524838
research-article2014
SRIXXX10.1177/1553350614524838Surgical InnovationTuomi et al
Equipping to Innovate
A Novel Classification and Online Platform for Planning and Documentation of Medical Applications of Additive Manufacturing
Surgical Innovation 2014, Vol. 21(6) 553–559 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1553350614524838 sri.sagepub.com
Jukka Tuomi, LicSc (Tech)1, Kaija-Stiina Paloheimo, MSc1, Juho Vehviläinen, MSc (Tech)1, Roy Björkstrand1, Mika Salmi, DSc (Tech)1, Eero Huotilainen, MSc (Tech)1, Risto Kontio, MD, PhD2, Stephen Rouse, DDS3, Ian Gibson, PhD4, and Antti A. Mäkitie, MD, PhD1,2,5
Abstract Additive manufacturing technologies are widely used in industrial settings and now increasingly also in several areas of medicine. Various techniques and numerous types of materials are used for these applications. There is a clear need to unify and harmonize the patterns of their use worldwide. We present a 5-class system to aid planning of these applications and related scientific work as well as communication between various actors involved in this field. An online, matrix-based platform and a database were developed for planning and documentation of various solutions. This platform will help the medical community to structurally develop both research innovations and clinical applications of additive manufacturing. The online platform can be accessed through http://www .medicalam.info. Keywords additive manufacturing (AM), medical applications, surgery, classification, rapid prototyping, innovation, education
Introduction Additive Manufacturing Additive manufacturing (AM) is a relatively new group of manufacturing technologies developed since the late 1980s. Physical parts can be manufactured from numerical definition (3-dimensional computer-aided design [3D-CAD]) automatically, layer-by-layer, in a process that does not have similar constraints with conventional manufacturing processes.1 There have been numerous ways to describe AM, including rapid prototyping, freeform fabrication, tool-less manufacturing, and 3D printing, which all emphasize its capabilities compared with other more conventional manufacturing technologies.2 Additive manufacturing is now the accepted umbrella term for a group of AM technologies.3 Additive manufacturing is well suited for the manufacture of complex, organic-shaped models that cannot easily be described in terms of geometric parameters. Furthermore, parts can be made relatively inexpensively and easily using an individual person’s imaging data, thus making it possible to create customized solutions. There
are a number of different types of AM processes and equipment installations available. Some of the processes result in physical parts out of plastics and powder composites. But processes for high-end metal parts manufacturing are also in use. The most popular manufacturing processes for plastic and composite parts are powder bed fusion, material extrusion, binder jetting, vat photopolymerization, and material jetting. Powder bed fusion is the most popular process for metals.2 1
Aalto University, Department of Engineering Design and Production, School of Engineering, Aalto, Espoo, Finland 2 Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland 3 Dynamics Research Corporation, Arlington, VA, USA 4 National University of Singapore, Singapore 5 Karolinska Institutet, Division of ENT Diseases, CLINTEC, Stockholm, Sweden Corresponding Author: Antti A. Mäkitie, Department of Otolaryngology–Head & Neck Surgery, Helsinki University Central Hospital and University of Helsinki, PO Box 220, FI-00029 HUCH, Helsinki, Finland. Email: [email protected]
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Surgical Innovation 21(6) engineering, design, surgery, and rehabilitation. Thus, the need for collaboration platforms and tools agreed on by all actors involved in the design and production process of medical applications of AM is evident. Well-structured, conceptual tools may have a great positive impact on the community by enhancing collaboration across borders and disciplines.
Materials and Methods Classification for Medical Applications of Additive Manufacturing We have developed an application solution oriented classification system to be used for medical applications of AM. For each category presented, common requirements for AM technologies can be identified.10 Representative examples for each of the 5 classes are presented in Figure 1.
Figure 1. Representative examples of each of the 5 classes of the classification.
