Advancements in biomaterials and bioactive solutions for lumbar spine fusion cages: Current trends and future perspectives.

Spinal fusion is considered today as the last treatment option for different spinal conditions, such as degenerative and infectious illnesses. It consists of fusing two or more vertebrae to obtain reinforcement/fixation based on several methods used to sustain osteosynthesis and grafting, such as cage insertion in the intervertebral space, which provides an important level of mechanical stability, impacting only a low amount of the natural biomechanics of the spine and facilitating the implant bony ingrowth. This review paper first explores the background of intervertebral fusion, emphasizing medical applications and material properties of interbody fusion cages. It then provides a brief historical overview and discusses antibacterial efficacy-related issues. Additionally, some of the most met-in-clinical practice lumbar interbody cages with a detailed description of their geometry and examples of clinical trials performed worldwide are provided. The biomaterials used in lumbar cage manufacture are comprehensively described. In the last part of this review paper, special attention is devoted to prospective biomaterials and coatings for spine fusion cages. Firstly, the rationale for using Mg-based alloys or high osteogenic polycaprolactone as biodegradable and bioresorbable alternatives in the spinal cage industry, addressing the clinical limitations of traditional Ti alloys and polyether ether ketone, is provided. Then, a more conservative approach, focusing on the use of bioactive or antibacterial coatings on the already certified biomaterials, is presented as a second alternative to the existing products on the market. Relevant literature studies are reviewed, and the osteointegrative, bioactive, or antibacterial character of the coatings is explained. Finally, our review identifies current clinical limitations and offers future perspectives that will provide better bioactive solutions, improving the existing biomaterials.