Rapid Fabrication Method Research Articles

One-Step Polylactic Acid Screen-Printing Microfluidic Paper-Based Analytical Device: Application for Simultaneous Detection of Nitrite and Nitrate in Food Samples

In this work, we report a one-step approach for fabricating screened-printed microfluidic paper-based analytical devices (μPADs) using polylactic acid as a new hydrophobic material. A polylactic acid solution was screen printed onto chromatography papers to create hydrophobic patterns for fluidic channels. The optimal polylactic acid concentration for successful device fabrication is 9% w/v. The μPADs were fabricated within 2 min and provided high reproducibility and stability. The utility of polylactic acid screen-printing was demonstrated for the simultaneous detection of nitrite and nitrate using colorimetric detection. Under optimized experimental conditions, the detection limits and the linear ranges, respectively, were 1.2 mg L−1 and 2–10 mg L−1 for nitrite and 3.6 mg L−1 and 10–50 mg L−1 for nitrate. The detection times for both ions were found to be within 12 min. The developed μPAD was applied for the simultaneous determination of these ions in food samples, and no significant differences in the analytical results were observed compared to those of the reference method. The polylactic acid screen-printing approach presented here provides a simple, rapid, and cost-effective alternative fabrication method for fabricating μPADs.

Rapid Fabrication of Malleable Fiber Reinforced Composites with Vitrimer Powder

We present a rapid fabrication method for fiber-reinforced polymer composites based on heat pressing woven carbon fibers and vitrimer powder. Vitrimer consists of a covalently cross-linked network ...

Rapid and Inexpensive Method for Fabrication and Integration of Electrodes in Microfluidic Devices

Electrodes are essential components in a number of microfluidic devices for sensing and actuation. Current methods for electrode fabrication in microfluidic devices are mostly derived from the electronic industry and rely on expensive photolithography and sputtering processes. Here, in this paper, we demonstrate that a combination of xurography and cold lamination can be used to fabricate and integrate electrodes in microfluidic devices. This method is fast, inexpensive, direct and does not require any intermediate layer for pattern transfer. This method utilizes thin metal foils that are commercially available at low-cost and with a large variety of materials in the fabrication of electrode structures. We demonstrate that using xurography, electrode sizes down to 66 $\mu \text{m}$ and pitch sizes as small as 25 $\mu \text{m}$ can be obtained using these foils. After patterning, the electrodes were bonded to plastic films using pressure sensitive adhesives and integrated into microfluidic devices which were also fabricated using xurography approach combined with cold lamination. We demonstrate various applications of these electrodes as electrochemical sensors, as heaters for temperature control and as electrokinetic mixers. This simple method is low-cost and produces electrode structures that are ideally suited for application in microfluidic and lab-on-a-chip devices. [2019-0048]

Printing of Quasi‐2D Semiconducting β‐Ga2O3 in Constructing Electronic Devices via Room‐Temperature Liquid Metal Oxide Skin

Quasi‐2D β‐Ga2O3 is a rediscovered metal‐oxide semiconductor with the advantage of an ultrawide bandgap of 4.6–4.9 eV. It is reported to be a promising material for next‐generation power and radio‐frequency electronics. However, realizing macroelectronics based on β‐Ga2O3 film is challenging due to the nonuniformity and improper thickness of the film. Herein, a straightforward and rapid impact fabrication method for depositing high‐quality β‐Ga2O3 films is introduced. Structural and film properties of the deposited β‐Ga2O3 are characterized using scanning electron microscopy, X‐ray diffraction, and atomic force microscopy. To illustrate the applicability of the deposited β‐Ga2O3 in constructing electronic devices, β‐Ga2O3‐based field‐effect transistors (FETs) are fabricated with a source–drain spacing of 400 μm. Films of β‐Ga2O3 exhibit a good performance with carrier mobilities as high as 21.3 cm2 V–1 s–1, transconductances of 1.4 μS, and on/off current ratios of 104. The device performances indicate a big potential of β‐Ga2O3 for future power device applications. The method paves the way for future application of β‐Ga2O3 in electronics. It also provides a scalable approach for the integration of 2D morphologies of industrially important semiconductors into emerging electronics and optical devices.

