An efficient surface modification using 2-methacryloyloxyethyl phosphorylcholine to control cell attachment via photochemical reaction in a microchannel

Recent progress and perspectives in applications of 2-methacryloyloxyethyl phosphorylcholine polymers in biodevices at small scales

Bioinspired materials have attracted attention in a wide range of fields. Among these materials, a polymer family containing 2-methacryloyloxyethyl phosphorylcholine (MPC), which has a zwitterionic phosphorylcholine headgroup inspired by the...

A simple and reversible glass-glass bonding method to construct a microfluidic device and its application for cell recovery

Compared with polymer microfluidic devices, glass microfluidic devices have advantages for diverse lab-on-a-chip applications due to their rigidity, optical transparency, thermal stability, and chemical/biological inertness. However, the bonding process to construct glass microfluidic devices usually involves treatment(s) like high temperature over 400 °C, oxygen plasma or piranha solution. Such processes require special skill, apparatus or harsh chemicals, and destroy molecules or cells in microchannels. Here, we present a simple method for glass-glass bonding to easily form microchannels. This method consists of two steps: placing water droplets on a glass substrate cleaned by neutral detergent, followed by fixing a cover glass plate on the glass substrate by binding clips for a few hours at room temperature. Surface analyses showed that the glass surface cleaned by neutral detergent had a higher ratio of SiOH over SiO than glass surfaces prepared by other cleaning steps. Thus, the suggested method could achieve stronger glass-glass bonding via dehydration condensation due to the higher density of SiOH. The pressure endurance reached over 600 kPa within 6 h of bonding, which is sufficient for practical microfluidic applications. Moreover, by exploiting the reversibility of this bonding method, cell recoveries after cultivating cells in a microchannel were demonstrated. This new bonding method can significantly improve both the productivity and the usability of glass microfluidic devices and extend the possibility of glass microfluidic applications in future.

Vacuum microcasting of 2-methacryloyloxyethyl phosphorylcholine polymer for stable cell patterning

This study demonstrates the rapid fabrication and utility of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer film for cell patterning. The film was obtained on a cell culture surface by microcasting MPC polymer ethanol solution into a degassed polydimethylsiloxane mold with a desired pattern. After removal of the mold, 293AD cells were cultured on the surface of the polymer film with the patterned microstructures. Patterned cell adhesion restricted by the film was successfully maintained during at least a 168-h cultivation. The microcast MPC polymer film can be prepared rapidly and used for efficient long-term cell confinement.

Tunable Protein/Cell Binding and Interaction with Neurite Outgrowth of Low-Impedance Zwitterionic PEDOTs

Zwitterionic poly(3,4-ethylenedioxythiophene) (PEDOT) is an effective electronic material for bioelectronics because it exhibits efficient electrical trade-off and diminishes immune response. To promote the use of zwitterionic PEDOTs in bioelectronic devices, especially for cell alignment control and close electrocoupling, features such as tunable interaction of PEDOTs with proteins/cells and spatially modulating cell behavior are required. However, there is a lack of reliable methods to assemble zwitterionic EDOTs with other functionalized EDOT materials, having different polarities and oxidation potentials, to prepare PEDOTs with the aforementioned surface properties. In this study, we have developed a surfactant-assisted electropolymerization to assemble phosphorylcholine (PC)-functionalized EDOT with other functionalized EDOTs. By adjusting compositions, the interaction of PEDOT copolymers with proteins/cells can be finely tuned; the composition adjustment has an ignorable influence on the impedance of the copolymers. We also demonstrate that the cell-repulsive force generated from PC can spatially guide the neurite outgrowth to form a neuron network at single-cell resolution and greatly enhance the neurite outgrowth by 179%, which is significantly more distinctive than the reported topography effect. We expect that the derived tunable protein/cell interaction and the PC-induced repulsive guidance for the neurite outgrowth can make low-impedance zwitterionic PEDOTs more useful in bioelectronics.

