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The trade-off between performance and complexity of the device manufacturing process should be balanced to enable the economic harvest of solar energy. Here, we demonstrate a conceptual, yet practical and well-regulated strategy to achieve efficient solar photocatalytic activity in TiO2 through controlled phase transformation and disorder engineering in the surface layers of TiO2 nanotubes. This approach enabled us to fine-tune the bandgap structure of undoped TiO2 according to our needs while simultaneously obtaining robust separation of photo-excited charge carriers. Introduction of specific surface defects also assisted in utilization of the visible part of sunlight to split water molecules for the production of oxygen. The strategy proposed here can serve as a guideline to overcome the practical limitation in the realization of efficient, non-toxic, chemically stable photoelectrochemical systems with high catalytic activity at neutral pH under visible illumination conditions. We also successfully incorporated TiO2 nanotube arrays (TNTAs) with free-based porphyrin affording a pathway with an overall 140% enhanced efficiency, an oxygen evolution rate of 436 µL h(-1) and faradic efficiencies over 100%.
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Coiled planar capillary chromatography columns (0.9 mm I.D. × 60 cm L) were 3D printed in stainless steel (316L), and titanium (Ti-6Al-4V) alloys (external dimensions of ~5 × 30 × 58 mm), and either slurry packed with various sized reversed-phase octadecylsilica particles, or filled with an in situ prepared methacrylate based monolith. Coiled printed columns were coupled directly with 30 × 30 mm Peltier thermoelectric direct contact heater/cooler modules. Preliminary results show the potential of using such 3D printed columns in future portable chromatographic devices.
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Polymer-based electrodes for interfacing biological tissues are becoming increasingly sophisticated. Their many functions place them at the cross-roads of electromaterials, biomaterials, and drug-delivery systems. For conducting polymers, the mechanism of conductivity requires doping with anionic molecules such as extracellular matrix molecules, a process that distinguishes them as biomaterials and provides a means to control interactions at the cellular-electrode interface. However, due to their complex structure, directly observing the selective binding of target molecules or proteins has so far eluded researchers. This situation is compounded by the polymer's ability to adopt different electronic states that alter the polymer-dopant interactions. Here, the ability to resolve sub-molecular binding specificity between sulfate and carboxyl groups of dopants and heparin binding domains of human plasma fibronectin is demonstrated. The interaction exploits a form of biological 'charge complementarity' to enable specificity. When an electrical signal is applied to the polymer, the specific interaction is switched to a non-specific, high-affinity binding state that can be reversibly controlled using electrochemical processes. Both the specific and non-specific interactions are integral for controlling protein conformation and dynamics. These details, which represent the first direct measurement of biomolecular recognition between a single protein and any type of organic conductor, give new molecular insight into controlling cellular interactions on these polymer surfaces.
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The deposition of noble metals on soft and/or flexible substrates is vital for several emerging applications including flexible electronics and the fabrication of soft bionic implants. In this paper, we describe a new strategy for the deposition of platinum electrodes on a range of materials, including insulators and flexible polymers. The strategy is enabled by two principle advances: (1) the introduction of a novel, low temperature strategy for reducing chloroplatinic acid to platinum using nitrogen plasma; (2) the development of a chloroplatinic acid based liquid ink formulation, utilizing ethylene glycol as both ink carrier and reducing agent, for versatile printing at nanoscale resolution using dip-pen nanolithography (DPN). The ink formulation has been printed and reduced upon Si, glass, ITO, Ge, PDMS, and Parylene C. The plasma treatment effects reduction of the precursor patterns in situ without subjecting the substrate to destructively high temperatures. Feature size is controlled via dwell time and degree of ink loading, and platinum features with 60 nm dimensions could be routinely achieved on Si. Reduction of the ink to platinum was confirmed by energy dispersive x-ray spectroscopy (EDS) elemental analysis and x-ray diffraction (XRD) measurements. Feature morphology was characterized by optical microscopy, SEM and AFM. The high electrochemical activity of individually printed Pt features was characterized using scanning electrochemical microscopy (SECM).
