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Comparing Technologies of Additive Manufacturing for the Development of Vascular Models
Abstract
The freedom of design and personalisation enabled by Additive Manufacturing (AM) has a high impact on the fabrication of vascular models. Intracranial vascular models replicate cerebral blood vessels as well as their diseases and can be used to train neurovascular interventions. Their patient-specific, branched geometries benefit from the fabrication with AM. To advance the clinical application of vascular models in simulated neurovascular intervention, it is valuable to identify convenient AM technologies. The development and manufacturing of vascular models is described in this paper. Recommended AM technologies are compared to each other with regard to their suitability for different training setups. The paper presents the comparison of 21 different technologies, machines, or synthetic materials. All models were tested in angiographic measurements by experienced physicians and assessed for different utilizations in neurovascular training.
... A vascular replication system with patient-specific aneurysm models applied to train neurovascular interventions was developed and adapted to individual patient diseases and specific demands of physicians [22,23]. The three types of individualisation processes are applied to the vascular replication system for various applications. ...
... Even though AM can theoretically produce any complex shape, there are restrictions when producing the hollow, branched vessel geometry. Powder-based procedures are not suitable, and Fused Deposition Modelling needs two dissimilar materials to solve the internal support structures [23]. ...
... Of lower relevance to the customer is the sort of vessel tree, which is either simplified by silicone tubes or by a silicone model of a human aorta, and the type of blood flow, which is with or without a pump for a pulsatile flow. More information to this topic is described in [23]. The neurovascular training system is installed in an angiographic system (Fig. 5). ...
Manufacturing companies face high demand for products that fulfil individual customer desires. Recent improvements in additive manufacturing (AM) enable the fabrication of customer-specific components of a product.
... A vascular replication system with patient-specific aneurysm models applied to train neurovascular interventions was developed and adapted to individual patient diseases and specific demands of physicians [22,23]. The three types of individualisation processes are applied to the vascular replication system for various applications. ...
... Even though AM can theoretically produce any complex shape, there are restrictions when producing the hollow, branched vessel geometry. Powder-based procedures are not suitable, and Fused Deposition Modelling needs two dissimilar materials to solve the internal support structures [23]. ...
... Of lower relevance to the customer is the sort of vessel tree, which is either simplified by silicone tubes or by a silicone model of a human aorta, and the type of blood flow, which is with or without a pump for a pulsatile flow. More information to this topic is described in [23]. The neurovascular training system is installed in an angiographic system (Fig. 5). ...
... HANNES is characterized by its high modularity, which allows for easy change of vessel models to represent a wide range of anatomies. Additive Manufacturing (AM) is used for the production of the vessel replicas because it offers a high degree of geometric freedom and enables fast production in small quantities [7]. ...
... It was shown that the procedures Material Jetting (MJ) and Stereolithography (SLA) are well suited for the fabrication of cerebral vessel models with aneurysms. For the MJ, the materials TangoPlus FLX930 and HeartPrint Flex (Materialise GmbH, Munich) on the Objet printer proved to be promising [7]. With the HeartPrint Flex material, Materialise is able to produce models such as vessels with elasticity similar to the real vessel. ...
For training physicians in endovascular techniques such as mechanical thrombectomy in acute stroke, synthetic in-vitro models may replace animal models. A neurointerventional training model was developed in previous works using additive manufacturing (AM) for the reproduction of patient specific anatomy. Different patient anatomies, such as curvatures, can complicate the pathway of treatment. For this reason, realistic training requires a simulation of the entire access path from the femoral artery to the affected vessel in the brain, which includes the simulation of the aorta. The training model currently uses a commercially available silicone aorta, which has several disadvantages, including high cost and unrealistic surface friction. Furthermore, the aortic model is not modular and therefore does not allow changes in configuration of the aortic arch, which is a strong factor influencing procedural difficulty and therefore an important variable for training. In this study, a modular aortic model is designed and manufactured according to the requirements for training endovascular stroke treatment. AM offers many advantages in the production of anatomical models. Therefore, different manufacturing alternatives are tested based on a modular concept, using both direct and indirect manufacturing. Criteria for an evaluation of the production processes and the resulting models are defined and the test set-up is described. In this study, the procedures are first evaluated under cost and time aspect and a first assessment of the qualitative criteria is given.
