3D printing technology (3DP), also known as additive manufacturing (AM), is a technology that extracts data to reconstruct a computer 3D model and prints objects layer by layer. By providing an effective combination mode, any material can be printed in any form. Stacked objects. This unique technical advantage enables 3D printing materials to accurately simulate the structure of autogenous bone for precise and personalized orthopedic treatment, bringing orthopedics into a new era of individual customization. The materials of 3D printed orthopedic implants that have been put into clinical application mainly include organic polyether ether ketone (PEEK) and metal titanium alloy. Titanium alloy has a long history of application, high specific strength, good biocompatibility, and good corrosion resistance, and is currently widely used. Other metal materials such as tantalum, zinc alloy, magnesium alloy, etc. have not been widely used. 3D printing of titanium alloys can be precisely regulated and rapidly constructed macroscopically and microscopically close to natural bone tissue implants. 3D printing is divided into three processes: first, collecting 3D image data, constructing a digital three-dimensional model, etc.; second, making titanium alloy powder and cytokines into "bio-ink", and finally, using a biological 3D printer, according to orthopedic parameters, to improve The structure and performance of the bioprinted body, and finally the orthopedic implants that meet the requirements are produced. At present, it is often used in hip joint prosthesis, knee joint prosthesis, artificial vertebral body, etc. in clinical practice. Ricles et al. summarized the proportions of various categories of 3D printed medical devices used in the United States since 2000, titanium alloys accounted for about 70%, and 3D printed titanium alloys have long been mature and put into market use. In this paper, the bioprinting methods, characteristics and clinical application progress of 3D printed titanium alloys in orthopedics are reviewed as follows.
3D titanium alloy printing method
The main methods of 3D printing include selective laser melting, stereolithography, electron beam melting and nozzle powder molding printing technology, etc. Among them, selective laser melting technology (SLM) and electron beam melting technology (EBM) are suitable for printing titanium alloy. EBM technology manufactures implants by applying a magnetoconductive electron beam to melt metal powder layer by layer under high vacuum. The molding precision of EBM is slightly worse, but the molding efficiency is high, and no secondary heat treatment is required, so it is suitable for the manufacture of orthopedic implants. At present, titanium alloy orthopedic implants are mostly prepared by EBM technology. SLM technology uses high-power optical lasers to fuse metal powder into solid implant shapes. SLM has high molding precision, but the molding efficiency is low and requires secondary heat treatment. It has certain advantages in the production of fine orthopedic implants and complex structure molding.
Properties of Titanium Alloys
The main component of titanium alloy is Ti6Al4V, which is widely used in orthopedics due to its good performance. Structurally, bone is mainly composed of outer cortical bone and inner cancellous bone, with elastic moduli of about 0.5 GPa and 10-20 GPa, respectively. The elastic modulus of dense titanium alloy is about 110GPa. After 3D printing, the elastic modulus of titanium alloy material is lower than that of ordinary titanium alloy, which is closer to the physiological structure of bone. Titanium alloy has good biocompatibility, is beneficial to bone ingrowth and osseointegration, and is suitable for the preparation of orthopedic implants. Titanium alloy is not only rigid, but also has outstanding flexibility and good fatigue resistance. It is suitable as a joint support and can replace other metal materials. Titanium alloys are insoluble in strong acids and alkalis, and still have high specific strength at 500°C, are non-toxic to the human body, have good chemical stability, and are suitable for implantation into the human body. Titanium alloy has good corrosion resistance, fatigue resistance and stability. Compared with other metal materials, its elastic modulus is closer to that of bone, so it is suitable for orthopedics.
Current status of clinical application of 3D printed titanium alloy in orthopedics
3D printing titanium alloy has been widely used in orthopedic clinics, such as the production of artificial prosthesis, internal fixation, intervertebral fusion, guide plate, artificial trabecular bone, etc.
