Patterning Hydrophobic Surfaces by Negative Microcontact Printing and Its Applications

Patient-derived tumor-like cell clusters for personalized chemo- and immunotherapies in non-small cell lung cancer

Many patient-derived tumor models have emerged recently. However, their potential to guide personalized drug selection remains unclear. Here, we report patient-derived tumor-like cell clusters (PTCs) for non-small cell lung cancer (NSCLC), capable of conducting 100-5,000 drug tests within 10 days. We have established 283 PTC models with an 81% success rate. PTCs contain primary tumor epithelium self-assembled with endogenous stromal and immune cells and show a high degree of similarity to the original tumors in phenotypic and genotypic features. Utilizing standardized culture and drug-response assessment protocols, PTC drug-testing assays reveal 89% overall consistency in prospectively predicting clinical outcomes, with 98.1% accuracy distinguishing complete/partial response from progressive disease. Notably, PTCs enable accurate prediction of clinical outcomes for patients undergoing anti-PD1 therapy by combining cell viability and IFN-γ value assessments. These findings suggest that PTCs could serve as a valuable preclinical model for personalized medicine and basic research in NSCLC.

Facile and Rapid Microcontact Printing of Additive-Free Polydimethylsiloxane for Biological Patterning Diversity

The development and application of micropatterning technology play a promising role in the manipulation of biological substances and the exploration of life sciences at the microscale. However, the universally adaptable micropatterning method with user-friendly properties for acceptance in routine laboratories remains scarce. Herein, a green, facile, and rapid microcontact printing method is reported for upgrading popularization and diversification of biological patterning. The three-step printing can achieve high simplicity and fidelity of additive-free polydimethylsiloxane (PDMS) micropatterning and chip fabrication within 8 min as well as keep their high stability and diversity. A detailed experimental report is provided to support the advanced microcontact printing method. Furthermore, the applications of easy-to-operate PDMS-patterned chips are extensively validated to complete microdroplet array assembly with spatial control, cell pattern formation with high efficiency and geometry customization, and microtissue assembly and biomimetic tumor construction on a large scale. This straightforward method promotes diverse micropatternings with minimal time, effort, and expertise and maximal biocompatibility, which might broaden its applications in interdisciplinary scientific communities. This work also offers an insight into the establishment of popularized and market-oriented microtools for biomedical purposes such as biosensing, organs on a chip, cancer research, and bioscreening.

Dielectric Liquid Microlens Array with Tunable Focal Length Based on Microdroplet Array Created via Dip-Coating Method

A dielectric liquid microlens array (LMA) with a tunable focal length was fabricated by using a microdroplet array generated through the dip-coating method. The process began with treating the octadecyltrichlorosilane (OTS) layer with selective UV/O3 irradiation for 20 min to establish a hydrophilic-hydrophobic patterning surface. The substrate was subsequently immersed in glycerol and then withdrawn at a constant rate to create a microdroplet array. Upon filling the cell with matching oil (SL5267) and placing it within a square array of a 200 μm diameter glycerol microdroplet array, the LMA was produced. The focal length ranged from approximately -0.96 to -0.3 mm within a voltage range of 0 to 60 Vrms. The glycerol microdroplets, characterized by their shapes, sizes, curvatures, and filling factors, can be precisely controlled by designing an OTS patterning or adjusting the dip-coating speed. This approach offers a rapid and high-throughput method for preparation. Our approach to fabricating tunable LMA offers several advantages, including simplicity of fabrication, uniform structural properties, cost-effectiveness, polarization independence, and excellent optical performance. These focus-tunable LMAs hold significant potential for applications in image processing, 3D displays, medical endoscopy, and military technologies.

