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.

Novel Collagen Surgical Patches for Local Delivery of Multiple Drugs.

Effective control of post-operative inflammation after tissue repair remains a clinical challenge. A tissue repair patch that could appropriately integrate into the surrounding tissue and control inflammatory responses would improve tissue healing. A collagen-based hybrid tissue repair patch has been developed in this work for the local delivery of an anti-inflammatory drug. Dexamethasone (DEX) was encapsulated into PLGA microspheres and then co-electrocompacted into a collagen membrane. Using a simple process, multiple drugs can be loaded into and released from this hybrid composite material simultaneously, and the ratio between each drug is controllable. Anti-inflammatory DEX and the anti-epileptic phenytoin (PHT) were co-encapsulated and released to validate the dual drug delivery ability of this versatile composite material. Furthermore, the Young's modulus of this drug-loaded collagen patch was increased to 20 KPa using a biocompatible riboflavin (vitamin B2)-induced UV light cross-linking strategy. This versatile composite material has a wide range of potential applications which deserve exploration in further research.

Lattice Distortion and H-passivation in Pure Carbon Electrocatalysts for Efficient and Stable Two-electron Oxygen Reduction to H2 O2.

The exploration of inexpensive and efficient catalysts for oxygen reduction reaction (ORR) is crucial for chemical and energy industries. Carbon materials have been proved promising with different catalysts enabling 2 and 4e- ORR. Nevertheless, their ORR activity and selectivity is still complex and under debate in many cases. Many structures of these active carbon materials are also chemically unstable for practical implementations. Unlike the well-discussed structures, this work presents a strategy to promote efficient and stable 2e- ORR of carbon materials through the synergistic effect of lattice distortion and H-passivation (on the distorted structure). We show how these structures can be formed on carbon cloth, and how the reproducible chemical adsorption can be realized on these structures for efficient and stable H2 O2 production. The work here gives not only new understandings on the 2e- ORR catalysis, but also the robust catalyst which can be directly used in industry.

Electrostatic catalysis of a Diels-Alder reaction.

It is often thought that the ability to control reaction rates with an applied electrical potential gradient is unique to redox systems. However, recent theoretical studies suggest that oriented electric fields could affect the outcomes of a range of chemical reactions, regardless of whether a redox system is involved. This possibility arises because many formally covalent species can be stabilized via minor charge-separated resonance contributors. When an applied electric field is aligned in such a way as to electrostatically stabilize one of these minor forms, the degree of resonance increases, resulting in the overall stabilization of the molecule or transition state. This means that it should be possible to manipulate the kinetics and thermodynamics of non-redox processes using an external electric field, as long as the orientation of the approaching reactants with respect to the field stimulus can be controlled. Here, we provide experimental evidence that the formation of carbon-carbon bonds is accelerated by an electric field. We have designed a surface model system to probe the Diels-Alder reaction, and coupled it with a scanning tunnelling microscopy break-junction approach. This technique, performed at the single-molecule level, is perfectly suited to deliver an electric-field stimulus across approaching reactants. We find a fivefold increase in the frequency of formation of single-molecule junctions, resulting from the reaction that occurs when the electric field is present and aligned so as to favour electron flow from the dienophile to the diene. Our results are qualitatively consistent with those predicted by quantum-chemical calculations in a theoretical model of this system, and herald a new approach to chemical catalysis.

Suitability of Marine- and Porcine-Derived Collagen Type I Hydrogels for Bioprinting and Tissue Engineering Scaffolds.

Collagens from a wide array of animals have been explored for use in tissue engineering in an effort to replicate the native extracellular environment of the body. Marine-derived biomaterials offer promise over their conventional mammalian counterparts due to lower risk of disease transfer as well as being compatible with more religious and ethical groups within society. Here, collagen type I derived from a marine source (Macruronus novaezelandiae, Blue Grenadier) is compared with the more established porcine collagen type I and its potential in tissue engineering examined. Both collagens were methacrylated, to allow for UV crosslinking during extrusion 3D printing. The materials were shown to be highly cytocompatible with L929 fibroblasts. The mechanical properties of the marine-derived collagen were generally lower than those of the porcine-derived collagen; however, the Young's modulus for both collagens was shown to be tunable over a wide range. The marine-derived collagen was seen to be a potential biomaterial in tissue engineering; however, this may be limited due to its lower thermal stability at which point it degrades to gelatin.

Nanoscale piezoelectric effect of biodegradable PLA-based composite fibers by piezoresponse force microscopy.