Medical Applications of Additive Manufacturing Additive manufacturing is already widely used in clinical practice, and the number of medical applications is increasing rapidly. Extremely complicated physical objects can be manufactured with these technologies in a fully automated process making them highly applicable in medical setting. Medical imaging data sets can be applied as the basis for geometry definition and there are several software tools available for reconstructing 3D models for creating physical models using AM for preoperative planning.4 Three-dimensional models have been also used to define geometry landmarks or 3D shapes for implant planning5 or special instruments.6,7 It is presently a common practice to apply AM preoperative models for surgical planning and training purposes. Such models can also be used for implant planning.8,9 We have recognized that it is quite common to combine several AM models in a single patient case. Also, these applications are often developed further during the design phase. Information and expertise in the field of medical applications of AM are quite scattered globally and thus, international collaboration is common. Furthermore, producing medical applications requires not only international collaboration but also collaboration across disciplines. It is truly a multidisciplinary field that draws resources from various fields, including radiography,
Medical Models for Pre- and Postoperative Planning, Education, and Training. Using primary data from medical images, AM can be used to manufacture models for preoperative planning or surgical simulation.4 Models can also be used for communication with technicians, education of students, and counseling of patients and families regarding complicated surgical procedures. Depending on the application, different qualities of the models such as anatomical accuracy, material characteristics, or haptic response of the model become important. Real haptic response of bone is especially desirable in surgical training models.11 Medical Aids, Orthoses, Splints, and Prostheses. Here, AM technologies are utilized for anatomic personalization of a (standard) device, to enhance healing from trauma, anomaly, or defect. The manufactured piece is either completely external to the body or at least noninvasive. The material should be nonirritant and surface requirements depend on each specific application. These products are typically wearable and external. Creating prosthetic sockets has traditionally been labor intensive, taking 2 to 3 days to make one socket. Using computer-aided manufacturing systems and AM technologies the time is reduced to less than 4 hours.12 Another example is treatment of dental malocclusion by AM of a mold for one or a series of clear and removable appliances.13,14 Also, noninvasive positioning guides, such as an auricular template for craniofacial implant positioning15 belong to this class. Tools, Instruments, and Parts for Medical Devices. Additive manufacturing may be used to create tools and hardware for medical applications, to enable or improve the efficacy of a medical or surgical procedure. In cochlear
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Tuomi et al implant surgery AM drill guides have been used and have reduced operative time and overall costs.5 Manufacture of operation specific instruments, such as custom fitting surgical guides16 or preforms belong to this class. Another example of a surgical tool is a prototype of an instrument for mandible fracture reduction.7 Oral appliances, which are made directly by AM,17 are also a representative application area of this class. Devices in this class are in contact with body fluids, mucous membranes, or tissues for a limited time, thus they are intended for transient or short-time use, are invasive but nonimplantable. The material must be sterilizable, and surface requirements depend on the specific application. These are predominantly invasive surgical products. Inert Implants. Devices in this class are intended for longterm use and are either wholly or partly implanted. AM implants may be used in surgical operations based on medical imaging and 3D modeling. Inert implants can be produced by AM technologies directly9 or indirectly.18 Janssens and Poukens19 have presented a cranial plate for direct implantation that has been digitally designed and manufactured by AM technologies. In the indirect approach, AM parts are used to create the implant through bending, deep drawing, casting, or other replication techniques. Eppley20 reported on a case where 7 patients with large bony lesions of the anterior cranial vault and orbit underwent simultaneous bony excision and reconstruction with preoperatively fabricated custom implants. Biomanufacturing. Freeform culture media can also be manufactured with AM technologies. These applications include biologically compatible parts and parts to be used when manufacturing these components. Such scaffolds can be used as a skeleton for cell cultures, to act as support or protection from external physical forces, and to provide an optimal medium for 3D cell cultures.21 The raw materials for scaffolds may be natural or synthetic, organic or inorganic, and their combinations. The AM structures are designed to be active whether they are resorbable or nonresorbable. The ultimate goal is to replace tissues such as bone, cartilage, liver, and heart, and corresponding research is currently increasing rapidly.22,23
Characteristics of Classes Table 1 shows the characteristics of the aforementioned classes. The relation of manufactured piece to patient determines the logical order of the classes. This approach helps categorize and define requirements for each class because patient contact is a key factor for determining which materials or finishing methods can be used in the manufacturing process.
Process Phases for Medical Applications of Additive Manufacturing Virtually, all medical applications of AM cases fall into 5 sequential phases regardless of the application class. This chapter introduces these 5 process phases and highlights the function and importance of each phase for the success of an end application.
Medical Imaging and 3-Dimensional Digitizing The process begins with a process phase called medical imaging and 3D digitizing. A number of different imaging technologies have been used for creating medical models, including magnetic resonance imaging and ultrasound, but computed tomography is the most common in medical applications of additive manufacturing.24 Medical imaging and 3D digitizing, being the first phase in the process, has a great impact on the quality of the medical application as it provides the raw data that is used in the next process phases. Therefore, radiographers and radiologists should be provided with detailed recommendations that will assist them to successfully implement this phase in the process.25 The recommendations should be given depending on the accuracy requirements of the application.
Three-Dimensional Modeling Three-dimenaional (3D) modeling converts anatomical multislice (a series of 2D images, such as DICOM) data to 3D STL (stereolithography or standard tessellation language) mesh format while making necessary adjustments like removing unnecessary tissue or imaging artifacts. Computer-aided design (CAD) of implants and tools can be done at this phase. Relevant information about this process step includes parameters such as the radiodensity threshold in Hounsfield scale, the reconstruction software for STL conversion, or the CAD/CAM software in design and STL manipulation.26
Additive Manufacturing Reconstructed data is taken to the additive manufacturing process for production of accurate, patient-specific, physical models. Many medical models, such as inert implants, have strict material requirements, which need to be taken into consideration for AM. In an application-oriented approach, the material, design, and production requirements for the manufactured piece must be compatible before the AM phase. More important, medical applications may have strict material or dimensional requirements, which the AM machines have to be able to meet.
