Additive manufacturing machines, based on the multimaterial jetting technology, are widely used for three-dimensional (3D) printing of sophisticated medical models, which are aimed to be used for preoperative planning and surgical training. Gaining knowledge of process-related influences on mechanical and dimensional properties of 3D-printed parts makes up an essential basis for the design and manufacture of medical models. There are few studies on characterization of multimaterial parts, and those are limited to tests that are not based on standardized methods. Within the scope of this work, mechanical and dimensional investigations were performed on multimaterial parts that were printed using an Objet500–Connex3 3D printer (Stratasys Ltd., Minnesota, Eden Prairie, MN, USA). Among test methods listed in DIN EN ISO 17296-3, tensile tests were chosen for mechanical characterization. In the tensile tests, combinations of four different materials (Tango+, VeroClear, VeroPureWhite, MED610) were tested in three build orientations (XY, YX, ZX). To investigate the orientation-dependent printing accuracy, the tensile specimens were further checked for their dimensional accuracy. Statistically significant variations in the mechanical properties were found between different orientation levels. In general, specimens printed in XY orientation show higher tensile strength than YX- and ZX-oriented specimens. The tensile moduli determined are in the range from 0.2 to 2,500 MPa and compare well with the tensile moduli found in soft biological tissues. Dimensional deviations were found highest for the length of ZX-oriented tensile specimens. For this orientation level, it could be observed that multimaterial specimens, which contain higher percentage of the soft material Tango+, are characterized by higher shrinkage. For tensile specimens printed from the pure photopolymer Tango+, a shrinkage of 4.6% in length was determined. In summary, it was found that with multimaterial jetting technology, the increased shrinkage and lower mechanical strength in the ZX direction must be considered in the design process.

IntroductionTranscatheter aortic valve implantation (TAVI) has become an alternative to surgical replacement of the aortic valve elderly patients. However, TAVI patients may suffer from paravalvular leaks (PVL). Detecting and grading is usually done by echocardiography, but is limited by resolution, 2D visualization and operator dependency. 4D flow magnetic resonance imaging (MRI) is a promising alternative, which did not reach clinical application in TAVI patients. The aim of this study was applying 3D printing technologies in order to evaluate flow patterns and hemodynamics of PVLs following TAVI, exploiting 4D flow MRI and standard ultrasound.Materials and methodsAn MR-compatible, anatomically left ventricle, aortic root, and ascending aorta model was fabricated by combining 3D-printed parts and various soft silicone materials to match physiological characteristics. An Abbott Portico™ valve was used in continuous antegrade flow (12–22 l/min), retrograde flow with varying transvalvular pressures (60–110 mmHg), and physiological pulsatile hemodynamics (aortic pressure: 120/80 mmHg, cardiac output: 5 l/min) Time-resolved MR measurements were performed above and below the TAVI stent and compared with color Doppler ultrasound measurements in exactly the same setup.ResultsThe continuous antegrade flow measurements from MRI largely agreed with the flowmeter measurements, and a maximum error of only 7% was observed. In the retrograde configuration, visualization of the paravalvular leaks was possible from the MR measurements, but flow was overestimated by up to 33%. The 4D MRI measurement in the pulsatile setup revealed a single main PVL, which was also confirmed by the color Doppler measurements, and velocities were similar (2.0 m/s vs. 1.7 m/s).Discussion4D MRI techniques were used to qualitatively assess flow in a patient-specific, MR-compatible and flexible model, which only became possible through the use of 3D printing techniques. Flow patterns in the ascending aorta, identification and quantification of PVLs was possible and the location and extent of PVLs were confirmed by ultrasound measurements. The 4D MRI flow technique allowed evaluation of flow patterns in the ascending aorta and the left ventricle below the TAVI stent with good results in identifying PVLs, demonstrating its capabilities over ultrasound by providing the ability to visualize the paravalvular jets in three dimensions at however, additional expenditure of time and money.

Rabbit inhalation anesthesia by endotracheal intubation involves a higher risk among small animals owing to several anatomical and physiological features, which is pathognomonic to this species of lagomorphs. Rabbit-specific airway devices have been designed to prevent misguided intubation attempts. However, it is believed that expert anesthetic training could be a boon in limiting the aftermaths of this procedure. Our research is aimed to develop a novel biomimetic 3D printed rabbit airway model with representative biomechanical material behavior and radiodensity. Imaging data were collected for two sacrificed rabbit heads using micro-computed tomography (μCT) and micro-magnetic resonance imaging for the first head and cone beam computed tomography (CBCT) for the second head. Imaging-based life-size musculoskeletal airway models were printed using polyjet technology with a combination of hard and soft materials in replicates of three. The models were evaluated quantitatively for dimensional accuracy and radiodensity and qualitatively using digital microscopy and endoscopy for technical, tactic, and visual realism. The results displayed that simulation models printed with polyjet technology have an overall surface representation of 93% for μCT-based images and 97% for CBCT-based images within a range of 0.0–2.5 mm, with μCT showing a more detailed reproduction of the nasotracheal anatomy. Dimensional discrepancies can be caused due to inadequate support material removal and due to the limited reconstruction of microstructures from the imaging on the 3D printed model. The model showed a significant difference in radiodensities in hard and soft tissue regions. Endoscopic evaluation provided good visual and tactile feedback, comparable to the real animal. Overall, the model, being a practical low-cost simulator, comprehensively accelerates the learning curve of veterinary nasotracheal intubation and paves the way for 3D simulation-based image-guided interventional procedures.

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