No abstract

No abstract

Schwann cells (SCs) are primarily responsible for the formation of myelin sheaths, yet bone marrow mesenchymal stem cell (BMSC)-derived SCs are often used to replace autologous SCs and assist with the repair of peripheral nerve myelin sheaths. In this study, the effects of the two cell types on remyelination were compared during the repair of peripheral nerves. Methods: An acellular nerve scaffold was prepared using the extraction technique. Rat BMSCs and autologous SCs were extracted. BMSCs were induced to differentiate into BMSC-derived SCs (B-dSCs) in vitro. Seed cells (BMSCs, B-dSCs, and autologous SCs) were cocultured with nerve scaffolds (Sca) in vitro. Rats with severed sciatic nerves were used as the animal model. A composite scaffold was used to bridge the broken ends. After surgery, electrophysiology, cell tracking analyses (EdU labeling), immunofluorescence staining (myelin basic protein (MBP)), toluidine blue staining, and transmission electron microscopy were conducted to compare remyelination between the various groups and to evaluate the effects of the seed cells on myelination. One week after transplantation, only a small number of B-dSCs expressed MBP, which was far less than the proportion of MBP-expressing autologous SCs (P<0.01) but was higher than the proportion of BMSCs expressing MBP (P<0.05). Four weeks after surgery, the electrophysiology results (latency time, conductive velocity and amplitude) and various quantitative indicators of remyelination (thickness, distribution, and the number of myelinated fibers) showed that the Sca+B-dSC group was inferior to the Sca+autologous SC group (P<0.05) but was superior to the Sca+BMSC group (P<0.05). Conclusions: Within 4 weeks after surgery, the use of an acellular nerve scaffold combined with B-dSCs promotes remyelination to a certain extent, but the effect is significantly less than that of the scaffold combined with autologous SCs.

Autologous nerves, artificial scaffolds or acellular nerve scaffolds are commonly used in bridging treatment for peripheral nerve defects. Xenogeneic acellular nerve scaffolds and allogeneic cellular nerve scaffolds have the same structural characteristics. Due to the wider source of raw materials, these latter scaffolds have high-potential value for applications. However, whether their heterogeneity will affect nerve regeneration is unknown. The current study evaluated the efficiency of xenogeneic acellular nerve scaffolds (XANs) combined with 5-ethynyl-2'-deoxyuridine (EdU)-labeling of autologous bone marrow-derived stem cells (BMSCs) for repair of a 1.5 cm gap in rat sciatic nerves. XANs from rabbit tibial nerves were prepared, the structure and components of the scaffolds were evaluated after completely removing the cellular components. Animals were divided into four groups based on graft: the simple XAN group, the XAN + BMSC group, the XAN + Media (from BMSC culture) group, and the autograft group. Serological immune tests showed that XANs induce an immune response in the first 2 weeks after transplantation. Moreover, cell tracking revealed that the proportion of EdU+ cells decreased over time, as shown by the measures at 2 days (70%), 4 days (20%), and 8 days (even <3%) postoperatively. Nerve functional analyses revealed that in contrast to the autograft group results, the XAN-BMSC, XAN + Media, and XAN groups did not exhibit good restoration of the sciatic functional index (SFI) or electrophysiological results (the peak action potential amplitudes) 12 weeks, postoperatively. However, the XAN-BMSC and autograft groups demonstrated greater remyelination and increased axon numbers and myelin thickness than the XAN + Media and XAN groups 12 weeks, postoperatively (p < .05). In conclusion, in the early stage of transplantation, XANs induce a certain degree of inflammation. Although the combination of XANs with autologous BMSCs enhanced the number of regenerated axons and the remyelination, the combination did not effectively improve the recovery of nervous motor function. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3065-3078, 2018.

Although precise point positioning (PPP) is a well-established and promising technique with the use of precise satellite orbit and clock products, it requires a long convergence time to reach a centimeter-level positioning accuracy. The availability of triple-frequency observations from a modernized global navigation satellite system (GNSS) constellations makes it possible to improve performance by formulating new observation models. The contribution of this paper is to propose two new observation models using triple-frequency data. The first model ( UofC3) is the triple-frequency extension of dualfrequency University of Calgary model. The second model (UofB) is a combining observation model with five-dimensional observation equations. Thereafter, by theoretically analyzing the dimension of the triplefrequency observation models, all feasible triple-frequency observation models are systematically found out. Finally, the positioning experiments with 3-h observation period using real data at four BeiDou Navigation Satellite System (BDS) Asia-Pacific distributed reference stations on the day of the year (DOY) 42-48, 2018 are conducted to compare the performance of observation models. The results show that the triplefrequency models have less convergence time than the dual-frequency models. Meanwhile, most of the triple-frequency models have approximate convergence time in an experiment. Furthermore, UofB, which is one of the most stabilized observation models as well as uncombined observation model with the triplefrequency data (UC3), has less processing time than UC3. Compared with UofB, UofC3 has less processing time with sacrificing stability. These results show the significance of the UofB and UofC3 for future PPP applications in modernized GNSS.