The piezoelectricity of the biocompatible and biodegradable polymer polylactic acid (PLA) was investigated as a potential magnetoelectric (ME) nanocomposite for biomedical applications. A key focus was to quantify the piezoelectric properties of single PLA fibers while tuning their polymer degradability through the addition of faster degrading polymer, poly (DL-lactide-co-glycolide) (PLGA), which is not a piezoelectric polymer. Piezoresponse Force Microscopy (PFM) showed that electrospun PLA fibers gave a piezoelectric response of 186 ± 28 pm. For comparison both PLA/PLGA (75/25) and PLA/PLGA (50/50) fibers gave significantly lower piezoelectric responses of 89 ± 12 pm and 50 ± 9.1 pm, respectively. For the highest content PLGA fibers, PLA/PLGA (25/75), only very few fibers exhibited a low response of 28 pm while most showed no response. Overall, an increasing PLGA content caused a decrease in the piezoelectric response, thus an expected trade-off existed between the biodegradability (i.e. PLA to PLGA content ratio) versus piezoelectricity. The findings were considered significant due to the existence of piezoelectricity in a tuneable biodegradable material that has potential to impart piezoelectric induced effects on biointeractions with the surrounding biological environment or drug interactions with the polymer to control the rate of drug release. In such applications, there is an opportunity to magnetically control the piezoelectricity and henceforth PLA/CoFe2O4 ME nanocomposite fibers with 5% and 10% of CoFe2O4 nanoparticles were also investigated. Both 5% and 10% PLA/CoFe2O4 nanocomposites gave lower piezoelectric responses compared to the PLA presumably due to the disturbance of polymer chains and dipole moments by the magnetic nanoparticles, in addition to effects from the possible inhomogeneous distribution of CoFe2O4 nanoparticles.

3D Printed Sugar-Sensing Hydrogels.

The ability of boronic acids (BAs) to reversibly bind diols, such as sugars, has been widely studied in recent years. In solution, through the incorporation of additional fluorophores, the BA-sugar interaction can be monitored by changes in fluorescence. Ultimately, a practical realization of this technology requires a transition from solution-based methodologies. Herein, the first example of 3D-printed sugar-sensing hydrogels, achieved through the incorporation of a BA-fluorophore pair in a gelatin methacrylamide-based matrix is presented. Through optimization of monomeric cocktails, it is possible to use extrusion printing to generate structured porous hydrogels which show a measurable and reproducible linear fluorescence response to glucose and fructose up to 100 mm.

Bioprinting an Artificial Pancreas for Type 1 Diabetes.

PURPOSE OF REVIEW: Pancreatic islet cell transplantation is currently the only curative cell therapy for type 1 diabetes mellitus. However, its potential to treat many more patients is limited by several challenges. The emergence of 3D bioprinting technology from recent advances in 3D printing, biomaterials, and cell biology has provided the means to overcome these challenges. RECENT FINDINGS: 3D bioprinting allows for the precise fabrication of complex 3D architectures containing spatially distributed cells, biomaterials (bioink), and bioactive factors. Different strategies to capitalize on this ability have been investigated for the 3D bioprinting of pancreatic islets. In particular, with co-axial bioprinting technology, the co-printability of islets with supporting cells such as endothelial progenitor cells and regulatory T cells, which have been shown to accelerate revascularization of islets and improve the outcome of various transplantations, respectively, has been achieved. 3D bioprinting of islets for generation of an artificial pancreas is a newly emerging field of study with a vast potential to improve islet transplantation.

A direct 3D suspension near-field electrospinning technique for the fabrication of polymer nanoarrays.

Near-field electrospinning (NFES) is widely recognized as a versatile nanofabrication method, one suitable for applications in tissue engineering. Rapid developments in this field have given rise to layered nanofibrous scaffolds. However, this electrostatic fabrication process is limited by the electric field inhibitory effects of polymer deposition. This leads to a major challenge: how to surpass this limitation on planar/layered constructs. While the current focus in this area largely lies with the investigation of new materials, techniques and increasing precision of NFES systems and patterning, exploration of complex collector substrates is often restricted by (i) available technology and (ii) access to complex electrode manufacturing tools. To achieve nanofiber arrays suspended in free space, this paper documents both the development of an integrated NFES system and the potential of standing electrodes manufactured via selective laser melting. This system was first tested by 2D patterning on planar silicon, using polyethylene oxide polymer solution. To demonstrate suspension NFES, two patterns operating within and around the standing electrodes produced high volume suspended nanoarrays. Image analysis of the arrays allowed for the assessment of fiber directionality and isotropy. By scanning electron microscopy, it was found that a mean fiber diameter of 310 nm of the arrays was achieved. Effectively manoeuvring between the electrode pillars required a precision automated system (unavailable off-the-shelf), developed in-house. This technique can be applied to the fabrication of nanofiber structures of sufficient volume for tissue engineering.

