## 1 Introduction  
Globally, due to the increasingly aging population, the demand for orthopedic and dental implants continues to rise. Aseptic loosening remains one of the most common complications impacting long-term implant failures [1]. Aseptic loosening may be driven by several factors, including insufficient bone-implant integration, micromotion, and inflammatory responses to wear particles. Enhancing early-stage osseointegration and bioactivity at implant-bone interfaces would likely reduce the incidence of aseptic loosening and extend implant lifetimes [1]. Titanium and its alloys are used to produce dental and orthopedic implants due to their excellent strategic combination of mechanical properties and corrosion resistance [1, 2, 3]. However, the amorphous oxide that naturally forms on titanium surfaces in oxygenated environments is bioinert and thus is a less-than-ideal implant surface [2, 3, 4]. Therefore, surface modifications are commonly utilized to improve bone-titanium implant interactions [2, 3, 4]. Anodization is a commonly used electrochemical surface modification technique due to its ability to easily coat complex surfaces in a single processing step. Anodization processes are capable of simultaneously modifying the surface chemistry, topography, and crystallinity of titanium implants [2, 3, 4]. Recent anodizationstrategies have focused on using electrolytes that mimic the mineral composition of natural bone to enhance the formation of bioactive oxide coatings [2; 3; 4; 5; 6; 7]. Bone is reported to have a composition of approximately 34.8 wt% of calcium (Ca), 15.2 wt% of phosphorus (P), and 0.72 wt% of magnesium (Mg) [8; 9]. Ca and P are critical for bone mineralization and play important roles in osteoblast signaling, matrix mineralization, and scaffold formation. Ca and P also play essential roles in enhancing cell adhesion through interactions with extracellular matrix proteins regulating osteoblast and osteoclast activity, promoting osteogenic marker expression, and supporting mineral deposition and matrix formation [9]. Anodization of titanium surfaces in electrolytes containing Ca and P has been shown to produce oxides with enhanced bioactivity and increased osteoblast activity [10; 11]. Hydroxapatite is a calcium phosphate compound that constitutes 50-70% of bone [12]. Hydroxapatite exhibits strong osteoconductive properties, facilitating the attachment of bone-forming cells and the development of new bone tissue [1; 13]. Conventional plasma-sprayed hydroxyapatite coatings are FDA-approved and are widely used for implant coatings [1]. However, plasma-sprayed hydroxyapatite coatings are typically 50-75 um thick and experience significant thermal decomposition of hydroxyapatite particles during the spraying process due to dehydroxylation and phase changes [1]. These factors often lead to less-than-ideal coating adhesion strengths and may result in early delamination [14; 15]. Anodization processes have also been used to produce hydroxyapatite-containing oxide coatings directly on titanium surfaces [2; 5; 6; 16]. The anodized hydroxyapatite-containing oxides have shown improved adhesion strengths to the substrate materials compared to their plasma-sprayed counterparts. The improved adhesion of the anodized hydroxyapatite-containing oxides has been attributed to the formation of an oxide interlayer between the titanium substrate and hydroxyapatite layer [5; 16]. Biological apatite, or bone-like apatite, is often non-stoichiometric as opposed to synthetic hydroxyapatite and consists of carbonate substitutions [17; 18]. The carbonate substitutions have been shown to increase the apatite solubility and resorption rate and are thus desirable for bone remodeling [1; 18]. As stated earlier, Mg is also an essential element found in natural bone. Arc ion-plated Mg coatings on titanium scaffolds have shown improved cellular adhesion, angiogenesis, and osteogenic differentiation compared to uncoated scaffolds [19].