H. D. Li

Tsinghua University, Beijing, Beijing Shi, China

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Publications (34)60 Total impact

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    ABSTRACT: Brain tissue engineering in the postinjury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for either transplanted or resident cells. In this article, a hyaluronic acid (HA)-poly-D-lysine (PDL) copolymer hydrogel with an open porous structure and viscoelastic properties similar to neural tissue has been developed for brain tissue engineering. The chemicophysical properties of the hydrogel with HA:PDL ratios of 10:1, 5:1, and 4:1 were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectrometry. Neural cells cultured in the hydrogel were studied by phase-contrast microscope and SEM. The incorporation of PDL peptides into the HA-PDL hydrogel allowed for the modulation of neuronal cell adhesion and neural network formation. Macrophages and multinucleated foreign body giant cells found at the site of implantation of the hydrogel in the rat brain within the first weeks postimplantation decreased in numbers after 6 weeks, consistent with the host response to inert implants in numerous tissues. Of importance was the infiltration of the hydrogel by glial fibrillary acidic protein-positive cells-reactive astrocytes-by immunohistochemistry and the contiguity between the hydrogel and the surrounding tissue demonstrated by SEM. These findings indicated the compatibility of this hydrogel with brain tissue. Collectively, the results demonstrate the promise of an HA-PDL hydrogel as a scaffold material for the repair of defects in the brain.
    Tissue Engineering 03/2005; 11(3-4):513-25. · 4.25 Impact Factor
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    ABSTRACT: Nogo-66 and NgR are important receptors inhibiting neuronal regeneration and therefore are targets for treating CNS injury. Antagonists of this receptor including blocking antibodies are potential therapeutic agents for CNS axonal injuries such as spinal cord and brain trauma. A new antibody (IgG) releasing system has been developed by covalently attaching IgG to the biodegradable hyaluronic acid (HA) hydrogel via the hydrolytically unstable hydrazone linkage, aiming to deliver the antibody of CNS regeneration inhibitors to the injured brain. In this paper we describe the synthesis, physico-chemical characteristics and test results of biological activity of antibody released from hyluronic acid hydrogel. To form the conjugates the antibody is attached to the polymer backbone using a condensation reaction between aldehyde group of the antibody and hydrazide group of the HA hydrogel. Furthermore, pH sensitive linkage-hydrozone has been formed between hydrogel and antibody. The amount of conjugated antibodies can reach 135 microg antibody/mg hydrogel in the dry state. At low pH, the antibodies released quite fast. However, the antibodies released much slower in neutral and alkaline environment. The bioactivity of antibody released from hydrogel was retained as demonstrated by indirect immunofluorescence technique.
    Journal of Controlled Release 02/2005; 102(1):13-22. · 7.63 Impact Factor
  • W. Y Zou, Q Cai, F. Z Cui, H. D Li
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    ABSTRACT: In summary, a new method for the electrochemical preparation of mesoporous alloy of Cu/Cu2O film was introduced. In terms of hierarchical order structure, the best results were achieved using low concentration of the anionic surfactant SDS (
    Materials Letters - MATER LETT. 01/2003; 57(13):1934-1940.
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    ABSTRACT: A biomimetic calcium phosphate coating is expected to enhance the bioactivity and bone inductivity of human implants. This study presents a very simple, highly effective biomimetic method to obtain a calcium phosphate coating on a titanium substrate. Using NaH2PO4, a stable solution was prepared with high calcium and phosphate ion concentrations. This solution turned to a supersaturated calcification solution (SCS) when NaHCO3 was added. The addition of NaHCO3 elevated the pH value of the solution gradually and steadily. A uniform coating approximately 40 μm thick was found on the substrates after 24 h immersion. The compositions of the coatings were adjustable from hydroxyapatite (HA) to HA/dicalcium phosphate dihydrate (DCPD). The calcium phosphate deposits were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transformed infrared (FT-IR) spectroscopy.
