Mengmeng Sun

Rare earth elements modification of laser-clad nickel-based alloy coatings

Abstract The effects of rare earth oxide CeO2 and La2O3 on the microstructure and wear resistance of laser-clad nickel-based alloy coatings were investigated. The nickel-based alloy powders with different contents of CeO2 or La2O3 were laser-clad on to a steel substrate. The coatings were examined and tested for microstructural features, compositions, phase structure, and wear resistance. The results were compared with those for coatings without CeO2 and La2O3. The comparison indicated that the additions of rare earth oxide CeO2 or La2O3 can refine and purify the microstructure of coatings, reduce the dilution of clad material from base metal, form some new hard crystallographic phase and increase the microhardness of the coatings. As a result, by CeO2 or La2O3 addition, the friction coefficient of the coatings was decreased and the wear resistance of the coatings was enhanced significantly. The mechanism of these effects is also discussed in this paper.

Microstructure and corrosion resistance of laser clad coatings with rare earth elements

The eAects of rare earth oxides CeO2 and La2O3 on the microstructure and corrosion resistance of laser clad nickel-based alloy coatings were investigated. The nickel-based alloy powder with CeO2 or La2O3 was laser clad on to a steel substrate. The coatings were examined for microstructural features, compositions, phase structure and corrosion resistance. The results were compared with those for coatings without CeO2 and La2O3. The comparison indicated that the addition of CeO2 or La2O3 can refine and purify the microstructure of coatings and reduce dilution of clad material from the substrate. Moreover, the addition of rare earth oxide can cause the following variations of phase structure of the coating: (a) increase of diAraction angle, (b) decrease of interplanar spacing, (c) reduction of lattice constant and (d) appearance of new compounds with the rare earth. The corrosion resistance of clad coating with rare earths was enhanced significantly. The mechanism of these eAects is also discussed in this paper. ” 2001 Elsevier Science Ltd. All rights reserved.

Microstructural characteristics of laser clad coatings with rare earth metal elements

The microstructural characteristics of laser clad nickel-based alloy coatings with rare earth (RE) oxide CeO2 or La2O3 were investigated. Nickel-based alloy powder with different contents of CeO2 or La2O3 was laser clad onto a steel substrate. The clad coatings were examined and tested for microstructural features, chemical compositions and phase structure of the clad coatings. A scanning electron microscope (SEM) equipped with energy dispersive analysis X-rays (EDAX) was employed to observe the microstructure and analyze the chemical compositions of the clad coatings. The percentage of inclusion in the coatings was quantified by an image analysis system. The crystallographic phase formed during laser cladding was characterized by an X-ray diffractometer. The results were compared with coatings without CeO2 and La2O3. The comparison indicated that additions of RE oxide CeO2 or La2O3 can refine and purify the microstructure of coatings, and reduce the dilution of clad material from the substrate. Moreover, the addition of RE oxide can form some new hard crystallographic phase in the coatings. The mechanism of these effects is also discussed in this paper.

Effect of rare earth cerium on the microstructure and corrosion resistance of laser cladded nickel-base alloy coatings

Abstract The effect of rare earth cerium on the microstructure and corrosion resistance of laser cladded nickel-base self-fluxing alloy coatings has been studied. The nickel-base powder, with or without Ce, was flame-sprayed over AISI 1045 carbon steel and then remelted by a CO 2 laser. The microstructure, inclusions, phase structure and microhardness of the coatings were investigated. The corrosion resistance of the coatings was also measured by means of the weight-loss method and anodic polarization curves. The experimental results showed that the addition of Ce can lead to a finer microstructure and less inclusions in the coatings. As to the coatings containing Ce, the microhardness increased slightly whilst the corrosion resistance increased significantly. The mechanism of these effects are also discussed in the paper.

Effect of laser surface cladding of ceria on the wear and corrosion of nickel-based alloys

Abstract The effect of ceria (CeO2) on the wear and corrosion of laser-clad nickel-based alloy coatings was investigated. The results of microstructure observations, wear tests and corrosion tests show that the addition of CeO2 can modify the microstructure and properties of laser-clad coatings. The microstructure gets refined, the microhardness is increased, the inclusion percentage is reduced and the wear resistance and corrosion resistance are both improved. The mechanism of these effects is also discussed in this paper.

Thermally Triggered in Situ Assembly of Gold Nanoparticles for Cancer Multimodal Imaging and Photothermal Therapy

The assembly of gold nanoparticles (AuNPs) to AuNP assemblies is of interest for cancer therapy and imaging. Herein we introduce a new and general paradigm, thermally triggered AuNP assembly, for the development of novel intelligent platforms for cancer photothermal therapy (PTT) and multimodal imaging. Site-specific conjugation of a thermally sensitive elastin-like polypeptide (ELP) to AuNPs yields thermally sensitive ELP-AuNPs. Interestingly, ELP-AuNPs can in situ form AuNP assemblies composed of short necklace-like gold nanostructures at elevated temperatures and thus show strong near-infrared light absorption and high photothermal effect. These thermally responsive properties of ELP-AuNPs enable simultaneous photothermal/photoacoustic/X-ray computed tomographic imaging and PTT of melanoma after single intratumoral injection of ELP-AuNPs. The thermally triggered assembly of a variety of nanoparticles with optical, electronic, and magnetic properties into nanoparticle assemblies may open new ways for the establishment of intelligent platforms for various applications in biomedicine.