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No patient contact
Relation of Piece to Patient Requirements
Based on patient geometryAnatomical accuracy but magnification or requirements depend miniaturization possible on case, sometimes sterilized
Primary Description
Transportability, storability, behavior in process, haptic response requirements depend on case
Other
External to body— May be combined to Nonallergic if in contact Includes external prostheses and noninvasive, wearable standard devices to with skin, mechanical and prosthetic sockets, personalized provide patient-specific surface requirements splints, drill-guiding microtables, fit; long-term and depend on case orthopedic braces and postoperative supports, appliances, orthodontic and oral (motion) guides, and appliances fixators Tools, instruments, and Enable or improve the efficacy of a Contact with body fluids, Patient-specific dimensions Sterilizable; no immediate Includes drill guides, specialty parts for medical devices medical or surgical procedure mucous membranes, and shapes may be toxicity or allergic surgical instruments tissues, or organs for incorporated reactions, no shedding a limited time: invasive of particles; mechanical but not implantable and surface requirements depend on case Inert implants Tissue replacement Wholly or partly Biocompatible; will not May attract cell adhesion Strict material requirements, long implanted, long-term change its characteristics on surface but mainly approval processes; includes contact with body (much) in vivo stays inactive; durability, dental applications: crowns and fluids, tissues, or organs mechanical properties, bridges surface properties depend on case Biomanufacturing Biologically active tissue Incorporated into body Shape personalized to Porous structures; Polymers, ceramics, and replacement; “organ match tissue defect, scaffolds must be cell composites; freeform culture manufacturing” porous structures, growth conductive, media in vitro; additive optimal morphology inductive, resorbable, manufacturing + tissue depends on cell type and controlled engineering application site
Plan or simulate surgical procedures pre-, intra-, or postoperatively; educate students, patients, and families, and train surgeons Enhance healing from trauma, anomaly, or defect
Medical models
Medical aids, supportive guides, splints, and prostheses
Purpose
Class
Table 1. Characteristics of Medical Applications of Additive Manufacturing Classes.
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Figure 2. Process and classification matrix.
Although AM equipment operates automatically some degree of specialist expertise is necessary to ensure efficient and accurate results. The accuracy of models varies between different materials, AM technologies and machine runs.27 Expertise is necessary for example to set the AM process parameters and for post processing of AM parts.28,29
Finishing Following AM, some manufactured pieces require a finishing phase. Finishing covers different surface treatments such as washing, coating, polishing, or sterilization. Inert implants and objects invading the body need to be sterilized prior to their clinical use.
Clinical Application Clinical application is the ultimate goal of the process and it describes the purpose of the manufactured piece. Applications may range from structural models for enhanced surgeon–surgeon or surgeon–patient communication to surgical tools, implants, and even laboratory-grown tissues. A case may include several of these processes during the full medical procedure and a framework describing the overall process from start to finish needs to have the flexibility to depict all process flows and process phases accurately and in detail.
Medical Applications of Additive Manufacturing Matrix Using this novel matrix framework for medical applications of AM with relevant content in each cell, a clinical case application may be planned and documented.
Logical sequences of data processing and manufacturing phases are presented in columns and classification-oriented AM applications are listed in rows. Figure 2 presents an example of a patient case documentation using the matrix. This case shows the role of AM in surgical reconstruction of the orbit. A patient-specific customized 3D model of an implant was designed for a 67-year-old male patient after a complicated facial trauma. A volumetric net was first formed and several test pieces produced by AM from stainless steel and titanium.9 A titanium reconstruction plate was finally obtained in a similar manner and implanted onto the injured orbital wall. To ensure the accuracy and the precise fit of the implant, it was tested on the preoperative model before being surgically placed on the patient’s orbital floor. Figure 2 presents a case study where 2 process flows were needed. First, a preoperative model was produced and it was used to help the design and production of the orbital implant. This was a straight-forward process that was depicted with ease on the framework. However, many medical cases are more complex and require more process flows before the end application. Previously, it was mentioned that it is common to combine several preoperative models in a single patient case. This can also be depicted using the proposed framework model because of its scalability. The proposed framework, and the online platform, allows users to input an arbitrary number of parallel and sequential subprocesses, making it possible to depict very complex medical cases from start to finish without omitting important case-specific information. The practical purpose of the matrix framework to a clinician is that it provides tools to determine quality specifications for the preceding process steps before these steps are implemented. In the example case, a patient specific preoperative model of the orbital floor and a titanium implant were designed and manufactured. To ensure the accuracy and the precise fit of the implant, it was tested on the preoperative model before being surgically placed on the patient’s orbital floor.
Online Platform and a Database To enhance the usability of the matrix framework, an online platform and a database for medical applications of AM cases was created. The online platform provides tools to examine previous medical case studies and upload new case studies to the database. The validity and usability of the platform was tested with 8 different case studies and more patient case studies are continuously uploaded to the database. The platform and the database were created using open source content management system and the case content is open for anyone. Some limitations to case information may apply when appropriate to maintain patient’s anonymity. The platform and the database will be developed further at Aalto University, Espoo, Finland.
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Surgical Innovation 21(6)
Furthermore, the medical case content will remain open for users also in the future. The online platform can be accessed through http://www.medicalam.info.
