Hydrophobic interaction-mediated capture and release of cancer cells on thermoresponsive nanostructured surfaces

Dual-mode droplet rolling strategy: mimicking Earth's rotation and revolution for dual-cycle synergy in the efficient capture and controlled release of trace targets

Current microchips functionalized with antibodies or aptamers primarily enhance the capture and detection efficiency of single targets in microfluidics by refining microchannel designs or developing functional enhancement materials. However, strategies to extend the interaction path for efficiency optimization remain underexplored, as they may cause elevated hydraulic pressure and fluid shear forces within the microchannels, and the potential for path extension is inherently limited. This study introduces a novel dual-mode droplet rolling strategy, mimicking Earth's rotation and revolution, which employs a closed-loop patterned superwetting chip to achieve efficient capture of trace biological targets in gravity-driven droplets. Specifically, the external cyclic motion in the "revolution" mode greatly extends the interaction path between the droplet-contained targets and the active interface. Meanwhile, the internal cyclic vortex flow in the "rotation" mode markedly increases the contact frequency between droplet-contained targets and the active substrate. Consequently, the dual-cycle synergistic amplification significantly enhances the effective contact opportunities between the targets and the functionalized closed-loop track, thereby markedly improving target capture efficiency. As a proof of concept, we demonstrate the specific and efficient capture of both micron-sized polystyrene microspheres (6 μm and 15 μm) and nanoscale AuNPs (50 nm) through multilayer modification of the superslippery track, highlighting the platform's versatility for targets of varying sizes. We achieved 91.3% capture efficiency for circulating tumor cells (MCF-7 cells, ∼20 μm), underscoring the chip's high efficiency in specific target capture. Furthermore, we showcase the strategy's applicability throughout the entire workflow, encompassing efficient capture, controlled release, immediate recovery, and downstream cultivation using pathogenic bacteria (E. coli, ∼1 μm). This strategy holds significant promise for detecting tumor markers and pathogens in body fluid samples, offering an innovative approach to capture-based diagnostics.

pH-responsive membranes: Mechanisms, fabrications, and applications

Understanding the mechanisms of pH-responsiveness allows researchers to design and fabricate membranes with specific functionalities for various applications. The pH-responsive membranes (PRMs) are particular categories of membranes that have an amazing aptitude to change their properties such as permeability, selectivity and surface charge in response to changes in pH levels. This review provides a brief introduction to mechanisms of pH-responsiveness in polymers and categorizes the applied polymers and functional groups. After that, different techniques for fabricating pH-responsive membranes such as grafting, the blending of pH-responsive polymers/microgels/nanomaterials, novel polymers and graphene-layered PRMs are discussed. The application of PRMs in different processes such as filtration membranes, reverse osmosis, drug delivery, gas separation, pervaporation and self-cleaning/antifouling properties with perspective to the challenges and future progress are reviewed. Lastly, the development and limitations of PRM fabrications and applications are compared to provide inclusive information for the advancement of next-generation PRMs with improved separation and filtration performance.

3D Temperature-Controlled Interchangeable Pattern for Size-Selective Nanoparticle Capture

Patterned surfaces with distinct regularity and structured arrangements have attracted great interest due to their extensive promising applications. Although colloidal patterning has conventionally been used to create such surfaces, herein, we introduce a novel 3D patterned poly(N-isopropylacrylamide) (PNIPAM) surface, synthesized by using a combination of colloidal templating and surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) polymerization. In order to investigate the temperature-driven 3D morphological variations at a lower critical solution temperature (LCST) of ∼32 °C, multifaceted characterization techniques were employed. Atomic force microscopy confirmed the morphological transformations at 20 and 40 °C, while water contact angle measurements, upon heating, revealed distinct trends, offering insights into the correlation between surface wettability and topography adaptations. Moreover, quartz crystal microbalance with dissipation monitoring and electrochemical measurements were employed to detect the topographical adjustments of the unique hollow capsule structure within the LCST. Tests using different sizes of PSNPs shed light on the size-selective capture-release potential of the patterned PNIPAM, accentuating its biomimetic open-close behavior. Notably, our approach negates the necessity for expensive proteins, harnessing temperature adjustments to facilitate the noninvasive and efficient reversible capture and release of nanostructures. This advancement hopes to pave the way for future innovative cellular analysis platforms.

Photo-Controlled Gating of Selective Bacterial Membrane Interaction and Enhanced Antibacterial Activity for Wound Healing

Reversible biointerfaces are essential for on-demand molecular recognition to regulate stimuli-responsive bioactivity such as specific interactions with cell membranes. The reversibility on a single platform allows the smart material to kill pathogens or attach/detach cells. Herein, we introduce a 2D-MoS2 functionalized with cationic azobenzene that interacts selectively with either Gram-positive or Gram-negative bacteria in a light-gated fashion. The trans conformation (trans-Azo-MoS2 ) selectively kills Gram-negative bacteria, whereas the cis form (cis-Azo-MoS2 ), under UV light, exhibits antibacterial activity against Gram-positive strains. The mechanistic investigation indicates that the cis-Azo-MoS2 exhibits higher affinity towards the membrane of Gram-positive bacteria compared to trans-Azo-MoS2 . In case of Gram-negative bacteria, trans-Azo-MoS2 internalizes more efficiently than cis-Azo-MoS2 and generates intracellular ROS to kill the bacteria. While the trans-Azo-MoS2 exhibits strong electrostatic interactions and internalizes faster into Gram-negative bacterial cells, cis-Azo-MoS2 primarily interacts with Gram-positive bacteria through hydrophobic and H-bonding interactions. The difference in molecular mechanism leads to photo-controlled Gram-selectivity and enhanced antibacterial activity. We found strain-specific and high bactericidal activity (minimal bactericidal concentration, 0.65 μg/ml) with low cytotoxicity, which we extended to wound healing applications. This methodology provides a single platform for efficiently switching between conformers to reversibly control the strain-selective bactericidal activity regulated by light.