Straightforward Cell Patterning with Ultra-Low Background Using Polydimethylsiloxane Through-Hole Membranes

Micropatterning is becoming an increasingly popular tool to realize microscale cell positioning and decipher cell activities and functions under specific microenvironments. However, a facile methodology for building a highly precise cell pattern still remains challenging. In this study, A simple and straightforward method for stable and efficient cell patterning with ultra-low background using polydimethylsiloxane through-hole membranes is developed. The patterning process is conveniently on the basis of membrane peeling and routine pipetting. Cell patterning in high quality involving over 97% patterning coincidence and zero residue on the background is achieved. The high repeatability and stability of the established method for multiple types of cell arrangements with different spatial profiles is demonstrated. The customizable cell patterning with ultra-low background and high diversity is confirmed to be quite feasible and reliable. Furthermore, the applicability of the patterning method for investigating the fundamental cell activities is also verified experimentally. The authors believe this microengineering advancement has valuable applications in many microscale cell manipulation-associated research fields including cell biology, cell engineering, cell imaging, and cell sensing.

Massively Parallel High-Throughput Single-Cell Patterning and Large Biomolecular Delivery in Mammalian Cells Using Light Pulses

The recent advancements of single-cell analysis have significantly enhanced the ability to understand cellular physiology when compared to bulk cellular analysis. Here a massively parallel single-cell patterning and very large biomolecular delivery is reported. Micro-pillar polydimethyl siloxane stamp with different diameters (40-100 µm with 1 cm × 1 cm patterning area) is fabricated and then imprint distinct proteins and finally pattern single-cell to small clusters of cells depending on the micro-pillar diameters. The maximum patterning efficiency is achieved 99.7% for SiHa, 96.75% for L929, and 98.6% for MG63 cells, for the 100 µm micro-pillar stamp. For intracellular delivery of biomolecules into the patterned cells, a titanium micro-dish device is aligned on top of the cells and exposed by infrared light pulses. The platform successfully delivers small to very large biomolecules such as PI dyes (668 Da), dextran 3000 Da, siRNA (20-24 bp), and large size enzymes (464 KDa) in SiHa, L929 and MG63 cells. The delivery efficiency for PI dye, Dextran 3000, siRNA, and enzyme for patterned cells are ≈95 ± 3%, 97 ± 1%, 96 ± 1% and 94 ± 3%, with cell viability of 98 ± 1%. Thus, the platform is compact, robust, easy for printing, and potentially applicable for single-cell therapy and diagnostics.

Surface modification for improving immunoassay sensitivity

Immunoassays are widely performed in many fields such as biomarker discovery, proteomics, drug development, and clinical diagnosis. There is a growing need for high sensitivity of immunoassays to detect low abundance analytes. As a result, great effort has been made to improve the quality of surfaces, on which the immunoassay is performed. In this review article, we summarize the recent progress in surface modification strategies for improving the sensitivity of immunoassays. The surface modification strategies can be categorized into two groups: antifouling coatings to reduce background noise and nanostructured surfaces to amplify the signals. The first part of the review summarizes the common antifouling coating techniques to prevent nonspecific binding and reduce background noise. The techniques include hydrophilic polymer based self-assembled monomers, polymer brushes, and surface attached hydrogels, and omniphobicity based perfluorinated surfaces. In the second part, some common nanostructured surfaces to amplify the specific detection signals are introduced, including nanoparticle functionalized surfaces, two dimensional (2D) nanoarrays, and 2D nanomaterial coatings. The third part discusses the surface modification techniques for digital immunoassays. In the end, the challenges and the future perspectives of the surface modification techniques for immunoassays are presented.

Rapid Assembly of Cellulose Microfibers into Translucent and Flexible Microfluidic Paper-Based Analytical Devices via Wettability Patterning

Microfluidic paper-based analytical devices (μPADs) are emerging as powerful analytical platforms in clinical diagnostics, food safety, and environmental protection because of their low cost and favorable substrate properties for biosensing. However, the existing top-down fabrication methods of paper-based chips suffer from low resolution (>200 μm). Additionally, papers have limitations in their physical properties (e.g., thickness, transmittance, and mechanical flexibility). Here, we demonstrate a bottom-up approach for the rapid fabrication of heterogeneously controlled paper-based chip arrays. We simply print a wax-patterned microchip with wettability contrasts, enabling automatic and selective assembly of cellulose microfibers to construct predefined paper-based microchip arrays with controllable thickness. This paper-based microchip printing technology is feasible for various substrate materials ranging from inorganic glass to organic polymers, providing a versatile platform for the full range of applications including transparent devices and flexible health monitoring. Our bottom-up printing technology using cellulose microfibers as the starting material provides a lateral resolution down to 42 ± 3 μm and achieves the narrowest channel barrier down to 33 ± 2 μm. As a proof-of-concept demonstration, a flexible paper-based glucose monitor is built for human health care, requiring only 0.3 μL of sample for testing.

