Changchun Zeng

Supercritical fluid deposition of vanadium oxide on multi-walled carbon nanotube buckypaper for supercapacitor electrode application

Composite electrodes were fabricated for supercapacitor applications by depositing vanadium oxide onto multi-walled carbon nanotube (MWCNT) buckypaper using supercritical fluid deposition (SFD). The deposited thin vanadium oxide layer showed amorphous structure with excellent uniformity. In aqueous KCl electrolyte, the vanadium oxide exhibited a constant pseudo-capacitance of ∼ 1024 F g(-1), which was independent of the oxide material loading (up to 6.92 wt%) and voltage scan rate (up to 100 mV s(-1)). The highest specific electrode capacitance achieved was ∼ 85 F g(-1), which was almost four times that of the pristine buckypaper electrode.

Crosslinking of extracellular matrix scaffolds derived from pluripotent stem cell aggregates modulates neural differentiation

UNLABELLED At various developmental stages, pluripotent stem cells (PSCs) and their progeny secrete a large amount of extracellular matrices (ECMs) which could interact with regulatory growth factors to modulate stem cell lineage commitment. ECMs derived from PSC can be used as unique scaffolds that provide broad signaling capacities to mediate cellular differentiation. However, the rapid degradation of ECMs can impact their applications as the scaffolds for in vitro cell expansion and in vivo transplantation. To address this issue, this study investigated the effects of crosslinking on the ECMs derived from embryonic stem cells (ESCs) and the regulatory capacity of the crosslinked ECMs on the proliferation and differentiation of reseeded ESC-derived neural progenitor cells (NPCs). To create different biological cues, undifferentiated aggregates, spontaneous embryoid bodies, and ESC-derived NPC aggregates were decellularized. The derived ECMs were crosslinked using genipin or glutaraldehyde to enhance the scaffold stability. ESC-derived NPC aggregates were reseeded on different ECM scaffolds and differential cellular compositions of neural progenitors, neurons, and glial cells were observed. The results indicate that ESC-derived ECM scaffolds affect neural differentiation through intrinsic biological cues and biophysical properties. These scaffolds have potential for in vitro cell culture and in vivo tissue regeneration study. STATEMENT OF SIGNIFICANCE Dynamic interactions of acellular extracellular matrices and stem cells are critical for lineage-specific commitment and tissue regeneration. Understanding the synergistic effects of biochemical, biological, and biophysical properties of acellular matrices would facilitate scaffold design and the functional regulation of stem cells. The present study assessed the influence of crosslinked embryonic stem cell-derived extracellular matrix on neural differentiation and revealed the synergistic interactions of various matrix properties. While embryonic stem cell-derived matrices have been assessed as tissue engineering scaffolds, the impact of crosslinking on the embryonic stem cell-derived matrices to modulate neural differentiation has not been studied. The results from this study provide novel knowledge on the interface of embryonic stem cell-derived extracellular matrix and neural aggregates. The findings reported in this manuscript are significant for stem cell differentiation toward the applications in stem cell-based drug screening, disease modeling, and cell therapies.

Room-Temperature, Near-Instantaneous Fabrication of Auxetic Materials with Constant Poisson's Ratio over Large Deformation.

A novel compressed carbon dioxide assisted fabrication method is demonstrated to produce auxetic PU foam. Auxetic PU foams can be fabricated at room temperature (25°C) in several seconds with compressed CO2. This technology overcomes some key challenging issues in the large-scale production of auxetic PU foams.

Recycling of woven carbon-fibre-reinforced polymer composites using supercritical water

Over the past few years, there has been great deal of interest in recycling carbon-fibre-reinforced polymer composites. One method that has shown promising results involves the use of supercritical fluids to achieve separation between matrix and fibres by effectively degrading the resin into lower molecular weight compounds. In addition, the solvents used are environmentally benign and can also be recovered and reused. In this study, supercritical water with 0.05 M KOH as the catalyst was used for the recycling of an aerospace-grade high-performance epoxy carbon fibre composite (Hexcel 8552/IM7). The morphology of the reclaimed fibres was observed by scanning electron microscopy, and the tensile properties of the fibres were measured by single filament testing. The effects of processing time on the resin elimination efficiency and fibre property retention were investigated. With the process developed in this research, as much as 99.2 wt% resin elimination was achieved, resulting in the recovery of clean, undamaged fibres. The reclaimed fibres retained the original tensile strength. The feasibility of recycling multiple layer composites was also explored.

Pluripotent stem cell expansion and neural differentiation in 3-D scaffolds of tunable Poisson's ratio.