Strategy for Nonenzymatic Harvesting of Cells via Decoupling of Adhesive and Disjoining Domains of Nanostructured Stimulus-Responsive Polymer Films

The nanostructured polymer film introduces a novel mechanism of nonenzymatic cell harvesting by decoupling solid cell-adhesive and soft stimulus-responsive cell-disjoining areas on the surface. The key characteristics of this architecture are the decoupling of adhesion from detachment and the impermeability to the integrin protein complex of the adhesive domains. This surface design eliminates inherent limitations of thermoresponsive coatings, namely, the necessity for the precise thickness of the coating, grafting or cross-linking density, and material of the basal substrate. The concept is demonstrated with nanostructured thermoresponsive films made of cell-adhesive epoxy photoresist domains and cell-disjoining poly(N-isopropylacrylamide) brush domains.

Advanced stimuli-responsive membranes for smart separation

Membranes have been extensively studied and applied in various fields owing to their high energy efficiency and small environmental impact. Further conferring membranes with stimuli responsiveness can allow them to dynamically tune their pore structure and/or surface properties for efficient separation performance. This review summarizes and discusses important developments and achievements in stimuli-responsive membranes. The most commonly utilized stimuli, including light, pH, temperature, ions, and electric and magnetic fields, are discussed in detail. Special attention is given to stimuli-responsive control of membrane pore structure (pore size and porosity/connectivity) and surface properties (wettability, surface topology, and surface charge), from the perspective of determining the appropriate membrane properties and microstructures. This review also focuses on strategies to prepare stimuli-responsive membranes, including blending, casting, polymerization, self-assembly, and electrospinning. Smart applications for separations are also reviewed as well as a discussion of remaining challenges and future prospects in this exciting field. This review offers critical insights for the membrane and broader materials science communities regarding the on-demand and dynamic control of membrane structures and properties. We hope that this review will inspire the design of novel stimuli-responsive membranes to promote sustainable development and make progress toward commercialization.

Hierarchical hydrogel microarrays fabricated based on a microfluidic printing platform for high-throughput screening of stem cell lineage specification

2D cell cultures are suitable for rapid exploration of the factors in the extracellular matrix affecting the development of cells. The technology of the micrometre-sized hydrogel array provides a feasible, miniaturized, and high-throughput strategy for the process. However, current microarray devices lack a handy and parallelized methodology in sample treatment, which makes the process of high-throughput cell screening (HTCS) expensive and inefficient. Here, based on the functionalization of micro-nano structures and the fluid control capability of microfluidic chips, we build a microfluidic spotting-screening platform (MSSP). The MSSP can print 20000 microdroplet spots within 5 min, coupled with a simple strategy for parallel addition of compound libraries. Compared with open microdroplet arrays, the MSSP can control the evaporation rate of nanoliter droplets, providing a stable fabrication platform for hydrogel-microarray-based materials. As a proof-of-concept demonstration, the MSSP successfully controlled the adhesion, adipogenic, and osteogenic differentiation behavior of mesenchymal stem cells by rationally designing the substrate stiffness, adhesion area, and cell density. We anticipate that the MSSP may provide an accessible and promising tool for hydrogel-based HTCS. STATEMENT OF SIGNIFICANCE: High-throughput screening of cells is a common approach to improve the efficiency of biological experiments, and one challenge of the existing technologies is to achieve rapid and precise cell screening with a low-cost and simple strategy. Through the integration of the microfluidic and micro-nanostructure technologies, we fabricated a microfluidic spotting-screening platforms. Benefiting from the flexible control of the fluids, the device can print 20000 microdroplet spots within 5 min, coupled with a simple procedure for parallel addition of compound libraries. High-throughput screening of stem cell lineage specification has also been achieved by the platform, which provides a high-throughput, high-content information extraction strategy for cell-biomaterial interaction research.

Capture and release of circulating tumor cells stimulated by pH and NIR irradiation of magnetic Fe3O4@ZIF-8 nanoparticles

Detecting and analyzing circulating tumor cells(CTCs) is significant for early diagnosis, management, and personalized treatment of tumors. Herein, a smart magnetic aptamer modified Fe₃O₄@ZIF-8 core/shell structured nanoparticle (NPs) was successfully constructed using for capture and simultaneous pH- and NIR-irradiation responsive release of CTCs. Taking MCF-7 as model CTCs, it could be captured ca. 60 % in low-concentration artificial blood by aptamer (SYL3C) on the surface of Fe₃O₄@ZIF-8 NPs. After magnetic separation, the ZIF-8 shell in aptamer-modified Fe₃O₄@ZIF-8 NPs carrying captured CTCs would disintegrate within 20 min under the synergistic effect of an acidic environment (pH=6.0) and NIR irradiation leading to the release of CTCs with high cell viability, which was benefited for the subsequent culture and analysis. This magnetic and core/shell structured device integrated high-efficiency capture, quick isolation and perfect release into one system, which showed great potentials for the detection of CTCs in the clinic.

