been an enduring shortcoming associated with soft lithography. Removing this residual layer requires additional postprocessing steps that are often incompatible with organic materials. This limits adaptation and widespread realization of soft lithography for broader applications particularly in drug discovery and drug delivery fields. A novel and versatile approach is demonstrated that enables fabrication of discrete, multilayered, fillable, and harvestable microparticles directly from any thermoplastic polymer, even at very high molecular weights. The approach, isolated microparticle replication via surface-segregating polymer blend mold, utilizes a random copolymer additive, designed with a highly fluorinated segment that, when blended with the mold's matrix, spontaneously orients to the surface conferring an extremely low surface energy and nonwetting properties to the template. The extremely nonwetting properties of the mold are further utilized to load soluble biologics directly into the built-in microwells in a rapid and efficient manner using an innovative screen-printing approach. It is believed that this approach holds promise for fabrication of large-array, 3D, complex microstructures, and is a significant step toward clinical translation of microfabrication technologies.

Spectroscopic ellipsometric study datasets of the fluorinated polymers: Bifunctional urethane methacrylate perfluoropolyether (PFPE) and polyvinylidene fluoride (PVDF)

The datasets in this work contain the experimentally measured (real) refractive indices, optical transmission intensity, and optical absorption spectra of bifunctional urethane methacrylate perfluoropolyether (PFPE; Fluorolink® MD700) substrate of (0.98 ± 0.13) mm thickness and polyvinylidene fluoride (PVDF; Kynar® 705) thin-film of (4.47 ± 0.29) µm thickness over a spectral range from 300 nm to 1000 nm, as measured via variable angle spectroscopic ellipsometry. The refractive indices data were determined by employing a single Cauchy optical constants function based layer using a Levenberg-Marquardt multi-iterative regression algorithm for all model minimizations. The mean-squared error (MSE) was used as the maximum likelihood estimator, with a convergence of the Levenberg-Marquardt algorithm reached when successive iterations were unable to improve the MSE. The resulting best-fit parameter values were evaluated for sensitivity (expressed as a confidence limit), and possible correlations. Furthermore, the experimentally measured optical transmission intensity and determined optical absorption of PFPE and PVDF, over a spectral range from 300 nm to 1000 nm, is also presented, as measured via ellipsometry and corrected using Fresnel equations to accommodate surface interference. Given the high transmission of (88.4 ± 0.5)% for PFPE and (95.6 ± 0.6) % for PVDF found, and the low refractive index 1.27 (λ = 589.3 nm) found for PFPE; it is thought that these datasets may be useful for optical applications, such as for photo-curable synthesis processes, or being used as a host-matrix material for photoluminescent compounds.

Additive Fabrication of a Vascular 3D Phantom for Stereotactic Radiosurgery of Arteriovenous Malformations

In this study, an efficient methodology for manufacturing a realistic three-dimensional (3D) cerebrovascular phantom resembling a brain arteriovenous malformation (AVM) for applications in stereotactic radiosurgery is presented. The AVM vascular structure was 3D reconstructed from brain computed tomography (CT) data acquired from a patient. For the phantom fabrication, stereolithography was used to produce the AVM model and combined with silicone casting to mimic the brain parenchyma surrounding the vascular structure. This model was made with tissues-equivalent materials for radiology. The hollow vascular system of the phantom was filled with a contrast agent usually employed on patients for CT scans. The radiological response of the phantom was tested and compared with the one of the clinical case. The constructed model demonstrated to be a very accurate physical representation of the AVM and its vasculature and good morphological consistency was observed between the model and the patient-specific source anatomy. These results suggest that the proposed method has potential to be used to fabricate patient-specific phantoms for neurovascular radiosurgery applications and medical research.

