Bioprinting of 3D anatomical models of flat and long thoracic limb bones of domestic cats (Felis catus Linnaeus, 1758)

Nathalia da Silva Ramos Elias1, Helton Carlos Sabino Pereira2, Antônio Francisco da Silva Lisboa Neto3, Erick Eduardo da Silveira4, Amilton César dos Santos5 & Antônio Chaves de Assis Neto6*  1 Undergraduate in Veterinary Medicine, Faculdade de Medicina Veterinária e Zootecnia (FMVZ), Universidade de São Paulo (USP), São Paulo, SP, Brazil 2 Biologist, Programa de Pós-Graduação em Anatomia dos Animais Domésticos e Silvestres (PPGAADS), FMVZ, USP, São Paulo, SP, Brazil 3 Veterinarian, DSc., PPGAADS, FMVZ, USP, São Paulo, SP, Brazil 4 Veterinarian, MSc., PPGAADS, FMVZ, USP, São Paulo, SP, Brazil 5 Biologist, DSc., FMVZ, USP, São Paulo, SP, Brazil 6 Veterinarian, DSc., FMVZ, USP, São Paulo, SP, Brazil

The 3D printing of compatible biomaterials and tissue media components is already a reality. A biomodel is a faithful representation of morphological characteristics, which can be virtual or physical. The use of 3D technology in the field of medicine and veterinary medicine is an important tool to assist in the detailed study of anatomy (Li et al., 2018) and for surgical planning (Cone et al., 2017).
The constant challenge of innovating the teaching of anatomy and discussing ethical issues related to the use of animals is in line with the concept of the 3Rs, which advocates the use of animals for teaching and research, based on three principles: Replacement, Reduction and Refinement (Pereira et al., 2017).
This work aimed to create a digital 3D anatomical collection and 3D print of flat and long bone models of the thoracic limb of domestic cats for interactive and dynamic uses and with great potential to be used in an educational environment.

3D scanning and editing
The bones were scanned separately using a "Go! 3D Scan" portable 3D scanner (Creaform Inc. Lévis, Quebec, Canada). The following parameters were used for the images: resolution of 0.5 mm, Optimize Scan Mesh and Decimate Scan Mesh between 80 and 100, Auto-fill Holes between 20 and 40 and Removes Isolated Patches between 20 and 25. Image capture was managed through a Software data acquisition and scanner interface, the program VXElements 6.1® (Lévis, Quebec, Canada), which allows visualization of scanned images.
The images obtained were saved and edited in the Geomagic 12.1® program (Cary, NC, USA), which enables the operator to join images, correct faults, change color, smooth surfaces, and shape edges. This step was performed when it was not possible to scan the entire bone in a single file, requiring more than one file of the same bone and then joining them in the editor. The prints of each bone took approximately 8 hours, the scanning procedures took 30 minutes, and the total cost per printed model was around R$ 40.00.

Results
The 3D models were created according to the specifications of the actual bones. Figures 1-4 demonstrate a comparative anatomical correspondence of a real bone and 3D model of the scapula, humerus, radio and ulna.
Anatomical details can be easily identified in 3D scanned models. The spine of the scapula lies on the lateral side of the scapula in its middle region, which separates the two fossae (supra and infraspinatus) ( Figures 1A, B, C). The suprahamate and hamate processes ( Figures 1A, B, C), supraglenoid tubercle ( Figures 1A, C), subscapular fossa, and coracoid process (Figures 1D-F) can be observed and are represented in the printed models.
Other structures can be easily evidenced and compared on real and 3D-printed bones. A depression can be observed on the caudal face of the distal epiphysis, the olecranon fossa, which articulates with part of the olecranon (Figures 2A-C). At the distal end on the cranial face there is also a depression, near the trochlea, that lodges the head of the radius when the elbow is flexed. Further, a supracondylar foramen can be seen in the distal epiphysis of the humerus ( Figures 2D-F), proximal to the medial epicondyle.
The tuberosity of the olecranon can be observed at the proximal end of the ulna and trochlear notch at the base of the olecranon, which supports the articulation of the humerus. The anechoic process can be found in the cranial notch in the cranial direction. At the distal end of the ulna, the projection of a lateral styloid process is observed, which articulates with the radius (Figures 3D-F).
The head, neck and radial tuberosity can be observed on the actual and printed 3D or scanned radius ( Figures 4A-C). At the distal end, the trochlea and ulnar notch can be observed. On the medial surface, the radius extends to form the radial styloid process (Figures 4D-F).

Discussion
This study describes an important method for producing accurate educational models of skeletal elements using a portable scanner and a 3D printer. The most prominent anatomical characteristics of the real bones were replicated in a reliable manner, except for tiny anatomical structures such as foramens. Nevertheless, Thomas et al. (2016) reported that this limitation does not interfere with the quality of printed materials and can be improved upon following the printing of good quality models.
As shown in this study, 3D-printed models are able to complement anatomy classes that are based only on traditional methods such as the use of cadaveric models. Moreover, they can serve as references for studies involving orthopedic surgical planning (Cone et al., 2017).
After the appropriate investment in scanning and printing equipment, the costs related to producing anatomical models are lower than the cost of purchasing or producing plastinated specimens (McMenamin et al., 2014). As in this study, Li et al. (2018) stated that all educators can produce useful 3D models in a relatively quick and easy manner after minimal operational training in the use of the 3D scanners and printers.
Printed models serve as a basis for describing and evaluating the replicated anatomical structures of a real specimen. However, although several studies demonstrate the importance of the use of 3D models, whether for surgical planning (Burzyńska et al., 2016;Kim et al., 2018;Mukherjee et al., 2017;Oxley, 2018;Silva & Gamarra-Rosado, 2014) or teaching (Dorbandt et al., 2017;Schoenfeld-Tacher et al., 2017;Suñol et al., 2019) the efficacy of this tool in veterinary medical practice still requires validation in future studies.
The production of bone replicas (bone biomodels) and organs from dogs, cats, horses, cattle and pigs using real mold scan or segmentation by computed tomography and 3D printing resonance is already a reality . Our experience with these models demonstrates the use of an innovative and high level of technological development for the rapid manufacturing of 3D-printed organ models using 3D scanning and printing technologies. Such models can then be used for teaching of veterinary anatomy, with the potential for expansion into other areas of veterinary medicine such as pathology, surgery (surgical planning), use of prostheses for animal rehabilitation and imaging studies . The use of printed and virtual models will complement teaching practices in these areas. Further, given the degree of similarity to the original bones, their use in teaching is likely to be very effective.

Conclusion
This study enabled the creation of interactive models for the anatomical study of long bones and planes of the thoracic limbs of cats, which can be continuously optimized. Thus, these digitized and printed bone models can contribute to future studies aiming to validate the use of 3D-printed models in the context of anatomy teaching and as a complement to the use of cadaveric anatomical specimens.