New porous titanium technology for implants developed by Russian scientists
Who
The Department of Materials Science and Materials Technology of the Moscow Aviation Institute claims to have developed a crystallization technology that allows for the relatively inexpensive production of titanium “cotton” for implants, which is set to be 5–6 times less expensive and more consistent than existing technologies.
3D printing from titanium powder is difficult and time-consuming, while results are not precise enough to build structures through which new bone material is able to grow. The approach taken by leading institutions, which uses titanium wires, is very expensive. It’s also nearly impossible to create wires with a thickness of micrometers.
Why it matters
Titanium that closely resembles bone tissue will facilitate better recovery after trauma.
Titanium is a popular material for prosthetics. It is highly biocompatible and stimulates bone growth. In some cases porous titanium is needed to make prostheses. The Moscow Aviation Institute has developed a technology to manufacture a material consisting of ultrafine fibers welded together.
Bone tissue easily grows into the metal, forming a single structure with the implant. The pore sizes can range from 30 to 500 microns. The smaller pores are necessary for the effective movement of fluids in the material, providing the capillary effect. The larger pores create the conditions for the existence and growth of bone tissue cells that must grow through the entire implant. The material is then firmly fixed in place in order to carry out all necessary functions. Scientists have developed two technologies for the creation of the material.
The first one involves the production of the fiber itself, and is based on the so-called method of high-speed melt solidification.
“A rapidly rotating copper crystallizer (a ring with internal water cooling channels) is fed with drops of molten titanium, before it solidifies and turns into filaments,” Mikhail Kollerov, project manager and professor at the MAI Department of Materials Science and Materials Technology explains. “The result is thin titanium fibers with a diameter of 20–30 microns and a length of 200–300 mm, which look like metal wool.”
The second technology involves sintering the fibers using a thermal hydrogen treatment. For this purpose, the fibers are pressed into casts in the shape of a cylinder or flat sheet, after which they are processed. “In a vacuum, at high temperature, we introduce hydrogen into the metal, which helps change its structure and properties,” Kollerov explained. “Hydrogen easily enters titanium and stimulates the rearrangement of the material, resulting in the sintering of the fibers. After the hydrogen is removed, we get a material that is tangled, but still reliably interconnected at many points, with very good porosity and a pore size of 30 to 500 μm.”
“Due to the porous structure of the implant it is possible to approximate the complex structure of a specific bone to achieve the required technical characteristics, thus ensuring that it is identical to human tissue,” claims Victor Komarov, senior researcher of the Ultrafine Grain Metal Materials laboratory at NUST MISIS. “Porosity allows for the repetition of the internal structure, and also provides for the migration of fibroblasts (connective tissue cells that synthesize the extracellular matrix and collagen), sprouting connective tissue inside the implant, thereby further increasing its fixation and ensuring integration with body tissues.”
According to the specialist, the method of high-speed solidification of the melt itself is used in various industries. “However, it should be kept in mind that obtaining fibers and subsequent sintering by thermal hydrogen treatment of titanium and its alloys, as well as ensuring process repeatability for manufacturing a series of implants, is a complex scientific and technological task, and its solution deserves high praise,” Komarov said. Over the next few years, the team expects to develop their technology further for use in the production of medical devices. 