Endophytic Nanotechnology: An Approach to Study Scope and Potential Applications

Nanotechnology has become a very advanced and popular form of technology with huge potentials. Nanotechnology has been very well explored in the fields of electronics, automobiles, construction, medicine, and cosmetics, but the exploration of nanotecnology's use in agriculture is still limited. Due to climate change, each year around 40% of crops face abiotic and biotic stress; with the global demand for food increasing, nanotechnology is seen as the best method to mitigate challenges in disease management in crops by reducing the use of chemical inputs such as herbicides, pesticides, and fungicides. The use of these toxic chemicals is potentially harmful to humans and the environment. Therefore, using NPs as fungicides/ bactericides or as nanofertilizers, due to their small size and high surface area with high reactivity, reduces the problems in plant disease management. There are several methods that have been used to synthesize NPs, such as physical and chemical methods. Specially, we need ecofriendly and nontoxic methods for the synthesis of NPs. Some biological organisms like plants, algae, yeast, bacteria, actinomycetes, and fungi have emerged as superlative candidates for the biological synthesis of NPs (also considered as green synthesis). Among these biological methods, endophytic microorganisms have been widely used to synthesize NPs with low metallic ions, which opens a new possibility on the edge of biological nanotechnology. In this review, we will have discussed the different methods of synthesis of NPs, such as top-down, bottom-up, and green synthesis (specially including endophytic microorganisms) methods, their mechanisms, different forms of NPs, such as magnesium oxide nanoparticles (MgO-NPs), copper nanoparticles (Cu-NPs), chitosan nanoparticles (CS-NPs), β-d-glucan nanoparticles (GNPs), and engineered nanoparticles (quantum dots, metalloids, nonmetals, carbon nanomaterials, dendrimers, and liposomes), and their molecular approaches in various aspects. At the molecular level, nanoparticles, such as mesoporous silica nanoparticles (MSN) and RNA-interference molecules, can also be used as molecular tools to carry genetic material during genetic engineering of plants. In plant disease management, NPs can be used as biosensors to diagnose the disease.

Preparation and application of carbon and hollow TiO2 microspheres by microwave heating at a low temperature

A fast, simple, and energy-saving microwave-assisted approach was successfully developed to prepare carbon microspheres. The carbon microspheres with a uniform particle size and good dispersity were prepared using glucose as the raw material and HCl as the dehydrating agent at low temperature (90°C) in an open system with the assistance of microwave heating. The carbon microspheres were characterized by elemental analysis, XRD, SEM, FTIR, TG, and Raman. The results showed that the carbon microspheres prepared under the condition of 18.5% (v/v) HCl and heating for 30 min by microwave had a narrow size distribution. The core–shell structure of the carbon core and TiO2 shell was prepared with (NH4)2TiF6, H3BO3 using the microwave-assisted method. The hollow TiO2 microspheres with good crystallinity and high photocatalytic properties were successfully prepared by sacrificing the carbon microspheres.

Integration of FISH and Microfluidics

Suitable molecular methods for a faster microbial identification in food and clinical samples have been explored and optimized during the last decades. However, most molecular methods still rely on time-consuming enrichment steps prior to detection, so that the microbial load can be increased and reach the detection limit of the techniques.In this chapter, we describe an integrated methodology that combines a microfluidic (lab-on-a-chip) platform, designed to concentrate cell suspensions and speed up the identification process in Saccharomyces cerevisiae , and a peptide nucleic acid fluorescence in situ hybridization (PNA-FISH) protocol optimized and adapted to microfluidics. Microfluidic devices with different geometries were designed, based on computational fluid dynamics simulations, and subsequently fabricated in polydimethylsiloxane by soft lithography. The microfluidic designs and PNA-FISH procedure described here are easily adaptable for the detection of other microorganisms of similar size.

