Junhua Wei

Bio: Junhua Wei is an academic researcher from Texas Tech University. The author has contributed to research in topics: Self-healing hydrogels & Graphene. The author has an hindex of 15, co-authored 32 publications receiving 1548 citations. Previous affiliations of Junhua Wei include PARC.

Additive manufacturing of carbon fiber reinforced thermoplastic composites using fused deposition modeling

Abstract: Additive manufacturing (AM) technologies have been successfully applied in various applications. Fused deposition modeling (FDM), one of the most popular AM techniques, is the most widely used method for fabricating thermoplastic parts those are mainly used as rapid prototypes for functional testing with advantages of low cost, minimal wastage, and ease of material change. Due to the intrinsically limited mechanical properties of pure thermoplastic materials, there is a critical need to improve mechanical properties for FDM-fabricated pure thermoplastic parts. One of the possible methods is adding reinforced materials (such as carbon fibers) into plastic materials to form thermoplastic matrix carbon fiber reinforced plastic (CFRP) composites those could be directly used in the actual application areas, such as aerospace, automotive, and wind energy. This paper is going to present FDM of thermoplastic matrix CFRP composites and test if adding carbon fiber (different content and length) can improve the mechanical properties of FDM-fabricated parts. The CFRP feedstock filaments were fabricated from plastic pellets and carbon fiber powders for FDM process. After FDM fabrication, effects on the tensile properties (including tensile strength, Young's modulus, toughness, yield strength, and ductility) and flexural properties (including flexural stress, flexural modulus, flexural toughness, and flexural yield strength) of specimens were experimentally investigated. In order to explore the parts fracture reasons during tensile and flexural tests, fracture interface of CFRP composite specimens after tensile testing and flexural testing was observed and analyzed using SEM micrograph.

Novel fluorescence resonance energy transfer optical sensors for vitamin B12 detection using thermally reduced carbon dots

Abstract: In this paper, a novel thermally-reduced carbon dot (t-CD) based fluorescence resonance energy transfer (FRET) sensor for the determination of vitamin B12 (VB12) in aqueous solutions is reported. Carbon dots (CDs) have attracted great attention due to their excellent tunable optical properties, low cost, easy fabrication and low toxicity, which make them ideal candidates for optical sensors. Through esterification reactions, blue luminescent t-CDs were prepared by the carbonization of citric acid and thermally reduced by a thermogravimetric analyzer. After thermal reduction, the quantum yield of the t-CDs demonstrated a 5-fold increase, which makes t-CDs excellent donors in the FRET process. The t-CDs were used to detect VB12 with concentrations ranging from 1 to 12 μg ml−1 and their limit of detection (LOD) was as low as 0.1 μg ml−1. The as-synthesized t-CD based optical probing technique is demonstrated to be simple, cost-effective, sensitive and selective for the detection of biologically significant VB12.

3D printing of an extremely tough hydrogel

Abstract: Because of their low viscosity and large gelling temperature range, precise 3D printing of agar hydrogels has not been achieved even though the agar double network hydrogels are tough and self-recoverable. In this work, a super tough agar double network hydrogel was precisely printed by adding alginate. The addition of alginate not only increases the ink viscosity and printable period, but also improves its rheological characteristics towards precise processing control. Moreover, the entanglement of the alginate chains with the agar double network hydrogel restricts the agar helical chain bundles from pulling out under stress, which toughens the hydrogel.

Efficient photothermal therapy of brain cancer through porphyrin functionalized graphene oxide

Abstract: Current clinical treatments including surgical resection, radiation therapy and chemotherapy for brain cancer result in high mortality due to the complex structure of the brain aggressiveness of brain cancer. Recently, non-invasive photothermal therapy (PTT) using near infrared laser irradiation has been developed as an alternative emerging therapy for brain cancer. In this paper, a biocompatible porphyrin functionalized graphene oxide (PGO) with high absorbance at 808 nm is synthesized as a photothermal platform for brain cancer therapy. Graphite oxide is exfoliated and conjugated with porphyrin through π–π interactions. This PGO is two times more stable than reduced graphene oxide (rGO) in aqueous solution. Most importantly, the efficiency of the photo-thermal conversion of PGO is increased by 89% and 33% compared to graphene oxide and rGO under 808 nm laser irradiation, causing ablation of a large number of brain cancer cells in vitro. This PGO platform containing active functional groups allows specific targeting in PTT without harming healthy cells and tissues.

A reduced graphene oxide based electrochemical biosensor for tyrosine detection.

Abstract: In this paper, a 'green' and safe hydrothermal method has been used to reduce graphene oxide and produce hemin modified graphene nanosheet (HGN) based electrochemical biosensors for the determination of l-tyrosine levels. The as-fabricated HGN biosensors were characterized by UV-visible absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy (FTIR) spectra and thermogravimetric analysis (TGA). The experimental results indicated that hemin was successfully immobilized on the reduced graphene oxide nanosheet (rGO) through π-π interaction. TEM images and EDX results further confirmed the attachment of hemin on the rGO nanosheet. Cyclic voltammetry tests were carried out for the bare glass carbon electrode (GCE), the rGO electrode (rGO/GCE), and the hemin-rGO electrode (HGN/GCE). The HGN/GCE based biosensor exhibits a tyrosine detection linear range from 5 × 10(-7) M to 2 × 10(-5) M with a detection limitation of 7.5 × 10(-8) M at a signal-to-noise ratio of 3. The sensitivity of this biosensor is 133 times higher than that of the bare GCE. In comparison with other works, electroactive biosensors are easily fabricated, easily controlled and cost-effective. Moreover, the hemin-rGO based biosensors demonstrate higher stability, a broader detection linear range and better detection sensitivity. Study of the oxidation scheme reveals that the rGO enhances the electron transfer between the electrode and the hemin, and the existence of hemin groups effectively electrocatalyzes the oxidation of tyrosine. This study contributes to a widespread clinical application of nanomaterial based biosensor devices with a broader detection linear range, improved stability, enhanced sensitivity and reduced costs.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

Abstract: Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

3D printing of polymer matrix composites: A review and prospective

Abstract: The use of 3D printing for rapid tooling and manufacturing has promised to produce components with complex geometries according to computer designs. Due to the intrinsically limited mechanical properties and functionalities of printed pure polymer parts, there is a critical need to develop printable polymer composites with high performance. 3D printing offers many advantages in the fabrication of composites, including high precision, cost effective and customized geometry. This article gives an overview on 3D printing techniques of polymer composite materials and the properties and performance of 3D printed composite parts as well as their potential applications in the fields of biomedical, electronics and aerospace engineering. Common 3D printing techniques such as fused deposition modeling, selective laser sintering, inkjet 3D printing, stereolithography, and 3D plotting are introduced. The formation methodology and the performance of particle-, fiber- and nanomaterial-reinforced polymer composites are emphasized. Finally, important limitations are identified to motivate the future research of 3D printing.