Biomedical subjects

Xiaoxia Zhao

Publications and source records attributed to Xiaoxia Zhao.

4 recordsLinked to original sources

PubMed2005

Effect of OH- on the luminescent efficiency and lifetime of Tb3+-doped yttrium orthophosphate synthesized by solution precipitation.

In this work, we use the solution precipitation method to synthesize Tb3+-doped yttrium orthophosphate, which is a green-emission luminescent material. The evolution of hydrated yttrium orthophosphate (YPO4.2H2O) to dehydrated yttrium orthophosphate (YPO4) is observed in the heat-treatment process, simultaneously, accompanying the structural transformation from monoclinic churchite-type to tetragonal xenotime-type structure. Furthermore, the luminescent efficiency of Tb3+-doped YPO4 presents a sharp jump at a critical temperature in this heat-treatment process. Interestingly, this critical temperature is close to the structural transformation temperature. The remarkable change of luminescent efficiency seems to be related to the structural transformation. However, the FTIR and fluorescent decay measurements at 10 and 300 K indicate that the OH group is the origin of luminescent efficiency change. OH- ions with high vibration frequency provide an efficient means to quench the luminescence. The comparison of the luminescent efficiency, OH- content, and lifetime of 5D4 of Tb3+ between two samples with the same crystal structure proves that the structural transformation has no significant effect on the luminescent efficiency and lifetime. On the basis of these results, it is proposed that correctly preventing OH- ions inside the host matrix or effectively eliminating them may improve the luminescent efficiency greatly. This idea also may be applied to other optical systems.

Journal Article↗

PubMed2005

[Experimental study on repairing segmental bone defects with three bio-bone derived materials].

OBJECTIVE: To evaluate the osteogenesis of three bio-bone derived materials in repairing segmental bone defects. METHODS: Sixty Japanese rabbits were made 10 mm radius segmental defects and divided into 5 groups (groups A, B, C, D and E, n=12). Composite fully deproteinised bone (CFDB, group A), partially deproteinised bone (PDPB, group B), partially decalcified bone (PDCB, group C), autogenous iliac bone graft (group D) and no implant (group E) were implanted into the radius segmental bone defects of rabbits. The specimens were examined after 4, 8, 12 and 24 weeks; the osteogenesis was evaluated through X-ray radiograph and undecalcified solid tissue histological examination. RESULTS: The border between the material and host's bone was distinct after 4 weeks and blurred after 8 weeks; the density of partial edge of the material was similar to that of radii after 12 weeks. The medullary cavity of bone reopened in group B; the density of most defect area was similar to that of the host bone and there was a few high density shadow in group C; the density of most defect area was higher than that of host bone in group A after 24 weeks. There was no significant difference in radiograph scoring between groups A, B and C after 4 weeks and 8 weeks (P>0.05); the scores of group B and C were higher than that of group A after 12 weeks (P<0.05); and the scores were arranged as follow: group D > group B > group C > group A after 24 weeks (P<0.05). Bone callus grew toward defect area and new bone adhered to the material after 4 weeks and 8 weeks; more new bone formed, and the materials were absorbed and degraded with time. The quantity of bone formation was more in group D than in group B and in group B than in group C and in group C than in group A after 24 weeks (P<0.05). CONCLUSION: PDPB had good osteogenesis in repairing the segmental bone defect, PDCB was inferior to it, both PDPB and PDCB are fit to repair segmental bone defect. Both of them were inferior to autogenous bone.

Animals↗

PubMed2003

The importance of alfalfa mosaic virus coat protein dimers in the initiation of replication.

Deletion and substitution mutations affecting the oligomerization of alfalfa mosaic virus (AMV) coat protein (CP) were studied in protoplasts to determine their effect on genome activation, an early step in AMV replication. The CP mutants that formed dimers, CPDeltaC9 and CPC-A(R)F, were highly active in initiating replication with 63-84% of wild-type (wt) CP activity. However, all mutants that did not form dimers, CPDeltaC18, CPDeltaC19, CPC-WFP, and CPC-W, were much less active with 19-33% of wt CP activity. The accumulation and solubility of mutant CPs expressed from a virus-based vector in Nicotiana benthamiana were similar to that of wt CP. Analysis of CP-RNA interactions indicated that CP dimers and CP monomers interacted very differently with AMV RNA 3' ends. These results suggest that CP dimers are more efficient for replication than CP monomers because of differences in RNA binding rather than differences in expression and accumulation of the mutant CPs in infected cells.

Alfalfa mosaic virus↗

PubMed2003

T-DNA recombination and replication in maize cells.

T-DNA recombination and replication was analyzed in 'black mexican sweet' (BMS) cells transformed with T-DNAs containing the replication system from wheat dwarf virus (WDV). Upon recombination between the T-DNA ends, a promoterless marker gene (gusA) was activated. Activation of the recombination marker gene was delayed and increased exponentially over time, suggesting that recombination and amplification of the T-DNA occurred in maize cells. Mutant versions of the viral initiator gene (rep), known to be defective in the replication function, failed to generate recoverable recombinant T-DNA molecules. Circularization of T-DNA by the FLP/FRT site-specific recombination system and/or homologous recombination was not necessary to recover circular T-DNAs. However, replicating T-DNAs appeared to be suitable substrates for site-specific and homologous recombination. Among 33 T-DNA border junctions sequenced, only one pair of identical junction sites was found implying that the population of circular T-DNAs was highly heterogenous. Since no circular T-DNA molecules were detected in treatments without rep, it suggested that T-DNA recombination was linked to replication and might have been stimulated by this process. The border junctions observed in recombinant T-DNA molecules were indicative of illegitimate recombination and were similar to left-border recombination of T-DNA into the genome after Agro-mediated plant transformation. However, recombination between T-DNA molecules differed from T-DNA/genomic DNA junction sites in that few intact right borders were observed. The replicating T-DNA molecules did not enhance genomic random integration of T-DNA in the experimental configuration used for this study.

Agrobacterium tumefaciens↗