3D printing is penetrating the medical field at an alarming rate. Although there is still a long distance from organ printing and will continue to face ethical and technical challenges, 3D printing can build a controllable 3D scaffold structure, with advances in cell printing and bioprinting, and innovations in printed materials. It is showing fascinating charm in the fields of tissue engineering and regenerative medicine. At present, 3D printing as a new type of additive manufacturing technology, the real scale of successful clinical treatment is mainly in the field of orthopedics and stomatology. A batch of customized osteotomy guides based on 3D printing, orthopedic implants, dental implants, etc. have been approved by CE and FDA and used in clinical practice. At the 2016 AAOS (American Association of Orthopaedic Surgeons), the world's leading orthopaedic companies have developed 3D printing for orthopaedic medical devices and new products for clinical use, which is sufficient to see the status of 3D printing in future orthopedics. Chinese orthopedics does not lag behind Western developed countries in terms of the number of patients, the number of surgical procedures, and surgical techniques, but it is clearly behind in orthopedic medical devices, especially implants. The emergence of 3D printing technology may give Chinese orthopaedic research and development of independent and innovative medical devices to catch up with Western developed countries. Fortunately, in 2015, CFDA also approved China's first 3D printed hip joint product, which has begun to be applied in clinical scale.

1, using rapid prototyping, assisted surgery design

Use CT, MR and other imaging techniques to reconstruct three-dimensional images of bones, then use layered solid manufacturing techniques to obtain prototypes of bones for teaching, demonstration and surgical design; use symmetry of human anatomy, or human anatomy stored in a database Learn data, reverse or simulate the three-dimensional image of the bone in the missing part, and assist the traditional mechanical processing to manufacture the bone replacement prosthesis that can be implanted into the human body; these are two more common and mature ways of using rapid prototyping and assisted surgery design. The Ninth People's Hospital affiliated to Shanghai Jiaotong University used rapid prototyping as an aid to develop a customized semi-pelvic prosthesis for reconstruction after semi-pelvic resection and reconstruction of severe acetabular defects in hip revision surgery. The research team's work was carried out earlier, but due to the limitations of metal 3D printing manufacturing technology, the implanted prosthesis still uses the traditional manufacturing process. With the maturity of 3D printing technology and the decline in the price of molding equipment, more and more doctors are using 3D printing for medical education and the design and demonstration of complex surgery.

2，Design and application of guide plate based on 3D printing

Although the value of personalized osteotomy guides in total knee arthroplasty remains controversial, especially the lack of evidence to improve long-term results, its advantages of saving operation time, improving force lines, and simplifying complex surgery still attract widespread attention. The major international joint joint companies have corresponding products for clinical supply. Due to the price limit (about US$1000 for each case), the period from the acquisition of patient image data to the osteotomy guide is about 4 weeks, which increases the cost of time and is therefore rarely used. Some artificial joint manufacturers in China have also started such research and started trials in some hospitals. Obviously, the personalized osteotomy guide also has a learning curve and is designed for experienced doctors, and is not a complete replacement for traditional surgical tools. In addition to the field of artificial joints, in the field of spine, trauma and orthopedics, the design and application of guides based on 3D printing is deepening and gradually revealing its special value. The research team of the Kunming General Hospital of Chengdu Military Region verified the safety and accuracy of the cervical pedicle screw placement guide in the spine cadaver specimens, and achieved satisfactory results in clinical practice. In view of the domestic situation, medical units interested in 3D printing can first explore from the guide plate type of equipment to improve the level of medical treatment.

3. Development of orthopedic metal implants based on 3D printing

The most important and valuable application direction of 3D printing in the field of orthopedics is the development of metal implants and personalized prostheses. This is determined by the materials, equipment and manufacturing characteristics available for 3D printing. The metal materials commonly used in orthopedics, Ti6Al4V, cobalt-chromium alloy and stainless steel, can be used for 3D printing. The accuracy and efficiency of high-energy 3D printing equipment such as electron beams and laser beams can meet the needs of manufacturing small components and scale. 3D printing enables the rapid manufacture of shaped implants in a computer-aided design, while at the same time making micropores of controlled size. These microporous structures reduce the elastic modulus of the metallic material in the solid portion of the implant, reducing stress occlusion; and promoting osseointegration between the metal and the bone at the surface of the implant. This unique advantage makes it promising in the development of orthopedic implants. The research team of the Third Hospital of Peking University designed a microporous 3D printed titanium alloy artificial vertebral body. Animal experiments confirmed that the artificial vertebral body and the surrounding bone have good osseointegration. The rough surface screws prepared by 3D printing have higher friction than traditional machined screws, and exhibit better anti-rotation force in the body. With the successful launch of the first domestic 3D printed metal implant prosthesis developed by Peking University Third Hospital and Beijing Aikang Yicheng Medical Equipment Co., Ltd., it has shown good results in preliminary clinical applications, and there are more and more medical treatments in China. Institutions, research institutes, and medical device manufacturers have begun to invest in 3D printing application research. Although the FDA approved Renovis's 3D printed intervertebral cage Tesera® in 2013, the use of microporous structures to replace traditional bone grafting in the human body and osseointegration efficiency remains to be confirmed by long-term results, especially for the spine. Integration. The 3D printed interbody fusion cage and artificial vertebral body project, which was developed by Peking University Third Hospital, has completed clinical research and entered the registration review stage.

4. Basic research

Due to the inherent biological inertness of metallic materials, osseointegration between them and the host bone is limited. One of the hotspots of basic research is concerned with the problem of metal microporous surface modification constructed by 3D printing. The goal is to promote the osseointegration effect on the surface of metal micropores, and to use it as a scaffold material to load other functional materials and drugs, and to manufacture antibacterial surfaces. The Xijing Hospital of the Fourth Military Medical University and the research team of Shanghai Jiaotong University introduced a chitosan/hydroxyapatite coating on the surface of 3D printed porous titanium alloy. After surface modification, the osseointegration effect was enhanced under the condition of diabetes induced injury. These studies will overcome the weaknesses of 3D printed materials and manufacturing processes themselves, thereby expanding the application of 3D printing in orthopedics. Admittedly, 3D printing of biodegradable biomaterials is also a hot topic, but there is still a considerable distance from clinical transformation.

The application of 3D printing in the field of orthopedics is deepening and has gone from the laboratory to the clinic. Only by realizing the true clinical transformation can the value of 3D printing be realized. Medical device manufacturers should work closely with medical institutions and research institutes to promote the application of 3D printing in orthopedics based on clinical needs and product guidance. Current laws and regulations from the government may be an important constraint, especially for the manufacture of 3D printed personalized implants. The good news is that we have seen the efforts of the government departments to make breakthroughs in the 3D printing of personalized implants through the construction of laws and regulations. In any case, 3D printing will be a good opportunity for Chinese orthopedic implantable medical device manufacturing to catch up with international pace.

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