**5. Conclusions**

It can be stated that the surfaces produced in the optimized casting process of Ti6Al4V are not different from the reference surfaces of the same alloy successfully used in orthopedic surgery with respect to cell-biologic interactions of human osteoblasts in vitro. Neither a difference in cell spreading, cell viability/proliferation nor an influence on osteogenic differentiation and mineralization of primary osteoblasts was detectable. The optimized casting process, therefore, provided equivalent biologic material quality in this first comprehensive in vitro analysis based on primary human osteoblasts. These results confirm our recent in vivo data on osseointegration in a rat model. [4] Thus, near net-shape precision casting of Ti6Al4V, avoiding high demand of stock material for machining as well as the cost for the machining itself, may present a promising and cost-effective alternative to the conventional machining-based process for uncemented orthopedic implants.

Ion implantation of calcium or phosphorus by ion beam, however, did not induce a positive effect on human osteoblastic cells in vitro, again confirming our previous data on osseointegration in the rat model [4] despite the use of different ion-implantation techniques (ion-beam versus plasma ion implantation), which makes the results not directly comparable. Therefore, further studies on the effect of different ion implantation doses should be performed.

**Author Contributions:** Conceptualization, B.R.E., F.J., M.H., K.G. and K.A.B.; methodology, B.R.E., F.J., M.H., K.G. and K.A.B.; validation, B.R.E., F.J., M.H., K.G. and K.A.B.; formal analysis, K.A.B., M.H. and K.G.; investigation, K.A.B., M.H. and K.G.; resources, B.R.E., M.H. and K.G.; data curation, F.J., M.H. and K.G.; writing—original draft preparation, J.F.; writing—review and editing, F.J., B.R.E., M.H., K.A.B. and K.G.; visualization, F.J. and M.H.; supervision, B.R.E.; project administration, B.R.E., M.H., K.G. and K.A.B.; funding acquisition, B.R.E. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study has been funded by a gran<sup>t</sup> from the German Federal Ministry of Education and Research (BMBF, No. 13 GW0020B/E).

**Acknowledgments:** We wish to acknowledge the support of Giovanni Ravalli for technical assistance and Paul Walther (Department of electron microscopy, University of Ulm, Germany) for his support in the electron microscopic studies). We gratefully thank Andreas Kolitsch from the Helmholtz-Zentrum Dresden-Rosssendorf (HZDR) for the ion beam implantation.

**Conflicts of Interest:** The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. The authors declare no conflict of interest.
