An Array of Carbon Nanofiber Bundle_Based 3D In Vitro Intestinal Microvilli for Mimicking Functional and Physical Activities of the Small Intestine.

Researchers have developed in vitro small intestine models of biomimicking microvilli, such as gut-on-a-chip devices. However, fabrication methods developed to date for 2D and 3D in vitro gut still have unsolved limitations. In this study, an innovative fabrication method of a 3D in vitro gut model is introduced for effective drug screening. The villus is formed on a patterned carbon nanofiber (CNF) bundle as a flexible and biocompatible scaffold. Mechanical properties of the fabricated villi structure are investigates. A microfluidic system is applied to induce the movement of CNFs villi. F-actin and Occludin staining of Caco-2 cells on a 2D flat-chip as a control and a 3D gut-chip with or without fluidic stress is observed. A permeability test of FD20 is performed. The proposed 3D gut-chip with fluidic stress achieve the highest value of Papp. Mechano-active stimuli caused by distinct structural and movement effects of CNFs villi as well as stiffness of the suggested CNFs villi not only can help accelerate cell differentiation but also can improve permeability. The proposed 3D gut-chip system further strengthens the potential of the platform to increase the accuracy of various drug tests.

Advances in the development paradigm of biosample-based biosensors for early ultrasensitive detection of alzheimer's disease.

This review highlights current developments, challenges, and future directions for the use of invasive and noninvasive biosample-based small biosensors for early diagnosis of Alzheimer's disease (AD) with biomarkers to incite a conceptual idea from a broad number of readers in this field. We provide the most promising concept about biosensors on the basis of detection scale (from femto to micro) using invasive and noninvasive biosamples such as cerebrospinal fluid (CSF), blood, urine, sweat, and tear. It also summarizes sensor types and detailed analyzing techniques for ultrasensitive detection of multiple target biomarkers (i.e., amyloid beta (Aß) peptide, tau protein, Acetylcholine (Ach), microRNA137, etc.) of AD in terms of detection ranges and limit of detections (LODs). As the most significant disadvantage of CSF and blood-based detection of AD is associated with the invasiveness of sample collection which limits future strategy with home-based early screening of AD, we extensively reviewed the future trend of new noninvasive detection techniques (such as optical screening and bio-imaging process). To overcome the limitation of non-invasive biosamples with low concentrations of AD biomarkers, current efforts to enhance the sensitivity of biosensors and discover new types of biomarkers using non-invasive body fluids are presented. We also introduced future trends facing an infection point in early diagnosis of AD with simultaneous emergence of addressable innovative technologies.

Tunable Chemical Grafting of Three-Dimensional Poly (3, 4-ethylenedioxythiophene)/Poly (4-styrenesulfonate)-Multiwalled Carbon Nanotubes Composite with Faster Charge-Carrier Transport for Enhanced Gas Sensing Performance.

The three-dimensional volumetric application of conductive poly (3,4-ethylenedioxythiophene)/poly (4-styrenesulfonate) (PEDOT:PSS) to multiwalled carbon nanotubes (MWCNTs) has not been widely reported. In this study, the applicability of the 3D PEDOT:PSS-MWCNT composite for a gas sensor was investigated with different PEDOT:PSS concentrations. The gas-sensing performance of the 3D PEDOT:PSS-MWCNT composites was investigated using ethanol and carbon monoxide (CO) gas. Overall, in comparison with the pristine MWCNTs, as the PEDOT:PSS concentration increased, the 3D PEDOT:PSS-MWCNT composites exhibited increased conductivity and enhanced gas sensing performances (fast response and recovery times) to both ethanol and CO gases. Importantly, although the PEDOT:PSS coating layer reduced the number of sites for the adsorption and desorption of gas molecules, the charge-carrier transport between the gas molecules and MWCNTs was significantly enhanced. Thus, PEDOT:PSS can be chemically grafted to MWCNTs to enhance the connectivity and conductivity of a 3D network, leading to possible applications in gas sensors.

One-step microchip for DNA fluorescent labeling.

In this study, we propose a microchip that is sequentially capable of fluorescently staining and washing DNAs. The main advantage of this microchip is that it allows for one-step preparation of small amounts of solution without degrading microscopic bio-objects such as the DNAs, cells, and biomolecules to be stained. The microchip consists of two inlets, the main channel, staining zone, washing zone, and one outlet, and was processed using a femtosecond laser system. High molecular transport of rhodamine B to deionized water was observed in the performance test of the microchip. Results revealed that the one-step procedure of on-chip DNA staining and washing was excellent compared to the conventional staining method. The one-step preparation of stained and washed DNAs through the microchip will be useful for preparing small volumes of experimental samples.

