An aqueous-based surface modification of poly(dimethylsiloxane) with poly(ethylene glycol) to prevent biofouling

Nanofluidic Lab-On-A-Chip Systems for Biosensing in Healthcare

Biosensing plays a vital role in healthcare monitoring, disease detection, and treatment planning. In recent years, nanofluidic technology has been increasingly explored to be developed into lab-on-a-chip biosensing systems. Given now the possibility of fabricating geometrically defined nanometric channels that are commensurate with the size of many biomolecules, nanofluidic-based devices are likely to become a key technology for the analysis of various clinical biomarkers, including DNA (deoxyribonucleic acid) and proteins in liquid biopsies. This review summarizes the fundamentals and technological advances of nanofluidics from the purview of single-molecule analysis, detection of low-abundance molecules, and single-cell analysis at the subcellular level. The extreme confinement and dominant surface charge effects in nanochannels provide unique advantages to nanofluidic devices for the manipulation and transport of target biomarkers. When coupled to a microfluidic network to facilitate sample introduction, integrated micro-nanofluidic biosensing devices are proving to be more sensitive and specific in molecular analysis compared to conventional assays in many cases. Based on recent progress in nanofluidics and current clinical trends, the review concludes with a discussion of near-term challenges and future directions for the development of nanofluidic-based biosensing systems toward enabling a new wave of lab-on-a-chip technology for personalized and preventive medicine.

Polymeric integration of structure-switching aptamers on transistors for histamine sensing

Aptamers that undergo large conformational rearrangements at the surface of electrolyte-gated field-effect transistor (EG-FETs)-based biosensors can overcome the Debye length limitation in physiological high ionic strength environments. For the sensitive detection of small molecules, carbon nanotubes (CNTs) that approach the dimensions of analytes of interest are promising channel materials for EG-FETs. However, functionalization of CNTs with bioreceptors using frequently reported surface modification strategies (e.g., π-π stacking), requires highly pristine CNTs deposited through methods that are incompatible with low-cost fabrication methods and flexible substrates. In this work, we explore alternative non-covalent surface chemistry to functionalize CNTs with aptamers. We harnessed the adhesive properties of poly-D-lysine (PDL), to coat the surface of CNTs and then grafted histamine-specific DNA aptamers electrostatically in close proximity to the CNT semiconducting channel. The layer-by-layer assembly was monitored by complementary techniques such as X-ray photoelectron spectroscopy, optical waveguide lightmode spectroscopy, and fluorescence microscopy. Surface characterization confirmed histamine aptamer integration into PDL-coated CNTs and revealed ∼5-fold higher aptamer surface coverage when using CNT networks with high surface areas. Specific aptamers assembled on EG-CNTFETs enabled histamine detection in undiluted high ionic strength solutions in the concentration range of 10 nM to 100 μM. Sequence specificity was demonstrated via parallel measurements with control EG-CNTFETs functionalized with scrambled DNA. Histamine aptamer-modified EG-CNTFETs showed high selectivity vs. histidine, the closest structural analog and precursor to histamine. Taken together, these results implied that target-specific aptamer conformational changes on CNTs facilitate signal transduction, which was corroborated by circular dichroism spectroscopy. Our work suggests that layer-by-layer polymer chemistry enables integration of structure-switching aptamers into flexible EG-CNTFETs for small-molecule biosensing.

Zwitterionic polymers-armored amyloid-like protein surface combats thrombosis and biofouling

Proteins, cells and bacteria adhering to the surface of medical devices can lead to thrombosis and infection, resulting in significant clinical mortality. Here, we report a zwitterionic polymers-armored amyloid-like protein surface engineering strategy we called as "armored-tank" strategy for dual functionalization of medical devices. The "armored-tank" strategy is realized by decoration of partially conformational transformed LZM (PCTL) assembly through oxidant-mediated process, followed by armoring with super-hydrophilic poly-2-methacryloyloxyethyl phosphorylcholine (pMPC). The outer armor of the "armored-tank" shows potent and durable zone defense against fibrinogen, platelet and bacteria adhesion, leading to long-term antithrombogenic properties over 14 days in vivo without anticoagulation. Additionally, the "fired" PCTL from "armored-tank" actively and effectively kills both Gram-positive and Gram-negative bacterial over 30 days as a supplement to the lacking bactericidal functions of passive outer armor. Overall, this "armored-tank" surface engineering strategy serves as a promising solution for preventing biofouling and thrombotic occlusion of medical devices.

Toward Effective and Adsorption-Based Antifouling Zipper Brushes: Effect of pH, Salt, and Polymer Design

The undesired spontaneous deposition and accumulation of matter on surfaces, better known as fouling, is a problematic and often inevitable process plaguing a variety of industries. This detrimental process can be reduced or even prevented by coating surfaces with a dense layer of end-grafted polymer: a polymer brush. Producing such polymer brushes via adsorption presents a very attractive technique, as large surfaces can be coated in a quick and simple manner. Recently, we introduced a simple and scalable two-step adsorption strategy to fabricate block copolymer-based antifouling coatings on hydrophobic surfaces. This two-step approach involved the initial adsorption of hydrophobic-charged diblock copolymer micelles acting as a primer, followed by the complexation of oppositely charged-antifouling diblock copolymers to form the antifouling brush coating. Here, we significantly improve this adsorption-based zipper brush via systematic tuning of various parameters, including pH, salt concentration, and polymer design. This study reveals several key outcomes. First of all, increasing the hydrophobic/hydrophilic block ratio of the anchoring polymeric micelles (i.e., decreasing the hydrophilic corona) promotes adsorption to the surface, resulting in the most densely packed, uniform, and hydrophilic primer layers. Second, around a neutral pH and at a low salt concentration (1 mM), complexation of the weak polyelectrolyte (PE) blocks results in brushes with the best antifouling efficacy. Moreover, by tuning the ratio between these PE blocks, the brush density can be increased, which is also directly correlated to the antifouling performance. Finally, switching to different antifouling blocks can increase the internal density or strengthen the bound hydration layer of the brush, leading to an additional enhancement of the antifouling properties (>99% lysozyme, 87% bovine serum albumin).

