**Preface to "Surface Engineering of Biomaterials"**

Unmet clinical needs, in terms of improved implant fixation, tissue regeneration, infection prevention, and complex reconstructive surgeries, present increasingly more sophisticated challenges that require the development of implants with multiple advanced functionalities. Moreover, a significant increase in life quality and expectancy, together with improvements in surgical techniques, have resulted in a steep increase in implant usage over the past 20 years. Therefore, many attempts have been devoted to the design and synthesis of new biomaterials which could potentially meet these increasing demands. In particular, additive manufacturing or 3D-printing enable us to fabricate biomaterials with much larger surface areas, thereby amplifying the functionalities which originate from their surfaces [1]. The huge surface area of the 3D-printed implants may be treated using various surface biofunctionalization techniques that modify its nano-topography and surface chemistry [2,3]. Furthermore, multifunctional coatings with bespoke release profiles of the active agents provide many opportunities to repair and reconstruct the damaged tissue or organ [4,5]. Nonetheless, there are still many complicated clinical scenarios that should be tackled in this field, and in response, we have focused this Special Issue of Coatings on emerging efforts in the surface engineering of biomaterials and their impact on reducing the abovementioned challenges.

Contributions to this Special Issue include original papers covering the development of different surface modification and coating techniques, which improve the bio-functionality of implants. In particular, Lee et al. [6] immobilized rhBMP-2 and/or rhPDGF-BB on titanium implant surfaces via heparin-dopamine interfaces and evaluated the bone regeneration performance of surface treated alveolar ridges in an animal study (beagle dogs). In an in vitro study, the solution plasma surface modification technique was used by Badruddoza Dithi et al. [7] to apply a thin and uniform hydroxyapatite film coating on titanium implants, which enhanced its bone formation. In another study [8], a novel bioactive glass was coated on a dental implant via electrophoretic deposition, which yielded a firm and non-cytotoxic coating. Furthermore, different surface modification techniques, namely electropolishing, micro-powder blasting and anodizing, were used by Yen et al. [9] to fabricate various micro-nano structure morphologies on an aluminum template. Finally, Muguruma et al. [10] investigated the mechanical and bonding properties of diamond-like carbon coating on stainless steel samples made by the plasma-based ion implantation/ deposition method.

In summary, this Special Issue provides different surface engineering approaches to improve implants' bioactivity, which could potentially be used for (pre-)clinical cases. As such, I hope that this Special Issue will act as a forum to highlight and identify emerging research in the field.
