Metal 3D Printing Technology Titanium Alloy Porous Materials-Medical Field



3D printing porous implants for bone defect treatment is a new breakthrough in the field of tissue engineering. Using 3D printing technology, the physical parameters such as pore size, porosity, pore shape and surface morphology of the implant material can be accurately designed, which is difficult to compare with the traditional bone implant scaffold. Therefore, personalized implants with more ideal biocompatibility and mechanical properties can be produced to fully meet the needs of patients.


Why choose titanium alloy (titanium alloy development history)


Titanium and titanium alloys are metal materials that gradually began to develop in the middle of the 20th century. It has the characteristics of low density, high specific strength, good corrosion resistance and good biocompatibility, and is widely used in aerospace, petrochemical and medical and health fields.


First stage

For the application of titanium in medical implants, as early as 1940, some scholars reported the inert performance between titanium implants and mouse femurs. In 1951, some scholars further confirmed that pure titanium has better biocompatibility than other traditional implant materials. However, due to the high production cost of titanium alloy at that time and the maturity of stainless steel in the implant market, the application and development of titanium alloy in the medical field has been relatively slow.


Second stage

Since the 1960 s, pure titanium has been used in clinical oral research as a human implant. With the development of Ti-6Al-4V alloys with more excellent performance, titanium alloys have been widely used in the medical implant market.


Problems faced

Although the elastic modulus of Ti-6Al-4V is only about 114GPa, which is lower than other biological materials such as stainless steel and cobalt-chromium alloy, it is still an order of magnitude higher than human cortical bone (15 ~ 25GPa) and cancellous bone (0.05 ~ 3GPa). Such a large difference will lead to the so-called "stress shielding" effect, which will lead to bone absorption around the implant for a long time, and even cause the implant to slip off, reducing the success rate of bone implantation.


The "stress shielding" effect refers to the large difference between the elastic modulus of the biological implant (>100GPa) and the elastic modulus of the receptor bone (<20GPa), which leads to the inconsistency between the deformation degree of the implant after stress and the bone. Long-term use will cause osteoporosis and bone ablation around the implant, and eventually lead to the phenomenon of implant slipping. The method of appropriately reducing the elastic modulus is one of the focuses of biomaterials research scholars in recent years. Generally, methods of reducing the elastic modulus include using an alloy with a lower elastic modulus or using a porous design to reduce the strength of the part.


At the same time, the elements such as Al and V contained in its composition have certain biological toxicity. Long-term use in the human body will cause tissue lesions around the implant, induce encephalopathy, anemia and other symptoms, and is not suitable for long-term use in the human body.




Biological toxicity aspects

In recent years, for biological titanium alloys, researchers have developed Gum alloy containing Ti-Nb-Ta-Zr, TLM alloy containing Ti-Nb-Zr-Mo-Sn, Ti2448 alloy containing Ti-Nb-Zr-Sn, etc. around the characteristics of non-toxicity and low elastic modulus. These alloys all use Nb, Zr, Mo and other elements with good biocompatibility. The experimental results show that the bone promotion and sensitization of this kind of titanium alloy are better than the Ti-6Al-4V and Ti-6Al-7Nb used in traditional implants.


Stress Masking Aspects

Research data show that the development of porous materials can effectively reduce the elastic modulus, and provide physical space for bone growth and enhance bone fixation. For bone implant porous materials, some scholars have reported that the porosity should be controlled between 65% and 80%. For the implant material with excessive porosity, the porosity will significantly reduce the compressive strength and fatigue performance of the material, which can hardly meet the normal use requirements of the material, while the porous material below this value, due to the high density, affects the bone tissue to grow into the material and reduces the bonding strength between the implant and the material.


Comparison of traditional methods of VS3D printing


In order to meet the design requirements of the porosity of the above materials, the traditional preparation methods of porous titanium alloy materials mainly include: powder metallurgy method, slurry method and fiber sintering method.


However, the porous materials made by such methods generally have small pore size, uneven pore distribution, low through hole rate, or a large number of micropores in the pore wall structure, which limits their further development in the field of biological materials. In recent years, with the development of "3D printing" technology, the advantages of using 3D printing to manufacture porous materials are becoming more and more obvious because of its processing characteristics.


The following table compares the characteristics of several common porous material preparation methods, and Figure XX shows the similarities and differences between the pore-forming agent sintering method and the 3D printing SLM process from raw materials to formed products.



Pore-forming agent method using powder VS SLM process using powder



Preparation of Porous Samples VS 3D Printing Products by Pore-forming Agent Method



Examples of three-dimensional models of common trabecular cellular structures


In the future, with the solution of porous material porosity and pore size, elastic modulus, biological toxicity and other issues, as well as the integration and breakthrough of various disciplines including materials science and stem cell technology, 3D printing titanium alloy substitute will become a personalized and accurate medical technology, which is widely used in orthopedic clinic and effectively solves the treatment problems of bone repair.


Radium laser titanium alloy printing case



Tensile properties of 3D printed titanium alloy bone beam porous structure
Animal experimental study on the effect of pore structure of 3D printed porous titanium alloy scaffold on bone growth effect
Research Progress of 3D Printing Medical Titanium Alloy

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