Scalable Fabrication of Reversible Antifouling Block Copolymer Coatings via Adsorption Strategies

Fouling remains a widespread challenge as its nonspecific and uncontrollable character limits the performance of materials and devices in numerous applications. Although many promising antifouling coatings have been developed to reduce or even prevent this undesirable adhesion process, most of them suffer from serious limitations, specifically in scalability. Whereas scalability can be particularly problematic for covalently bound antifouling polymer coatings, replacement by physisorbed systems remains complicated as it often results in less effective, low-density films. In this work, we introduce a two-step adsorption strategy to fabricate high-density block copolymer-based antifouling coatings on hydrophobic surfaces, which exhibit superior properties compared to one-step adsorbed coatings. The obtained hybrid coating manages to effectively suppress the attachment of both lysozyme and bovine serum albumin, which can be explained by its dense and homogeneous surface structure as well as the desired polymer conformation. In addition, the intrinsic reversibility of the adhered complex coacervate core micelles allows for the successful triggered release and regeneration of the hybrid coating, resulting in full recovery of its antifouling properties. The simplicity and reversibility make this a unique and promising antifouling strategy for large-scale underwater applications.

Interface Engineering of "Clickable" Organic Electrochemical Transistors toward Biosensing Devices

"Clickable" organic electrochemical transistors (OECTs) allow the reliable and straightforward functionalization of electronic devices through the well-known click chemistry toolbox. In this work, we study various aspects of the click chemistry-based interface engineering of "clickable" OECTs. First, different channel architectures are investigated, showing that PEDOT-N₃ films can properly work as a channel of the transistors. Furthermore, the Cu(I)-catalyzed click reaction of ethynyl-ferrocene is studied under different reaction conditions, endowing the spatial control of the functionalization. The strain-promoted and catalyst-free cycloaddition of a dibenzocyclooctyne-derivatized poly-l-lysine (PLL-DBCO) is also performed on the OECTs and validated by a fiber optic (FO)-SPR setup. The further immobilization of an azido-modified HD22 aptamer yields OECT-based biosensors that are employed for the recognition of thrombin. Finally, their performance is evaluated against previously reported architectures, showing higher density of the immobilized HD22 aptamer, and originating similar K_D values and higher maximum signal change upon analyte recognition.

Spatial configuration of charge and hydrophobicity tune particle transport through mucus

Mucus is a selectively permeable hydrogel that protects wet epithelia from pathogen invasion and poses a barrier to drug delivery. Determining the parameters of a particle that promote or prevent passage through mucus is critical, as it will enable predictions about the mucosal passage of pathogens and inform the design of therapeutics. The effect of particle net charge and size on mucosal transport has been characterized using simple model particles; however, predictions of mucosal passage remain challenging. Here, we utilize rationally designed peptides to examine the integrated contributions of charge, hydrophobicity, and spatial configuration on mucosal transport. We find that net charge does not entirely predict transport. Specifically, for cationic peptides, the inclusion of hydrophobic residues and the position of charged and hydrophobic residues within the peptide impact mucosal transport. We have developed a simple model of mucosal transport that predicts how previously unexplored amino acid sequences achieve slow versus fast passage through mucus. This model may be used as a basis to predict transport behavior of natural peptide-based particles, such as antimicrobial peptides or viruses, and assist in the engineering of synthetic sequences with desired transport properties.

Brush-like polymers: design, synthesis and applications

With the development of controlled polymerisation, almost all polymerisation strategies have been successfully transplanted to surface-initiated polymerisation. The resulting polymer brushes have emerged as an effective tool for surface functionalization and modulation of the surface properties of materials. To meet various demands it is possible to tailor a material surface with polymer brushes that have diverse dimensionalities, morphologies and compositions. The crowded environment within polymer brushes as well as the stretched conformation of polymer chains sometimes provide unique physicochemical properties, which lead to the delicate creation of inorganic-organic hybridised nanostructures, anti-fouling coatings, biomedical carriers, and materials for use in lubrication, photonics and energy storage. So far, challenges remain in the high-precision synthesis and topological control needed to realize extended applications of polymer brushes. In this Feature Article, we highlight the topology, potential application prospects and various synthetic protocols, particularly for recently established methods, for the efficient synthesis of polymer brushes, as well as their benefits and limitations.

A slicing mechanism facilitates host entry by plant-pathogenic Phytophthora

Phytophthora species, classified as oomycetes, are among the most destructive plant pathogens worldwide and pose a substantial threat to food security. Plant pathogens have developed various methods to breach the cuticle and walls of plant cells. For example, plant-pathogenic fungi use a 'brute-force' approach by producing a specialized and fortified invasion organ to generate invasive pressures. Unlike in fungi, the biomechanics of host invasion in oomycetes remains poorly understood. Here, using a combination of surface-deformation imaging, molecular-fracture sensors and modelling, we find that Phytophthora infestans, Phytophthora palmivora and Phytophthora capsici slice through the plant surface to gain entry into host tissues. To distinguish this mode of entry from the brute-force approach of fungi that use appressoria, we name this oomycete entry without appressorium formation 'naifu' invasion. Naifu invasion relies on polarized, non-concentric, force generation onto the surface at an oblique angle, which concentrates stresses at the site of invasion to enable surface breaching. Measurements of surface deformations during invasion of artificial substrates reveal a polarized mechanical geometry that we describe using a mathematical model. We confirm that the same mode of entry is used on real hosts. Naifu invasion uses actin-mediated polarity, surface adherence and turgor generation to enable Phytophthora to invade hosts without requiring specialized organs or vast turgor generation.

State of the art in nonthermal plasma processing for biomedical applications: Can it help fight viral pandemics like COVID-19?

Plasma processing finds widespread biomedical applications, such as the design of biosensors, antibiofouling surfaces, controlled drug delivery systems, and in plasma sterilizers. In the present coronavirus disease (COVID-19) situation, the prospect of applying plasma processes like surface activation, plasma grafting, plasma-enhanced chemical vapor deposition/plasma polymerization, surface etching, plasma immersion ion implantation, crosslinking, and plasma decontamination to provide timely solutions in the form of better antiviral alternatives, practical diagnostic tools, and reusable personal protective equipment is worth exploring. Herein, the role of nonthermal plasmas and their contributions toward healthcare are timely reviewed to engage different communities in assisting healthcare associates and clinicians, not only to combat the current COVID-19 pandemic but also to prevent similar kinds of future outbreaks.