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The properties of two forms of polyaniline (PAni) synthesised under acidic and basic conditions have been investigated both individually and as combined complexes. The PAni polymerised within alkaline media was redox inactive and non-conducting while the PAni emeraldine salt (ES) was electroactive and conducting. Raman, electron spin resonance, UV-Vis and fluorescence spectroscopies were used to monitor the changes in electronic properties of these conducting polymer composites. Solution cast films of alkaline synthesised (A-PAni) with the PAni ES resulted in an increase in the high spin polaron population suggesting that it acts as a pseudodopant. The ability of the A-PAni to increase and maintain the population of the polaron charge carrier was confirmed by UV-vis and Raman spectroscopy. Significantly, the presence of the A-PAni in PAni ES helped to sustain higher electrical conductivities at loading levels that were well below the percolation threshold of an insulating polystyrene sulfonate polymeric oligomer model. Fluorescence studies indicated that the A-PAni was fluorescent. However, mixtures of A-PAni with the PAni ES resulted in quenching of the A-PAni emission. The quenching process was observed to involve both static and dynamic processes, with the static quenching being dominant. These results suggest that the two polymers are strongly associated with each other when in the solid state. In stark contrast, the alkaline synthesized PAni did not influence the electrochemical properties of the emeraldine salt. These results deviate significantly from the expected outcome of the addition of an insulating A-PAni additive and highlight the unusual interactions occurring between PAni and its alkaline analogue.
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Compostos de Anilina/química , Elétrons , Condutividade Elétrica , Espectroscopia de Ressonância de Spin Eletrônica , Concentração de Íons de Hidrogênio , Espectrofotometria Ultravioleta , Análise Espectral RamanRESUMO
Recent developments in both materials science and printing technologies have led to a rapid expansion in the field of printed conducting polymers. This review provides an overview of the most common printing methods currently in use and the material requirements of each. Examples of printed devices fabricated from a range of conducting polymers are given with an emphasis on the development of sensors.
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Polímeros/química , Impressão/instrumentação , Condutividade Elétrica , Teste de Materiais , Tamanho da Partícula , Propriedades de SuperfícieRESUMO
Poly(3,4-ethylenedioxythiophene) (PEDOT) films were electrochemically polymerised with several synthetic (dodecylbenzosulfonic acid (DBSA)) and biological (dextran sulphate (DS), chondroitin sulphate (CS), alginic acid (ALG) and ulvan (ULV)) dopant anions, and their physical, mechanical and electrochemical properties characterised. PEDOT films incorporating the biological dopants ALG and ULV produced films of the greatest surface roughness (46 ± 5.1 and 31 ± 1.9 nm, respectively), and demonstrated significantly lower shear modulus values relative to all other PEDOT films (2.1 ± 0.1 and 1.2 ± 0.2 MPa, respectively). Quartz crystal microgravimetry was used to study the adsorption of the important extracellular matrix protein fibronectin, revealing protein adsorption to be greatest on PEDOT doped with DS, followed by DBSA, ULV, CS and ALG. Electrical stimulation experiments applying a pulsed current using a biphasic waveform (250 Hz) were undertaken using PEDOT doped with either DBSA or ULV. Electrical stimulation had a significant influence on cell morphology and cell differentiation for PEDOT films with either dopant incorporated, with the degree of branching per cell increased by 10.5× on PEDOT-DBSA and 6.5× on PEDOT-ULV relative to unstimulated cells, and mean neurite length per cell increasing 2.6× and 2.2× on stimulated vs. unstimulated PEDOT-DBSA and PEDOT-ULV, respectively. We demonstrate the cytocompatibility of synthetic and biologically doped PEDOT biomaterials, including the new algal derived polysaccharide dopant ulvan, which, along with DBSA doped PEDOT, is shown to significantly enhance the differentiation of PC12 neuronal cells under electrical stimulation.
