Zhilian Yue

Buckled, stretchable polypyrrole electrodes for battery applications

Research on stretchable electronics is motivated by the need for electronic systems that can sustain large mechanical strain and still maintain their function. They can be wrapped conformally around complex and unconventional shapes, and have found applications in the biomedical fi elds, electronic paper display devices, sensor skins and photovoltaics. [ 1 ] Within the biomedical fi elds, these electronics need to conform to body shape for use as wearables with a match in mechanical properties to minimise discomfort. [ 2–5 ] As an indispensable component of stretchable electronics, a stretchable power-source device should also be able to accommodate large strain while retaining its function. Recently, there has been an emerging interest in stretchable power sources including energy storage [ 6–8 ] and energy harvesting. [ 9 , 10 ] Energy storage devices, including batteries and supercapacitors, play an important role in powering systems of portable electronic devices or implantable medical devices. Stretchable supercapacitor electrodes using single-walled carbon nanotubes (SWNT) integrated into poly(dimethylsiloxane) (PDMS) or textile substrates have been developed. [ 6 , 7 ] Ultracompliant electrochemical dry gel cells have been reported, comprising a cathode (MnO 2 ) and anode (Zn) paste plotted on a carbon black with structured elastomer as substrate. [ 8 ] To date, however, the application of inherently conducting polymers (ICPs) as stretchable supercapacitor or battery electrodes has not been reported. In particular, ICPs have been shown to be biocompatible with potential applications in biomedical implants, devices and tissue engineering. [ 11 , 12 ] This class of materials has attracted widespread attention in the applications in energy storage devices such as batteries or supercapacitors. [ 13 , 14 ] Here we report a stretchable battery electrode material based on buckled polypyrrole (PPy) and its application in a biocompatible battery system with a bioadsorbable Mg alloy (AZ61) in phosphate buffered saline (PBS). Remarkably, this PPy electrode demonstrates excellent stretchability. It can endure 2000 stretching cycles with 30% tensile strain applied at a 5% s − 1

Intrinsically stretchable supercapacitors composed of polypyrrole electrodes and highly stretchable gel electrolyte

There has been an emerging interest in stretchable power sources compatible with flexible/wearable electronics. Such power sources must be able to withstand large mechanical strains and still maintain function. Here we report a highly stretchable H3PO4-poly(vinyl alcohol) (PVA) polymer electrolyte obtained by optimizing the polymer molecular weight and its weight ratio to H3PO4 in terms of conductivity and mechanical properties. The electrolyte demonstrates a high conductivity of 3.4 × 10(-3) S cm(-1), and a high fracture strain at 410% elongation. It is mechanically robust with a tensile strength of 2 MPa and a Youngs modulus of 1 MPa, and displays a small plastic deformation (5%) after 1000 stretching cycles at 100% strain. A stretchable supercapacitor device has been developed based on buckled polypyrrole electrodes and the polymer electrolyte. The device shows only a small capacitance loss of 5.6% at 30% strain, and can retain 81% of the initial capacitance after 1000 cycles of such stretching.

Conducting polymers with immobilised fibrillar collagen for enhanced neural interfacing

Conducting polymers with pendant functionality are advantageous in various bionic and organic bioelectronic applications, as they allow facile incorporation of bio-regulative cues to provide bio-mimicry and conductive environments for cell growth, differentiation and function. In this work, polypyrrole substrates doped with chondroitin sulfate (CS), an extracellular matrix molecule bearing carboxylic acid moieties, were electrochemically synthesized and conjugated with type I collagen. During the coupling process, the conjugated collagen formed a 3-dimensional fibrillar matrix in situ at the conducting polymer interface, as evidenced by atomic force microscopy (AFM) and fluorescence microscopy under aqueous physiological conditions. Cyclic voltammetry (CV) and impedance measurement confirmed no significant reduction in the electroactivity of the fibrillar collagen-modified conducting polymer substrates. Rat pheochromocytoma (nerve) cells showed increased differentiation and neurite outgrowth on the fibrillar collagen, which was further enhanced through electrical stimulation of the underlying conducting polymer substrate. Our study demonstrates that the direct coupling of ECM components such as collagen, followed by their further self-assembly into 3-dimensional matrices, has the potential to improve the neural-electrode interface of implant electrodes by encouraging nerve cell attachment and differentiation.