Injection compression molding of transmission-type Fano resonance biochips for multiplex sensing applications

Nanostructure-based surface plasmon resonance biosensors have attracted considerable attention since the phenomenon of extraordinary light transmission in metallic nanohole arrays was discovered. However, the mass production of uniform metallic nanostructures with a low-cost, rapid, and high-throughput fabrication process remains a key issue for various multiplex sensing applications. We successfully utilized injection compression molding to mass fabricate transmission-type Fano resonance biochips with a feature size of 60nm for multiplex sensing applications. Two types of metallic nanostructures, aluminum nanoslits and capped aluminum nanoslits with 24 sensing arrays, were made on polycarbonate substrates. The bulk sensitivity and uniformity of the nanostructure arrays were tested. A Fano resonance with a full-width at half-maximum bandwidth of 8nm was observed in the visible light region for 470-nm-period capped aluminum nanoslit arrays. The refractive index sensitivity was 460nm/RIU, and a figure of merit of 58 was achieved. Moreover, aluminum nanoslits had a dip resonance with a bandwidth of 25nm and a refractive index sensitivity of 463nm/RIU. The coefficients of variation of the refractive index sensitivities for 24 arrays on a biochip and 10 biochips from different fabrication batches were both below 3%, which indicates that uniform nanostructures can be fabricated by injection compression molding and that the reproducibility is controllable. In addition, the multiplex sensing capability of the aluminum nanostructure arrays was demonstrated by simultaneously monitoring 24 water/glycerin solutions with a hyperspectral imaging system. Protein–protein interactions between bovine serum albumin and anti-bovine serum albumin demonstrated proof of concept of the biological detection capability of the chips. To benefit various multiplex sensing applications such as clinical disease diagnosis, drug screening, and protein biomarker discovery, 96-array aluminum nanoslit biochips the same size as a standard 96-well plate were successfully fabricated. Such a nanostructure-based plasmonic biochip produced by a low-cost, rapid, and high-throughput fabrication method can benefit commercial applications.

Fabrication of high-aspect-ratio structures using Bessel-beam-activated photopolymerization.

Microfabrication based on photopolymerization is typically achieved by scanning a focal spot within the material point by point, which significantly limits fabrication speed. In this paper, we explore a method for rapid fabrication of high-aspect-ratio microstructures based on photopolymerization using a femtosecond laser beam that is converted into a Bessel beam by an axicon. With stationary exposure, a polymer fiber measured at 200μm in length and 400nm in width (500∶1 aspect ratio) was fabricated within 50ms of exposure time. The exposure conditions can be adjusted to produce fibers with variable widths. A phenomenological polymerization-threshold model is adapted for Bessel-beam exposure. The revised model is applied to analyze the structure width and estimate the order of multi-photon absorption. Examination of the cross section of the fibers shows that they are nearly monolithic, suggesting that active species diffuse during photopolymerization. By scanning the Bessel beam in the plane transverse to the direction of beam propagation, mesh structures are fabricated with a single-pass scan, showing the potential of this method for rapid fabrication of large-scale high-aspect-ratio microstructures for applications in photonics, micro-machines, and tissue engineering.

Cutting edge microfluidics: Xurography and a microwave

Microfluidic technologies enable precise fluidic manipulation at the microscale, with applications ranging from inexpensive medical diagnostics to automaton devices for extraterrestrial in situ analysis. However, development of microfluidic tools typically requires high-maintenance infrastructure and resource-intensive development processes, limiting their broad adoption. Furthermore, the development of effective microfluidic tools requires iterative design processes, multiplicatively increasing development time and cost. Rapid prototyping techniques minimize these expenses, accelerating development time and reducing manufacturing cost of microfluidic devices. Here, we use the print-and-peel (PAP) technique of xurography to fabricate master molds in conjunction with microwave thermal processing of polydimethylsiloxane (PDMS) to rapidly fabricate PDMS-based microfluidics. Three types of tape (3M Blue Platinum, PVC and Kapton Tape) and three types of backing substrates (Soda lime glass, Silicon, Ceramic glass) were employed, enabling fabrication of microfluidic devices from design to device in as little as five minutes. Minimum feature widths of ˜200 μm and feature heights of ˜60 μm were determined. Proof-of-concept devices made using these methods were employed for electrophoretic flow focusing applications. To the best of our knowledge, this process represents the most rapid method for fabrication of PDMS microfluidics to date due to microwave thermal processing, enabling curing of PDMS in as little as 90 s. This work can significantly minimize device fabrication time and the start-up cost of fabrication infrastructure, enhancing efficiency and making microfluidics accessible to a broader user base.