Bio-Microfabrication of 2D and 3D Biomimetic Gut-on-a-Chip.

Traditional goal of microfabrication was to limitedly construct nano- and micro-geometries on silicon or quartz wafers using various semiconductor manufacturing technologies, such as photolithography, soft lithography, etching, deposition, and so on. However, recent integration with biotechnologies has led to a wide expansion of microfabrication. In particular, many researchers studying pharmacology and pathology are very interested in producing in vitro models that mimic the actual intestine to study the effectiveness of new drug testing and interactions between organs. Various bio-microfabrication techniques have been developed while solving inherent problems when developing in vitro micromodels that mimic the real large intestine. This intensive review introduces various bio-microfabrication techniques that have been used, until recently, to realize two-dimensional and three-dimensional biomimetic experimental models. Regarding the topic of gut chips, two major review subtopics and two-dimensional and three-dimensional gut chips were employed, focusing on the membrane-based manufacturing process for two-dimensional gut chips and the scaffold-based manufacturing process for three-dimensional gut chips, respectively.

Single Microdroplet Breakup-Assisted Viscosity Measurement.

Recently, with the development of biomedical fields, the viscosity of prepolymer fluids, such as hydrogels, has played an important role in determining the mechanical properties of the extracellular matrix (ECM) or being closely related to cell viability in ECM. The technology for measuring viscosity is also developing. Here, we describe a method that can measure the viscosity of a fluid with trace amounts of prepolymers based on a simple flow-focused microdroplet generator. We also propose an equation that could predict the viscosity of a fluid. The viscosity of the prepolymer was predicted by measuring and calculating various lengths of the disperse phase at the cross junction of two continuous-phase channels and one disperse-phase channel. Bioprepolymer alginates and gelatin methacryloyl (GelMA) were used to measure the viscosity at different concentrations in a microdroplet generator. The break-up length of the dispersed phase at the cross junction of the channel gradually increased with increasing flow rate and viscosity. Additional viscosity analysis was performed to validate the standard viscosity calculation formula depending on the measured length. The viscosity formula derived based on the length of the alginate prepolymer was applied to GelMA. At a continuous phase flow rate of 400 uL/h, the empirical formula of alginate showed an error within about 2%, which was shown to predict the viscosity very well in the viscometer. Results of this study are expected to be very useful for hydrogel tuning in biomedical and tissue regeneration fields by providing a technology that can measure the dynamic viscosity of various prepolymers in a microchannel with small amounts of sample.

Controlled Thin Polydimethylsiloxane Membrane with Small and Large Micropores for Enhanced Attachment and Detachment of the Cell Sheet.

Polydimethylsiloxane (PDMS) membranes can allow the precise control of well-defined micropore generation. A PDMS solution was mixed with a Rushton impeller to generate a large number of microbubbles. The mixed solution was spin-coated on silicon wafer to control the membrane thickness. The microbubbles caused the generation of a large number of small and large micropores in the PDMS membranes with decreased membrane thickness. The morphology of the thinner porous PDMS membrane induced higher values of roughness, Young's modulus, contact angle, and air permeability. At day 7, the viability of cells on the porous PDMS membranes fabricated at the spin-coating speed of 5000 rpm was the highest (more than 98%) due to their internal networking structure and surface properties. These characteristics closely correlated with the increased formation of actin stress fibers and migration of keratinocyte cells, resulting in enhanced physical connection of actin stress fibers of neighboring cells throughout the discontinuous adherent junctions. The intact detachment of a cell sheet attached to a porous PDMS membrane was demonstrated. Therefore, PDMS has a great potential for enhancing the formation of cell sheets in regenerative medicine.

Miniaturized optimal incident light angle-fitted dark field system for contrast-enhanced real-time monitoring of 2D/3D-projected cell motions.

In the field of biology, dark field microscopy provides superior insight into cells and subcellular structures. However, most dark field microscopes are equipped with a dark field filter and a light source on a 2D-based specimen, so only a flat sample can be observed in a limited space. We propose a compact cell monitoring system with built-in dark field filter with an optimized incident angle of the light source to provide real-time cell imaging and spatial cell monitoring for long-term free from phototoxicity. 2D projection imaging was implemented using a modular condenser lens to acquire high-contrast images. This enabled the long-term monitoring of cells, and the real-time monitoring of cell division and death. This system was able to image, by 2D projection, cells on the surface thinly coated with multiwalled carbon nanotubes, as well as living cells that migrated along the surface of glass beads and hydrogel droplets with a diameter of about 160 µm. The optimal incident light angle-fitted dark field system combines high-contrast imaging sensitivity and high spatial resolution to even image cells on 3D surfaces.

Parylene-C coated microporous PDMS structure protecting from functional deconditioning of platelets exposed to cardiostimulants.

