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Cranial reconstruction: 3D biomodel and custom-built implant created using additive manufacturing
Accepted Manuscript Cranial reconstruction: 3D biomodel and custom-built implant created using additive manufacturing André Luiz Jardini, Maria Aparecida Larosa, Rubens Maciel Filho, Cecília Amélia de Carvalho Zavaglia, Luis Fernando Bernardes, Carlos Salles Lambert, Davi Reis Calderoni, Paulo Kharmandayan PII:
S1010-5182(14)00230-3
DOI:
10.1016/j.jcms.2014.07.006
Reference:
YJCMS 1850
To appear in:
Journal of Cranio-Maxillo-Facial Surgery
Received Date: 10 February 2014 Revised Date:
27 June 2014
Accepted Date: 29 July 2014
Please cite this article as: Jardini AL, Larosa MA, Maciel Filho R, Zavaglia CAdC, Bernardes LF, Lambert CS, Calderoni DR, Kharmandayan P, Cranial reconstruction: 3D biomodel and custom-built implant created using additive manufacturing, Journal of Cranio-Maxillo-Facial Surgery (2014), doi: 10.1016/j.jcms.2014.07.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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CRANIAL RECONSTRUCTION: 3D BIOMODEL AND CUSTOM-BUILT IMPLANT CREATED USING ADDITIVE MANUFACTURING
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André Luiz Jardinia,b, Maria Aparecida Larosaa,b*, Rubens Maciel Filhoa,b, Cecília Amélia de Carvalho Zavagliaa,c, Luis Fernando Bernardesa,b, Carlos Salles Lamberta,d, Davi Reis Calderonia,e, Paulo
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Kharmandayana,e
a
National Institute of Biofabrication (INCT-BIOFABRIS), Campinas, Brazil
b
School of Chemical Engineering, State University of Campinas, Campinas, Brazil
c
d
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School of Mechanical Engineering, State University of Campinas, Campinas, Brazil Institute of Physics, State University of Campinas, Campinas, Brazil
e
* Corresponding author:
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Maria Aparecida Larosa
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School of Medical Sciences, State University of Campinas, Campinas, Brazil
National Institute of Biofabrication, School of Chemical Engineering, State University of Campinas,
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Campinas, Brazil
Tel.: 55 19 3521-3900; Fax: 55 19 3521-3910. E-mail address: [email protected]
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Cranial reconstruction: 3D biomodel and custom-built implant created using additive manufacturing Summary. Additive manufacturing (AM) technology from engineering has helped to achieve several
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advances in the medical field, particularly as far as fabrication of implants is concerned. The use of AM has made it possible to carry out surgical planning and simulation using a three-dimensional physical model which accurately represents the patient's anatomy. AM technology enables the production of models and implants directly from a 3D virtual model, facilitating surgical procedures and reducing risks.
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Furthermore, AM has been used to produce implants designed for individual patients in areas of medicine such as craniomaxillofacial surgery, with optimal size, shape and mechanical properties. This work
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presents AM technologies which were applied to design and fabricate a biomodel and customized implant for the surgical reconstruction of a large cranial defect. A series of computed tomography data was obtained and software was used to extract the cranial geometry. The protocol presented was used to create an anatomic biomodel of the bone defect for surgical planning and, finally, the design and manufacture of the patient-specific implant.
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Keywords. Additive manufacturing, DMLS, Cranial reconstruction, Titanium alloy, Customized implants INTRODUCTION
The malfunction or loss of total or partial function of an organ or tissue, resulting from trauma or disease, is currently one of the most important and troubling public health problems and affects a
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significant number of people around the world. To meet the great demand for orthopedic surgical procedures to repair or replace body parts, it is necessary to develop biomaterials and more advanced
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surgical techniques.
The combination of high mechanical resistance, high toughness, manufacturing ease, good resistance to degradation by corrosion and low cost makes some metallic materials the preferred biomaterials in the manufacture of orthopedic implants subjected to severe mechanical stresses within the human body. Nowadays, pure titanium and its alloys are some of the most frequently used metallic biomaterials in temporary or permanent orthopedic applications. Temporary implants perform their function of fixing fractures over a predetermined period, until the member is completely recovered so that the implant can be removed. The fixing plates, screws, wires, and intramedullary pins to repair broken bones are
ACCEPTED MANUSCRIPT examples of temporary implants. Permanent implants replace body parts and need to play their role for the rest of the patient's life, as in hip, knee, shoulder, elbow or wrist prosthetics. These implants, as well as other structural components, may fail due to mechanical fracture, wear or corrosion. The combination of the electrochemical process of corrosion and cyclical mechanical stress
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can speed up the release of particles and metal ions, leading to premature failure of the implant (Giordani et al., 2003; Pereira et al., 2006). As an example, articulated implants that are exposed to high loads and severe wear due to the patient’s movement can be mentioned. Moreover, the degradation of metallic implants inside the human body may not only impair the integrity of the material, but also generate
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biocompatibility problems such as infection or allergic reactions, leading to premature removal of the implant (Rondelli et al., 1997; Terada, 2007). The derived detritus is harmful to the tissues that are in
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contact with the implant and can be taken into the bloodstream, settling in organs and impairing their function. Thus, metallic biomaterials must have properties such as resistance to fatigue and wear, fracture toughness and high corrosion resistance (Geetha et al., 2009).
Titanium is particularly suitable for work in corrosive environments or for applications in which low density is essential. It has a high strength/weight ratio, non-magnetic properties and high corrosion
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resistance due to the formation of a compact protective film of titanium oxide (TiO2) on the metal surface. Due to its highly reactive nature in the presence of oxygen, the casting must be conducted in vacuum furnaces (Park and Kim, 2003; Pereira et al., 2006).
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Two types of crystalline formation can occur in titanium. The first one is called alpha and has a hexagonal close-packed (hcp) crystalline structure, while the second is termed beta with a body-centered cubic (bcc) crystalline structure. In pure titanium the alpha phase is stable at room temperature. Alloying
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elements are added to pure titanium and tend to modify the temperature at which the phase transformation occurs and the amount of each phase present. The alloying additions to titanium tend to stabilize the alpha or the beta phase. The alpha phase is stabilized at higher temperatures, by elements called alpha stabilizers, such as aluminum, tin and zirconium; while the beta phase is stabilized by beta stabilizers at lower temperatures, such as vanadium, molybdenum, niobium, chromium, iron and manganese. There are three structural types of titanium alloys: alpha alloys (α), alpha-beta alloys (α + β) and beta alloys (β) (Brown and Lemons, 1996; Brunette et al., 2001; Niinomi, 2002; Abramson et al., 2004; Silva and Mei, 2006).