Capacity degradation of Laves phase-related body-centered-cubic solid solution metal hydride alloys in battery

The nickel/metal hydride (Ni/MH) is a good example of using metal hydride alloy which is cable of reversely storing the hydrogen energy in an electrochemical environment. The failure mode of two Laves phase-related body-centered-cubic metal hydride alloys doped with Y, and Ce separately in sealed Ni/MH batteries is studied by scanning electron microscopy with x-ray energy dispersive spectroscopy and x-ray diffraction analysis. These two alloys come from a series of studies targeting toward using Ni/MH battery as a low-cost and high-durability alternative to rival Li-ion battery in the electric vehicle application. This group of alloys demonstrates a discharge capacity up to 400 mAh g−1 under a C/4 discharge rate. The main failure mode of these two alloys is found to be selective dissolution of C14 phase which contributes to a fast increase in internal resistance. Due to the deprival of Cr from the first solidified BCC phase, the next solidified C14 phase does not have enough Cr to protect it from the KOH corrosion. Rapid quench fabrication method and addition of other corrosion-resistant non-BCC former, such as Cu, Pd, and Hf, in the alloy composition are suggested.

Marine-derived natural polymer-based bioprinting ink for biocompatible, durable, and controllable 3D constructs

3D bioprinting (3DBP) is a rapid solid-form fabrication method with a high degree of automation and reproducibility for constructing structural bioscaffolds. However, the development of the 3DBP field has been slowed due to difficulty in acquiring suitable ink materials especially with natural polymers that satisfy all requirements, such as printability, mechanical integrity, and biocompatibility. In this study, a new 3DBP ink of bioengineered sea anemone-derived silk-like protein (aneroin) was used based on its durable mechanical properties and biodegradability in previous studies. The hyaluronic acid and mussel adhesive protein (MAP) were applied for improved printability and cell adhesiveness, respectively. The aneroin-based 3DBP ink (named aneroin ink) was solidified in a few second by dityrosine photo-crosslinking, and its fast reaction was suitable for noncollapsed spaces in printed 3D constructs. Actual-sized human ear, vascular graft, and rectangular multi-layered lattice were bioprinted with high controllability and durable structural integrity. Thus, the developed aneroin ink showed good printability, structural integrity, and biocompatibility for successful application to the construction of various 3D shaped bioscaffolds in tissue and biomedical engineering fields.

Fabrication of continuous phase plate using atmospheric pressure plasma processing

Continuous phase plate (CPP) with complex surface structures is used to smooth the focal spot of laser beam. Great demand for CPP in laser fusion system requires mass production technology with low cost. Therefore, the rapid fabrication method for CPP using atmospheric pressure plasma processing (APPP) is presented in this paper. Firstly, the fundamental characteristics of APPP were studied to obtain the optimal processing parameters. Considering the influence on etching rate from surface temperature, trench machining experiments were conducted to establish the exponential model of influence function. Based on this model, the iterative calculation method for dwell time was developed to minimize the thermal effect on machining error, and the sinusoidal surface experiments prove its effectiveness. At last, a 320 mm × 320 mm × 2 mm CPP of BOROFLOAT33 (B33) with 2.78 μm PV was fabricated within 16 h using APPP, and the RMS of form error is 96 nm. The far field focal spot of the machined CPP was calculated. The result shows that the machined CPP has an acceptable beam-shaping function, which demonstrates the potential for fabricating CPP using APPP.

Rapid and Inexpensive Fabrication of Multi-Depth Microfluidic Device using High-Resolution LCD Stereolithographic 3D Printing