Discussion We propose our novel matrix platform be used in the planning and documentation of medical applications using AM. This system is based on an application-oriented classification. The present representative case studies9,26 and the available literature10,27 suggest that there is a need for location independent, enhanced interdisciplinary collaboration on this matter. Expertise on medical applications of AM is quite scattered globally and a platform based on a uniform structural concept could help the current research and development work in this field. One of the strengths of our proposed model is its eminent scalability: Virtually any AM case—from simple to extremely complex—can be described since the platform allows an arbitrary number of parallel and sequential subprocesses, each with their own parameters and information. In addition, the platform offers a quick overview of the big picture, regardless of the amount of subprocesses. This will help professionals to mentally tie the parallel processes together and set their minds to the ultimate target, that is, the actual application and its benefits to the patient—be it in the planning phase for a completely new case, or assessing documented previous cases. Most medical applications of additive manufacturing require extensive collaboration across disciplines—notably, but not limited to, various fields of expertise including radiography, engineering, design, surgery, and rehabilitation. Since the experts involved come from different academic backgrounds or working cultures, conceptual tools such as the presented platform are essential to enable a clear and coherent discourse of medical applications of AM cases and the field in general. This should help all the actors involved to develop a better understanding of this truly complex, interdisciplinary process and help to realize the potential that additive manufacturing has to offer to medical practice. Finally, this will lead to improved patient care.
Conclusion Additive manufacturing permits us to create complex physical objects within hours in a fully automated process. Therefore, AM is widely used clinically and the number of new applications is rising rapidly. The process of including AM into medical applications consists of process phases as follows; medical imaging and 3D digitizing, 3D modeling, AM, part finishing, and finally, the actual clinical application. In the proposed matrix platform for medical applications of AM, the logical sequence
of data processing and manufacturing phases are presented in columns whereas the classification-oriented AM applications are listed in rows. This will make it a comprehensive framework for depicting medical applications of AM cases. Medical applications of AM require extensive collaboration across various disciplines. We have proposed a scalable, application-oriented solution to help all the involved actors to develop a better understanding of this complex process. Matrix-based platform for the medical applications of AM should help the medical community to structurally plan and document various solutions. Authors’ Note Kaija-Stiina Paloheimo and Juho Vehviläinen contributed equally. Part of this article was presented at the Fourth International Conference on VRAP, Leiria, Portugal, October 6-10, 2009.
Acknowledgments The Finnish Funding Agency for Technology and Innovation (TEKES), Helsinki University Central Hospital Research Funds, DeskArtes Oy, EOS Finland Oy, Vektor Claims Administration, and Planmeca Oy are thanked for financial support. Mr Pekka Paavola, MSc(Tech), is thanked for photographical work.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Finnish Funding Agency for Innovation (research grant numbers 2926/31/2009 and 660/31/2010; 70% of total research budget) and Aalto University (research funding; 26% of total research budget).
References 1. Kruth JP. Material ingress manufacturing by rapid prototyping techniques. Ann CIRP 1991;40:603-614. 2. Gibson I, Rosen DW, Stucker B. Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing. New York, NY: Springer; 2009. 3. American Society for Testing and Materials, ASTM International. Standard terminology for additive manufacturing technologies, 2013; F2792–12a. 4. McDonald JA, Ryall CJ, Wimpenny DI. Rapid Prototyping Casebook. London, England; Professional Engineering; 2001. 5. Labadie RF, Noble JH, Dawant BM, Balachandran R, Majdani O, Fitzpatrick JM. Clinical validation of percutaneous
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Tuomi et al cochlear implant surgery: initial report. Laryngoscope. 2008;118:1031-1039. 6. Bibb R, Eggbeer D, Evans P, Bocca A, Sugar A. Rapid manufacture of custom-fitting surgical guides. Rapid Prototyping J. 2009;15:346-354. 7. Kontio R, Björkstrand R, Salmi M, et al. Designing and additive manufacturing a prototype for a novel instrument for mandible fracture reduction. Surgery. 2012;S1:002. doi:10.4172/2161-1076.S1-002. 8. Poukens J, Laeven P, Beerens M, et al. A classification of cranial implants based on the degree of difficulty in computer design and manufacture. Int J Med Robot Comput Assist Surg. 2008;4:46-50. 9. Salmi M, Tuomi J, Paloheimo K-S, et al. Patient specific reconstruction with 3D modeling and DMLS additive manufacturing. Rapid Prototyping J. 2012;18:209-214. 10. Tuomi J, Paloheimo K-S, Björkstrand R, Salmi M, Paloheimo M, Mäkitie AA. Medical applications of rapid prototyping— from applications to classification. In: Proceedings of VR@ P4, Advanced Research in Virtual and Rapid Prototyping. London, England: CRC Press; 2009:701-704. 11. Mäkitie A, Paloheimo KS, Paloheimo M, et al. Development of rapid prototype models for temporal bone dissection simulation. Paper presented at: The 2nd International Conference on Additive Technologies, DAAAM Specialized Conference; September 17-18, 2008; Ptuj, Slovenia. 12. Ng P, Lee PSV, Goh JCH. Prosthetic sockets fabrication using rapid prototyping technology. Rapid Prototyping J. 2002;8:53-59. 13. Miller JR, Derakhshan M. The Invisalign system: case report of a patient with deep bite, upper incisor flaring, and severe curve of Spee. Semin Orthod. 2002;8:43-50. 14. Salmi M, Tuomi J, Sirkkanen R, Ingman T, Mäkitie A. Rapid tooling method for soft customized removable oral appliances. Open Dent J. 2012;6:85-89. 15. Ciocca L, Mingucci R, Bacci G, Scotti R. CAD-CAM construction of an auricular template for craniofacial implant positioning: a novel approach to diagnosis. Eur J Radiol. 2009;71:253-256. 16. Bibb R, Eggbeer D, Evans P, Bocca A, Adrian S. Rapid manufacture of custom-fitting surgical guides. Rapid Prototyping J. 2009;15:346-354. 17. Salmi M, Paloheimo KS, Tuomi J, Ingman T, Mäkitie A. A digital process for additive manufacturing of