Biomimetic Polymer-Based Method for Selective Capture of C-Reactive Protein in Biological Fluids

Selective capturing and purification of C-reactive protein (CRP) from complex biological fluids plays a pivotal role in studying biological activities of CRP in various diseases. However, obvious nonspecific adsorption of proteins was observed on current affinity sorbents, and thus additional purification steps are often required, which could compromise the recovery of the target protein and/or introduce new impurities. In this study, inspired by the highly specific interaction between CRP and the cell membrane, an excellent anti-biofouling compound 2-(methacryloyloxy)ethyl phosphorylcholine and a highly hydrophilic crosslinker N, N'-methylenebisacrylamide were employed to fabricate a novel cell membrane biomimetic polymer for selective capture of CRP in the presence of calcium ions. Based on the polymer described above, a facile enrichment approach was established after systematic optimization of the washing and elution conditions. With its favorable properties, such as good porosity, weak electrostatic interaction, high hydrophilicity, and biocompatibility, the novel biomimetic polymer exhibits good specificity, selectivity, recovery (near 100%), purity (95%), and a lower nonspecific protein adsorption for CRP in comparison with commercial immobilized p-aminophenyl phosphoryl choline gel and other purification materials. Furthermore, the structural integrity and functionality of CRP in the elution fraction were well preserved and confirmed by circular dichroism spectroscopy, fluorescence spectroscopy, and immunoturbidimetric assay. Finally, the biomimetic polymer was successfully applied to the selective enrichment of CRP from sera of patients with inflammation and rats. The proposed novel enrichment approach based on the versatile biomimetic polymer can be used for effective CRP purification, which will benefit the in-depth study of its biological roles.

Embryonic body culturing in an all-glass microfluidic device with laser-processed 4 μm thick ultra-thin glass sheet filter

In this paper, we report the development and demonstration of a method to fabricate an all-glass microfluidic cell culturing device without circulation flow. On-chip microfluidic cell culturing is an indispensable technique for cellular replacement therapies and experimental cell biology. Polydimethylsiloxane (PDMS) have become a popular material for fabricating microfluidic cell culture devices because it is a transparent, biocompatible, deformable, easy-to-mold, and gas-permeable. However, PDMS is also a chemically and physically unstable material. For example, PDMS undergoes aging easily even in room temperature conditions. Therefore, it is difficult to control long term experimental culturing conditions. On the other hand, glass is expected to be stable not only in physically but also chemically even in the presence of organic solvents. However, cell culturing still requires substance exchanges such as gases and nutrients, and so on, which cannot be done in a closed space of a glass device without circulation flow that may influence cell behavior. Thus, we introduce a filter structure with micropores onto a glass device to improve permeability to the cell culture space. Normally, it is extremely difficult to fabricate a filter structure on a normal glass plate by using a conventional fabrication method. Here, we demonstrated a method for fabricating an all-glass microfluidic cell culturing device having filters structure. The function of this all-glass culturing device was confirmed by culturing HeLa, fibroblast and ES cells. Compared with the closed glass devices without a filter structure, the numbers of cells in our device increased and embryonic bodies (EBs) were formed. This method offers a new tool in microfluidic cell culture technology for biological analysis and it expands the field of microfluidic cell culture.

Antifouling Stripes Prepared from Clickable Zwitterionic Copolymers

In this study, we have fabricated robust patterned surfaces that contain biocompatible and antifouling stripes, which cause microorganisms to consolidate into bare silicon spaces. Copolymers of methacryloyloxyethyl phosphorylcholine (MPC) and a methacrylate-substituted dihydrolipoic acid (DHLA) were spin-coated onto silicon substrates. The MPC units contributed biocompatibility and antifouling properties, and the DHLA units enabled cross-linking and the formation of robust thin films. Photolithography enabled the formation of 200-μm-wide poly(MPC-DHLA) stripped patterns that were characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and rhodamine 6G staining. Regardless of the spacing between poly(MPC-DHLA) stripes (10, 50, or 100 μm), Escherichia coli rapidly adhered to the bare silicon gaps that lacked the copolymer, confirming the antifouling nature of MPC. Overall, this work provides a surface modification strategy for generating alternating biofouling and nonfouling surface structures that are potentially applicable for researchers studying cell biology, drug screening, and biosensor technology.

