Yiquan Wu

Fabrication of Elastin-Like Polypeptide Nanoparticles for Drug Delivery by Electrospraying

The development of environmentally responsive drug carriers requires new methods for assembling stimuli-responsive nanoparticulates. This communication describes a novel application of electrospray to construct bioresponsive peptide-based particulates, which can encapsulate drugs. These particles are composed from genetically engineered elastin-like polypeptides (ELPs), a biodegradable, biocompatible, and bioresponsive polymer. To generate nanoparticles (300-400 nm in diameter), ELPs and drugs are codissolved in organic solvent, accelerated across a voltage gradient, dried by evaporation during transit, and collected from a target surface. These findings indicate that particle diameter, polydispersity, and morphology are strong functions of the solvent concentration, spraying voltage, and polymer molecular weight. Surprisingly, the loading of drug at 20 w/w% did not influence particle morphology; furthermore, drug release from these particles correlated with the pH-dependent solubility of the parent ELPs. These studies suggest that electrospray is an efficient and flexible method for generating stimuli-responsive drug particles.

Influence of AlF3 and ZnF2 on the phase transformation of gamma to alpha alumina

Abstract This paper focused on the effect of AlF 3 and ZnF 2 additives on the phase transformation of gamma to alpha alumina. AlF 3 and ZnF 2 were found to be effective accelerating agents on the gamma to alpha phase transformation. A single phase of alpha alumina, with an average particle size of 22 nm, can be obtained at 920 °C with AlF 3 additive. ZnF 2 can reduce the gamma to alpha transformation temperature to 900 °C, the average size of the particles is about 40 nm and the morphology of some particles is platelike with an aspect ratio of 2–4. The reduction of the transformation temperature was mainly attributed to the formation of intermediate compound of AlOF, which was considered to accelerate the mass transportation from transition alumina to alpha alumina. Moreover, mechanical milling and introducing alumina seeds uniformly worn from the milling mediums are also beneficial for reducing the transformation temperatures.

Electrosprayed core-shell microspheres for protein delivery.

This communication describes a single-step electrospraying technique that generates core-shell microspheres (CSMs) with encapsulated protein as the core and an amphiphilic biodegradable polymer as the shell. The protein release profiles of the electrosprayed CSMs showed steady release kinetics over 3 weeks without a significant initial burst.

Effect of glass additives on the strength and toughness of polycrystalline alumina

Abstract The effect of stress at grain boundaries on the mechanical properties of alumina ceramics was investigated. Residual stresses at grain-boundaries resulted from a mismatch in thermal expansion coefficient (TEC) between the alumina matrix and the glass-phase segregated at grain-boundaries. The BaO–Al2O3–SiO2 (BAS) system and the Li2O–Al2O3–SiO2 (LAS) system glasses were chosen to have a higher and a lower TEC than that of alumina, respectively, resulting in microscopic tensile and compressive stresses at grain-boundaries for Al2O3/BAS and Al2O3/LAS composites, respectively. The experimental results showed that the Al2O3/BAS composite fractured intergranularly with a fracture toughness higher than that of monolithic alumina. On the other hand, the Al2O3/LAS composite experienced transgranular fracture and high bending strength despite its low toughness. Both composites could be sintered to full density at 1500°C for 2 h due to the presence of a liquid phase. It was concluded that strengthening and toughening of alumina ceramics could be tailored by designing their grain-boundary microstresses.

Projectile impact and penetration in loose granular bed

Abstract Dynamics of a projectile impacting on a loose granular bed under the acceleration due to gravity g has been studied by fast video photograph. Granular jet formation and projectile penetration are observed in 3D and quasi-2D experiments. It is found that the penetration velocity u can be described by m du/dt=−γu−kz+mg′, where ³ and k are the parameters which characterize the viscous damping and hydrostatic drag forces of the bed, respectively, z is the penetration distance of the projectile, and g′ is a modified gravity term. The viscous damping term is found important in quasi-2D experiments. For 3D, the damping term is only important at the beginning of the impact, and can be neglected during penetration.