occlusal splints: a clinical pilot study. J R Soc Interface. 2013;10:20130203. 18. Sekou S, Qin L, Wei PW, Jue W, Yaxiong L. Rapid prototyping assisted surgery planning and custom implant design. Rapid Prototyping J. 2009;15:19-23. 19. Janssens M, Poukens J. Rapid technologies in medicine: what can, can’t be done and why. Paper presented at: The International Conference on Competitive Manufacturing; January 31-February 6; Stellenbosch, South Africa; 2007. 20. Eppley BL. Craniofacial reconstruction with computergenerated HTR patient-matched implants: use in primary bony tumor excision. J Craniofac Surg. 2002;13: 650-657. 21. Yan Y, Zhang R, Lin F. Research and application on biomanufacturing. Paper presented at: The First International Conference on Advanced Research in Virtual and Rapid Prototyping; October 1-4, 2003; Leiria, Portugal. 22. Tan JY, Chua CK, Leong KF, et al. Esophageal tissue engineering: an in-depth review on scaffold design. Biotechnol Bioeng. 2012;109:1-15. 23. Badylak SF, Weiss DJ, Caplan A, Macchiarini P. Engineered whole organs and complex tissues. Lancet. 2012;379:943-952. 24. Bibb R, Winder J. A review of the issues surrounding threedimensional computed tomography for medical modeling using rapid prototyping techniques. Radiography. 2010;16:78-83. 25. Bibb R. Medical Modeling: The Application of Advanced Design and Development Techniques in Medicine. Cambridge, England: Woodhead; 2006. 26. Cabibihan J-J. Patient-specific prosthetic fingers by remote collaboration—a case study. PLoS One. 2011;6(5):e19508. doi:10.1371/journal.pone.0019508. 27. Robiony M, Salvo I, Costa F, et al. Virtual reality surgical planning for maxillofacial distraction osteogenesis: the role of reverse engineering, rapid prototyping and cooperative work. J Oral Maxillofac Surg. 2007;65: 1198-1208. 28. Salmi M, Paloheimo KS, Tuomi J, Wolff J, Mäkitie A. Accuracy of medical models made by additive manufacturing (rapid manufacturing). J Craniomaxillofac Surg. 2013;41:603-609. 29. Winder RJ, Bibb R. Medical rapid prototyping technologies: state of the art and current limitations for application in oral and maxillofacial surgery. J Oral and Maxillofac Surg. 2005;63:1006-1015.
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research-article2014
SRIXXX10.1177/1553350614524838Surgical InnovationTuomi et al
Equipping to Innovate
A Novel Classification and Online Platform for Planning and Documentation of Medical Applications of Additive Manufacturing
Surgical Innovation 2014, Vol. 21(6) 553–559 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1553350614524838 sri.sagepub.com
Jukka Tuomi, LicSc (Tech)1, Kaija-Stiina Paloheimo, MSc1, Juho Vehviläinen, MSc (Tech)1, Roy Björkstrand1, Mika Salmi, DSc (Tech)1, Eero Huotilainen, MSc (Tech)1, Risto Kontio, MD, PhD2, Stephen Rouse, DDS3, Ian Gibson, PhD4, and Antti A. Mäkitie, MD, PhD1,2,5
Abstract Additive manufacturing technologies are widely used in industrial settings and now increasingly also in several areas of medicine. Various techniques and numerous types of materials are used for these applications. There is a clear need to unify and harmonize the patterns of their use worldwide. We present a 5-class system to aid planning of these applications and related scientific work as well as communication between various actors involved in this field. An online, matrix-based platform and a database were developed for planning and documentation of various solutions. This platform will help the medical community to structurally develop both research innovations and clinical applications of additive manufacturing. The online platform can be accessed through http://www .medicalam.info. Keywords additive manufacturing (AM), medical applications, surgery, classification, rapid prototyping, innovation, education
Introduction Additive Manufacturing Additive manufacturing (AM) is a relatively new group of manufacturing technologies developed since the late 1980s. Physical parts can be manufactured from numerical definition (3-dimensional computer-aided design [3D-CAD]) automatically, layer-by-layer, in a process that does not have similar constraints with conventional manufacturing processes.1 There have been numerous ways to describe AM, including rapid prototyping, freeform fabrication, tool-less manufacturing, and 3D printing, which all emphasize its capabilities compared with other more conventional manufacturing technologies.2 Additive manufacturing is now the accepted umbrella term for a group of AM technologies.3 Additive manufacturing is well suited for the manufacture of complex, organic-shaped models that cannot easily be described in terms of geometric parameters. Furthermore, parts can be made relatively inexpensively and easily using an individual person’s imaging data, thus making it possible to create customized solutions. There
are a number of different types of AM processes and equipment installations available. Some of the processes result in physical parts out of plastics and powder composites. But processes for high-end metal parts manufacturing are also in use. The most popular manufacturing processes for plastic and composite parts are powder bed fusion, material extrusion, binder jetting, vat photopolymerization, and material jetting. Powder bed fusion is the most popular process for metals.2 1
Aalto University, Department of Engineering Design and Production, School of Engineering, Aalto, Espoo, Finland 2 Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland 3 Dynamics Research Corporation, Arlington, VA, USA 4 National University of Singapore, Singapore 5 Karolinska Institutet, Division of ENT Diseases, CLINTEC, Stockholm, Sweden Corresponding Author: Antti A. Mäkitie, Department of Otolaryngology–Head & Neck Surgery, Helsinki University Central Hospital and University of Helsinki, PO Box 220, FI-00029 HUCH, Helsinki, Finland. Email: [email protected]
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Surgical Innovation 21(6) engineering, design, surgery, and rehabilitation. Thus, the need for collaboration platforms and tools agreed on by all actors involved in the design and production process of medical applications of AM is evident. Well-structured, conceptual tools may have a great positive impact on the community by enhancing collaboration across borders and disciplines.