A method of packaging molecule/cell-patterns in an open space into a glass microfluidic channel by combining pressure-based low/room temperature bonding and fluorosilane patterning

A fabrication method of a “post-molecule/cell patterned” glass microchip was developed by pressure-based bonding and patterning with a fluorosilane coupling reagent.

An all-glass 12 μm ultra-thin and flexible micro-fluidic chip fabricated by femtosecond laser processing

This study investigated and established a method, using femtosecond laser processing, to fabricate a 100%-glass-based 12 μm ultra-thin and flexible micro-fluidic chip. First we investigated the suitable pulse energy of the laser to fabricate ultra-thin glass sheets and then we fabricated a prototype glass micro-fluidic chip. Two 1 mm-in-diameter orifices for facilitating alignment in the bonding step and one channel with a width of 20 μm and a length of 25 mm were fabricated in a 4 μm thickness ultra-thin glass sheet using the femtosecond laser; this forms layer 2 in the completed device. Next, the glass sheet with the channel was sandwiched between another glass sheet having an inlet hole and an outlet hole (layer 1) and a base glass sheet (layer 3); the three sheets were bonded to each other, resulting in a flexible, 100%-glass micro-fluidic chip with a thickness of approximately 12 μm and a weight of 3.6 mg. The basic function of the glass micro-fluidic chip was confirmed by flowing 1 and 2 μm in-diameter bead particles through the channel. The fabrication method clearly scales down the thickness limitation of flexible glass devices and offers a possible element technology for fabricating ultra-thin glass devices that can be applied to convection-enhanced delivery, implantable medical devices, wearable devices, and high-resolution imaging of small biological objects such as bacteria and proteins in the channel.

Large-Scale Integration of All-Glass Valves on a Microfluidic Device

In this study, we developed a method for fabricating a microfluidic device with integrated large-scale all-glass valves and constructed an actuator system to control each of the valves on the device. Such a microfluidic device has advantages that allow its use in various fields, including physical, chemical, and biochemical analyses and syntheses. However, it is inefficient and difficult to integrate the large-scale all-glass valves in a microfluidic device using conventional glass fabrication methods, especially for the through-hole fabrication step. Therefore, we have developed a fabrication method for the large-scale integration of all-glass valves in a microfluidic device that contains 110 individually controllable diaphragm valve units on a 30 mm × 70 mm glass slide. This prototype device was fabricated by first sandwiching a 0.4-mm-thick glass slide that contained 110 1.5-mm-diameter shallow chambers, each with two 50-μm-diameter through-holes, between an ultra-thin glass sheet (4 μm thick) and another 0.7-mm-thick glass slide that contained etched channels. After the fusion bonding of these three layers, the large-scale microfluidic device was obtained with integrated all-glass valves consisting of 110 individual diaphragm valve units. We demonstrated its use as a pump capable of generating a flow rate of approximately 0.06–5.33 μL/min. The maximum frequency of flow switching was approximately 12 Hz.

Blood-compatible poly (2-methoxyethyl acrylate) for the adhesion and proliferation of lung cancer cells toward the isolation and analysis of circulating tumor cells