ACCEPTED MANUSCRIPT Among the titanium alloys, the most employed in the manufacture of surgical implants is Ti6Al4V. The standard that describes the requirements for this alloy is ASTM F136 (2011). The structure of this alloy is α + β type, in which the α-phase stabilizing element is aluminum and the one in the β-phase is vanadium (Black, 1988). In the same way as other materials, this titanium alloy that can be wrought,
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quenched or annealed and can be machined by conventional means (Walker, 1977). Products marketed for medical use must be strictly tested for chemical composition and mechanical and structural features to ensure that they are in accordance with the standards established by the specific rules for implants. The manufacture of metallic implants can include a series of procedures that depend on
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factors such as shape and size of the final product, metal features, and manufacturing cost. The methods employed are casting, machining, forging and powder metallurgy. Good alternatives to conventional
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machining techniques are provided by additive manufacturing technologies such as direct metal laser sintering (DMLS) (Balazic et al., 2007). Usually, after the melting and mechanical forming of the material, an annealing thermal treatment is performed in order to relieve residual stresses, to make the material more ductile and tough, and to produce a specific microstructure without changing the material properties (Callister, 2002).
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Following the manufacturing step, the implant may be subjected to surface modification procedures and finishing techniques such as ionic implantation, nitriding, porous or microporous coating application, polishing, chemical cleaning and passivation. The surface features of the implants are essential in their
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biological performance. Additive manufacturing
Additive manufacturing (AM) or rapid prototyping (RP) is a fabrication technique using the additive
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method, based on the successive addition of fine layers of material. This technology allows the production of physical components (such as prototypes, models, molds) from information obtained directly from a three-dimensional geometric model CAD (computer aided design) system. The process starts with a 3D computer model of the part, which is electronically sliced. These slices are used to provide 2D contour lines which will define, in each layer, exactly where material is going to be added. These layers are sequentially processed, generating the physical part through stacking and adhesion of them, beginning at the bottom and working up to the top part (Gibson et al., 2006; Carvalho and Volpato, 2007).
ACCEPTED MANUSCRIPT The construction of parts with complex geometry in a variety of materials; the use of only one piece of equipment to build the part from beginning to end; and less time and cost to obtain prototypes are some advantages that rapid prototyping offers when compared with other manufacturing processes (Hieu et al., 2003; Foggiato, 2006; Volpato, 2007).
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In the medical field, additive manufacturing has been integrated with the digital imaging techniques of computed tomography (CT) and magnetic resonance (MR), making it possible to obtain solid biomodels that reproduce anatomical structures. The internal structural images acquired by these techniques are handled by a medical imaging system. From these images, specific algorithms of segmentation are
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applied to separate out the structure of interest (bone or tissue). From the image data, a 3D model is generated on specific computer software (InVesalius or Mimics) and exported for the creation of
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biomodels (biomedical prototypes) by additive manufacturing (Truscott et al., 2007; Antas et al., 2008). These biomodels can be used for surgical planning, didactic purposes, the diagnosis and treatment of patients, and communication between professionals and patients. As a result, biomodels facilitate surgery, and reduce infection and rejection risks, complications and length of surgery (Hench, 1991; Gopakumar, 2004; Oliveira et al., 2007; Wu et al., 2009; Bertol, 2010).
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Nowadays, additive manufacturing also allows for the design of customized prosthetic implants, suited to an individual patient’s needs, including the size, shape and mechanical properties of the implant. To achieve this, only digital information is used. Physical models are no longer required; the computer
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generated pattern allows direct production of the final implant, reducing the manufacturing time. The use of these integrated techniques offers a significant potential of cost savings for health systems as well as the possibility of providing an improved quality of life for a huge number of people (Ferreira et
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al., 2007; Singare et al., 2009). Additive manufacturing can be used by health professionals in many specialties including orthopedics, neurosurgery, maxillofacial and orthognathic surgery and traumatology, craniofacial and plastic surgery, implant dentistry, and oncology (Ciocca et al., 2011; Salmi et al., 2012; Huotilainen et al., 2013a; Philippe, 2013; Stübinger et al., 2013). The proposed solution is a way to make the use of AM technology in planning surgical procedures viable, through the development and improvement of services, materials and equipment related to 3D printing technology. Surgical planning with the aid of rapid prototyping allows medical staff to have a physical model to evaluate and even simulate the surgical procedure before its performance. As a result,
ACCEPTED MANUSCRIPT surgical procedures can be optimized and executed in a shorter time, with less time spent in the operating room, thus enabling significant cost savings to hospitals and fewer risks to the patient. Therefore, this solution can provide more security and reliability to the process as a whole. One medical application to be considered is bone reconstruction surgery, for instance, craniofacial
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reconstruction (Hieu et al., 2003; Gopakumar, 2004). Craniofacial anomalies are a highly diverse and complex group of congenital defects that affect a significant proportion of people in the world. In addition to congenital deformities, craniofacial defects can be acquired due to other diseases, such as tumors. In the last four decades, increasing numbers of cases of facial trauma have been observed, which is closely
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related with the increase of traffic accidents and urban violence. Additive manufacturing can also be used in prosthetic implants because the models provide information about size, direction and location of the
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implants, as well as anatomical information. In cases of bone abnormalities, it is important to note that the gain to the patient in functional and psychological terms and the increased quality of life after surgery justify the costs of the application of new technologies (Foggiato, 2006).
There are more than 20 types of additive manufacturing systems on the market which, in spite of using different technologies to add the material, are based on the same principle of manufacturing by
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layer. The main additive manufacturing technologies used are stereolithography (SLA), selective laser sintering (SLS), direct metal laser sintering (DMLS), selective laser melting (SLM), fused deposition modeling (FDM), 3D printing (3DP) and electron beam melting (EBM). These systems are classified
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according to the initial state of raw material, which can be liquid, solid or powder form (Milovanović and Trajanović, 2007; Khan and Dalgarno, 2009). The additive manufacturing technique used in this work is 3D printing (3DP) to create an anatomic
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biomodel of the bone defect for surgical planning and DMLS to design and manufacture the patientspecific implant. Among the advantages of the DMLS technique, is the ability to process titanium (TiCp and Ti64) and other metallic biomaterial (CoCr) directly on the machine. MATERIALS AND METHODS
The procedure for making 3D medical models (biomodels) using additive manufacturing technologies involves a few steps: patient selection; 3D digital image, data transfer, processing and segmentation; evaluation of design and medical model production and validation.