Application of spine surgery Spine surgery is delicate and complex, and the operation is difficult. Over time, degeneration of adjacent segments at the surgical site and poor vertebral body mobility are common complications of vertebral body surgery. Selecting implant materials suitable for the vertebral body and improving complications are problems that need to be solved in spinal surgery. Titanium alloy has good mechanical properties and compression resistance, and 3D printing technology is used to personalize implants, which are suitable for spinal surgery. On August 19, 2014, Liu Zhongjun's team from the Third Hospital of Peking University announced that the axis of a 12-year-old patient with Ewing's sarcoma was resected and replaced with a 3D printed axis, which overcomes the traditional titanium cage's tendency to sink and wear the front esophagus. shortcoming. This is the first reported case in the world of using 3D printing technology for axial spine replacement. Lu et al performed 3D printed artificial vertebral body implantation on 15 patients who should have undergone anterior fusion surgery, and concluded through postoperative follow-up that using this precise treatment method can restore the anatomical structure to a greater extent and prevent surgery. post-complications. With the development of 3D printing technology, the integrated rapid prototyping of titanium alloy combined with 3D printing technology, and the preparation of personalized intervertebral fusion cages have also been clinically applied. Siu et al. used 3D printing titanium alloy to treat a patient with osteoporotic lumbar fracture. Traditional intervertebral fusion could not match the deformed endplate of this patient. 3D printing technology used the shape of the endplate as a reference to prepare a patient with a high degree of matching. After 6 months of follow-up, the intervertebral height recovered, and there were no complications such as vertebral body deformation. The accuracy of pedicle screw placement in spinal surgery is very important, if the screw placement is inaccurate, it may cause damage to adjacent tissues and organs. The application of 3D printing guide plate improves the success rate of nail placement, reduces the perforation rate and error rate of nail placement, makes the operation more accurate, and reduces the radiation caused by the doctor's fluoroscopy during the nail placement process. The application of 3D printed titanium alloys in artificial vertebral bodies, intervertebral fusion devices, and auxiliary spinal repair surgery has improved the precision of surgical treatment and reduced surgical complications.
Application of Trauma Surgery Trauma surgery patients are complex and individual, and patients are often accompanied by multiple fractures or fractures that are severely damaged and difficult to repair. Titanium alloy has high stability and is suitable for fracture repair. Combined with 3D printing technology, it can be used for intuitive judgment and preoperative simulation in advance, which is conducive to the accurate implementation of preoperative planning, thereby improving surgical accuracy and efficiency, shortening operation time, and improving prognosis. Kim et al. evaluated the efficacy of 3D printed locking titanium plates and traditional locking titanium plates in patients with severe comminuted fractures of the distal radius. The results showed that 3D printed locking titanium plates had similar strength to traditional locking titanium plates. The design of fracture morphology and bone anatomy affirms the research prospect of 3D printing in fracture treatment. Shuang et al. counted 13 patients with humeral intercondylar fractures, of which 6 cases used 3D printed titanium plates and 7 cases used traditional titanium plates. The results showed that the application of 3D printed titanium plates can shorten the operation time and reduce complications. The application of 3D printed titanium alloy in trauma surgery is more conducive to fracture repair and healing and improves prognosis.
Application of joint surgery Artificial joint replacement is an effective method for treating severe joint diseases. Joint replacement can significantly improve clinical symptoms and restore function. Titanium alloy has good compression resistance and high wear resistance, and is suitable for the preparation of orthopedic artificial joints. In recent years, the combination of titanium alloy and 3D printing technology has attracted more and more attention for the personalized preparation of implants that match the joint lesions. Ding Yujian et al. reported a case of hip revision in 2019. The patient had undergone open reduction and internal fixation twice for "left femoral neck fracture". He underwent hip replacement in 2006 and revision in 2019. The patient's physical condition and history of multiple operations made the operation difficult and risky. In order to improve the success rate of the operation, the surgical team obtained imaging data and reconstructed it using 3D printing technology to print out a model consistent with the patient's pelvis and the 3D printed model to be replaced. The titanium alloy prosthesis has been rehearsed to ensure the smooth progress of the operation. Li Juehong et al. used 3D printed titanium alloy pads to repair complex acetabular bone defects. No loosening of the prosthesis was found in postoperative follow-up, and the curative effect was reliable. An important indicator to evaluate the success of joint replacement is whether the pain and other symptoms are improved after operation, and the quality of life is improved. The application of 3D printing technology combined with titanium alloy to prepare implants not only has the excellent characteristics of titanium alloys, but also the implants are compatible with the joint defects of patients. It has good compatibility, reduces complications such as joint wear