Modulus of elasticity of human periodontal ligament by optical measurement and numerical simulation.

OBJECTIVE: To determine the elastic modulus of the periodontal ligament (PDL). MATERIALS AND METHODS: This study was carried out on eight human maxillary jaw segments containing central incisors. Displacements were measured under load using a laser sensing system, electronic speckle pattern interferometry (ESPI). Subsequently, finite element models presenting the same individual geometry as the respective autopsy material were developed by the software of Mimics and Ansys, based on scanning data from micro computed tomography (micro CT), to simulate tooth mobility numerically under the same force systems as were used in the experiment. Numerical force/deflection curves obtained from the models were fitted to the experimental curves by repeatedly calculating theoretical tooth deflections and varying the elasticity parameters of the human PDL. RESULTS: A bilinear material parameter set was assumed to simulate tooth deflections. Mean values of E1  =  0.04 MPa, E2  =  0.16 MPa, and ultimate strain of ε12  =  7.3% were derived for the elastic behavior of the PDL. CONCLUSION: Force/deflection curves from the measurements showed a significant nonlinear behavior of elastic stiffness of the PDL. A bilinear material parameter set was suitably assumed to be a description of nonlinear properties of the PDL.

Influence of periodontal ligament injury on initial stability for immediately loaded mini-implant / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the influence of periodontal ligament (PDL) injury on initial stability for immediately loaded mini-implant anchorage.</p><p><b>METHODS</b>The sample consisted of 153 adult patients with maxillary protrusion deformity. Guiding by the positioning device designed by Choi, 306 mini-implants were inserted by self-tapping in the upper right and left buccal areas between the first molars and second premolars. The mini-implants were divided into two groups according to CT scanning. The mini-implant was absolutely separated from PDL (group I), the mini-implant appeared to touch or overlay on PDL, but not contact to the adjacent roots (group II). If orthodontic force could be applied to the mini-implants for four months, the mini-implant was recorded as successful anchorage. After immediate loading for four months, the analyses were completed by SPSS 9.0 software.</p><p><b>RESULTS</b>Of the 306 inserted mini-implants, 162 were absolutely separated from PDL, 136 appeared to touch or overlay on PDL, but not contact to the adjacent roots, and 8 were excluded from this study because of injury to the adjacent root. The success rates of group I and II were 87.0% and 65.4% respectively. There were significant differences in the success rates between the two groups (P<0.001). The differences between the two groups in distribution of the upper right and left area had statistical significance (P<0.05).</p><p><b>CONCLUSION</b>PDL injury is one of the main reasons leading to early loosening of the mini-implant.</p>

Accessory gene regulator in Staphylococcus biofilm formation and infection / 中南大学学报(医学版)

The most important factor in the pathogenesis of biomaterial-associated Staphylococcal infections is the formation of bacterial biofilms. Biofilm formation was regulated or influenced by quorum sensing. One of the quorum sensing systems agr is genus specific which controls the expression of a series of toxins and virulence factors and the interaction with the innate immune system. New research indicates that the role of agr during infection is controversial. The research progress will play an important role in the development of novel antibacterial agents and management of device-related infection of Staphylococci.

Expression, purification and characterization of a phyA(m)-phyCs fusion phytase / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

The phyA(m) gene encoding acid phytase and optimized neutral phytase phyCs gene were inserted into expression vector pPIC9K in correct orientation and transformed into Pichia pastoris in order to expand the pH profile of phytase and decrease the cost of production. The fusion phytase phyA(m)-phyCs gene was successfully overexpressed in P. pastoris as an active and extracellular phytase. The yield of total extracellular fusion phytase activity is (25.4+/-0.53) U/ml at the flask scale and (159.1+/-2.92) U/ml for high cell-density fermentation, respectively. Purified fusion phytase exhibits an optimal temperature at 55 degrees C and an optimal pH at 5.5~6.0 and its relative activity remains at a relatively high level of above 70% in the range of pH 2.0 to 7.0. About 51% to 63% of its original activity remains after incubation at 75 degrees C to 95 degrees C for 10 min. Due to heavy glycosylation, the expressed fusion phytase shows a broad and diffuse band in SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). After deglycosylation by endoglycosidase H (EndoH(f)), the enzyme has an apparent molecular size of 95 kDa. The characterization of the fusion phytase was compared with those of phyCs and phyA(m).

Multipoint Mutation and Over-expression in Pichia pastoris of Phytase Gene / 中国生物工程杂志

According to bias in codon choice of Pichia pastoris, The phytase phyA gene from Aspergillus niger N25 was mutated without changing its amino acid sequence. The expression plasmid pPIC9k-phyAm was constructed and transformed into GS115 strain. Positive clones,of which the chromosomes were integrated with phyA gene,were identified by the phenotype and PCR. SDS-PAGE analysis suggust that the size of enzyme protein of the expression product was about 70.15kDa.Southern blotting analysis to the yeast transformants showed that phyA gene was intergrated into the chromosome genome. The phytase activity of PP-NP m-4-4 with codons optimized reached 136 000U/ml in malt wort culture medium after being induced with 36h, which was the 2.8 times of the original strain PP-NPm-8.

Improving thermostability of Aspergillus niger phytase by elongation mutation / 生物工程学报

The phytase gene phyA(m) from Aspergillus niger N25 was recombined into E. coli expression vector pET-30b(+). Recombined at expression vectors pET30b-FphyA(m) was served as a template to amplify phytase gene, and the PCR product named elongation mutation gene phyA(e) was expanded with a 13 amino acid sequence from pET-30b-FphyA(m) vector at C-terminal of phytase gene phyA(m). Furthermore, phyA(e) gene was recombined into expression vector pPIC9k and expressed in Pichia pastoris. The comparison experiment of mutant phytase PP-NP0 with wild-type phytase PP-NP(m)-8 showed that: the optimum temperature of PP-NPe was increased by 3 degrees C, and its thermostability was increased by 21% when it was exposed to 10 min at 75 degrees C. Its effective reaction pH range with catalysis efficiency above 70% was pH 4.6 - pH 6.6, and wider 0.4 pH value than that of wild-type phytase.

Research and Progress on Feed Phytase Reform by Protein Engineering / 微生物学通报

As a kind of additive in feed of monogastric animals, the application of natural phytase is limited due to its disadvantages. In this paper, the strategies of phytse reform was introduced. Furthermore, the research and progress on protein engineering of feed phytase was reviewed, including phytase over-expression, phytase thermostability, catalytic efficiency and optimum pH.