ACCEPTED MANUSCRIPT Patient selection A 22-year-old male patient was injured in a bike accident with a large post trauma defect in the rightfrontal bone (Fig. 1). The cranial section missing extended to an area of approximately 12.5 × 8.4 cm2. The large bone defect was the result of a decompressive craniotomy. Following the initial management of
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the patient and the healing process, reconstruction of the cranial defect was required to restore the structural integrity of the skull and the patient’s facial aesthetics. CT digital image
3D digital image can be obtained by using computer tomography – CT scanner or MRI data. These
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imaging technologies are used for modeling internal structures of the human body. Medical models made from this data must be very accurate and because of this they require a spiral scanning technique which
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allows full volume scanning. This makes it possible to generate a high number of slices (recommended thickness 1–2 mm) and it is very important that the pixel dimension in each slice can be reduced depending on the case. Most CT and MRI units have the ability to export data in the common medical file format – DICOM (digital imaging and communication in medicine). After saving the CT or MRI image data, they should be transferred to the AM system. The next step is processing the data, which is a very
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complex and important step that the quality of the final medical model depends on. For this step the engineers need a software package (InVesalius) in which they can perform segmentation of the anatomy image, achieve a high resolution 3D rendering in different colors, make a
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3D virtual model and finally convert the CT or MRI scanned image data from DICOM to an STL (structure triangularization language) file format. These software packages perform the segmentation
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whilst using a threshold technique which looks at tissue density. In this way, at the end of image segmentation, there are only pixels with a value equal to, or higher than the threshold value (Huotilainen et al., 2013b; de Beer and van der Merwe, 2013; Salmi et al., 2013). Segmentation and CAD design Specific biomedical software is required to manipulate the images. Software used in biomedical prototyping includes Analyze® (Mayo Foundation, USA), Mimics® (Materialise, Belgium), and Biobuild® (Anatomics, Australia). Such software has some basic functions for processing and converting image files. They are necessary as the image files generated by the apparatus and CT represent 2D cuts and are saved in the DICOM format. Nonetheless, for the manufacturing of a biomodel the station needs 3D files,
ACCEPTED MANUSCRIPT preferably in the STL format which is the standard format for manufacturing. Currently, there is free Brazilian software, InVesalius from the ProMED project developed at CTI (Center for Information Technology Renato Archer), which meets the basic functions to integrate biomedical imaging equipment and AM, associated with imaging manipulation and 3D visualization. Fig. 2 shows the CT-image results
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of a patient’s skull segmentation using the system for medical imaging InVesalius. After the segmentation, the 3D model should be converted into a format for additive manufacturing (Fig. 3). The conversion of the 3D files to STL format, performed by biomedical software, generates a mesh of triangles, so that it can adequately represent the complex topography of the craniomaxillofacial
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region. This can cause problems of file size, which derails the process of manufacturing due to the volume of processing required for slicing the model. For this reason, the STL file needs to be worked on
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specific software for AM such as Magics (Materialise, Belgium).
The models coming from InVesalius are surface models that are build up out of facets (triangles). They are transferred through an STL-file. Conventional CAD-systems usually can import these files but in order to do operations on these data, it is necessary to convert the facet model into CAD-surfaces through the usually lengthy and difficult process of reverse engineering. For making surgical tools,
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incorporating other objects (fixation devices, implants), bone replacements, producing patterns for making fixtures or templates or other complex problems in different medical fields, this virtual model in IGES or STL format is processed using a CAD package. This is necessary for evaluation of design,
individual case.
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quality of the made model, and checking possible errors or other important steps which depend on the
3D Printer (3DP) and DMLS systems
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The AM system used in the case presented here includes two steps: (1) the creation of the medical biomodel using 3D printer system; and (2) the DMLS system for the design and manufacture of the customized implant required. The process of three-dimensional printing (3DP), which was developed by the Massachusetts Institute of Technology (MIT), after being licensed by some companies, has considerably increased its market of AM equipment. The operating principle of the Z Corporation 3DP process is described as the technique which refers to an entire class of devices which use inkjet technology. The biomodels are built on a platform located in a container filled with powdered gypsum or starch. An inkjet printhead selectively
ACCEPTED MANUSCRIPT prints a binder liquid that binds the powder in the desired areas. The loose powder remains on the platform to support the prototype that is being formed. The platform is slightly lowered, a new layer of powder is added, and the process is repeated. The prosthetic implant was fabricated by the DMLS technique using the EOSINT M270 system. In
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the DMLS technique, the powder is spread and processed by the action of an infrared laser in an inert and thermally controlled environment inside the chamber. A scanning mirror system controls the laser beam describing the geometry of the layer on the surface of the spread material. With the incidence of the laser beam, the particles of material are heated and reach melting point, joining to each other and also to the
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previous layer. When the material solidifies, a new powder layer is added and the laser scans the desired areas once more; in other words, after the sintering of a layer, a new layer is deposited, and this process
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goes on until the construction of the part is finished. Thus, the implant is built layer by layer. The biomaterial powder of the Ti6Al4V alloy was used for the implant (Joshi, 2006; Lütjering and Wiliams, 2007; Vandenbroucke and Kruth, 2007; Facchini et al., 2010; Ramosoeu et al., 2010). RESULTS Creation of a 3D virtual model of the patient’s skull
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The patient was submitted to a CT examination of the affected bone structure. An acquisition protocol was used: 1 mm for increment between slices and 1 mm of thickness, zero degrees of gantry inclination of the orientation.
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Data obtained in the exams (DICOM format) were converted into a 3D virtual model using InVesalius software (CTI-ProMED, Brazil). The software made it possible to isolate the bone structure through segmentation for the threshold to export them in an STL file. The STL file was edited using Magics 15.0
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software (Materialise, Belgium) in order to minimize surface imperfections. This treatment enables a softening of the model in the upper skull region that contained more widely space slices. CAD system modeling to design the implant For prosthesis generation, a subtraction Boolean was accomplished with a 3D virtual model generated from the exam. This aims to create a prosthesis which is a good fit, allowing for better anchorage between prosthesis and bone. In order to create a perfect model for the implant, points from the symmetric right solid part of the head bone were used. Three key points in the nose were selected for the datum plane definition. These points were mirrored according to the created datum plane. Boolean operations were
ACCEPTED MANUSCRIPT then applied to isolate the set of points required to reconstruct the cranial defect surface and produce the implant model. The new generated point cloud that defines the implant 3D geometry was processed to develop a CAD surface model. The commercial software SolidWorks was used for development of the implant CAD model (Fig. 4).
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Creation of a biomodel and customized implant The biomodel was constructed by 3D virtual model from computed tomography using 3D Zprinter 510 systems (Z Corporation, UK), and materials ZP 130 (powder gypsum), ZB 58 (binder) and Z Bond (resin). The biomodel was created in according to the specifications of an anatomical drawing, in order to
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serve as a test before the surgery. In other words, we can say that the biomodel is a virtual or real experiment that tries to mimic a real system. They can be used for teaching aims, in the manufacturing of
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customized prosthetic implants, in the early diagnosis and treatment of facial deformities, and for facilitating communication between professionals and patients. Biomodels allow the measurement of structures, the simulation of osteotomies and of resection techniques, not to mention a complete planning of several types of craniomaxillofacial surgery. This tends to reduce the surgical procedure time and, as a result, the anesthesia period, as well as the risk of infection. There is also improvement in the result and
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reduction in the overall cost of the treatment.
The biocompatible implant fabricated using the DMLS system based cranial reconstruction approach was an exact fit to the patient’s cranial defect and produced a symmetric skull outline. The material used
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was EOS Titanium Ti64 ELI (EOS GmbH, Germany), because it fulfills the mechanical and chemical requirements of ASTM F 136 standard for surgical implant applications. This material has been used for implant and is inert. Ti64 ELI is its pre-alloyed Ti6Al4V and ELI (extra-low interstitial) version, which
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has a particularly low level of impurities. The implant surface was finished by polishing and sterilization. The preoperative model and titanium implant are shown in Fig. 5. Clinical application
During the surgical procedure using a conventional cranioplasty approach the patient’s custom made cranial reconstruction implant was placed onto the right-frontal bone and fixed to the bone with two screws. The surgery took about 2 hours. When the reconstruction plate is formulated manually during an operation this kind of surgery takes approximately 3 hours. The immediate outcome was successful and
ACCEPTED MANUSCRIPT the implant fitted precisely onto the large cranial defect (Fig. 6). Fig. 7 shows the patient 8 months after surgery. DISCUSSION Conventional cranioplasty is based on the open, cold cure molding technique and reconstruction of the
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implant on a freehand basis. Taking impressions of the defect directly through the patient’s scalp is a major problem. Intraoperative moulding extends the duration of the operation and has been associated with complications due to localized tissue damage from the exothermic reaction during the material curing process. Furthermore, the limited intraoperative overview of larger osseous areas impedes
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judgment of symmetry. Conventional cranioplasty techniques are primarily based on the manual skills and experience of the surgeon. Only an accurately fabricated prosthesis fits into the defect properly and
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reduces the probability of subsequent movement, dislodgement and extrusion (Muller et al., 2003; Maravelakis et al., 2008).
