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Talks and Poster Presentations (without Proceedings-Entry):

J. Eichler, S. Fischerauer, L. Berger, E. Martinelli, M. Cihova, T. Kraus, J. Löffler, A. Weinberg:
"Pre-clinical characterization of RE-free bioresorbable magnesium screws in a growing sheep model";
Poster: 10th World Biomaterials Congress, Montreal; 2016-05-17 - 2016-05-22.



English abstract:
Pre-clinical characterization of RE-free bioresorbable magnesium screws in a growing sheep model
Johannes Eichler1, Stefan F. Fischerauer2, Leopold Berger3, Elisabeth Martinelli1, Martina Cihova4, Tanja Kraus5, Jörg F. Löffler4 and Annelie M. Weinberg1
1 Medical University of Graz, Department of Orthopaedics, Austria
2 Medical University of Graz, Department of Trauma Surgery, Austria
3 TU Wien, Institute of Building Construction, Austria
4 ETH Zurich, Laboratory of Metal Physics and Technology, Department of Materials, Switzerland
5 Medical University of Graz, Department of Paediatric Orthopaedics, Austria
Introduction: Screw osteosynthesis is a common method to treat fractures with small and middle sized related bone fragments in an easy and effective way. After fracture reduction, the corresponding fragments are stabilized by osteosynthesis with screws made of stainless steel or Titanium. However, the remaining metal may cause unwanted discomfort such as loosening or chronical inflammation. Therefore screw removal is required when the fracture has healed. So additional morbidity for the patient due to a second surgical intervention may be a consequence. Biodegradable Mg screws have great potential for deployment in paediatric, adolescent and also adult osteosynthesis, as they achieve reasonable mechanical properties, obviate a second surgical intervention and might be able to support the healing process. However, a huge drawback of Mg implants is their fast degradation rate, which can be retarded by adding rare-earth (RE) elements for alloying. Nevertheless, they are considered to be noxious for the human body and not suitable for a growing skeleton.
The development of RE-free Mg implants resulted in first Mg-Zn-Ca alloys containing 5 wt.% Zn (ZX50), which developed huge amounts of gas inside the bone and was degrading too rapid. [1]. Mg-Zn-Ca alloys containing less Zn (ZX10) [2] were observed, showing a suitable degradation behaviour and acceptable hydrogen gas evolution in a living rat model.
The aim of this study was to evaluate the degradation and gas evolution, as well as bone incorporation and bone reaction on Zn-poor Mg-Zn-Ca (ZX00) screws in an in vivo sheep model. An additional group with surface treatment (polishing) was evaluated regarding the mentioned parameters to evaluate the influence of expected surface impurities caused by the manufacturing process.
Methods: n=7 RE-free magnesium screws with a diameter of 3.5 mm and a length of 16 mm were dry machined using the alloy ZX00 (Mg-0.3Zn-0.4Ca) and divided into two groups. N=3 screws received a chemical surface treatment (polishing with ethanol and phosphoric acid) and n=4 screws were used without this treatment. All implants were cleaned, packaged and gamma sterilized and implanted into the diaphyseal right tibiae of two growing sheep (n=1 with polished screws and n=1 with unpolished screws). The study was accredited by the Austrian Ministry of Science, Research and Economy, accreditation number BMWFW-66.010/0190-WF/V/3b/2014.
Under general anaesthesia, small skin incisions in the mid-diaphyseal region and the proximal and distal diaphysis of the sheep tibiae were performed. Soft tissue was mobilized carefully to reach the bone. A monocortical drill-hole was made. Due to the use of a non-self-tapping screw design, a thread was cut in advance and the screws were inserted into the bones. Afterwards the wounds were closed in layers. All surgical interventions were performed under sterile clinical conditions.
The in vivo degradation behaviour was evaluated by clinical CT imaging (Siemens Sensatom 64) at 2 and 6 weeks after implantation. After week 6 both animals were euthanized and their tibiae were harvested for micro CT evaluation (Siemens Inveon micro CT) of bone incorporation as well as bone and tissue reactions. Implant volume and surface as well as gas volume were quantified with Materialise MIMICS, ver. 17.
Results: All screws were well tolerated by the animals and did not show adverse effects like inflammatory signs (redness, swelling) or osteolytic bone reactions on CT scans. New bone formation during the growth period of the animal was found forming a tight bone-screw interface which differs in slightly lower bone contact for the polished screws. Moderate degradation could be measured in both screw types and also the amount of gas was low in polished and unpolished versions.
Discussion and Conclusions: Polished and unpolished ZX00 screws showed good results after a period of 6 W in vivo. The slightly lower bone contact of polished screws may be caused by changed surface condition or slight volume loss through polishing. However, further investigations are required to assess longterm effects.
This work was financially supported by Laura Bassi BRIC, Austrian Promotion Agency.
References:
[1] Kraus T, Fischerauer SF et al. (2012) Magnesium alloys for temporary implants in osteosynthesis: in vivo studies of their degradation and interaction with bone, Acta Biomater. 8:1230-8.
[2] Hofstetter J, Becker M, Martinelli E et al. (2014) High-strength low-alloy (HSLA) Mg-Zn-Ca alloys with excellent biodegradation performance, JOM 66 (2014) 566 - 572


"Official" electronic version of the publication (accessed through its Digital Object Identifier - DOI)
http://dx.doi.org/10.3389/conf.FBIOE.2016.01.00615


Created from the Publication Database of the Vienna University of Technology.