Application of 3D printing technology in otology
1. Basic principles of applying 3D printing technology to the medical field
The basic principle of 3D printing technology applied in the medical field is to use medical imaging examinations such as CT, MRI, PET-CT (Positron emission tomography, positron emission tomography) and optical scanning to obtain comprehensive and clear individual information Data, and then use computer 3D reconstruction software (such as MIMICS, FitMe, etc.) to convert the data, draw model data, and then convert the model data into a G code file that can be read by the 3D printer, and finally import it into the 3D printer to complete from bottom to top print. According to the status and forming method of the materials used for 3D printing, 3D printing technology can be divided into Fused Deposition Modeling (FDM), Stereolithography Apparatus (SLA), and Laminated Object Manufacturing (LOM) , Electron Beam Melting (EBM), Selective Laser Sintering (SLS), Laser Direct Melting Deposition (LDMD), Electron Beam Freeform Fabrication (EBF) .
2. Application of 3D printing technology in otology teaching and anatomy training
2.1 Teaching application of the 3D printing model of the temporal bone: The temporal bone is one of the most complex and precise osseous structures in the human body, and it is part of the lateral skull base. It not only has cerebral nerves, internal jugular arteriovenous and other important nerves and blood vessels passing through it, and The important terminal organs related to hearing and balance are also implicitly included, and the cavity is narrow, deep, and prone to anatomical variation. Based on the above characteristics, traditional two-dimensional image teaching has great limitations. With the advent and development of 3D printing technology, medical teaching has ushered in a "new weather." Suzuki et al. [Used 3D printing technology to create a double-sized temporal bone model and a triple-sized inner ear model, respectively, clearly restoring the structure of bone labyrinth, ossicular chain, etc. By combining this model with teaching videos, students can More intuitive grasp of anatomical positioning. In addition, the use of the 3D printing model as a medium can achieve the replication and restoration of classic cases and rare cases, breaking through the limitations of standardized temporal bone molds that cannot be individualized, bringing anatomical variations into clinical teaching to help students better understand.
2.2 The anatomical training application of the 3D printed model of the temporal bone: For otolaryngology doctors, especially otomicrosurgery and lateral skull base surgeons, master the anatomical structure of the temporal bone and combine it with CT imaging to form the spatial conformation concept of the important anatomical structure of the temporal bone to Important. Traditional temporal bone anatomy training is dominated by cadavers, but the anatomical materials (cadavers) are quite scarce and expensive, which severely restricts the temporal bone anatomy training and affects the improvement of clinical skills of otologists. It is reported in the literature that the temporal bone of sheep can be used for skill training for cochlear implantation and stapedectomy, but considering the differences in cochlear length, average diameter of spiral neurons, electrical stimulation, etc., the temporal bone of sheep is The role of anatomical training is very limited.
With the development of virtual reality (Virtual Reality, VR) technology, many countries have developed computer-based virtual temporal bone models based on force feedback technology, which breaks the time, space, and frequency limitations of traditional anatomical training, and the virtual surgical system can also be evaluated The surgical level of the operator. However, VR technology does not yet fully possess true three-dimensionality, and the simulation degree is not good. Operators cannot use real surgical instruments and cannot experience the real touch of drilling, and thus have not been widely used. The advent of 3D printed temporal bone models has largely solved these problems. The temporal bone model made by Hochman et al. using 3D printing technology can be used to practice mastoidectomy and posterior tympanectomy, etc. In the model, the wire simulating the facial nerve is double-surfaced, and the operator can immediately know if the facial nerve is damaged during the practice. The 3D model made by Bakhos et al. can be used for training of middle ear prosthesis implantation. Roosli et al. [The manufactured temporal bone model shows the indispensable anatomical details of cochlear implantation, including the structure of the cochlear lumen and the scale of the extended temporal bone. This model is considered to be not suitable for the anatomical training of cochlear implantation. Inferior to the temporal bone of the body.
