Bone with Shape memory
Scientists have created self-healing bones
Scientists of the NUST MISIS Center for Composite Materials have developed a material for bone implants, with the possibility of self-healing of cracks. The basis was a polymer with shape memory, which restores its structure under local heating. The results of the research were presented at the videoconference "Scientific and technological solutions for the medicine of the future" (Moscow-Delhi), held at the MMPC MIA "Russia Today".
We are talking about the possibility of replacing small or large parts of the bone with injuries, as well as operations to remove a fragment of bone tissue with the development of a malignant tumor. The human body does not have the resources to independently replace a large amount of bone tissue, so there is a need for implants.
If the implant inside the body is under cyclic load (this usually occurs when bone fragments are replaced in the limbs, especially the legs), cracks form in it, the occurrence of which is very difficult to control. It is impossible to prevent their formation, however, it is possible to create an implant from a material with the possibility of self-healing.
"We are developing an approach to using materials with shape memory," explains Fyodor Senatov, Candidate of Physical and Mathematical Sciences, researcher at the Center for Composite Materials at NUST MISIS. – "Initially, the implant has a certain shape, then the crack changes it, but when heated, the structure is restored. The shape memory effect requires the coexistence of a rigid phase in the polymer (chemical or physical crosslinking, interweaving of molecules or intermolecular interactions) and a soft phase, which determines the entropic elasticity of macromolecules and could be deformed into a temporary form. You can imagine that the piece of polymer that our implant consists of is a kind of spring in jelly. Let's say you deform this piece of plastic, that is, stretch the spring. Frozen jelly does not allow it to close back. However, if you warm up the jelly, it will become soft and the spring will be able to return to its original shape," he added.
Demonstration of the closure of a crack in a bone implant.
Provided by the press service of NUST MISIS.
The driving force for the shape restoration is a change in the mobility of polymer molecules and the transition from a more ordered time configuration after deformation to a thermodynamically advantageous configuration with higher entropy and lower internal energy.
At the moment, animal experiments are being conducted in various laboratories around the world to study the possibilities of local heating of such an implant without affecting the surrounding tissues. To heat it up, you need to perform a minimally invasive operation, that is, make a puncture and bring the waveguide directly to the replaced bone fragment. The main problem is that while the shape of the implant is being restored at temperatures above 50 degrees, which can cause great damage to living cells. In addition, the activation temperature of the shape memory effect is high for polymers suitable for use in bone implants.
If we strive to make the implant like a bone that can withstand large cyclic loads, then the heating temperature will still rise. It will be 60-70 degrees, which will undoubtedly be detrimental to the surrounding tissues.
"Unfortunately, humanity at the moment does not have a single material that is, on the one hand, solid and durable, and on the other hand, easily transforms its structure at acceptable temperatures. I think it will be necessary to experiment with the technology of careful heating or find the optimum by creating composite materials and changing their internal structure. We managed to "grope" such compounds, but so far their self–healing occurs at 50 degrees," explained Fedor Senatov.
At the moment, scientists at the NUST MISIS Center for Composite Materials use different polymers as the basis for implants, mainly bioresorbable, that is, self-absorbable. They can replace small fragments of bones, which is in demand in maxillofacial surgery. Ultra-high molecular weight polyethylene is used for large fragments.
The hardness of the polymer increases due to the introduction of additional particles, for example, hydroxyapatite is the mineral basis of bones and teeth. To achieve the desired temperature, direct heating, electric current, ultrasound and an alternating magnetic field are used. In order to achieve the heating effect using a magnetic field, magnetic nanoparticles are specially introduced into the polymer. After applying an alternating magnetic field, the particles inside the implant begin to warm up and transfer heat to the surrounding material. Now scientists are experimenting with the compositions of materials, trying to increase strength, while reducing the heating temperature.
Portal "Eternal youth" http://vechnayamolodost.ru