Search

Diluting organic semiconductors with a host insulating polymer is used to increase the electronic mobility in organic electronic devices, such as thin film transistors, while considerably reducing material costs. In contrast to organic electronics, bioelectronic devices such as the organic electrochemical transistor (OECT) rely on both electronic and ionic mobility for efficient operation, making it challenging to integrate hydrophobic polymers as the predominant blend component. This work shows that diluting the n-type conjugated polymer p(N-T) with high molecular weight polystyrene (10 KDa) leads to OECTs with over three times better mobility-volumetric capacitance product (µC*) with respect to the pristine p(N-T) (from 4.3 to 13.4 F V−1 cm−1 s−1) while drastically decreasing the amount of conjugated polymer (six times less). This improvement in µC* is due to a dramatic increase in electronic mobility by two orders of magnitude, from 0.059 to 1.3 cm2 V−1 s−1 for p(N-T):Polystyrene 10 KDa 1:6. Moreover, devices made with this polymer blend show better stability, retaining 77% of the initial drain current after 60 minutes operation in contrast to 12% for pristine p(N-T). These results open a new generation of low-cost organic mixed ionic-electronic conductors where the bulk of the film is made by a commodity polymer., QC 20240429

Organic mixed ionic–electronic conductors (OMIECs) are being explored in applications such as bioelectronics, biosensors, energy conversion and storage, and optoelectronics. OMIECs are largely composed of conjugated polymers that couple ionic and electronic transport in their structure as well as synthetic flexibility. Despite extensive research, previous studies have mainly focused on either enhancing ion conduction or enabling synthetic modification. This limited the number of OMIECs that excel in both domains. Here, a series of OMIECs based on functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) copolymers that combine efficient ion/electron transport with the versatility of post-functionalization were developed. EDOT monomers bearing sulfonic (EDOTS) and carboxylic acid (EDOTCOOH) groups were electrochemically copolymerized in different ratios on oxygen plasma-treated conductive substrates. The plasma treatment enabled the synthesis of copolymers containing high ratios of EDOTS (up to 68%), otherwise not possible with untreated substrates. This flexibility in synthesis resulted in the fabrication of copolymers with tunable properties in terms of conductivity (2–0.0019 S/cm) and ion/electron transport, for example, as revealed by their volumetric capacitances (122–11 F/cm3). The importance of the organic nature of the OMIECs that are amenable to synthetic modification was also demonstrated. EDOTCOOH was successfully post-functionalized without influencing the ionic and electronic transport of the copolymers. This opens a new way to tailor the properties of the OMIECs to specific applications, especially in the field of bioelectronics.

One factor with great bearing on the electrochemical performance of conjugated polymers is the film morphology. A balance between crystalline and amorphous domains needs to be achieved for the polymer to have an optimal ionic-electronic conductance. Herein, the morphological and electrochemical properties of poly(ethylenedioxythiophene) polymers functionalized with phosphonate groups separated by methylene and butylene alkyl spacers from the backbone are compared. Extending the spacer from methylene to butylene increases structural ordering in the solid state as revealed by grazing-incidence wide-angle X-ray scattering. However, the ordered domains are only short range, suggestive of a paracrystalline morphology in which ordered regions are separated by amorphous regions. This has a negative impact on the intermolecular charge transport. The longer spacer appears to have impeded the uptake of hydrated counterions, seen by the increase in the ionization potential and energy requirement for electrochemical switching, as well as the decrease in the volumetric capacitance. These results elucidate the advantages of having the phosphonate pendant group close to the backbone, separated only by a methylene spacer. This synthetic design likely facilitates hydrated counterions to accumulate around the polar phosphonate groups, close to the doped backbone where they can easily compensate the charge carriers formed upon oxidation., A.L., D.L.O., and D.M. would like to acknowledge the Australian Research Council, Discovery Project Grant DP190102560, for funding this research. The authors would like to acknowledge the use of facilities and the assistance of Dr. David Miskovic of the UNSW School of Materials Science and Engineering, Dr. Anne Rich of the Spectroscopy Laboratory, Dr. Bill Bin Gong and Dr. Yu Wang in the Solid State & Elemental Analysis Unit, as well as the members of the NMR Facility under the Mark Wainwright Analytical Centre at UNSW Sydney., Peer Reviewed, Postprint (published version)