... Main benefit and innovation of AM is that it eliminates tooling which, in turn, allows for high geometrical freedom as well as production flexibility, especially for low quantities [2]. Tool-less fabrication direct from digital information offers various application possibilities, taking into account that various AM technologies offer different advantages and restrictions [3,4]. AM applications in product life cycle can be divided into three main groups: (1) Fabricating prototypes, e.g. for concept models, functional or technical prototypes used in the design phase, or as display models in marketing and sales, was the earliest application of AM technologies [1]. ...
... AM applications in product life cycle can be divided into three main groups: (1) Fabricating prototypes, e.g. for concept models, functional or technical prototypes used in the design phase, or as display models in marketing and sales, was the earliest application of AM technologies [1]. In the two remaining groups, AM is used either directly (2) or indirectly (3) for producing end-use parts. In direct additive manufacturingalso known as rapid manufacturing or direct digital manufacturing [4] a final part of a product is manufactured additively. ...
Technological advancements in additive manufacturing (AM) has enabled the usage of AM for end-use parts more than ever before. Deciding whether or not to apply AM for final parts and knowing how to design for AM is fundamental in the design phase, which is why Design for AM (DfAM) methods are currently being elaborated.
... Properties of the AM materials chosen to manufacture the phantoms during this work, together with respective printing resolution(Spallek et al 2016, Wegner et al 2020. Sample volume: 1.37 cm 3 . ...
Objective:
In radiation oncology, experiments are often carried out using mice as a model for in-vivo research studies. Due to recent technological advances in the development of high-precision small-animal irradiation facilities, the importance of quality assurance for both dosimetry and imaging is increasing. Additive manufacturing (AM) offers the possibility to produce complex models from a three-dimensional data set and to build cost-effective phantoms that can easily be adapted to different purposes. The aim of this work was therefore to develop detailed anatomical mouse models for quality assurance and end-to-end testing of small-animal irradiation and imaging by means of AM.
Approach. Two mouse phantom concepts were designed, constructed, and examined for this purpose. The first model includes cavities corresponding to the most important organs. The final solid model was constructed using AM in two separate parts that can be attached with a plug connection after filling these cavities with tissue-equivalent mixtures. Moreover, different radiation dosimeters can be placed in the lower part of the model. For the second concept, AM was used for building modules like the phantom outer shell and bones, so that different mixtures can be used as a filling, without modifying the phantom structure.
Main results:
CT as well as Micro-CT scans of both concepts showed an excellent quality and adequate image contrast, with material attenuation properties close to those of mouse tissues, apart from the current bone surrogates. Radiation dose measurements with radiochromic films were, with some exceptions in areas with larges bone volumes, in agreement with calculations within less than ± 4 %.
Significance:
AM shows great potential for the development of mouse models that are inexpensive, easy to adapt, and accurate, thus enabling their use for quality assurance in small-animal radiotherapy and imaging. The introduction of such 3D-printable mouse phantoms in the workflow could also significantly reduce the use of living animals for optimization and testing of new imaging and irradiation protocols.
... Appropriate tissue equivalence for the materials is also given, classified according to typical values from literature [3]. Further material information like elasticity and transparency of the materials can be found in [4]. ...
In radiotherapy, X-ray imaging and dose quality assurance is often carried out using physical phantoms, which simulate the X-ray attenuation of biological tissue. Additive manufacturing (AM) allows to produce cost-effective phantoms that can easily be adapted to different purposes. The aim of this work was to compare mechanical and X-ray attenuation properties of a selection of AM technologies, machines, and materials. The average Hounsfield Units (HU) were measured by means of computed tomography (CT).
... Due to the modular platform of HANNES (Fig.1c), single modules can be replaced easily to represent different anatomies in one training model. Additive manufacturing (AM) is used for the production of patient-original vessels, as it offers advantages for the small number of pieces to be produced and with regard to freedom of geometry [8]. ...
