Electrofluidic control for textile-based cell culture: Identification of appropriate conditions required to integrate cell culture with electrofluidics.

Electric field-driven microfluidics, known as electrofluidics, is a novel attractive analytical tool when it is integrated with low-cost textile substrate. Textile-based electrofluidics, primarily explored on yarn substrates, is in its early stages, with few studies on 3D structures. Further, textile structures have rarely been used in cellular analysis as a low-cost alternative. Herein, we investigated novel 3D textile structures and develop optimal electrophoretic designs and conditions that are favourable for direct 3D cell culture integration, developing an integrated cell culture textile-based electrofluidic platform that was optimised to balance electrokinetic performance and cell viability requirements. Significantly, there were contrasting electrolyte compositional conditions that were required to satisfy cell viability and electrophoretic mobility requiring the development of and electrolyte that satisfied the minimum requirements of both these components within the one platform. Human dermal fibroblast cell cultures were successfully integrated with gelatine methacryloyl (GelMA) hydrogel-coated electrofluidic platform and studied under different electric fields using 5 mM TRIS/HEPES/300 mM glucose. Higher analyte mobility was observed on 2.5% GelMA-coated textile which also facilitated excellent cell attachment, viability and proliferation. Cell viability also increased by decreasing the magnitude and time duration of applied electric field with good cell viability at field of up to 20 V cm-1.

Novel 3D textile structures and geometries for electrofluidics.

The integration of microfluidics with electric field control, commonly referred to as electrofluidics, has led to new opportunities for biomedical analysis. The requirement for closed microcapillary channels in microfluidics, typically formed via complex microlithographic fabrication approaches, limits the direct accessibility to the separation processes during conventional electrofluidic devices. Textile structures provide an alternative and low-cost approach to overcome these limitations via providing open and surface-accessible capillary channels. Herein, we investigate the potential of different 3D textile structures for electrofluidics. In this study, 12 polyester yarns were braided around nylon monofilament cores of different diameters to produce functional 3D core-shell textile structures. Capillary electrophoresis performances of these 3D core-shell textile structures both before and after removing the nylon core were evaluated in terms of mobility and bandwidth of a fluorescence marker compound. It was shown that the fibre arrangement and density govern the inherent capillary formation within these textile structures which also impacts upon the solute analyte mobility and separation bandwidth during electrophoretic studies. Core-shell textile structures with a 0.47 mm nylon core exhibited the highest fluorescein mobility and presented a narrower separation bandwidth. This optimal textile structure was readily converted to different geometries via a simple heat-setting of the central nylon core. This approach can be used to fabricate an array of miniaturized devices that possess many of the basic functionalities required in electrofluidics while maintaining open surface access that is otherwise impractical in classical approaches.

Toward Three-Dimensional Printed Thermal Conductive Polymeric Composites Using a Binary-Composite Hybrid Based on Boron Nitride Nanoparticles and Micro-Diamonds.

Thermally conductive polymeric composites are promising for heat management in microelectronic devices. This work presents a binary-hybrid composite of boron nitride (BN) nanoparticles and micro-diamond (D) fillers in an elastomeric polyurethane (PU) matrix which can be three- dimensionally printed to produce a highly flexible and self-supporting structure. The research shows that a combination of 16.7 wt% BN and 16.7 wt% D results in a robust network within the polymer matrix to improve the tensile modulus more than nine times with respect to neat PU. Significantly, the hybrid matrix enhances the thermal conductivity by more than two times when compared to neat PU. The enhancement in mechanical, and thermal features make this three-dimensional printable multiscale hybrid composite suitable for flexible and stretchable microelectronic applications.

Nanomaterial-assisted thread-based isotachophoresis with on-thread solute trapping.