    Surface and Coatings Technology 01/2002; · 1.94 Impact Factor
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    Q. L Feng, X Zhu, H. D Li, T. N Kim
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    ABSTRACT: The structure and crystallographic orientation of different layers (the cone layer, palisade layer and the crystal layer) in ostrich eggshells were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM) with selected area electron diffraction (SAED). It is found that the degree of 001 preferred orientation enhanced from inner to outer ostrich eggshells. A crystallographic orientation regulation was observed for the first time. The adjacent 1–5 calcite crystals with the same three-dimensional orientation are proposed to form a crystalline cluster with the size of several microns. The a-axes in the neighboring clusters orient from several degrees to tens of degrees.
    Journal of Crystal Growth 01/2001; 233(3):548-554. · 1.55 Impact Factor
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    ABSTRACT: The structure and crystallographic orientation of mineral phase in the oblique prismatic layer of Mytilus edulis shell were studied by SEM, XRD and TEM with selected area electron diffraction (SAED). A crystallographic orientation regulation, i.e. the adjacent 1–5 calcite prisms with the same three-dimensional orientation in the oblique prismatic layer, was found for the first time. It is observed that the calcite prisms in the oblique prismatic layer were grown with their (104) parallel to the shell surface.
    Journal of Materials Science 01/2000; 35(13):3337-3340. · 2.31 Impact Factor
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    ABSTRACT: Based on the investigations of crystal structure of nacre using SEM, TEM and XRD, it is proposed that there exists a domain structure of crystal orientation in the nacre. The orientation domain consists of continuous 3–10 tablets along the direction perpendicular to nacreous plane, and 1–5 tablets in a single lamina. The tablets in a domain are crystallographic identical in three dimensions. From the crack morphologies, it is found that the crack deflection, fibre pull-out and organic matrix bridging are the three main toughening mechanisms acting on nacre. The organic matrix plays an important role in the toughening of this biological composite. The biomimetically synthesized composite made of alumina and kevlar showed significant increase in the fracture energy compared with the single ceramics. The soluble proteins extracted from nacre can induce aragonite and the one from prism can induce calcite grown with a preferred orientation of [104]. The insoluble proteins control the nucleation site and thus lead to a finer crystallization of CaCO3.
    Materials Science and Engineering C 01/2000; · 2.40 Impact Factor
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    ABSTRACT: Degradability is among the most important properties in the biomedical field, which is crucial to bone apposition on implants, bone-implant bonding and implantation longevity. The present paper evaluated the degradability of ion beam-assisted deposition (IBAD) hydroxyapatite (HA) coatings in vitro and in vivo. In vitro testing showed that IBAD HA coatings degraded little in 37°C sterile Hank’s physiologic (pH 5.2) balanced salt solution throughout the testing time, while the plasma-sprayed HA coating tested in comparison underwent an increasing degradation: the concentration of Ca increased from the initial 1 ml to 2.75 ml at 3 days post-incubation. In vivo testing revealed that no significant degradation occurred throughout the whole implant period (12 weeks). All the results consistently suggest that the IBAD HA coating is slightly degradable. High magnification SEM observation and HRTEM investigations of the coating further pointed out that the low degradability of the IBAD HA coating derives from its dense microstructure and unique properties such as no sharp grain boundaries. The present study demonstrates that IBAD HA coatings are much more chemically stable than plasma-sprayed HA coatings. The IBAD HA coating possesses more superior adhesive properties, as would be of clinical importance in that it may favor a longer longevity of orthopedic implants.
    Surface and Coatings Technology 01/2000; 131(1):192-195. · 1.94 Impact Factor
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    Journal of Materials Science Letters 09/1999; 18(19):1547-1549.
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    ABSTRACT: Carbon nitride thin films have been prepared by NH3-ion-beam-assisted deposition with bombardment energies of 200-800 eV at room temperature. These films have been characterized by transmission electron microscopy, Auger electron spectroscopy and x-ray photoelectron spectroscopy for chemical analysis. It was found that the structure of the films varied with the bombardment energy. In the case of 400 eV bombardment, the tiny crystallites immersed on an amorphous matrix were identified to be beta -C3N4. X-ray photoelectron spectroscopy indicated that some carbon atoms and nitrogen atoms form unpolarized covalent bonds in these films.