Patterning and process parameter effects in 3D suspension near-field electrospinning of nanoarrays.

The extracellular matrix (ECM) contains nanofibrous proteins and proteoglycans. Nanofabrication methods have received growing interest in recent years as a means of recapitulating these elements within the ECM. Near-field electrospinning (NFES) is a versatile fibre deposition method, capable of layer-by-layer nano-fabrication. The maximum layer height is generally limited in layer-by-layer NFES as a consequence of electrostatic effects of the polymer at the surface, due to residual charge and polymer dielectric properties. This restricts the total volume achievable by layer-by-layer techniques. Surpassing this restriction presents a complex challenge, leading to research innovations aimed at increasing patterning precision, and achieving a translation from 2D to 3D additive nanofabrication. Here we investigated a means of achieving this translation through the use of 3D electrode substrates. This was addressed by in-house developed technology in which selective laser melt manufactured standing pillar electrodes were combined with a direct suspension near-field electrospinning (SNFES) technique, which implements an automated platform to manoeuvre the pillar electrodes around the emitter in order to suspend fibres in the free space between the electrode support structures. In this study SNFES was used in multiple operation modes, investigating the effects of varying process parameters, as well as pattern variations on the suspended nanoarrays. Image analysis of the nanoarrays allowed for the assessment of fibre directionality, isotropy, and diameter; identifying optimal settings to generate fibres for tissue engineering applications.

Electrochemical and Electrostatic Cleavage of Alkoxyamines.

Alkoxyamines are heat-labile molecules, widely used as an in situ source of nitroxides in polymer and materials sciences. Here we show that the one-electron oxidation of an alkoxyamine leads to a cation radical intermediate that even at room temperature rapidly fragments, releasing a nitroxide and carbocation. Digital simulations of experimental voltammetry and current-time transients suggest that the unimolecular decomposition which yields the "unmasked" nitroxide (TEMPO) is exceedingly rapid and irreversible. High-level quantum computations indicate that the collapse of the alkoxyamine cation radical is likely to yield a neutral nitroxide radical and a secondary phenylethyl cation. However, this fragmentation is predicted to be slow and energetically very unfavorable. To attain qualitative agreement between the experimental kinetics and computational modeling for this fragmentation step, the explicit electrostatic environment within the double layer must be accounted for. Single-molecule break-junction experiments in a scanning tunneling microscope using solvent of low dielectric (STM-BJ technique) corroborate the role played by electrostatic forces on the lysis of the alkoxyamine C-ON bond. This work highlights the electrostatic aspects played by charged species in a chemical step that follows an electrochemical reaction, defines the magnitude of this catalytic effect by looking at an independent electrical technique in non-electrolyte systems (STM-BJ), and suggests a redox on/off switch to guide the cleavage of alkoxyamines at an electrified interface.

An Electrosynthesized 3D Porous Molybdenum Sulfide/Graphene Film with Enhanced Electrochemical Performance for Lithium Storage.

Molybdenum sulfide/graphene composites are promising anode materials for lithium-ion batteries (LIBs). In this work, MoSx /graphene composite film with an ideal 3D porous structure is developed via a facile and straightforward electrochemical route. The MoSx nanoparticles are uniformly anchored on the graphene nanosheets that are randomly arranged, resulting in MoSx /graphene composites with well-developed porous structure. Benefiting from such structure and the synergistic effect from two components, this material shows a high specific capacity over 1200 mA h g-1 , an excellent rate performance, and superior cycling stability. The dominating pseudocapacitive behavior in Li storage contributes to the outstanding rate capacity. Importantly, this kind of novel material can be easily produced as 3D microelectrodes for microscaled LIBs that are highly demanded for autonomous microelectronic systems.

A contactless approach for monitoring the mechanical properties of swollen hydrogels.