Circulating tumor cells have received attention for their role in cancer diagnosis and the decision on which chemotherapeutic course to take. For these purposes, the isolation of circulating tumor cells has been important. Previously, we reported that non-blood cells can adhere on blood-compatible polymer substrates, such as poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate). In this study, we examined whether blood-compatible poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) allow the adhesion and growth of A549 lung cancer cells for isolating circulating tumor cells by adhesion-mediated manner to diagnose metastatic cancer and to decide on the chemotherapeutic course. A549 cells can adhere on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates via an integrin-dependent mechanism after 1 h of incubation, suggesting that blood-compatible poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates possess the ability to capture circulating tumor cells selectively from peripheral blood. After 1 day of culture, A549 cells started to spread on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates. A549 can also grow on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates. Additionally, the chemoresistance of A549 cells against 5-fluorouracil on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates was similar to that on the conventional cell culture substrate, tissue culture polystyrene. These results indicate that circulating tumor cells can be cultured on poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates after they are isolated from peripheral blood, and poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates can be used as circulating tumor cell culture substrates for screening anti-cancer drugs. Therefore, poly(2-methoxyethyl acrylate) and poly(tetrahydrofurfuryl acrylate) substrates might be able to be applied to the development of a new device for a circulating tumor cell–based diagnosis of metastatic cancer and a personalized medicine approach regarding the decision of which chemotherapeutic course should be taken.

Adhesion-based simple capture and recovery of circulating tumor cells using a blood-compatible and thermo-responsive polymer-coated substrate

Circulating tumor cells (CTCs) have been a focus of study for metastatic cancer diagnostics, in in vitro anti-cancer drug screening to decide the chemotherapeutic course, and cancer biology research.

Spontaneous Packaging and Hypothermic Storage of Mammalian Cells with a Cell-Membrane-Mimetic Polymer Hydrogel in a Microchip

Currently, continuous culture/passage and cryopreservation are two major, well-established methods to provide cultivated mammalian cells for experiments in laboratories. Due to the lack of flexibility, however, both laboratory-oriented methods are unable to meet the need for rapidly growing cell-based applications, which require cell supply in a variety of occasions outside of laboratories. Herein, we report spontaneous packaging and hypothermic storage of mammalian cells under refrigerated (4 °C) and ambient conditions (25 °C) using a cell-membrane-mimetic methacryloyloxyethyl phosphorylcholine (MPC) polymer hydrogel incorporated within a glass microchip. Its capability for hypothermic storage of cells was comparatively evaluated over 16 days. The results reveal that the cytocompatible MPC polymer hydrogel, in combination with the microchip structure, enabled hypothermic storage of cells with quite high viability, high intracellular esterase activity, maintained cell membrane integrity, and small morphological change for more than 1 week at 4 °C and at least 4 days at 25 °C. Furthermore, the stored cells could be released from the hydrogel and exhibited the ability to adhere to a surface and achieve confluence under standard cell culture conditions. Both hypothermic storage conditions are ordinary flexible conditions which can be easily established in places outside of laboratories. Therefore, cell packaging and storage using the hydrogel incorporated within the microchip would be a promising miniature and portable solution for flexible supply and delivery of small amounts of cells from bench to bedside.

Site-specific nanopatterning of functional metallic and molecular arbitrary features in nanofluidic channels

We established a versatile method for site-specific nanopatterning of functional metallic and molecular arbitrary features in glass nanofluidic channels, with well-controlled feature sizes ranging from tens to hundreds of nanometers and precisely controlled placements in the range of several tens of nanometers. With the method, we achieved the fabrication of quasi-0D, quasi-1D, 2D, and 3D gold nanopatterns in nanofluidic channels, as well as a high-density fluorescent molecular nanoarray in arrayed femtoliter nanofluidic channels. The method opens the way for precise functionalization of nanofluidic channels, which has been greatly challenging in the field of nanofluidics.

Collagen surfaces modified with photo-cleavable polyethylene glycol-lipid support versatile single-cell arrays of both non-adherent and adherent cells

Cell patterning on photo-responsive materials are a promising tool for preparing unique single-cell arrays. However, most conventional single-cell arrays on such smart materials can be applied only to adherent cells and limit cellular functions such as extension and migration within the patterned adhesive surfaces. In this study, a versatile single cell array that works with both non-adherent and adherent cells was constructed using a photo-cleavable polyethylene glycol (PEG)-lipid/collagen surface. On this single-cell array, cells behaved similar to their native functions without limitation from the patterned surface. Furthermore, quantitative imaging analyses of cellular motility and morphological changes were performed in a high-throughput manner.