This research describes a nanomaterial-assisted thread-based isotachophoresis (TB-ITP) setup for the clean-up, preconcentration, and trapping of alkaloids (coptisine, berberine, and palmatine) in biological fluids, followed by their on-thread desorption electrospray ionization mass spectrometry (DESI-MS) determination. The reusable TB-ITP setup and a DESI compatible thread holder were 3D printed. A single nylon thread was employed as the ITP substrate for solute isolation and enrichment, and a short piece of graphene oxide (GO) functionalized nylon thread was tied around the main 'separation' thread as the 'trap' for the trapping of ITP focused alkaloids. Compared to the direct DESI-MS sample analysis, the sensitivity of the proposed method for the model solutes was increased up to 10-fold, benefiting from the TB-ITP focusing and enrichment strategy. This proof-of-concept use of nanomaterial-modified threads in electrofluidic separation and concentration procedures opens up a promising avenue to explore, particularly with regard to the sensitivity and selectivity of thread-based electrofluidic separation coupled with ambient ionization MS.

Substrate-Dependent Electron-Transfer Rate of Mixed-Ligand Electrolytes: Tuning Electron-Transfer Rate without Changing Driving Force.

To meet various requirements for electron transfer (ET) at the substrate/electrolyte interface, mixed redox couples assigned to different functions have been applied. While in all studies the mixed redox species had different redox potentials, such redox systems inherently lose energy by ET between the species. We report interfacial ET kinetics employing mixed-ligand electrolytes based on Co2+/3+ complexes with mixtures of dimethyl- and dinonyl-substituted bipyridyl (bpy) ligands with the same redox potential. The ET rates of the mixed electrolytes decrease with the increasing ratio of the dinonyl-bpy ligand, with substrates adsorbed by molecules without alkyl chains due to a blocking effect. However, when the molecules on substrates have four alkyl chains, the ET rate between the molecules and the electrolytes with increasing ratio of the dinonyl-bpy ligand is enhanced. The substrate-dependent behavior is explained by selective intermolecular interactions. The results open design flexibility for mixed-redox electrolyte systems to control ET at multi-substrate interfaces and provide a novel means to tune ET rates simultaneously for various ET processes in a system without losing energy by the ET.

The impact of insufficient time resolution on dye regeneration lifetime determined using transient absorption spectroscopy.

Dye regeneration lifetimes of a combination of dyes and redox mediators were determined by two transient absorption (TA) spectrometers with 0.5 ns (sub-ns) and 6 ns (ns) time resolutions to elucidate the impact of insufficient time resolution on the measurements of dye regeneration kinetics in dye-sensitised semiconductor electrodes. Due to the disordered nature of the dye-sensitised electrodes, the dye regeneration lifetime is often characterised by half-decay time (τ1/2) of the initial signal magnitude. Alternatively, τ1/2,S is calculated from stretched-exponential lifetime (τww) and the distribution of lifetimes characterised by the stretch parameter (ß). Stretched-exponential functions were numerically modelled, showing that to keep the error in τ1/2 ≤ 10%, τww needs to be at least 20 times longer than the time resolution in case of non-dispersive transients (ß = 0.9) but at least 870 times longer when dispersive (ß = 0.5). To test the predictions, TA decays of a combination of organic and porhyrin dyes and three cobalt-complex mediators are analysed, spanning a range of τww and ß. These examples show that a 262% error in τ1/2 is possible if the time resolution of the TA setup is only 13 times faster than τww and smaller ß results in larger error when τww is similar. Determining τ1/2,S by stretched-exponential fitting generally reduces the error compared to that determined directly from the graph. However, if the stretched-exponential function does not correctly describe the early signal transient, even a larger error by stretched-exponetial fitting is introduced. The key requirement for accurate measurement is to have a fast-enough TA setup to resolve the initial plateau of the TA signal. To demonstrate the impact of the measured errors, the measured regeneration lifetimes are plotted versus the driving force of the reaction and modelled using Marcus theory. Erroneous regeneration rates lead to an underestimated electronic coupling term by 2.2 times in case of a series of porphyrin dyes matched with Co complex electrolytes, a significant impact when the interpretation of factors affecting electron transfer at dye-sensitised semiconductor/electrolyte interface is discussed.

Thread-based isoelectric focusing coupled with desorption electrospray ionization mass spectrometry.

