Titanium and stainless steel are commonly known as osteosynthesis materials with high strength and good biocompatibility. However, they have the big disadvantage that a second operation for hardware removal is necessary. Although resorbable systems made of polymers or magnesium are increasingly used, they show some severe adverse foreign body reactions or unsatisfying degradation behavior. Therefore, we started to investigate molybdenum as a potential new biodegradable material for osteosynthesis in craniomaxillofacial surgery. To characterize molybdenum as a biocompatible material, we performed in vitro assays in accordance with ISO Norm 10993-5. In four different experimental setups, we showed that pure molybdenum and molybdenum rhenium alloys do not lead to cytotoxicity in human and mouse fibroblasts. We also examined the degradation behavior of molybdenum by carrying out long-term immersion tests (up to 6 months) with molybdenum sheet metal. We showed that molybdenum has sufficient mechanical stability over at least 6 months for implants on the one hand and is subject to very uniform degradation on the other. The results of our experiments are very promising for the development of new resorbable osteosynthesis materials for craniomaxillofacial surgery based on molybdenum.

Molybdenum is an essential trace element, considered in recent work to be a promising 3D-printable biodegradable material for medical applications. Specifically, in our recent in vitro work, we were able to show that molybdenum is a material of high biocompatibility, sufficient stability, and uniform degradation. Thus, it seems to fulfill the optimal requirements for a resorbable osteosynthesis material. To confirm these results in a complex organism, we tested molybdenum against the gold standard titanium. For this purpose, we implanted either molybdenum or titanium implants into the nuchal folds of 48 Wistar rats. We examined all animals daily for clinical inflammatory parameters and euthanized one-third of the cohort after 12, 24, and 52 weeks, respectively. Subsequently, the tissues surrounding the samples, as well as the spleens, livers, and kidneys of all animals, were pathologically processed and examined. Subsequently, selected samples were examined metallographically. No significant increased inflammatory reaction of the material molybdenum versus titanium could be detected, either clinically or pathologically. The animals did not show any significant differences regarding their general condition or weight development. However, the introduced molybdenum platelets showed significantly less degradation than previously in the in vitro model. This is most likely due to the capsule formation, which has already been described for other implants.

Titanium continues to be the gold standard in the field of osteosynthesis materials. This also applies to pediatric craniofacial surgery. Various resorbable materials have already been developed in order to avoid costly and risky second operations to remove metal in children. However, none of these resorbable materials have been able to completely replace the previous gold standard, titanium, in a satisfactory manner. This has led to the need for a new resorbable osteosynthesis material that fulfills the requirements for biocompatibility, stability, and uniform resorption. In our previous in vitro and in vivo work, we were able to show that molybdenum fulfills these requirements. To further confirm these results, we conducted a proof of concept in four domestic pigs, each of which was implanted with a resorbable molybdenum implant. The animals were then examined daily for local inflammatory parameters. After 54 days, the animals were euthanized with subsequent computer tomography imaging. We also removed the implants together with the surrounding tissue and parts of the spleen, liver, and kidney for histopathological evaluation. The molybdenum implants were also analyzed metallographically and using scanning electron microscopy. A blood sample was taken pre- and post-operatively. None of the animals showed clinical signs of inflammation over the entire test period. Histopathologically, good tissue compatibility was found. Early signs of degradation were observed after 54 days, which were not sufficient for major resorption. Resorption is expected with longer in situ residence times based on results of similar earlier investigations.