Extrusion-based additive manufacturing of Mg-Zn alloy scaffolds

Porous biodegradable Mg and its alloys are considered to have a great potential to serve as ideal bone substitutes.The recent progress in additive manufacturing(AM) has prompted its application to fabricate Mg scaffolds with geometrically ordered porous structures.Extrusionbased AM,followed by debinding and sintering,has been recently demonstrated as a powerful approach to fabricating such Mg scaffolds,which can avoid some crucial problems encountered when applying powder bed fusion AM techniques.However,such pure Mg scaffolds exhibit a too high rate of in vitro biodegradation.In the present research,alloying through a pre-alloyed Mg-Zn powder was ultilized to enhance the corrosion resistance and mechanical properties of AM geometrically ordered Mg-Zn scaffolds simultaneously.The in vitro biodegradation behavior,mechanical properties,and electrochemical response of the fabricated Mg-Zn scaffolds were evaluated.Moreover,the response of preosteoblasts to these scaffolds was systematically evaluated and compared with their response to pure Mg scaffolds.The Mg-Zn scaffolds with a porosity of 50.3% and strut density of 93.1% were composed of the Mg matrix and MgZn2second phase particles.The in vitro biodegradation rate of the Mg-Zn scaffolds decreased by 81% at day 1,as compared to pure Mg scaffolds.Over 28 days of static immersion in modified simulated body fluid,the corrosion rate of the Mg-Zn scaffolds decreased from 2.3± 0.9 mm/y to 0.7±0.1 mm/y.The yield strength and Young’s modulus of the Mg-Zn scaffolds were about 3 times as high as those of pure Mg scaffolds and remained within the range of those of trabecular bone throughout the biodegradation tests.Indirect culture of MC3T3-E1 preosteoblasts in Mg-Zn extracts indicated favorable cytocompatibility.In direct cell culture,some cells could spread and form filopodia on the surface of the Mg-Zn scaffolds.Overall,this study demonstrates the great potential of the extrusion-based AM Mg-Zn scaffolds to be further developed as biodegradable bone-substituting biomaterials.

Corrosion and passive film characteristics of 3D-printed NiTi shape memory alloys in artificial saliva

Electrochemical tests and surface analysis were applied to study the corrosion behavior and passive film characteristics of three-dimensional-printed NiTi shape memory alloys fabricated by laser-powder bed fusion(LPBF) in artificial saliva at 37.C. The passivity of L-PBF NiTi shows to be influenced by the process parameters and resulting morphological and physicochemical surface properties. The results show that the defects at the surface of L-PBF Ni Ti can promote the passivation rate in the early stages of exposure but a slowly formed passive film shows the best corrosion protection. The thickness of the passive film is positively correlated with its corrosion protective performance. The L-PBF NiTi alloy prepared at a linear energy density of 0.2 J·m^(-1) and volumetric energy density of 56 J·mm^(-3) shows the least defects and best corrosion protection. An outer Ti-rich and inner Ni-rich dense passive film could be also obtained showing higher corrosion resistance.

Exploring water and ion transport process at silicone/copper interfaces using in-situ electrochemical and Kelvin probe approaches

In general,packaging materials which encapsulate light emitting diodes(LEDs)and microelectronic devices offer barrier protection against several environmental hazards such as water and ionic contaminants.However,these encapsulants may provide pathways for water and ionic contaminants to reach the metal/polymer interfaces and provoke local corrosion of electronics,which is a major reliability concern for polymer encapsulated LEDs and microelectronics.As the water and corrosive constituents play a crucial role in their reliability,water uptake kinetics,interfacial ion transport and delamination behaviour of silicone coated copper model system,mimicking a typical microelectronics packaging system,is explored in the present work.Electrochemical impedance spectroscopy(EIS)integrated with attenuated total reflection Fourier transform infrared(ATR-FTIR)spectroscopy studies revealed that water diffusion inside the silicone network is Fickian in nature and the evolution of the observed time constants are related to the diffusion and interfacial reactions.A decrease of impedance magnitude with time was observed in EIS measurements concurrently with water absorption bands shifting towards lower wavenumber in ATR-FTIR measurements,implying the growth of strong hydrogen bonding between water molecules and the silicone network.The estimated diffusion constant of water using the capacitance method was in the order of 7×10^(-12)m^(2)s^(-1)and the water absorption volume fraction was in the range of 0%to 0.30%.Scanning Kelvin probe studies elucidated the ion transport process occurring at the silicone/copper interface in a humid atmosphere.The interfacial ion transport process is controlled by the interfacial electrochemical reactions at the cathodic delamination front and the estimated average delamination rate is 0.43 mm h^(-1/2).This work demonstrates that exploring ion and water transport in the silicone coating and along the silicone/copper interface is of pivotal importance as part of a detailed reliability assessment of the polymer encapsulated LEDs and microelectronics.