INTRODUCTION
Additive manufacturing (AM) is a technique used for fabricating complex geometries and structures using the three-dimensional (3D) computer-aided design (CAD) data. The process consists of successive printing layers of material depositing one layer over another. AM is gaining importance in the field of medicine, especially for orthopedics applications. In the medical field, AM eases in the fabrication of complex implants such as a heart valve, cartilage, and trachea. In this article, we have systematically printed a cast model of a patient's wrist fracture using a fused-deposition modeling (FDM) 3D printer by capturing the data with the help of computed tomography (CT) scan. This 3D printed model can be used to evaluate the minute details of fracture before the surgery.[1][2]
FDM 3D printing can fabricate the parts using a variety of materials, including elastomers, acrylonitrile butadiene styrene (ABS), and polylactic acid (PLA). In this article, we tend to explore the benefits of manufacturing of patient-specific implant (PSI) using 3D printing.[3][4][5] The primary purpose of using 3D printing technology is to make the patient-specific fracture bone model in less time and with intricate designs and structure to overcome the difficulties of traditional manufacturing processes. Furthermore, the repair of critical bone defects remains a challenge for orthopedic surgeons.[6][7][8]
PROBLEM DEFINITION
Our main aim is to develop the skills and learn about AM in the context of orthopedics and to print a 3D object by using a simple nonstandard FDM 3D printer. This 3D model made from patient-specific data, as captured by a CT scan, is converted into a 3D CAD data using mimic software. The main aim of printing this patient-specific 3D model is to create a model of bone for surgical planning. PLA is used to print this model using a locally made FDM 3D printer.
METHODS FOLLOWED TO WRITE THIS PAPER
In this article, how 3D printing is beneficial in developing a PSI has been studied. The authors have studied about AM and its applications in manufacturing industries and also in the medical field. Furthermore, for the experimental data, a 3D object is printed using a simple FDM 3D printer. It is observed that this AM is useful for surgical planning, and we need to explore their applications in the field of orthopedics. The method followed to write this article is shown in Figure 1.
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Figure 1: Research methods followed
We have organized this article into 11 sections. Section 1 is about the introduction part; Section 2 describes the aim of this article. Section 3 describes the stepwise methods to construct a 3D printed model of a fractured wrist. Section 4 provides the significant benefits and impact of AM in the society. In Section 5, a literature review about AM in orthopedics has been discussed, and in Section 6, 3D printing applications in orthopedics are listed. Section 7 consists of the design and printing of patient-specific fracture bone implants. Section 8 has a discussion. In Section 9, the limitations are provided. Section 10 describes future scopes, and Section 11 contains the conclusion of the paper.
For the printing process, a case of the patient fracture bone was taken, and it was scanned using computer tomography and then converted into.stl format using the mimic software. Then, the PSI was printed using FDM for surgical planning.
MAJOR BENEFITS OF ADDITIVE MANUFACTURING
AM has a substantial impact on society in the field of health care, aerospace, automotive, and various other fields. The present study shows that AM technology has been in the existence for more than 30 years and is ever-growing. These technologies are opening new opportunities in terms of manufacturing and production.[9][10][11] It makes existing products and their application better as well as creates opportunities to manufacture products that were initially very difficult to make. The significant applications of this technology are as under:
- Reverse engineering
- Component remanufacturing
- Reduction of weight of the final part
- Lesser use of raw materials
- Cost of producing complex structures is low
- Allows product lifecycle leverage
- Reduction in manufacturing, design, and prototype lead-time
- Reduction in manufacturing costs for single-item production
- Reduction in repair costs
- Reduction in inventory, during the product life cycle
- Reduction in the cost involved in the product development
- Quick production of customized and exact replacement parts on the site
- Allow for design changes that are lighter and more efficient
- Fabricating custom implants, such as prosthetics and hearing aids
- Manufacturing or printing of human organs and their parts
- Reconstructing body part, bones, hip joint, and skull implants
- Reduced the risk of postoperative complications.
