In clinical practice, for patients with severe craniocerebral injury, ruptured hemorrhage of cerebral aneurysm, cerebral hemorrhage and other patients, decompressive bone removal is often required after surgery. When the postoperative skull defect is large (≥3cm), skull defect syndrome may appear, which is manifested as headache and dizziness, which will increase the discomfort of the defect site when the posture changes. For skull defects, skull repair surgery can reduce the local tension of the dura and the skin flap, increase cerebral arterial perfusion in the area adjacent to the bone window, and thus significantly improve neurological dysfunction. Skull repair materials have become one of the factors that affect the effectiveness of skull repair surgery, and have achieved rapid development in lightweight manufacturing and tissue biocompatibility.
At present, the materials used in skull repair surgery are dominated by titanium alloys with stable morphology and good biocompatibility. 3D printing technology is a new technology that emerged at the end of the 20th century. It is based on image data and uses plastic particles, growth factors, metal powders, ceramics and other elements as source materials. Through layer-by-layer printing and accurate accumulation of materials, it can quickly manufacture any configuration. Digital molding technology. By controlling the porosity, pore distribution and pore size, 3D printing technology makes the implanted material have a porous structure, which is closer to the elastic modulus of human bone tissue and reduces the effect of stress shielding. In order to promote better fusion of autogenous bone and implant material, improve biotissue compatibility, and increase the mechanical stability of implant material-autogenous bone by increasing the bone-material binding site. With the development of technology and the innovation of materials, 3D printed implant materials have gradually entered the stage of clinical application.
1. Traditional skull repair materials
1.1 Autologous bone
That is, the patient's own ribs, iliac bones, or skull flaps, because they have a complete osseous structure and the potential to induce bone growth, can improve biocompatibility, postoperative rejection, subcutaneous effusion and infection probability Low, it is a kind of repair material with exact effect. However, it has defects such as limited bone source, increased surgical trauma when storing bone flaps and bone extraction, some cases of postoperative implant bone absorption and difficulty in shaping, etc., which cannot be widely promoted in clinical practice.
1.2 bone cement
Introduced in the early 1960s, the chemical name is polymethyl methacrylate. It is a water-soluble polymer compound with excellent performance and wide range of uses. It is shaped after being compatible in operation. It has simple shaping, low cost and mechanical strength. High advantages, stable chemical properties, and not easy to be absorbed. However, it is easy to damage the surrounding tissue with heat generation during compatibility, and there are problems such as subcutaneous effusion and infection after operation. Very few cases have events such as diffuse intravascular coagulation and deep vein thrombosis due to the influence of bone cement on hemodynamics.
1.3 Plexiglass
In the early days, plexiglass repair materials were widely used in clinic because of its thermal insulation and non-conduction, no artifacts in CT and MRI imaging tests, and easy shaping after heating. However, this kind of material has high brittleness, poor impact resistance, high probability of subcutaneous effusion after surgery, and the risk of puncturing the brain tissue after accidental fracture, which is currently not used clinically.
1.4 Medical silicone
Less irritating to the body, non-toxic, small proportion of allergic reactions, reliable biocompatibility, stable physical and chemical properties, can maintain the original flexibility and elasticity after implantation in the body, and is not easy to degrade; and high temperature resistance, plastic Fast shape and convenient disinfection. However, in practical application, there are unstable frontal and temporal fixation, and impurities in the material will increase the risk of epilepsy, so there are limitations in clinical practice.
1.5 Ceramic materials
That is biomedical inorganic non-metallic materials, including glass, ceramics and carbon. It has good biocompatibility and stable chemical properties. Ceramic materials such as zirconia have better compression resistance, chemical stability and wear resistance than organic materials and metal materials, but the main problems of these materials are brittleness and poor toughness, which limits their practical application.
2. Current status of application of skull repair materials
Titanium alloy materials have experienced three stages of development, the first is pure titanium and titanium alloy Ti-6Al-4V stage, in the middle experienced a new α + β type mainly Ti-5A1-2.5Fe and Ti-6AI-7Nb Alloys, titanium alloy materials that have appeared in recent years have better biocompatibility and reasonable elastic modulus. Because the β-type titanium alloy has good wear resistance, high strength, and an elastic modulus that is superior to the α and α + β-type titanium alloys, the β-type titanium alloy has become the main object of recent research in biomedical materials. Titanium mesh is used as a skull repair material in the early days. Most of them are manually shaped. During the operation, the titanium mesh is directly shaped according to the actual situation of the patient's bone window, and the titanium mesh is cut according to the shape of the bone window. The shaping increases the operation and anesthesia time. Increased the probability of postoperative infection.