Additive manufacturing is a relatively new technology capable of being physically reproduced in various types of materials, a virtual model, represented as data in a computer. The goal is to obtain a physical model with the same geometric characteristics as the virtual one, so that it can be manipulated
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for various purposes. One application that has emerged as highly promising is the reproduction of anatomical structures, through image acquisition by medical imaging equipment, obtaining thereby a socalled biomodel to aid surgery.
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The virtual model of internal structures of the human body, which is needed for final production of a 3D physical model, requires very good segmentation with a high resolution and pixels of a small size. Good knowledge of the field will help engineers to exclude all structures which are not the subject of
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interest in the scanned image and correctly select the region of interest (separate bone from tissue; include just part of a bone; exclude anomalous structures, noise or other problems which can be faced). Depending on the complexity of the problem, this step usually demands collaboration between engineers and radiologists and surgeons who will help to achieve good segmentation, resolution and finally an accurate 3D virtual model. In image acquisition for biotemplating, the traditional tomographic technique is hardly changed, since the current standards for the craniomaxillofacial region already advocate thin slices. It was noted,
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Avoid inclination of the gantry, because some biomedical prototyping software does not correct
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Metallic artifacts from manufacturing – related to the tomographic technique – this is worrisome
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it;
as phantom images will be reproduced in the biomodel if they are not manually edited in a long and tedious process. In this work, when editing is done by the radiologist in the radiology clinic with software without an interface for Rapid Prototyping file format, these images cannot be sent completely edited for
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the prototyping service. This problem is due to the fact that the editing is only applied to the 3D reconstruction displayed on screen, however, the sent images are of the 2D unedited slices; Positioning the patient with the occlusal plane parallel to the cut plane minimizes the production
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•
area of artifacts, keeping them almost restricted to the tooth region. If this positioning is not considered in patients with metal dental restoration, this can result in artifacts in various cuts, increasing the number of slices to be manually edited and therefore the time needed for segmentation of images; and •
Another important factor to be considered is the radiation dose related to CT scans. In the facial
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region, this is much discussed, because the protocols for obtaining images typically involve a large number of cuts. Thus, compared with other regions, the radiation dose for face exams is considered high. However, it is important to observe that in radiobiology what matters is not total radiation dose of the
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exam, but its effective dose. In a maxillofacial region exam, this dose does not exceed biosecurity limits. CONCLUSION
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Additive manufacturing (AM) medical models have found application for planning treatment for complex surgery procedures, training, surgical simulation, diagnosis, design and manufacturing of implants as well as medical tools. DMLS additive manufacturing techniques have been applied in the production of custom-built implants that meet the physical characteristics of each patient. The development of complex medical models and implants – virtual and physical – of a patient’s anatomical structure, from the digital image data acquired through hospital scanners, have proven to be a powerful tool for biomedical analysis and to have the capability to design and manufacture customized implants and prostheses prior to surgical procedures. This reduces duration of surgery due to preoperative planning
ACCEPTED MANUSCRIPT using correct geometrical and anatomical details. The virtual and manufacturing process also improves surgical accuracy. CONFLICT OF INTEREST None.
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ACKNOWLEDGEMENTS The authors wish to acknowledge the financial support provided by the Scientific Research Foundation for the State of São Paulo (FAPESP - Process 2008/57860-3 and 2010/05321-1) and National Council for Scientific and Technological Development (CNPq – Process 573661/2008-1).
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prototyping of cranioplasty implants. Rapid Prototyp J 9: 175 186, 2003. Huotilainen E, Paloheimo M, Salmi M, Paloheimo KS, Björkstrand R, Tuomi J. et al.: Imaging requirements for medical applications of additive manufacturing. Acta Radiol 55: 78 85, 2013a. Huotilainen E, Jaanimets R, Valášek J, Marcián P, Salmi M, Tuomi J, et al.: Inaccuracies in additive manufactured medical skull models caused by the DICOM to STL conversion process. J Craniomaxillofac Surg, http://dx.doi.org/10.1016/j.jcms.2013.10.001, 2013b. Joshi VA: Titanium alloys: an atlas of structures and fracture features. New York: CRC Press, 2006.
ACCEPTED MANUSCRIPT Khan SF, Dalgarno KW: Design of customized medical implants by layered manufacturing. School of Mechanical and Systems Engineering, NC University, UK, 2009. Lütjering G, Williams JC: Titanium. Berlin: Springer-Verlag, 2007. Maravelakis E, David K, Antoniadis A, Manjos A, Bilalis N, Papaharilaou Y: Reverse engineering
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techniques for cranioplasty: a case study. J Med Eng Technol 32: 115 121, 2008. Milovanović J, Trajanović M: Medical applications of rapid prototyping. Mech Eng 5: 79 85, 2007.
Muller A, Krishnan K, Uhl E, Mast G: The application of rapid prototyping techniques in cranial reconstruction and preoperative planning in neurosurgery. J Craniofac Surg 14: 899 914, 2003.
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Niinomi M: Recent metallic materials for biomedical applications. Metallurgical and Mater Transactions A 33A: 477 486, 2002.
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Oliveira RS, Brigato R, Madureira JF, Cruz AA, Mello Filho FV, Alonso N, et al.: Reconstruction of a large complex skull defect in a child: a case report and literature review. Childs Nerv Syst 23: 1097 1102, 2007.
Park JB, Kim YK: Metallic Biomaterials. In: Park JB, Bronzino JD (eds.) Biomaterials: Principles and applications. New York: CRC Press, 1 20, 2003.
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Pereira MM, Buono VTL, Zavaglia CAC: Materiais metálicos – ciência e aplicação como biomateriais. In: Oréfice RL, Pereira MM, Mansur HS (eds.) Biomateriais: fundamentos e aplicações. Rio de Janeiro: Guanabara Koogan, 39 58, 2006.
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Philippe, B: Custom-made prefabricated titanium miniplates in Le Fort I osteotomies: principles, procedure and clinical insights. Int J Oral Maxillofac Surg 42: 1001 1006, 2013. Ramosoeu ME, Chikwanda HK, Bolokang AS, Booysen G Ngonda TN: Additive manufacturing:
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Characterization of Ti-6Al-4V alloy intended for biomedical application. Light Metals Conference, South Africa, 2010.
