Converting cheap resins like polypropylene (PP) copolymer into near-spherical powder materials with a wide sintering window (SW) is highly desired for broadening the feedstock palette for laser powder bed fusion (PBF-LB/P). Herein, a novel “melt extrusion-in blend annealing” strategy was proposed to achieve this aim, which involved dispersing the copolymer into a water-soluble matrix and then annealing the blend at temperatures near the melting point of the copolymer for a certain time. Spherical PP copolymer powders with largely widened SW (>30ºC) were obtained after removing the matrix. Two advantageous effects of in-blend annealing were identified. The first one was the elevation in the onset melting temperature due to crystal perfection. Another one was the decline in the onset crystallization temperature , which was suggested to relate to the migration of heterogeneous nuclei out of copolymer particles but required further verification. The obtained powder with optimized SW was fabricated into parts with low warpage at the cost of a slightly inferior mechanical performance possibly related to material degradation and changes in the crystal structure. The strategy proposed offers a promising prospect for developing new powders with optimized processing features for PBF-LB/P from commercially available resins.
The repair of abdominal wall defects is currently a clinical challenge. A naturally derived extracellular matrix (ECM) such as small intestine submucosa (SIS) has received great attention in abdominal wall defect repair because of its remarkable bioactivity, biodegradability and tissue regeneration. The match between material degradation and tissue remodeling is very important for the realization of ideal repair effectiveness. In this study, a near-infrared (NIR) fluorescent dye Cy5.5 NHS ester was used to label ECM-based (ECMB) composites consisting of SIS and chitosan/elastin electrospun nanofibers for monitoring material degradation. The tissue remodeling in the ECMB composites for a full-thickness abdominal wall defect repair was systematically investigated by a series of tests including wall thickness measurement, muscle regeneration analysis and angiogenesis assessment. The main findings were: (1) real-time and noninvasive degradation monitoring of the ECMB composites until complete degradation could be realized by chemical conjugation with a Cy5.5 NHS ester. (2) In a full-thickness abdominal wall defect model, the explant thickness could be used as an intuitional indicator for evaluating the tissue remodeling efficiency in the ECMB composites, and the accuracy of this indicator was verified by various examinations including collagen deposition, angiogenesis, and muscle regeneration. The present study could provide new insight into evaluating tissue repair effectiveness of the ECMB composites.
Degradable plastics, the substitute for conventional plastics, are becoming the new pollutant in the ocean. However, studies investigating the impact of freshwater and seawater on the basic aging process of microplastics and involving degradable plastics are still lacking. To accurately compare the potential hazards of degradable microplastics aging in seawater and freshwater, the role of salinity in the ultra-violet ray (UV) aging process of degradable microplastics (MPs) was explored in this study. Polylactic acid (PLA) aged under UV and 0‰, 10‰, and 40‰ salinities was taken as the subject. The results showed that salinity combined with UV accelerated the aging process, and PLA had more holes and cracks on the surface, larger specific area (SBET), and significantly more oxygen-containing functional groups and negative charges. The SBET of PLA aged under UV and 40‰ salinity was 2.97±0.11, 33% more than that aged by UV only. Additionally, salinity increased the adsorption capacity of PLA. The adsorption quantity of oxytetracycline (OTC) and Cu2+ by 40‰ salinity-aged PLA were 4.822 and 9.606 mg/g, 30% and 32% more than that aged by UV only. There was a drop in the desorption rate of OTC but a rise in that of Cu2+ by PLA aged in salinities. Moreover, the desorption quantity and rate of pollutants on PLA in simulated intestinal fluid were greater than those in water, and PLA might have a higher carrier effect on pollutants after aging under salinity conditions. These results showed that the potential hazard of PLA existing in seawater may be more serious than that in freshwater. This study also revealed the effect of salinity, enabling the environmental risk assessment of degradable MPs to be more scientific and more comprehensive.
危险品化学品经营许可证（带存储）