In an AM, an object is created by laying down the successive layers of the material until the complete object is formed. Each of these layers can be seen as a thinly sliced horizontal cross-section of the object that is being created.[12][13] 3D printing is the opposite of subtractive manufacturing which is cutting out/hollowing out a piece of metal or plastic with machines such as a milling machine. 3D printing enables us to produce intricate shapes using less material than traditional manufacturing methods.
LITERATURE REVIEW ON AM IN ORTHOPEDICS
Mok et al., 2016[14] in their article “From the printer: Potential of 3D printing for orthopedic applications” has reviewed the way that 3D printing can be used for patients and the way it can be used to print PSI. The authors have also discussed the techniques and the technologies used, the materials needed for an implant based on their cell-material interactions, processing methods, mechanical properties, and chemical properties. Titanium (Ti) has excellent mechanical properties and is considered biocompatible for implantation. They have also discussed other materials that can also be used in 3D printing and bioprinting, such as natural polymers, bioceramics, synthetic, and metals. Materials for 3D printing are needed to be carefully chosen based on the proposed application of the construct. The article also discussed the various dimensions of application of 3D printing in orthopedics, including implants and prostheses for support, designing and printing customized equipment for surgical planning, and regenerating musculoskeletal tissues, including bone, cartilage, and soft tissues such as tendon, ligament, and muscles.
Trombetta et al., 2017[15] performed a methodical review regarding the manufacturing of calcium phosphate (CaP) ceramics using 3D printing and their use in an orthopedic application, such as bone grafting and drug delivery. In this article “3D printing of CaP ceramics for bone tissue engineering and drug delivery,” they have described the manufacturing of CaP materials using powder bed fusion, vat polymerization, binder jetting, and material extrusion. They concluded that without the addition of osteoinductive elements such as cells or biofactors, complete bone regeneration could typically not be attained.
Wong et al., 2017[16] reviewed the application of 3D printing and its applications in orthopedic surgery. The 3D printing technique is different from conventional methods in terms of design freedom and flexibility. It has been applied successfully in bone tissue engineering for the manufacturing of structurally advanced bioscaffolds, surgical planning for complicated cases, and in the manufacture of instruments for specific patients and implants to match individuals' anatomy and to achieve error-free resection.
Wong and Scheinemann, 2018[17] reviewed the metallic biomedical materials used for fabricating orthopedic implants such as Ti-6Al-V4 (Ti-6 aluminium-4Vanadium) and CoCrMo (Cobalt-Chromium-Molybdenum) alloys in their paper “additive manufactured metallic implants for orthopedic applications.” That paper also described the processing chain in metallic implants and the AM technology based on metallic implants. Metallic implants are PSI which can be used in various orthopedic surgeries, such as spinal instrumentation, bone tumor surgery, joint replacement, and fracture fixation.
Wodajo and Jakus, 2019,[4] in their paper, “Nanopatterning and Bioprinting in Orthopedic Surgery” reviewed about nanopatterning. In Part I, the nanoscale pillars on passive surfaces such as insect wings inhibit the release of bactericidal agents, precoating metallic surfaces with proteins like albumin or some kind of lipids provide adhesion, and coating metal devices with antibiotics-containing hydroxyapatite (HA) have decreased the infection rates. In Part II, they reviewed bioprinting in orthopedics.
Tai et al., 2018[18] in their paper “3D printed composite for simulating thermal and mechanical responses of the cortical bone in orthopedic surgery” introduce about namely 3D polymer-infiltrated composite (3DPIC), which is a newly discovered bone-mimicking material fabricated by the binder-jetting technology and epoxy is used for the post-strengthening process. Different experiments were carried out to test 3DPIC, including the four-point bending, which is used for measuring the mechanical properties and the measurement of thermal properties. For the comparison of 3DPIC to cortical bone, thermal responses and drilling haptic of it are being tested.
Javaid and Haleem, 2019[19] have reviewed AM in orthopedics for the replica of bones which helps in the treatment of bones. The current status shows growing research work in the field of AM and its applications and various challenges in the orthopedics field. This technology provides education about implant designing and preoperative planning and also creates manufacturing flexibility. It allows the fabrication of customized prosthetic implants as per the patient's specific requirements in terms of shape, size, dimension, and mechanical properties. Advancement of AM in orthopedics helps in the printing of bones which are made accurately up of CaP and collagen. This technology can overcome the challenges of engineers encountered in bone tissue engineering and regenerative medicine fields.
