Reaction of bone nanostructure to a biodegrading Magnesium WZ21 implant – A scanning small-angle X-ray scattering time study

Understanding the implant–bone interaction is of prime interest for the development of novel biodegrading implants. Magnesium is a very promising material in the class of biodegrading metallic implants, owing to its mechanical properties and excellent immunologic response during healing. However, the influence of degrading Mg implants on the bone nanostructure is still an open question of crucial importance for the design of novel Mg implant alloys. This study investigates the changes in the nanostructure of bone following the application of a degrading WZ21 Mg implant (2 wt% Y, 1 wt% Zn, 0.25 wt% Ca and 0.15 wt% Mn) in a murine model system over the course of 15 months by small angle X-ray scattering. Our investigations showed a direct response of the bone nanostructure after as little as 1 month with a realignment of nano-sized bone mineral platelets along the bone–implant interface. The growth of new bone tissue after implant resorption is characterized by zones of lower mineral platelet thickness and slightly decreased order in the stacking of the platelets. The preferential orientation of the mineral platelets strongly deviates from the normal orientation along the shaft and still roughly follows the implant direction after 15 months. We explain our findings by considering geometrical, mechanical and chemical factors during the process of implant resorption.Statement of significanceThe advancement of surgical techniques and the increased life expectancy have caused a growing demand for improved bone implants. Ideally, they should be bio-resorbable, support bone as long as necessary and then be replaced by healthy bone tissue. Magnesium is a promising candidate for this purpose. Various studies have demonstrated its excellent mechanical performance, degradation behaviour and immunologic properties. The structural response of bone, however, is not well known. On the nanometer scale, the arrangement of collagen fibers and calcium mineral platelets is an important indicator of structural integrity. The present study provides insight into nanostructural changes in rat bone at different times after implant placement and different implant degradation states. The results are useful for further improved magnesium alloys.

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