Donglu Shi

A carbon nanotube strain sensor for structural health monitoring

A carbon nanotube polymer material was used to form a piezoresistive strain sensor for structural health monitoring applications. The polymer improves the interfacial bonding between the nanotubes. Previous single walled carbon nanotube buckypaper sensors produced distorted strain measurements because the van der Waals attraction force allowed axial slipping of the smooth surfaces of the nanotubes. The polymer sensor uses larger multi-walled carbon nanotubes which improve the strain transfer, repeatability and linearity of the sensor. An electrical model of the nanotube strain sensor was derived based on electrochemical impedance spectroscopy and strain testing. The model is useful for designing nanotube sensor systems. A biomimetic artificial neuron was developed by extending the length of the sensor. The neuron is a long continuous strain sensor that has a low cost, is simple to install and is lightweight. The neuron has a low bandwidth and adequate strain sensitivity. The neuron sensor is particularly useful for detecting large strains and cracking, and can reduce the number of channels of data acquisition needed for the health monitoring of large structures.

Fluorescent, Superparamagnetic Nanospheres for Drug Storage, Targeting, and Imaging: A Multifunctional Nanocarrier System for Cancer Diagnosis and Treatment

For early cancer diagnosis and treatment, a nanocarrier system is designed and developed with key components uniquely structured at nanoscale according to medical requirements. For imaging, quantum dots with emissions in the near-infrared range (∼800 nm) are conjugated onto the surface of a nanocomposite consisting of a spherical polystyrene matrix (∼150 nm) and the internally embedded, high fraction of superparamagnetic Fe(3)O(4) nanoparticles (∼10 nm). For drug storage, the chemotherapeutic agent paclitaxel (PTX) is loaded onto the surfaces of these composite multifunctional nanocarriers by using a layer of biodegradable poly(lactic-co-glycolic acid) (PLGA). A cell-based cytotoxicity assay is employed to verify successful loading of pharmacologically active drug. Cell viability of human, metastatic PC3mm2 prostate cancer cells is assessed in the presence and absence of various multifunctional nanocarrier populations using the MTT assay. PTX-loaded composite nanocarriers are synthesized by conjugating anti-prostate specific membrane antigen (anti-PSMA) for targeting. Specific detection studies of anti-PSMA-conjugated nanocarrier binding activity in LNCaP prostate cancer cells are carried out. LNCaP cells are targeted successfully in vitro by the conjugation of anti-PSMA on the nanocarrier surfaces. To further explore targeting, the nanocarriers conjugated with anti-PSMA are intravenously injected into tumor-bearing nude mice. Substantial differences in fluorescent signals are observed ex vivo between tumor regions treated with the targeted nanocarrier system and the nontargeted nanocarrier system, indicating considerable targeting effects due to anti-PSMA functionalization of the nanocarriers.

Engineered Redox-Responsive PEG Detachment Mechanism in PEGylated Nano-Graphene Oxide for Intracellular Drug Delivery

In biomedical applications, polyethylene glycol (PEG) functionalization has been a major approach to modify nanocarriers such as nano-graphene oxide for particular biological requirements. However, incorporation of a PEG shell poses a significant diffusion barrier that adversely affects the release of the loaded drugs. This study addresses this critical issue by employing a redox-responsive PEG detachment mechanism. A PEGylated nano-graphene oxide (NGO-SS-mPEG) with redox-responsive detachable PEG shell is developed that can rapidly release an encapsulated payload at tumor-relevant glutathione (GSH) levels. The PEG shell grafted onto NGO sheets gives the nanocomposite high physiological solubility and stability in circulation. It can selectively detach from NGO upon intracellular GSH stimulation. The surface-engineered structures are shown to accelerate the release of doxorubicin hydrochloride (DXR) from NGO-SS-mPEG 1.55 times faster than in the absence of GSH. Confocal microscopy shows clear evidence of NGO-SS-mPEG endocytosis in HeLa cells, mainly accumulated in cytoplasm. Furthermore, upon internalization of DXR-loaded NGO with a disulfide-linked PEG shell into HeLa cells, DXR is effectively released in the presence of an elevated GSH reducing environment, as observed in confocal microscopy and flow cytometric experiments. Importantly, inhibition of cell proliferation is directly correlated with increased intracellular GSH concentrations due to rapid DXR release.

