Abstract
The degradation rate of magnesium (Mg) alloys is a key parameter to develop Mg-based biomaterials and ensure in vivo-mechanical stability as well as to minimize hydrogen gas production, which otherwise can lead to adverse effects in clinical applications. However, in vitro and in vivo results of the same material often differ largely. In the present study, a dynamic test bench with several single bioreactor cells was constructed to measure the volume of hydrogen gas which evolves during magnesium degradation to indicate the degradation rate in vivo. Degradation medium comparable with human blood plasma was used to simulate body fluids. The media was pumped through the different bioreactor cells under a constant flow rate and 37 °C to simulate physiological conditions. A total of three different Mg groups were successively tested: Mg WE43, and two different WE43 plasma electrolytically oxidized (PEO) variants. The results were compared with other methods to detect magnesium degradation (pH, potentiodynamic polarization (PDP), cytocompatibility, SEM (scanning electron microscopy)). The non-ceramized specimens showed the highest degradation rates and vast standard deviations. In contrast, the two PEO samples demonstrated reduced degradation rates with diminished standard deviation. The pH values showed above-average constant levels between 7.4–7.7, likely due to the constant exchange of the fluids. SEM revealed severe cracks on the surface of WE43 after degradation, whereas the ceramized surfaces showed significantly decreased signs of corrosion. PDP results confirmed the improved corrosion resistance of both PEO samples. While WE43 showed slight toxicity in vitro, satisfactory cytocompatibility was achieved for the PEO test samples. In summary, the dynamic test bench constructed in this study enables reliable and simple measurement of Mg degradation to simulate the in vivo environment. Furthermore, PEO treatment of magnesium is a promising method to adjust magnesium degradation.
Highlights
In medicine, the right choice of biomaterial in an important aspect for the overall success of a surgical therapy
The evolved hydrogen gas from Mg degradation was captured by an upside-down funnel and measured in a scaled cylinder placed over the funnel
The fluid dynamic testing was established by considering physiological body temperature (37 ◦C), a corrosive medium similar to the human blood plasma (MEM + 10% FCS and Glutamine) and choosing a reasonable methodical approach to determine the degradation of the magnesium by measuring the evolving H2-volumes
Summary
The right choice of biomaterial in an important aspect for the overall success of a surgical therapy. Throughout the years, biomaterials have been used in the field of medicine to enhance the outcome and quality of a procedure. Bony defects require a biomaterial that mimics the characteristics of bone, such as magnesium, whereas the regeneration of soft tissue demands fewer rigid biomaterials, such as polymers and their derivatives [1,2,3,4]. Of the various fields of medicine demanding reliable biomaterials, the fields of orthopedic and maxillofacial surgery, in particular, have been experimenting with different biomaterials to reach an optimal outcome [5,6,7]. Magnesium is an important physiological element in the human body and can be found in skeletal bones, muscles, soft tissues and in the extracellular compartments as an important regulator of physiological processes [11,12,13]. Magnesium reacts according to the following equation [16]: Mg + 2H2O → Mg(OH)2 + H2
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