Advanced Fabrication Techniques of Microengineered Physiological Systems

The field of organs-on-chips (OOCs) has experienced tremendous growth over the last decade. However, the current main limiting factor for further growth lies in the fabrication techniques utilized to reproducibly create multiscale and multifunctional devices. Conventional methods of photolithography and etching remain less useful to complex geometric conditions with high precision needed to manufacture the devices, while laser-induced methods have become an alternative for higher precision engineering yet remain costly. Meanwhile, soft lithography has become the foundation upon which OOCs are fabricated and newer methods including 3D printing and injection molding show great promise to innovate the way OOCs are fabricated. This review is focused on the advantages and disadvantages associated with the commonly used fabrication techniques applied to these microengineered physiological systems (MPS) and the obstacles that remain in the way of further innovation in the field.

Modular Fabrication of Intelligent Material-Tissue Interfaces for Bioinspired and Biomimetic Devices

One of the goals of biomaterials science is to reverse engineer aspects of human and nonhuman physiology. Similar to the body's regulatory mechanisms, such devices must transduce changes in the physiological environment or the presence of an external stimulus into a detectable or therapeutic response. This review is a comprehensive evaluation and critical analysis of the design and fabrication of environmentally responsive cell-material constructs for bioinspired machinery and biomimetic devices. In a bottom-up analysis, we begin by reviewing fundamental principles that explain materials' responses to chemical gradients, biomarkers, electromagnetic fields, light, and temperature. Strategies for fabricating highly ordered assemblies of material components at the nano to macro-scales via directed assembly, lithography, 3D printing and 4D printing are also presented. We conclude with an account of contemporary material-tissue interfaces within bioinspired and biomimetic devices for peptide delivery, cancer theranostics, biomonitoring, neuroprosthetics, soft robotics, and biological machines.

Photofabrication of polymeric biomicrofluidics: New insights into material selection

We propose a versatile method to evaluate the suitability of polymers for the fabrication of microfluidic devices for biomedical applications, based on the concept that the selection and the design of convenient materials should involve different properties depending on the final microfluidic application. Here polymerase chain reaction (PCR) is selected as biological model and target microfluidic reaction. A class of photocured siloxanes is introduced as device building polymers and copolymerization is adopted as strategy to finely tune and optimize the final material properties. All-polymeric flexible devices are easily fabricated exploiting the rapidity of the photopolymerization reaction: they resist to thermal cycles without leakage or de-bonding (i.e., without separation of different chip parts made of the same material bonded together), show very limited water swelling and permeability, are bioinert and prevent the inhibition of the biochemical reaction. PCR is thus successfully conducted in the photocured microfluidic devices made with a specifically designed siloxane copolymer.

Soft thermal nanoimprint with a 10 nm feature size

Nanoimprinting with rigid molds offers almost unlimited pattern resolution, but it suffers from high sensitivity to defects, and is limited to pattering flat surfaces. These limitations can be addressed by nanoimprinting with soft molds. However, soft molds have been used so far with UV resists, and could not achieve a resolution and minimal feature size comparable to those of rigid molds. Here, we explore the miniaturization edge of soft nanoimprint molds, and demonstrate their compatibility with thermal imprint resists. To that end, we produced a pattern with 10 nm critical dimensions, using electron beam lithography, and used it to replicate nanoimprint molds by direct casting of an elastomer onto the patterned resist. We showed that the produced pattern can be faithfully transferred from the mold by thermal nanoimprinting. In addition, we showed that similar nanoimprint molds can also be produced by double replication, which includes nanoimprinting of a thermal resist with an ultrahigh resolution rigid mold, and replication of a soft mold from the imprint pattern. We also demonstrated our novel nanoimprinting approach in two unconventional applications: nanopatterning of a thermal resist on a lens surface, and direct nanoimprinting of chalcogenide glass. Our novel nanoimprint approach pushes the envelope of standard nanofabrication, and demonstrates its potential for numerous applications impossible up to now.