The combination of a thread-based electrofluidic analytical device and desorption electrospray ionization mass-spectrometry (DESI-MS) was investigated for the separation and concentration of proteins. The combination delivered a low-cost novel approach for sample pretreatment and target focusing, with direct "on-thread" ambient mass spectrometry detection. For this purpose, a platform for thread-based isoelectric focusing (TB-IEF) was 3D-printed, optimised, and applied to the separation and focusing of three model proteins. Successful separation and focusing was achieved within 30 min. The TB-IEF device was coupled with DESI-MS by direct exposure of the focused solutes on the dried thread to the DESI source. As a proof-of-concept, a 10-fold increase in the DESI-MS response for insulin was achieved following the TB-IEF preconcentration, whilst simultaneously isolating the target solutes from their sample matrix.

Exploiting Intermolecular Interactions between Alkyl-Functionalized Redox-Active Molecule Pairs to Enhance Interfacial Electron Transfer.

The strategies to enhance electron transfer rates between redox-active, light-harvesting molecules attached to semiconductor surfaces and redox mediators in solution by modifying molecular structure are not fully investigated yet. Therefore, the design of molecules with controlled electron transfer rates remains a challenge. The aims of this work are to quantify the effect of long alkyl chain substitution on the electron transfer from cobalt(II/III) tris(2,2'-bipyridine) to organic molecules containing carbazole and thiophene and to demonstrate that alkyl chains can be used to enhance electron transfer between donor-acceptor pairs. To this end, we study the effect of using a combination of donor and acceptor molecules with and without alkyl chains on electron transfer kinetics. Using transient absorption spectroscopy, we show that when only the molecules or the mediators have long alkyl chains, electron transfer is slightly blocked as expected. Counterintuitively, electron transfer is up to 13 times faster when long alkyl chains are attached to both the redox-active molecules and the redox mediators. The faster electron transfer is explained by an alkyl-alkyl chain interaction between the donor/acceptor, leading to the proximity (trapping) of the redox mediators close to the π-conjugated backbone of the molecules. These results suggest that intermolecular interactions can be used to enhance the electron transfer rates significantly even with well-established insulating alkyl chains attached to molecules without changing the electrochemical driving force.

Characterisation of graphene fibres and graphene coated fibres using capacitively coupled contactless conductivity detector.

The use of capacitively coupled contactless conductivity detection (C(4)D) for the characterisation of thin conductive graphene fibres, graphene composite fibres, and graphene coated fibrous materials is demonstrated for the first time. Within a few seconds, the non-destructive C(4)D detector provides a profile of the longetudinal physical homogeneity of the fibre, as well as extra information regarding fibre mophology and composition. In addition to the theoretical considerations related to the factors affect the output signal, this work evaluates the properties of graphene fibres using scanning C(4)D following the manufacturing process of wet-spinning. Furthermore, conductive graphene-coated fibrous materials and the effectiveness of the coating and reduction procedures applied could be investigated. Apart from the application of C(4)D in the monitoring of such processes, the feasibility of this small, highly sensitive and rapidly-responsive detector to monitor strain and elasticity responses of conductive and elastomeric composite fibres for applications in motion sensing, biomedical monitoring, and stretchable electronics was also demonstrated.

Tuning the electrophoretic separations on a surface-accessible and flexible fibre-based microfluidic devices.

Electrophoresis on textile fiber substrates provides a unique surface-accessible platform for the movement, separation and concentration of charged analytes. The method employs the inherently inbuilt capillary channels existing within textile structures, which can support electroosmotic and electrophoretic transport processes upon applying an electric field. Unlike confined microchannels in classical chip-based electrofluidic devices, the capillaries formed by the roughly oriented fibers within textile substrates can impact the reproducibility of the separation process. Here, we report an approach for precise experimental conditions affecting the electrophoretic separation of two tracer solutes, fluorescein (FL) and rhodamine B (Rh-B) on textile-based substrates. A Box-Behnken response surface design methodology has been used to optimise the experimental conditions and predict the separation resolution of a solute mixture using polyester braided structures. The magnitude of the electric field, sample concentration and sample volume are of primary importance to the separation performance of the electrophoretic devices. Here, we use a statistical approach to optimise these parameters to achieve rapid and efficient separation. While a higher potential was shown to be required to separate solute mixtures of increasing concentration and sample volume, this was counteracted by a reduced separation efficiency due to joule heating, which caused electrolyte evaporation on the unenclosed textile structure at electric fields above 175 V cm-1. Using the approach presented here, optimal experimental conditions can be predicted to limit joule heating and attain effective separation resolution without compromising the analysis time on simple and low-cost textile substrates.

