Making aortic prostheses suitable for surgery with spider aid

Vascular prostheses made from the blood protein fibrin: The biocompatible alternative to synthetic plastic prostheses is now to be made increasingly fit for clinical use with spider silk.

[Translate to Englisch:] Eine Spinne krabbelt über ein Röhrchen, worin sich eine mit Spinnenseide verstärkte Gefäßprothese aus Fibrin befindet.

[Translate to Englisch:] Helfer für die Implantatentwicklung: Die Seide der Goldenen Radnetzspinne soll Aortenprothesen aus körpereigenem Fibrin stabiler machen. Copyright: Karin Kaiser / MHH

The aorta is the largest blood vessel in the human body. It originates in the heart and carries oxygen-rich blood to all parts of the body. The most common disease of the aorta that requires treatment is an aneurysm. Because the diameter of the aorta is enlarged at this point, its wall thickness decreases and therefore the wall tension increases at the same time. This increases the risk of a life-threatening rupture. Early surgery with an artificial vascular prosthesis can protect against this.

There are about 13,000 aortic replacement operations per year in Germany alone. So far, such prostheses have been made of synthetic plastics, but they have insufficient biocompatibility: There is a risk of blood clots forming. Their surfaces can also become infected with bacterial biofilms, which are very difficult to treat. Researchers at the Clinic for Cardiothoracic, Transplantation and Vascular Surgery at the Hannover Medical School (MHH) are working on developing vascular prostheses based on the body's own fibrin. The big disadvantage: the fibrin prostheses cannot withstand the high pressure loads that prevail in the aortic bloodstream.

Silk is extremely thin and tear-resistant

A new project led by Dr Florian Helms in cooperation with the Clinic for Plastic, Aesthetic, Hand and Reconstructive Surgery is now investigating how the bio-prostheses can be stabilised. For this, the researchers relied on spider silk from the Spider Silk Laboratory at PÄHW. "We are intensively involved with the use of spider silk in the field of regenerative medicine and have developed many application techniques and medical products," says Clinic Director Professor Dr Peter Vogt. For example, the silk has already been successfully used to reconstruct peripheral nerve defects. "We use the holding thread of the golden wheel web spider Trichonephila edulis from our own breeding," says laboratory manager Dr Sarah Strauß. Extracting the silk is painless for the animals and does not harm them, the biologist emphasises. The holding thread is the spider's "safety rope", so to speak, and is produced by it reflexively. The silk is extremely thin and tear-resistant and completely degradable in the human body. Using a special apparatus that assistant physician Dr Helms constructed himself, the thread is wrapped around the pre-produced fibrin tubes. "The support structure not only increases stability, but also prevents the prosthesis from tearing out when it is sewn in during the operation," the physician notes.

Fibrin prostheses are protected by the immune system

Researchers have been working on bioartificial vascular prostheses to replace damaged or missing vessels for a few years now. "The need is great," says Dr Helms. Cardiovascular diseases are still responsible for most deaths in western industrial nations. Vascular calcification (atherosclerosis) is often the cause, which makes it necessary to replace arterial vessels, for example in the context of bypass operations. At the Lower Saxony Centre for Biomedical Engineering, Implant Research and Development (NIFE), the "Vascular Tissue Engineering" working group is experimenting with the development of vascular tubes based on fibrin, a water-insoluble protein from our blood. As part of the coagulation system, it helps close wounds. 

"Fibrin is particularly suitable as a matrix for vascular prostheses because it can be obtained from the blood of the prosthesis recipients and is therefore optimally compatible," explains project leader Dr Florian Helms. The fibrin scaffold can also be easily shaped into the desired form and populated with all the cells that make up blood vessels.

Unlike the common plastic models, the biologically active aortic prostheses are recognised by the immune system as the body's own and are included in the infection defence. This means that the formation of biofilms can be prevented from the outset. "This would dramatically improve the situation for patients," says Dr Helms. Because in the worst case, artificial prostheses have to be removed again due to biofilm infections, as they hardly respond to antibiotics. Often, the only option is a new vascular graft - an intervention that about half of those affected do not survive. The project "Development of a bioartificial aortic prosthesis based on a spider silk-reinforced fibrin matrix" is funded by the Else-Kröner-Fresenius Foundation for two years with about 127,000 euros. The researchers hope to have cleared the last hurdle for a clinical application of their fibrin prostheses by the end of the project period and to achieve a decisive breakthrough in the supply of replacement vessels.

Text: Kirsten Pötzke