2D/3D hybrid cell culture systems are constructed by increasing the temperature of the thermogelling poly(ethylene glycol)‐poly(l‐alanine) diblock copolymer (PEG‐l‐PA) aqueous solution in which tonsil tissue‐derived mesenchymal stem cells and graphene oxide (GO) or reduced graphene oxide (rGO) are suspended, to 37 °C. The cells exhibit spherical cell morphologies in 2D/3D hybrid culture systems of GO/PEG‐l‐PA and rGO/PEG‐l‐PA by using the growth medium. The cell proliferations are 30%–50% higher in the rGO/PEG‐l‐PA hybrid system than in the GO/PEG‐l‐PA hybrid system. When chondrogenic culture media enriched with TGF‐β3 is used in the 2D/3D hybrid systems, cells extensively aggregate, and the expression of chondrogenic biomarkers of SOX 9, COL II A1, COL II, and COL X significantly increases in the GO/PEG‐l‐PA 2D/3D hybrid system as compared with the PEG‐l‐PA 3D systems and rGO/PEG‐l‐PA 2D/3D hybrid system, suggesting that the GO/PEG‐l‐PA 2D/3D hybrid system can be an excellent candidate as a chondrogenic differentiation platform of the stem cell. This paper also suggests that a 2D/3D hybrid system prepared by incorporating 2D materials with various surface biofunctionalities in the in situ forming 3D hydrogel matrix can be a new cell culture system.
[1] In this study we have examined the occurrence probability of solar proton events and their peak fluxes depending on three flare parameters (X-ray peak flux, longitude, and impulsive time). For this we used NOAA solar energetic particle events from 1976 to 2006 and their associated X-ray flare data. As a result, we selected 166 proton events that were associated with major flares: 85 events associated with X-class flares and 81 events associated with M-class flares. The occurrence probability especially strongly depends on three parameters as follows. (1) We found that about only 3.5% (1.9% for M-class and 21.3% for X-class) of the flares are associated with the proton events. (2) It is also found that this fraction strongly depends on longitude; for example, the fraction for 30°W < L ≤ 90°W is about three times larger than that for 30°E < L ≤ 90°E. (3) We also note that the occurrence probability of solar proton events associated with long-duration (≥0.3 h) flares is about 2 (X-class flare) to 7 (M-class flare) times larger than that with short-duration (<0.3 h) flares. (4) The largest difference is found between the eastern short-duration M-class flare group (0.3%) and the western long-duration X-class flare group (46.5%). In addition, the relationship between X-ray flare peak flux and proton peak flux as well as its correlation coefficient are strongly dependent on longitude and impulsive time.
In this study we examine the occurrence probabilities of solar proton events (SPEs) and their peak fluxes depending on both flare and coronal mass ejection (CME) parameters: flare peak flux, longitude, impulsive time, CME linear speed, and angular width. For this we use the NOAA SPEs, their associated X-ray flares, and CME from 1997 to 2011. We divide the data into 16 subgroups according to the flare and CME parameters and estimate the SPE probabilities for the subgroups. The three highest probabilities are found for the following subgroups: (1) fast full halo (55.3%) and fast partial halo (42.9%) CMEs associated with strong flares from the western region and (2) slow full halo CMEs associated with strong flares from the western region (31.6%). It is noted that the events whose SPE probabilities are nearly 0% belong to the following subgroups: (1) slow and fast partial halo CMEs from the eastern region, (2) slow partial halo CMEs from the western region, and (3) slow full halo CMEs from the eastern region. These results show that important parameters to control SPE occurrences are CME linear speed, angular width, and source longitude, which can be understood by the piston-driven shock formation of fast CMEs and magnetic field connectivity from the source site to the Earth. It is also shown that when the subgroups are separately considered by flare impulsive time and source longitude, the correlation coefficients between the observed and the predicted SPE peak fluxes are greatly improved.
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