Versatile Dynamic Bioactive Lubricant-Infused Surface for Effective Isolation of Circulating Tumor Cells

The rarity of circulating tumor cells (CTCs) and the complexity of blood components present major challenges for the efficient isolation of CTCs in blood. The coexisting matters could interfere with the detection of CTCs by adhering to the binding sites on the material surface, leading to the reduced accuracy of biomarker capture in blood. Herein, we developed dynamic bioactive lubricant-infused slippery surfaces by grafting the 1H,1H,2H,2H-heptadecafluorodecyl acrylate polymer and 3-acrylamidophenylboronic acid polymer brushes on quartz plates by UV light-initiated and then grafted cancer cell-binding peptides via reversible catechol-boronate chemistry between phenylboronic acid groups and 3,4-dihydroxy-l-phenylalanine groups of peptides for high-efficient capture of CTCs and nondestructive release of the desired cells in sugar response. Patterned dynamic bioactive lubricant-infused surfaces (PDBLISs) further exhibited the improved capture efficiency of CTCs and more effective antifouling properties for nonspecific cells and blood components. Moreover, the PDBLIS can efficiently capture rare cancer cells from the mimic of cancer patient's blood samples. We anticipate that the strategy we proposed would be used in further clinical diagnosis of complicated biofluids related to a variety of tumors and exhibit good prospects and potential in future liquid biopsies.

Adsorption of soft NIPAM nanogels at hydrophobic and hydrophilic interfaces: Conformation of the interfacial layers determined by neutron reflectivity

The application of stimuli-responsive microgels and nanogels in drug delivery, catalysis, sensing, and coatings is restricted currently by the limited understanding of the factors influencing their adsorption dynamics and structural changes at interfaces. We have used neutron reflectivity to resolve, on the Ångström scale, the structure of 5% crosslinked N-isopropylacrylamide nanogels at both hydrophobic and hydrophilic interfaces in situ, as a function of temperature and bulk nanogel concentration. Our results show that the higher flexibility given by the low crosslinker content allows for a more ordered structure and packing. The adsorption of the thermoresponsive nanogels is primarily driven by temperature, more specifically its proximity to its volume phase transition temperature, while concentration plays a secondary role. Hydrophobic interactions drive the conformation of the first layer at the interface, which plays a key role in influencing the overall nanogel structure. The mobility of the first layer at the air-water interface as opposed to the interfacial confinement at the solid (SiC8)-liquid interface, results in a different conformation, a more compact and less deformed packing structure, which ultimately drives the structure of the subsequent layers. The evidence for the different structural conformations determined by the degree of hydrophobicity of the interface provides new knowledge, which is essential for the development of further applications. The key role of hydrophobic interactions in driving adsorption and interfacial behavior was also confirmed by fluid AFM experiments which visualized adherence of the nanogels to SiC8 modified surfaces.

Probing Hydrophobic Interactions between Polymer Surfaces and Air Bubbles or Oil Droplets: Effects of Molecular Weight and Surfactants

Hydrophobic interaction plays an important role in numerous interfacial phenomena and biophysical and industrial processes. In this work, polystyrene (PS) was used as a model hydrophobic polymer for investigating its hydrophobic interaction with highly deformable objects (i.e., air bubbles and oil droplets) in aqueous solutions. The effects of polymer molecular weight, solvent (i.e., addition of ethanol to water), the presence of surface-active species, and hydrodynamic conditions were investigated, via direct surface force measurements using the bubble/drop probe atomic force microscopy (AFM) technique and theoretical calculations based on the Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. It was found that the PS of low molecular weight (i.e., PS590 and PS810) showed slightly weaker hydrophobic interactions with air bubbles or oil droplets, as compared to glassy PS of higher molecular weight (i.e., PS1110, PS2330, PS46300, and PS1M). The hydrophobic interaction between PS and air bubbles in a 1 M NaCl aqueous solution with 10 vol % ethanol was weaker than that in the bare aqueous solution. Such effects on the hydrophobic interactions are possibly achieved by influencing the structuring/ordering of water molecules close to the hydrophobic polymer surfaces by tuning the surface chain mobility and surface roughness of polymers. It was found that the addition of three surface-active species, i.e., cetyltrimethylammonium chloride (CTAC), Pluronic F-127, and sodium dodecyl sulfate (SDS), to the aqueous media could suppress the attachment of the hydrophobic polymer and air bubbles or oil droplets, most likely caused by the additional steric repulsion due to the adsorbed surface-active species at the bubble/polymer/oil interfaces. Our results have improved the fundamental understanding of the interaction mechanisms between hydrophobic polymers and gas bubbles or oil droplets, with useful implications on developing effective methods for modulating the related interfacial interactions in many engineering applications.