    Journal of Physics Condensed Matter 12/1998; 6(31):6125. · 2.22 Impact Factor
  • J.L He, W.Z Li, H.D Li, C.H Liu
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    ABSTRACT: Nanoscale TiC–metal (Al, Cu, Fe, W) multilayers were prepared by ion beam sputtering deposition with an intent to study the plastic properties of the ceramic–metal combinations. The multilayers were designed to have different layer thickness arrangements, including component fraction, modulation wavelength, etc. Their toughness and hardness were systematically investigated as well as the laminated structures. It was found that for most TiC–metal multilayers the toughness was significantly improved in comparison with monolithic TiC, but the hardness showed great dependence on the material system. In TiC–Fe and TiC–W systems, the multilayer hardness exhibited a peak value which was even higher than the hardness of TiC. In TiC–Al and TiC–Cu systems, no superhardness effect was detected.
    Surface and Coatings Technology 05/1998; · 1.94 Impact Factor
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    ABSTRACT: The structure and morphology of Si3N4/TiN multilayer synthesized by ion beam assisted deposition (IBAD) were studied by X-ray diffraction (XRD), Auger electron spectrum (AES) and Field-emmision scanning electron microscopy (FESEM). It was found that a well-defined multilayer structure was formed. The multilayer was composed of polycrystalline TiN and amorphous Si3N4. The compositions were determined as N:Ti=1 and N:Si=0.9, respectively. Ion beam etching technique was employed to prepare special specimen for FESEM morphology observation. Cross-sectional FESEM was also conducted. Results showed that the Si3N4 layers consisted of granular particles of about 100 nm in size and the particles in TiN layers were much smaller.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 02/1998; 135(s 1–4):397–400. · 1.19 Impact Factor
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    ABSTRACT: Ion beam sputter deposition was employed to prepare nanoscale multilayers of TiC and a polymeric material, Teflon. The multilayers were synthesized to simulate nacre not only on laminated structures but also on individual layer thicknesses. The laminated architecture was studied as well as the structures of individual layers. Multilayer toughness and hardness were systematically investigated. It was found that the toughness of TiC/Teflon multilayers was significantly improved in comparison with monolithic TiC. But the multilayer hardness experienced a serious decrease. The individual layer thickness arrangement had an influence on both the multilayer hardness and the toughness.
    Surface & Coatings Technology - SURF COAT TECH. 01/1998; 103:109-112.
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    ABSTRACT: Ion beam sputtering technique was employed to prepare thin films of Polytetrafluoroethylene (PTFE). Simultaneous ion beam bombardment during film growth was also conducted in order to study the bombardment effects. Infrared absorption (IR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis was used to evaluate the material's integrity. It was found that PTFE thin films could be grown at room temperature by direct sputtering of a PTFE target. The film's composition and structure were shown to be dependent on the sputtering energy. Films deposited by single sputtering at higher energy (~1500eV) were structurally quite similar to the original PTFE material. Simultaneous ion beam bombarding during film growth caused defluorination and structural changes. Mechanism for sputtering deposition of such a polymeric material is also discussed.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/1998; 135:512-516. · 1.19 Impact Factor
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    ABSTRACT: Inspired by the ingenious architecture of nacre and its outstanding mechanical properties, we prepared nanoscale ceramic (TiC, Si3N4, B4C) /Teflon multilayers by ion beam sputtering deposition at room temperature. The toughness, hardness and tribological properties were systematically investigated as well as the multilayer structures. It was found that the toughness of ceramic/Teflon multilayers were all significantly improved in comparison with the corresponding monolithic ceramic material, but the hardness was decreased. However, there were optimized layer thickness arrangements with which the multilayer toughness and hardness can be favorably combined to obtain better comprehensive properties. It was found by this study that ceramic/polymer multilayers with the optimized layer thickness arrangement had good performance in wear resistance.
