Evaluierung der Wirksamkeit eines neuartigen RIA/mPCL-TCP Scaffold-Systems zur Behandlung kritischer segmentaler Knochendefekte im Vergleich zum Goldstandard des autologen Knochentransplantates am Schaf-Großtiermodell
Biomaterialien
Herstellung und Eigenschaften von Funktionsmaterialien
Zusammenfassung der Projektergebnisse
It was the aim of this research project to analyse the regenerative capacity of a novel combination of medical-grade composite scaffolds with autologous bone grafting material harvested from two different sites of the body, that is the iliac crest (current clinical gold standard autograft harvesting site) and the femoral endosteal cortex using the Reamer-Irrigator-Aspirator-System (RIA) in an ovine tibial defect model. I started working first in order to fully establish and characterise the 6cm tibial defect ovine animal model at QUT. While feasibility to extend the defect length to 6cm had been shown by Prof. Hutmacher and his team in two pilot surgeries before, I was now able to establish a full study protocol including standardised surgical procedures and postoperative care plans for such a large volume tibial defect animal model during my time at QUT. In this first part of my research project, I have successfully operated 8 sheep creating a 6cm tibial defect that was bridged with a porous 6cm mPCL-TCP-scaffold loaded with 2mg rhBMP-7 and autologous platelet rich plasma (PRP). Results so far show a well guided bone regeneration pattern, but results for biomechanical properties and bone volume are significantly lower than for non-operated tibial bone (ABG-control group for 6cm defect is currently being created). With the final results still pending, it seems that a total dose of 2mg rhBMP-7 may be too low to induce full bony regeneration of such a large volume tibial defect and to restore the properties of healthy bone. However, the results are still promising given the large nature of the bone defect and that no autografting material has been used at all. Once the Collaborative Research Agreement with DePuy Synthes had been established I had access to the Reamer Irrigator Aspirator (RIA)-System to investigate its best surgical use in the QUT ovine animal model. In cadaveric mock surgeries I found that the RIA-system cannot be used to harvest bone grafts from the sheep femur due to the anatomy of the ovine thighbone (thin cortex, wide medullary canal, curvature of longitudinal axis). I therefore decided to harvest ABG-material from the contralateral tibia instead. I started surgeries with the 12 month-time point Iiac Crest ABG+Scaffold-Group due to its less complex procedure. In a total of 10 male merino sheep for each animal 6ml cancellous bone autograft were harvested from both iliac crests and inserted into the internal lumen of a porous 6cm long mPCL-TCP scaffold. The hereby created tissue engineering construct was then press-fitted into the tibial defect site. The iliac crests were bandaged the right hind leg immobilised in a circular cast for 4 weeks after surgery. No complications occurred in this group and serial X-ray images so far show variable results with some sheep showing well-guided bone regeneration in the defect site (despite not fully bridging the defect yet after 9 months) while some animals fail to start bridging the defect so far (possibly due to graft resorption in the avascular defect site). Final results are pending and further analyses are currently ongoing. Afterwards, surgeries for the RIA-bone graft-only- and RIA+Scaffold-groups commenced. In 12 male merino sheep, 6ml autograft were harvested from the contralateral tibia shaft and combined with our porous scaffold (RIA+Scaffold-group= 2 sheep) or inserted directly into the defect site (RIA only-group=10 sheep), respectively. All sheep tolerated the complex surgical procedure well and no intraoperative complications occurred. However, spiral fractures of the left tibia (RIA-reamed leg) occurred in four sheep during the postoperative phase (between day 1 and 19 postoperatively). In post-mortem analyses the fractures were found to originate from the interface between the reamed and non-reamed endosteal cortex. Despite thorough re-evaluation of the surgical technique and despite the use of the smallest reamer heads available plus protective placement in slings postoperatively, we had to conclude that creating the large segmental defect in the right tibia and harvesting bone graft from the left sided tibia is not a safe option in our animal model and leads to a high risk of postoperative fractures of the reamed leg. The decision was therefore made to euthanise the remaining 8 sheep from the RIA-groups to prevent further fractures and potential suffering of the animals. All animals were euthanised and samples were explanted for further analysis, which is currently ongoing (graft viability, early inflammation, vascularisation etc). I had to re-design the study and found a possible solution to harvest bone graft material using the RIA-system from the 6cm long segment of the tibia that is normally removed en bloc from the diaphysis of the tibia after a proximal and distal osteotomy. Options are currently being tested for feasibility, safety and graft volume yield in mock surgeries. Surgeries for the study will re-commence as soon as the new technique has been proven to be safe and effective.
Projektbezogene Publikationen (Auswahl)
- Bone Regeneration based on Tissue Engineering Conceptions – A 21st Century Perspective. Bone Research (2013) 3: 216-248
J. Henkel, M. Woodruff, D.R. Epari, R. Steck, V. Glatt, I.C. Dickson, P.F. Choong, M.A. Schuetz, D.W. Hutmacher
- Design and fabrication of scaffold-based tissue engineering. BioNanoMaterials, Volume 14, Issue 3-4, Pages 171–193, ISSN (Online) 2193-066X, ISSN (Print) 2193-0651, December 2013
J. Henkel, D.W. Hutmacher
- Delayed Minimally Invasive Injection of Allogenic Bone Marrow Stromal Cell Sheets Regenerates Large Bone Defects in an Ovine Preclinical Animal Model. Stem Cells Transl Med. 2015 May;4(5):503-12. Epub 2015 April
Berner A, Henkel J, Woodruff MA, Steck R, Nerlich M, Schuetz MA, Hutmacher DW
(Siehe online unter https://doi.org/10.5966/sctm.2014-0244)
