Special Issue "Orthopaedic Biomaterials"

Guest Editor
Prof. Dr. I. M. Ward
Polymer IRC, School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
Website: http://www.pcf.leeds.ac.uk/people/view/info/imw/
E-Mail:
Phone: 00 44 113 343 3808
Fax: 00 44 113 343 3846

Guest Editor
Prof. Dr. Thomas J. Webster
Divisions of Engineering and Orthopaedics, Brown University, Box D, 224 Barus and Holley, 182 Hope Street, Providence, RI 02912, USA
Website: http://www.websternano.com/
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Title: In vivo Corrosion of Two Novel Magnesium Alloys ZEK100 and AX30 and Their Mechanical Suitability as Biodegradable Implants
Authors: T. A. Huehnerschulte ¹, N. Angrisani ¹, D. Rittershaus ¹, D. Bormann ², H. Windhagen ³ and A. Meyer-Lindenberg ⁴
Affiliations: ¹ University of Veterinary Medicine Hanover, Foundation, Small Animals Clinic, Buenteweg 9, 30559 Hannover, Germany;
E-Mail: Tim.Andreas.Huehnerschulte@tiho-hannover.de (T.A.H.)
² University of Hanover, Hannover Center for Production Technology, Institute of Materials Science, An der Universitaet 2, 30823 Garbsen, Germany
³ Hanover Medical School, Department of Orthopedics, Anna-von-Borries Straße 11, 30167 Hannover, Germany
⁴ Ludwig-Maximilians-Universität München, Faculty of Veterinary Medicine, Clinic for Small Animal Surgery and Reproduction, Centre of Clinical Veterinary Medicine, Veterinärstr. 13, 80539 München, Germany
Abstract: Prior studies pointed out that magnesium alloys are suitable as material for biodegradable implants, because they excel the widely used polymeric implants in stability and their corrosion products induce fewer inflammatory reactions. In magnesium alloys the ligands modify the corrosion properties and the mechanical characteristics. For implants in contact to bone the alloys most commonly examined are magnesium-aluminum-alloys and magnesium-rare earths-alloys. Rare earths were shown to improve corrosion resistance and to increase mechanical strength, but their exact composition is hard to predict. Therefore a reduced content of rare earths could be favorable. With ZEK100 and AX30 two novel magnesium alloys, that have a reduced content of rare earths (ZEK100; magnesium with 1wt% zinc, <1wt% zirconium and <1wt% of rare earths) or contain no rare earths at all (AX30; magnesium with 3wt% aluminum and <1 wt% calcium) and which were shown to be in vitro promising are to be investigated. AX30 also contains calcium, which improves the corrosion resistance and the biocompatibility. In research on magnesium implants, no noninvasive method to measure the true in vivo corrosion of implants in hard tissue existed so far. The in vivo micro computed tomography (µCT) can be used for in vivo scans of the experimental animals and may therefore be a suitable tool to asses the in vivo corrosion without influencing it. The aim of the study was to investigate the in vivo degradation characteristics of the two new magnesium alloys AX30 and ZEK100 in an animal model and at the same time to asses the suitability of the in vivo µCT as a tool to examine the corrosion of magnesium implants. To do so, 24 female New Zealand White Rabbits were randomized into 4 groups, differing in time and/or material (AX30 3 months, AX30 6 months, ZEK100 3 months and ZEK100 6 months). An implant was inserted in the medullary cavity of both tibiae of each animal. During the follow up clinical examinations, X-rays and in vivo micro computed tomography scans were done regularly. After euthanasia implants were gathered and subjected to further analyzes, like REM with EDX, weighing and mechanical testing. The results show, that the in vivo µCT is of great advantage in analyzing the in vivo degradation of magnesium alloys, because it allows a true 3D quantification of the corrosion rate over time and qualitative assessment of the corrosion morphology, without any interference with the ongoing animal experiment. Furthermore, it allows an examination of the host reactions at the same. It was shown that the location within the bone has a remarkable effect on the rate of corrosion, which is of great importance for possible designs of intramedullar implants made of magnesium alloys and it emphasizes importance to test biodegradable magnesium implants in vivo and in their target location. Due to its initial mechanical strength and its degradation characteristics ZEK100 seems to be suitable as a material for biodegradable implants in weight bearing bones. AX30 displays good degradation behavior but it is of too little mechanical strength for applications in weight bearing bones. It might be a material suitable for mechanically less demanding applications.

Title: Calcium Sulfate with Stearic Acid as an Encouraging Carrier for the Reindeer Bone Protein Extract
Authors: Hanna Tölli ^1,2,3, Elli Birr ³, Kenneth Sandström ³, Timo Jämsä ^2,4 and Pekka Jalovaara ^1,3
Affiliations: ¹ Division of Orthopaedic and Trauma Surgery, Department of Surgery, Institute of Clinical Medicine, Oulu University Hospital, FIN-90014 University of Oulu, Finland; E-Mail: hanna.tolli@bbs-artebone.fi
² Department of Medical Technology, Institute of Biomedicine, University of Oulu, FIN-90014 University of Oulu, Finland
³ BBS- Bioactive Bone Substitutes Ltd, FIN-90220 Oulu, Finland
⁴ Department of Diagnostic Radiology, Institute of Diagnostics, Oulu University Hospital, FIN-90014 University of Oulu, Finland
Abstract: Various bone proteins and growth factors in specific concentrations are required for bone formation. If the body cannot produce sufficient quantities of these factors, bone trauma can be healed with an implant that includes the required factors in a carrier. This study was designed as an evaluation of various calcium salt candidates that can be used as carrier with reindeer bone protein extract to induce ectopic bone formation in the muscle pouch model of mouse. The bone protein extract was either impregnated into the disc form of carrier or mixed with carrier powder before implantation. The radiographic analysis indicated increased bone formation in all of the active groups containing the bone protein extract compared to the controls within 21 days follow-up. The highest bone formation was seen in the group with calcium sulfate with stearic acid where new bone and calcified cartilage were clearly visible. The greatest bone formation occurred in the groups that had the bone protein extract readily available. That indicated that the bone forming factors in sufficient concentrations are required at the early stage of bone formation. The calcium sulfate with stearic acid was the most suitable and effective carrier for the reindeer bone protein extract.
Keywords: bone protein extract; bone trauma; calcium salt; carrier; growth factor