Zheng et al., 2019[20] presented the repairing of critical-size defects, which are a challenge for orthopedics' surgeons. In the research article “3D bioprinting in orthopedics' translational research” it has been carried out that 3D bioprinting is a technology that connects biomaterial and living cells and is an important method that can be used in tissue engineering projects. 3D bioprinting is a technology which can be used to create various scaffolds with a broad range of advanced material and cell types. In the orthopedic field, the smallest bone defect that cannot be repaired by itself is called a critical size defect, which will not heal without interference. The maturity of 3D bioprinting technology helps us with a new way to promote bone regeneration and also enables biomaterials and tissue engineering to be more closely integrated. As 3D printing technology continues to become faster, affordable and more accurate, its use in medical research and biological manufacturing is likely to become routine, especially in the research field.
Feng et al., 2019[21] has reviewed in the paper “design and implementation of a 3D model for medical image for bone defect” that a model of bone defect was constructed by using 3D printing technology, which was tailor made for doctors to simulate the bone defect before the operation. First, CT files of bone defects were imported into the Mimics medical image control system; then the pathological model was formed by 3D reconstruction and image processing. Second, the 3-Matic forward engineering software was used to realize the design model of bone defect repair by describing bone repair and mirror image. Third, after processing the design model with Cura chip software, the PLA macromolecule material was used to make the actual object by a 3D printer. At present, the methods of treating bone defects mainly include autogenous bone transplantation, artificial material filling, and allogeneic bone transplantation. Autogenous bone transplantation method is the most critical at present, but it may cause new bone defect trauma and cannot cope up with significant area defects.
Zamborsky et al., 2019[5] in their paper “perspectives of 3D printing technology in orthopedic surgery” reviewed rapid prototyping technologies in medicine focusing on surgery, preoperative model printing in fractures and patient-specific surgical guides, custom orthopedic implants, instruments and plastic or metal implant prototypes, printing bone constructs-bone grafts, periprosthetic infection, and spinal fusion. A detailed review of the topics, as mentioned above, was done. Science, called regenerative medicine, has already succeeded in the engineering of skin, cartilage, bladders, urine tubes, and blood vessels and so on can be successfully implanted in patients.
Bedo et al., 2019[22] in their paper “method for translating 3D bone defects into personalized implants made by AM,” has suggested a method for translating 3D bone defects into personalized prosthetic implants, to be further produced by AM methods, based on CT imaging. This method consists of delimiting bone defect areas in CT, isolation of defects, and the construction of a virtual implant that is saved in the.stl format for 3D printing.
Zadpoor, 2019[23] present “mechanical performance of additively manufactured meta-biomaterials” reviewed about remarkable mechanical properties such as in auxetic meta-biomaterials, negative Poisson's ratios can be observed, superelasticity, and shape memory behavior of AM meta-biomaterials. This article also focuses on applications of these different behaviors, for example, to make deployable implants. Some 3D printed meta-biomaterials such as metallic ones can be used as orthopedic implants for patients and substitutes for bones.
Zadpoor, 2020[24] reviewed the new material called metamaterials, which are architectural materials with rational design and having extraordinary properties not present in materials naturally. For the development of meta-biomaterials, they aim to mimic biological tissues and therefore replace either temporarily or if possible permanently. There is clinical evidence at different levels to prove that the geometrical design of meta-biomaterials helps to achieve the superior performance.
Haleem et al., 2020[25] state 3D Printing applications in bone tissue engineering and performed a systematic review on it. The article also described 3D printing technology and its significant contributions, steps used, benefits, material properties and the essential elements of bone tissue engineering and identified its significant advancements when 3D printing is used. It also discusses the limitations and future scope in bone tissue engineering using 3D printing. Bone tissue engineering is an interdisciplinary approach which utilizes cells, biomaterials, and it is combinations to restore required functions of tissues. Scaffolds are an essential part of bone tissue engineering.