Hierarchical Nanoparticle Assemblies Formed via One-Step Catalytic Stamp Pattern Transfer

The one-step catalytic stamp pattern transfer process is described for producing arrays of hierarchical nanoparticle assemblies. The method simply combines in situ nanoparticle synthesis triggered by free residual Si-H groups on PDMS stamps and the lift-off pattern transfer technique. No additional nanoparticle synthesis procedure is required before the pattern transfer process. Exquisitely uniform and precisely spaced hierarchical nanoparticle assemblies with designed geometry can be rapidly produced using the catalytic stamp pattern transfer process. Sequential catalytic stamp pattern transfer also is described to generate multilayered, hierarchical nanoparticle assemblies with various geometries. The hierarchical nanoparticle assemblies catalytically transferred onto the surface are not just nanoparticles but nanoparticle-polydimethylsiloxane residue composites. The in situ-synthesized nanoparticles retain optical properties. The hierarchical nanoparticle assemblies with precisely controlled geometry further show potential in the application of surface-enhanced Raman scattering. The capability of one-step catalytic stamp pattern transfer allows the scalable and reproducible fabrication of well-defined hierarchical nanoparticle assemblies.

Step-growth Production of Nanogels for Use as Macromers with Dimethacrylate Monomers

A series of functional nanogels were synthesized by a step-growth mechanism that involved diisocyanate addition to a modest stoichiometric excess of multi-thiols. Nanogels with sizes less than 10 nm were obtained as room temperature liquids with residual thiol groups used to attach methacrylate functionality. Depending on nanogel structure, bulk nanogel properties varied widely, as did the properties of the nanogel-derived and nanogel-modified polymers. Photopolymerization of the reactive nanogels in combination with a dimethacrylate monomer showed dramatically enhanced reaction rate and conversion compared with the dimethacrylate homopolymer. Polymerization shrinkage/ stress as well as mechanical properties of the polymer networks were controlled by changing the ratio of nanogels and dimethacrylate monomers used in formulations. Thus, this study shows the potential of step-growth nanogels for beneficial changes in resin reactivity and application-based performance.

How to design preclinical studies in nanomedicine and cell therapy to maximize the prospects of clinical translation

The clinical translation of promising products, technologies and interventions from the disciplines of nanomedicine and cell therapy has been slow and inefficient. In part, translation has been hampered by suboptimal research practices that propagate biases and hinder reproducibility. These include the publication of small and underpowered preclinical studies, suboptimal study design (in particular, biased allocation of experimental groups, experimenter bias and lack of necessary controls), the use of uncharacterized or poorly characterized materials, poor understanding of the relevant biology and mechanisms, poor use of statistics, large between-model heterogeneity, absence of replication, lack of interdisciplinarity, poor scientific training in study design and methods, a culture that does not incentivize transparency and sharing, poor or selective reporting, misaligned incentives and rewards, high costs of materials and protocols, and complexity of the developed products, technologies and interventions. In this Perspective, we discuss special manifestations of these problems in nanomedicine and in cell therapy, and describe mitigating strategies. Progress on reducing bias and enhancing reproducibility early on ought to enhance the translational potential of biomedical findings and technologies.

Selection of UV-resins for nanostructured molds for thermal-NIL

Nanoimprint molds made of soft polymeric materials have advantages of low demolding force and low fabrication cost over Si or metal-based hard molds. However, such advantages are often sacrificed by their reduced replication fidelity associated with the low mechanical strength. In this paper, we studied replication fidelity of different UV-resin molds copied from a Si master mold via UV nanoimprint lithography (NIL) and their thermal imprinting performance into a thermoplastic polymer. Four different UV-resins were studied: two were high surface energy UV-resins based on tripropyleneglycol diacrylate (TPGDA resin) and polypropyleneglycol diacrylate (PPGDA resin), and the other two were commercially available, low surface energy poly-urethane acrylate (PUA resin) and fluorine-containing (MD 700) UV-resins. The replication fidelity among the four UV-resins during UV nanoimprint lithograph from a Si master with sharp nanostructures was in the increasing order of (poorest) PUA resin < MD 700 < PPGDA resin < TPGDA resin (best). The results show that the high surface energy and small monomer size are keys to achieving good UV-resin filling into sharp nanostructures over the viscosity of the resin solution. When the four UV-resin molds were used for thermal-NIL into a thermoplastic polymer, the replication fidelity was in the increasing order of (poorest) MD 700 < TPGDA resin < PUA resin (best), which follows the same order of their Young's moduli. Our results indicate that the selection of an appropriate UV-resin for NIL molds requires consideration of the replication fidelities in the mold fabrication and the subsequent thermal-NIL into thermoplastic polymers.