Biofunctionalized anti-corrosive silane coatings for magnesium alloys

Biodegradable magnesium alloys are advantageous in various implant applications, as they reduce the risks associated with permanent metallic implants. However, a rapid corrosion rate is usually a hindrance in biomedical applications. Here we report a facile two step procedure to introduce multifunctional, anti-corrosive coatings on Mg alloys, such as AZ31. The first step involves treating the NaOH-activated Mg with bistriethoxysilylethane to immobilize a layer of densely crosslinked silane coating with good corrosion resistance; the second step is to impart amine functionality to the surface by treating the modified Mg with 3-amino-propyltrimethoxysilane. We characterized the two-layer anticorrosive coating of Mg alloy AZ31 by Fourier transform infrared spectroscopy, static contact angle measurement and optical profilometry, potentiodynamic polarization and AC impedance measurements. Furthermore, heparin was covalently conjugated onto the silane-treated AZ31 to render the coating haemocompatible, as demonstrated by reduced platelet adhesion on the heparinized surface. The method reported here is also applicable to the preparation of other types of biofunctional, anti-corrosive coatings and thus of significant interest in biodegradable implant applications.

Galactosylated cellulosic sponge for multi-well drug safety testing

Hepatocyte spheroids can maintain mature differentiated functions, but collide to form bulkier structures when in extended culture. When the spheroid diameter exceeds 200 μm, cells in the inner core experience hypoxia and limited access to nutrients and drugs. Here we report the development of a thin galactosylated cellulosic sponge to culture hepatocytes in multi-well plates as 3D spheroids, and constrain them within a macroporous scaffold network to maintain spheroid size and prevent detachment. The hydrogel-based soft sponge conjugated with galactose provided suitable mechanical and chemical cues to support rapid formation of hepatocyte spheroids with a mature hepatocyte phenotype. The spheroids tethered in the sponge showed excellent maintenance of 3D cell morphology, cell-cell interaction, polarity, metabolic and transporter function and/or expression. For example, cytochrome P450 (CYP1A2, CYP2B2 and CYP3A2) activities were significantly elevated in spheroids exposed to β-naphthoflavone, phenobarbital, or pregnenolone-16α-carbonitrile, respectively. The sponge also exhibits minimal drug absorption compared to other commercially available scaffolds. As the cell seeding and culture protocols are similar to various high-throughput 2D cell-based assays, this platform is readily scalable and provides an alternative to current hepatocyte platforms used in drug safety testing applications.

Bio-functionalisation of polydimethylsiloxane with hyaluronic acid and hyaluronic acid – Collagen conjugate for neural interfacing

In this work, polydimethylsiloxane was activated with oxygen plasma and treated with silanes bearing ethylene imine units. Hyaluronic acid was then grafted covalently onto the aminated surfaces. The influence of silane structure on surface amination was assessed and the influence of the modification on surface physiochemical properties and protein adsorption of modified polydimethylsiloxane were investigated. Collagen type I was conjugated onto the modified polydimethylsiloxane to improve its cyto-compatibility for neural applications. In vitro cultivation of rat pheochromocytoma cells on the bioactive polydimethylsiloxane showed a significant increase in cell growth and differentiation. The potential applications of the bio-functionalized polydimethylsiloxane in cochlear implant electrode arrays were discussed.

Controlled delivery for neuro-bionic devices

Implantable electrodes interface with the human body for a range of therapeutic as well as diagnostic applications. Here we provide an overview of controlled delivery strategies used in neuro-bionics. Controlled delivery of bioactive molecules has been used to minimise reactive cellular and tissue responses and/or promote nerve preservation and neurite outgrowth toward the implanted electrode. These effects are integral to establishing a chronically stable and effective electrode-neural communication. Drug-eluting bioactive coatings, organic conductive polymers, or integrated microfabricated drug delivery channels are strategies commonly used.

