Surface-modified hydroxyapatite linked byL-lactic acid oligomer in the absence of catalyst

Journal of Polymer Science Part A Polymer Chemistry (Impact Factor: 3.54). 01/2005; 43(21):5177-5185. DOI:10.1002/pola.21006
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    ABSTRACT: The objectives of this study are to investigate the properties of high aspect-ratio hydroxyapatite (HAP) nanofibers and the reinforcing effect of such fibers on bisphenol A glycidyl methacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) dental resins (without silica microparticle filler) and dental composites (with silica microparticle filler) with various mass fractions (loading rates). HAP nanofibers were synthesized using a wet-chemical method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermal gravimetric analysis (TGA). Biaxial flexural strength (BFS) of the HAP nanofibers reinforced dental resins without any microsized filler and dental composites with silica microparticle filler was tested and analysis of variance (ANOVA) was used for the statistically analysis of acquired data. The morphology of fracture surface of tested dental composite samples was examined by SEM. The HAP nanofibers with aspect-ratios of 600 to 800 can be successfully fabricated with a simple wet-chemical method in aqueous solution. Impregnation of small mass fractions of the HAP nanofibers (5 wt% or 10 wt%) into the BisGMA/TEGDMA dental resins or impregnation of small mass fractions of the HAP nanofibers (2 wt% or 3 wt%) into the dental composites can substantially improve the biaxial flexural strength of the resulting dental resins and composites. A percolation threshold of HAP nanofibers, beyond which more nanofibers will no longer further increase the mechanical properties of dental composites containing HAP nanofibers, was observed for the dental composites with or without silica microparticle filler. Our mechanical testing and fractographic analysis indicated that the relatively good dispersion of HAP nanofibers at low mass fraction is the key reason for the significantly improved biaxial flexural strength, while higher mass fraction of HAP nanofibers tends to lead to bundles that cannot effectively reinforce the dental resins or composites and may even serve as defects and thus degrade the resulting dental resin and composite mechanical properties. The incorporation of small mass fraction of HAP nanofibers with good dispersion can improve the mechanical property of dental resins and dental composites.
    Dental materials: official publication of the Academy of Dental Materials 09/2011; 27(11):1187-95. · 2.88 Impact Factor
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    ABSTRACT: Although microRNAs are expressed extensively in the central nervous system in physiological and pathological conditions, their expression in neurological disorder of epilepsy has not been well characterized. Here we investigated microRNA expression pattern in post status epilepticus rats (24h after status). Rat MicroRNA array and differential analysis had detected 19 up-regulated microRNAs and 7 down-regulated microRNAs in rat hippocampus, and four randomly selected deregulated microRNAs (microRNA-34a, microRNA-22, microRNA-125a, microRNA-21) were confirmed by qRT-PCR, then their expression alterations in rat peripheral blood were analyzed. We found that these four deregulated microRNAs were also differentially expressed in rat peripheral blood, and trends for their blood expression alterations were just the same as their counterparts in rat hippocampus. Thus, our results have not only characterized the microRNA expression profile in post status epilepticus rat hippocampus but also demonstrated that some rat hippocampal microRNAs were probably associated with rat peripheral blood microRNAs. Moreover, targets of these deregulated microRNAs were analyzed using bioinformatics and the identified enriched MAPK pathway and long-term potentiation pathway might have been involved in molecular mechanisms concerning neuronal death, inflammation and epileptogenesis.
    Neuroscience Letters 01/2011; 488(3):252-7. · 2.03 Impact Factor
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    ABSTRACT: 3-aminopropyltrimethoxysilane (APS) surface modification of sol-gel bioactive glass (BG) was performed to improve the phase compatibility between poly-L-lactide (PLLA) and BG. The composite based on PLLA and modified BG was fabricated by using hot pressing methods. The effects of APS modification on the morphology of BG and mechanical properties of the PLLA/BG composite were investigated. The results indicated that uniformly dispersed BG particles, without agglomeration, were obtained after surface modification. Furthermore, the bending strength, bending modulus and shearing strength of PLLA/BG-APS composites were all higher than those of unmodified composites. However, the bending strength and shearing strength of PLLA/BG-APS composites significantly decreased with increasing BG content for all, whereas the bending modulus increased.
    Journal of Macromolecular Science, Part B. 01/2012;