Thermoresponsive Smart Gating Wood Membranes

Smart membranes that can open and/or close their pores in a controlled manner by external stimuli possess potential in various applications, such as water flow manipulation, indoor climate regulation, and sensing. The design of smart gating membranes with high flux, immediate response, and mechanical robustness is still an open challenge, limiting their versatility and practical applicability. Inspired by the controlled opening and closure of plant stomata, we have developed a smart gating wood membrane, taking advantage of the unique wood scaffold with its hierarchical porous structure to carry thermoresponsive hydrogel gates. Laser drilling was applied to cut channels in the wood scaffold with well-aligned pores to incorporate the smart gating membranes. In situ polymerization of poly(N-isopropylacrylamide) above its lower critical solution temperature inside the channels resulted in a hydrogel with a heterogeneous microstructure acting as a thermoresponsive gate. The wood-based smart gating membranes exhibited reversible and stable pore opening/closing under heating/cooling stimuli. The achieved rapid response and feasibility of scale-up open the venue for various practical applications. In this work, we demonstrated their potential for indoor light regulation and as a water flow manipulator.

Smart biomaterial platforms: Controlling and being controlled by cells

Across diverse research and application areas, dynamic functionality-such as programmable changes in biochemical property, in mechanical property, or in microscopic or macroscopic architecture-is an increasingly common biomaterials design criterion, joining long-studied criteria such as cytocompatibility and biocompatibility, drug release kinetics, and controlled degradability or long-term stability in vivo. Despite tremendous effort, achieving dynamic functionality while simultaneously maintaining other desired design criteria remains a significant challenge. Reversible dynamic functionality, rather than one-time or one-way dynamic functionality, is of particular interest but has proven especially challenging. Such reversible functionality could enable studies that address the current gap between the dynamic nature of in vivo biological and biomechanical processes, such as cell traction, cell-extracellular matrix (ECM) interactions, and cell-mediated ECM remodeling, and the static nature of the substrates and ECM constructs used to study the processes. This review assesses dynamic materials that have traditionally been used to control cell activity and static biomaterial constructs, experimental and computational techniques, with features that may inform continued advances in reversible dynamic materials. Taken together, this review presents a perspective on combining the reversibility of smart materials and the in-depth dynamic cell behavior probed by static polymers to design smart bi-directional ECM platforms that can reversibly and repeatedly communicate with cells.

Reversible dougong structured receptor-ligand recognition for building dynamic extracellular matrix mimics

Dynamic biomaterials excel at recapitulating the reversible interlocking and remoldable structure of the extracellular matrix (ECM), particularly in manipulating cell behaviors and adapting to tissue morphogenesis. While strategies based on dynamic chemistries have been extensively studied for ECM-mimicking dynamic biomaterials, biocompatible molecular means with biogenicity are still rare. Here, we report a nature-derived strategy for fabrication of dynamic biointerface as well as a three-dimensional (3D) hydrogel structure based on reversible receptor-ligand interaction between the glycopeptide antibiotic vancomycin and dipeptide d-Ala-d-Ala. We demonstrate the reversible regulation of multiple cell types with the dynamic biointerface and successfully implement the dynamic hydrogel as a functional antibacterial 3D scaffold to treat tissue repair. In view of the biogenicity and high applicability, this nature-derived reversible molecular strategy will bring opportunities for malleable biomaterial design with great potential in biomedicine.

Recapitulating dynamic ECM ligand presentation at biomaterial interfaces: Molecular strategies and biomedical prospects

The extracellular matrix (ECM) provides not only physical support for the tissue structural integrity, but also dynamic biochemical cues capable of regulating diverse cell behaviors and functions. Biomaterial surfaces with dynamic ligand presentation are capable of mimicking the dynamic biochemical cues of ECM, showing ECM-like functions to modulate cell behaviors. This review paper described an overview of present dynamic biomaterial interfaces by focusing on currently developed molecular strategies for dynamic ligand presentation. The paradigmatic examples for each strategy were separately discussed. In addition, the regulation of some typical cell behaviors on these dynamic biointerfaces including cell adhesion, macrophage polarization, and stem cell differentiation, and their potential applications in pathogenic cell isolation, single cell analysis, and tissue engineering are highlighted. We hope it would not only clarify a clear background of this field, but also inspire to exploit novel molecular strategies and more applications to match the increasing demand of manipulating complex cellular processes in biomedicine.

Photothermal scaffolds/surfaces for regulation of cell behaviors

Regulation of cell behaviors and even cell fates is of great significance in diverse biomedical applications such as cancer treatment, cell-based therapy, and tissue engineering. During the past decades, diverse methods have been developed to regulate cell behaviors such as applying external stimuli, delivering exogenous molecules into cell interior and changing the physicochemical properties of the substrates where cells adhere. Photothermal scaffolds/surfaces refer to a kind of materials embedded or coated with photothermal agents that can absorb light with proper wavelength (usually in near infrared region) and convert light energy to heat; the generated heat shows great potential for regulation of cell behaviors in different ways. In the current review, we summarize the recent research progress, especially over the past decade, of using photothermal scaffolds/surfaces to regulate cell behaviors, which could be further categorized into three types: (i) killing the tumor cells via hyperthermia or thermal ablation, (ii) engineering cells by intracellular delivery of exogenous molecules via photothermal poration of cell membranes, and (iii) releasing a single cell or an intact cell sheet via modulation of surface physicochemical properties in response to heat. In the end, challenges and perspectives in these areas are commented.