Preparation of a soft and interconnected macroporous hydroxypropyl cellulose methacrylate scaffold for adipose tissue engineering

This study describes the preparation and characterization of a biodegradable 3D hydrogel constructed from hydroxypropyl cellulose (HPC), modified with bifunctional methacrylic anhydride (MA) to form hydroxypropyl cellulose methacrylate (HPC-MA), for adipose tissue engineering applications. The hydrogels were prepared from three different concentrations (10 wt%, 15 wt% and 20 wt%) of HPC-MA with 0.35 degree of substitution. HPC-MA hydrogel scaffolds with open biphasic features were prepared by exploiting the thermal responsive phase behavior of HPC and temperature mediated phase separation of HPC-MA. The resulting scaffolds exhibited pore sizes ranging from 30 to 300 μm and an interconnected porosity of ∼90%. The swelling ratio (SR) and storage modulus of HPC-MA scaffolds were in the range of 12.94 to 35.83 and 0.75 to 4.28 kPa, respectively. The swelling ratio and storage modulus suggested that the scaffold exhibits high water retention, allowing medium exchange during cell culturing and that it is suitable for adipose tissue regeneration. The HPC-MA scaffolds were found to be biocompatible to human adipose-derived stem cells (ASCs). ASCs were successfully differentiated into the adipocytes inside the scaffolds, and therefore demonstrated the potential application of these HPC-MA scaffolds for adipose tissue engineering.

Control of in vitro neural differentiation of mesenchymal stem cells in 3D macroporous, cellulosic hydrogels

BACKGROUND Mesenchymal stem cells (MSCs) are multipotent cells that can be induced to differentiate into multiple cell lineages, including neural cells. They are a good cell source for neural tissue-engineering applications. Cultivation of human (h)MSCs in 3D scaffolds is an effective means for the development of novel neural tissue-engineered constructs, and may serve as a promising strategy in the treatment of nerve injury. AIM This study presents the in vitro growth and neural differentiation of hMSCs in 3D macroporous, cellulosic hydrogels. RESULTS The number of hMSCs cultivated in the 3D scaffolds increased by more than 14-fold after 7 days. After 2 days induction, most of the hMSCs in the 3D scaffolds were positive for nestin, a marker of neural stem cells. After 7 days induction, most of the hMSCs in the 3D scaffolds showed glial fibrillary acidic protein, tubulin or neurofilament M-positive reaction and a few hMSCs were positive for nestin. After 14 days induction, hMSCs in the 3D scaffolds could completely differentiate into neurons and glial cells. The neural differentiation of hMSCs in the 3D scaffolds was further demonstrated by real-time PCR. CONCLUSION These results show that the 3D macroporous cellulosic hydrogel could be an appropriate substrate for neural differentiation of hMSCs and its possible applications in neural tissue engineering are discussed.

Aqueous solution behaviour and membrane disruptive activity of pH-responsive PEGylated pseudo-peptides and their intracellular distribution

The effect of PEGylation on the aqueous solution properties and cell membrane disruptive activity of a pH-responsive pseudo-peptide, poly(l-lysine iso-phthalamide), has been investigated by dynamic light scattering, haemolysis and lactate dehydrogenase (LDH) assays. Intracellular trafficking of the polymers has been examined using confocal and fluorescence microscopy. With increasing degree of PEGylation, the modified polymers can form stabilised compact structures with reduced mean hydrodynamic diameters. Poly(l-lysine iso-phthalamide) with a low degree of PEGylation (17.4 wt%) retained pH-dependent solution behaviour and showed enhanced kinetic membrane disruptive activity compared to the parent polymer. It facilitated trafficking of endocytosed materials into the cytoplasm of HeLa cells. At levels of PEGylation in excess of 25.6 wt%, the modified polymers displayed a single particle size distribution unresponsive to pH, as well as a decrease in cell membrane lytic ability. The mechanism involved in membrane destabilisation was also investigated, and the potential applications of these modified polymers in drug delivery were discussed.