Fabrication and performance of Zinc-based biodegradable metals: From conventional processes to laser powder bed fusion

Zinc (Zn)-based biodegradable metals (BMs) fabricated through conventional manufacturing methods exhibit adequate mechanical strength, moderate degradation behavior, acceptable biocompatibility, and bioactive functions. Consequently, they are recognized as a new generation of bioactive metals and show promise in several applications. However, conventional manufacturing processes face formidable limitations for the fabrication of customized implants, such as porous scaffolds for tissue engineering, which are future direction towards precise medicine. As a metal additive manufacturing technology, laser powder bed fusion (L-PBF) has the advantages of design freedom and formation precision by using fine powder particles to reliably fabricate metallic implants with customized structures according to patient-specific needs. The combination of Zn-based BMs and L-PBF has become a prominent research focus in the fields of biomaterials as well as biofabrication. Substantial progresses have been made in this interdisciplinary field recently. This work reviewed the current research status of Zn-based BMs manufactured by L-PBF, covering critical issues including powder particles, structure design, processing optimization, chemical compositions, surface modification, microstructure, mechanical properties, degradation behaviors, biocompatibility, and bioactive functions, and meanwhile clarified the influence mechanism of powder particle composition, structure design, and surface modification on the biodegradable performance of L-PBF Zn-based BM implants. Eventually, it was closed with the future perspectives of L-PBF of Zn-based BMs, putting forward based on state-of-the-art development and practical clinical needs.

An adaptive biodegradable zinc alloy with bidirectional regulation of bone homeostasis for treating fractures and aged bone defects

Healing of fractures or bone defects is significantly hindered by overactivated osteoclasts and inhibited osteogenesis in patients with abnormal bone metabolism.Current clinical approaches using titanium alloys or stainless steel provide mechanical support but have no biological effects on bone regeneration.Therefore,designing and fabricating degradable metal materials with sufficient mechanical strength and bidirectional regulation of both osteoblasts and osteoclasts is a substantial challenge.Here,this study first reported an adaptive biodegradable Zn-0.8 Mg alloy with bidirectional regulation of bone homeostasis,which promotes osteogenic differentiation by activating the Pi3k/Akt pathway and inhibits osteoclast differentiation by inhibiting the GRB2/ERK pathway.The anti-osteolytic ability of the Zn-0.8 Mg alloy was verified in a mouse calvarial osteolysis model and its suitability for internal fracture fixation with high-strength screws was confirmed in the rabbit femoral condyle fracture model.Furthermore,in an aged postmenopausal rat femoral condyle defect model,3D printed Zn-0.8 Mg scaffolds promoted excellent bone regeneration through adaptive structures with good mechanical properties and bidirectionally regulated bone metabolism,enabling personalized bone defect repair.These findings demonstrate the substantial potential of the Zn-0.8 Mg alloy for treating fractures or bone defects in patients with aberrant bone metabolism.

A drug-loaded composite coating to improve osteogenic and antibacterial properties of Zn-1Mg porous scaffolds as biodegradable bone implants

Zinc(Zn)alloy porous scaffolds produced by additive manufacturing own customizable structures and biodegradable functions,having a great application potential for repairing bone defect.In this work,a hydroxyapatite(HA)/polydopamine(PDA)composite coating was constructed on the surface of Zn-1Mg porous scaffolds fabricated by laser powder bed fusion,and was loaded with a bioactive factor BMP2 and an antibacterial drug vancomycin.The microstructure,degradation behavior,biocompatibility,antibacterial performance and osteogenic activities were systematically investigated.Compared with as-built Zn-1Mg scaffolds,the rapid increase of Zn2+,which resulted to the deteriorated cell viability and osteogenic differentiation,was inhibited due to the physical barrier of the composite coating.In vitro cellular and bacterial assay indicated that the loaded BMP2 and vancomycin considerably enhanced the cytocompatibility and antibacterial performance.Significantly improved osteogenic and antibacterial functions were also observed according to in vivo implantation in the lateral femoral condyle of rats.The design,influence and mechanism of the composite coating were discussed accordingly.It was concluded that the additively manufactured Zn-1Mg porous scaffolds together with the composite coating could modulate biodegradable performance and contribute to effective promotion of bone recovery and antibacterial function.

Landsat-Based Monitoring of Landscape Dynamics in Arctic Permafrost Region

Ice-rich permafrost thaws as a result of Arctic warming,and the land surface collapses to form characteristic thermokarst landscapes.Thermokarst landscapes can bring instability to the permafrost layer,affecting regional geomorphology,hydrology,and ecology and may further lead to permafrost degradation and greenhouse gas emissions.Field observations in permafrost regions are often limited,while satellite imagery provides a valuable record of land surface dynamics.Currently,continuous monitoring of regional-scale thermokarst landscape dynamics and disturbances remains a challenging task.In this study,we combined the Theil–Sen estimator with the LandTrendr algorithm to create a process flow for monitoring thermokarst landscape dynamics in Arctic permafrost region on the Google Earth Engine platform.A robust linear trend analysis of the Landsat Tasseled Cap index time series based on the Theil–Sen estimator and Mann–Kendall test showed the overall trends in greenness,wetness,and brightness in northern Alaska over the past 20 years.Six types of disturbances that occur in thermokarst landscape were demonstrated and highlighted,including long-term processes(thermokarst lake expansion,shoreline retreat,and river erosion)and short-term events(thermokarst lake drainage,wildfires,and abrupt vegetation change).These disturbances are widespread throughout the Arctic permafrost region and represent hotspots of abrupt permafrost thaw in a warming context,which would destabilize fragile thermokarst landscapes rich in soil organic carbon and affect the ecological carbon balance.The cases we present provide a basis for understanding and quantifying specific disturbance analyses that will facilitate the integration of thermokarst processes into climate models.