17 June 2014

Heike Walles – A diverse toolbox for regenerating bones

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A toolbox of diverse tissue engineering approaches may help to meet the increasing demand in bone grafts. But translating the approaches into clinical praxis is not an easy task.

Bone grafts are among the most sought after tissue transplants in clinical practice. And this demand is expected to rise due to an ageing population. Now, the EU-funded project Vascubone, due to be completed in December 2014, aims at providing various methods and materials for creating bone substitutes. The project coordinator is Heike Walles, professor of tissue engineering and regenerative medicine at the University Hospital of Würzburg and head of the project group regenerative technologies in oncology at the Fraunhofer Institute IGB in Würzburg, Germany. Walles talks to youris.com about the content of the project’s toolbox and the challenges of translating research into applicable approaches.

What is the goal of your research?
Researchers often claim to have found the ideal material or the ideal therapy for bone regeneration. But bones are complex. The cranial bone is quite different from the jawbone or the shinbone. And defects differ from each other. The therapy requirements are very different. We provide a toolbox to be able to assemble the ideal therapy at the surgical table depending on the location and size of the bone defect and the patient’s age.

What does this toolbox contain?
We have different materials. For example, a granulate or a small bowl segment of a pig containing blood vessels. This is for creating transplants for large and complex bone defects. If it is not sufficient to implant material, so-called mesenchymal stem cells are used for growing bone substitutes. Another cell type, so-called endothelial cells, may be used for treating large bone defects. Moreover, we provide bioreactors for growing large and complex bone substitutes outside the body. These vessels can also be used for transporting the substitute to hospital before it is implanted. We have also developed tracers and apply imaging technologies to control the healing process. So-called in-silico models allow us to specifically look at the bone defect of each patient and simulate the ideal combination of tools for treating the defect.

Which bone defects can be targeted?
One example is, so-called femoral head necrosis. The bone dies from the inside to the outside because of insufficient supply by blood vessels. In this case, we use a combination of a granulate material and cells as therapeutic approach. We were able to show that our tools work in the animal model. Now we want to run the first clinical trials. Ultimately, the approach could be used even in advanced necrosis stages instead of implanting an artificial hip joint. Often, a piece of bone is transplanted from another part of the body to rebuild it. This means you cause a defect in an otherwise healthy site. Instead, we have developed a material based on a modified commercially available material called beta-tri-Calcium phosphate and nano-diamonds. It is able to rebuild the jawbone. The first clinical trials are going to start this year.

What are the challenges of translating such research findings into applicable approaches for regenerative bone therapies?
To be able to actually sell a product, one has to ensure right from the outset that the applied methods conform to the regulations. This is a major challenge. For example, if you want to grow cells you need so-called foetal calf serum. But this is no longer accepted in clinical settings. Also, authorities no longer approve certain growth factors. There is a fear of transferring animal diseases to humans or to induce tumours.

We therefore had to develop new cell culture media. We also developed a test to control whether cells start to turn into tumours. Another important issue are animal tests. If you want to sell transplants later on, you need to run appropriate tests in animal models before running clinical trials in humans. The problem is that only few standardised animal models exist. For example, we had to develop an animal model for femoral head necrosis, because animals do not have this defect. In this case we used the sheep. Our aim is to develop standard-animal tests, which can be used to test and compare newly developed material.

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