Rondelli G, Vicentini B, Cigada A: Localised corrosion tests on austenitic stainless steel for biomedical applications. Br Corrosion J 32: 193 196, 1997. Salmi M, Tuomi J, Paloheimo KS, Björkstrand R, Paloheimo M, Salo F, et al.: Patient-specific reconstruction with 3D modeling and DMLS additive manufacturing. Rapid Prototyp J 18: 209 214, 2012.
ACCEPTED MANUSCRIPT Salmi M, Paloheimo KS, Tuomi J, Wolff J, Mäkitie A: Accuracy of medical models made by additive manufacturing (rapid manufacturing). J Craniomaxillofac Surg 41: 603 609, 2013. Silva ALVC, Mei PR: Aços e ligas especiais. São Paulo: Edgard Blücher, 2006. Singare S, Lian Q, Wang WP, Wang F, Liu Y, Li D, Bingheng L: Rapid prototyping assisted surgery
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planning and custom implant design. Rapid Prototyp J 15: 19 23, 2009. Stübinger S, Mosch I, Robotti P, Sidler M, Klein K, Ferguson SJ, et al.: Histological and biomechanical analysis of porous additive manufactured implants made by direct metal laser sintering: A pilot study in sheep. J Biomed Mater Res B 101B: 1154 1163, 2013.
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Terada M: Corrosion resistance of three austenitic stainless steels for biomedical applications. Mater Corrosion 58: 762 766, 2007.
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Truscott M, Beer D, Vicatos G, Hosking K, Barnard L, Booysen G, Campbell RI: Using RP to promote collaborative design of customised medical implants. Rapid Prototyp J 13: 107 114, 2007. Vandenbroucke B, Kruth JP: Selective laser melting of biocompatible metals for rapid manufacturing of medical parts. Rapid Prototyp J 13: 196 203, 2007.
Volpato N: Os principais processos de prototipagem rápida. In: Volpato N (ed.) Prototipagem rápida:
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tecnologias e aplicações. São Paulo: Edgard Blücher, 55 100, 2007.
Walker PS: Human joints and their artificial replacements. Illinois: Thomas, 1977. Wu W, Zhang Y, Li H, Wang W: Fabrication of repairing skull bone defects based on the rapid
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prototyping. J Bioact Compat Polym 24: 125 136, 2009.
CAPTIONS TO FIGURES
ACCEPTED MANUSCRIPT Fig. 1. Cranial large defect in the right-frontal bone. Fig. 2. CT-images of the patient using InVesalius free-software packages for image segmentation. Fig. 3. Virtual 3D model using InVesalius software. Fig. 4. 3D CAD design for surgical device.
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Fig. 5. Biomodel and customized implant for craniofacial reconstruction surgery. Fig. 6. Customized implant to provide an aesthetically pleasing forehead contour.
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Fig. 7. Photographs of patient taken 8 months after surgery.
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S1010-5182(14)00230-3
DOI:
10.1016/j.jcms.2014.07.006
Reference:
YJCMS 1850
To appear in:
Journal of Cranio-Maxillo-Facial Surgery
Received Date: 10 February 2014 Revised Date:
27 June 2014
Accepted Date: 29 July 2014
Please cite this article as: Jardini AL, Larosa MA, Maciel Filho R, Zavaglia CAdC, Bernardes LF, Lambert CS, Calderoni DR, Kharmandayan P, Cranial reconstruction: 3D biomodel and custom-built implant created using additive manufacturing, Journal of Cranio-Maxillo-Facial Surgery (2014), doi: 10.1016/j.jcms.2014.07.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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CRANIAL RECONSTRUCTION: 3D BIOMODEL AND CUSTOM-BUILT IMPLANT CREATED USING ADDITIVE MANUFACTURING
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André Luiz Jardinia,b, Maria Aparecida Larosaa,b*, Rubens Maciel Filhoa,b, Cecília Amélia de Carvalho Zavagliaa,c, Luis Fernando Bernardesa,b, Carlos Salles Lamberta,d, Davi Reis Calderonia,e, Paulo
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Kharmandayana,e
a
National Institute of Biofabrication (INCT-BIOFABRIS), Campinas, Brazil
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School of Chemical Engineering, State University of Campinas, Campinas, Brazil
c
d
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School of Mechanical Engineering, State University of Campinas, Campinas, Brazil Institute of Physics, State University of Campinas, Campinas, Brazil
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* Corresponding author:
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Maria Aparecida Larosa
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School of Medical Sciences, State University of Campinas, Campinas, Brazil
National Institute of Biofabrication, School of Chemical Engineering, State University of Campinas,
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Campinas, Brazil
Tel.: 55 19 3521-3900; Fax: 55 19 3521-3910. E-mail address: [email protected]
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Cranial reconstruction: 3D biomodel and custom-built implant created using additive manufacturing Summary. Additive manufacturing (AM) technology from engineering has helped to achieve several
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advances in the medical field, particularly as far as fabrication of implants is concerned. The use of AM has made it possible to carry out surgical planning and simulation using a three-dimensional physical model which accurately represents the patient's anatomy. AM technology enables the production of models and implants directly from a 3D virtual model, facilitating surgical procedures and reducing risks.
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Furthermore, AM has been used to produce implants designed for individual patients in areas of medicine such as craniomaxillofacial surgery, with optimal size, shape and mechanical properties. This work
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presents AM technologies which were applied to design and fabricate a biomodel and customized implant for the surgical reconstruction of a large cranial defect. A series of computed tomography data was obtained and software was used to extract the cranial geometry. The protocol presented was used to create an anatomic biomodel of the bone defect for surgical planning and, finally, the design and manufacture of the patient-specific implant.
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Keywords. Additive manufacturing, DMLS, Cranial reconstruction, Titanium alloy, Customized implants INTRODUCTION
The malfunction or loss of total or partial function of an organ or tissue, resulting from trauma or disease, is currently one of the most important and troubling public health problems and affects a
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significant number of people around the world. To meet the great demand for orthopedic surgical procedures to repair or replace body parts, it is necessary to develop biomaterials and more advanced
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surgical techniques.
The combination of high mechanical resistance, high toughness, manufacturing ease, good resistance to degradation by corrosion and low cost makes some metallic materials the preferred biomaterials in the manufacture of orthopedic implants subjected to severe mechanical stresses within the human body. Nowadays, pure titanium and its alloys are some of the most frequently used metallic biomaterials in temporary or permanent orthopedic applications. Temporary implants perform their function of fixing fractures over a predetermined period, until the member is completely recovered so that the implant can be removed. The fixing plates, screws, wires, and intramedullary pins to repair broken bones are
ACCEPTED MANUSCRIPT examples of temporary implants. Permanent implants replace body parts and need to play their role for the rest of the patient's life, as in hip, knee, shoulder, elbow or wrist prosthetics. These implants, as well as other structural components, may fail due to mechanical fracture, wear or corrosion. The combination of the electrochemical process of corrosion and cyclical mechanical stress
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can speed up the release of particles and metal ions, leading to premature failure of the implant (Giordani et al., 2003; Pereira et al., 2006). As an example, articulated implants that are exposed to high loads and severe wear due to the patient’s movement can be mentioned. Moreover, the degradation of metallic implants inside the human body may not only impair the integrity of the material, but also generate
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biocompatibility problems such as infection or allergic reactions, leading to premature removal of the implant (Rondelli et al., 1997; Terada, 2007). The derived detritus is harmful to the tissues that are in
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contact with the implant and can be taken into the bloodstream, settling in organs and impairing their function. Thus, metallic biomaterials must have properties such as resistance to fatigue and wear, fracture toughness and high corrosion resistance (Geetha et al., 2009).