Spontaneous Registration of Sub-10 nm Features Based on Subzero Celsius Spin-Casting of Self-Assembling Building Blocks Directed by Chemically Encoded Surfaces

For low-cost and facile fabrication of innovative nanoscale devices with outstanding functionality and performance, it is critical to develop more practical patterning solutions that are applicable to a wide range of materials and feature sizes while minimizing detrimental effects by processing conditions. In this study, we report that area-selective sub-10 nm pattern formation can be realized by temperature-controlled spin-casting of block copolymers (BCPs) combined with submicron-scale-patterned chemical surfaces. Compared to conventional room-temperature spin-casting, the low temperature ( e.g., -5 °C) casting of the BCP solution on the patterned self-assembled monolayer achieved substantially improved area selectivity and uniformity, which can be explained by optimized solvent evaporation kinetics during the last stage of film formation. Moreover, the application of cold spin-casting can also provide high-yield in situ patterning of light-emitting CdSe/ZnS quantum dot thin films, indicating that this temperature-optimized spin-casting strategy would be highly effective for tailored patterning of diverse organic and hybrid materials in solution phase.

Perfluoropolyether (PFPE) Intermediate Molds for High-Resolution Thermal Nanoimprint Lithography

Among soft lithography techniques, Thermal Nanoimprint Lithography (NIL) is a high-throughput and low-cost process that can be applied to a broad range of thermoplastic materials. By simply applying the appropriate pressure and temperature combination, it is possible to transfer a pattern from a mold surface to the chosen material. Usually, high-resolution and large-area NIL molds are difficult to fabricate and expensive. Furthermore, they are typically made of silicon or other hard materials such as nickel or quartz for preserving their functionality. Nonetheless, after a large number of imprinting cycles, they undergo degradation and become unusable. In this paper, we introduce and characterize an innovative two-step NIL process based on the use of a perfluoropolyether (PFPE) intermediate mold to replicate sub-100 nm features from a silicon mold to the final thermoplastic material. We compare PFPE elastomeric molds with molds made of the standard polydimethylsiloxane (PDMS) elastomer, which demonstrates better resolution and fidelity of the replica process. By using PFPE intermediate molds, the nanostructured masters are preserved and the throughput of the process is significantly enhanced.

Poly(dimethylsiloxane) Stamp Coated with a Low-Surface-Energy, Diffusion-Blocking, Covalently Bonded Perfluoropolyether Layer and Its Application to the Fabrication of Organic Electronic Devices by Layer Transfer

It is demonstrated that a stamp composed of a poly(dimethylsiloxane) (PDMS) bulk and perfluoropolyether (PFPE) coating fabricated by a simple dip-coating method has the following properties that are ideal for the transfer patterning of various materials. Deposited by a condensation reaction between PDMS and PFPE molecules as well as the adjacent PFPE molecules, the PFPE coating has a strong adhesion to the PDMS surface and strong internal cohesion, while providing a low energy surface. Furthermore, it is found to function as a bidirectional diffusion barrier: it effectively prevents organic small molecules deposited on the stamp from being absorbed into free volumes of PDMS; it also prevents PDMS oligomers from migrating onto the layer to be transferred, thereby avoiding the contamination of that layer. Morphological and elemental characterization of the surfaces of the transferred organic semiconductor and graphene layers confirms a successful transfer with a high degree of surface cleanliness. The quality of interfaces mechanically bonded using the PFPE-coated stamps and the cleanliness of the transferred layers are remarkably high that the electronic functions of a transfer-bonded organic heterojunction are comparable to those of the same interface formed by vacuum deposition, and that the charge transport across the transfer-bonded graphene-graphene and graphene-MoO₃ interfaces is efficient. Our results demonstrate that the PFPE-coated stamp enables patterned depositions of materials with high quality interfaces while avoiding a high temperature or wet process.

