**1. Introduction**

Biocompatible titanium (Ti) and its alloys are broadly accepted metallic materials for hard tissue repair (orthopedic and dental) for its exceptional combination of biomedical and mechanical properties [1]. Even though Ti and its alloys are used as an implant material for more than three decades, there are still some inadequacies that need to be addressed. Especially, bacterial associated diseases/infections during surgery always carry serious hazards leading to a severe clinical economic consequence such as re-hospitalization, complex re-surgeries, implant loosening, high economic associated costs and sometimes even death. Recent studies estimated the current incidence of bacterial infection had incurred a total financial cost of \$10 billion with close to 100,000 infections and 8000 reported deaths in the United States alone [2,3]. The reason being, when compared to bioactivity enhancement modifications, relatively very few efforts have been made to address antibacterial activity on the surface before the implantation. It is a known fact that treating an infected orthopedic implant materials post-surgery is hugely complicated, primarily due to the inherent difficulties of treating an established biofilm formed by microorganisms on the surface [4].

Nevertheless, many preventative strategies have been proposed by academics to improve the antibacterial ability of the material before the implantation/surgery [5,6]. But, most of the solutions proposed for obtaining antibacterial surfaces without losing its bioactivity require a complex coatings technique. In this view, several novel strategies such as topographical modifications (nanotubes), incorporating antibacterial agents (Ag, Cu) and various surface treatments [7–10] were suggested/developed to disinfect the bacterial colonization on biomedical implants before the implantation. However, still traces of evidence of bacterial invasion can be still found even after the post-surgery. Nevertheless, these findings highlight the crucial need modifications to the material to prevent bacterial implant-associated infections at early stages. Among these, surface modification either by treatment or coating on the implant material has been well recognized as the best substitute to design and alter the biological performance of the Ti and its alloys [11].

Titanium dioxide (titania, TiO2), a bioceramic material have become a focus of significant research due to its versatile characteristics [12,13]. TiO2 nanoparticles are well-known for its stability, non-toxicity, UV resistance and found its application in cosmetics, electronics, biomedical, optics and also as a cleaning reagent [14]. Ever since first reported by Matsunaga et al., TiO2 photocatalytic properties have drawn more attention in the biomedical field for its specific ability to a kill wide variety of microorganisms under a strong UV radiation [15,16]. In brief, when the surface of TiO2 is exposed to a strong UV light, electron-hole pairs (*e*−-*h*+) are generated in the valence band and reacts with oxygen and atmospheric water (OH−) thereby yielding to reactive oxygen species (ROS). The generated ROS acts a powerful oxidizing agent capable of decomposing organic molecules and inactivating micro-organisms through a series of chemical reactions, leading to the powerful antibacterial agent [17–19]. Also, for enhancing the composite cell attachment and proliferation properties, TiO2 nanoparticles are projected as a secondary phase material for biodegradable polymer matrices [20–25].

Over the past few years, polymer/ceramic nanocomposites as scaffold materials have attracted more attention for bone tissue engineering. Many works have been described in the literature which explains the enhancement of Ti-based implants with organic or organic-inorganic substitute surface coatings [26–28]. In particular, because of the high porosity and large specific surface area, nanocomposite fiber scaffolds have been successfully explored in tissue engineering for orthopedic implants. Among the various techniques for nanocomposite scaffold fabrication, the electrospinning process is described as the most reliable process for producing long and continuous fibers. Electrospinning is a simple and economical fiber fabrication technique that utilizes electrical forces to produce ultrafine micro and nanofibers templets with a wide range of polymers for a variety of applications [29,30]. In most typical tissue engineering strategies, the engineered 3D porous scaffolds serve as a pattern for cell adhesion, expansion, and proliferation of cells ingrowth. Electrospun nanofibers are favorably proficient of imitating microarchitecture of native ECMs owing to their high surface area to volume ratio and relatively large internal porosity. This technique also enables to entrap inorganic ceramic nanoparticles into the organic polymer in a very convenient way to enhance physical, chemical and mechanical properties.

Polycaprolactone (PCL), a semi-crystalline biodegradable polymer, known for its superior mechanical properties, excellent biocompatibility, and slower degradation rate. It is a widely accepted polymer for drug release carriers, biodegradable packaging materials, and more importantly for the development of 3D scaffolds for bone tissue engineering applications. Numerous techniques have been developed to fabricate PCL-based scaffold to a simple two-dimensional structure (casting) to complex three-dimensional (3D printing) objects [31,32]. However, PCL in current form is hydrophobic, which results in lack of wettability and poor cell attachment. Successful blending with bioceramics haven been reported elsewhere [9,23,27,33] for improved biological properties.

The current study aims to incorporate TiO2 nanoparticles into the PCL scaffolds for improving mechanical properties, biological properties (bioactivity, anti-bacterial, cell adhesion, and cell proliferation) and physiochemical properties (hydrophilicity) for orthopedic applications. To achieve that, PCL/TiO2-nanocomposite scaffolds were synthesized by electrospinning and coated on cpTi substrates.