Modification strategies to improve the membrane hemocompatibility in extracorporeal membrane oxygenator (ECMO)

ABSTRACT

Since extracorporeal membrane oxygenator (ECMO) has been utilized to save countless lives by providing continuous extracorporeal breathing and circulation to patients with severe cardiopulmonary failure. In particular, it has played an important role during the COVID-19 epidemic. One of the important composites of ECMO is membrane oxygenator, and the core composite of the membrane oxygenator is hollow fiber membrane, which is not only a place for blood oxygenation, but also is a barrier between the blood and gas side. However, the formation of blood clots in the oxygenator is a key problem in the using process. According to the study of the mechanism of thrombosis generation, it was found that improving the hemocompatibility is an efficient approach to reduce thrombus formation by modifying the surface of materials. In this review, the corresponding modification methods (surface property regulation, anticoagulant grafting, and bio-interface design) of hollow fiber membranes in ECMO are classified and discussed, and then, the research status and development prospects are summarized.

Microphase Arrangement of Smart Superhydrophilic Segmented Polyurethanes at Their Interface with Water

Smart coatings have aroused a growing interest because of the performance of predefined surface functions upon reacting to external stimuli. Among them, responsive polymer coatings to water, which often benefit from the presence of a mobile hydrophilic material, are of great interest. Polyurethanes (PUs) are versatile materials with respect to the structure-property relationship. Therefore, the incorporation of hydrophilic segments in PUs is a rational way to produce water-sensitive smart coatings; however, having a considerable amount of hydrophilic material deteriorates the physical properties because of a large amount of water uptake. In this study, we have analyzed previously synthesized smart PUs, based on hydrophobic polycarbonate (PC) and hydrophilic polyethylene glycol (PEG) soft segments, in which only a limited amount of PEG is used. These coatings maintain, more or less, zero water contact angle, whereas the water uptake remains below 15 wt %. The combination of experimental analysis and coarse-grained molecular dynamics (CG MD) simulations reveals that PEG segments migrate to the coating/water interface and partially cover the surface, whereas the hydrophobic nature of the PC keeps the bulk of the coating intact when the coating is covered with water. Moreover, our CG MD simulations and experimental analysis suggest a reversible phase arrangement under wet/dry cycles on molecular and macroscopic scales.

Endothelialization of PDMS-based microfluidic devices under high shear stress conditions

Microfluidic systems made out of polydimethylsiloxane (PDMS) offer a platform to mimic vascular flow conditions in model systems at well-defined shear stresses. However, extracellular matrix (ECM) proteins that are physisorbed on the PDMS are not reliably attached under high shear stress conditions, which makes long-term experiments difficult. To overcome this limitation, we functionalized PDMS surfaces with 3-aminopropyltriethoxysilane (APTES) by using different surface activation methods to develop a stable linkage between the PDMS surface and collagen, which served as a model ECM protein. The stability of the protein coating inside the microfluidic devices was evaluated in perfusion experiments with phosphate-buffered saline (PBS) at 10-40 dynes/cm² wall shear stress. To assess the stability of cell adhesion, endothelial cells were grown in a multi-shear device over a shear stress range of 20-150 dynes/cm². Cells on the APTES-mediated collagen coating were stable over the entire shear stress range in PBS (pH 9) for 48 h. The results suggest that at high pH values, the electrostatic interaction between APTES-coated surfaces and collagen molecules offer a very promising tool to modify PDMS-based microfluidic devices for long-term endothelialization under high shear stress conditions.

Dense Assembly of Finely Patterned Semiconducting Single-Walled Carbon Nanotubes via a Selective Transfer Method of Nanotube-Attracting Layers

Development of technology for assembled single-walled carbon nanotube (SWCNT) film with the fine resolution is an essential technique for penetrating practical electronic applications. A promising approach is the assembly method by adding a chemical-functionalizing substrate to enhance affinity between the SWCNTs and the substrate. However, the various introduced approaches for solution-based assembly have suffered from low SWCNT deposition selectivity or low SWCNT deposition density. Herein, we demonstrated a facile method for selectively assembling semiconducting SWCNT network on the substrate. The substrate was prepared via a transfer printing of a poly-l-lysine (PLL)-coated poly(dimethylsiloxane) (PDMS) stamp. The thermal-assisted transfer method enabled an ultrafine PLL pattern (≤4 μm) and a high transfer yield (96.5%) by only one-time stamping without a change of the SWCNT-attracting nature. So, semiconducting SWCNTs were deposited on the patterned regions selectively and precisely. The benefit of the patterned semiconducting SWCNTs was lowering leakage current and turn-on voltage in the transfer characteristics by suppressing attachment of unnecessary SWCNT network. They showed excellent electrical performance, a log₁₀(I_on/I_off) ratio of 4.76, and an average value of linear field-effect mobility of 7.56 cm²/(V s). This research provides a simple but high-quality assembling technique of semiconducting SWCNTs, thereby improving the feasibility of solution-processed SWCNT-TFTs.

Thromboresistance of Polyurethanes Modified with PEO-Silane Amphiphiles

Surface-induced thrombosis is problematic in blood-contacting devices composed of silicones or polyurethanes (PUs). Poly(ethylene oxide)-silane amphiphiles (PEO-SA) are previously shown effective as surface modifying additives (SMAs) in silicones for enhanced thromboresistance. This study investigates PEO-SAs as SMAs in a PU at various concentrations: 5, 10, 25, 50, and 100 µmol g^-1 PU. PEO-SA modified PUs are evaluated for their mechanical properties, water-driven surface restructuring, and adhesion resistance against a human fibrinogen (HF) solution as well as whole human blood. Stability is assessed by monitoring hydrophilicity, water uptake, and mass loss following air- or aqueous-conditioning. PEO-SA modified PUs do not demonstrate plasticization, as evidenced by minimal changes in glass transition temperature, modulus, tensile strength, and percent strain at break. These also show a concentration-dependent increase in hydrophilicity that is sustained following air- and aqueous-conditioning for concentrations ≥25 µmol g^-1 . Additionally, water uptake and mass loss are minimal at all concentrations. Although protein resistance is not enhanced versus an HF solution, PEO-SA modified PUs have significantly reduced protein adsorption and platelet adhesion from human blood at concentrations ≥10 µmol g^-1 . Overall, this study demonstrates the versatility of PEO-SAs as SMAs in PU, which leads to enhanced and sustained hydrophilicity as well as thromboresistance.

