Tissue engineering is a multidisciplinary science combining medicine, biology, materials science and nanotechnology, and its purpose is to replace damaged tissue or organs by other individually tailored ones. To do this, the patient's cells and nanoscaffolds, placed where the new artificial tissue develops, are used. One of the biggest challenges facing scientists is the efficient transporting through the ‘scaffold' of oxygen and nutrients needed for the cells to function correctly.
A piece of research by the UPV/EHU and the University of Oxford has come up with a strategy to solve this problem in the materials used as scaffolding in tissue engineering. The paper has been published in the Journal of Materials Chemistry of the Royal Society and has been chosen by the editors of the journal as one of the most important ones of 2015.
To make the scaffolds, the UPV/EHU's research team has used a natural biopolymer called chitosan. "The scaffolds are positioned where the damaged tissue needs to be replaced. For example, if the patient loses a piece of bone, the gap left by the missing part is filled with a scaffold that imitates the properties of the bone. The cells grow naturally in these scaffolds sometimes assisted by growth factors. But there are various obstacles because many cells are present in our tissue: we have more cells in our bodies that there are stars in our galaxy: approximately 1,000 million cells for every gram of tissue. Likewise, another major difficulty facing tissue engineering is that all of it needs to breathe and feed. Otherwise the cells die and the new tissue is not formed", explained Eneko Axpe, a UPV/EHU researcher and author of the paper Sub-nanoscale free volume and local elastic modulus of chitosan–carbon nanotube biomimetic nanocomposite scaffold-materials, published in the Journal of Materials Chemistry.
The main innovation in the study is that it is proposing a new strategy to improve the transport of oxygen and nutrients through the ‘scaffold' made possible by modifying the free volume: "The free volume consists of the small empty spaces that are located between the molecules. To explain: when you travel by train and there are few people on it, you can get on and move around easily. Yet during the rush hour and when the carriage is full, it is difficult to get on and move around easily. The same thing happens on a molecular level. The bigger the free volume is, the greater the mobility the molecules are going to have, for example the oxygen and sugar. Our strategy is clear: if we increase the free volume of the material (the chitosan biopolymer), we will make it more diffuse and this will allow the cells to receive the necessary oxygen and nutrients. To modify the size of the free volume in the scaffold, we have added various carbon nanotubes to the chitosan matrix, and that way we have managed to alter the free volume as we want".
The leading Journal of Materials Chemistry published by the Royal Society has selected the publication, the outcome of the collaboration between the nanomedicine group of the University of Oxford led by Sonia Contera and the UPV/EHU's MIMASPEC group, from among the "hot papers" of 2015 —the articles regarded by the journal's specialists as important, high-quality documents—. This paper is also part of the recent international PhD thesis cum laude by Eneko Azpe, the UPV/EHU researcher and visiting researcher at the University of Oxford.
Eneko Axpe, a physicist by profession, highlights the "outstanding role" that will be played by his colleagues in 21st century biology: "Until quite recently most physicists merely created techniques such as PET, magnetic resonance imaging, radiotherapies, etc. in biomedicine. But the role has now begun to change and we are starting to discover the physical and mechanical properties of cells. Cells ‘sense' the properties of the material in which they are growing on a very small scale, on a nanometric scale. For example, if you change properties such as elasticity on a nanometric scale of the material, or the free volume that the material might have, you will be changing the properties of the cells. A very clear example: if the material in which the stem cells are growing is similar to cartilage, these cells will form an ear. But if the properties of the material are exactly the same as those of bone, the stem cells will form bone".
Despite the fact that we find ourselves in the research phase in this specific case, the creation of tissue and organs is not in fact in an embryonic situation. "At the biggest congress on tissue engineering held recently in Boston, there were researchers who presented patients who had been living for years with organs (such as the bladder or skin, etc.) that had been created artificially by means of tissue engineering. There is still a lot to do but it is already a reality," explained Axpe.
Eneko Axpe, Loic Bugnicourt, David Merida, Maite Goiriena-Goikoetxea, Iraultza Unzueta, Ruben Sanchez-Eugenia, Jose Angel Garcia, Fernando Plazaola and Sonia Contera. (2015). Sub-nanoscale free volume and local elastic modulus of chitosan–carbon nanotube biomimetic nanocomposite scaffold-materials. J. Mater. Chem. B, 2015,3, 3169-3176 DOI: 10.1039/C5TB00154D
Image: Carbone nanotubes and chitosan. Author Contera Lab
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