A hydrogel with supramolecular surface functionalization for cancer cell capture and multicellular spheroid growth and release

A hydrogel scaffold with a non-fouling but specific cancer cell-adhesive surface was fabricated through surface modification using β-cyclodextrin-based host-guest chemistry. Interestingly, the hydrogel surface not only selectively captured specific cancer cells, but also grew the cells into multicellular spheroids. The spheroids could be released without damaging the cell viability through replacing the host moieties on the scaffold, and the released spheroids showed no changes in size or morphology.

Engineering Photoresponsive Ligand Tethers for Mechanical Regulation of Stem Cells

Regulating stem cell functions by precisely controlling the nanoscale presentation of bioactive ligands has a substantial impact on tissue engineering and regenerative medicine but remains a major challenge. Here it is shown that bioactive ligands can become mechanically "invisible" by increasing their tether lengths to the substrate beyond a critical length, providing a way to regulate mechanotransduction without changing the biochemical conditions. Building on this finding, light switchable tethers are rationally designed, whose lengths can be modulated reversibly by switching a light-responsive protein, pdDronpa, in between monomer and dimer states. This allows the regulation of the adhesion, spreading, and differentiation of stem cells by light on substrates of well-defined biochemical and physical properties. Spatiotemporal regulation of differential cell fates on the same substrate is further demonstrated, which may represent an important step toward constructing complex organoids or mini tissues by spatially defining the mechanical cues of the cellular microenvironment with light.

Electrostatic Potential Analysis in Polyelectrolyte Brush-Grafted Microchannels Filled with Polyelectrolyte Dispersion

In this study, the model framework that includes almost all relevant parameters of interest has been developed to quantify the electrostatic potential and charge density occurring in microchannels grafted with polyelectrolyte brushes and simultaneously filled with polyelectrolyte dispersion. The brush layer is described by the Alexander-de Gennes model incorporated with the monomer distribution function accompanying the quadratic decay. Each ion concentration due to mobile charges in the bulk and fixed charges in the brush layer can be determined by multi-species ion balance. We solved 2-dimensional Poisson–Nernst–Planck equations adopted for simulating electric field with ion transport in the soft channel, by considering anionic polyelectrolyte of polyacrylic acid (PAA). Remarkable results were obtained regarding the brush height, ionization, electrostatic potential, and charge density profiles with conditions of brush, dispersion, and solution pH. The Donnan potential in the brush channel shows several times higher than the surface potential in the bare channel, whereas it becomes lower with increasing PAA concentration. Our framework is fruitful to provide comparative information regarding electrostatic interaction properties, serving as an important bridge between modeling and experiments, and is possible to couple with governing equations for flow field.

Thermo-Responsive Jamming of Nanoparticle Dense Suspensions towards Macroscopic Liquid-Solid Switchable Materials

Nanoparticle aggregation for constructing functional materials has shown enormous advantages in various applications. Most efforts focused on ordered nanoparticle aggregation for specific functions but were often limited to irreversible aggregation processes due to the thermodynamic equilibrium. Herein, we report a reversible disordered aggregation of SiO₂ -PNIPAAm nanoparticles (SPNPs) through thermo-responsive jamming, obtaining smart liquid-solid switchable materials. The smart materials can display a switch between liquid-like state and solid-like state responding to a temperature change. This unique macroscopic behavior originates from the reversible disordered aggregation modulated by temperature-dependent hydrophobic interactions among the SPNPs. Notably, the materials at the solid-like state show anti-impact properties and can withstand the impact of a steel sphere with a speed of 328 cm s^-1 . We envision that this finding offers inspiration to design smart liquid-solid switchable materials for impact protection.

Evaporation-Induced rGO Coatings for Highly Sensitive and Non-Invasive Diagnosis of Prostate Cancer in the PSA Gray Zone

The prostate-specific antigen (PSA) has been widely used for the early diagnosis of prostate cancer during routine check-ups. However, the low sensitivity of regular PSA tests in the PSA gray zone often means that patients are required to undergo further invasive needle biopsy for the diagnosis of prostate cancer, which may lead to potential overdiagnosis and overtreatment. In this study, a circulating tumor cell (CTC)-chip based on an evaporation-induced reduced graphene oxide (rGO) coating is presented, which enables a highly specific and non-invasive diagnosis of prostate cancer in the PSA gray zone. During the evaporation process of the rGO dispersion, the Marangoni effect induces the self-assembly of a hierarchical micro/nanowrinkled rGO coating, which can capture CTCs after subsequent surface modification of capture agents. Compared to the low diagnostic sensitivity (58.3%) of regular PSA tests, a combination of CTC detection and PSA-based hematological tests via machine-learning analysis can greatly upgrade the diagnostic sensitivity of this disease to 91.7% in clinical trial. Therefore, this study provides a non-invasive alternative with high sensitivity for the diagnosis of prostate cancer in the PSA gray zone.

Dip-Pen Nanolithography(DPN): from Micro/Nano-patterns to Biosensing

Dip-pen nanolithography is an emerging and attractive surface modification technique that has the capacity to directly and controllably write micro/nano-array patterns on diverse substrates. The superior throughput, resolution, and registration enable DPN an outstanding candidate for biological detection from the molecular level to the cellular level. Herein, we overview the technological evolution of DPN in terms of its advanced derivatives and DPN-enabled versatile sensing patterns featuring multiple compositions and structures for biosensing. Benefitting from uniform, reproducible, and large-area array patterns, DPN-based biosensors have shown high sensitivity, excellent selectivity, and fast response in target analyte detection and specific cellular recognition. We anticipate that DPN-based technologies could offer great potential opportunities to fabricate multiplexed, programmable, and commercial array-based sensing biochips.