Piezoelectricity, which directly couples mechanical and electrical energies, has been demonstrated in many biological tissues such as tendon, bone, trachea and intestines. Biopolymers such as chitin and chitosan have been shown to exhibit a piezoelectric response. Using biopolymers to harvest our biomechanical energy has attracted great interest for the development of new kinds of energy source to power, medical devices, and portable electronics. This is mainly due to the good biocompatibility, biodegradability, and bioactivity of biopolymers. The aim of this thesis was to optimize the processing parameters for the fabrication of a chitosan thin film with excellent mechanical and piezoelectric properties.Chitosan thin films were prepared by drop-casting a chitosan acetic acid solution and drying at room temperature. Films were then treated with either deionized water (Ch-H2O) or sodium hydroxide (Ch-NaOH) to remove residual acid and neutralize the films. The morphology of the films was characterized by X-ray diffraction (XRD) and their thermal transitions by differential scanning calorimetry (DSC). Their mechanical properties were investigated by tensile testing and conductivity was measured. To study the piezoelectric response, chitosan films, having gold electrodes on both sides, were electrically poled using a high electric field (5 kV/mm to 50 kV/mm). Optical microscopy and scanning electron microscopy (SEM) were used to observe the morphology of the gold electrodes. The dielectric properties, along with the polarization, were investigated by applying low voltages (0 to 5 V) over a wide frequency range using frequency domain spectroscopy (FDS) and by recording the charging currents of the films.Treating the films had a significant impact on their physical, piezoelectric, and dielectric properties. The crystallinity of Ch-NaOH and Ch-H2O increased as represented by the appearance of the anhydrous polymorph around 2θ = 15° in the XRD pattern. Treating the films wi

Nanocomplexes are made of different components, benefiting from properties of each of the constituent material. As such, nanocomplexes present unique properties including chemical activity due to high surface area, tuneable size and morphology, variable surface charges and efficient uptake by cells. They have been used in different therapeutic approaches such as drug delivery systems, biosensors and tissue engineering. Introducing an electrically conductive material, such as metal or conjugated polymer, as one component of nano-complexes adds electronic and optical properties to the system, broadening their applications. While metals are excellent conductors, their hard nature does not match the soft tissue. Conjugated polymers on the other hand, as organic materials, are soft and flexible; thus, they are the choice material in this thesis for the development of soft and hard conjugated polymer nanocomplexes. Liposome and anionic polymeric nanoparticles with a core morphology were used as soft and hard templates, respectively, around which conjugated polymers, polyaniline and polypyrrole, were synthesised. Their chemical, physical, electrochemical and biomedical properties were optimised and fully characterised. A single-step synthesis was developed for fabricating the soft polyaniline-liposome nano-complexes in which polyaniline, doped with phytic acid, was either embedded in the liposome bilayer or bound on the liposome outer surface. Hard polypyrrole nanocomplexes were based on the anionic poly(potassium 3- sulfopropyl methacrylate)-block- poly (benzyl methacrylate) nanoparticle. In a novel step, the nanoparticle served as the dopant for the conjugated polymer. The conjugated polymer nanocomplexes were water-dispersible, conductive and exhibited low impedance. In-vitro cell studies demonstrated the complexes are not cytotoxic with capability of targeted cell uptakes. This research presents novel and promising routes for xiv fabrication of water-dispersible conduc