With the dramatic increment of complexity, more microfluidic devices require 3D structures, such as multi-depth and -layer channels. The traditional multi-step photolithography is time-consuming and labor-intensive and also requires precise alignment during the fabrication of microfluidic devices. Here, we present an inexpensive, single-step, and rapid fabrication method for multi-depth microfluidic devices using a high-resolution liquid crystal display (LCD) stereolithographic (SLA) three-dimensional (3D) printing system. With the pixel size down to 47.25 μm, the feature resolutions in the horizontal and vertical directions are 150 μm and 50 μm, respectively. The multi-depth molds were successfully printed at the same time and the multi-depth features were transferred properly to the polydimethylsiloxane (PDMS) having multi-depth channels via soft lithography. A flow-focusing droplet generator with a multi-depth channel was fabricated using the presented 3D printing method. Experimental results show that the multi-depth channel could manipulate the morphology and size of droplets, which is desired for many engineering applications. Taken together, LCD SLA 3D printing is an excellent alternative method to the multi-step photolithography for the fabrication of multi-depth microfluidic devices. Taking the advantages of its controllability, cost-effectiveness, and acceptable resolution, LCD SLA 3D printing can have a great potential to fabricate 3D microfluidic devices.

Simply realizing durable dual Janus superwettable membranes integrating underwater low-oil-adhesive with super-water-repellent surfaces for controlled oil–water permeation

Janus wetting/non-wetting membranes are emerging asymmetric materials with opposing wettable interfacial properties. Because of the difference between the sides at an interface, they have been used in various practical applications such as unidirectional liquid transportation. However, newly developed Janus superwettable membranes are still highly desired and challenging, considering their conventional time-consuming preparation, oil-fouling contamination, and susceptible surface to mechanical damage. Herein, we propose a rapid and green fabrication method for durable dual Janus superhydrophilic (underwater superoleophobic)/superhydrophobic (superoleophilic) membranes, which integrate an underwater low-oil-adhesive with super-water-repellent surfaces for controlled oil–water permeation. The robust superhydrophilic and underwater superoleophobic surface can be rapidly created using a one-step chemical etching method. Then, underwater low-oil-adhesion is obtained for anti-oil-fouling. Moreover, a mechanically durable superhydrophobic coating with a super-water-repellent characteristic can be directly capped onto an etched stainless steel mesh (ESSM) through a rapid mechanical transferring process. Therefore, four kinds of wettable behaviors from one common interface can be readily realized for controlled oil–water permeation with an anti-oil-fouling property and high durability. The multifunctional membranes can combine superwettability-based oil–water separation and oil collection by a Janus membrane-based oil diode in the future. This will inspire the development of additional facial Janus superwettable membrane systems with extended applications.

Programmable Electrofabrication of Porous Janus Films with Tunable Janus Balance for Anisotropic Cell Guidance and Tissue Regeneration

AbstractJanus films with controlled pore structures can be particularly important in diverse applications. There remains a challenge for simple, rapid, and scalable fabrication methods to control Janus balance (JB) including the thickness of the individual face as well as porosity and pore size. Here the electrofabrication of a porous Janus film with controlled Janus balance from aminopolysaccharide chitosan under the salt effect is reported. Sequential deposition of chitosan under programmable salt environment and electrochemical conditions enables construction of Janus films with precisely controlled Janus balance. Bioactive partially soluble calcium phosphate (CaP) salts can also generate porous structure in Janus film. It is specifically reported that a chitosan/hydroxyl apatite (HAp) composite Janus film can serve as an effective scaffold for guided bone regeneration. The dense layer functions to provide mechanical support and serves as a barrier for fibrous connective tissue penetration. The porous composite layer functions to provide the microenvironment for osteogenesis. In vivo studies using a rat calvarial defect model confirm the beneficial features of this Janus composite for guided bone regeneration. These results suggest the potential of electrofabrication as a simple and scalable platform technology to tune the self‐organization of soft matter for a range of emerging applications.

Microfluidics Assisted Fabrication of Three-Tier Hierarchical Microparticles for Constructing Bioinspired Surfaces.