Biophysical properties of the scaffolds such as the elastic modulus, have been recently shown to impact stem cell lineage commitment. On the other hand, the contribution of the Poissons ratio, another important biophysical property, to the stem cell fate decision, has not been studied. Scaffolds with tunable Poissons ratio (ν) (termed as auxetic scaffolds when Poissons ratio is zero or negative) are anticipated to provide a spectrum of unique biophysical 3-D microenvironments to influence stem cell fate. To test this hypothesis, in the present work we fabricated auxetic polyurethane scaffolds (ν=0 to -0.45) and evaluated their effects on neural differentiation of mouse embryonic stem cells (ESCs) and human induced pluripotent stem cells (hiPSCs). Compared to the regular scaffolds (ν=+0.30) before auxetic conversion, the auxetic scaffolds supported smaller aggregate formation and higher expression of β-tubulin III upon neural differentiation. The influences of pore structure, Poissons ratio, and elastic modulus on neural lineage commitment were further evaluated using a series of auxetic scaffolds. The results indicate that Poissons ratio may confound the effects of elastic modulus, and auxetic scaffolds with proper pore structure and Poissons ratio enhance neural differentiation. This study demonstrates that tuning the Poissons ratio of the scaffolds together with elastic modulus and microstructure would enhance the capability to generate broader, more diversified ranges of biophysical 3-D microenvironments for the modulation of cellular differentiation. STATEMENT OF SIGNIFICANCE Biophysical signaling from the substrates and scaffolds plays a critical role in neural lineage commitment of pluripotent stem cells. While the contribution of elastic modulus has been well studied, the influence of Poissons ratio along with microstructure of the scaffolds remains unknown largely due to the lack of technology to produce materials with tailorable Poissons ratio. This study fabricated auxetic polyurethane scaffolds with different elastic modulus, Poissons ratio and microstructure and evaluated neural differentiation of pluripotent stem cells. The findings add a novel angle to understand the impact of biophysical microenvironment on stem cell fate decisions.

Charge storage and transport in oriented and non-oriented polytetrafluoroethylene films

The charge storage and transport in oriented and non-oriented polytetrafluoroethylene (PTFE) films, charged by the corona method at room temperature, were investigated by isothermal decay and thermally stimulated discharge (TSD) techniques. The crystallinity of the PTFE films was determined by differential scanning calorimetry (DSC). The results obtained from isothermal decay of the surface potential and the spectra of the TSD charge and current indicate that the thermal stability of both positive and negative charges in oriented PTFE films is significantly better than that of non-oriented PTFE films. This is probably due to the higher crystallinity in oriented PTFE films. The transport of the de-trapped positive charges in oriented PTFE films, which occurred due to thermal excitation, can be explained by a model that takes thermal ion emission into consideration.

Vascular differentiation from pluripotent stem cells in 3-D auxetic scaffolds

Auxetic scaffolds, that is, scaffolds that can display negative Poissons ratio, have unique physical properties and can expand transversally when axially strained or contract under compression. Auxetic materials have been used for bioprostheses and artery stents due to the enhanced compressive strength and shear stiffness. In vascular tissue engineering, auxetic scaffolds allow the widening of blood vessels when blood flows through (creating compressive stress) to prevent the blockage. However, the influence of auxetic materials on the cellular fate decision in local environment is unclear. In this study, auxetic polyurethane foams were used to support vascular differentiation from pluripotent stem cells. The expression of alkaline phosphatase, Oct‐4, and Nanog was lower after 4 days of differentiation for the cells grown in auxetic scaffolds. Higher expression of vascular markers CD31 and VE‐cadherin was observed for the cells from auxetic scaffolds compared with those from the scaffolds before auxetic conversion. Little influence on the expression of cardiac marker α‐actinin was observed. The vascular cells secreted extracellular matrix proteins vitronectin and laminin and expressed membrane‐bound matrix metalloproteinase 9. The examination of Yes‐associated protein expression indicated more cytoplasmic retention in the cells from auxetic scaffolds compared with those from regular scaffolds, suggesting that the auxetic scaffolds may affect cellular contraction. This study demonstrates a novel 3‐D culture based on auxetic scaffolds for vascular differentiation and provides a platform to study the influence of biophysical microenvironments on differentiation of pluripotent stem cells. The outcome of this study has implications for regenerative medicine and drug discovery.

On the Dynamics of Polypropylene Melt: Long Chain Branching and Physical Cross-links

A series of polypropylene containing long chain branches and amine groups (PP-g-NH2) were prepared via reaction between maleic anhydride grafted polypropylene (PP-g-MAH) and ethylene diamine (EDA). As shown in Scheme 1, multiple pathways are possible when PP-g-MA reacts with EDA depending on the ratio of amine over maleic anhydride group The LCB-PPs were prepared via scCO2 assisted reactive extrusion(Cao et al, 2010; Cao et al, 2011; Liu et al, 2010). PP-g-NH2 was synthesized using a solution process.

Investigation into polarization and piezoelectricity in polymer films with artificial void structure

Fluorocarbon polymer films with regular void structure are prepared by using a patterning-fusion bonding process. The critical voltage necessary for the build-up of the “macro-dipoles” in the inner voids observed in the experiments agrees well with the calculated value. The fabricated films show improved thermal stability of the d 33 coefficients.

Fabrication and piezoelectricity of fluoropolymer films with patterned structure

Laminated fluoroethylenepropylene (FEP) and porous polytetrafluoroethylene (PTFE) films with patterned void structure were successfully fabricated. An improved model taking into account of both the mechanical structure and charge distribution was used to describe the behavior of the fabricated films. The Youngs modulus of the three-layer FEP/PTFE film is ~0.5 MPa. Maximum quasi-static piezoelectric d33 coefficient up to 500 pC/N is achieved. Compared to the PP piezoelectrets, which loose their piezoelectric activity completely at the annealing temperature of 150 °C within 60 min, the laminated FEP/PTFE films show significantly improved thermal stability. For example, the d33-coefficient retains ~22% of the initial value for samples annealed at 150 °C for 4500 min.