3D Microprinting of Super‐Repellent Microstructures: Recent Developments, Challenges, and Opportunities

Liquid super-repellent surfaces, characterized by a low liquid–solid contact fraction, allow various liquids to bead up and freely roll off. Apart from liquid repellency, these surfaces feature several unique properties, including inter alia, self-cleaning, low-friction, anti-icing, and anti-biofouling, making them valuable for a vast array of applications involving liquids. Essential to achieve such super-repellency is the bio-inspired reentrant or doubly reentrant micro-topography. However, despite their unique interfacial properties, the fabrication of these delicate 3D topographies by conventional microfabrication methods is extremely challenging. Recently, emerging 3D microprinting technologies, particularly two-photon lithography, have brought new scope to this field. With unparalleled design freedom and flexibility, 3D microprinting greatly facilitates the design, testing, and studying of complex 3D microstructures. Here, applications of 3D microprinting in the design and fabrication of super-repellent microstructures are summarized, with a focus on their remarkable properties, and new functionalities offered by these intricate 3D topographies. Current challenges and new opportunities of emerging 3D microprinting techniques to further advance liquid super-repellent materials are also discussed

Precision Medicine in Oncology: In Vitro Drug Sensitivity and Resistance Test (DSRT) for Selection of Personalized Anticancer Therapy

Precision or personalized medicine aims to determine an optimal therapy for each individual patient. In oncology techniques such as next generation sequencing, mRNA-sequencing, ChIP-sequencing, and mass spectrometry are used to perform a full molecular profiling for each patient. However, it is not always possible to determine a suitable treatment for an individual cancer based on molecular profiling, mostly due to the high level of tumor heterogeneity. In vitro drug sensitivity and resistance test (DSRT) can be performed on cancer cells or tissues obtained from a patient with a panel of anticancer compounds in order to experimentally define sensitivity and resistance of each individual cancer. In combination with molecular profiling, DSRT can provide a fuller picture about the nature of disease, allowing for finding more appropriate therapy for each individual patient. In this progress report, studies describing in vitro DSRTs on 2D and 3D cell models based on patient-derived cells are reviewed and challenges and future steps needed for the adaptation of these systems in clinics are discussed

Palladium‐Catalyzed Combinatorial Synthesis of Biphenyls on Droplet Microarrays at Nanoliter Scale

The rising costs of pharmaceutical research are currently limiting the productivity of drug discovery and development, but can potentially be diminished via miniaturization of the synthesis and screening of new compounds. As droplet microarrays already present themselves as a versatile tool for highly miniaturized biological screening of various targets, their use for chemical synthesis is still limited. In this study, the influential palladium-catalyzed Suzuki–Miyaura reaction is successfully implemented at the nanoliter scale on droplet microarrays for the synthesis of an 800-compound library of biphenyls. Each reaction is carried out in individual 150 nL droplets. Remarkably, the synthesis of these 800 compounds requires a minimal amount of reagents, totaling 80 µmol, and a solvent volume of 400 µL. Furthermore, the cleavage kinetics and purity of the obtained biphenylic compounds are investigated. Via the solid-phase synthesis approach, the compounds could be purified from excess reactants and catalyst prior to the analysis and a UV-cleavable linker allows for fast and additive-free cleavage of each compound into the individual 100 nL droplet. This novel approach expands the toolbox of the droplet microarray for miniaturized high-throughput chemical synthesis and paves the way for future synthesis and screening of chemical compounds in a single platform

Facile fabrication of robust superhydrophobic surfaces: comparative investigation

Superhydrophobic (SH) surfaces have various unique and important properties, including extreme water-repellency, self-cleaning, anti-icing and cell repellency. The range of applications and the interest in these surfaces have increased enormously during the last years. To obtain superhydrophobicity a surface requires both micro- and nano-scale roughness and a low surface energy coating. During the last 15 years many methods have been published to produce SH surfaces. Most of the methods described in the literature require multiple steps and harsh conditions. In addition, the comparability of the distinct studies is challenging, due to the fact that the produced surfaces were not characterized with sufficiently standardized parameters and methods. A comparative study with a wide space of parameters, characterizing both the method and the surface properties, could be helpful to find the right functionalization method for a certain application. The goal of this study was to compare the most facile methods for the fabrication of superhydrophobic surfaces. We selected eight coating methods and characterized produced surfaces in respect of water contact angles (WCAs) (static, advancing, receding), sliding angle, mechanical stability, stability in water/buffer/solvent, transparency and micro/nano surface topography

High‐Throughput Synthesis and Machine Learning Assisted Design of Photodegradable Hydrogels

Due to the large chemical space, the design of functional and responsive soft materials poses many challenges but also offers a wide range of opportunities in terms of the scope of possible properties. Herein, an experimental workflow for miniaturized combinatorial high-throughput screening of functional hydrogel libraries is reported. The data created from the analysis of the photodegradation process of more than 900 different types of hydrogel pads are used to train a machine learning model for automated decision making. Through iterative model optimization based on Bayesian optimization, a substantial improvement in response properties is achieved and thus expanded the scope of material properties obtainable within the chemical space of hydrogels in the study. It is therefore demonstrated that the potential of combining miniaturized high-throughput experiments with smart optimization algorithms for cost and time efficient optimization of materials properties

High‐Performance Pressure Sensors Based on Shaped Gel Droplet Arrays

Polymer gel-based pressure sensors offer numerous advantages over traditional sensing technologies, including excellent conformability and integration into wearable devices. However, challenges persist in terms of their performance and manufacturing technology. In this study, a method for fabricating gel pressure sensors using a hydrophobic/hydrophilic patterned surface is introduced. By shaping and fine-tuning the droplets of the polymer gel prepolymerization solution on the patterned surface, remarkable sensitivity improvements compared to unshaped hydrogels have been achieved. This also showcased the potential for tailoring gel pressure sensors to different applications. By optimizing the configuration of the sensor array, an uneven conductive gel array is fabricated, which exhibited a high sensitivity of 0.29 kPa$^{−1}$ in the pressure range of 0–30 kPa, while maintaining a sensitivity of 0.13 kPa$^{−1}$ from 30 kPa up to 100 kPa. Furthermore, the feasibility of using these sensors for human motion monitoring is explored and a conductive gel array for 2D force detection is successfully developed. This efficient and scalable fabrication method holds promise for advancing pressure sensor technology and offers exciting prospects for various industries and research fields

Controlling Geometry and Flow Through Bacterial Bridges on Patterned Lubricant‐Infused Surfaces (pLIS)

Spatial control of bacteria and biofilms on surfaces is necessary to understand the biofilm formation and the social interactions between bacterial communities, which could provide useful hints to study the biofilm‐involved diseases. Here patterned lubricant‐infused surfaces (pLIS) are utilized to fabricate connective structures named “bacterial bridges” between bacterial colonies of Pseudomonas aeruginosa by a simple dewetting method. It is demonstrated that the bacteria attached to hydrophilic areas and bacteria precipitated on lubricant infused borders both contribute to the formation of bacterial bridges. The geometry and distribution of bridges can be controlled using predesigned superhydrophobic–hydrophilic patterns. It is demonstrated that bacterial bridges connecting bacteria colonies act as bio‐microfluidic channels and can transport liquids, nutrients, and antibacterial substances between neighboring bacteria clusters. Thus, bacterial bridges can be used to study formation, spreading, and development of bacterial colonies, and communication within and between isolated biofilms