Improved Corrosion Resistance on Selective Laser Melting Produced Ti-5Cu Alloy after Heat Treatment.

A Ti-5Cu alloy produced by selective laser melting exhibits a nonuniform Ti2Cu phase structure, which contains a small amount of α' phase in melt pool boundaries thereby resulting in reduced corrosion resistance. The heat-treatment process proposed in this work eliminates the deleterious effect of α' phase and the Ti2Cu phase is refined using different cooling rates, which improves the corrosion resistance. The electrochemical results indicate that the heat-treated Ti-5Cu samples have similar corrosion behavior to pure CP-Ti. A slower cooling rate produces a larger spacing between the Ti2Cu phases in the microstructure of the sample, resulting in higher corrosion resistance. The corrosion behavior of SLM-produced Ti-5Cu and heat-treated counterparts with different microstructure are detailed discussed.

Mechanical behaviour of alginate-gelatin hydrogels for 3D bioprinting.

Hydrogels comprised of alginate and gelatin have demonstrated potential as biomaterials in three dimensional (3D) bioprinting applications. However, as with all hydrogel-based biomaterials used in extrusion-based bioprinting, many parameters influence their performance and there is limited data characterising the behaviour of alginate-gelatin (Alg-Gel) hydrogels. Here we investigated nine Alg-Gel blends by varying the individual constituent concentrations. We tested samples for printability and print accuracy, compressive behaviour and change over time, and viability of encapsulated mesenchymal stem cells in bioprinted constructs. Printability tests showed a decrease in strand width with increasing concentrations of Alg-Gel. However due to the increased viscosity associated with the higher Alg-Gel concentrations, the minimum width was found to be 0.32mm before blends became too viscous to print. Similarly, printing accuracy was increased in higher concentrations, exceeding 90% in some blends. Mechanical properties were assessed through uniaxial compression testing and it was found that increasing concentrations of both Alg and Gel resulted in higher compressive modulus. We also deemed 15min crosslinking in calcium chloride to be sufficient. From our data, we propose a blend of 7%Alg-8%Gel that yields high printability, mechanical strength and stiffness, and cell viability. However, we found the compressive behaviour of Alg-Gel to reduce rapidly over time and especially when incubated at 37°C. Here we have reported relevant data on Alg-Gel hydrogels for bioprinting. We tested for biomaterial properties and show that these hydrogels have many desirable characteristics that are highly tunable. Though further work is needed before practical use in vivo can be achieved.

Characterisation of hyaluronic acid methylcellulose hydrogels for 3D bioprinting.

Hydrogels containing hyaluronic acid (HA) and methylcellulose (MC) have shown promising results for three dimensional (3D) bioprinting applications. However, several parameters influence the applicability bioprinting and there is scarce data in the literature characterising HAMC. We assessed eight concentrations of HAMC for printability, swelling and stability over time, rheological and structural behaviour, and viability of mesenchymal stem cells. We show that HAMC blends behave as viscous solutions at 4°C and have faster gelation times at higher temperatures, typically gelling upon reaching 37°C. We found the storage, loss and compressive moduli to be dependent on HAMC concentration and incubation time at 37°C, and show the compressive modulus to be strain-rate dependent. Swelling and stability was influenced by time, more so than pH environment. We demonstrated that mesenchymal stem cell viability was above 75% in bioprinted structures and cells remain viable for at least one week after 3D bioprinting. The mechanical properties of HAMC are highly tuneable and we show that higher concentrations of HAMC are particularly suited to cell-encapsulated 3D bioprinting applications that require scaffold structure and delivery of cells.

Antimicrobial Cu-bearing stainless steel scaffolds.

Copper-bearing stainless steel scaffolds with two different structures (Body Centered Cubic and Gyroid labyrinth) at two solid fractions (25% and 40%) were fabricated from both 316L powder and a mixture of 316L and elemental Cu powder using selective laser melting, and relative 316L scaffolds were served as control group. After processing, the antimicrobial testing demonstrated that the 316L-Cu scaffolds presented excellent antimicrobial activity against Escherichia coli and Staphylococcus aureus, and the cell viability assay indicated that there was no cytotoxic effect of 316L-Cu scaffolds on rat marrow mesenchymal stem cells. As such, these have the potential to reduce implant-associated infections. The Cu was also found to homogeneously distribute within the microstructure by scanning electronic microcopy. The addition of Cu would not significantly affect its strength and stiffness compared to 316L scaffold, and the stiffness of all the scaffolds (3-20GPa) is similar to that of bone and much less than that of bulk stainless steel. Consequently, fabrication of such low stiffness porous structures, especially coupled with the addition of antimicrobial Cu, may provide a new direction for medical stainless steels.