Novel Nano-Materials and Nano-Fabrication Techniques for Flexible Electronic Systems

Recent progress in fabricating flexible electronics has been significantly developed because of the increased interest in flexible electronics, which can be applied to enormous fields, not only conventional in electronic devices, but also in bio/eco-electronic devices. Flexible electronics can be applied to a wide range of fields, such as flexible displays, flexible power storages, flexible solar cells, wearable electronics, and healthcare monitoring devices. Recently, flexible electronics have been attached to the skin and have even been implanted into the human body for monitoring biosignals and for treatment purposes. To improve the electrical and mechanical properties of flexible electronics, nanoscale fabrications using novel nanomaterials are required. Advancements in nanoscale fabrication methods allow the construction of active materials that can be combined with ultrathin soft substrates to form flexible electronics with high performances and reliability. In this review, a wide range of flexible electronic applications via nanoscale fabrication methods, classified as either top-down or bottom-up approaches, including conventional photolithography, soft lithography, nanoimprint lithography, growth, assembly, and chemical vapor deposition (CVD), are introduced, with specific fabrication processes and results. Here, our aim is to introduce recent progress on the various fabrication methods for flexible electronics, based on novel nanomaterials, using application examples of fundamental device components for electronics and applications in healthcare systems.

A facile method to functionalize gold nano-tripods with high suspension stability in an aqueous environment

Here we aim to develop a facile emulsion-based method to prepare tripod gold nanoparticles (AuNPs) with high suspension stability in an aqueous environment. A gyroid-structured polymer template formed by the hydrolysis of a degradable block copolymer, polystyrene (PS)-b-poly(l-lactide), is used for the fabrication of AuNPs. Also, a successful emulsification of dichloromethane (DCM) in the aqueous phase is developed by using thiolated polyethylene glycol (PEG-SH) as the stabilizer. Subsequently, the nanohybrids of PS/Au can be fabricated by templated electroless plating, and then selectively dissolving in the DCM dispersive phase. Most interestingly, a dedicated process for the simultaneous release of the tripod AuNPs from the dissolution of PS associated with PEG-SH at the interface of the emulsion is achieved, giving PEG-SH-functionalized tripod AuNPs dispersed in the aqueous phase, which significantly improves the suspension stabilization of tripod AuNPs. The in situ temperature-programmed electrospray-differential mobility analysis provides a quantitative, statistical analysis of mobility diameter, dynamic shape factor, polydispersity, and colloidal stability.

Polymeric nanorods with aggregation-induced emission characteristics for enhanced cancer targeting and imaging

Polymeric nanorods loaded with AIEgens are synthesized via nano-precipitation under ultrasound sonication, where prolonged sonication time could induce a nanodot-to-nanorod transition. These AIE nanorods, but not the nanodots, could be selectively internalized into cancer cells, which show better tumor accumulation, higher tumor penetration and more efficient in vivo cancer cell uptake.

Real-Time Tunable Colors from Microfluidic Reconfigurable All-Dielectric Metasurfaces

Structural colors arising from all-dielectric nanostructures are very promising for high-resolution color nanoprinting and high-density optical storage. However, once the all-dielectric nanostructures are fabricated, their optical performances are usually static or change slowly, significantly limiting the practical applications in advanced displays. Herein, we experimentally demonstrate the real-time tunable colors with microfluidic reconfigurable all-dielectric metasurfaces. The metasurface is composed of an array of TiO₂ nanoblocks, which are embedded in a polymeric microfluidic channel. By injecting solutions with a different refractive index into the channel, the narrow band reflection peak and the corresponding distinct colors of a TiO₂ metasurface can be precisely controlled. The transition time is as small as 16 ms, which is orders of magnitude faster than the current techniques. By varying the lattice size of TiO₂ metasurfaces, the real-time tunable colors are able to span the entire visible spectrum. Meanwhile, the injection and ejection of solvent have also shown the capability of the erasion and the restoration of information encoded in TiO₂ metasurfaces. The combination of all-dielectric nanostructures with microfluidic channels shall boost their applications in functional color display, banknote security, anticounterfeiting, and point-of-care devices.