Using a customized ultrasound setup we investigate the feasibility of using a contactless approach to study the bulk mechanical properties of swollen hydrogels. The study involved two different hydrogels, gelatin methacrylate (GelMa) and green algae extract methacrylate (GAEM), which were prepared to provide materials with varying modulus and different swelling properties. Two approaches have been developed. In the first case, ultrasound was compared to Young's modulus measured by indentation. It was found that can be linearly related to indentation modulus values only when the hydrogel swelling ratio is taken into account. In the second approach, an exponential dependency between swelled thickness and indentation modulus was found. This is representative for each hydrogel and purification method in addition to being independent of the conditions used within the toughness range explored. The results of this study indicate that a simple thickness measurement via the proposed approach can provide a direct relationship to Young's modulus upon calibration.

Tailoring the mechanical properties of gelatin methacryloyl hydrogels through manipulation of the photocrosslinking conditions.

Photo-crosslinkable hydrogels, in particular gelatin methacryloyl (GelMa), are gaining increasing importance in biofabrication and tissue engineering. While GelMa is often described as mechanically 'tunable', clear relationships linking the photocrosslinking conditions to reaction rates, and the resulting mechanical properties, have not been described. Meanwhile the conditions employed in the literature are disparate, and difficult to compare. In this work, in situ rheological measurements were used to quantify the relative rate of reaction of GelMa hydrogels with respect to light intensity, exposure time and photo-initiator concentration. In addition the UV degradation of the photo-initiator Irgacure 2959 was measured by UV-vis spectroscopy, and used to estimate the rate of free radical production as a function of light exposure. Using these data an expression was derived which predicts the mechanical properties of GelMa hydrogels produced across a wide range of crosslinking conditions. The model was validated through fabrication of a GelMa gradient which matched predicted properties. Human mesenchymal stem cells encapsulated in crosslinked GelMa exhibited high (>90%) viability post encapsulation, however metabolic activity over one week was influenced by the intensity of light used during crosslinking. The expressions described may be used to aid rational choices of GelMa photocrosslinking conditions, especially in cell encapsulation experiments where minimising the cytotoxic elements in the reaction is a priority.

Electro-mechano responsive properties of gelatin methacrylate (GelMA) hydrogel on conducting polymer electrodes quantified using atomic force microscopy.

Electrical stimulation of hydrogels has been performed to enable micro-actuation or controlled movement of ions and biomolecules such as in drug release applications. Hydrogels are also increasingly used as low modulus, biocompatible coatings on electrode devices and thus are exposed to the effects of electrical stimulation. As such, there is growing interest in the latter, especially on the dynamic and nanoscale physical properties of hydrogels. Here, we report on the electro-mechano properties of photocrosslinkable gelatin methacrylate (GelMA) hydrogel applied as coatings on conducting polymer polypyrrole-dodecylbenze sulfonate (PPy-DBSA) electrodes. In particular, Electrochemical-Atomic Force Microscopy (EC-AFM) was used to quantify the nanoscale actuation and dynamic changes in Young's modulus as the GelMA coating was electrically stimulated via the underlying PPy-DBSA electrode. Pulsed electrical stimulation was shown to induce dynamic expansion and contraction, or nanoscale actuation, of the GelMA hydrogel due to the reversible ingress of electrolyte ions and associated changes in osmotic pressure during oxidation and reduction of the PPy-DBSA film. In addition, dynamic changes in the Young's modulus of up to 50% were observed in the hydrogel and correlated with the actuation process and ion diffusion during oxidation and reduction of the underlying PPy-DBSA film. These dynamic properties were investigated for hydrogels with varying degrees of cross-linking, porosity and modulus, the latter ranging from ≈0.2-1 kPa. The study demonstrates an AFM-based approach to quantify the dynamic physical properties of hydrogels, which are shown to be modulated via electrical stimulation. This can enable a better understanding of the electro-mechano mechanisms that are important for the controlled release of drugs or controlling cell interactions at the hydrogel-cell interface.

Quantitative characterisation of conductive fibers by capacitive coupling.