THREE-DIMENSIONAL PRINTING APPLICATIONS IN ORTHOPEDICS
Orthopedics is a branch of surgery which deals with the treatment of patients with musculoskeletal deformities. Now, 3D printing technology is used successfully in orthopedic surgery through innovative applications. 3D printing can be used for preoperative planning before the surgery. The prototypes of bones can be used for surgery, teaching, and associated work. It can also be used for complex joint replacements for developing a model and get details about possible intraoperative difficulties and plan surgery accordingly by the surgeon.[26][27][28][29] The numerous applications of 3D printing in orthopedics are as under:
Surgical planning
Surgical planning is the method used before the operation for pre-visualization of surgical intervention, performed by using CT planning software. It is used to predefine the surgical steps and to understand the details about surgical anatomy. Surgical planning has gone through different stages in the evolution of modern medicine. AM is identified for better preoperative planning, and the chances of exposure of radiation during surgeries can be reduced using this technology. Surgical planning using 3D printing technology might reduce perioperative blood loss and operation time, but there was the same complication rate.
Manufacturing of patient-specific surgical implants and guides
It is used mainly in deformity correction, tumor, and total joint arthroplasty. 3D printing helps in the designing guides used for surgical cutting that can excellently match the anatomy of patients and achieving accurate resection. This technology has advantages over conventional instruments because the intramedullary instrumentation is avoided; there is a reduction in blood loss during bilateral total knee replacement. The results can also be seen in correction surgeries for tumor and deformity. The accuracy of the resection margin might also be improved using 3D printing. There are some complicated cases for the PSI and synthetic devices, such as pelvic tumors and the spinal tumor, they can be resolved by 3D printing.
Bone tissue engineering
Nowadays, 3D printing technology is used for the manufacturing of structurally advanced bioscaffolds. The 3D bioscaffold should be designed to attain remarkable mechanical and biological properties such as for mechanical strength is recommended for hard tissue regeneration, while for cartilage regeneration, a flexible bioscaffold is recommended. For porous scaffold fabrication, the main biomaterials are HA and Cap as they are highly biocompatible and biodegradable.
Drug delivery
The physiological attributes and microenvironment of bone tissue are specific; therefore, drug delivery becomes difficult to the bone tissue or damaged site. 3D printing can be used as a means for manufacturing implantable drug delivery devices and fixation implants for particular patients that allow drug delivery to localized sites. Methotrexate (MTX) and gentamicin (GS)-loaded fixation devices, including pins, screws, and bone plates can be manufactured using 3D printing because MTX and GS-impregnated constructs have considerably lower compressive and flexural strength as compared to the PLA constructs.
Traumatology
3D printing technology can be now used by orthopedic trauma surgeons to construct 3D anatomical models from CT or magnetic resonance imaging (MRI) data of trauma patients. Implants for particular injured patients and healthy body parts can be made to help surgeons to know about patients' precise path morphology, regarding both soft-tissue and injured bones, as well as the non-lesion area on the contralateral side to the limb injuries, and therefore, help in better surgical planning.
Bioprinting
3D printing technologies are used for fabricating objects that are not only mimicking the anatomic form and providing structural support but also they imitate the biofunctionality of tissues they are made to replace. They may even transform into tissues indistinguishable, in both form and function. The term “bioprinting” refers to the process of AM usually 3D printing such as jetting, or direct extrusion in which live cells are used as feedstock materials during the manufacturing of 3D-printed living tissues or organs, such as the ears and heart.
Orthopedic corsets
Biopolymers, such as PLA have properties like biocompatibility and biodegradability, which provide significant advantages and increase their potential use in various medical applications. PLA bioplastic has excellent biocompatibility, and it is used for the production of orthopedic corsets using the FDM method.
Meta-biomaterials
In recent times, discoveries have been made for the development of rationally designed materials, which are called metamaterials. These metamaterials exhibit extraordinary properties. Meta-biomaterials are architectured to replace biological tissues. The meta-biomaterials are aimed at imitating unique properties displayed by biological tissues including negative Poisson's ratios, a combination of ultrahigh toughness with stiffness, and connection of extremely tough material with soft tissues such as bone-tendon or bone cartilage connections.