Titanium is particularly suitable for work in corrosive environments or for applications in which low density is essential. It has a high strength/weight ratio, non-magnetic properties and high corrosion
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resistance due to the formation of a compact protective film of titanium oxide (TiO2) on the metal surface. Due to its highly reactive nature in the presence of oxygen, the casting must be conducted in vacuum furnaces (Park and Kim, 2003; Pereira et al., 2006).
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Two types of crystalline formation can occur in titanium. The first one is called alpha and has a hexagonal close-packed (hcp) crystalline structure, while the second is termed beta with a body-centered cubic (bcc) crystalline structure. In pure titanium the alpha phase is stable at room temperature. Alloying
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elements are added to pure titanium and tend to modify the temperature at which the phase transformation occurs and the amount of each phase present. The alloying additions to titanium tend to stabilize the alpha or the beta phase. The alpha phase is stabilized at higher temperatures, by elements called alpha stabilizers, such as aluminum, tin and zirconium; while the beta phase is stabilized by beta stabilizers at lower temperatures, such as vanadium, molybdenum, niobium, chromium, iron and manganese. There are three structural types of titanium alloys: alpha alloys (α), alpha-beta alloys (α + β) and beta alloys (β) (Brown and Lemons, 1996; Brunette et al., 2001; Niinomi, 2002; Abramson et al., 2004; Silva and Mei, 2006).
ACCEPTED MANUSCRIPT Among the titanium alloys, the most employed in the manufacture of surgical implants is Ti6Al4V. The standard that describes the requirements for this alloy is ASTM F136 (2011). The structure of this alloy is α + β type, in which the α-phase stabilizing element is aluminum and the one in the β-phase is vanadium (Black, 1988). In the same way as other materials, this titanium alloy that can be wrought,
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quenched or annealed and can be machined by conventional means (Walker, 1977). Products marketed for medical use must be strictly tested for chemical composition and mechanical and structural features to ensure that they are in accordance with the standards established by the specific rules for implants. The manufacture of metallic implants can include a series of procedures that depend on
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factors such as shape and size of the final product, metal features, and manufacturing cost. The methods employed are casting, machining, forging and powder metallurgy. Good alternatives to conventional
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machining techniques are provided by additive manufacturing technologies such as direct metal laser sintering (DMLS) (Balazic et al., 2007). Usually, after the melting and mechanical forming of the material, an annealing thermal treatment is performed in order to relieve residual stresses, to make the material more ductile and tough, and to produce a specific microstructure without changing the material properties (Callister, 2002).
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Following the manufacturing step, the implant may be subjected to surface modification procedures and finishing techniques such as ionic implantation, nitriding, porous or microporous coating application, polishing, chemical cleaning and passivation. The surface features of the implants are essential in their
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biological performance. Additive manufacturing
Additive manufacturing (AM) or rapid prototyping (RP) is a fabrication technique using the additive
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method, based on the successive addition of fine layers of material. This technology allows the production of physical components (such as prototypes, models, molds) from information obtained directly from a three-dimensional geometric model CAD (computer aided design) system. The process starts with a 3D computer model of the part, which is electronically sliced. These slices are used to provide 2D contour lines which will define, in each layer, exactly where material is going to be added. These layers are sequentially processed, generating the physical part through stacking and adhesion of them, beginning at the bottom and working up to the top part (Gibson et al., 2006; Carvalho and Volpato, 2007).
ACCEPTED MANUSCRIPT The construction of parts with complex geometry in a variety of materials; the use of only one piece of equipment to build the part from beginning to end; and less time and cost to obtain prototypes are some advantages that rapid prototyping offers when compared with other manufacturing processes (Hieu et al., 2003; Foggiato, 2006; Volpato, 2007).
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In the medical field, additive manufacturing has been integrated with the digital imaging techniques of computed tomography (CT) and magnetic resonance (MR), making it possible to obtain solid biomodels that reproduce anatomical structures. The internal structural images acquired by these techniques are handled by a medical imaging system. From these images, specific algorithms of segmentation are
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applied to separate out the structure of interest (bone or tissue). From the image data, a 3D model is generated on specific computer software (InVesalius or Mimics) and exported for the creation of
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biomodels (biomedical prototypes) by additive manufacturing (Truscott et al., 2007; Antas et al., 2008). These biomodels can be used for surgical planning, didactic purposes, the diagnosis and treatment of patients, and communication between professionals and patients. As a result, biomodels facilitate surgery, and reduce infection and rejection risks, complications and length of surgery (Hench, 1991; Gopakumar, 2004; Oliveira et al., 2007; Wu et al., 2009; Bertol, 2010).
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Nowadays, additive manufacturing also allows for the design of customized prosthetic implants, suited to an individual patient’s needs, including the size, shape and mechanical properties of the implant. To achieve this, only digital information is used. Physical models are no longer required; the computer
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generated pattern allows direct production of the final implant, reducing the manufacturing time. The use of these integrated techniques offers a significant potential of cost savings for health systems as well as the possibility of providing an improved quality of life for a huge number of people (Ferreira et
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al., 2007; Singare et al., 2009). Additive manufacturing can be used by health professionals in many specialties including orthopedics, neurosurgery, maxillofacial and orthognathic surgery and traumatology, craniofacial and plastic surgery, implant dentistry, and oncology (Ciocca et al., 2011; Salmi et al., 2012; Huotilainen et al., 2013a; Philippe, 2013; Stübinger et al., 2013). The proposed solution is a way to make the use of AM technology in planning surgical procedures viable, through the development and improvement of services, materials and equipment related to 3D printing technology. Surgical planning with the aid of rapid prototyping allows medical staff to have a physical model to evaluate and even simulate the surgical procedure before its performance. As a result,
ACCEPTED MANUSCRIPT surgical procedures can be optimized and executed in a shorter time, with less time spent in the operating room, thus enabling significant cost savings to hospitals and fewer risks to the patient. Therefore, this solution can provide more security and reliability to the process as a whole. One medical application to be considered is bone reconstruction surgery, for instance, craniofacial
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reconstruction (Hieu et al., 2003; Gopakumar, 2004). Craniofacial anomalies are a highly diverse and complex group of congenital defects that affect a significant proportion of people in the world. In addition to congenital deformities, craniofacial defects can be acquired due to other diseases, such as tumors. In the last four decades, increasing numbers of cases of facial trauma have been observed, which is closely
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related with the increase of traffic accidents and urban violence. Additive manufacturing can also be used in prosthetic implants because the models provide information about size, direction and location of the
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implants, as well as anatomical information. In cases of bone abnormalities, it is important to note that the gain to the patient in functional and psychological terms and the increased quality of life after surgery justify the costs of the application of new technologies (Foggiato, 2006).