This work presents a study on a capacitively coupled contactless conductivity detector (C4D) for micron-sized fibers. Following a previous report on the qualitative application of C4D for fibers, the present study provides a thorough analysis of the signal response to fiber conductivity. Using reduced graphene oxide (RGO) fibers, the detector response as a function of fiber length, cross-sectional area and resistance has been investigated. To study the effect of insulating coatings, Parylene-coated RGO fibers were also investigated. In addition, measurements were performed in different coupling environments, such as in a capillary tube or air. The analysis of the measured data allowed the determination of the C4D conductivity of various RGO fibers, and the correlation with contact methods through empirical relationships to be determined. It was found that the detection limit and sensitivity of resistance measurements are mainly dependent on the sensor design, and also on the fiber properties. The detection threshold can be defined as the ratio of the coupling impedance to fiber resistance. In our case, the detection limit was found for impedance ratios equal to 14. This limit sets a functioning mode in C4D for fibers, which may be used as an area or resistance detector for the impedance ratio above or below the detection threshold. A semi-log linear response of the fiber resistance to the voltage output was found for impedance ratios between 2.66 and 0.63. These impedance ratios may serve as a reference for designing C4D, depending on the fibers to be tested and the analytical information needed. In summary, we suggest that C4D has the capacity to emerge as a new characterisation tool for micron-sized fibers, due to its applicability to any conductive material, ease of use, and the contactless nature of the measurement.

Local probing of magnetoelectric properties of PVDF/Fe3O4 electrospun nanofibers by piezoresponse force microscopy.

The coupling of magnetic and electric properties in polymer-based magnetoelectric composites offers new opportunities to develop contactless electrodes, effectively without electrical connections, for less-invasive integration into devices such as energy harvesters, sensors, wearable and implantable electrodes. Understanding the macroscale-to-nanoscale conversion of the properties is important, as nanostructured and nanoscale magnetoelectric structures are increasingly fabricated. However, whilst the magnetoelectric effect at the macroscale is well established both theoretically and experimentally, it remains unclear how this effect translates to the nanoscale, or vice versa. Here, PVDF/Fe3O4 polymer-based composite nanofibers are fabricated using electrospinning to investigate their piezoelectric and magnetoelectric properties at the single nanofiber level.

In vivo biocompatibility of porous and non-porous polypyrrole based trilayered actuators.

Trilayered polypyrrole (PPy) actuators have high stress density, low modulus and have wide potential biological applications including use in artificial muscles and in limb prosthesis after limb amputation. This article examines the in vivo biocompatibility of actuators in muscle using rabbit models. The actuators were specially designed with pores to encourage tissue in growth; this study also assessed the effect of such pores on the stability of the actuators in vivo. Trilayered PPy actuators were either laser cut with 150 µm pores or left pore-less and implanted into rabbit muscle for 3 days, 2 weeks, 4 weeks and 8 weeks and retrieved subsequently for histological analysis. In a second set of experiments, the cut edges of pores in porous actuator strips were further sealed by PPy after laser cutting to further improve its stability in vivo. Porous actuators with and without PPy sealing of pore edges were implanted intramuscularly for 4 and 8 weeks and assessed with histology. Pore-less actuators incited a mild inflammatory response, becoming progressively walled off by a thin layer of fibrous tissue. Porous actuators showed increased PPy fragmentation and delamination with associated greater foreign body response compared to pore-less actuators. The PPy fragmentation was minimized when the pore edges were sealed off by PPy after laser cutting showing less PPy debris. Laser cutting of the actuators with pores destabilizes the PPy. This can be overcome by sealing the cut edges of the pores with PPy after laser. The findings in this article have implications in future design and manufacturing of PPy actuator for use in vivo.

TEMPO Monolayers on Si(100) Electrodes: Electrostatic Effects by the Electrolyte and Semiconductor Space-Charge on the Electroactivity of a Persistent Radical.

This work demonstrates the effect of electrostatic interactions on the electroactivity of a persistent organic free radical. This was achieved by chemisorption of molecules of 4-azido-2,2,6,6-tetramethyl-1-piperdinyloxy (4-azido-TEMPO) onto monolayer-modified Si(100) electrodes using a two-step chemical procedure to preserve the open-shell state and hence the electroactivity of the nitroxide radical. Kinetic and thermodynamic parameters for the surface electrochemical reaction are investigated experimentally and analyzed with the aid of electrochemical digital simulations and quantum-chemical calculations of a theoretical model of the tethered TEMPO system. Interactions between the electrolyte anions and the TEMPO grafted on highly doped, i.e., metallic, electrodes can be tuned to predictably manipulate the oxidizing power of surface nitroxide/oxoammonium redox couple, hence showing the practical importance of the electrostatics on the electrolyte side of the radical monolayer. Conversely, for monolayers prepared on the poorly doped electrodes, the electrostatic interactions between the tethered TEMPO units and the semiconductor-side, i.e., space-charge, become dominant and result in drastic kinetic changes to the electroactivity of the radical monolayer as well as electrochemical nonidealities that can be explained as an increase in the self-interaction "a" parameter that leads to the Frumkin isotherm.