Integration of PEGylated Polyaniline Nanocoatings with Multiple Plastic Substrates Generates Comparable Antifouling Performance

Conducting polymer nanocoatings render plastics to possess interesting optical, chemical, and electrical properties. It nevertheless remains technically challenging to deposit uniform conducting polymer nanocoatings on ambient plastic substrates ascribed to the inert and varied chemical properties of plastics and the notorious processability of conducting polymers. Previous studies have made progress in delivering various conducting polymer thin films via oxidative chemical vapor deposition. Herein, we develop a solution-based approach to polyaniline (PANI) and PEGylated PANI nanocoatings on multiple engineering plastics followed by evaluating their antifouling performance. The procedure relies on the formation of uniform, lyotropic V₂O₅·nH₂O thin films on plastics assisted by a surfactant-sodium N-lauroylsarcosinate. Next, in situ, oxidative polymerization causes the formation of nanofibrous PANI nanocoatings. Finally, interfacial functionalization leads to PEGylated PANI nanocoatings, and the steric nanolayer effectively repels the adsorption of bovine serum albumin and the attachment of the bacterium Pseudoalteromonas sp. on the surface. It is worth noting that the antifouling properties rely mainly on the presence of PEGylated PANI nanocoatings, irrespective of the type of plastic substrates underneath. The current study therefore opens an avenue for the solution-based delivery of conducting polymer-based, functional nanocoatings on hydrophobic substrates in a controllable manner with the availability of further modification.

Assessing and improving the biocompatibility of microfluidic artificial lungs

Microfluidic artificial lungs (µALs) have the potential to improve the treatment and quality of life for patients with acute or chronic lung injury. In order to realize the full potential of this technology (including as a destination therapy), the biocompatibility of these devices needs to be improved to produce long-lasting devices that are safe for patient use with minimal or no systemic anticoagulation. Many studies exist which probe coagulation and thrombosis on polydimethyl siloxane (PDMS) surfaces, and many strategies have been explored to improve surface biocompatibility. As the field of µALs is young, there are few studies which investigate biocompatibility of functioning µALs; and even fewer which were performed in vivo. Here, we use both in vitro and in vivo models to investigate two strategies to improve µAL biocompatibility: 1) a hydrophilic surface coating (polyethylene glycol, PEG) to prevent surface fouling, and 2) the addition of nitric oxide (NO) to the sweep gas to inhibit platelet activation locally within the µAL. In this study, we challenge µALs with clottable blood or platelet-rich plasma (PRP) and monitor the resistance to blood flow over time. Device lifetime (the amount of time the µAL remains patent and unobstructed by clot) is used as the primary indicator of biocompatibility. This study is the first study to: 1) investigate the effect of NO release on biocompatibility in a microfluidic network; 2) combine a hydrophilic PEG coating with NO release to improve blood compatibility; and 3) perform extended in vivo biocompatibility testing of a µAL. We found that µALs challenged in vitro with PRP remained patent significantly longer when the sweep gas contained NO than without NO. In the in vivo rabbit model, neither approach alone (PEG coating nor NO sweep gas) significantly improved biocompatibility compared to controls (though with larger sample size significance may become apparent); while the combination of a PEG coating with NO sweep gas resulted in significant improvement of device lifetime. STATEMENT OF SIGNIFICANCE: The development of microfluidic artificial lungs (µALs) can potentially have a massive impact on the treatment of patients with acute and chronic lung impairments. Before these devices can be deployed clinically, the biocompatibility of µALs must be improved and more comprehensively understood. This work explores two strategies for improving biocompatibility, a hydrophilic surface coating (polyethylene glycol) for general surface passivation and the addition of nitric oxide (NO) to the sweep gas to quell platelet and leukocyte activation. These two strategies are investigated separately and as a combined device treatment. Devices are challenged with clottable blood using in vitro testing and in vivo testing in rabbits. This is the first study to our knowledge that allows statistical comparisons of biocompatible µALs in animals, a key step towards eventual clinical use.

Tug-of-war between actomyosin-driven antagonistic forces determines the positioning symmetry in cell-sized confinement

Symmetric or asymmetric positioning of intracellular structures including the nucleus and mitotic spindle steers various biological processes such as cell migration, division, and embryogenesis. In typical animal cells, both a sparse actomyosin meshwork in the cytoplasm and a dense actomyosin cortex underneath the cell membrane participate in the intracellular positioning. However, it remains unclear how these coexisting actomyosin structures regulate the positioning symmetry. To reveal the potential mechanism, we construct an in vitro model composed of cytoplasmic extracts and nucleus-like clusters confined in droplets. Here we find that periodic centripetal actomyosin waves contract from the droplet boundary push clusters to the center in large droplets, while network percolation of bulk actomyosin pulls clusters to the edge in small droplets. An active gel model quantitatively reproduces molecular perturbation experiments, which reveals that the tug-of-war between two distinct actomyosin networks with different maturation time-scales determines the positioning symmetry.

Recent Advances in Hybrid Biomimetic Polymer-Based Films: from Assembly to Applications

Biological membranes, in addition to being a cell boundary, can host a variety of proteins that are involved in different biological functions, including selective nutrient transport, signal transduction, inter- and intra-cellular communication, and cell-cell recognition. Due to their extreme complexity, there has been an increasing interest in developing model membrane systems of controlled properties based on combinations of polymers and different biomacromolecules, i.e., polymer-based hybrid films. In this review, we have highlighted recent advances in the development and applications of hybrid biomimetic planar systems based on different polymeric species. We have focused in particular on hybrid films based on (i) polyelectrolytes, (ii) polymer brushes, as well as (iii) tethers and cushions formed from synthetic polymers, and (iv) block copolymers and their combinations with biomacromolecules, such as lipids, proteins, enzymes, biopolymers, and chosen nanoparticles. In this respect, multiple approaches to the synthesis, characterization, and processing of such hybrid films have been presented. The review has further exemplified their bioengineering, biomedical, and environmental applications, in dependence on the composition and properties of the respective hybrids. We believed that this comprehensive review would be of interest to both the specialists in the field of biomimicry as well as persons entering the field.