There are more than 20 types of additive manufacturing systems on the market which, in spite of using different technologies to add the material, are based on the same principle of manufacturing by
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layer. The main additive manufacturing technologies used are stereolithography (SLA), selective laser sintering (SLS), direct metal laser sintering (DMLS), selective laser melting (SLM), fused deposition modeling (FDM), 3D printing (3DP) and electron beam melting (EBM). These systems are classified
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according to the initial state of raw material, which can be liquid, solid or powder form (Milovanović and Trajanović, 2007; Khan and Dalgarno, 2009). The additive manufacturing technique used in this work is 3D printing (3DP) to create an anatomic
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biomodel of the bone defect for surgical planning and DMLS to design and manufacture the patientspecific implant. Among the advantages of the DMLS technique, is the ability to process titanium (TiCp and Ti64) and other metallic biomaterial (CoCr) directly on the machine. MATERIALS AND METHODS
The procedure for making 3D medical models (biomodels) using additive manufacturing technologies involves a few steps: patient selection; 3D digital image, data transfer, processing and segmentation; evaluation of design and medical model production and validation.
ACCEPTED MANUSCRIPT Patient selection A 22-year-old male patient was injured in a bike accident with a large post trauma defect in the rightfrontal bone (Fig. 1). The cranial section missing extended to an area of approximately 12.5 × 8.4 cm2. The large bone defect was the result of a decompressive craniotomy. Following the initial management of
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the patient and the healing process, reconstruction of the cranial defect was required to restore the structural integrity of the skull and the patient’s facial aesthetics. CT digital image
3D digital image can be obtained by using computer tomography – CT scanner or MRI data. These
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imaging technologies are used for modeling internal structures of the human body. Medical models made from this data must be very accurate and because of this they require a spiral scanning technique which
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allows full volume scanning. This makes it possible to generate a high number of slices (recommended thickness 1–2 mm) and it is very important that the pixel dimension in each slice can be reduced depending on the case. Most CT and MRI units have the ability to export data in the common medical file format – DICOM (digital imaging and communication in medicine). After saving the CT or MRI image data, they should be transferred to the AM system. The next step is processing the data, which is a very
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complex and important step that the quality of the final medical model depends on. For this step the engineers need a software package (InVesalius) in which they can perform segmentation of the anatomy image, achieve a high resolution 3D rendering in different colors, make a
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3D virtual model and finally convert the CT or MRI scanned image data from DICOM to an STL (structure triangularization language) file format. These software packages perform the segmentation
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whilst using a threshold technique which looks at tissue density. In this way, at the end of image segmentation, there are only pixels with a value equal to, or higher than the threshold value (Huotilainen et al., 2013b; de Beer and van der Merwe, 2013; Salmi et al., 2013). Segmentation and CAD design Specific biomedical software is required to manipulate the images. Software used in biomedical prototyping includes Analyze® (Mayo Foundation, USA), Mimics® (Materialise, Belgium), and Biobuild® (Anatomics, Australia). Such software has some basic functions for processing and converting image files. They are necessary as the image files generated by the apparatus and CT represent 2D cuts and are saved in the DICOM format. Nonetheless, for the manufacturing of a biomodel the station needs 3D files,
ACCEPTED MANUSCRIPT preferably in the STL format which is the standard format for manufacturing. Currently, there is free Brazilian software, InVesalius from the ProMED project developed at CTI (Center for Information Technology Renato Archer), which meets the basic functions to integrate biomedical imaging equipment and AM, associated with imaging manipulation and 3D visualization. Fig. 2 shows the CT-image results
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of a patient’s skull segmentation using the system for medical imaging InVesalius. After the segmentation, the 3D model should be converted into a format for additive manufacturing (Fig. 3). The conversion of the 3D files to STL format, performed by biomedical software, generates a mesh of triangles, so that it can adequately represent the complex topography of the craniomaxillofacial
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region. This can cause problems of file size, which derails the process of manufacturing due to the volume of processing required for slicing the model. For this reason, the STL file needs to be worked on
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specific software for AM such as Magics (Materialise, Belgium).
The models coming from InVesalius are surface models that are build up out of facets (triangles). They are transferred through an STL-file. Conventional CAD-systems usually can import these files but in order to do operations on these data, it is necessary to convert the facet model into CAD-surfaces through the usually lengthy and difficult process of reverse engineering. For making surgical tools,
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incorporating other objects (fixation devices, implants), bone replacements, producing patterns for making fixtures or templates or other complex problems in different medical fields, this virtual model in IGES or STL format is processed using a CAD package. This is necessary for evaluation of design,
individual case.
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quality of the made model, and checking possible errors or other important steps which depend on the
3D Printer (3DP) and DMLS systems
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The AM system used in the case presented here includes two steps: (1) the creation of the medical biomodel using 3D printer system; and (2) the DMLS system for the design and manufacture of the customized implant required. The process of three-dimensional printing (3DP), which was developed by the Massachusetts Institute of Technology (MIT), after being licensed by some companies, has considerably increased its market of AM equipment. The operating principle of the Z Corporation 3DP process is described as the technique which refers to an entire class of devices which use inkjet technology. The biomodels are built on a platform located in a container filled with powdered gypsum or starch. An inkjet printhead selectively
ACCEPTED MANUSCRIPT prints a binder liquid that binds the powder in the desired areas. The loose powder remains on the platform to support the prototype that is being formed. The platform is slightly lowered, a new layer of powder is added, and the process is repeated. The prosthetic implant was fabricated by the DMLS technique using the EOSINT M270 system. In
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the DMLS technique, the powder is spread and processed by the action of an infrared laser in an inert and thermally controlled environment inside the chamber. A scanning mirror system controls the laser beam describing the geometry of the layer on the surface of the spread material. With the incidence of the laser beam, the particles of material are heated and reach melting point, joining to each other and also to the
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previous layer. When the material solidifies, a new powder layer is added and the laser scans the desired areas once more; in other words, after the sintering of a layer, a new layer is deposited, and this process
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goes on until the construction of the part is finished. Thus, the implant is built layer by layer. The biomaterial powder of the Ti6Al4V alloy was used for the implant (Joshi, 2006; Lütjering and Wiliams, 2007; Vandenbroucke and Kruth, 2007; Facchini et al., 2010; Ramosoeu et al., 2010). RESULTS Creation of a 3D virtual model of the patient’s skull
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The patient was submitted to a CT examination of the affected bone structure. An acquisition protocol was used: 1 mm for increment between slices and 1 mm of thickness, zero degrees of gantry inclination of the orientation.
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Data obtained in the exams (DICOM format) were converted into a 3D virtual model using InVesalius software (CTI-ProMED, Brazil). The software made it possible to isolate the bone structure through segmentation for the threshold to export them in an STL file. The STL file was edited using Magics 15.0
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software (Materialise, Belgium) in order to minimize surface imperfections. This treatment enables a softening of the model in the upper skull region that contained more widely space slices. CAD system modeling to design the implant For prosthesis generation, a subtraction Boolean was accomplished with a 3D virtual model generated from the exam. This aims to create a prosthesis which is a good fit, allowing for better anchorage between prosthesis and bone. In order to create a perfect model for the implant, points from the symmetric right solid part of the head bone were used. Three key points in the nose were selected for the datum plane definition. These points were mirrored according to the created datum plane. Boolean operations were
ACCEPTED MANUSCRIPT then applied to isolate the set of points required to reconstruct the cranial defect surface and produce the implant model. The new generated point cloud that defines the implant 3D geometry was processed to develop a CAD surface model. The commercial software SolidWorks was used for development of the implant CAD model (Fig. 4).