3D printing is an innovative technology used in orthopedics for preoperative planning of surgeries, specific implants for individual patients, and bone tissue engineering. There are various materials used for 3D printing in orthopedics such as metals, ceramics, polymers, plastics, and bio-glass. Research has been conducted to find out biodegradable and biocompatible materials having desirable mechanical properties.
METHODS FOLLOWED TO CONSTRUCT THREE-DIMENSIONAL MODEL
Image acquisition and computed tomography scan preprocessing for three-dimensional printing
The foremost step for 3D printing is the acquisition of images. The image data are acquired from computerized CT scan, MRI, or any other imaging methods. However, the most common one is CT images for 3D printing in orthopedics surgery.
Mimics software is developed for medical preprocessing of images and used for the partitioning of 3D medical images (coming from ultrasound, CT, MRI, etc.), and the result will be perfectly precise 3D models of a patient's anatomy. Mimics software converts Digital Imaging and Communications in Medicine format files containing sliced CT images into sliced digital images. Various tools are used for afterward processing of 3D models, including visualized tools and cutting tools. The cutting tool is used to separate the single target region, whereas the visualized tool is used for maximal/minimal projection, surface/volume rendering, and multiplane improvement.
Slicing and resizing the model
Cura is powerful but easy to use 3D slicing software. The software is used for slicing 3D files for different 3D printers. Cura supports STL, OBJ, and 3MF 3D file format. It also has a function of importing and converting 2D images (.JPEG,.JPG,.PNG,.GIF, and.BMP) to 3D extruded models. Using Cura, we can also adjust the size of the model. It also shows the exact time that will be taken for printing the 3D model. Cura software has different printing parameters, mainly printing speed, layer thickness, filling rate, printing temperature, support and platform attachment, and they can be set for a particular model. For our model, the printing parameters of FDM are shown in Table 1.
Table 1: Printing parameters of bone manufacturing using fused deposition modelling
Three-dimensional printing
After slicing a 3D object, it generates a readable language for the 3D printer called G-code. The 3D printer reads G-code only, and the 3D object is printed using co-ordinates.
3D printers have inbuilt 3D Printing software for the creation of actual 3D physical objects. The commands are given by 3D printing software to 3D printers and material comes out of a nozzle in the form of thread or wire, which is then joined together layer upon layer and solidifies to create a real 3D object.
The limitation of 3D modeling software is that it can only create a virtual model of an object. Therefore, 3D printing software is used to translate the 3D model into a readable format, such as G-code for the 3D printer. Figure 2 shows the printing of orthopedics parts using FDM 3D printing.
Figure 2: Printing of orthopaedics part using fused deposition modelling 3D printing
The quality of the model is determined by the critical parameter, i.e., printing speed. If the printing speed is high, then the quality of the model will be reduced, and it can cause machine failure too. Furthermore, faster printing speed means that there is not enough time for each layer to cool down and solidify to a particular shape. This will result in overheating, and this will further lead to easy deformation of the model. The nozzle temperature is determined by the type of material used for 3D printing. Currently, we have used PLA for our model. The corresponding nozzle temperature will be 198 degrees.
DESIGN AND PRINTING OF PATIENT-SPECIFIC FRACTURE BONE IMPLANT
For the printing process, the CT scanning of the fractured bone is used, which is most appropriate for preoperative planning in orthopedic surgery and trauma. This method is also useful for defining the fracture in intricate bone anatomy and studying geometry. The primary step used in this process is as under:
- CT of a patient-specific fractured bone
- Conversion of CT data into the CAD model using Mimics software
- 3D printing of fracture bone using FDM 3D printing
- Surgical planning.
The scanned CT data are converted into a virtual 3D model using the Mimics software. The use of 3D modeling facilitates the implementation of fracture operative techniques, as shown in Figure 3.