Micro-patterned cell populations as advanced pharmaceutical drugs with precise functional control

Human cells are both advanced pharmaceutical drugs and 'drug deliverers'. However, functional control prior to or after cell implantation remains challenging. Micro-patterning cells through geometrically defined adhesion sites allows controlling morphogenesis, polarity, cellular mechanics, proliferation, migration, differentiation, stemness, cell-cell interactions, collective cell behavior, and likely immuno-modulatory properties. Consequently, generating micro-patterned therapeutic cells is a promising idea that has not yet been realized and few if any steps have been undertaken in this direction. This review highlights potential therapeutic applications, summarizes comprehensively the many cell functions that have been successfully controlled through micro-patterning, details the established micro-pattern designs, introduces the available fabrication technologies to the non-specialized reader, and suggests a quality evaluation score. Such a broad review is not yet available but would facilitate the manufacturing of therapeutically patterned cell populations using micro-patterned cell-instructive biomaterials for improved functional control as drug delivery systems in the context of cells as pharmaceutical products.

Advances in Single-Cell Printing

Single-cell analysis is becoming an indispensable tool in modern biological and medical research. Single-cell isolation is the key step for single-cell analysis. Single-cell printing shows several distinct advantages among the single-cell isolation techniques, such as precise deposition, high encapsulation efficiency, and easy recovery. Therefore, recent developments in single-cell printing have attracted extensive attention. We review herein the recently developed bioprinting strategies with single-cell resolution, with a special focus on inkjet-like single-cell printing. First, we discuss the common cell printing strategies and introduce several typical and advanced printing strategies. Then, we introduce several typical applications based on single-cell printing, from single-cell array screening and mass spectrometry-based single-cell analysis to three-dimensional tissue formation. In the last part, we discuss the pros and cons of the single-cell strategies and provide a brief outlook for single-cell printing.

Patient-derived tumor-like cell clusters for drug testing in cancer therapy

Several patient-derived tumor models emerged recently as robust preclinical drug-testing platforms. However, their potential to guide clinical therapy remained unclear. Here, we report a model called patient-derived tumor-like cell clusters (PTCs). PTCs result from the self-assembly and proliferation of primary epithelial, fibroblast, and immune cells, which structurally and functionally recapitulate original tumors. PTCs enabled us to accomplish personalized drug testing within 2 weeks after obtaining the tumor samples. The defined culture conditions and drug concentrations in the PTC model facilitate its clinical application in precision oncology. PTC tests of 59 patients with gastric, colorectal, or breast cancers revealed an overall accuracy of 93% in predicting their clinical outcomes. We implemented PTC to guide chemotherapy selection for a patient with mucinous rectal adenocarcinoma who experienced recurrence with metastases after conventional therapy. After three cycles of a nonconventional therapy identified by the PTC, the patient showed a positive response. These findings need to be validated in larger clinical trials, but they suggest that the PTC model could be prospectively implemented in clinical decision-making for therapy selection.

Multifunctional Printable Micropattern Array for Digital Nucleic Acid Assay for Microbial Pathogen Detection

