Three-dimensional bioprinting is an emerging technology for fabricating living 3D constructs, and it has shown great promise in tissue engineering. Bioinks are scaffold materials mixed with cells used by 3D bioprinting to form a required cell-laden structure. In this paper, a novel bioink made of gelatin methacrylamide (GelMA) and collagen (Col) doped with tyrosinase (Ty) is presented for the 3D bioprinting of living skin tissues. Ty has the dual function of being an essential bioactive compound in the skin regeneration process and also as an enzyme to facilitate the crosslink of Col and GelMA. Further, enzyme crosslinking together with photocrosslinking can enhance the mechanical strength of the bioink. The experimental results show that the bioink is able to form stable 3D living constructs using the 3D bioprinting process. The cell culture shows that three major cell lines: human melanocytes (HEM), human keratinocytes (HaCat) and human dermal fibroblasts (HDF) exhibit high cell viabilities. The viability of these three cell lines is above 90%. The proliferation and scratching test show that Ty can enhance the proliferation of HEM, inhibit the growth and migration of HDF and not affect HaCat significantly. Animal tests show that the doped bioinks for 3D bioprinting can help form an epidermis and dermis, and thus have high potential as a skin bioink.

We report the discovery of a highly dispersed fast radio burst (FRB), FRB181123, from an analysis of ∼1500 hr of drift scan survey data taken using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulse has three distinct emission components, which vary with frequency across our 1.0-1.5 GHz observing band. We measure the peak flux density to be >0.065 Jy and the corresponding fluence >0.2 Jy ms. Based on the observed dispersion measure of 1812 cm −3 pc, we infer a redshift of ∼1.9. From this, we estimate the peak luminosity and isotropic energy to be 2×10 43 erg s −1 and 2×10 40 erg, respectively. With only one FRB from the survey detected so far, our constraints on the event rate are limited. We derive a 95% confidence lower limit for the event rate of 900 FRBs per day for FRBs with fluences >0.025 Jy ms. We performed follow-up observations of the source with FAST for four hours and have not found a repeated burst. We discuss the implications of this discovery for our understanding of the physical mechanisms of FRBs.

No abstract

We describe PSR J1926−0652, a pulsar recently discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using sensitive single-pulse detections from FAST and long-term timing observations from the Parkes 64-m radio telescope, we probed phenomena on both long and short time scales. The FAST observations covered a wide frequency range from 270 to 800 MHz, enabling individual pulses to be studied in detail. The pulsar exhibits at least four profile components, short-term nulling lasting from 4 to 450 pulses, complex subpulse drifting behaviours and intermittency on scales of tens of minutes. While the average band spacing P 3 is relatively constant across different bursts and components, significant variations in the separation of adjacent bands are seen, especially near the beginning and end of a burst. Band shapes and slopes are quite variable, especially for the trailing components and for the shorter bursts. We show that for each burst the last detectable pulse prior to emission ceasing has different properties compared to other pulses. These complexities pose challenges for the classic carousel-type models.

No abstract