For the evaluation of the advantages and disadvantages of the 3D printed temporal bone model, we usually use two aspects: surface validity and content validity: if the model has the appearance, sound, feeling and other characteristics of the prototype, then the model has good surface validity. The hardness of the model, the depth of the touch, the completeness of the anatomical structure, the recognition of the fine structure, and the operator's grinding touch, auditory feedback, and the simulation of the mixture of bone meal and irrigation fluid can be used as the surface of the 3D printed temporal bone model Evaluation content of validity. Similarly, if the temporal bone model is beneficial to the corresponding clinical teaching and anatomical skills training, it has satisfactory content validity. The evaluation content includes whether the model can improve students' anatomical skills, improve eye-hand coordination, and whether it is an effective training tool. The disadvantage is that the evaluation of surface validity and content validity has a certain degree of subjectivity. It is difficult to quantify the content of the evaluation. It is necessary to further explore the establishment of a set of objective and unified evaluation methods.
There are many types of printing materials used to 3D print the temporal bone model, such as: acrylonitrile-butadiene-styrene (acrylonitrile-butadi-ene-styrene, ABS) plastic, liquid photosensitive resin, various thermoplastic materials, etc. However, the most commonly used is gypsum powder. Based on the principle of micro-jetting, by changing the concentration and type of the binder, and then using different colors of dyes, the layered printing and assembly technology is used to create a 3D model, and the compressed air method is used later. The excess material remaining in the cavity structure is removed, and the temporal bone model created in this way can reproduce important structures such as the internal carotid artery, sigmoid sinus, and vestibule, and inexpensive printing materials are conducive to the popularization of technology.
Although 3D printed temporal bone models have many advantages, their development is still limited by many factors. For example: the lack of new printing materials: the most common plaster 3D printed temporal bone model is soft and not as hard as the cadaver temporal bone. Moreover, there is no standard for 3D printing materials in China, and most of them depend on imports. The printing technology is not accurate enough: due to the complex anatomy of the temporal bone, which contains many small structures, the current 3D printing technology can easily lead to incomplete shaping or fusion of the ossicles, and fine structures such as stapes, drums, etc. are difficult to reproduce or unrecognizable. High printing costs: Not only are the printing materials expensive, but the corresponding 3D printing equipment prices range from tens of thousands to tens of millions of yuan. Low work efficiency: the current technical model design and production time is relatively long, taking an average of about 3 days, which takes too long.
3. Application of 3D printing technology in pre-operative planning and surgical simulation of otology
When 3D printing technology is used in preoperative planning and surgical simulation, that is, "rehearsal with makeup" before surgery, it can provide personalized surgical treatment plans for patients with complex lesions. The 3D printing models created based on CT, MRI and other imaging data, computer design software, and 3D printing technology can not only provide a visual three-dimensional structure, but also reproduce the relationship between the lesion site and the surrounding area, and can be repeatedly simulated on the model. Surgery, anticipate possible problems in the operation, personalize the surgical plan, avoid potential risks, shorten the operation time, improve the quality of the operation, and reduce the pain of the patient [. At the same time, the use of 3D printing models can better communicate with patients and their families before surgery.
Due to the complexity of the anatomical structure and function of the temporal bone, the operation of the temporal bone requires extremely high clinical skills of the otologist. Using the 3D printed temporal bone model and performing surgical simulation on the model before surgery, not only can the surgeon achieve Qiu gully", and personalized treatment plan can improve the safety of surgery. Experts at home and abroad have applied 3D printing technology to preoperative planning and simulated surgery for patients with complicated temporal bone lesions. The Suzuki team used three-dimensional reconstruction of the CT scan data of the temporal bone in two children with congenital external auditory meatus atresia, and then used 3D printing technology to create the temporal bone and inner ear models.
Simulated surgery on the temporal bone model of one of the children not only confirmed the dysplasia of the middle ear on the CT film, but also further found the ectopic oval window, the anterior facial nerve segment, and the developmental deformity of the posterior semicircular canal. The model suggests that the risk of surgery is higher and provides a basis for doctors' clinical decisions. The operation simulation was also performed on the 3D model of another child, which indicates that the operation effect is good, and the child's hearing improves after the operation, confirming the preoperative judgment. Yang Jingya and others used 3D printing technology to prepare the temporal bone models of 2 patients with chronic otitis media and performed simulated surgery before surgery. Among them, one model showed that cholesteatoma adhered to the dura mater. Dura. Another temporal bone model showed limited lesion range and complete ossicular chain, suggesting that the risk of surgery is relatively low.
