The process to successfully synthesize polybenzoxazine (PBO)-based aerogels has recently been optimized; however, the biocompatibility of these materials has never been investigated. PBO is synthesized from bisphenol A and aniline, which are both precursors to many commonly used biomaterials, including polyurethane. Surface-wise these new aerogels resemble the innate extracellular matrix of bone and if these new aerogels exhibit acceptable biocompatibility, they may be used as a scaffold for bone tissue engineering. Here, we aimed to characterize some of the physical properties of PBO aerogels, PBO aerogels co-polymerized with resorcinol and formaldehyde (RF) and their conversion to carbon aerogel, while determining the compatibility of all of these materials towards human osteoblasts. Biocompatibility was determined with a live/dead cell cytotoxicity assay, a metabolic activity assay, alkaline phosphatase activity and osteocalcin production, after incubation with PBO-based aerogels for up to 5 days. PBO aerogels co-polymerized with RF tended to have a low density, porosity and elastic modulus and provided the weakest substrate for bone cell growth. PBO-derived carbon aerogels tended to have a high density, a large porosity and improved mechanical properties and provided the best substrate for bone cell growth. These results suggest that PBO based carbon aerogels have a suitable biocompatibility towards osteoblasts and that they may be able to be used for bone tissue engineering scaffolds.

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By combining numerical simulation and experimental investigation, this paper intensively investigated the influence rules of adding three active agents (SiO2, TiO2 and NaF) on the dynamic behaviors of flow field in the laser welding 304 stainless steel thick plate pool. First of all, the mathematical model of the activating laser welding stainless steel thick plate was constructed to numerically investigate the impact of active agents on the fluid flow in the pool. Secondly, based on the tungsten particle tracing principle test, the high speed camera system was adopted for real-time monitoring to investigate the mechanism of action of the active agents on the flow field in the pool. The results suggested that, the active agents partially affected the mode of fluid flow. The velocity vector from both sides of the pool to the center occurred on the pool surface, while vortex from the pool margin to the center occurred on the pool cross section. The phenomenon that the tracing tungsten particles moving from the pool margin to the center, it shows that the flow direction of the fluid changed after coating with the active agent, the fluid flew from the pool margin to the center. At the same time, the coating of active agents changed the flow velocity of fluid inside the pool, and SiO2 active agent has the most significant increase effect, the maximum velocity of fluid flow on the upper surface, the longitudinal and cross sections at the same position of the SiO2 active agent coated specimen increased by 25.8%, 8% and 33.8%, respectively, compared with that without the active agents.

Dynamic behaviors of molten pools during active laser welding of thick 304 stainless steel plates are monitored in real time by utilizing a high-speed camera system. The effects of various active fluxes on the dynamic variations of molten pools are analyzed, and the results are compared with the uncoated specimens. The research reveals that all the molten pools present periodic variations. Among them, the specimen coated with NaF active flux exhibits the shortest cycle of molten pool change, with a single cycle duration of approximately 0.5 s. The specimen coated with TiO2 active flux exhibits the longest cycle of molten pool change, and the single cycle duration is around 1.1 s. Moreover, the molten pools also show varying widths. The maximum molten pool width is found with the specimen coated with CeO2 active flux, whose value is 3.277 mm. Meanwhile, the minimum molten pool width is found with the specimen coated with NaF active flux, whose value is 1.799 mm. In addition, the coating of active fluxes also produces certain effects on molten pool stability. The specimen coated with NaF active flux presents intense emission of metal vapor during welding, drastic oscillation of the molten pool, and severe spattering of metal particles. Contrastively, the molten pool of the specimen coated with Cr2O3 active flux is rather stable. In conclusion, by selecting an appropriate active flux, the cycle of molten pool variation can be prolonged, the pool stability can be enhanced, and the occurrence of spattering and other defects can be suppressed.

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