Construction of textured bioinspired surfaces with refined structures that exhibit superior wetting properties is of great importance for many applications ranging from self-cleaning, antibiofouling, anti-icing, oil/water separation, smart membrane, and microfluidic devices. Previously, the preparation of artificial surfaces generally relies on the combination of different approaches together, which is a lack of flexibility to control over the individual architecture unit, the surface topology, as well as the complex procedure needed. In this work, we report a method for rapid fabrication of three-tier hierarchical microunits (structures consisting of multiple levels) using a facile droplet microfluidics approach. These units include the first-tier microspheres consisting of the second-tier close-packed polystyrene (PS) nanoparticles decorated with the third-tier elegant polymer nanowrinkles. These nanowrinkles on the PS nanoparticles are formed according to the interfacial instability induced by gradient photopolymerization of N-isopropylacrylamide (NIPAM) monomers. The formation process and topologies of nanowrinkles can be regulated by the photopolymerization process and the fraction of carboxylic groups on the PS nanoparticle surface. Such a hierarchical microsphere mimics individual units of bioinspired surfaces. Therefore, the surfaces from self-assembly of these fabricated two-tier and three-tier hierarchical microunits collectively exhibit "gecko" and "rose petal" wetting states, with the micro- and nanoscale structures amplifying the initial hydrophobicity but still being highly adhesive to water. This approach offers promising advantages of high-yield fabrication, precise control over the size and component of the microspheres, and integration of microfluidic droplet generation, colloidal nanoparticle self-assembly, and interfacial polymerization-induced nanowrinkles in a straightforward manner.

Process optimization of parameterized single shot method for a rapid production of photon sireve with direct write lithography

Photon sieves are promising elements for high-resolution optics. Fabrication of photon sieves is a raising topic of microscale optic fabrication. In order to fabricate photon sieves, many technics featured recently. Common production difficulties for fabrication are time consumption and complexity of process. This study provides direct write lithography process optimization for rapid and simple fabrication method. Using the direct write laser technology to pattern photoresist with parameterized single laser shot is the main idea of this study. Writing pattern with the parameterized single shot method gives good structures for photon sieves. Parameterized single shot method uses variable focus distance and modulation to write patterns with direct write lithography. Rapid patterning with better geometrical structures is the most important result of this study. In microscopic scale, geometrical results and time consumption are some drawbacks of continuous exposure laser method. It is inadequate for small structures such as photon sieves outermost pinholes. The main approach of this study is the optimization of the writing process for rapid and well-shaped production of smaller structures for photon sieves. The process optimization for Kloe direct write lithography system serves better structure for photon sieve pinhole than conventional writing methods.

Rapid and inexpensive method for the simple fabrication of PDMS-based electrochemical sensors for detection in microfluidic devices.

The fabrication of PDMS microfluidic structures through soft lithography is widely reported. While this well-established method gives high precision microstructures and has been successfully used for many researchers, it often requires sophisticated instrumentation and expensive materials such as clean room facilities and photoresists. Thus, we present here a simple protocol that allows the rapid molding of simple linear microchannels in PDMS substrates aiming microfluidics-based applications. It might serve as an alternative to researchers that do not have access to sophisticated facilities such as clean rooms. The method developed here consists on the use of pencil graphite leads as template for the molding of PDMS channels. It yields structures that can be used for several applications, such as housing support for electrochemical sensors or channels for flow devices. Here, the microdevices produced through this protocol were employed for the accommodation of carbon black paste, which was utilized for the first time as amperometric sensor in microchip electrophoresis. This platform was successfully used for the separation and detection of model analytes. Ascorbic acid and iodide were separated within 45 s with peak resolution of 1.2 and sensitivities of 198 and 492 pA/μM, respectively. The background noise was ca. 84 pA. The analytical usefulness of the system developed was successfully tested through the quantification of iodide in commercial pharmaceutical formulations. It demonstrates good efficiency of the microfabrication protocol developed and enables its use for the easy and rapid prototyping of PDMS structures over a low fabrication cost.

Rapid and inexpensive method for fabrication of multi-material multi-layer microfluidic devices

The vast majority of polymeric microfluidic devices that have been developed so far feature the use of a single or two material of construction. This is mainly due to the difficulty in integrating multiple materials into these devices using conventional microfabrication techniques such as photolithography, soft lithography or hot embossing either due to mismatch in the processing conditions or due to poor bonding between the materials. Nevertheless, integration of multiple materials into microfluidic devices can enable new and interesting functionalities.In this study, a rapid and inexpensive fabrication technique has been developed in which xurography and cold lamination methods were combined to create microfluidic devices integrating different materials. Materials with different surface energy and properties were used to provide unique functionality. This functionality was shown by fabricating channels that can have varying capillary filling rates from 33 mm s−1 to 24 mm s−1 by changing the surface energy of the materials that constitute the top and bottom of the microchannels. Similarly, highly robust and integrated passive valves that were able to stop capillary filling was also demonstrated by combining patterned features of hydrophobic and hydrophilic surfaces. Integration of thin elastomeric membrane with thermoplastic materials was also demonstrated by fabrication an active pneumatic valve that was capable of stopping capillary flow. Finally, this method of integration of multiple materials, was also used to integrate hydrogels into microfluidic devices in a parallel manner and to confine it locally in specific regions.

