Bone defect is a common type of disease in clinical practice, characterized by high surgical difficulty, long treatment cycle, and multiple complications. How to quickly and effectively promote bone defect repair is a huge challenge faced by clinical physicians. For bone defects, the current treatment methods mainly rely on surgical treatment, including traction osteogenesis, bone transplantation techniques, etc. In recent years, 3D printing has become increasingly widely used in the medical field. This article reviews the application of 3D printing in the treatment of bone defects, and focuses on the promising 3D printing tissue engineering scaffolds.

The application of 3D printing before bone defect repair surgery With the continuous development of material engineering and medical imaging technology, 3D reconstruction is carried out through computer-aided design. Based on personalized simulation, a solid 3D model with completely consistent size and shape is manufactured. The application of preoperative diagnosis and surgical models in bone defect repair directly or indirectly improves surgical accuracy.

3D printed bone implant material for repairing bone defects

Clinical commonly used bone implants

Autologous bone transplantation: Autologous bone transplantation is the "gold standard" for repairing bone defects, as it possesses all the required characteristics while retaining complete tissue compatibility. Due to the presence of growth factors, they have osteogenic and osteoinductive properties, significant histocompatibility, can provide structural support, contain live osteoblasts, and do not transmit diseases. The disadvantage of using autologous bone transplantation is that its supply is limited, and extensive use of autologous bone transplantation is prone to bone resorption. Collecting autologous bone can increase time and blood loss, and may require general anesthesia, thereby increasing the difficulty of surgery. The donor site may experience complications such as infection, prolonged wound drainage, reoperation, pain and loss of sensation lasting for more than 6 months.

Allogeneic bone transplantation: Allogeneic bone is widely used in clinical practice due to its abundant sources and unrestricted shape and size. However, allogeneic bone has low tissue compatibility, has rejection reactions, and completely relies on host cell invasion for osteogenesis. However, the deep revascularization of large allogeneic bones is very slow, often becoming dead bones, and there is a high incidence of refractures. It has been proven that there are a large number of failure records in long-term use.

3D printing personalized customization of internal prosthetic implants

The reconstruction methods for bone defects include allogeneic bone grafting, autologous bone grafting, and prosthetic repair. Among them, prosthetic repair has the advantages of beautiful appearance, early mobility, good stability, and good functional recovery.

The application of 3D printing in the repair of large bone defects

Large bone defects are caused by congenital defects, trauma, infections, and bone tumors, which can lead to delayed or non union during the recovery period. 3D printing plays an increasingly important role in the treatment of large bone defects. Clinical data from multiple patients indicate that 3D printed prostheses are feasible in reconstructing large bone defects caused by bone tumor resection, with good postoperative function and fewer complications; 3D printed prosthesis implantation can achieve bone anatomical reconstruction and biomechanical stability reconstruction, and effective intervention measures can reduce the occurrence of postoperative complications in patients; The in-situ 3D printing robot can quickly and accurately perform artificial bone tissue engineering implantation, and has good postoperative recovery effects, which has great prospects in clinical applications.

The application of 3D printing in the repair of large bone defects

Large bone defects are caused by congenital defects, trauma, infections, and bone tumors, which can lead to delayed or non union during the recovery period. 3D printing plays an increasingly important role in the treatment of large bone defects. Clinical data from multiple patients indicate that 3D printed prostheses are feasible in reconstructing large bone defects caused by bone tumor resection, with good postoperative function and fewer complications; 3D printed prosthesis implantation can achieve bone anatomical reconstruction and biomechanical stability reconstruction, and effective intervention measures can reduce the occurrence of postoperative complications in patients; The in-situ 3D printing robot can quickly and accurately perform artificial bone tissue engineering implantation, and has good postoperative recovery effects, which has great prospects in clinical applications.