On-chip investigation of cell-drug interactions

Investigation of cell-drug interaction is of great importance in drug discovery but continues to pose significant challenges to develop robust, fast and high-throughput methods for pharmacologically profiling of potential drugs. Recently, cell chips have emerged as a promising technology for drug discovery/delivery, and their miniaturization and flow-through operation significantly reduce sample consumption while dramatically improving the throughput, reliability, resolution and sensitivity. Herein we review various types of miniaturized cell chips used in investigation of cell-drug interactions. The design and fabrication of cell chips including material selection, surface modification, cell trapping/patterning, concentration gradient generation and mimicking of in vivo environment are presented. Recent advances of on-chip investigations of cell-drug interactions, in particular the high-throughput screening, cell sorting, cytotoxicity testing, drug resistance analysis and pharmacological profiling are examined and discussed. It is expected that this survey can provide thoughtful basics and important applications of on-chip investigations of cell-drug interactions, thus greatly promoting research and development interests in this area.

Cytophilic/cytophobic design of nanomaterials at biointerfaces

To control interactions between cells and nanomaterials has been a great challenge because numerous nanomaterials have been intensively explored in the fields of biology and medicine. However, current surface modification of nanomaterials is mainly carried out in an empirical way. Herein, a general strategy to tune the surface chemistry of nanomaterials is proposed based on cell affinity, that is, cytophilic or cytophobic. The cell affinity of nanomaterials directly affects cellular response to materials at the very early stage of cell-material interactions before other events, such as endocytosis, cell spreading, and cell differentiation, occur. In this Concept, it is suggested that there is a developing library of cytophilic and cytophobic moieties, and how the cell affinity of nanomaterials functions at biointerfaces is discussed by exemplifying several applications, namely therapy, tissue engineering, and biosensors. It is believed that control of the cytophilic/cytophobic property will be helpful in guiding the design of functional nanomaterials for their biomedical applications.

Copolymer coatings consisting of 2-methacryloyloxyethyl phosphorylcholine and 3-methacryloxypropyl trimethoxysilane via ATRP to improve cellulose biocompatibility

AB diblock copolymers comprised of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly(3-methacryloxypropyl trimethoxysilane) (PMTSi) segments, which are used for biocompatible coatings, were investigated. Block copolymers with various compositions were synthesized by atomic transfer radical polymerization (ATRP). The obtained copolymers were dissolved in an ethanol solution, and dynamic light scattering showed that all block copolymers were capable of existing as micelles. After a convenient "one-step" reaction, the cellulose membranes could be covalently modified by these copolymers with stable chemical bonds (C-O-Si and Si-O-Si). Block copolymers with different PMPC chain length were applied to surface modification to find the most suitable copolymer. The functional MPC density can be controlled by adjusting the ratio of the two monomers (MPC and MTSi), which also affect surface properties, including the surface contact angle, surface morphology, and number of functional PC groups. The low-fouling properties were measured by protein adsorption, platelet adhesion and activation, and cell adhesion. Protein adsorption of bovine serum albumin (BSA), fibrinogen, and human plasma were also tested and a moderate monomer composite was attained. The protein adsorption behavior on the novel interfaces depends both on MPC density and PMPC chain length. Platelet adhesion and activation were reduced on all the modified surfaces. The adhesion of Human Embryonic Kidney 293 (293T) cells on the coated surfaces also decreased.

Endothelial cell micropatterning: methods, effects, and applications

The effects of flow on endothelial cells (ECs) have been widely examined for the ability of fluid shear stress to alter cell morphology and function; however, the effects of EC morphology without flow have only recently been observed. An increase in lithographic techniques in cell culture spurred a corresponding increase in research aiming to confine cell morphology. These studies lead to a better understanding of how morphology and cytoskeletal configuration affect the structure and function of the cells. This review examines EC micropatterning research by exploring both the many alternative methods used to alter EC morphology and the resulting changes in cellular shape and phenotype. Micropatterning induced changes in EC proliferation, apoptosis, cytoskeletal organization, mechanical properties, and cell functionality. Finally, the ways these cellular manipulation techniques have been applied to biomedical engineering research, including angiogenesis, cell migration, and tissue engineering, are discussed.