Microstructural development and mechanical properties of self-reinforced alumina with CAS addition

Abstract In-situ development of platelike alumina grains were obtained by adding CAS glass powder (CaO–Al2O3–SiO2) into fine alpha alumina powder sintered in the range from 1550 to 1600°C. The sintering behavior, microstructural development and mechanical properties of self-reinforced alumina ceramics with different amount of additives were investigated. The theoretical densities of the samples sintered at 1550°C reached >97% which appeared to be the optimal sintering temperature and the addition of CAS slightly decreased the densities of samples sintered from 1300 to 1600°C, compared with the samples without CAS additive. The platelike grains were not formed in alumina ceramics without adding CAS, even sintered at 1600°C. When the 0.1∼0.5 wt.% CAS glass powder was added to the starting composition, the platelike grains were formed completely at 1550°C. The formation of platelike grains increased the fracture toughness but decreased the bending strength, the combined action of crack deflection and crack bridging accounted for the observed increase of fracture toughness. The mechanical properties decreased with increasing the sintering temperatures from 1550 to 1660°C. Adding nano γ-Al2O3 can enhance the mechanical properties of the samples sintered at 1550 and 1600°C.

Electrical conductivity anomaly and X-ray photoelectron spectroscopy investigation of YCr1−xMnxO3 negative temperature coefficient ceramics

Electrical conductivity anomaly of perovskite-type YCr1−xMnxO3 negative temperature coefficient (NTC) ceramics produced by spark plasma sintering (SPS) has been investigated by using defect chemistry theory combination with X-ray photoelectron spectroscopy (XPS) analysis. From the results of the lnρ-1/T curves and the XPS analysis, it can be considered that YCr1−xMnxO3 ceramics exhibit the hopping conductivity. The major carriers in YCrO3 are holes, which are compensated by the oxygen vacancies produced due to the introduction of Mn ions. The Mn4+ ion contents increase monotonically in the range of 0.2 ≤ x ≤ 0.5. The resistivity increases at first and then decreases with increasing Mn contents, which has the same varying tendency with activation energy. The electrical conductivity anomaly appearing in these ceramics may be due to the variation of Cr4+ and Mn4+ ions concentration as Mn content changes.

Polymeric particle formation through electrospraying at low atmospheric pressure.

Electrospraying is a simple and versatile technique capable of producing polymeric particles. However, most investigations carried out thus far have been performed at ambient atmospheric pressure without studying the influences of pressure on the formation of polymeric particles. Here, we report our investigation on the effects of varying the pressure and the solution concentration on the microstructures of electrosprayed polymeric particles. Pressures are varied from ambient atmospheric pressure to 380 mmHg below ambient pressure, and solution concentrations are varied over a range of 3-7 w/v %. By varying these parameters, we manipulated the rate of solvent evaporation and the solidification of the electrosprayed particles. The results show that changes to the pressure had significant effects on the microstructure and morphology of poly(epsilon-caprolactone) (PCL) particles. The average particle size became larger as the chamber pressure decreased. At a solution concentration of 5 w/v % and a pressure 150 mmHg below ambient pressure, uniform and spherical PCL particles were generated. Electrospun fibers were formed when a solution concentration of 7 w/v % was used. The developed technique can be applied to prepare polymeric drug delivery carriers though a low-pressure-assisted spray-drying method, and is particularly suitable for fabricating delivery microspheres encapsulated with temperature-sensitive drugs and biomolecules.

In-situ growth of needlelike LaAl11O18 for reinforcement of alumina composites

Abstract In situ growth of needlelike LaAl11O18 grains reinforcing Al2O3 composites can be fabricated by a coprecipitation method using La(NO3)3 6H2O and Al(NO3)3 9H2O as starting materials. The new two-step process involved firstly preparing needlelike LaAl11O18 grains distributed homogeneously in Al2O3 powder and then pressureless sintering the composite powders. The Al2O3/25 vol.%LaAl11O18 samples pressureless sintered at 1550°C for 4 h achieve relative density up to 96.5% and exhibit a bending strength of 420±30 MPa and a fracture toughness of 4.3±0.4 MPa m1/2.

Luminescence of delafossite-type CuAlO2 fibers with Eu substitution for Al cations

Abstract CuAlO2 has been examined as a potential luminescent material by substituting Eu for Al cations in the delafossite structure. CuAlO2:Eu3+ nanofibers have been prepared via electrospinning for the ease of mitigating synthesis requirements and for future optoelectronics and emerging applications. Single-phase CuAlO2 fibers could be obtained at a temperature of 1100 °C in air. The Eu was successfully doped in the delafossite structure and two strong emission bands at ~405 and 610 nm were observed in the photoluminescence spectra. These bands are due to the intrinsic near-band-edge transition of CuAlO2 and the f-f transition of the Eu3+ activator, respectively. Further electrical characterization indicated that these fibers exhibit semiconducting behavior and the introduction of Eu could act as band-edge modifiers, thus changing the thermal activation energies. In light of this study, CuAlO2:Eu3+ fibers with both strong photoluminescence and p-type conductivity could be produced by tailoring the rare earth doping concentrations.