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Alginatos/química , Materiais Biocompatíveis/síntese química , Compostos Bicíclicos Heterocíclicos com Pontes/química , Sulfatos de Condroitina/química , Dextranos/química , Neurônios/efeitos dos fármacos , Polímeros/química , Polissacarídeos/química , Sulfonamidas/química , Animais , Materiais Biocompatíveis/farmacologia , Ácido Glucurônico/química , Ácidos Hexurônicos/química , Neurogênese , Neurônios/citologia , Células PC12 , Ratos , Resistência ao CisalhamentoRESUMO
Both the chemical and the electrochemical synthesis of poly(2-methoxyaniline-5-sulfonate) (PMAS) in aqueous media have been found to give two distinct polymer fractions with molecular weights of approximately 8-10 and 2 kDa, respectively. It is now possible to isolate the pure high molecular weight (HMWT) PMAS and low molecular weight (LMWT) PMAS oligomer and to study their individual and combined photochemistry and redox chemistry. The HMWT PMAS fraction was confirmed to be an emeraldine salt by its characteristic redox and pH switching behavior, in contrast to the oligomeric LMWT PMAS, which was inert under the same conditions. Mixtures of these two fractions exhibit photoluminescence arising from the oligomeric LMWT PMAS fraction. The observed LMWT PMAS emission was modulated by the presence of the conducting HMWT PMAS emeraldine salt via a static resonant energy transfer arising from quenching at 460 nm when excited at 355 nm. The nonlinear fluorophore-quencher behavior suggests that the two PMAS fractions are strongly associated. The behavior fitted the static Perrin quenching model in which the oligomeric LMWT PMAS fluorophore is diffusionally restricted by the presence of HMWT PMAS quencher.
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Compostos de Anilina/química , Luminescência , Polímeros/química , Ácidos Sulfônicos/química , Compostos de Anilina/síntese química , Concentração de Íons de Hidrogênio , Estrutura Molecular , Peso Molecular , Oxirredução , Fotoquímica , Polímeros/síntese química , Sensibilidade e Especificidade , Espectrofotometria Infravermelho/métodos , Ácidos Sulfônicos/síntese químicaRESUMO
Single-walled carbon nanotube (SWNT) papers were successfully prepared by dispersing SWNTs in Triton X-100 solution, then filtered by PVDF membrane (0.22 microm pore size). The electrochemical behavior and the reversible hydrogen storage capacity of single-walled carbon nanotube (SWNT) papers have been investigated in alkaline electrolytic solutions (6 N KOH) by cyclic voltammetry, linear micropolarization, and constant current charge/discharge measurements. The effect of thickness and the addition of carbon black on hydrogen adsorption/desorption were also investigated. It was found that the electrochemical charge-discharge mechanism occurring in SWNT paper electrodes is somewhere between that of carbon nanotubes (physical process) and that of metal hydride electrodes (chemical process), and consists of a charge-transfer reaction (Reduction/Oxidation) and a diffusion step (Diffusion).
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Eletroquímica/métodos , Hidrogênio , Nanotecnologia/métodos , Nanotubos de Carbono/química , Nanotubos de Carbono/ultraestrutura , Papel , Ultrafiltração/métodos , Absorção , Teste de Materiais , Tamanho da PartículaRESUMO
Conductive colloidal probe Atomic Force-Scanning Electrochemical Microscopy (AFM-SECM) is a new approach, which employs electrically insulated AFM probes except for a gold-coated colloid located at the end of the cantilever. Hence, force measurements can be performed while biasing the conductive colloid under physiological conditions. Moreover, such colloids can be modified by electrochemical polymerization resulting, e.g. in conductive polymer-coated spheres, which in addition may be loaded with specific dopants. In contrast to other AFM-based single cell force spectroscopy measurements, these probes allow adhesion measurements at the cell-biomaterial interface on multiple cells in a rapid manner while the properties of the polymer can be changed by applying a bias. In addition, spatially resolved electrochemical information e.g., oxygen reduction can be obtained simultaneously. Conductive colloid AFM-SECM probes modified with poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate ( PEDOT: PSS) are used for single cell force measurements in mouse fibroblasts and single cell interactions are investigated as a function of the applied potential.
