coatings Article Development of Cerium-Doped Hydroxyapatite Coatings with Antimicrobial Properties for Biomedical Applications Daniela Predoi 1 , Simona Liliana Iconaru 1 , Mihai Valentin Predoi 2 , Andreea Groza 3 , Sofia Gaiaschi 4 , Krzysztof Rokosz 5 , Steinar Raaen 6 , Catalin Constantin Negrila 1 , Alina-Mihaela Prodan 7,8 , Adrian Costescu 9 , Monica Luminita Badea 10 and Patrick Chapon 4, * 1 National Institute of Materials Physics, Atomistilor Street, No. 405A, P.O. Box MG 07, 077125 Magurele, Romania; dpredoi@gmail.com (D.P.); simonaiconaru@gmail.com (S.L.I.); catalin.negrila@infim.ro (C.C.N.) 2 Department of Mechanics, University Politehnica of Bucharest, BN 002, 313 Splaiul Independentei, Sector 6, 060042 Bucharest, Romania; predoi@gmail.com 3 Plasma and Radiation Physics, National Institute for Laser, 409 Atomistilor Street, P.O. Box MG 36, 077125 Magurele, Romania; andreeagroza75@gmail.com 4 HORIBA Jobin Yvon S.A.S., 6-18, Rue du Canal, 91165 Longjumeau CEDEX, France; sofia.gaiaschi@horiba.com 5 Division of Surface Electrochemistry & Technology, Faculty of Mechanical Engineering, Koszalin University of Technology, Raclawicka 15-17, PL 75-620 Koszalin, Poland; krzysztof.rokosz@tu.koszalin.pl 6 Department of Physics, Norwegian University of Science and Technology (NTNU), Realfagbygget E3-124 Høgskoleringen 5, 7491 Trondheim, Norway; steinar.raaen@ntnu.no 7 Department of General Surgery, Carol Davila University of Medicine and Pharmacy, 8 Eroii Sanitari, Sector 5, 050474 Bucharest, Romania; prodan1084@gmail.com 8 Emergency Hospital Floreasca Bucharest, 8 Calea Floreasca, 014461 Bucharest, Romania 9 Faculty of Exact Sciences & Engineering, Hyperion University of Bucharest, 169 Calea Călăras , i, 030615 Bucharest, Romania; adrian.costescu@gmail.com 10 Faculty of Horticulture, University of Agronomic Sciences and Veterinary Medicine, 59 Marasti Blvd., 011464 Bucharest, Romania; monibadea78@gmail.com * Correspondence: patrick.chapon@horiba.com Received: 1 May 2020; Accepted: 25 May 2020; Published: 28 May 2020   Abstract: Antibacterial cerium-doped hydroxyapatite (Ce-HAp) layers have been researched sparingly in recent years. The Ce-HAp powder, Ca 10−x Ce x (PO 4 ) 6 (OH )2 with x Ce = 0.05, was obtained by an adapted chemical co-precipitation method at room temperature. The target was prepared using the Ce-HAp (x Ce = 0.05) powder sintered in air at 600 ◦ C. The coatings on the Ti substrate were generated in plasma using a radio frequency (RF) magnetron sputtering discharge in an Ar gas flow in a single run. To collect the most complete information regarding the antimicrobial activity of cerium-doped hydroxyapatite with x Ce = 0.05, (5Ce-HAp), antimicrobial studies were carried out both on the final suspensions and on the coated surfaces. The target was tested using ultrasound measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), glow-discharge optical emission spectroscopy (GDOES), and X-ray photoelectron spectroscopy (XPS). The present study exhibited for the first time results of the homogeneous coatings of hydroxyapatite doped with cerium using a radio frequency magnetron sputtering technique. In addition, this study highlighted for the first time the stability of the cerium-doped hydroxyapatite gels used in the creation of the coating. Ultrasound measurements on the concentrated suspension of 5Ce-HAp showed a good stability compared to double distilled, water which was chosen as the reference fluid. Particles with spherical shape were observed by both TEM and SEM analysis. The broadening of the IR bands in the IR spectrum of the 5Ce-HAp film in comparison with the IR spectrum of the precursor target indicate the formation of interlinked bonds Coatings 2020, 10, 516; doi:10.3390/coatings10060516 www.mdpi.com/journal/coatings