In addition, cutting will reduce the integrity of the titanium mesh, causing its stability to be destroyed. The hand-shaping material has poor adhesion to the bone window, and its appearance is limited. Some patients also suffer from the deformation of the titanium mesh and damage to the scalp, which reduces the success rate of surgery. In the current clinical work, digital 3D shaping technology is often used instead, which can easily solve the above problems. The preparation is based on the thin layer CT scan data of the head, through the computer to obtain a 3D model conforming to the shape of the patient's skull defect, through the simulation test on the computer, to obtain a repair material with a satisfactory degree of fit, and then the CNC milling machine has no mold Suppress the skull repair materials needed for production.
Compared with traditional manual shaping, the digital 3D shaping technology takes less time, has a good fit, and conforms to the physiological anatomy, and because the implant material has a good fit with the edge of the bone window, it reduces the number of titanium nails and surgery. Field exposure time and incidence of complications. Because the titanium alloy skull repair material is characterized by suitable strength and rigidity, the thickness of the material is thin, the weight is light, the compression resistance is strong, the shaping is simple, the titanium nail fixation stability is good, and it has suitable biocompatibility and stability Sex, hypoallergenic, non-toxic and non-carcinogenic, can be permanently retained after implantation in humans; therefore, the current titanium alloy skull patch is a commonly used clinical skull repair material.
However, in some cases of large-scale skull defects, due to the limited mechanical strength of the titanium mesh, the impact strength against external forces is limited. Especially when repairing the skull defect with the orbital edge, it is difficult for the titanium mesh material to maintain the predetermined design shape. The soft tissue covered by local friction will make it thin and cause the titanium mesh to be exposed. And titanium implants also have some insurmountable shortcomings: for example, the modulus of titanium is 2 to 3 orders of magnitude higher than bone, stress shielding can cause osteolysis and loosening; furthermore, titanium implants are used in medical imaging such as CT and MRI There are problems such as artifacts and ghosting, which will have a significant impact on the patient's brain diagnosis at a later stage. Polyether-ether-ketone (PEEK) is an aromatic polymer material connected by ketone chain. It was successfully developed by British ICI company in 1977, and a high-performance special engineering plastic realized by British Victrex company in the early 1980s. PEEK mainly uses 4,4'-difluorobenzophenone, hydroquinone, anhydrous sodium carbonate as raw materials, diphenyl sulfone as solvent, and undergoes nucleophilic condensation polymerization under anhydrous conditions at 300 ~ 340 ℃ Get.
PEEK was first used in orthopedic surgery. Its biomechanical properties are similar to bone cortex, and it has good bio-tissue compatibility, high temperature resistance and resistance to ionizing radiation. The currently used PEEK material is designed and produced by computer aided pre-surgery. It is ideal to fit the remaining bone around the surgery, and has the same thickness as the defected bone edge. Because of the good shape before surgery and no need for shaping, the time of surgical anesthesia is greatly reduced, and the infection rate after surgery is significantly reduced. For cases of irregular skull defects such as periorbital, zygomatic arch and partial maxillary bone, PEEK implant materials accurately designed and cut by computer can quickly obtain excellent shape repair effect. PEEK is firmly fixed to the surrounding bone window through micro titanium plates and titanium nails. Compared with other pre-shaped implant materials, compared with materials such as titanium mesh and porous polyethylene, PEEK material is semi-permeable to X-rays, and is non-magnetic, does not produce imaging artifacts, and is convenient for postoperative CT and MRI examinations . Moreover, the PEEK material implanted in the body has thermal insulation properties, avoiding the same thermal conductivity as the titanium mesh material, and preventing damage to brain tissue.