A versatile pH-responsive peptide based dynamic biointerface for tracking bacteria killing and infection resistance

Herein we reported a versatile dynamic biointerface based on pH-responsive peptide self-assembly and disassembly to capture the bacteria to avoid bacteria further infected tissue around that can release peptides from the surface in a slightly acidic environment to kill the bacteria with the specificity. The exposed biointerface still presented infection resistance.

An electroactive and thermo-responsive material for the capture and release of cells

Non-invasive collection of target cells is crucial for research in biology and medicine. In this work, we combine a thermo-responsive material, poly(N-isopropylacrylamide), with an electroactive material, poly(3,4-ethylene-dioxythiopene):poly(styrene sulfonate), to generate a smart and conductive copolymer for the label-free and non-invasive detection of the capture and release of cells on gold electrodes by electrochemical impedance spectroscopy. The copolymer is functionalized with fibronectin to capture tumor cells, and undergoes a conformational change in response to temperature, causing the release of cells. Simultaneously, the copolymer acts as a sensor, monitoring the capture and release of cancer cells by electrochemical impedance spectroscopy. This platform has the potential to play a role in top-notch label-free electrical monitoring of human cells in clinical settings.

DNAzyme-Triggered Sol-Gel-Sol Transition of a Hydrogel Allows Target Cell Enrichment

Enrichment of rare cancer cells from various cell mixtures for subsequent analysis or culture is essential for understanding cancer formation and progression. In particular, maintaining the viability of captured cancer cells and gently releasing them for relevant applications remain challenging for many reported methods. Here, a physically cross-linked deoxyribozyme (DNAzyme)-based hydrogel strategy was developed for the specific envelopment and release of targeted cancer cells, allowing the aptamer-guided capture, 3D envelopment, and Zn²⁺-dependent release of viable cancer cells. The DNAzyme hydrogel is constructed through the intertwinement and hybridization of two complementary DNAzyme strands located on two rolling circle amplification-synthesized ultralong DNA chains. The enveloping and separation of target cells were achieved during the formation of the DNAzyme hydrogel (sol-gel transition). Triggered by Zn²⁺, the encapsulated cells can be gently released from the dissociated DNAzyme hydrogel with high viability (gel-sol transition). Successful isolations of target cells from cancer cell mixtures and peripheral blood mononuclear cells (PBMC) were demonstrated. This method offers an attractive approach for the separation of target cancer cells for various downstream applications that require viable cells.

Spiropyran-based photoswitchable acrylic nanofibers: A stimuli-responsive substrate for light controlled C6 glioma cells attachment/detachment

Reversible and remote cell manipulation with high spatiotemporal precision is now a highly attractive subject in various biological applications such as tissue engineering and cell-matrix interaction. Herein, photoresponsive poly(methyl methacrylate-co-hydroxy ethyl methacrylate-co-spiropyran ethyl acrylate) terpolymer (MHSP) was prepared using emulsion polymerization and the corresponding nanofibers (MHSP@NF) and film (MHSP@F) were prepared using electrospinning and drop-casting techniques, respectively. Structure of MHSP@NF with cylindrical cross-section and uniform diameter size of 169 nm were characterized by ¹H-NMR and SEM analyses. Time-dependent UV-vis spectra of the prepared acrylic nanofibers and films demonstrated maximum forward photoisomerization after 3- and 8-min UV irradiation at 365 nm together with a 96° and 5° decrement in their surface water contact angles, respectively. High photoresponsivity of the nanofibers was attributed to their extensive surface area which exposes more spiropyran groups to UV light. MHSP@F and MHSP@NF with chemically-attached spiropyran groups demonstrated significant biocompatibility with negligible toxicity toward C6 glioma cancer cells up to 5 days. However, MH/SP@NF with doped SPOH exhibited a sudden decrease in cell viability relating to the migration and leakage of SPOH molecules. Photoreversible cell adhesion results showed a dramatic and switchable C6 cells attachment/detachment upon alternating UV and visible lights irradiations for MHSP@NF sample, while this was not observed for the similar film. These indicate potentiality of MHSP@NF as a promising substrate for dynamic switching of biomolecules and cell sheet engineering.

In-line characterization of nanostructures produced by roll-to-roll nanoimprinting

We present an in-line metrology solution for dimensional characterization of roll-to-roll imprinted nanostructures. The solution is based on a scatterometric analysis of optical data from a hyperspectral camera deployed at a production facility, where nanostructures are produced at speeds of 10m/min. The system combines the ease of use of a real-space imaging system with the spectral information used in scatterometry. We present nanoscale dimensional measurements on one-dimensional line gratings with various periods and orientations. The depths of the produced structures are accurately characterized with uncertainties on the scale of a few nanometers. The hyperspectral imaging capabilities of the system can also be used to avoid vibrational effects.

Selective capture and non-invasive release of cells using a thermoresponsive polymer brush with affinity peptides

Thermoresponsive block copolymer brush with cell affinity peptides was prepared via two steps of ATRP and subsequent click reaction. The prepared polymer brush can purify cells with high selectivity by simply changing temperature.

