Research progress of 3D printing porous titanium alloy after tumor resection

Compared with stainless steel and other metal materials, titanium alloy with solid structure has the advantages of high strength and good corrosion resistance. However, the elastic modulus is still too high compared with the hard tissue of the human body, and it is easy to produce stress shielding phenomenon with the surrounding tissue, resulting in a great decline in the integration ability of titanium alloy implants with bone. In order to solve this problem, in recent years, materials biology researchers have proposed to introduce pore structure into titanium alloys and successfully prepared porous titanium alloys. The results show that porous titanium alloys have the following advantages: (1) The unique three-dimensional penetrating structure is conducive to the adhesion, proliferation, differentiation and mineralization of osteoblasts, as well as the transport of nutrients and the growth of bone histiocytes, forming biological fixation, improving bone integration ability and prolonging the service life of implants; ② Pore parameters can be adjusted to adjust its compressive strength, elastic modulus, density, etc., so that the mechanical property can match the bone tissue, reduce or remove the stress shielding phenomenon.

In recent years, the development of 3D printing technology has provided a new choice for the preparation of porous titanium alloys. 3D printing technology can complete the accurate control of the overall shape of porous titanium alloy according to the anatomical structure of the defect site after tumor resection, and achieve personalized customization to meet the needs of post-tumor resection repair. We divided 3D printed porous titanium alloy implants into two categories according to whether they have undergone anti-tumor functionalization. The first category is porous titanium alloy prepared by 3D printing technology without any surface modification, that is, simple 3D printed porous titanium alloy implants (hereinafter referred to as "porous titanium alloy implants"); The second category is the porous titanium alloy implant prepared by 3D printing technology after anti-tumor modification (hereinafter referred to as "anti-tumor porous titanium alloy implant"). In this paper, the performance of porous titanium alloy implants, the clinical application after tumor resection and the research progress of anti-tumor porous titanium alloy implants are reviewed.

Preparation, microstructure and properties of porous titanium alloy implants

1.1 Preparation of porous titanium alloy implants

The results show that the finished porous titanium alloy prepared by traditional processes such as sintering and pore-forming agent have different degrees of closed pores, low porosity and poor connectivity. Compared with the traditional process, 3D printing technology is modeled and formed through computer-aided design software, which has fast forming speed and high degree of freedom, and can achieve accurate control of the micro-pore parameters and overall shape of porous titanium alloy implants. At present, the commonly used 3D printing porous titanium alloy technologies in the medical field mainly include laser selective melting technology and electron beam selective melting technology.

1.2 Microstructure of porous titanium alloy implants

A large number of studies have shown that the ideal porous titanium alloy implant has a porosity of 60% to 90% and a pore size of 300 to 900 μm, which is similar to the human cancellous bone and can promote the osteogenic activity in vitro and the inward growth of new bone tissue in vivo. This parameter can also be achieved by 3D printing technology, so that the porous titanium alloy implant has a suitable porosity, aperture and high connectivity; When it is implanted into the bone defect after tumor resection, the porous titanium alloy implant can promote the formation of biological fixation with the surrounding bone tissue, and rebuild the stability of the skeletal system.

1.3 Properties of porous titanium alloy implants

The properties of porous titanium alloy implant mainly include mechanical properties, wear resistance, corrosion resistance, biosafety and histocompatibility.

Mechanical properties: The results show that the mechanical property parameters of porous titanium alloy implants can be changed within a certain range by adjusting the elemental composition and microscopic pore structure of porous titanium alloy implants. The final elastic modulus is similar to that of human bone (5-30 GPa), and the strength is higher than the compressive strength of human dense bone (100-230 MPa). That is, the mechanical strength of the implant is increased while the stress shielding phenomenon is reduced.

Wear and corrosion resistance, biosafety: At present, the most widely used porous titanium alloy implant material is Ti6Al4V alloy. Although compared with medical stainless steel and cobalt-chromium-based alloy, Ti6Al4V alloy has stronger wear resistance and corrosion resistance, with the increase of body movement and the extension of implantation time, It will still lead to a certain degree of corrosion and friction of Ti6Al4V alloy in the physiological environment, especially the aluminum (Al) and vanadium (V) elements in Ti6Al4V alloy have potential toxic effects, and there is a risk of spreading to the surrounding tissues and causing toxic side effects. In recent years, biomaterials researchers at home and abroad are committed to developing new titanium alloys with lower toxicity and corrosion resistance. Studies have shown that adding molybdenum (Mo), zirconium (Zr), tantalum (Ta) and other β-stable non-toxic elements to titanium alloys can not only improve the corrosion resistance of titanium alloys, but also improve their biosafety.

Histocompatibility: From the perspective of pore structure and mechanical properties, the elastic modulus of porous titanium alloy implants is significantly reduced, which can reduce the stress shielding effect between implants and bone tissue and provide suitable space for the growth of bone tissue. However, due to the lack of surface bioactivity and bone induction ability of porous titanium alloy implant, it is difficult to form stable chemical bond with surrounding bone tissue quickly. At this time, the surface modification of porous titanium alloy implants can further improve its surface activity and bone induction ability. The main approaches include: (1) Physical and chemical processes are used to convert the original passivated oxide film of porous titanium alloy implants into an active oxide film (mainly composed of TiO2), which can enhance the corrosion resistance and biohistocompatibility of porous titanium alloy implants. ② Bioactive coatings such as hydroxyapatite (HA) were prepared on the surface of porous titanium alloy implants. However, although there are a lot of surface modification methods and basic research on porous titanium alloy implants, due to cumbersome modification processes and other reasons, no coating products for porous titanium alloy implants have been clinically approved by relevant departments.

In the context of 3D printing technology, porous titanium alloy implants can be personalized, and are gradually applied to the clinical practice of post-tumor resection repair, and the simple porous titanium alloy implants without anti-tumor functionalization have achieved good clinical efficacy. However, the current clinical application reports are mostly early and medium-term follow-up, and longer follow-up is needed in the future to evaluate the clinical application efficacy of porous titanium alloy implants. In addition, the current clinical use of porous titanium alloy materials are Ti6Al4V alloy, the future hope to devote to the development of more wear and corrosion resistance, no potential toxicity of porous titanium alloy implants. The anti-tumor porous titanium alloy implant is currently in the stage of in vitro research and animal experiments, and it is expected to continuously improve the anti-tumor mechanism of the anti-tumor porous titanium alloy implant and successfully apply it to the repair and reconstruction after tumor resection.Yesino provide Titanium Bar, Titanium Sheet, Titanium Wire, Titanium Plate, Titanium Forging and other titanium product.