4. Application of 3D printing technology in otology repair and reconstruction
In recent years, the application of 3D printing technology combined with digital modeling in the field of surgery, especially orthopedics and maxillofacial surgery, has become more and more mature, providing important technical support for the repair and reconstruction of tissue and organ defects. And its application in otolaryngology head and neck surgery has gradually emerged.
The pinna is an organ that includes many subunit structures. Congenital microtia deformity ear reconstruction requires the shaping of the external ear wheel, the contra-helix, the scaphoid fossa, the triangular fossa, the ear cavity, the tragus, and the tragus The subunit structure such as the notch between the tragus, and the individual differences of the auricle of different patients are very different, which brings great difficulty for the surgeon to sculpt the costal cartilage and shape the ear support. Liang Jiulong et al. performed a three-dimensional CT scan of the patient's costal cartilage and healthy ear before the operation, converted the imaging data and then used 3D printing technology to obtain a personalized 3D model of the ipsilateral costal cartilage, healthy ear cartilage and healthy ear. In this first-stage operation, the operator can not only select the position of the costal cartilage according to the costal cartilage model, and design the length of the costal cartilage to be removed, but also have a specific reference when carving the costal cartilage and shaping the ear support, avoiding the traditional surgical method The blindness and randomness of the procedure improve the efficiency of surgery. In addition, the "tailor-made" 3D model can improve the symmetry and similarity with the healthy ear.
For the second-stage surgery, based on the thickness of the mirror ear model and the reconstructed ear model of the first-stage surgery, the shape and thickness of the stent required in the second-stage surgery of the reconstructed ear are simulated again, so that the reconstructed auricle cranial ear angle is consistent with the healthy side. Roberto et al. collected the imaging data of the patient’s healthy ear before digitization, digitized it, and formed the contralateral model after inversion. By deepening the structure of the boat-shaped fossa and triangular fossa to highlight the contour of the model, it was then digitally deconstructed and separated. The individual auricle components are reconstructed and the contralateral 3D auricle model is finally obtained, which can be used as a "guide" to guide the surgeon to shape. In addition, Kozin et al. pointed out that 3D printing technology was used to construct tympanic membrane stents using polydimethylsiloxane, polylactic acid, and polycaprolactone as raw materials, and then filled with fibrin-collagen composite hydrogel. The tympanic membrane is more resistant to degeneration than the superficial temporal fascia, and no additional flaps need to be collected, avoiding additional surgical incisions.
At present, the accurate restoration of internal structure based on imaging data has enabled the rapid development of 3D printing technology in medical teaching, anatomical training, preoperative planning, and surgical simulation. In the future, if VR technology can be combined with the 3D printing model, the 3D printing model can be used to solve the problem of the lack of three-dimensionality and the sense of simulation of the virtual technology. The virtual technology can be used to make up for the shortcomings of the fine structure of the 3D printing model that are difficult to reproduce or unrecognizable. I believe that through the complementarity of the two, 3D printing technology can be better applied to anatomical training and simulated surgery. Furthermore, for organ printing, the biggest obstacle is how to make a blood vessel network that transports oxygen and removes metabolic waste.
With the development of new materials, 3D printing technology can be used to build vascular structures with biological materials, and then biocompatible scaffold materials, even cells or growth factors, etc. can be printed and assembled layer by layer according to computer instructions to construct a physiological function. Implants (such as personalized ossicular chains, cochlea, etc.) are used to repair damaged tissues or organs of the human body, and are expected to achieve in-situ repair of living human tissues. In addition, if it can be combined with cloning technology, it is not only expected to solve the rejection reaction in the transplantation process, but also to provide biological specimens for the development of new drugs without violating the principles of medical ethics, so as to obtain accurate and detailed research data. There is reason to believe that the 3D printing technology that fully integrates materials science, computer software design and tissue engineering will bring more impact to the medical field in the near future, and its application in the field of otology will also be more In-depth and diversified, its potential value will be further explored by people with lofty ideals.