Fibronectin and bovine serum albumin adsorption and conformational dynamics on inherently conducting polymers: a QCM-D study.

Quartz crystal microbalance with dissipation monitoring (QCM-D) was employed to characterize the adsorption of the model proteins, bovine serum albumin (BSA) and fibronectin (FN), to polypyrrole doped with dextran sulfate (PPy-DS) as a function of DS loading and surface roughness. BSA adsorption was greater on surfaces of increased roughness and was above what could be explained by the increase in surface area alone. Furthermore, the additional mass adsorbed on the rough films was concomitant with an increase in the rigidity of the protein layer. Analysis of the dynamic viscoelastic properties of the protein adlayer reveal BSA adsorption on the rough films occurs in two phases: (1) arrival and initial adsorption of protein to the polymer surface and (2) postadsorption molecular rearrangement to a more dehydrated and compact conformation that facilitates further recruitment of protein to the polymer interface, likely forming a multilayer. In contrast, FN adsorption was independent of surface roughness. However, films prepared from solutions containing the highest concentration of DS (20 mg/mL) demonstrated both an increase in adsorbed mass and adlayer viscoelasticity. This is attributed to the higher DS loading in the conducting polymer film resulting in presentation of a more hydrated molecular structure indicative of a more unfolded and bioactive conformation. Modulating the redox state of the PPy-DS polymers was shown to modify both the adsorbed mass and viscoelastic nature of FN adlayers. An oxidizing potential increased both the total adsorbed mass and the adlayer viscoelasticity. Our findings demonstrate that modification of polymer physicochemical and redox condition alters the nature of protein-polymer interaction, a process that may be exploited to tailor the bioactivity of protein through which interactions with cells and tissues may be controlled.

Thread-based isotachophoresis coupled with desorption electrospray ionization mass spectrometry for clean-up, preconcentration, and determination of alkaloids in biological fluids.

A thread-based isotachophoresis method coupled with desorption electrospray ionization mass spectrometry (TB-ITP-DESI-MS) was developed and applied for clean-up, preconcentration, and determination of alkaloids in biological fluids. This simple approach enables the focusing and rapid analysis of analytes of interest in complex matrices that are otherwise challenging using direct ambient mass spectrometry. The TB-ITP platform components were rapidly and reproducibly fabricated at low-cost using 3D printing. A single string of nylon 6 thread was used as the electrophoresis substrate and a cotton knot, tied to the nylon thread, was used as the trapping zone of the ITP focused model analytes (coptisine, berberine and palmatine). The trapping efficiency was evaluated upon different commercially available threads with different chemical properties and cotton was selected as the best material due to its highest trapping efficiency and subsequent DESI-MS ionization efficiency. Up to 11.6-fold increase in signal to noise ratio (S/N) was obtained using the proposed method compared to direct DESI-MS detection, due to the reduced matrix interference and focusing. The results demonstrated that the TB-ITP-DESI-MS approach is a viable solution for the analysis of complicated biological fluid samples.

Wireless bipolar electrode-based textile electrofluidics: towards novel micro-total-analysis systems.

Point of care testing using micro-total-analysis systems (µTAS) is critical to emergent healthcare devices with rapid and robust responses. However, two major barriers to the success of this approach are the prohibitive cost of microchip fabrication and poor sensitivity due to small sample volumes in a microfluidic format. Here, we aimed to replace the complex microchip format with a low-cost textile substrate with inherently built microchannels using the fibers' spaces. Secondly, by integrating this textile-based microfluidics with electrophoresis and wireless bipolar electrochemistry, we can significantly improve solute detection by focusing and concentrating the analytes of interest. Herein, we demonstrated that an in situ metal electrode simply inserted inside the textile-based electrophoretic system can act as a wireless bipolar electrode (BPE) that generates localized electric field and pH gradients adjacent to the BPE and extended along the length of the textile construct. As a result, charged analytes were not only separated electrophoretically but also focused where their electrophoretic migration and counter flow (EOF) balances due to redox reactions proceeding at the BPE edges. The developed wireless redox focusing technique on textile constructs was shown to achieve a 242-fold enrichment of anionically charged solute over an extended time of 3000 s. These findings suggest a simple route that achieves separation and analyte focusing on low-cost surface-accessible inverted substrates, which is far simpler than the more complex ITP on conventional closed and inaccessible capillary channels.