"Plug-n-Play" Polymer Substrates: Surface Patterning with Reactive-Group-Appended Poly-l-lysine for Biomolecule Adhesion

The immobilization of biomolecules onto polymeric surfaces employed in the fabrication of biomedical and biosensing devices is generally a challenging issue, as the absence of functional groups in such materials does not allow the use of common surface chemistries. Here we report the use of modified poly-l-lysine (PLL) as an effective method for the selective modification of polymeric materials with biomolecules. Cyclic olefin polymer (COP), Ormostamp, and polydimethylsiloxane (PDMS) surfaces were patterned with modified PLLs displaying either biotin or maleimide functional groups. Different patterning techniques were found to provide faithful microscale pattern formation, including micromolding in capillaries (MIMIC) and a hydrogel-based stamping device with micropores. The surface modification and pattern stability were tested with fluorescence microscopy, contact angle and X-ray photoelectron spectroscopy (XPS), showing an effective functionalization of substrates stable for over 20 days. By exploiting the strong biotin-streptavidin interaction or the thiol-maleimide coupling, DNA and PNA probes were displayed successfully on the surface of the materials, and these probes maintained the capability to specifically recognize complementary DNA sequences from solution. The printing of three different PNA-thiol probe molecules in a microarray fashion allowed selective DNA detection from a mixture of DNA analytes, demonstrating that the modified PLL methodology can potentially be used for multiplexed detection of DNA sequences.

Two-Dimensional Materials in Biosensing and Healthcare: From In Vitro Diagnostics to Optogenetics and Beyond

Since the isolation of graphene in 2004, there has been an exponentially growing number of reports on layered two-dimensional (2D) materials for applications ranging from protective coatings to biochemical sensing. Due to the exceptional, and often tunable, electrical, optical, electrochemical, and physical properties of these materials, they can serve as the active sensing element or a supporting substrate for diverse healthcare applications. In this review, we provide a survey of the recent reports on the applications of 2D materials in biosensing and other emerging healthcare areas, ranging from wearable technologies to optogenetics to neural interfacing. Specifically, this review provides (i) a holistic evaluation of relevant material properties across a wide range of 2D systems, (ii) a comparison of 2D material-based biosensors to the state-of-the-art, (iii) relevant material synthesis approaches specifically reported for healthcare applications, and (iv) the technological considerations to facilitate mass production and commercialization.

Asynchronous generation of oil droplets using a microfluidic flow focusing system

Here, we show that long-term exposure of PDMS based microfluidic droplet generation systems to water can reverse their characteristics such that they generate oil-in-water droplets instead of water-in-oil droplets. The competition between two oil columns entering via the two side channels leads to asynchronous generation of oil droplets. We identify various modes of droplet generation, and study the size, gap and generation rate of droplets under different combinations of oil and water pressures. Oil droplets can also be generated using syringe pumps, various oil viscosities, and different combinations of immiscible liquids. We also demonstrate the ability to dynamically change the gap between the oil droplets from a few hundred microns to just a few microns in successive cycles using a latex balloon pressure pump. This method requires no special equipment or chemical treatments, and importantly can be reversed by long-term exposure of the PDMS surfaces to the ambient air.

Assessing reusability of microfluidic devices: Urinary protein uptake by PDMS-based channels after long-term cyclic use

In the search for transformative technologies for person-centered health monitoring, reusability of microfluidic chips would be a critical design consideration in many biomedical applications. With this unmet need in mind, in this study, we develop and validate a novel microfluidic platform for automated sample pumping with an integrated channel-cleaning procedure. The proposed system leverages micropumps and on-chip solenoid valves to dynamically control fluid flow. We provide a thorough characterization of the custom-designed chip, including quantitative measures of the protein uptake by the chip, as well as cross-contamination using both simulated samples and human urine samples. The effectiveness of the cleaning procedure is assessed by testing the samples collected from the cleaning chip with commercially available urine dipstick protein tests. The results of the longitudinal protein level measurement of the urine samples after the cleaning cycles show high accuracy of protein measurement and negligible protein cross-contamination. Additionally, the cleaning procedure after pumping each sample results in a very low protein uptake (150 ng/cm²). We have also demonstrated that the efficiency of the automated cleaning microfluidic device can be further improved by an anti-fouling coating via PLL-g-PEG pretreatment and a posttreatment via Trypsin. The developed platform could potentially be further miniaturized and integrated into point-of-care devices to provide an effective cleaning process and to enable the reusability of microfluidic devices.

The Relationship between Bulk Silicone and Benzophenone-Initiated Hydrogel Coating Properties

Polydimethylsiloxane (PDMS) is a silicone elastomer-based material that is used in various applications, including coatings, tubing, microfluidics, and medical implants. PDMS has been modified with hydrogel coatings to prevent fouling, which can be done through UV-mediated free radical polymerization using benzophenone. However, to the best of our knowledge, the properties of hydrogel coatings and their influence on the bulk properties of PDMS under various preparation conditions, such as the type and concentration of monomers, and UV treatment time, have never been investigated. Acrylate-based monomers were used to perform free radical polymerization on PDMS surfaces under various reaction conditions. This approach provides insights into the relationship between the hydrogel coating and bulk properties of PDMS. Altering the UV polymerization time and the monomer concentration resulted in different morphologies with different roughness and thickness of the hydrogel coating, as well as differences in the bulk material stiffness. The surface morphology of the coated PDMS was characterized by AFM. The cross section and thickness of the coatings were examined using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The dependence of coating development on the monomer type and concentration used was evaluated by surface hydrophilicity, as measured by water contact angle. Elongation-until-break analysis revealed that specific reaction conditions affected the bulk properties and made the coated PDMS brittle. Therefore, boundary conditions have been identified to enable high quality hydrogel coating formation without affecting the bulk properties of the material.

