Sometimes soft is better than hard

Hard implants irritate the brain

Kirill Stasevich, Compulenta

Doctors face the problem of rejection not only during organ transplantation, but also when artificial implants made of non-biological materials have to be introduced into the body. In response to the appearance of a foreign body, the immune system triggers inflammation, which leads to scarring of the tissue around the implant, and such a scar, once in the internal organ, can greatly disrupt its work.

Although scientists have been trying for decades to find a way to suppress the conflict between the body and the implant, almost no one has thought about how this collision is affected by the physical properties of the foreign body material. Meanwhile, the reaction of, for example, the brain to the electrodes inserted into it will still be very aggressive, even if the electrodes are made of chemically inert material, and even when they do not work. That is, the body's response in this case does not depend on either the chemical composition or electrical irritation.

In fact, as researchers from Cambridge (UK) have shown, it's all about the rigidity of the implanted electrode.

The rigidity of the electrode and the rigidity of the brain differ by orders of magnitude, so the nervous tissue may well experience severe stress for mechanical reasons. To test their assumption, Kristian Franze and his colleagues tried to grow mouse astrocytes and microglia cells (auxiliary cells of nervous tissue) on several substrates that are identical in chemical composition, but differ in hardness: in one case, the substrate was as soft as the brain, in the other – its rigidity was comparable with muscle stiffness, and the third was even tougher.

As the researchers write in the journal Biomaterials (Moshayedi et al., The relationship between glial cell mechanosensitivity and foreign body reactions in the central nervous system), the cells that grew on a more or less rigid material were too flat, and those that grew on the softest substrate looked more like natural cells from the brain. In addition, genes and proteins associated with an inflammatory reaction to a foreign body worked more actively in those who grew up on a hard one.

Mouse brain astrocyte grown on a hard (left) and soft (right) substrate
(photo of the authors of the work).

Finally, scientists have tested how the brain of mice will react if foreign bodies of different stiffness are introduced into it. It is easy to guess that the inflammatory disturbance of the brain was directly proportional to the rigidity of the object.

This means that the chemical inertia of the implant is not everything: it is necessary to take into account its physical characteristics, at least relative rigidity. Electrodes are inserted into the brain not only for the sake of scientific experiments, but also for therapeutic purposes – for example, to suppress muscle trembling in Parkinson's disease, so the results obtained are of the most urgent importance. In the future, the researchers are going to check how other tissues react to the physical parameters of foreign bodies.

Prepared based on the materials of the University of Cambridge: Filling me softly.

Portal "Eternal youth" http://vechnayamolodost.ru14.02.2014