Materials and Methods Classification for Medical Applications of Additive Manufacturing We have developed an application solution oriented classification system to be used for medical applications of AM. For each category presented, common requirements for AM technologies can be identified.10 Representative examples for each of the 5 classes are presented in Figure 1.
Figure 1. Representative examples of each of the 5 classes of the classification.
Medical Applications of Additive Manufacturing Additive manufacturing is already widely used in clinical practice, and the number of medical applications is increasing rapidly. Extremely complicated physical objects can be manufactured with these technologies in a fully automated process making them highly applicable in medical setting. Medical imaging data sets can be applied as the basis for geometry definition and there are several software tools available for reconstructing 3D models for creating physical models using AM for preoperative planning.4 Three-dimensional models have been also used to define geometry landmarks or 3D shapes for implant planning5 or special instruments.6,7 It is presently a common practice to apply AM preoperative models for surgical planning and training purposes. Such models can also be used for implant planning.8,9 We have recognized that it is quite common to combine several AM models in a single patient case. Also, these applications are often developed further during the design phase. Information and expertise in the field of medical applications of AM are quite scattered globally and thus, international collaboration is common. Furthermore, producing medical applications requires not only international collaboration but also collaboration across disciplines. It is truly a multidisciplinary field that draws resources from various fields, including radiography,
Medical Models for Pre- and Postoperative Planning, Education, and Training. Using primary data from medical images, AM can be used to manufacture models for preoperative planning or surgical simulation.4 Models can also be used for communication with technicians, education of students, and counseling of patients and families regarding complicated surgical procedures. Depending on the application, different qualities of the models such as anatomical accuracy, material characteristics, or haptic response of the model become important. Real haptic response of bone is especially desirable in surgical training models.11 Medical Aids, Orthoses, Splints, and Prostheses. Here, AM technologies are utilized for anatomic personalization of a (standard) device, to enhance healing from trauma, anomaly, or defect. The manufactured piece is either completely external to the body or at least noninvasive. The material should be nonirritant and surface requirements depend on each specific application. These products are typically wearable and external. Creating prosthetic sockets has traditionally been labor intensive, taking 2 to 3 days to make one socket. Using computer-aided manufacturing systems and AM technologies the time is reduced to less than 4 hours.12 Another example is treatment of dental malocclusion by AM of a mold for one or a series of clear and removable appliances.13,14 Also, noninvasive positioning guides, such as an auricular template for craniofacial implant positioning15 belong to this class. Tools, Instruments, and Parts for Medical Devices. Additive manufacturing may be used to create tools and hardware for medical applications, to enable or improve the efficacy of a medical or surgical procedure. In cochlear
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Tuomi et al implant surgery AM drill guides have been used and have reduced operative time and overall costs.5 Manufacture of operation specific instruments, such as custom fitting surgical guides16 or preforms belong to this class. Another example of a surgical tool is a prototype of an instrument for mandible fracture reduction.7 Oral appliances, which are made directly by AM,17 are also a representative application area of this class. Devices in this class are in contact with body fluids, mucous membranes, or tissues for a limited time, thus they are intended for transient or short-time use, are invasive but nonimplantable. The material must be sterilizable, and surface requirements depend on the specific application. These are predominantly invasive surgical products. Inert Implants. Devices in this class are intended for longterm use and are either wholly or partly implanted. AM implants may be used in surgical operations based on medical imaging and 3D modeling. Inert implants can be produced by AM technologies directly9 or indirectly.18 Janssens and Poukens19 have presented a cranial plate for direct implantation that has been digitally designed and manufactured by AM technologies. In the indirect approach, AM parts are used to create the implant through bending, deep drawing, casting, or other replication techniques. Eppley20 reported on a case where 7 patients with large bony lesions of the anterior cranial vault and orbit underwent simultaneous bony excision and reconstruction with preoperatively fabricated custom implants. Biomanufacturing. Freeform culture media can also be manufactured with AM technologies. These applications include biologically compatible parts and parts to be used when manufacturing these components. Such scaffolds can be used as a skeleton for cell cultures, to act as support or protection from external physical forces, and to provide an optimal medium for 3D cell cultures.21 The raw materials for scaffolds may be natural or synthetic, organic or inorganic, and their combinations. The AM structures are designed to be active whether they are resorbable or nonresorbable. The ultimate goal is to replace tissues such as bone, cartilage, liver, and heart, and corresponding research is currently increasing rapidly.22,23
Characteristics of Classes Table 1 shows the characteristics of the aforementioned classes. The relation of manufactured piece to patient determines the logical order of the classes. This approach helps categorize and define requirements for each class because patient contact is a key factor for determining which materials or finishing methods can be used in the manufacturing process.