Easy to Apply Polyoxazoline-Based Coating for Precise and Long-Term Control of Neural Patterns

Arranging cultured cells in patterns via surface modification is a tool used by biologists to answer questions in a specific and controlled manner. In the past decade, bottom-up neuroscience emerged as a new application, which aims to get a better understanding of the brain via reverse engineering and analyzing elementary circuitry in vitro. Building well-defined neural networks is the ultimate goal. Antifouling coatings are often used to control neurite outgrowth. Because erroneous connectivity alters the entire topology and functionality of minicircuits, the requirements are demanding. Current state-of-the-art coating solutions such as widely used poly(l-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) fail to prevent primary neurons from making undesired connections in long-term cultures. In this study, a new copolymer with greatly enhanced antifouling properties is developed, characterized, and evaluated for its reliability, stability, and versatility. To this end, the following components are grafted to a poly(acrylamide) (PAcrAm) backbone: hexaneamine, to support spontaneous electrostatic adsorption in buffered aqueous solutions, and propyldimethylethoxysilane, to increase the durability via covalent bonding to hydroxylated culture surfaces and antifouling polymer poly(2-methyl-2-oxazoline) (PMOXA). In an assay for neural connectivity control, the new copolymer's ability to effectively prevent unwanted neurite outgrowth is compared to the gold standard, PLL-g-PEG. Additionally, its versatility is evaluated on polystyrene, glass, and poly(dimethylsiloxane) using primary hippocampal and cortical rat neurons as well as C2C12 myoblasts, and human fibroblasts. PAcrAm-g-(PMOXA, NH₂, Si) consistently outperforms PLL-g-PEG with all tested culture surfaces and cell types, and it is the first surface coating which reliably prevents arranged nodes of primary neurons from forming undesired connections over the long term. Whereas the presented work focuses on the proof of concept for the new antifouling coating to successfully and sustainably prevent unwanted connectivity, it is an important milestone for in vitro neuroscience, enabling follow-up studies to engineer neurologically relevant networks. Furthermore, because PAcrAm-g-(PMOXA, NH₂, Si) can be quickly applied and used with various surfaces and cell types, it is an attractive extension to the toolbox for in vitro biology and biomedical engineering.

Recent advances in nonbiofouling PDMS surface modification strategies applicable to microfluidic technology

In the last decade microfabrication processes including rapid prototyping techniques have advanced rapidly and achieved a fairly mature stage. These advances have encouraged and enabled the use of microfluidic devices by a wider range of users with applications in biological separations and cell and organoid cultures. Accordingly, a significant current challenge in the field is controlling biomolecular interactions at interfaces and the development of novel biomaterials to satisfy the unique needs of the biomedical applications. Poly(dimethylsiloxane) (PDMS) is one of the most widely used materials in the fabrication of microfluidic devices. The popularity of this material is the result of its low cost, simple fabrication allowing rapid prototyping, high optical transparency, and gas permeability. However, a major drawback of PDMS is its hydrophobicity and fast hydrophobic recovery after surface hydrophilization. This results in significant nonspecific adsorption of proteins as well as small hydrophobic molecules such as therapeutic drugs limiting the utility of PDMS in biomedical microfluidic circuitry. Accordingly, here, we focus on recent advances in surface molecular treatments to prevent fouling of PDMS surfaces towards improving its utility and expanding its use cases in biomedical applications.

Antifouling silicones based on surface-modifying additive amphiphiles

Surface modifying additives (SMAs), which may be readily blended into silicones to improve anti-fouling behavior, must have excellent surface migration potential and must not leach into the aqueous environment. In this work, we evaluated the efficacy of a series of poly(ethylene oxide) (PEO)-based SMA amphiphiles which varied in terms of crosslinkability, siloxane tether length (m) and diblock versus triblock architectures. Specifically, crosslinkable, diblock PEO-silane amphiphiles with two oligodimethylsiloxane (ODMS) tether lengths [(EtO)3Si-(CH2)3-ODMS m -PEO8, m = 13 and 30] were compared to analogous non-crosslinkable, diblock (H-Si-ODMS m -PEO8) and triblock (PEO8-ODMS m -PEO8) SMAs. Prior to water conditioning, while all modified silicone coatings exhibited a high degree of water-driven surface restructuring, that prepared with the non-crosslinkable diblock SMA (m = 13) was the most hydrophilic. After conditioning, all modified silicone coatings were similarly hydrophilic and remained highly protein resistant, with the exception of PEO8-ODMS 30 -PEO8. Notably, despite twice the PEO content, triblock SMAs were not superior to diblock SMAs. For diblock SMAs, it was shown that water uptake and leaching were also similar whether or not the SMA was crosslinkable.

EFFECTS OF VARIOUS TREATMENTS ON SILICONE RUBBER SURFACE

Hydroxy groups were generated on a poly(dimethylsiloxane) (PDMS) surface using different methods. Attempts were made to prepare a homogeneous film on the PDMS surface and eliminate microwrinkles from the surface. Because the hydroxylation process changes the chemical composition of the PDMS surface, resulting in a cracked surface, selecting the best method for surface treatment with minimized surface microwrinkles and cracks was attempted. The results obtained from scanning electron microscopy showed that using the pulsed ultraviolet-ozone (UVO) radiation method with a controlled duration time, ozone treatment, continuous UVO treatment using a glass filter, and water media in UVO treatment was more effective than other methods evaluated in this study to prevent microwrinkles. The results obtained from contact angle measurements and attenuated total reflectance Fourier transform infrared spectroscopy revealed that the UVO treatment in the presence of a water medium created more hydroxy groups compared with other methods.

Dynamic contact angle on a reconstructive polymer surface by segregation

A peculiar time evolution of contact angle of water on reconstructive polymer surface was analyzed.

Isolation and Characterization of Bacterial Nucleoids in Microfluidic Devices

We report methods for isolation of Escherichia coli nucleoids in microfluidic devices, allowing characterization of nucleoids during a controlled in vivo to in vitro transition. Biochemically, nucleoids are isolated by gentle osmotic lysis, which minimally perturbs nucleoid-associated proteins (NAPs). Biophysically, nucleoids are isolated in microfluidic chambers, which mimic confinement within the cell, as well as facilitate diffusive buffer exchange around nucleoids without subjecting them to flow. These methods can be used to characterize interactions between NAPs and whole nucleoids, and to investigate nucleoid structure and dynamics in confinement. We present protocols for isolation, quantification, and perturbation of nucleoids in microfluidic confinement.

Exploring the inhibitory effect of membrane tension on cell polarization

Cell polarization toward an attractant is influenced by both physical and chemical factors. Most existing mathematical models are based on reaction-diffusion systems and only focus on the chemical process occurring during cell polarization. However, membrane tension has been shown to act as a long-range inhibitor of cell polarization. Here, we present a cell polarization model incorporating the interplay between Rac GTPase, filamentous actin (F-actin), and cell membrane tension. We further test the predictions of this model by performing single cell measurements of the spontaneous polarization of cancer stem cells (CSCs) and non-stem cancer cells (NSCCs), as the former have lower cell membrane tension. Based on both our model and the experimental results, cell polarization is more sensitive to stimuli under low membrane tension, and high membrane tension improves the robustness and stability of cell polarization such that polarization persists under random perturbations. Furthermore, our simulations are the first to recapitulate the experimental results described by Houk et al., revealing that aspiration (elevation of tension) and release (reduction of tension) result in a decrease in and recovery of the activity of Rac-GTP, respectively, and that the relaxation of tension induces new polarity of the cell body when a cell with the pseudopod-neck-body morphology is severed.