3D Gold-Modified Cerium and Cobalt Oxide Catalyst on a Graphene Aerogel for Highly Efficient Catalytic Formaldehyde Oxidation.

A hard template method is used to prepare porous gold-doped cerium and cobalt oxide (Au-Cex Coy ) materials. A series of 3D Au-Ce x Coy /graphene aerogel (GA) composites is then fabricated by a facile heating method. The obtained catalysts possess a well-defined structure of ordered arrays of nanotubes and good performance in formaldehyde (HCHO) oxidation. The composition and surface elemental valence states of the catalysts are modulated by the Ce/Co molar ratio. The Au-Cex Coy catalyst and graphene oxide sheets are well compounded within 60 s through a diamine cross-linker to form 3D Au-Cex Coy /GA composites. In addition, the resulting catalyst of 3 wt% Au-Ce3 Co/GA achieves ≈55% conversion at room temperature and 100% conversion when the reaction temperature is raised at 60 °C. The synergistic effect between CeO2 and Co3 O4 promotes the migration of oxygen species and the activation of Au, which facilitates HCHO oxidation. The method used to prepare the 3D catalyst could be used to produce other catalytic materials with good replication of the template. In addition, these findings provide a simple method for rapid fabrication of catalyst/GA composites. The superior activity and stability of the 3D Au-Ce3 Co/GA catalyst make it potentially applicable in HCHO removal.

Facile fabrication and mechanistic understanding of a transparent reversible superhydrophobic \u2013 superhydrophilic surface

We report a simple, inexpensive and rapid method for fabrication of a stable and transparent superhydrophobic (TSHB) surface and its reversible transition to a transparent superhydrophilic (TSHL) surface. We provide a mechanistic understanding of the superhydrophobicity and superhydrophilicity and the reversible transition. The proposed TSHB surface was created by candle sooting a partially cured n-hexane + PDMS surface followed by washing with DI water. The nano/microscopic grooved structures created on the surface conforms Cassie – Baxter state and thus gives rise to superhydrophobicity (water contact angle (WCA) = 161° ± 1°). The TSHB surface when subjected to oxygen plasma develops -OH bonds on the surface thus gets transformed into a TSHL surface (WCA < 1°). Both surface chemistry and surface morphology play important roles for the superhydrophobic to superhydrophilic transition. In the Cassie – Baxter relation for a composite surface, due to the capillary spreading of liquid in the nano/micro grooves, both θ1, θ2 = 0, thus giving rise to complete wetting. Rapid recovery of superhydrophobicity from superhydrophilicity was achieved by heating the TSHL surface at 150 °C for 30 min, due to a much faster adsorption of the -OH bonds into the PDMS. Thus it is possible to achieve reversible transition from TSHB to TSHL and vice versa by exposing to oxygen plasma and heat, respectively.

One-step bonding and hydrophobic surface modification method for rapid fabrication of polycarbonate-based droplet microfluidic chips

Chip bonding and hydrophobic surface modification are two critical processes for the fabrication of a droplet microfluidic chip from the thermoplastic polycarbonate (PC) material. In this paper, we describe a novel one-step method, which simultaneously bonded and modified two PC substrates. The mechanism of this one-step method is that n-pentane acts as a sacrificial solvent and acetone is the solvent that bonds the PC substrates. Additionally, entrapment functionalization and the Si-O-Si cross-linked network play a central role in the hydrophobic surface modification process. The method was optimized to achieve a high bonding strength, low surface roughness, and high optical transmittance. The naturally hydrophilic PC substrate surface was modified to become a hydrophobic surface, with surface tension decreased from 33.6 mN/m to 14.8 mN/m. Monodisperse droplets generated using a droplet generation chip fabricated by this method had an average diameter of 101.3 μm and coefficient of variation of 0.55%. A droplet digital polymerase chain reaction experiment was successfully carried out using droplets generated from this chip, which demonstrated the effectiveness of this method. This novel one-step method holds great potential for manufacturing droplet-based microfluidic chips using PC in large-scale, and it may have broad applications in microfluidic research fields.