The digital nucleic acid assay is a precise, sensitive, and reproducible method for determining the presence of individual target molecules separated in designated partitions; thus, this technique can be used for the nucleic acid detection. Here, we propose a multifunctional micropattern array capable of isolating individual target molecules into partitions and simultaneous on-site cell lysis to achieve a direct DNA extraction and digitized quantification thereof. The multifunctional micropattern array is fabricated by the deposition of a copolymer film, poly(2-dimethylaminomethyl styrene-co-hydroxyethyl methacrylate) (pDH), directly on a microfluidic chip surface via the photoinitiated chemical vapor deposition process, followed by hydrophobic microcontact printing (μCP) to define each partition for the nucleic acid isolation. The pDH layer is a positively charged surface, which is desirable for the bacterial lysis and DNA capture, while showing exceptional water stability for more than 24 h. The hydrophobic μCP-treated pDH surface is stable under aqueous conditions at a high temperature (70 °C) for 1 h and enables the rapid and reliable formation of thousands of sessile microdroplets for the compartmentalization of an aqueous sample solution without involving bulky and costly microfluidic devices. By assembling the multifunctional micropattern array into the microfluidic chip, the isothermal amplification in each partition can detect DNA templates over a concentration range of 0.01-2 ng/μL. The untreated bacterial cells can also be directly compartmentalized via the microdroplet formation, followed by the on-site cell lysis and DNA capture on the compartmentalized pDH surface. For Escherichia coli O157:H7, Salmonella enteritidis, and Staphylococcus aureus cells, cell numbers ranging from 1.4 × 10⁴ to 1.4 × 10⁷ can be distinguished by using the multifunctional micropattern array, regardless of the cell type. The multifunctional micropattern array developed in this study provides a novel multifunctional compartmentalization method for rapid, simple, and accurate digital nucleic acid assays.

Patterning a Superhydrophobic Area on a Facile Fabricated Superhydrophilic Layer Based on an Inkjet-Printed Water-Soluble Polymer Template

An elaborated surface with a superhydrophilic area and a superhydrophobic area was fabricated by inkjet printing a water-soluble polymer template on a superhydrophilic layer. Titanate was used to generate the superhydrophilic layer with an in situ reaction. A water-soluble polymer template was inkjet printed on the facile fabricated superhydrophilic layer. Superhydrophobic treatment was carried out on the inkjet-printed surface with perfluorinated molecules. A superhydrophilic-superhydrophobic patterned surface (SSPS) was obtained by washing out the water-soluble polymer template. Various patterns of SSPS were fabricated with the different water-soluble polymer templates. Then, adhesion and deposition of water droplets were studied on the SSPS with the different wetting abilities on the surface. Meanwhile, a microreaction with a microfluidic chip was realized on the SSPS. In this work, systematic research on fabricating an SSPS based on a facile fabricated superhydrophilic layer with an inkjet-printed water-soluble polymer template is presented. It will have great potential for patterning materials, fabricating devices, and researching interfaces, such as microdroplet self-removal, analyte enrichment, and liquid-liquid interface reaction.

Flexible Functional Surface for Efficient Water Collection

Inspired by both the water collection strategy of desert beetles and the lubrication effect of Nepenthes pitcher plants, a new flexible functional surface for water collection is designed and can be easily fabricated. Such a functional surface consists mainly of a superhydrophobic region and a hydrophobic region with infused lubricating oil. Different functional patterns can be easily manipulated by different templates. Due to the flexibility of the surface, not only a two-dimensional surface but also a three-dimensional one can be designed. Directional water collection can be achieved. Furthermore, it is an integrative bioinspired functional surface that does not require any tailoring. Compared with existing functional surfaces, the present surface has higher water collection efficiency in fog and such a function can last 15 days. The functional degraded surfaces can also be easily reused.

Universal Strategy for Efficient Fabrication of Blood Compatible Surfaces via Polydopamine-Assisted Surface-Initiated Activators Regenerated by Electron Transfer Atom-Transfer Radical Polymerization of Zwitterions

Implant and blood-contacting biomaterials are challenged by biofouling and thrombus formation at their interface. Zwitterionic polymer brush coating can achieve excellent hemocompatibility, but the preparation often involves tedious, expensive, and complicated procedures that are designed for specific substrates. Here, we report a facile and universal strategy of creating zwitterionic polymer brushes on variety of materials by polydopamine (PDA)-assisted and surface-initiated activators regenerated by electron transfer atom-transfer radical polymerization (PDA-SI-ARGET-ATRP). A PDA adhesive layer is first dipcoated on a substrate, followed by covalent immobilization of 3-trimethoxysilyl propyl 2-bromo-2-methylpropionate (SiBr, ATRP initiator) on the PDA via condensation. Meanwhile, the trimethoxysilyl group of SiBr also cross-links the PDA oligomers forming stabilized PDA/SiBr complex coating. Finally, SI-ARGET-ATRP is performed in a zwitterionic monomer solution catalyzed by the parts per million level of CuBr₂ without deoxygenization. The conveniently fabricated zwitterionic polymer brush coatings are demonstrated to have stable, ultralow fouling, and extremely blood compatible and functionalizable characteristics. This facile, versatile, and universal surface modification strategy is expected to be widely applicable in various advanced biomaterials and devices.