3-D Microwell Array System for Culturing Virus Infected Tumor Cells

Cancer cells have been increasingly grown in pharmaceutical research to understand tumorigenesis and develop new therapeutic drugs. Currently, cells are typically grown using two-dimensional (2-D) cell culture approaches, where the native tumor microenvironment is difficult to recapitulate. Thus, one of the main obstacles in oncology is the lack of proper infection models that recount main features present in tumors. In recent years, microtechnology-based platforms have been employed to generate three-dimensional (3-D) models that better mimic the native microenvironment in cell culture. Here, we present an innovative approach to culture Kaposi’s sarcoma-associated herpesvirus (KSHV) infected human B cells in 3-D using a microwell array system. The results demonstrate that the KSHV-infected B cells can be grown up to 15 days in a 3-D culture. Compared with 2-D, cells grown in 3-D had increased numbers of KSHV latency-associated nuclear antigen (LANA) dots, as detected by immunofluorescence microscopy, indicating a higher viral genome copy number. Cells in 3-D also demonstrated a higher rate of lytic reactivation. The 3-D microwell array system has the potential to improve 3-D cell oncology models and allow for better-controlled studies for drug discovery.

Dielectric and Mechanical Investigations on the Hydrophilicity and Hydrophobicity of Polyethylene Oxide Modified on a Silicon Surface

Polyethylene oxide (PEO) has been widely used in biomedical fields. The antibiofouling property of the PEO-modified surface has been extensively investigated but is far from being fully understood. A series of PEOs with narrowly distributed molecular weight (M_w), synthesized with the technique of high vacuum anionic polymerization, have been successfully grafted onto the surface of silicon wafers. The power-law relationship between the thickness of the monolayer versus the M_w of the grafted PEO shows a scaling of 0.3, indicating compact condensing of the chains. The static contact angles show higher hydrophobicity for the layer of PEO with higher M_w, which can be attributed to the closely packed conformation of the chains with high density. The frequency shift of the contact resonance indicates that the Young's modulus decreases and the loss factor increases with the increase in the M_w of PEO and the thickness of the PEO layers. Dielectric spectroscopy of bare or PEO-grafted wafers in the aqueous solutions reveals an interfacial polarization, which results from compositional and structural changes in the interface layer and depends on temperatures and salt concentrations. At a given grafting density, the PEO chains are swollen in pure water, demonstrating hydrophilic behavior, whereas they collapse in salt solutions, showing hydrophobic characteristics.

Nano- and microstructured materials for in vitro studies of the physiology of vascular cells

The extracellular environment of vascular cells in vivo is complex in its chemical composition, physical properties, and architecture. Consequently, it has been a great challenge to study vascular cell responses in vitro, either to understand their interaction with their native environment or to investigate their interaction with artificial structures such as implant surfaces. New procedures and techniques from materials science to fabricate bio-scaffolds and surfaces have enabled novel studies of vascular cell responses under well-defined, controllable culture conditions. These advancements are paving the way for a deeper understanding of vascular cell biology and materials-cell interaction. Here, we review previous work focusing on the interaction of vascular smooth muscle cells (SMCs) and endothelial cells (ECs) with materials having micro- and nanostructured surfaces. We summarize fabrication techniques for surface topographies, materials, geometries, biochemical functionalization, and mechanical properties of such materials. Furthermore, various studies on vascular cell behavior and their biological responses to micro- and nanostructured surfaces are reviewed. Emphasis is given to studies of cell morphology and motility, cell proliferation, the cytoskeleton and cell-matrix adhesions, and signal transduction pathways of vascular cells. We finalize with a short outlook on potential interesting future studies.

Protein resistance efficacy of PEO-silane amphiphiles: Dependence on PEO-segment length and concentration

In contrast to modification with conventional PEO-silanes (i.e. no siloxane tether), silicones with dramatically enhanced protein resistance have been previously achieved via bulk-modification with poly(ethylene oxide) (PEO)-silane amphiphiles α-(EtO)3Si(CH2)2-oligodimethylsiloxane13-block-PEOn-OCH3 when n=8 and 16 but not when n=3. In this work, their efficacy was evaluated in terms of optimal PEO-segment length and minimum concentration required in silicone. For each PEO-silane amphiphile (n=3, 8, and 16), five concentrations (5, 10, 25, 50, and 100μmol per 1g silicone) were evaluated. Efficacy was quantified in terms of the modified silicones' abilities to undergo rapid, water-driven surface restructuring to form hydrophilic surfaces as well as resistance to fibrinogen adsorption. Only n=8 and 16 were effective, with a lower minimum concentration in silicone required for n=8 (10μmol per 1g silicone) versus n=16 (25μmol per 1g silicone).

STATEMENT OF SIGNIFICANCE

Silicone is commonly used for implantable medical devices, but its hydrophobic surface promotes protein adsorption which leads to thrombosis and infection. Typical methods to incorporate poly(ethylene oxide) (PEO) into silicones have not been effective due to the poor migration of PEO to the surface-biological interface. In this work, PEO-silane amphiphiles - comprised of a siloxane tether (m=13) and variable PEO segment lengths (n=3, 8, 16) - were blended into silicone to improve its protein resistance. The efficacy of the amphiphiles was determined to be dependent on PEO length. With the intermediate PEO length (n=8), water-driven surface restructuring and resulting protein resistance was achieved with a concentration of only 1.7wt%.