and tear, and improves the quality of life of patients. Wan et al. divided 42 patients who needed acetabular repair into two groups, one group used 3D printed porous titanium alloy materials, followed up at 3 months, 6 months, and 9 months after surgery, and found that the observation group followed Compared with the control group, the SF-36 score was significantly higher, and the VAS score was significantly lower, indicating that the 3D printing group had a better curative effect. Zhang et al. applied 3D printing titanium alloy to reconstruct trabecular bone to treat early osteonecrosis of the femoral head. In order to evaluate the function of the hip joint, the postoperative Harris score and pain visual analog scale (VAS) were used. During the 24-month follow-up, the postoperative Harris score increased significantly and the VAS score decreased significantly at 12 months after operation. With the aggravation of femoral head necrosis, the Harris score decreased slightly and the VAS score increased slightly. Postoperative improvement rates were 100% for ARCO IIA stage, 70% for IIB stage and 0% for IIC stage. The hip preservation rate was 100% for stage IIA, 100% for stage IIB, and 50% for stage IIC. The results show that the 3D printing titanium alloy treatment method has a satisfactory effect on early necrosis of the femoral head, and the clinical symptoms are alleviated.
Application of bone tumor surgery Bone tumor surgery often requires the preparation of prostheses to replace part of the limbs. The application of 3D printed titanium alloys has high stability and good plasticity, and is suitable for implant preparation. Less postoperative complications are more conducive to postoperative repair of bone tumors. In 2020, Lin Yunzhi et al. reported a case of giant cell tumor of bone that applied 3D printing technology before and during the operation. Imaging data were collected before the operation, and a 3D printing model was made for intuitive observation. 3D printed implants with good results. From 2017 to 2019, Lei Qing et al. used 3D printed guide plate combined with 3D printed titanium alloy trabecular bone to treat 2 cases of patients with humeral shaft tumors. Follow-up was carried out after operation. Among them, 1 case had good follow-up results, and the other case had a good follow-up after operation. The prosthesis loosened at 14 months and was reinforced by surgery again. Follow-up up to 34 months after operation showed no re-displacement of the prosthesis. Wang et al. used 3D printing technology to print prostheses and applied them to 11 patients with pelvic tumors. The postoperative effect was good and no prosthesis loosening was found. In 2019, Feng reported a case of radical resection of tibial fibroblastoma and the use of 3D printed titanium alloy to salvage the limb. The prosthesis was followed up for 1 year and no loosening of the prosthesis was found. According to the MSTS score, the function recovery was 86.7%. There is good integration between the body and the patient's bone. The application of 3D printed titanium alloy implants in bone tumor surgery can obtain more accurate anatomical reconstruction, speed up the recovery of patients, and achieve better surgical results.
Technical improvement of 3D printing titanium alloy
Titanium alloy combined with 3D printing technology can simulate the autologous bone structure to the greatest extent, and its microscopic pore size, porosity, and pore shape will all affect the biocompatibility of the material. The existing literature shows that the research conclusions on the optimal pore size of 3D printed titanium alloys are not completely consistent. Studies by Peng et al. have shown that the porosity of 3D printed titanium alloys is between 60.95% and 81.23%, and the pore size is between 480 and 685 μm, which is suitable for orthopedic implants. Between 265μm, Young's modulus is between 2.23-6.36Gpa, yield strength is 21.36-122.85Mpa, and has good elastic modulus and strength. Li et al. studied the biocompatibility of three groups of 3D printed titanium alloys with pore sizes of 300-400 μm, 400-500 μm, and 500-700 μm, and finally proved that materials with pore sizes between 300-400 μm have significantly better biocompatibility in the remaining two groups. Taniguchi et al. made a rabbit tibial defect model, and used three groups of porous titanium alloys of 300, 600, and 900 μm for implantation. The results showed that the bone ingrowth effect of the 600 μm group was the best. Cheng et al. made (15.0±2.9)%, (37.9±4.0)%, (70.0±3.5)% three kinds of porous titanium alloy materials, inoculated bone marrow mesenchymal stem cells, The results showed that the cells in the 70% group grew the most vigorously. This is consistent with the findings of Tamaddon et al. In addition, studies have shown that titanium alloy materials with rough surfaces are more conducive to the growth of osteoblasts. The optimal pore size of implants remains to be explored. The application of 3D printing titanium alloy can continue to be improved, adding different components for optimization according to the actual situation of patients. For orthopedic surgical infections, 3D printed titanium alloys can be combined with silver, zinc, copper and other antibacterial metals through surface modification technology. The introduction methods mainly include introduction of materials in the form of alloys and introduction in the form of surface modification. The methods include: micro-arc oxidation, electrochemical modification, magnetron sputtering, spraying method, nanosphere photolithography technology, etc. For wound non-healing after orthopedic surgery, osteoinductive components can be introduced to speed up the healing speed. For different patients, the introduction of different components, the improved technology of 3D printing titanium alloy can further improve healing and realize personalized treatment for patients.