Partially Cured Photopolymer with Gradient Bingham Plastic Behaviors as a Versatile Deformable Material

We present rheological and mechanical behaviors of a partially cured photopolymer. When an ultraviolet (UV)-curable resin is exposed to UV light in atmospheric conditions, a partially cured layer is formed on the top of the resin owing to inhibitory effects of oxygen. Interestingly, such a partially cured resin behaves like a Bingham plastic with a yield stress, being a rigid solid at low shear stress and a viscous liquid at high stress. Unlike typical Bingham plastic materials, however, deformation rate saturation is observed with an increase in applied stress, which is attributed to the gradient in the degree of photopolymerization of the resin (termed "gradient Bingham plastic"). This gradient Bingham plastic can be utilized for the robust fabrication of diverse 3D, multiscale structures.

Toward Scalable Flexible Nanomanufacturing for Photonic Structures and Devices

Continuous and scalable nanopatterning over flexible substrates is highly desirable for both commercial and scientific interests, but is difficult to realize with traditional photolithographic processes. The recent advancements in nanofabrication methodologies enable light management with photonic structures on flexible materials, providing an increasingly popular strategy to control the light harvesting in the optoelectronic devices of photovoltaics, and in organic and inorganic light-emitting diodes. Here, the current status of nanopatterning technologies for the fabrication of optoelectronic devices is summarized. Scalable nanopatterning technologies for nanomanufacturing on flexible materials are emphasized. Critical challenges in various patterning techniques when considering the resolution, scalability, processing throughput, and the use of masks and resists are addressed. The integration of flexible nanopatterned substrates with light manipulation in organic optoelectronic devices is also discussed; this enables the control of light flux and spectra. Finally, potential development directions are highlighted.

Diazoketo-functionalized POSS resists for high performance replica molds of ultraviolet-nanoimprint lithography

Novel polyhedral oligomeric silsesquioxane (POSS) resists, which are based on a new photo-crosslinking system via Wolff rearrangement, are developed as ideal replica mold materials for ultraviolet-nanoimprint lithography. These POSS resist materials are synthesized by incorporating diazoketo and hydroxyl groups into the POSS core. The resist materials have exhibited a variety of desirable properties as replica molds, such as high modulus, low shrinkage ratio, high transparency, low surface energy, and resistance to organic solvents. The resultant replica molds exhibit a high resolution patterning capacity. These economic fabrication methods of replica molds with high mechanical durability and good releasing properties are potentially useful for versatile applications in the area of mold-based lithography.

Organic Polymer Chemistry in the Context of Novel Processes

This article was written to shed light on a series of what some have stated are not so obvious connections that link polymer synthesis in supercritical CO₂ to cancer treatment and vaccines, nonflammable polymer electrolytes for lithium ion batteries, and 3D printing. In telling this story, we also attempt to show the value of versatility in applying one's primary area of expertise to address pertinent questions in science and in society. In this Outlook, we attempted to identify key factors to enable a versatile and nimble research effort to take shape in an effort to influence diverse fields and have a tangible impact in the private sector through the translation of discoveries into the marketplace.