Organic electronics based on conjugated polymers (CPs) are being explored as active semiconductor materials in the bioelectronics field. CPs can be embedded in flexible substrates to obtain a passive conductive device or employed in active devices such as organic electrochemical transistors (OECTs). Their potential use in the clinic hinges on their development into advanced bioelectronic circuitry for higher functionalities. Furthermore, their translation into the clinic will require their sterilization without degrading their physical and electronic properties, as well as consideration of self-powering functionalities. The thesis objective was to address these challenges by 1) developing a complementary logic circuit based on polyaniline (PANI) as the active channel, 2) investigating the effect of sterilization methods on PANI properties, and 3) exploring its optoelectronic properties towards a flexible wireless optoelectronic device. In this thesis, a complementary logic circuit was built from a single PANI based active channel OECT, exhibiting a gain of 7.2. It was also engineered into a flexible bioelectronic circuit that operates in aqueous electrolyte. An in vivo study was performed on PANI-patches sterilized by ethylene oxide and gamma radiation. Results showed that the patches maintained their mechanical and conductive nature after sterilization, and the inflammatory response after implantation significantly diminished by week 4. The optical properties of PANI were also exploited; the PANI-patch showed photoconductivity when illuminated with visible light. In conclusion, the electrochemical properties of PANI were exploited to build a new flexible complementary circuit featuring two identical OECTs. This drastically simplifies the manufacturing process eliminating the need for materials with matching performance. Sterilized patches maintained their mechanical and electrical properties and induced a minimal inflammatory response. Additionally, the demonstrate

Organic electrochemical transistors (OECTs) for bioelectronic applications require the design of conjugated polymers that are stable in aqueous environments and afford high energy efficiency and good performance in OECTs. Polymers based on poly(ethylenedioxythiophene) (PEDOT) are promising in this area due to their low oxidation potential and reversible redox, but they often require cross-linking to prevent dissolution and yield OECTs operating in the less efficient depletion mode. In this work, a new conjugated polymer PEDOT-Phos is presented, which combines a conjugated poly(ethylenedioxythiophene) (PEDOT) backbone with alkyl-protected phosphonate groups. PEDOT-Phos exhibits a low oxidation onset potential (-0.157 V vs Ag/AgCl) and its nanoporous morphology affords it a high volumetric capacitance (282 ± 62 F cm–3). Without any cross-linking, additives, or post-treatment, PEDOT-Phos can be used in aqueous OECTs with efficient accumulation mode operation, long-term stability when immersed in aqueous media, low threshold voltages (-0.161 ± 0.005 V), good transconductances (9.3 ± 1.8 mS), and ON/OFF current ratios (618 ± 54) comparable to other PEDOT-based materials in OECTs. These results highlight the great promise of PEDOT-Phos as a stand-alone channel material for energy-efficient, bioelectronic devices., Peer Reviewed, Postprint (author's final draft)

The encapsulation of pancreatic islets in hydrogels is of topical interest for its potential for treatment of type-1 diabetes. Clinical investigations have demonstrated only partial success of traditional immunoisolation by physical exclusion. This limitation highlights a complementary approach in the form of local immunomodulation for long-term islet survival.The present work focused on the development of an immunomodulatory hydrogel system for islet encapsulation. The anti-inflammatory and cell-protective properties of fucoidan and carrageenans suggest their potential to inhibit immune cell activation and to act as biological cues to support islet survival. Consequently, fucoidan and carrageenans were functionalised with methacrylate groups and the immunomodulatory properties were assessed. The polysaccharides were crosslinked with methacrylate-functionalised poly(vinyl alcohol) (PVA-MA) in order to fabricate biosynthetic hydrogels using UV photopolymerisation. Two hydrogel configurations were fabricated, one with low crosslink density for islet encapsulation and the other with high crosslink density for size-based exclusion. The former, which encapsulated pancreatic islets, was characterised by cell survival and functionality testing. The latter was characterised by the permeation of IgG and IL-1β, two harmful inflammatory molecules.The results demonstrated that fucoidan is an effective immunomodulatory agent that downregulates molecules responsible for islet dysfunction, particularly the expression of CD86, which is a major co-stimulatory molecule that contributes to the activation of T cells. Fucoidan also significantly decreased cellular nitric oxide production and demonstrated effective scavenging (>90%) of superoxide free radicals. In contrast, the carrageenans exhibited only the latter two effects. The hydrogel of high crosslink density was effective in blocking permeation of IL-1β in ~24 h while allowing permeation of BSA. The favourable effects of fucoida