Summary and Outlook
3D printing technology has the great advantages of personalized and precise customization. Combined with the excellent characteristics of titanium alloy, it can be customized according to the patient's original bone structure, and an implant that is consistent with its own bone shape and similar in microstructure can be manufactured. Advantages Maximize the restoration of biomechanics, shorten the process of soft tissue re-adaptation, achieve better bone ingrowth, and achieve faster bone healing. The current clinical application of 3D printing technology also has its limitations: (1) Accurate and personalized 3D printing is too dependent on imaging data, which requires extremely high accuracy of imaging data. Influence the implementation of 3D printing materials. (2) Collecting image data and making 3D titanium alloy printing requires 3D printers, supporting CT, MRI equipment, titanium alloy materials, modeling and software systems, and the cost of materials is high, which is unbearable for some patients; the investment and use of equipment requires doctors and Engineers cooperate with each other, coordinate and participate among multiple disciplines; currently, due to technical limitations, the production cycle is long, and emergency surgery is difficult to apply. (3) In terms of manufacturing orthopedic implants, the optimal mechanical properties, degradation degree, pore size and void size of 3D printed titanium alloys still need further research; (4) The short-term effect of 3D printed titanium alloys is satisfactory, but due to the short application time, Long-term follow-up results and management of complications are still lacking.
In recent years, 3D printing technology has made remarkable progress in the medical field. Specifically, 3D printing of titanium alloys has revolutionized the way we approach orthopedic surgeries. In this article, we will explore the various clinical applications of 3D printed titanium alloys in orthopedics.
First and foremost, 3D printing technology enables the fabrication of personalized implants that are specifically tailored to a patient's unique anatomy. This greatly improves surgical outcomes, reduces the risk of complications, and shortens recovery times. For example, surgeons can now use 3D printed titanium hip implants with porous surfaces that promote bone growth, which can greatly reduce the risk of dislocation.
Additionally, 3D printed titanium alloys can be used to create patient-specific cutting guides that help surgeons accurately cut bones during surgery. This not only improves the safety and accuracy of the procedure but also ensures that the surrounding tissues are preserved, reducing the risk of post-surgery complications.
Moreover, 3D printing technology has expanded the possibilities for the treatment of complex bone fractures. For example, 3D printed titanium alloy plates and screws can be custom-made to fit a patient's unique bone structure. This allows for a more stable fixation of the fracture, improving the outcome and reducing the need for additional surgeries.
Lastly, the use of 3D printing in orthopedics has the potential to reduce healthcare costs. By combining personalized implants, cutting guides, and surgical instrumentation into a single surgery, operating time can be reduced, along with the associated costs.
In conclusion, the advancements in 3D printing technology have greatly improved the clinical application of titanium alloys in orthopedics. The personalized implants, cutting guides, and surgical instrumentation have revolutionized the field. The future looks bright in this area, and we can expect further developments in the use of 3D printing in orthopedics. although there are still many problems to be solved urgently in 3D printing titanium alloy technology, this technology has unique advantages, which is consistent with the concept of precision medicine currently advocated, and has great research value in the field of orthopedics. It is believed that with the continuous and in-depth development of technology, 3D printing titanium alloy can overcome its current shortcomings and produce a qualitative leap.