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Microscopia de Força Atômica , Microscopia Eletrônica de Varredura , Sondas Moleculares/química , Poliestirenos/química , Tiofenos/química , Animais , Adesão Celular/fisiologia , Linhagem Celular , Técnicas Eletroquímicas , Eletrodos , CamundongosRESUMO
Engineering complex tissues for research and clinical applications relies on high-performance biomaterials that are amenable to biofabrication, maintain mechanical integrity, support specific cell behaviours, and, ultimately, biodegrade. In most cases, complex tissues will need to be fabricated from not one, but many biomaterials, which collectively fulfill these demanding requirements. Gellan gum is an anionic polysaccharide with potential to fill several key roles in engineered tissues, particularly after modification and blending. This review focuses on the present state of research into gellan gum, from its origins, purification and modification, through processing and biofabrication options, to its performance as a cell scaffold for both soft tissue and load bearing applications. Overall, we find gellan gum to be a highly versatile backbone material for tissue engineering research, upon which a broad array of form and functionality can be built.
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Materiais Biocompatíveis/química , Polissacarídeos Bacterianos/química , Polissacarídeos Bacterianos/metabolismo , Engenharia Tecidual/métodos , Alicerces Teciduais/química , Materiais Biocompatíveis/metabolismo , HumanosRESUMO
The development of inherently conducting polymers as controllable/programmable drug delivery systems has attracted significant interest in medical bionics, and the interfacial properties of the polymers, in particular, protein adsorption characteristics, is integral to the stability of the overall performance. Herein we report a hybrid conducting system based on polypyrrole doped with an anti-inflammatory prodrug, dexamethasone phosphate (DexP), upon which post-surface modification was conducted to render the polymer more biostable. We firstly investigated the influence of the current density and DexP concentration on the physiochemical properties and surface characteristics of the resulting polymer films. Films were then surface modified with thiolated poly(ethylene glycol). The influence of surface modification on inhibition of nonspecific protein adsorption to the polymer surfaces was evaluated using electrochemistry and quartz crystal microbalance. Furthermore, studies were undertaken to examine the effect of surface coatings on the drug release behaviour triggered by electrical stimulation. Our results demonstrated that both the physiochemical and interfacial properties of conducting polymers can be modulated to enhance the performance of the materials as biocompatible drug delivery systems. This provides important insight into molecular engineering of conducting polymers to facilitate their applications in medical bionics.
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Continuous composite fibres composed of polypyrrole (PPy) nanoparticles and reduced graphene oxide (rGO) at different mass ratios were fabricated using a single step wet-spinning approach. The electrical conductivity of the composite fibres increased significantly with the addition of rGO. The mechanical properties of the composite fibres also improved by the addition of rGO sheets compared to fibres containing only PPy. The ultimate tensile strength of the fibres increased with the proportion of rGO mass present. The elongation at break was greatest for the composite fibre containing equal mass ratios of PPy nanoparticles and rGO sheets. L929 fibroblasts seeded onto fibres showed no reduction in cell viability. To further assess toxicity, cells were exposed to media that had been used to extract any aqueous-soluble leachates from developed fibre. Overall, these composite fibres show promising mechanical and electrical properties while not significantly impeding cell growth, opening up a wide range of potential applications including nerve and muscle regeneration studies.
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Gellan gum (GG) is an anionic polysaccharide with potential as a biopolymer for additive manufacturing (3D-bioprinting) and tissue engineering. Previous studies have shown GG to be highly cytocompatible, but lacking specific attachment sites required for anchorage-dependent cells. In this work, we modify purified-GG polymer with a short peptide containing the arginine-glycine-aspartic acid (RGD) sequence that is known to enhance integrin-mediated cell attachment. Radiolabelling of the peptide was used in optimisation of the conjugation procedure to achieve an overall efficiency of 40%. The purification of divalent cations from commercial GG samples was found to be critical for successful conjugation. Rheological studies revealed that the peptide coupling did not prevent gelation behaviour. C2C12 cells showed improved attachment on the surface of and encapsulated within RGD-GG hydrogels, differentiating to multinucleated myofibers after 5-7 days. PC12 cells showed minimal interactions with both GG and RGD-GG, with formation of cell clusters and impedance of terminal differentiation and neurite extension.