Electrically Controlled Localized Charge Trapping at Amorphous Fluoropolymer-Electrolyte Interfaces

Charge trapping is a long-standing problem in electrowetting on dielectric, causing reliability reduction and restricting its practical applications. Although this phenomenon is investigated macroscopically, the microscopic investigations are still lacking. In this work, the trapped charges are proven to be localized at the three-phase contact line (TPCL) region by using three detecting methods-local contact angle measurements, electrowetting (EW) probe, and Kelvin probe force microscopy. Moreover, it is demonstrated that this EW-assisted charge injection (EWCI) process can be utilized as a simple and low-cost method to deposit charges on fluoropolymer surfaces. Charge densities near the TPCL up to 0.46 mC m^-2 and line widths of the deposited charge ranging from 20 to 300 µm are achieved by the proposed EWCI method. Particularly, negative charge densities do not degrade even after a "harsh" testing with a water droplet on top of the sample surfaces for 12 h, as well as after being treated by water vapor for 3 h. These findings provide an approach for applications which desire stable and controllable surface charges.

Single-cell patterning technology for biological applications

Single-cell patterning technology has revealed significant contributions of single cells to conduct basic and applied biological studies in vitro such as the understanding of basic cell functions, neuronal network formation, and drug screening. Unlike traditional population-based cell patterning approaches, single-cell patterning is an effective technology of fully understanding cell heterogeneity by precisely controlling the positions of individual cells. Therefore, much attention is currently being paid to this technology, leading to the development of various micro-nanofabrication methodologies that have been applied to locate cells at the single-cell level. In recent years, various methods have been continuously improved and innovated on the basis of existing ones, overcoming the deficiencies and promoting the progress in biomedicine. In particular, microfluidics with the advantages of high throughput, small sample volume, and the ability to combine with other technologies has a wide range of applications in single-cell analysis. Here, we present an overview of the recent advances in single-cell patterning technology, with a special focus on current physical and physicochemical methods including stencil patterning, trap- and droplet-based microfluidics, and chemical modification on surfaces via photolithography, microcontact printing, and scanning probe lithography. Meanwhile, the methods applied to biological studies and the development trends of single-cell patterning technology in biological applications are also described.

Microcontact Printing with Laser Direct Writing Carbonization for Facile Fabrication of Carbon-Based Ultrathin Disk Arrays and Ordered Holey Films

A nanometer-thick carbon film with a highly ordered pattern structure is very useful in a variety of applications. However, its large-scale, high-throughput, and low-cost fabrication is still a great challenge. Herein, microcontact printing (µCP) and direct laser writing carbonization (DLWc) are combined to develop a novel method that enables ease of fabrication of nanometer-thick and regularly patterned carbon disk arrays (CDAs) and holey carbon films (HCFs) from a pyromellitic dianhydride-oxydianiline-based polyamic acid (PAA) solution. The effect of PAA concentration and pillar lattice structure of the polydimethyl siloxane stamp are systematically studied for their influence on the geometrical parameter, surface morphology, and chemical structure of the finally achieved CDAs and HCFs. Within the PAA concentration being investigated, the averaged thickness of CDAs and HCFs can be tailored in a range from a few tens to a few hundred of nanometers. The µCP+DLWc-enabled electrically conductive CDAs and HCFs possess the characteristics of ease-of-fabrication, nanometer-thickness, highly regular and controlled patterns and structures, and the ability to form on both hard and soft substrates, which imparts usefulness in electronics, photonics, energy storage, catalysis, tissue engineering, as well as physical, chemical, and bio-sensing applications.