Bone is an organ that can repair itself naturally through various mechanisms. This is called the natural bone regeneration.
In some cases, however, when the trauma is too great or the bone is damaged, such as osteoporosis, it is necessary to use bone grafts or the installation of implants.
However, the use of these can, at the moment, lead to complications or withdrawal after some time in the body through surgery. One of the causes of the complications is a poor rate of degradation of the prosthesis.
If it deteriorates too quickly, it leaves a void to fill in the bone that will not have had time to regenerate. Otherwise, too slow degradation of the prosthesis will hamper bone regeneration. This is why it is necessary to overcome this problem.
The processing time and the cost of current prostheses are also particularly high. The objective is therefore to design a prosthesis at lower cost, in a short period of time and promoting bone regeneration.
It is a subject that caught my attention, because it was similar to a project carried out during my studies in connection with the medical sector, and it concerned a concrete application. Since the field of 4D printing is also completely new, the topic piqued my curiosity and my desire to know more.
A “bone powder” biomaterial
The use of polymers, which can be associated with large molecules or more roughly with plastic, makes it possible to be the raw material of the prosthesis. The polymers have a low cost and some of them have properties similar to bone, while being accepted by the human body, due to their biocompatibility.
However, using only polymers would be insufficient to improve bone regeneration. That is why l’hydroxyapatite, considered bone powder, is added to form a biomaterial, which then has a composition similar to bone.
In order to develop the biomaterial that will constitute the prosthesis, the polymers and the hydroxyapatite will be mixed hot within a extruder – a kind of sausage chopper. The biomaterial obtained is then found in the form of a filament or granules. This is a crucial step which involves optimizing the processing parameters and avoiding blockages as much as possible and therefore a waste of time. It is then pleasant to observe without difficulty the development of these filaments and granules.
A 3D printed object
It then only remains to shape the prosthesis, and to always achieve this at low cost and in minimal time, theimpression 3D lends itself very well. It is a process which will make it possible to obtain an object according to the three dimensions of space, by depositing the material layer by layer in the molten state.
As it cools, it solidifies, thus forming the final object. But before using 3D printing, it is imperative to design the structure of the desired object, in this case the prosthesis.
Using a modeling software, it is possible to assemble simple geometric shapes such as cylinders, cubes… to constitute the structure of the object in the form of an STL file. This constitutes the development plan of the object necessary for the 3D printer to design the 3D object.
It then becomes possible to print the object, taking care to optimize the process parameters such as the printing speed, the temperature of the print head or nozzle.
Stimulus and degradation of the prosthesis
Only, in order to respond to the problem of speed of degradation, a fourth dimension will intervene: time. We then speak ofimpression 4D.
The latter has the same principle as 3D printing, except that following this process, the printed object will change shape, property or functionality over time, under the action of an external stimulus. .
This can take the form of heat, light, humidity or even an electric / electromagnetic field. In other words, a 4D printed object in the shape of a bud could open into a flower under the action of an external stimulus.
As part of our research project, irradiations are used as an external stimulus in order to prematurely modify the biomaterial obtained. It is a bit like premature aging of the material in order to modify the rate of degradation and therefore the lifespan of the prosthesis. All this obviously does not represent any danger for the human body.
Challenges at every step
Analyzes on the biomaterial are therefore carried out at each stage of the development of the prosthesis in order to ensure that its properties remain close to those of the bone. Several biomaterials containing different amounts of hydroxyapatite and polymer are tested to determine the optimal mixture.
Then comes the optimization of the printing parameters according to the biomaterial used, in order to obtain prototypes with the fewest possible defects. As with the development of filament or granule biomaterial, finding the right print parameters during optimization is particularly time consuming and requires hundreds or even thousands of tests which often result in failure. When the printing finally goes smoothly, imagine the satisfaction of seeing the prototypes of prostheses that we have designed appear.
From now on, it is for us to determine the adequate irradiation dose so that the rate of degradation of the 4D-printed prosthesis is the same as the rate of bone regeneration, while maintaining the mechanical properties of the prosthesis.
This work would make it possible to obtain a prosthesis at a lower cost and in a short time with properties similar to bone, and which over time would disappear without leaving a trace so that only bone remains.
Although this project still requires a lot of work, it is very rewarding to lend a helping hand to u who could help so many people.
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