Metallic implant materials with superior mechanical properties and biocompatibility are in high demand driven by the growing aging population and heightened expectations for quality of life [1,2]. These materials can be divided into non-degradable and degradable implants. Among non-degradable implants, titanium (Ti) and its alloys have been extensively utilized in biomedical applications due to their high mechanical properties, good corrosion resistance and favorable biocompatibility [3,4]. However, the elastic moduli of common Ti alloys (∼110 GPa of Ti-6Al-4V, ∼100 GPa of commercially pure Ti (CP-Ti)) are significantly higher than those of human bone (0.01-30GPa), which can induce the “stress shielding” effect [2,3,5]. This phenomenon may lead to osteoporosis, implant loosening, or even bone fracture. Although a series of β-type Ti alloys have been developed to reduce the elastic modulus (e.g., ∼42 GPa of Ti-24Nb-4Zr-7.9Sn, ∼45 GPa of Ti-25Nb-11Sn), dense Ti alloys still exhibit relatively high moduli [[6], [7], [8], [9]]. In contrast, Ti alloys with a porous structure have emerged as a promising implant, offering significantly lower elastic moduli compared to their dense counterparts [10]. Moreover, the enhanced specific surface area of the porous structure facilitates bone ingrowth within the material [[10], [11], [12]]. However, the porous Ti presents challenges in providing adequate mechanical support and promoting early-stage bone regeneration in vivo owing to the bio-inertness of Ti.

Magnesium (Mg) and its alloys are increasingly applied as degradable implants owing to their high specific strength and low elastic modulus (41-45 GPa) [13,14]. During degradation, the released Mg ions (Mg2+) induce the osteogenic effects [[13], [14], [15], [16]]. As an essential element in the human body, Mg has a recommended daily intake of 240-420 mg, and ∼60% of total bodily Mg stored in the bone matrix [17,18]. However, the mechanical strength of common Mg alloys remains lower than that of Ti alloys, raising doubts about their use as load-bearing components. Incorporating Mg element into Ti alloys via micro-arc oxidation and ion implantation has emerged as a promising solution to enhance bioactivity [[19], [20], [21]]. Nevertheless, the Mg content and phase dimensions are often insufficient to generate adequate pores for bone ingrowth through degradation.

To capitalize on the benefits of Ti and Mg alloys while mitigating their respective drawbacks, a Ti-Mg composite has been developed for long-term implant applications. This engineered Ti-Mg composite system consists of a porous Ti matrix encapsulating biodegradable Mg components, enabling controlled degradation behavior through the Ti framework’s structural continuity. The composite architecture synergistically combines the durability of the Ti skeleton with the degradable characteristics of Mg, providing stable mechanical support while facilitating gradual bioactive transition at the tissue interface. The introduction of Mg reduces the elastic modulus of the Ti-Mg composite, with the modulus further decreasing as Mg degradation. During implantation, the porous structure forms with Mg degrades, and bone tissue is guided to grow into the pores. The Ti matrix with high corrosion resistance maintains its original structure, exhibiting performance comparable to that of conventional porous Ti alloys.

To achieve synergistic performance enhancement, Ti alloys and Mg alloys with superior mechanical and functionalized properties have been strategically incorporated into the Ti-Mg composite system as key constituents, as illustrated in Fig. 1. For instance, Ti-6Al-4V imparts higher strength compared to CP-Ti, while Ti-Ni alloys (eg, Ti49.2Ni50.8, at.%) provides superelasticity [[22], [23], [24]]. Mg-Zn alloys (eg, Mg-3Zn, wt.%), on the other hand, enhance antibacterial properties via Zn²⁺ release during degradation [25].

To date, several methods have been employed to create Ti-Mg composites with exceptional overall performance, demonstrating significant potential for applications in orthopedic and dental implants. This work provides a comprehensive review of the current state of Ti-Mg composites, organized into four sections (Fig. 2). The first section outlines manufacturing technologies for Ti-Mg composites, while the second section details their macrostructure design and typical microstructures. The third section examines their properties, including mechanical performance, degradation behavior, and biological compatibility. Future prospects are discussed in the final section.