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Creation of a biomodel and customized implant The biomodel was constructed by 3D virtual model from computed tomography using 3D Zprinter 510 systems (Z Corporation, UK), and materials ZP 130 (powder gypsum), ZB 58 (binder) and Z Bond (resin). The biomodel was created in according to the specifications of an anatomical drawing, in order to
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serve as a test before the surgery. In other words, we can say that the biomodel is a virtual or real experiment that tries to mimic a real system. They can be used for teaching aims, in the manufacturing of
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customized prosthetic implants, in the early diagnosis and treatment of facial deformities, and for facilitating communication between professionals and patients. Biomodels allow the measurement of structures, the simulation of osteotomies and of resection techniques, not to mention a complete planning of several types of craniomaxillofacial surgery. This tends to reduce the surgical procedure time and, as a result, the anesthesia period, as well as the risk of infection. There is also improvement in the result and
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reduction in the overall cost of the treatment.
The biocompatible implant fabricated using the DMLS system based cranial reconstruction approach was an exact fit to the patient’s cranial defect and produced a symmetric skull outline. The material used
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was EOS Titanium Ti64 ELI (EOS GmbH, Germany), because it fulfills the mechanical and chemical requirements of ASTM F 136 standard for surgical implant applications. This material has been used for implant and is inert. Ti64 ELI is its pre-alloyed Ti6Al4V and ELI (extra-low interstitial) version, which
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has a particularly low level of impurities. The implant surface was finished by polishing and sterilization. The preoperative model and titanium implant are shown in Fig. 5. Clinical application
During the surgical procedure using a conventional cranioplasty approach the patient’s custom made cranial reconstruction implant was placed onto the right-frontal bone and fixed to the bone with two screws. The surgery took about 2 hours. When the reconstruction plate is formulated manually during an operation this kind of surgery takes approximately 3 hours. The immediate outcome was successful and
ACCEPTED MANUSCRIPT the implant fitted precisely onto the large cranial defect (Fig. 6). Fig. 7 shows the patient 8 months after surgery. DISCUSSION Conventional cranioplasty is based on the open, cold cure molding technique and reconstruction of the
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implant on a freehand basis. Taking impressions of the defect directly through the patient’s scalp is a major problem. Intraoperative moulding extends the duration of the operation and has been associated with complications due to localized tissue damage from the exothermic reaction during the material curing process. Furthermore, the limited intraoperative overview of larger osseous areas impedes
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judgment of symmetry. Conventional cranioplasty techniques are primarily based on the manual skills and experience of the surgeon. Only an accurately fabricated prosthesis fits into the defect properly and
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reduces the probability of subsequent movement, dislodgement and extrusion (Muller et al., 2003; Maravelakis et al., 2008).
Additive manufacturing is a relatively new technology capable of being physically reproduced in various types of materials, a virtual model, represented as data in a computer. The goal is to obtain a physical model with the same geometric characteristics as the virtual one, so that it can be manipulated
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for various purposes. One application that has emerged as highly promising is the reproduction of anatomical structures, through image acquisition by medical imaging equipment, obtaining thereby a socalled biomodel to aid surgery.
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The virtual model of internal structures of the human body, which is needed for final production of a 3D physical model, requires very good segmentation with a high resolution and pixels of a small size. Good knowledge of the field will help engineers to exclude all structures which are not the subject of
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interest in the scanned image and correctly select the region of interest (separate bone from tissue; include just part of a bone; exclude anomalous structures, noise or other problems which can be faced). Depending on the complexity of the problem, this step usually demands collaboration between engineers and radiologists and surgeons who will help to achieve good segmentation, resolution and finally an accurate 3D virtual model. In image acquisition for biotemplating, the traditional tomographic technique is hardly changed, since the current standards for the craniomaxillofacial region already advocate thin slices. It was noted,
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Avoid inclination of the gantry, because some biomedical prototyping software does not correct
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Metallic artifacts from manufacturing – related to the tomographic technique – this is worrisome
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it;
as phantom images will be reproduced in the biomodel if they are not manually edited in a long and tedious process. In this work, when editing is done by the radiologist in the radiology clinic with software without an interface for Rapid Prototyping file format, these images cannot be sent completely edited for
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the prototyping service. This problem is due to the fact that the editing is only applied to the 3D reconstruction displayed on screen, however, the sent images are of the 2D unedited slices; Positioning the patient with the occlusal plane parallel to the cut plane minimizes the production
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area of artifacts, keeping them almost restricted to the tooth region. If this positioning is not considered in patients with metal dental restoration, this can result in artifacts in various cuts, increasing the number of slices to be manually edited and therefore the time needed for segmentation of images; and •
Another important factor to be considered is the radiation dose related to CT scans. In the facial
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region, this is much discussed, because the protocols for obtaining images typically involve a large number of cuts. Thus, compared with other regions, the radiation dose for face exams is considered high. However, it is important to observe that in radiobiology what matters is not total radiation dose of the
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exam, but its effective dose. In a maxillofacial region exam, this dose does not exceed biosecurity limits. CONCLUSION
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Additive manufacturing (AM) medical models have found application for planning treatment for complex surgery procedures, training, surgical simulation, diagnosis, design and manufacturing of implants as well as medical tools. DMLS additive manufacturing techniques have been applied in the production of custom-built implants that meet the physical characteristics of each patient. The development of complex medical models and implants – virtual and physical – of a patient’s anatomical structure, from the digital image data acquired through hospital scanners, have proven to be a powerful tool for biomedical analysis and to have the capability to design and manufacture customized implants and prostheses prior to surgical procedures. This reduces duration of surgery due to preoperative planning
ACCEPTED MANUSCRIPT using correct geometrical and anatomical details. The virtual and manufacturing process also improves surgical accuracy. CONFLICT OF INTEREST None.
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ACKNOWLEDGEMENTS The authors wish to acknowledge the financial support provided by the Scientific Research Foundation for the State of São Paulo (FAPESP - Process 2008/57860-3 and 2010/05321-1) and National Council for Scientific and Technological Development (CNPq – Process 573661/2008-1).
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CAPTIONS TO FIGURES
ACCEPTED MANUSCRIPT Fig. 1. Cranial large defect in the right-frontal bone. Fig. 2. CT-images of the patient using InVesalius free-software packages for image segmentation. Fig. 3. Virtual 3D model using InVesalius software. Fig. 4. 3D CAD design for surgical device.
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Fig. 5. Biomodel and customized implant for craniofacial reconstruction surgery. Fig. 6. Customized implant to provide an aesthetically pleasing forehead contour.
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Fig. 7. Photographs of patient taken 8 months after surgery.
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