Xenopus extract approaches to studying microtubule organization and signaling in cytokinesis

We report optimized methods for preparing actin-intact Xenopus egg extract. This extract is minimally perturbed, undiluted egg cytoplasm where the cell cycle can be experimentally controlled. It contains abundant organelles and glycogen and supports active metabolism and cytoskeletal dynamics that closely mimic egg physiology. The concentration of the most abundant ∼11,000 proteins is known from mass spectrometry. Actin-intact egg extract can be used for analysis of actin dynamics and interaction of actin with other cytoplasmic systems, as well as microtubule organization. It can be spread as thin layers and naturally depletes oxygen though mitochondrial metabolism, which makes it ideal for fluorescence imaging. When combined with artificial lipid bilayers, it allows reconstitution and analysis of the spatially controlled signaling that positions the cleavage furrow during early cytokinesis. Actin-intact extract is generally useful for probing the biochemistry and biophysics of the large Xenopus egg. Protocols are provided for preparation of actin-intact egg extract, control of the cell cycle, fluorescent probes for cytoskeleton and cytoskeleton-dependent signaling, preparation of glass surfaces for imaging experiments, and immunodepletion to probe the role of specific proteins and protein complexes. We also describe methods for adding supported lipid bilayers to mimic the plasma membrane and for confining in microfluidic droplets to explore size scaling issues.

Versatile multiple protein nanopatterning within a microfluidic channel for cell recruitment studies

A novel approach combining self-assembly-based colloidal lithography and polydimethylsiloxane (PDMS) micromolding to generate complex protein nanopatterns for studying the mechanisms of leukocyte extravasation within microchannels is presented. Nanostructured surfaces sealed onto PDMS-molded microchannels are chemically functionalized in situ in an all-aqueous process to generate bi-functional chemical nanopatterns. Subsequent co-immobilization with proteins makes use of common non-covalent coupling (e.g. HIS-tags, FC-tags and biotin-tags), giving nanopatterns of arbitrary combinations of oriented, functional proteins. Up to three different proteins were simultaneously co-immobilized into the microchannel with nanoscale precision, demonstrating the complex patterns. As a proof-of-principle, a mimic of an inflamed endothelium was constructed using a macro- and nanoscale pattern of intercellular adhesion molecule 1 (ICAM1) and P-selectin, and the response of leukocytes through live cell imaging was measured. A clear result on the rolling behavior of the cells was observed with rolling limited to areas where ICAM1 and P-selectin are present. This micro/nano-interface will open new doors to investigations of how spatial distributions of proteins control cellular activity.

Surface modification on polydimethylsiloxane-based microchannels with fragmented poly(l-lactic acid) nanosheets

Surface modification is a critical issue in various applications of polydimethylsiloxane (PDMS)-based microfluidic devices. Here, we describe a novel method through which PDMS-based microchannels were successfully modified with fragmented poly(l-lactic acid) (PLLA) nanosheets through a simple patchwork technique that exploited the high level of adhesiveness of PLLA nanosheets. Compared with other surface modification methods, our method required neither complicated chemical modifications nor the use of organic solvents that tend to cause PDMS swelling. The experimental results indicated that the modified PDMS exhibited excellent capacity for preventing the adhesion and activation of platelets. This simple yet efficient method can be used to fabricate the special PDMS microfluidic devices for biological, medical, and even hematological purposes.

Tailoring biomaterial surface properties to modulate host-implant interactions: implication in cardiovascular and bone therapy

Host body response to a foreign medical device plays a critical role in defining its fate post implantation. It is thus important to control host-material interactions by designing innovative implant surfaces. In the recent years, biochemical and topographical features have been explored as main target to produce this new type of bioinert or bioresponsive implants. The review discusses specific biofunctional materials and strategies to achieve a precise control over implant surface properties and presents possible solutions to develop next generation of implants, particularly in the fields of bone and cardiovascular therapy.

Anti-fouling Coatings of Poly(dimethylsiloxane) Devices for Biological and Biomedical Applications

Fouling initiated by nonspecific protein adsorption is a great challenge in biomedical applications, including biosensors, bioanalytical devices, and implants. Poly(dimethylsiloxane) (PDMS), a popular material with many attractive properties for device fabrication in the biomedical field, suffers serious fouling problems from protein adsorption due to its hydrophobic nature, which limits the practical use of PDMS-based devices. Effort has been made to develop biocompatible materials for anti-fouling coatings of PDMS. In this review, typical nonfouling materials for PDMS coatings are introduced and the associated basic anti-fouling mechanisms, including the steric repulsion mechanism and the hydration layer mechanism, are described. Understanding the relationships between the characteristics of coating materials and the accompanying anti-fouling mechanisms is critical for preparing PDMS coatings with desirable anti-fouling properties.

In vitro evaluation and in vivo demonstration of a biomimetic, hemocompatible, microfluidic artificial lung

Despite the promising potential of microfluidic artificial lungs, current designs suffer from short functional lifetimes due to surface chemistry and blood flow patterns that act to reduce hemocompatibility. Here, we present the first microfluidic artificial lung featuring a hemocompatible surface coating and a biomimetic blood path. The polyethylene-glycol (PEG) coated microfluidic lung exhibited a significantly improved in vitro lifetime compared to uncoated controls as well as consistent and significantly improved gas exchange over the entire testing period. Enabled by our hemocompatible PEG coating, we additionally describe the first extended (3 h) in vivo demonstration of a microfluidic artificial lung.

Microfluidic single sperm entrapment and analysis

Selection of healthy spermatozoa is of crucial importance for the success rates of assisted reproduction technologies (ART) such as in vitro fertilization and intra-cytoplasmic sperm injection. Although sperm selection for ART procedures is predominantly based on sperm motility, successful fertilization is not predicted by good motility alone. For example, sperm characteristics such as the acrosome state and DNA integrity have shown significant impact on ART outcome. Although fertilization can be achieved with a single spermatozoon of high quality, current quality assessments are population-based and do not allow investigation of multiple sperm characteristics on a single spermatozoon simultaneously. In order to study sperm cells on the single cell level, we designed and characterized a PDMS microfluidic platform that allows single sperm entrapment. After spatially confining individual sperm cells within microfluidic cell traps, the cell viability, chromosomal content and acrosome state were studied. This platform is suitable for the analysis of individual sperm cells, which could be exploited for (non-invasive) sperm analysis and selection by impedance or Raman spectroscopy.

Easy-to-fabricate thin-film coating on PDMS substrate with super hydrophilicity and stability

With the fast expansion of microfluidic applications, stable, and easy-to-fabricate PDMS surface coating with super hydrophilicity is highly desirable. In this study, we introduce a new kind of copolymer-based, single-layer thin-film coating for PDMS. The coating can exist in air at room temperature for at least 6 months without any noticeable deterioration in the super hydrophilicity (water contact angle ∼7°), resistance of protein adsorption, or inhibition of the EOF. In addition, this coating enables arbitrary patterning of cells on planar surfaces.