Fused filament fabrication 3D printed polylactic acid electroosmotic pumps.

Additive manufacturing (3D printing) offers a flexible approach for the production of bespoke microfluidic structures such as the electroosmotic pump. Here a readily accessible fused filament fabrication (FFF) 3D printing technique has been employed for the first time to produce microcapillary structures using low cost thermoplastics in a scalable electroosmotic pump application. Capillary structures were formed using a negative space 3D printing approach to deposit longitudinal filament arrangements with polylactic acid (PLA) in either "face-centre cubic" or "body-centre cubic" arrangements, where the voids deliberately formed within the deposited structure act as functional micro-capillaries. These 3D printed capillary structures were shown to be capable of functioning as a simple electroosmotic pump (EOP), where the maximum flow rate of a single capillary EOP was up to 1.0 µl min-1 at electric fields of up to 750 V cm-1. Importantly, higher flow rates were readily achieved by printing parallel multiplexed capillary arrays.

Thermally drawn biodegradable fibers with tailored topography for biomedical applications.

There is a growing demand for polymer fiber scaffolds for biomedical applications and tissue engineering. Biodegradable polymers such as polycaprolactone have attracted particular attention due to their applicability to tissue engineering and optical neural interfacing. Here we report on a scalable and inexpensive fiber fabrication technique, which enables the drawing of PCL fibers in a single process without the use of auxiliary cladding. We demonstrate the possibility of drawing PCL fibers of different geometries and cross-sections, including solid-core, hollow-core, and grooved fibers. The solid-core fibers of different geometries are shown to support cell growth, through successful MCF-7 breast cancer cell attachment and proliferation. We also show that the hollow-core fibers exhibit a relatively stable optical propagation loss after submersion into a biological fluid for up to 21 days with potential to be used as waveguides in optical neural interfacing. The capacity to tailor the surface morphology of biodegradable PCL fibers and their non-cytotoxicity make the proposed approach an attractive platform for biomedical applications and tissue engineering.

EPR characterisation of platinum nanoparticle functionalised carbon nanotube hybrid materials.

The use of nanostructured carbon materials as electrodes for energy storage and conversion is an expanding area of research in recent years. Herein, platinum nanoparticles have been deposited onto both multi-walled and single-walled carbon nanotubes (CNTs) via a microwave assisted polyol reduction method. This interaction has been probed with electron paramagnetic resonance (EPR) and Raman spectroscopies to elucidate the charge/electron transfer interactions between the Pt nanoparticles and the CNTs. Observed shifts in the g factors of the CNTs are indicative of such an electronic interaction, strongly suggesting the covalent attachment of the nanoparticles to the carboxylic groups on the CNTs, formed during the microwave-assisted reduction process. The Pt decorated CNTs show a dramatic increase in electrochemical behaviour in terms of high reversible capacity and relatively stable cycle performance compared to unmodified CNTs increasing their applicability in energy storage devices. For instance, significant increases in the electrochemical double layer capacitance are observed for the CNT-NP composite electrode.

Novel Approach toward Electrofluidic Substrates Utilizing Textile-Based Braided Structure.

