Irati Diez Virto
The biomaterials are substances created to keep in contact with tissues or biological fluids. One of the most common and well-known biomaterials is dental fillings. However, the use of these materials goes further and its field is extended to the development of implants that, for example, replace joints, repair organs or imitate a set of physical properties of organs such as the brain. Facing the design of a synthetic material, which contains the properties of a tissue as complex as the brain, is a great challenge. A challenge faced by various research groups today.
The use of biomaterials has increased exponentially since the creation of the first biomaterial in the 1920s, called Vitallium a metal alloy of use dental. Today, there are countless applications for these types of materials, including around 2,700 medical devices and about 39,000 pharmaceutical preparations. Although these materials have had a great positive impact on global health, there is still a need to design more refined polymers and more sophisticated methods to characterize and test these materials. This is the case of biomaterials that claim to mimic brain tissue.
Over the years, various types of biomaterials have been designed for this purpose. These synthetic tissues are required in various emerging technologies, such as the development of models of neurological diseases, the characterization of neuronal tissue or the design of brain organoids (miniaturized and simplified version of an organ, created in vitro ). Furthermore, they could also be used for applications in vivo that is, to perform implants directly in the brain tissue of patients with various pathologies. It is believed that the use of more sophisticated biomaterials would minimize the immune response of patients and tissue rejection. But to be able to apply these materials successfully, it is vitally important to imitate the physical characteristics of the brain.
The greatest challenge in designing a tissue similar to brain tissue lies in a physical characteristic of the brain, which makes it difficult to manipulate: is very soft . This is due in part to the high degree of hydration of this organ. The water content of brain tissue ranges between 73 and 85% of the total mass, thanks to its high content of proteoglycans, molecules that trap water. It also has very little collagen fiber, which is related to the rigidity of different organs. For this reason, quantifying the stiffness of this organ is one of the tasks that research in this field is addressing.
This quantification is carried out by measuring elastic modulus an elastic constant that determines the degree elasticity (or stiffness) of a particular material. To date, it has not been possible to fully characterize this measure for brain tissue. In addition, there are different experimental methods for the determination of the elastic modulus and these methods differ substantially from one laboratory to another, as well as the conditions under which said measurement is carried out. This great variety of techniques used generates very different results between different research groups, which makes comparison between them almost impossible. For this reason, until now it has not been possible to synthesize any material that mimics the complex properties of this tissue.
Even so, there are potential candidates that, although not sophisticated enough, could provide great results combining them with other materials. One of them is hydrogel injections which are being studied for the treatment after removal of glioblastoma (the most common tumor of the glia). Also, this injectable material offers the possibility of administering drugs in a continuous way. Although the viscoelastic properties of these injections have not yet been directly compared to those of the brain, the mere possibility that they can be injected directly into a patient is extremely promising. This would make it possible to replace the rigid and hard materials currently used ( Gliade l for example) to fill postoperative brain cavities.
Therefore, current research is working on characterizing the firmness of the tissue brain on all scales, from visible morphology to the nanometric scale (neurons and glial cells) and under physiological conditions. This characterization, likewise, should be carried out using standardized methods and protocols, in order to ensure a reliable comparison between different studies.
Only when we fully understand the properties of brain tissue, will we be able to develop biomaterials that are sufficiently similar to the complexity of it. This task will entail an effort and will be a challenge for researchers, the technology that we currently have will help to tackle the work.
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Biomaterials. (2017, September). Retrieved October 26, 2020, from https://www.nibib.nih.gov/science-education/science-topics/biomaterials
About the author: Irati Diez Virto has a degree in biology from the UPV / EHU and a collaborator in the Chair of Scientific Culture
The article In search of biomaterials that resemble brain tissue has been written in Cuaderno de Cultura Científica .