Natural Fish Trap-Like Nanocage for Label-Free Capture of Circulating Tumor Cells

Nanomaterials have achieved several breakthroughs in the capture of circulating tumor cells (CTCs) over the past decades. However, artificial fabrication of label-free nanomaterials used for high-efficiency CTC capture is still a challenge. Through billions of years of evolution and natural selection, various complicated and precise hierarchical structures are developed. Here, a novel fish trap-like "nanocage" structure derived from the natural Chrysanthemum pollen is reported and a nanocage-featured film for the label-free capture of CTCs and CTC clusters is constructed. The nanocage-featured film effectively captures 92% rare cancer cells with a broad spectrum of cancer types, due to the synergistic effect of nanocage-CTC filopodia matching, high contact area, and strong adhesion force between the cancer cells and the nanocage. Furthermore, the nanocage-featured film successfully detects CTCs and CTC clusters in 2 or 4 mL blood taken from 21 cancer patients (stages I-IV) suffering from various types of cancers. This novel, abundant, and economical fish trap-like "nanocage" may provide new perspectives for the application of natural nanomaterials in clinical CTC capture and analysis.

Emerging Roles of 1D Vertical Nanostructures in Orchestrating Immune Cell Functions

Engineered nano-bio cellular interfaces driven by 1D vertical nanostructures (1D-VNS) are set to prompt radical progress in modulating cellular processes at the nanoscale. Here, tuneable cell-VNS interfacial interactions are probed and assessed, highlighting the use of 1D-VNS in immunomodulation, and intracellular delivery into immune cells-both crucial in fundamental and translational biomedical research. With programmable topography and adaptable surface functionalization, 1D-VNS provide unique biophysical and biochemical cues to orchestrate innate and adaptive immunity, both ex vivo and in vivo. The intimate nanoscale cell-VNS interface leads to membrane penetration and cellular deformation, facilitating efficient intracellular delivery of diverse bioactive cargoes into hard-to-transfect immune cells. The unsettled interfacial mechanisms reported to be involved in VNS-mediated intracellular delivery are discussed. By identifying up-to-date progress and fundamental challenges of current 1D-VNS technology in immune-cell manipulation, it is hoped that this report gives timely insights for further advances in developing 1D-VNS as a safe, universal, and highly scalable platform for cell engineering and enrichment in advanced cancer immunotherapy such as chimeric antigen receptor-T therapy.

Nanotechnology-Assisted Isolation and Analysis of Circulating Tumor Cells on Microfluidic Devices

Circulating tumor cells (CTCs), a type of cancer cell that spreads from primary tumors into human peripheral blood and are considered as a new biomarker of cancer liquid biopsy. It provides the direction for understanding the biology of cancer metastasis and progression. Isolation and analysis of CTCs offer the possibility for early cancer detection and dynamic prognosis monitoring. The extremely low quantity and high heterogeneity of CTCs are the major challenges for the application of CTCs in liquid biopsy. There have been significant research endeavors to develop efficient and reliable approaches to CTC isolation and analysis in the past few decades. With the advancement of microfabrication and nanomaterials, a variety of approaches have now emerged for CTC isolation and analysis on microfluidic platforms combined with nanotechnology. These new approaches show advantages in terms of cell capture efficiency, purity, detection sensitivity and specificity. This review focuses on recent progress in the field of nanotechnology-assisted microfluidics for CTC isolation and detection. Firstly, CTC isolation approaches using nanomaterial-based microfluidic devices are summarized and discussed. The different strategies for CTC release from the devices are specifically outlined. In addition, existing nanotechnology-assisted methods for CTC downstream analysis are summarized. Some perspectives are discussed on the challenges of current methods for CTC studies and promising research directions.

On the Interaction between 1D Materials and Living Cells

One-dimensional (1D) materials allow for cutting-edge applications in biology, such as single-cell bioelectronics investigations, stimulation of the cellular membrane or the cytosol, cellular capture, tissue regeneration, antibacterial action, traction force investigation, and cellular lysis among others. The extraordinary development of this research field in the last ten years has been promoted by the possibility to engineer new classes of biointerfaces that integrate 1D materials as tools to trigger reconfigurable stimuli/probes at the sub-cellular resolution, mimicking the in vivo protein fibres organization of the extracellular matrix. After a brief overview of the theoretical models relevant for a quantitative description of the 1D material/cell interface, this work offers an unprecedented review of 1D nano- and microscale materials (inorganic, organic, biomolecular) explored so far in this vibrant research field, highlighting their emerging biological applications. The correlation between each 1D material chemistry and the resulting biological response is investigated, allowing to emphasize the advantages and the issues that each class presents. Finally, current challenges and future perspectives are discussed.

Interfacial ion specificity modulates hydrophobic interaction

HYPOTHESIS

Ion specificity is crucial in assembly and aggregation of polymers in water driven by hydrophobic interaction. An increasing number of studies have suggested that specific ion adsorption and consequent impact on interfacial water molecules should play an important role in modulating hydrophobic interaction.

EXPERIMENTS

Here, bubble probe atomic force microscopy (AFM) combined with theoretical modeling analysis was applied to quantify hydrophobic interactions involving three model polymers in solutions containing different ions.