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Composites of graphene in a chitosan-lactic acid matrix were prepared to create conductive hydrogels that are processable, exhibit tunable swelling properties and show excellent biocompatibility. The addition of graphene to the polymer matrix also resulted in significant improvements to the mechanical strength of the hydrogels, with the addition of just 3 wt% graphene resulting in tensile strengths increasing by over 200%. The composites could be easily processed into three-dimensional scaffolds with finely controlled dimensions using additive fabrication techniques and fibroblast cells demonstrate good adhesion and growth on their surfaces. These chitosan-graphene composites show great promise for use as conducting substrates for the growth of electro-responsive cells in tissue engineering.
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The adsorption of two model proteins, human serum albumin and immunoglobulin G, on a gold electrode surface was investigated using 125I radiolabeling and cyclic voltammetry (CV). 125I radiolabeling was used to determine the extent of protein adsorption, while CV was used to ascertain the effect of the adsorbed protein layer on the electron transfer between the gold electrode and an electroactive moiety in solution, namely, K3Fe(CN)6. The adsorbed amounts of HSA and IgG agreed well with previous results and showed approximately monolayer coverage. The amount of adsorbed protein increased when a positive potential (700 mV) was applied to the electrode, while the application of a negative potential (-800 mV) resulted in a decrease. When the solution pH was varied to alter the charge on the protein, the adsorption trends appeared to follow electrostatic interaction, namely, greater adsorption when the electrode and the protein possessed opposite charge and vice versa. The adsorbed protein layer had the effect of blocking the electron transfer. It was possible to correlate the degree of electron blocking with the amount of adsorbed protein to show that the greater the adsorption, the larger the blocking effect. Of the two proteins used, HSA proved to be more efficient at blocking the electron transfer.
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Eletroquímica , Ouro , Proteínas/química , Proteínas/farmacocinética , Adsorção , Eletrodos , Concentração de Íons de Hidrogênio , RadioisótoposRESUMO
An inherent difficulty associated with the application of suitable bioscaffolds for tissue engineering is the incorporation of adequate mechanical characteristics into the materials which recapitulate that of the native tissue, whilst maintaining cell proliferation and nutrient transfer qualities. Biomaterial composites fabricated using rapid prototyping techniques can potentially improve the functionality and patient-specific processing of tissue engineering scaffolds. In this work, a technique for the coaxial melt extrusion printing of core-shell scaffold structures was designed, implemented and assessed with respect to the repeatability, cell efficacy and scaffold porosity obtainable. Encapsulated alginate hydrogel/thermoplastic polycaprolactone (Alg-PCL) cofibre scaffolds were fabricated. Selective laser melting was used to produce a high resolution stainless steel 316 L coaxial extrusion nozzle, exhibiting diameters of 300 µm/900 µm for the inner and outer nozzles respectively. We present coaxial melt extrusion printed scaffolds of Alg-PCL cofibres with ~0.4 volume fraction alginate, with total fibre diameter as low as 600 µm and core material offset as low as 10% of the total diameter. Furthermore the tuneability of scaffold porosity, pore size and interconnectivity, as well as the preliminary inclusion, compatibility and survival of an L-929 mouse fibroblast cell-line within the scaffolds were explored. This preliminary cell work highlighted the need for optimal material selection and further design reiteration in future research.