Process Phases for Medical Applications of Additive Manufacturing Virtually, all medical applications of AM cases fall into 5 sequential phases regardless of the application class. This chapter introduces these 5 process phases and highlights the function and importance of each phase for the success of an end application.
Medical Imaging and 3-Dimensional Digitizing The process begins with a process phase called medical imaging and 3D digitizing. A number of different imaging technologies have been used for creating medical models, including magnetic resonance imaging and ultrasound, but computed tomography is the most common in medical applications of additive manufacturing.24 Medical imaging and 3D digitizing, being the first phase in the process, has a great impact on the quality of the medical application as it provides the raw data that is used in the next process phases. Therefore, radiographers and radiologists should be provided with detailed recommendations that will assist them to successfully implement this phase in the process.25 The recommendations should be given depending on the accuracy requirements of the application.
Three-Dimensional Modeling Three-dimenaional (3D) modeling converts anatomical multislice (a series of 2D images, such as DICOM) data to 3D STL (stereolithography or standard tessellation language) mesh format while making necessary adjustments like removing unnecessary tissue or imaging artifacts. Computer-aided design (CAD) of implants and tools can be done at this phase. Relevant information about this process step includes parameters such as the radiodensity threshold in Hounsfield scale, the reconstruction software for STL conversion, or the CAD/CAM software in design and STL manipulation.26
Additive Manufacturing Reconstructed data is taken to the additive manufacturing process for production of accurate, patient-specific, physical models. Many medical models, such as inert implants, have strict material requirements, which need to be taken into consideration for AM. In an application-oriented approach, the material, design, and production requirements for the manufactured piece must be compatible before the AM phase. More important, medical applications may have strict material or dimensional requirements, which the AM machines have to be able to meet.
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No patient contact
Relation of Piece to Patient Requirements
Based on patient geometryAnatomical accuracy but magnification or requirements depend miniaturization possible on case, sometimes sterilized
Primary Description
Transportability, storability, behavior in process, haptic response requirements depend on case
Other
External to body— May be combined to Nonallergic if in contact Includes external prostheses and noninvasive, wearable standard devices to with skin, mechanical and prosthetic sockets, personalized provide patient-specific surface requirements splints, drill-guiding microtables, fit; long-term and depend on case orthopedic braces and postoperative supports, appliances, orthodontic and oral (motion) guides, and appliances fixators Tools, instruments, and Enable or improve the efficacy of a Contact with body fluids, Patient-specific dimensions Sterilizable; no immediate Includes drill guides, specialty parts for medical devices medical or surgical procedure mucous membranes, and shapes may be toxicity or allergic surgical instruments tissues, or organs for incorporated reactions, no shedding a limited time: invasive of particles; mechanical but not implantable and surface requirements depend on case Inert implants Tissue replacement Wholly or partly Biocompatible; will not May attract cell adhesion Strict material requirements, long implanted, long-term change its characteristics on surface but mainly approval processes; includes contact with body (much) in vivo stays inactive; durability, dental applications: crowns and fluids, tissues, or organs mechanical properties, bridges surface properties depend on case Biomanufacturing Biologically active tissue Incorporated into body Shape personalized to Porous structures; Polymers, ceramics, and replacement; “organ match tissue defect, scaffolds must be cell composites; freeform culture manufacturing” porous structures, growth conductive, media in vitro; additive optimal morphology inductive, resorbable, manufacturing + tissue depends on cell type and controlled engineering application site
Plan or simulate surgical procedures pre-, intra-, or postoperatively; educate students, patients, and families, and train surgeons Enhance healing from trauma, anomaly, or defect
Medical models
Medical aids, supportive guides, splints, and prostheses
Purpose
Class
Table 1. Characteristics of Medical Applications of Additive Manufacturing Classes.
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Figure 2. Process and classification matrix.
Although AM equipment operates automatically some degree of specialist expertise is necessary to ensure efficient and accurate results. The accuracy of models varies between different materials, AM technologies and machine runs.27 Expertise is necessary for example to set the AM process parameters and for post processing of AM parts.28,29
Finishing Following AM, some manufactured pieces require a finishing phase. Finishing covers different surface treatments such as washing, coating, polishing, or sterilization. Inert implants and objects invading the body need to be sterilized prior to their clinical use.
Clinical Application Clinical application is the ultimate goal of the process and it describes the purpose of the manufactured piece. Applications may range from structural models for enhanced surgeon–surgeon or surgeon–patient communication to surgical tools, implants, and even laboratory-grown tissues. A case may include several of these processes during the full medical procedure and a framework describing the overall process from start to finish needs to have the flexibility to depict all process flows and process phases accurately and in detail.