    Materials Chemistry and Physics 01/1998; 54(1):334-337. · 2.07 Impact Factor
  • J. L. He, W. Z. Li, H. D. Li
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    ABSTRACT: TiN/Pt multilayers with individual thicknesses between 1 and 8 nm were prepared by ion beam sputtering deposition to simulate the micro-laminated architecture of nacre. Multilayer hardness and the laminated structure were investigated. It was found that sharp but incoherent interfaces were formed between individual layers. The multilayer hardness had strong dependence on layer arrangement. The range of layer thickness appropriate for high hardness was experimentally determined. Hardness enhancement of 30–70% was generally observed. With the layer thickness properly adjusted, the multilayer can even be harder than the hard component (TiN). Annealing experiments indicated that the hardness enhancement was an intrinsic property of the TiN/Pt multilayers.
    Journal of Materials Research. 10/1997; 12(11):3140 - 3145.
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    ABSTRACT: Multi-functional ion beam assisted deposition (IBAD) equipment with 8 targets and 4 ion sources has been developed to synthesize coatings and multi-layers of many combinations.DLC, TiN, TiC coatings have been investigated with special attention paid to DLC. It is found that a narrow energy window exists at about 200 eV in order to serve more prominent diamond bondings and diamond-like properties. The surface is hard and smooth with a friction coefficient of less than 0.05. The improvement of the interfacial structure enables DLC coatings on 52100 steel to sustain uniform wear at high wear loads (up to 120 N). Applications of DLC and other coatings in material surface modification are being explored.By alternate sputtering, TiC/Metal multi-layers have been prepared. The individual layers vary in thickness from 1 to 10 nm and the periods vary from 3 to 18 nm. The ceramic phase has been maintained as TiC, whilst Fe, Cr, Nb, Zr, Ni, Cu and Al have been used as the metal phase. The hardness and toughness of these laminated nanocrystalline films have been investigated, the results showing the dependence of the properties on the modulation of the multi-layers as well as on the characteristics of the metal phase.
    Journal of Materials Processing Technology 01/1997; 63(1):902-907. · 1.95 Impact Factor
  • J. L. He, J. Wang, W. Z. Li, H. D. Li
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    ABSTRACT: TiN/Pt multilayers with individual layer thickness between 1 and 8 nm have been prepared by ion beam sputtering deposition to simulate the nacreous structure in natural nacre. Both the hardness and toughness were systematically investigated together with a study of structures of the multilayer. It was found that [111] texture developed during the alternative deposition of TiN and Pt. The multilayer toughness was higher than that of pure TiN. The hardness was greater than the volume weighted mean of the hardness of two components (i.e. TiN and Pt). Both the multilayer hardness and toughness showed a strong dependence on the individual layer thickness arrangement. When the individual thickness was properly adjusted, the multilayer can even be harder than its hard component (TiN) while the toughness was also greatly improved. Annealing experiment indicated that such an enhancement was an intrinsic property of the multilayers. Some suggestions for microdesigning of materials are thus proposed.
    Materials Science and Engineering B 01/1997; 49(2):128-134. · 1.85 Impact Factor
  • J.L. He, W.Z. Li, H.D. Li
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    ABSTRACT: Nanometer scale multilayers have been prepared by ion beam sputtering deposition to mimic the structure of natural nacre. The hardness of these multilayers was studied. It was found that the multilayer hardness was greater than the volume weighted mean of the component hardness. It also showed a dependence on the individual layer thickness arrangement. With the individual thickness property adjusted, the multilayer was even harder than its hard component (TiN). Annealing experiments indicated that such a hardness enhancement was an intrinsic property of multilayers.
    Materials Letters. 01/1997; 30(1):15-18.
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    ABSTRACT: Carbon nitride thin films were prepared by nitrogen-ion-beam-assisted deposition. Auger electron spectroscopy shows that the N/C atomic composition ratio increases with increasing current density and decreasing bombarding energy of the nitrogen ion beam. At a bombarding energy of 200 eV and a current density of 0.2 mA cm−2, a maximum N/C ratio of 0.54 is obtained and crystalline β-C3N4 grains with dimensions of about 0.1 μm are observed by transmission electron microscopy. This film displays a high Knoop hardness of 4450 kgf mm−2 and a resistivity of 109Ω cm.
    Surface and Coatings Technology 10/1996; 84:388-391. · 1.94 Impact Factor