Effect of silver and silver oxide additions on the mechanical and superconducting properties of YBa2Cu3O7−δ superconductors

The effects of Ag and Ag2 O additions on the mechanical and superconducting properties of YBa2 Cu3 O7−δ superconductors were studied. The addition of 20‐vol % Ag resulted in an increase in strength from ≊40 to 75 MPa and a twofold increase in the critical current density (Jc ) of YBa2 Cu3 O7−δ bar specimens. These improvements are believed to be due to the increased density. Furthermore, Ag particles may relax the residual stresses resulting from the expansion anisotropy of individual grains, and may provide increased resistance to crack propagation by pinning the propagating cracks; these effects would also increase the strength. The addition of 30‐vol % Ag resulted in an increase in strength to 87 MPa, but it was associated with a decrease in Jc . This decrease in Jc at high Ag content is believed to be due to the presence of oxygen deficient nonsuperconducting tetragonal phase as well as continuous Ag phase. Similar effects were also observed after Ag2 O additions.

Plasma coating of carbon nanofibers for enhanced dispersion and interfacial bonding in polymer composites

Ultrathin films of polystyrene were deposited on the surfaces of carbon nanofibers using a plasma polymerization treatment. A small percent by weight of these surface-coated nanofibers were incorporated into polystyrene to form a polymer nanocomposite. The plasma coating greatly enhanced the dispersion of the nanofibers in the polymer matrix. High-resolution transmission-electron-microscopy (HRTEM) images revealed an extremely thin film of the polymer layer (∼3 nm) at the interface between the nanofiber and matrix. Tensile test results showed considerably increased strength in the coated nanofiber composite while an adverse effect was observed in the uncoated composites; the former exhibited shear yielding due to enhanced interfacial bonding while the latter fractured in a brittle fashion.

Preparation of Bi‐Sr‐Ca‐Cu‐O superconductors from oxide‐glass precursors

A superconductor and precursor therefor from oxide mixtures of Ca, Sr, Bi and Cu. Glass precursors quenched to elevated temperatures result in glass free of crystalline precipitates having enhanced mechanical properties. Superconductors are formed from the glass precursors by heating in the presence of oxygen to a temperature below the melting point of the glass.

Dual Surface-Functionalized Janus Nanocomposites of Polystyrene/Fe3O4@SiO2 for Simultaneous Tumor Cell Targeting and Stimulus-Induced Drug Release

Folic acid (FA) and doxorubicin (DOX) are coupled separately onto Fe3 O4 @SiO2 and polystyrene surfaces of a unique polystyrene/Fe3 O4 @SiO2 Janus structure. This super-paramagnetic, dual-functionalized Janus nanocomposite enables effective tumor cell targeting and internalization via the folate receptor, and induces significant cancer cell death by controlled, stimulus-induced drug release under acidic conditions in endosomal compartments.

Uniform deposition of ultrathin polymer films on the surfaces of Al2O3 nanoparticles by a plasma treatment

Surface modification of nanoparticles will present great challenges due to their extremely small dimensions, high surface areas, and high surface energies. In this research, we demonstrate the uniform deposition of ultrathin polymer films of 2 nm on the surfaces of alumina nanoparticles. The deposited film can also be tailored to multilayers. Time-of-flight secondary ion mass spectroscopy was used to confirm the pyrrole thin film on the nanoparticle surfaces. Using such a nanocoating, it is possible to alter the intrinsic properties of materials that cannot be achieved by conventional methods and materials.

Plasma deposition of Ultrathin polymer films on carbon nanotubes

Ultrathin films of pyrrole were deposited on the surfaces of carbon nanotubes using a plasma polymerization treatment. High-resolution electron transmission microscopy images revealed that an extremely thin film of the polymer layer (2∼7 nm) was uniformly deposited on the outer and inner surfaces of the nanotubes. The nanotubes of all sizes exhibited equally uniform ultrathin films, indicating well-dispersed nanotubes in the fluidized bed reactor during the plasma treatment. In particular, the inner wall of the nanotube was also coated with a uniform ultrathin film of only ∼1–3 nm. Time-of-flight secondary ion mass spectroscopy experiments confirmed the highly branched and cross-linked polymer thin films on the carbon nanotubes. The plasma deposition mechanism is discussed in this letter.

Introduction to biomaterials

# Bioactive Ceramics and Metals: # Introduction to Bioceramics # Bioactive Ceramics: Structure, Synthesis, and Mechanical Properties # Bioceramic Processing # Coating of Hydroxyapatite onto Inner Pore Surfaces of the Reticulated Alumina # Properties and Characterization of Biomaterials # Bioactivity of Hydroxyapatite # Hydroxyapatite Deposition Mechanisms # Biomedical Metallic Materials # Polymeric Biomaterials: # Polymer Basics # Naturally Occurring Polymer Biomaterials # Synthetic Non-Biodegradable Polymers # Synthetic Biodegradable Polymers # Polymer Matrix Composite Biomaterials # Tissue Engineering: A New Era of Regenerative Medicine: # Biomaterials for Tissue Engineering # Cells and Biomolecules for Tissue Engineering # Transport and Vascularization in Tissue Engineering # Host Response to Tissue Engineered Grafts # Other Important Issues and Future Challenges in Tissue Engineering