Medical Applications of Additive Manufacturing Matrix Using this novel matrix framework for medical applications of AM with relevant content in each cell, a clinical case application may be planned and documented.
Logical sequences of data processing and manufacturing phases are presented in columns and classification-oriented AM applications are listed in rows. Figure 2 presents an example of a patient case documentation using the matrix. This case shows the role of AM in surgical reconstruction of the orbit. A patient-specific customized 3D model of an implant was designed for a 67-year-old male patient after a complicated facial trauma. A volumetric net was first formed and several test pieces produced by AM from stainless steel and titanium.9 A titanium reconstruction plate was finally obtained in a similar manner and implanted onto the injured orbital wall. To ensure the accuracy and the precise fit of the implant, it was tested on the preoperative model before being surgically placed on the patient’s orbital floor. Figure 2 presents a case study where 2 process flows were needed. First, a preoperative model was produced and it was used to help the design and production of the orbital implant. This was a straight-forward process that was depicted with ease on the framework. However, many medical cases are more complex and require more process flows before the end application. Previously, it was mentioned that it is common to combine several preoperative models in a single patient case. This can also be depicted using the proposed framework model because of its scalability. The proposed framework, and the online platform, allows users to input an arbitrary number of parallel and sequential subprocesses, making it possible to depict very complex medical cases from start to finish without omitting important case-specific information. The practical purpose of the matrix framework to a clinician is that it provides tools to determine quality specifications for the preceding process steps before these steps are implemented. In the example case, a patient specific preoperative model of the orbital floor and a titanium implant were designed and manufactured. To ensure the accuracy and the precise fit of the implant, it was tested on the preoperative model before being surgically placed on the patient’s orbital floor.
Online Platform and a Database To enhance the usability of the matrix framework, an online platform and a database for medical applications of AM cases was created. The online platform provides tools to examine previous medical case studies and upload new case studies to the database. The validity and usability of the platform was tested with 8 different case studies and more patient case studies are continuously uploaded to the database. The platform and the database were created using open source content management system and the case content is open for anyone. Some limitations to case information may apply when appropriate to maintain patient’s anonymity. The platform and the database will be developed further at Aalto University, Espoo, Finland.
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Surgical Innovation 21(6)
Furthermore, the medical case content will remain open for users also in the future. The online platform can be accessed through http://www.medicalam.info.
Discussion We propose our novel matrix platform be used in the planning and documentation of medical applications using AM. This system is based on an application-oriented classification. The present representative case studies9,26 and the available literature10,27 suggest that there is a need for location independent, enhanced interdisciplinary collaboration on this matter. Expertise on medical applications of AM is quite scattered globally and a platform based on a uniform structural concept could help the current research and development work in this field. One of the strengths of our proposed model is its eminent scalability: Virtually any AM case—from simple to extremely complex—can be described since the platform allows an arbitrary number of parallel and sequential subprocesses, each with their own parameters and information. In addition, the platform offers a quick overview of the big picture, regardless of the amount of subprocesses. This will help professionals to mentally tie the parallel processes together and set their minds to the ultimate target, that is, the actual application and its benefits to the patient—be it in the planning phase for a completely new case, or assessing documented previous cases. Most medical applications of additive manufacturing require extensive collaboration across disciplines—notably, but not limited to, various fields of expertise including radiography, engineering, design, surgery, and rehabilitation. Since the experts involved come from different academic backgrounds or working cultures, conceptual tools such as the presented platform are essential to enable a clear and coherent discourse of medical applications of AM cases and the field in general. This should help all the actors involved to develop a better understanding of this truly complex, interdisciplinary process and help to realize the potential that additive manufacturing has to offer to medical practice. Finally, this will lead to improved patient care.
Conclusion Additive manufacturing permits us to create complex physical objects within hours in a fully automated process. Therefore, AM is widely used clinically and the number of new applications is rising rapidly. The process of including AM into medical applications consists of process phases as follows; medical imaging and 3D digitizing, 3D modeling, AM, part finishing, and finally, the actual clinical application. In the proposed matrix platform for medical applications of AM, the logical sequence
of data processing and manufacturing phases are presented in columns whereas the classification-oriented AM applications are listed in rows. This will make it a comprehensive framework for depicting medical applications of AM cases. Medical applications of AM require extensive collaboration across various disciplines. We have proposed a scalable, application-oriented solution to help all the involved actors to develop a better understanding of this complex process. Matrix-based platform for the medical applications of AM should help the medical community to structurally plan and document various solutions. Authors’ Note Kaija-Stiina Paloheimo and Juho Vehviläinen contributed equally. Part of this article was presented at the Fourth International Conference on VRAP, Leiria, Portugal, October 6-10, 2009.
Acknowledgments The Finnish Funding Agency for Technology and Innovation (TEKES), Helsinki University Central Hospital Research Funds, DeskArtes Oy, EOS Finland Oy, Vektor Claims Administration, and Planmeca Oy are thanked for financial support. Mr Pekka Paavola, MSc(Tech), is thanked for photographical work.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Finnish Funding Agency for Innovation (research grant numbers 2926/31/2009 and 660/31/2010; 70% of total research budget) and Aalto University (research funding; 26% of total research budget).
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