Figure 3: Fractured patient-specific bone manufactured by using fused deposition modeling 3D Printing
The main purpose of printing this object is to facilitate better geometry, shape, and size for surgical planning. The accuracy, surface finish, and the strength of the object also depend on the material used for the printing.
Implantation of patient-specific implant
A 20-year-old male patient, who is right hand dominant, presented to the clinic with fracture of distal-end radius of the right side. He was a musician by profession. He was very anxious about the proper functionality of his hand after the surgery. Thus, the concern of the patient for his future in the field becomes a prime concern for us.
The various benefits in the latest advancements in medicine (3D printing) were discussed with the patient such as preoperative accurate assessment of the bony injury, technique, and ease of reduction of the multiple fracture fragments and preparation of patient-specific jig, that can facilitate accurate surgery to reconstruct the fractured bone like the one before the fracture was amongst the few advantages described.
Furthermore, the plate to be implanted could be chosen and premolded before the actual surgical day. All these processes not only helped us to achieve an accurate reduction but also provided an excellent functional outcome, which is indirectly a result of reduced surgical time, lesser anesthesia time, and lower blood loss.
The patient returned to the activities of daily living in 3 weeks with a full range of motion. After 3 months, he was able to play his musical equipment.
DISCUSSION
AM enables personalized implants, prosthetics, and implantation, which is valuable in the field of orthopedics. This technology fabricates the implants of any desired shape rapidly. It increases the patient's safety and satisfaction and also helps to give training to medical students and doctors for better understanding of various types of patient-specific pathology, fractures, and anatomy. In the FDM process, PLA was used to create the bone. The temperature of the material was increased so that it comes out from the nozzle in the molten form. It increases the accuracy and strength of the bone implant.
A comprehensive evaluation of a patient's anatomy is made by using 3D printing. It is done before the actual surgery and therefore helps to develop more accurate surgical plans. The anatomy of every patient is different; therefore, 3D printing of PSI seems more beneficial than traditional mass-production methods of implant manufacturing.
Limitations
The major limitation of AM is the huge cost of software, hardware, skilled operators, maintenance, as well as printing material. Furthermore, AM includes the timescale model production, which varies according to different parameters such as density, porosity, and dimensions. Furthermore, data processing and image accomplishment take time. In orthopedics, sometimes mechanical strength is not achieved that is required and thus makes the object unusable for long-term use. In the case of FDM 3D printing, one of the significant disadvantages is that the process must be uninterrupted, if once the machine is disturbed, then the entire process is to be repeated. While the machine is working, the operator must take care that the material is appropriately fed to the nozzle. The study in this field requires a much higher type of machines. While printing the bone (object), many factors of 3D printing technology are still not considered. The printing of defected bone is limited only for the use of surgical planning and not for the implementation of the human body.
FUTURE SCOPE
Nowadays, AM is also used in orthopaedics. In this field, it is used for various applications in surgical planning, manufacturing of PSI, bone tissue engineering, drug delivery, traumatology, bioprinting, and orthopedics' corsets. We need more biocompatible material available for 3D printing at lesser rates. Also, bio meta-materials are going to be used to make deployable implants. As the implant reaches the intended implantation site, it will take a full size and full load-bearing due to the activation of the deployment mechanism. Available machines of 3D printing take more time for jobs needing intricate detailing and better finishing. The time taken for the 3D printing of a better surface finish product needs to be reduced. The future study to focus on the risk of implant-associated infections in orthopedics' implants.
CONCLUSION
AM is an emerging technology and has applications in wide areas such as aerospace, automotive, medical, and production. It is used to fabricate a wide range of complex geometries and structures from 3D model data. Freedom of design, waste minimization, mass customization, and the ability to manufacture complex geometries, as well as fast prototyping, are the main benefits of 3D printing. Based on CT or MRI, a bone 3D image can be rebuilt, and we can obtain a prototype which is helpful in medical and orthopedics' surgery. Another application of AM is the manufacturing of scaffolds for bone tissue engineering, which is used for the fabrication of sophisticated bioscaffolds. AM can 3D print small quantities of customized products with lower costs. This is especially useful in the orthopedics field, whereby unique patient-customized products are commonly and routinely required.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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