Tumour-homing chimeric polypeptide-conjugated polypyrrole nanoparticles for imaging-guided synergistic photothermal and chemical therapy of cancer

Near-infrared (NIR)-absorbing conjugated polymer nanoparticles are interesting for imaging-guided combination therapy, especially for synergistic photothermal therapy and chemotherapy; however, most of them target tumours passively through the enhanced permeability and retention (EPR) effect, leading to low utilization efficiency. To address this problem, we report an active tumour-targeting strategy of tumour-homing chimeric polypeptide-conjugated NIR-absorbing conjugated-polymer nanoparticles as a new class of drug nanocarriers for imaging-guided combination therapy of cancer. Methods: A tumour-homing chimeric polypeptide C-ELP-F3 was genetically engineered, and chemoselectively conjugated to polypyrrole (PPy) nanoparticles via a facile thiol-maleimide coupling reaction to form ELP-F3 conjugated PPy (PPy-ELP-F3) nanoparticles. Doxorubicin (DOX) was physically adsorbed onto PPy-ELP-F3 nanoparticles to yield DOX-loaded PPy-ELP-F3 (DOX/PPy-ELP-F3) nanoparticles. The physicochemical properties of DOX/PPy-ELP-F3 were characterized. The pharmacokinetics of DOX/PPy-ELP-F3 was studied in a mouse model. The photoacoustic imaging and photothermal imaging of tumours were tested in a melanoma-bearing mouse model. The photothermal-chemical combination therapy of tumours was investigated by using melanoma cells in vitro and in a melanoma-bearing mouse model. Results: DOX/PPy-ELP-F3 nanoparticles showed enhanced cytotoxicity to melanoma cells in vitro and improved tumour-targeting efficiency in vivo, as compared with both DOX/PPy-ELP nanoparticles without the tumour-homing function and free DOX. The photothermal effect of DOX/PPy-ELP-F3 nanoparticles could accelerate the release of DOX from PPy-ELP-F3. Under the guidance of photoacoustic and photothermal imaging, the synergy of photothermal and chemical therapy could completely abolish tumours without detectable systemic toxicity. Conclusion: Tumour-homing chimeric polypeptide-conjugated NIR-absorbing conjugated-polymer nanoparticles are promising as a new multifunctional drug delivery platform for highly-efficient imaging guided combination therapy.

Polymerization Induced Self-Assembly of a Site-Specific Interferon α-Block Copolymer Conjugate into Micelles with Remarkably Enhanced Pharmacology

Conjugating a hydrophilic and protein-resistant polymer to a protein is a widely used strategy to extend the in vivo half-life of the protein; however, the benefit of the half-life extension is usually limited by the bioactivity decrease. Herein we report a supramolecular self-assembly strategy of site-specific in situ polymerization induced self-assembly (SI-PISA) to address the dilemma. An amphiphilic block copolymer (POEGMA-PHPMA) was directly grown from the C-terminus of an important therapeutic protein interferon-α (IFN) to in situ form IFN-POEGMA-PHPMA conjugate micelles. Notably, the in vitro bioactivity of the micelles was 21.5-fold higher than that of the FDA-approved PEGylated interferon-α PEGASYS. Particularly, the in vivo half-life of the micelles (83.8 h) was 1.7- and 100-fold longer than those of PEGASYS (49.5 h) and IFN (0.8 h), respectively. In a tumor-bearing mouse model, the micelles completely suppressed tumor growth with 100% animal survival, whereas at the same dose, PEGASYS and IFN were much less effective. These findings suggest that SI-PISA is promising as a next-generation technology to remarkably enhance the pharmacological performance of therapeutic proteins with short circulation half-lives.

Site-Selective in situ Growth-Induced Self-Assembly of Protein-Polymer Conjugates into pH-Responsive Micelles for Tumor Microenvironment Triggered Fluorescence Imaging

Self-assembly of site-selective protein-polymer conjugates into stimuli-responsive micelles is interesting owing to their potential biomedical applications, ranging from molecular imaging to drug delivery, but remains a significant challenge. Herein we report a method of site-selective in situ growth-induced self-assembly (SIGS) to synthesize site-specific human serum albumin-poly(2-(diisopropylamino)ethyl methacrylate) (HSA-PDPA) conjugates that can in situ self-assemble into pH-responsive micelles with tunable morphologies. Indocyanine green (ICG) was selectively loaded into the core of sphere-like HSA-PDPA micelles to form pH-responsive fluorescence nanoprobes. The nanoprobes rapidly dissociated into protonated individual unimers at a transition pH of around 6.5, that is the extracellular pH of tumors, which resulted in a sharp fluorescence increase and markedly enhanced cellular uptake. In a tumor-bearing mouse model, they exhibited greatly enhanced tumor fluorescence imaging as compared to ICG alone and pH-nonresponsive nanoprobes. These findings suggest that pH-responsive and site-selective protein-polymer conjugate micelles synthesized by SIGS are promising as a new class of tumor microenvironment-responsive nanocarriers for enhanced tumor imaging and therapy.