Most elderly patients after orthopedic and dental implant surgeries are exposed to cardiostimulants to reduce potential blood pressure-related risks of cardiovascular diseases. Such treatments lead to deconditioning of platelet function, which is an important factor in wound healing treatments. We introduced an innovative parylene-C coated microporous PDMS structure that can prevent the functional deconditioning of platelets caused by certain cardiostimulants. At different concentrations of cardiostimulants (IPR; isoprenaline and DA; dopamine), pre-activation, activation, and post-activation of platelets were intensively examined under mechanical and chemical stimulation mimicking the physiological environment on four different surfaces (glass, flat parylene-C coated glass (F-PPXC), microporous PDMS structure (P-PDMS), and parylene-C-coated microporous PDMS structure (S-PPXC)). The 3D microporous structure with parylene-C (S-PPXC) surface could attenuate the deconditioning of platelet function caused by IPR. Moreover, the S-PPXC surface further enhanced the DA-dependent stimulation of platelet function. The reason for this is that the 3D microporous structure with parylene-C S-PPXC induced stable and fast adhesion of platelets through increased surface roughness and softness, resulting in a significant enhancement of platelet activity. Therefore, we propose the use of functional S-PPXC surfaces as a novel strategy in the development of biomedical products.

Bioactive multiple-bent MWCNTs for sensitive and reliable electrochemical detection of picomolar-level C-reactive proteins.

We present multiple-bent multi-walled carbon nanotubes (MWCNTs) that enable the picomolar detection of C-reactive protein (CRP), which is considered to be a promising biomarker for various diseases. The MWCNTs were grown via chemical vapor deposition repeating the asymmetric catalytic CNT growth on atypical carbon nanoparticles that were generated by carbon coating on a silicon substrate. The multiple-bent MWCNTs with the carbon film (CF) possessed abundant hydrophilic functional groups (-COOH and -OH) at their bending sites, resulting in enhanced bioadhesion to collagen and platelets, compared to MWCNTs grown without a CF layer. Interestingly, the bent MWCNTs enhanced the reliability and sensitivity of the electrochemical detection at low CRP concentrations, possibly due to molecular affinity at the bent site. The bioactive bent MWCNTs can play a significant role in ultrasensitive biosensors to improve their detection limit, thereby achieving early detection and monitoring of CRP-related diseases such as cardiovascular events and melanoma.

Controlled generation of nanopatterned electrical DNA interface.

Techniques that manipulate DNA, a biomolecule with electrical properties, are in demand in various medical fields. This study fabricated a nanochannel with a conductive/semi-conductive interface using focused ion beams (FIBs) and introduced a nanochip technology to freely align, attach, and detach lambda DNAs in the interface via electrophoresis. Two-step fabrication process of nanochannels was quantitatively characterized according to the different conditions of the FIB dose (1~30 nC/µm2) and current (1~500 pA). For electrophoresis test, four different nanofluidic channels with depths of 200 nm and lengths of 0.5, 1.0, 1.5, and 2.0 µm were processed at the center of the rectangular channel (10 µm × 10 µm). Different voltages (1~30 V) were applied for 15 min to attach the DNAs. As the voltage increased, more lambda DNAs attached to the nanochannel interface. Furthermore, an inverse voltage (-30 V) was applied to the lambda DNAs attached to the interface for 15 min to confirm that DNAs could be successfully detached. The results showed that this method could produce a highly promising nanochip technology to align and manipulate DNAs in the desired direction according to a conductive/semi-conductive nano-sized interface, which is applicable in various biomedical fields.

Comprehensive tuning of bioadhesive properties of polydimethylsiloxane (PDMS) membranes with controlled porosity.

Polydimethylsiloxane (PDMS)-based elastomers have become the de facto platform for various biomedical applications. But the stable attachment of biomolecules to PDMS for more robust and long-term performance of the PDMS-based devices has been a significant challenge, owing to its unique physical properties (e.g. hydrophobicity, dynamic molecular mobility). Herein, the PDMS membrane with tunable surface porosity is developed via high-pressure saturated steam technology in order to promote a strong and lasting bioadhesion to the PDMS membrane without additional processing steps. The resulting porous PDMS membranes demonstrate enhanced physical properties (e.g. Young's modulus, roughness, and air permeability), which is dependent on the membrane thickness. The bioactivity of porous PDMS membranes, evaluated by measuring the adhesion of various biomolecules and bioactivity of cells, shows significant improvement over conventional non-porous control. This effect can be attributed to the strong physical adsorption on the porous PDMS membrane by increased surface roughness and stiffness. In sum, the porous PDMS membrane provides a simple and yet highly effective platform to create bioactive surface for various biomedical devices.