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Back pain, affecting 80% of the population, significantly strains the healthcare system. In European countries, spine-related hospital discharges account for 14.2% to 45.6% of all musculoskeletal disease discharges. Conservative treatments like medication and physical therapy are generally preferred, but surgical intervention may be necessary for some. Spinal surgeries often involve implants, such as spinal cages, spinal instrumentation, or total disc replacements, used to treat abnormal spinal curvatures or intervertebral disc degeneration.

Despite their widespread use, spinal implants face challenges such as failed vertebral fusion, infections, and implant failure, which can release harmful ions and particles. Researchers are developing new materials with antibacterial properties and improved interaction with bone tissue. Innovations include wear-resistant coatings to prevent metal ion release and biodegradable materials that the body gradually replaces, reducing infection risks and the need for revision surgeries. However, these advances present challenges. Degradation by-products can migrate more easily to other parts of the body and may elicit unwanted biological responses.

The primary aim of this thesis was to investigate the biological effects of these degradation products from an in vitro perspective. This involved using several relevant cell types and examining morphological and functional changes. A composite of calcium phosphate and polylactic acid was initially examined for spinal fusion. The cell response to the degradation products was comparable to those of a clinically successful calcium phosphate, showing no negative impact on preosteoblast cells. Additionally, silicon nitride (SiN) coatings, known for their wear resistance properties, were explored. The incorporation of additional elements into SiN coatings was studied to enhance stability and durability. It was found that fibroblast and microglial cells tolerated the ions and particles released during degradation similarly to current orthopedic materials. Lastly, the effects of particles from spinal implants on glial cells were evaluated. While most particles did not trigger inflammation, high doses of SiN particles negatively affected microglial cells, reducing their ability to neutralize infectious agents. This highlights the need for further research to fully understand the biological safety of silicon nitride in spinal implants.

In summary, this thesis expands the understanding of the biological responses to spinal implant degradation products, aiding the development of safer and more effective implants.