PEEK material occupies an important position in the field of biomedicine by virtue of its excellent comprehensive performance, and its good creep resistance and high heat resistance characteristics make it used in the manufacture of human bone repair implant materials; the wear resistance and resistance of PEEK material The corrosive nature of chemicals makes it a substitute for long-life artificial bones; its potential bacteriostasis has played an important role in clinical treatment. However, because the preparation time in China is long and the operation cost is expensive, it is difficult for this kind of implant material to be widely used in clinic. There are many other materials used in the preparation of skull repair materials, such as cobalt-zirconium alloy, polylactic acid-glycolic acid copolymer, hydroxyapatite, chitosan, and alginate, among which nano-scale hydroxyapatite is Calcium phosphate compound, the mineral component of naturally occurring bones. Nano-grade hydroxyapatite can be combined with titanium mesh to become a higher strength repair material, with active bone formation activity, and its structure is very similar to the composition of autogenous bone, so its biocompatibility is extremely high and can be easily shaped The prosthesis is perfectly contoured. However, hydroxyapatite is limited in its use due to its brittleness, low tensile strength, and high infection rate. This type of material is still being explored and researched in the field of alternative use of human bone materials.
3.3 Application status of 3D printing technology and its prospect in the preparation of skull repair materials
3D printing technology is a kind of additive manufacturing. The more mature branches include layered solid manufacturing technology, electron beam sintering, laser cladding technology, laser forming technology, direct metal laser sintering, three-dimensional lithography technology, and selective laser sintering. , UV forming technology, etc. After the emergence of 3D printing technology at the end of the last century, it was early used in the design of surgical guides, the design of individual surgical plans, and the simulation exercises of some difficult operations. With the further development of this technology, through the control of pore distribution, porosity and pore size The size makes the implant material have a porous structure, similar to the body's own tissue structure, and solves the defects of high loss and sinking of the implant material. The design of the porous structure makes it have suitable mechanical properties and sufficient pore structure. The pore structure that communicates with each other allows tissue mosaic growth and reduces the chance of loosening of the implant material. The porous titanium alloy interbody fusion cage material manufactured by electron beam sintering has less micro-movability and excellent bone-bonding properties than the conventional PEEK interbody fusion cage material. Because of the advantages listed above, currently 3D printed implant materials are widely used in artificial joint replacement, vertebral body replacement and other operations.
3D printing technology is a revolutionary and innovative technology. Compared with the preparation of traditional skull repair materials, titanium alloy mesh plates and PEEK materials and other implants, 3D printing technology has broken through the bottleneck of design and traditional preparation technology. Digital visualization design greatly shortens the design and preparation cycle, reduces the material consumption rate, and the source material is not limited. Due to the customization and individualization, the skull repair material prepared by 3D printing can meet more special requirements and difficult operations, and has the following advantages: â‘ Pre-operative visual digital design and preparation of the repair material, without shaping during surgery To shorten the exposure time of surgery;
â‘¡The repaired material prepared has a high degree of personalization, rapid prototyping and short processing time
â‘¢The digital molding repair material and the bone window are more ideal to fit, good alignment, and improved appearance;
â‘£3D printing technology will gradually promote the lightweight design of repair materials. The porous structure of the material itself will promote the infiltration and fusion of osteoblasts after surgery, improve biocompatibility, and reduce rejection after surgery.
In summary, 3D printing technology has great potential in the field of neurosurgery individualized surgical treatment. Compared with the traditional manufacturing process, the preparation process of skull repair materials has made significant progress and improvement. At present, there are certain technical bottlenecks in the field of 3D printing technology. In addition to the limited types of source materials and the high cost, the current 3D printing technology field lacks related product quality evaluation and certification systems, and the corresponding clinical access system is not comprehensive enough. To a certain extent, it hindered the rapid development of this technology. However, with the further deepening of research on smart materials and bioactive materials, implant materials of any complex shape can be manufactured through 3D printing technology in the future, and these materials can change correspondingly with time and the external environment, which will better interact with human tissue Fusion, growth.
In recent years, cell- and tissue-based 3D printing technologies are being studied in depth. The fusion and application of this technology and the preparation process of skull repair materials will promote the production of light-weight design skull repair materials with biological activity. By then, the existing difficulties in the use of skull repair materials will be solved. 3D printing technology is still in the initial stage in the field of biomedical materials preparation. To achieve the application of 3D printing technology in the preparation of skull repair materials still faces many challenges, but the prospects are broad.
Author: Puren Hospital of Wuhan University of Science and Technology Affiliated neurosurgery (Chen Jun, Zhou Chi Zhong, Liu Rong) 
Editor in charge: null
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