Electrofluidics is the unique combination of electrophoresis and microfluidics, which has opened up broad opportunities for bioanalysis and multiplexed assay. These systems typically comprise inaccessible and fully enclosed microcapillary or microchannels, with limited sample loading capacities and no direct access to the solutes within. Here, we investigate the application of multiyarn textile assemblies which provides an open and surface accessible electrophoretic separation platform. Three-dimensional (3D) textile structures have been produced using conventional knitting and braiding techniques from a range of commercially available yarns. Capillary zone electrophoresis separation studies have been carried out on these substrates using fluorescent anionic (fluorescence, FL) and cationic (rhodamine-B, Rh-B) markers. The effects of different yarn surface chemistry, textile fabrication technique, and electrolyte ionic strength on the electrophoretic mobility of the test analytes have been studied. From the broad range of yarns investigated, polyester was shown to have the highest electrophoretic mobility for Rh-B (6 × 10-4 cm2 V-1 s-1) and for FL (4 × 10-4 cm2 V-1 s-1). The braiding approach, being simple and versatile, was found to be the most effective route to produce 3D textile-based structures and offered the potential for selective movement and targeted delivery to different channels. Composite braids made with yarns of differential surface chemistries further revealed a unique behavior of separation and parallel movement of oppositely charged ionic species. We also demonstrate the feasibility to apply isotachophoresis (ITP) on these braided textile substrates to rapidly focus dispersed FL sample bands. Here, we demonstrate the focusing of FL from a dispersed band into narrow band with a 400 times reduction in sample width over 90 s. Owing to the simplicity and reproducibility of the developed approach, textile-based inverted microfluidic applications are expected to enable opportunities in bioanalysis, proteomics, and rapid clinical diagnostics.

Solid state photochemistry of novel composites containing luminescent metal centers and poly(2-methoxyaniline-5-sulfonic acid).

Steady state luminescence and measurements of the luminescent lifetime as well as cyclic voltammetry have been used to elucidate the mechanism and dynamics of interaction between a luminescent ruthenium metal center and two different fractions of poly(2-methoxyaniline-5-sulfonic acid) (PMAS). The two fractions, high molecular weight (HMWT) PMAS and low molecular weight (LMWT) PMAS oligomer, showed significantly distinctive influences on the luminophore. The HMWT PMAS, confirmed to be an emeraldine salt by its characteristic redox chemistry, greatly impacted the diffusion coefficient of the Ru2+/3+ within the composite film, increasing the diffusion coefficient, DCT, by 2 orders of magnitude. The HMWT PMAS also resulted in quenching of the ruthenium-based emission. Significantly, these results indicate that quenching involves both static and dynamic processes, with the static quenching being the dominant process, suggesting that the metal center and polymer backbone were strongly associated. In stark contrast, the LMWT PMAS did not influence the electrochemical properties of the ruthenium metal center; however, it did double the emission observed from the ruthenium metal center. The insensitivity of the luminescence lifetime does suggest that, as with the HMWT PMAS, LWMT PMAS is strongly associated with the ruthenium metal center. The enhanced luminescence may allow for many potential sensor developments based on the luminescent ruthenium metal center, while the HMWT PMAS quenching could be utilized within quenching-based strategies or electrochemical devices.

Life-Saving Threads: Advances in Textile-Based Analytical Devices.

Novel approaches that incorporate electrofluidic and microfluidic technologies are reviewed to illustrate the translation of traditional enclosed structures into open and accessible textile based platforms. Through the utilization of on-fiber and on-textile microfluidics, it is possible to invert the typical enclosed capillary column or microfluidic "chip" platform, to achieve surface accessible efficient separations and fluid handling, while maintaining a microfluidic environment. The open fiber/textile based fluidics approach immediately provides new possibilities to interrogate, manipulate, redirect, extract, characterize, and quantify solutes and target species at any point in time during such processes as on-fiber electrodriven separations. This approach is revolutionary in its simplicity and provides many potential advantages not otherwise afforded by the more traditional enclosed platforms.

Facile Development of a Fiber-Based Electrode for Highly Selective and Sensitive Detection of Dopamine.

A facile one-step method was used to create a selective and sensitive electrode for dopamine (DA) detection based upon a stainless steel (SS) filament substrate and reduced graphene oxide (rGO). The electrode successfully and selectively detects DA in the presence of uric acid and ascorbic acid without the need for a Nafion coating. The proposed electrode is easy to fabricate, low-cost, flexible, and strong. The rGO-SS electrode could also be incorporated into a three-dimensional braided structure enabling DA detection in a two-electrode fiber system. The sensor is an excellent candidate for production of an affordable, robust, and flexible wearable and portable sensor and expands the application of textiles in point of care diagnostic devices.