Standard Reticle Slide To Objectively Evaluate Spatial Resolution and Instrument Performance in Imaging Mass Spectrometry

Spatial resolution is a key parameter in imaging mass spectrometry (IMS). Aside from being a primary determinant in overall image quality, spatial resolution has important consequences on the acquisition time of the IMS experiment and the resulting file size. Hardware and software modifications during instrumentation development can dramatically affect the spatial resolution achievable using a given imaging mass spectrometer. As such, an accurate and objective method to determine the working spatial resolution is needed to guide instrument development and ensure quality IMS results. We have used lithographic and self-assembly techniques to fabricate a pattern of crystal violet as a standard reticle slide for assessing spatial resolution in matrix-assisted laser desorption/ionization (MALDI) IMS experiments. The reticle is used to evaluate spatial resolution under user-defined instrumental conditions. Edgespread analysis measures the beam diameter for a Gaussian profile and line scans measure an "effective" spatial resolution that is a convolution of beam optics and sampling frequency. The patterned crystal violet reticle was also used to diagnose issues with IMS instrumentation such as intermittent losses of pixel data.

Highly conformal fabrication of nanopatterns on non-planar surfaces

While the number of techniques for patterning materials at the nanoscale exponentially increases, only a handful of methods approach the conformal patterning of strongly non-planar surfaces. Here, using the direct surface self-assembly of colloids by electrostatics, we produce highly conformal bottom-up nanopatterns with a short-range order. We illustrate the potential of this approach by devising functional nanopatterns on highly non-planar substrates such as pyramid-textured silicon substrates and inherently rough polycrystalline films. We further produce functionalized polycrystalline thin-film silicon solar cells with enhanced optical performance. The perspective presented here to pattern essentially any surface at the nanoscale, in particular surfaces with high inherent roughness or with microscale features, opens new possibilities in a wide range of advanced technologies from affordable photovoltaics and optoelectronics to cellular engineering.

Athermal Azobenzene-Based Nanoimprint Lithography

A novel nanoimprint lithography technique based on the photofluidization effect of azobenzene materials is presented. The tunable process allows for imprinting under ambient conditions without crosslinking reactions, so that shrinkage of the resist is avoided. Patterning of surfaces in the regime from micrometers down to 100 nm is demonstrated.

Ultrafast direct fabrication of flexible substrate-supported designer plasmonic nanoarrays

Fabrication of plasmonic nanostructures has been an important topic for their potential applications in photonic and optoelectronic devices. Among plasmonic materials, gold is one of the most promising materials due to its low ohmic loss at optical frequencies and high oxidation resistance. However, there are two major bottlenecks for its industrial applications: (1) the need for large-scale fabrication technology for high-precision plasmonic nanostructures; and (2) the need to integrate the plasmonic nanostructures on various substrates. While conventional top-down approaches involve high cost and give low throughput, bottom-up approaches suffer from irreproducibility and low precision. Herein, we report laser shock induced direct imprinting of large-area plasmonic nanostructures from physical vapor deposited (PVD) gold thin film on a flexible commercial free-standing aluminum foil. Among the important characteristics of the laser-shock direct imprinting is their unique capabilities to reproducibly deliver designer plasmonic nanostructures with extreme precision and in an ultrafast manner. Excellent size tunability (from several μm down to 15 nm) has been achieved by varying mold dimensions and laser parameters. The physical mechanism of the hybrid film imprinting is elaborated by finite element modeling. A mechanical robustness test of the hybrid film validates a significantly improved interfacial contact between gold arrays and the underlying substrate. The strong optical field enhancement was realized in the large-area fabricated engineered gold nanostructures. Low concentration molecular sensing was investigated employing the fabricated structures as surface-enhanced Raman scattering (SERS) substrates. The ability to ultrafast direct imprint plasmonic nanoarrays on a flexible substrate at multiscale is a critical step towards roll-to-roll manufacturing of multi-functional devices which is poised to inspire several emerging applications.

Solvent compatible microfluidic platforms for pharmaceutical solid form screening

The use of SIFEL in the crystallization fluid layers renders the microfluidic crystallization array compatible with solvents such as tetrahydrofuran, acetonitrile, chloroform, hexane, and toluene.