**5. Conclusion**

The high entropy alloys in the CrFeMoNbTaTiZr, CrFeMoNbTaTi, CrFeMoNbTaZr, CrFeMoTaTiZr, CrFeTaNbTiZr, CrTaNbTiZrMo, and FeTaNbTiZrMo alloying systems can be produced in the RAV furnace provided that the batch volume is large enough to allow the dissolution of hard-to-melt elements. Raw materials need to be introduced in the form of smaller grain particles (below 1 mm in diameter) in order to favor the dissolution phenomena by diffusion in the common molten metal bath. Moreover, the liquid state holding time must be increased so as to achieve the complete dissolution of particles from hard-to-melt elements. Heat treatments produce superficial oxidation effects, forming oxide layers of approx. 42 microns thick, partly fractured or peeled. The hardness value in case of the CrFeMoTaTiZr alloy increased from 800 HV0.2 to approx. 1290 HV0.2 after applying the heat treatment. The epifluorescence microscopy technique showed that mesenchymal stem cells adhered to the surface of the alloy.

## **Acknowledgements**

The researches were financed by the Executive Agency for Higher Education, Research, Development and Innovation (CNCS CCDI—UEFISCDI), under the grant project no. PN-III-P1-1.2-PCCDI-2017-239/60PCCDI 2018—Obtaining and expertise of new biocompatible materials for medical applications—MedicalMetMat within PNCDI III.

**Author details**

Victor Geanta<sup>1</sup>

**195**

, Ionelia Voiculescu<sup>1</sup>

*High Entropy Alloys for Medical Applications DOI: http://dx.doi.org/10.5772/intechopen.89318*

1 University Politehnica of Bucharest, Bucharest, Romania

2 Gheorghe Asachi Technical University of Iasi, Romania

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: ioneliav@yahoo.co.uk

provided the original work is properly cited.

\*, Petrica Vizureanu<sup>2</sup> and Andrei Victor Sandu<sup>2</sup>

#### **Thanks**

The authors would like to thank their colleagues and collaborators Mirela Codescu, Alina Vlădescu, Hajnal Kelemen, Sanda Manu, and Dumitru Mitrică for their contribution to the testing and characterization of experimental materials.

*High Entropy Alloys for Medical Applications DOI: http://dx.doi.org/10.5772/intechopen.89318*

**4. Cell viability preliminary tests**

*Engineering Steels and High Entropy-Alloys*

AM and Propidium Iodide.

**Acknowledgements**

within PNCDI III.

**Thanks**

**194**

**5. Conclusion**

In order to evaluate the cell viability of the new alloys with high entropy in simulated biological environments, a series of experiments on bone fragments taken from bone extractions from human patients were performed. Bone fragments were transferred to minimally modified Dulbecco essential medium (DMEM) (Sigma cat. No. D6046) supplemented to the final concentration of 1% with penicillin/streptomycin (Sigma cat.no.P4333) and 10% fetal bovine serum (FBS) (Sigma F7524) and centrifuged at 4000 rpm for 10 min to dislodge stem cells. Bone fragments were cultured as explants in a vial with a surface of 75 cm<sup>2</sup> (Eppendorf No. 0030711122) at 37°C, in a humid atmosphere, with 5% CO2. After 7–10 days, the first cells that migrated from the explants were observed under the microscope. Cells directly in contact with the alloy samples were analyzed in the Leica DMi8 inverted microscope, using FITC and Rhodamine fluorescence cubes, after incubation with Calcein

The high entropy alloys in the CrFeMoNbTaTiZr, CrFeMoNbTaTi, CrFeMoNbTaZr, CrFeMoTaTiZr, CrFeTaNbTiZr, CrTaNbTiZrMo, and

FeTaNbTiZrMo alloying systems can be produced in the RAV furnace provided that the batch volume is large enough to allow the dissolution of hard-to-melt elements. Raw materials need to be introduced in the form of smaller grain particles (below 1 mm in diameter) in order to favor the dissolution phenomena by diffusion in the common molten metal bath. Moreover, the liquid state holding time must be increased so as to achieve the complete dissolution of particles from hard-to-melt elements. Heat treatments produce superficial oxidation effects, forming oxide layers of approx. 42 microns thick, partly fractured or peeled. The hardness value in case of the CrFeMoTaTiZr alloy increased from 800 HV0.2 to approx. 1290 HV0.2 after applying the heat treatment. The epifluorescence microscopy technique showed that mesenchymal stem cells adhered to the surface of the alloy.

The researches were financed by the Executive Agency for Higher Education, Research, Development and Innovation (CNCS CCDI—UEFISCDI), under the grant project no. PN-III-P1-1.2-PCCDI-2017-239/60PCCDI 2018—Obtaining and expertise of new biocompatible materials for medical applications—MedicalMetMat

The authors would like to thank their colleagues and collaborators Mirela Codescu, Alina Vlădescu, Hajnal Kelemen, Sanda Manu, and Dumitru Mitrică for their contribution to the testing and characterization of experimental materials.
