polymers Article Bioactive Coatings Loaded with Osteogenic Protein for Metallic Implants Oana Gherasim 1,2 , Alexandru Mihai Grumezescu 1,3,4 , Valentina Grumezescu 2,3, *, Ecaterina Andronescu 1,3 , Irina Negut 2 , Alexandra Cătălina Bîrcă 1 , Bianca Gălăt , eanu 5 and Ariana Hudit , ă 5   Citation: Gherasim, O.; Grumezescu, A.M.; Grumezescu, V.; Andronescu, E.; Negut, I.; Bîrc˘ a, A.C.; G ˘ al˘ at , eanu, B.; Hudit , ˘ a, A. Bioactive Coatings Loaded with Osteogenic Protein for Metallic Implants. Polymers 2021, 13, 4303. https://doi.org/10.3390/ polym13244303 Academic Editor: Vijay Kumar Thakur Received: 20 November 2021 Accepted: 6 December 2021 Published: 9 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Science and Engineering of Oxide Materials and Nanomaterials, Faculty of Applied Chemistry and Materials Science, Politehnica University of Bucharest, 011061 Bucharest, Romania; oana.fufa@gmail.com (O.G.); grumezescu@yahoo.com (A.M.G.); ecaterina.andronescu@upb.ro (E.A.); ada_birca@yahoo.com (A.C.B.) 2 Lasers Department, National Institute for Lasers, Plasma, and Radiation Physics, RO-77125 Magurele, Romania; negut.irina@inflpr.ro 3 Academy of Romanian Scientists, Ilfov No. 3, 50044 Bucharest, Romania 4 Research Institute of the University of Bucharest—ICUB, University of Bucharest, 050657 Bucharest, Romania 5 Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Bucharest, 91–95 Splaiul Independentei, 050095 Bucharest, Romania; bianca.galateanu@bio.unibuc.ro (B.G.); arianahudita@yahoo.com (A.H.) * Correspondence: valentina_grumezescu@yahoo.com Abstract: Osteoconductive and osteoinductive coatings represent attractive and tunable strategies towards the enhanced biomechanics and osseointegration of metallic implants, providing accurate local modulation of bone-to-implant interface. Composite materials based on polylactide (PLA) and hydroxyapatite (HAp) are proved beneficial substrates for the modulation of bone cells’ develop- ment, being suitable mechanical supports for the repair and regeneration of bone tissue. Moreover, the addition of osteogenic proteins represents the next step towards the fabrication of advanced biomaterials for hard tissue engineering applications, as their regulatory mechanisms beneficially contribute to the new bone formation. In this respect, laser-processed composites, based on PLA, Hap, and bone morphogenetic protein 4(BMP4), are herein proposed as bioactive coatings for metallic implants. The nanostructured coatings proved superior ability to promote the adhesion, viability, and proliferation of osteoprogenitor cells, without affecting their normal development and further sustaining the osteogenic differentiation of the cells. Our results are complementary to previous studies regarding the successful use of chemically BMP-modified biomaterials in orthopedic and orthodontic applications. Keywords: hydroxyapatite; bone morphogenetic protein; MAPLE 1. Introduction Besides biomechanical support and functional performance, surface characteristics of metallic implants are essential aspects to be considered during the fabrication of implantable devices for orthopedic and orthodontic applications. It has been shown that specific surface features of metallic implants are responsible for their long-term mechanical stability and tribological outcomes [1–3], corrosion resistance, and potential ion-mediated toxicity [4–6], as well as for their osseointegration (by influencing the behavior of cells that control the final bone formation) [7–9]. As metallic biomaterials represent key elements for hard tis- sue replacement and restoration, a plethora of efforts have been undertaken to limit their main shortcomings, namely bioinertness and poor bioactivity. Many studies confirmed the importance of surface characteristics for reaching a proper and augmented osseointegra- tion [10–13], with a special emphasis forming a bioactive implant-to-bone interface. Surface modification of metallic implants, either performed by mechanical, chemical, or physical techniques [14–16], results in beneficial outcomes in implants’ reactivity, hy- Polymers 2021, 13, 4303. https://doi.org/10.3390/polym13244303 https://www.mdpi.com/journal/polymers