Photopatterned materials in bioanalytical microfluidic technology

Microfluidic technologies are playing an increasingly important role in biological inquiry. Sophisticated approaches to the microanalysis of biological specimens rely, in part, on the fine fluid and material control offered by microtechnology, as well as a sufficient capacity for systems integration. A suite of techniques that utilize photopatterning of polymers on fluidic surfaces, within fluidic volumes, and as primary device structures underpins recent technological innovation in bioanalysis. Well-characterized photopatterning approaches enable previously fabricated or commercially fabricated devices to be customized by the user in a straight-forward manner, making the tools accessible to laboratories that do not focus on microfabrication technology innovation. In this review of recent advances, we summarize reported microfluidic devices with photopatterned structures and regions as platforms for a diverse set of biological measurements and assays.

The effects of shear stress on isolated receptor-ligand interactions of Staphylococcus epidermidis and human plasma fibrinogen using molecularly patterned microfluidics

Staphylococcus epidermidis is an opportunistic pathogen that has been implicated in hospital-acquired infections, specifically related to implanted intravascular devices. S. epidermidis adhesion is a mechanism of colonization, leading to pathogenesis. Here we demonstrate an easily fabricated and robust parallel microfluidic platform to investigate the physiologically-relevant effects of fluid shear on S. epidermidis adhesion to human fibrinogen (hFg) with increased experimental throughput. In situ molecular patterning using fluid flow boundaries allows for isolation of the molecular interactions in highly defined shear stress environments, while keeping the device operation simple and reproducible. We characterize two modes of attachment of S. epidermidis to hFg coated surfaces. Single colonies adhere in high fractions at low shear stresses (~1 dyne cm(-2)) and adhesion decays with increasing shear. However, clusters of bacteria adhere the highest at median wall shear stress (up to 10 dyne cm(-2)), and adhesion subsequently decays above this critical shear stress. This initial characterization suggests a previously unobserved phenomenon of shear activated cell-cell adhesion in S. epidermidis, which acts to increase the overall attachment strength to hFg. Both of these modes of attachment are dependant upon the presence of intact hFg, indicating that adhesion is resultant from specific molecular recognition between the bacteria and human fibrinogen. This platform provides new insight into complex host-pathogen interactions, and will allow for further investigation of colonization and pathogenesis in more physiologically relevant conditions.

Single-cell attachment and culture method using a photochemical reaction in a closed microfluidic system

Recently, interest in single cell analysis has increased because of its potential for improving our understanding of cellular processes. Single cell operation and attachment is indispensable to realize this task. In this paper, we employed a simple and direct method for single-cell attachment and culture in a closed microchannel. The microchannel surface was modified by applying a nonbiofouling polymer, 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, and a nitrobenzyl photocleavable linker. Using ultraviolet (UV) light irradiation, the MPC polymer was selectively removed by a photochemical reaction that adjusted the cell adherence inside the microchannel. To obtain the desired single endothelial cell patterning in the microchannel, cell-adhesive regions were controlled by use of round photomasks with diameters of 10, 20, 30, or 50 μm. Single-cell adherence patterns were formed after 12 h of incubation, only when 20 and 30 μm photomasks were used, and the proportions of adherent and nonadherent cells among the entire UV-illuminated areas were 21.3%±0.3% and 7.9%±0.3%, respectively. The frequency of single-cell adherence in the case of the 20 μm photomask was 2.7 times greater than that in the case of the 30 μm photomask. We found that the 20 μm photomask was optimal for the formation of single-cell adherence patterns in the microchannel. This technique can be a powerful tool for analyzing environmental factors like cell-surface and cell-extracellular matrix contact.