FINDINGS

For polystyrene, the hydrophobic interaction's decay length D₀ was reduced from 0.75 nm to 0.60 nm by introducing weakly hydrated cations (e.g., K⁺ and NH₄⁺), while varying anion type had little effect. For poly(methyl methacrylate) and polydimethylsiloxane, anion specificity was demonstrated more evident in shortening the hydrophobic interaction range, with D₀ decreasing from 0.63 nm to 0.50 nm and from 0.72 nm to 0.58 nm respectively when strongly hydrated F^- or Cl^- was replaced by weakly hydrated I^-. Such results could arise from specific ion adsorption at water/polymer interface which disrupts the water structuring effect. From the nanomechanical perspective, this work has revealed the importance of interfacial ion specificity in modulating hydrophobic interaction, which offers novel implications for tuning assembly behavior of macromolecules in relevant engineering applications such as micelle formation and foam stabilization.

Facile synthesis of 3D hierarchical micro-/nanostructures in capillaries for efficient capture of circulating tumor cells

The efficient capture of rare circulating tumor cells (CTCs) with high viability is of great importance in cancer diagnosis. The integration of three-dimensional (3D) nanobiointerfaces with capillary flow channel platforms can efficiently improve CTC capture performance by providing abundant binding sites and increasing the likelihood of contact as samples flow through the microchannels. However, due to the complex preparation processes, facile synthesis of nanostructures for use as substrates in flow channels for biomedical applications is still challenging. To reduce the encapsulation steps in the fabricating of nanostructured flow channel devices, we chose the enclosed glass capillaries as flow channels and accomplished all the experiments in the microchannels, including 3D nanostructure synthesis, surface modification and capture/release of CTCs. In this work, we constructed a novel 3D Zn(OH)F/ZnO nanoforest array in capillaries for CTC isolation via a facile microfluidic wet chemistry method. Because of the abundant binding sites of the 3D Zn(OH)F/ZnO nanoforest array, the capture efficiency was remarkably enhanced compared with that of vertical nanowires (90.3% vs 69.1%). In addition, a high release efficiency and cell viability of released cells were achieved by grafting poly(N-isopropylacrylamide) (PNIPPAm). These results may provide evidence for a novel method to fabricate hierarchical 3D substrates with a combination of biomolecule recognition and topographical interaction for biomedical applications.

Recent Advances in the Quantification and Modulation of Hydrophobic Interactions for Interfacial Applications

Hydrophobic interaction is responsible for a variety of colloidal phenomena, which also plays a key role in achieving the desired characteristics and functionalities for a wide range of interfacial applications. In this feature article, our recent advances in the quantification and modulation of hydrophobic interactions at both solid/water and air/water interfaces in different material systems have been reviewed. On the basis of surface forces apparatus (SFA) measurements of hydrophobic polymers (e.g., polystyrene), a three-regime hydrophobic interaction model that could satisfactorily encompass the hydrophobic interaction with different ranges was proposed. In addition, the atomic force microscope (AFM) coupled with various techniques such as the colloidal probe, the electrochemical process, and force mapping were employed to quantify the hydrophobic interaction from different perspectives. For the hydrophobic interactions involving deformable bubbles, the bubble probe AFM combined with reflection interference contrast microscopy (RICM) was used to simultaneously measure the interaction force and spatiotemporal evolution of the thin film drainage process between air bubbles and hydrophobized mica surfaces in an aqueous medium. The studies on the interactions of air bubbles with self-assembled monolayers (SAMs) demonstrated that the range of hydrophobic interactions does not always increase monotonically with the hydrophobicity of interacting surfaces as characterized by the static water contact angle; viz., surfaces with similar hydrophobicity can exhibit different ranges of hydrophobic interaction, while surfaces with different hydrophobicities can exhibit a similar range of hydrophobic interactions. It is found that the hydrophobic interaction can be modulated by tuning the surface nanoscale structure and chemistry. Moreover, the long-range "hydrophilic" attraction that resembles the hydrophobic interaction was discovered between water droplets and polyelectrolyte surfaces in an oil medium, on the basis of which polyelectrolyte coating materials were designed for oil cleaning, oil/water separation, and demulsification. The interfacial applications, remaining challenges, and future perspectives of hydrophobic interactions are discussed.

Double Rolling Circle Amplification Generates Physically Cross-Linked DNA Network for Stem Cell Fishing

Stem cells have been widely studied in cell biology and utilized in cell-based therapies, and fishing stem cells from marrow is highly challenging due to the ultralow content. Herein, a physically cross-linked DNA network-based cell fishing strategy is reported, achieving efficient capture, 3D envelop, and enzyme-triggered release of bone marrow mesenchymal stem cells (BMSCs). DNA network is constructed via a double rolling circle amplification method and through the intertwining and self-assembly of two strands of ultralong DNA chains. DNA-chain-1 containing aptamer sequences ensures specific anchor with BMSCs from marrow. Hybridization between DNA-chain-1 and DNA-chain-2 enables the cross-link of cell-anchored DNA chains to form a 3D network, thus realizing cell envelop and separation. DNA network creates a favorable microenvironment for 3D cell culture, and remarkably the physically cross-linked DNA network shows no damage to cells. DNA network is digested by nuclease, realizing the deconstruction from DNA network to fragments, and achieving enzyme-triggered cell release; after release, the activity of cells is well maintained. The strategy provides a powerful and effective method for fishing stem cells from tens of thousands of nontarget cells.

Stereospecific interactions between chiral inorganic nanomaterials and biological systems

Chirality is ubiquitous in nature and plays mysterious and essential roles in maintaining key biological and physiological processes.