3D printing porous bracket

Bone tissue engineering is a discipline that utilizes scaffolds to implant cells or incorporate bioactive growth factors to promote bone repair and regeneration. Its main research content includes scaffold materials, seed cells, osteogenic factors, and other aspects. In addition to meeting mechanical and structural requirements, bone tissue engineering scaffolds must also meet the characteristics required by biology. To overcome these limitations, metal materials, polymer materials, or bioactive ceramic materials can be combined to construct composite materials that can meet various requirements for scaffolds, including biocompatibility, biodegradability, bone conductivity, mechanical strength, etc.

Metal bracket

Metals are widely used in bone tissue engineering due to their good biocompatibility, strong fatigue resistance, and excellent mechanical properties. Currently, common metal scaffold materials include titanium and its alloys, cobalt, nickel alloys, etc. Among all metal materials, titanium and its alloys are currently the most widely used metal support materials. Due to its good biocompatibility, reliable mechanical properties, and corrosion resistance, it is widely used in the manufacturing of orthopedic implant scaffolds. Magnesium is also a biodegradable metal. Research has shown that compared to other metal implants, magnesium alloys have higher physical properties such as mechanical strength and elastic modulus, are closer to natural human bone, and have excellent bone promoting ability.

Bioceramic scaffold

Bioceramic materials contain both metallic and non-metallic components, which have good biocompatibility, appropriate biodegradability, and inherent bone induction ability. Their chemical properties are similar to those of bone, with high compressive strength and low ductility, and are widely used in 3D printing. Commonly used bioceramic materials include hydroxyapatite β- TCP, calcium silicate, biphasic calcium phosphate, magnesium phosphate, alumina, zirconia, etc. Calcium phosphate is a major component of natural bone tissue and has been proven to stimulate osteogenesis in stem cells and bone progenitor cells. The phosphate ions released by calcium phosphate derivatives play a crucial role in inducing osteogenic differentiation of stem cells. β- TCP is a common calcium phosphate material and is often used for bone regeneration due to its good biodegradability.

Polymer material support

Polymers have been widely used as biomaterials for manufacturing tissue engineering scaffolds, which can be either natural or synthetic. Natural polymers, such as fibrin, hyaluronic acid, chitosan, and collagen, exhibit structures similar to the small molecular components of the human body, exhibiting high biocompatibility, excellent biodegradability, bone conductivity, and low immunogenicity. Compared with natural polymer materials, synthetic polymer materials have better mechanical strength, higher processability, and controllable degradation rate, and the toxicity of degradation products is low, enabling complete metabolism. These synthetic polymer materials include polylactic acid, polyglycolic acid, polycaprolactone, polyethylene glycol, PLGA, etc. These controllable properties can be used to make customized scaffolds for specific needs and applications.

Composite bracket

Composite materials are composed of two or more materials with different properties, each of which only shows some advantages and specific disadvantages. This combination can take the form of copolymers, polymer polymer blends, or polymer ceramic composites. Because human bone is a composite material made by mixing inorganic HA crystals and organic collagen fibers, polymer ceramic composite materials have more advantages in biomimetic aspects among numerous composite scaffolds. PCL and β- The 3D printed composite stent composed of TCP is implanted into the fissure of the femoral head in rabbits. Compared with the control group, the composite stent has a higher ability to promote the inward growth of new bones β- The TCP/PCL stent may be a promising absorbable implant for the treatment of early femoral head necrosis.

Summary and Outlook

In the field of bone defect repair, 3D printing technology is widely used, mainly including preoperative planning and simulation surgery, in order to reduce surgical difficulty, shorten surgical time, reduce surgical trauma, and promote postoperative recovery. 3D printed implants or prostheses can solve the repair problem of large and complex bone defects that are difficult to solve with some allogeneic or autologous bones. The preparation of tissue engineering scaffolds using 3D printing technology is a rapidly developing research field. With the emergence of new technologies and biomaterials in the future, and the optimization of microstructure, these 3D printed tissue engineering scaffolds may ultimately be the key to providing opportunities for bone defect patients to improve their quality of life.