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Materiais Biocompatíveis/química , Engenharia Tecidual/métodos , Alicerces Teciduais/química , Alginatos/química , Animais , Biotecnologia/instrumentação , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Desenho de Equipamento , Ácido Glucurônico/química , Ácidos Hexurônicos/química , Camundongos , Poliésteres/químicaRESUMO
Injury to nerve tissue in the peripheral nervous system (PNS) results in long-term impairment of limb function, dysaesthesia and pain, often with associated psychological effects. Whilst minor injuries can be left to regenerate without intervention and short gaps up to 2 cm can be sutured, larger or more severe injuries commonly require autogenous nerve grafts harvested from elsewhere in the body (usually sensory nerves). Functional recovery is often suboptimal and associated with loss of sensation from the tissue innervated by the harvested nerve. The challenges that persist with nerve repair have resulted in development of nerve guides or conduits from non-neural biological tissues and various polymers to improve the prognosis for the repair of damaged nerves in the PNS. This study describes the design and fabrication of a multimodal controlled pore size nerve regeneration conduit using polylactic acid (PLA) and (PLA):poly(lactic-co-glycolic) acid (PLGA) fibers within a neurotrophin-enriched alginate hydrogel. The nerve repair conduit design consists of two types of PLGA fibers selected specifically for promotion of axonal outgrowth and Schwann cell growth (75:25 for axons; 85:15 for Schwann cells). These aligned fibers are contained within the lumen of a knitted PLA sheath coated with electrospun PLA nanofibers to control pore size. The PLGA guidance fibers within the nerve repair conduit lumen are supported within an alginate hydrogel impregnated with neurotrophic factors (NT-3 or BDNF with LIF, SMDF and MGF-1) to provide neuroprotection, stimulation of axonal growth and Schwann cell migration. The conduit was used to promote repair of transected sciatic nerve in rats over a period of 4 weeks. Over this period, it was observed that over-grooming and self-mutilation (autotomy) of the limb implanted with the conduit was significantly reduced in rats implanted with the full-configuration conduit compared to rats implanted with conduits containing only an alginate hydrogel. This indicates return of some feeling to the limb via the fully-configured conduit. Immunohistochemical analysis of the implanted conduits removed from the rats after the four-week implantation period confirmed the presence of myelinated axons within the conduit and distal to the site of implantation, further supporting that the conduit promoted nerve repair over this period of time. This study describes the design considerations and fabrication of a novel multicomponent, multimodal bio-engineered synthetic conduit for peripheral nerve repair.
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Regeneração Nervosa/fisiologia , Próteses Neurais , Doenças do Sistema Nervoso Periférico/cirurgia , Engenharia Tecidual/instrumentação , Engenharia Tecidual/métodos , Animais , Movimento Celular/fisiologia , Ácido Láctico , Masculino , Células PC12 , Doenças do Sistema Nervoso Periférico/fisiopatologia , Ácido Poliglicólico , Copolímero de Ácido Poliláctico e Ácido Poliglicólico , Ratos , Ratos Sprague-Dawley , Células de Schwann/fisiologiaRESUMO
Phase imaging in atomic force microscopy (AFM) is a useful technique for determining dissipative tip-sample interactions related to changes in the material surface properties such as local stiffness or adhesion. In this work, we applied both phase imaging and phase spectroscopy measurements to conducting polymer (polypyrrole) doped with either hyaluronic acid or chondroitin sulfate. As observed in previous studies, phase-separated regions correlating with the characteristic nodular topography of polypyrrole and attributed to crystalline (doped) and amorphous (undoped) regions were observed. However, through additional phase spectroscopy measurements, we show that the phase-separated regions can arise due to variation in attractive and repulsive tip-sample interactions across the polymer surface. We show that these attractive and repulsive interactions are dependent on the redox state and degree of doping and suggest that they are related to phase separation of the polymer surface charge and/or energy. The latter may have implications for these materials when under investigation in a fluid, or biological, environment. For example, such surface variations will play a role in electrostatic forces, which in turn can influence protein and cellular interactions.
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Sulfatos de Condroitina/química , Ácido Hialurônico/química , Microscopia de Força Atômica/métodos , Polímeros/química , Pirróis/química , Estimulação ElétricaRESUMO
The nexus of any bionic device can be found at the electrode-cellular interface. Overall efficiency is determined by our ability to transfer electronic information across that interface. The nanostructure imparted to electrodes plays a critical role in controlling the cascade of events that determines the composition and structure of that interface. With commonly used conductors: metals, carbon and organic conducting polymers, a number of approaches that promote control over structure in the nanodomain have emerged in recent years with subsequent studies revealing a critical dependency between nanostructure and cellular behaviour. As we continue to develop our understanding of how to create and characterise electromaterials in the nanodomain, this is expected to have a profound effect on the development of next generation bionic devices. In this review, we focus on advances in fabricating nanostructured electrodes that present new opportunities in the field of medical bionics. We also briefly evaluate the interactions of living cells with the nanostructured electromaterials, in addition to highlighting emerging tools used for nanofabrication and nanocharacterisation of the electrode-cellular interface.