The success of treatment of acute ischemic stroke depends essentially on the time passed until the vessel is reopened. For this reason, training is necessary for the already complicated endovascular stroke treatment under high time pressure. Current in-vitro models do not offer the full range of different stroke cases and the use of various treatment options. This paper describes a conceptual design of a stroke in-vitro model using additive manufacturing to map a range of patient-based training cases. The model considers special aspects of vessels of elderly patients, such as curvatures and stenoses, which complicate the removal of clots.
... elasticity, transparency, and the feasibility of support removal in the inner hollow vascular structure. A comprehensive comparison of AM materials for plastic vessel models is presented in Spallek (2016a). Models fabricated by Fused Deposition Modeling (FDM) offer replication at acceptably high accuracy (Frölich et al., 2015). ...
A neurointerventional training model called HANNES (Hamburg ANatomical NEurointerventional Simulator) has been developed to replace animal models in catheter-based aneurysm treatment training. A methodical approach to design for mass adaptation is applied so that patient-specific aneurysm models can be designed recurrently based on real patient data to be integrated into the training system.
HANNES’ modular product structure designed for mass adaptation consists of predefined and individualized modules that can be combined for various training scenarios. Additively manufactured, individualized aneurysm models enable high reproducibility of real patient anatomies. Due to the implementation of a standardized individualization process, order-related adaptation can be realized for each new patient anatomy with modest effort. The paper proves how the application of design for mass adaptation leads to a well-designed modular product structure of the neurointerventional training model HANNES, which supports quality treatment and provides an animal-free and patient-specific training environment.
... The aim is to analyse the impacts that the use of AM technologies can have on design processes for customization. The various AM technologies offer different material and geometric properties [Eyers and Dotchev 2010], [Spallek et al. 2016]; even so, there are diverse restrictions in material selection and production quality [Campbell et al. 2012], which is the subject of current research. Each AM technology requires different construction guidelines and knowledge of the product designer. ...
Additive manufacturing (AM) has a high impact on the fabrication of customised components of a product. The paper presents AM-specific influences to customised design processes. A gradual range of product design processes for different levels of customization through AM utilisation was derived, reaching from standardised individualisation processes to specific product adaptation. The characteristics of the two poles are detailed and applied in a case for personalised vascular replications.
The replication of blood vessels for training and research purposes is possible with the help of additively manufactured (AM) models. However, a meaningful evaluation of the quality of the haptics, here concentrating on friction characteristics, of additively manufactured blood vessel models compared to human vessels is difficult and often only based on subjective assessments. To enable an objective comparison of friction of different AM materials, tests were performed in which a braided stent was pulled through straight test tubes. The force required to do so was measured. The same test setup was used to examine animal blood vessels so that these results could be compared with the findings of the AM materials. In addition, physicians were asked for their assessment of the haptics concerning friction of different materials. Summarizing the results, for the tested Formlabs materials Flexible 80A and Elastic 50A, it can be stated that Flexible 80A is strongly recommended for the replication of blood vessels - even though it is comparatively smooth. The Elastic 50A should only be used for training with increased difficulty since the models are stickier and a flipping of instruments is possible. Coating the materials only involve effort that is not reflected in the benefits.
Ein wichtiger Bestandteil der Forschungsarbeiten des PKT stellt das Arbeiten mit verschiedensten Prüfständen dar.
Dabei steht neben dem Betrieb dieser Prüfstände zu Forschungszwecken auch die Entwicklung und Konstruktion dieser im Fokus. So sind, teilweise in Kooperation mit weiteren Insti-tuten, eine Reihe von Sonderprüfständen und das dazugehörende Know-How am PKT entstanden, die dabei in den Anwendungsgebieten des Instituts Luftfahrt, Maschinen-und Anlagenbau sowie Medizintechnik zum Einsatz kommen. Die vorhandenen Sonderprüfstände reichen dabei von Tests für Hydraulik-, Material-oder Kompo-nententests bis zu hochspezialisierten Anlagen der Tiefseeprüftechnik oder der Medizintechnik.In diesem Kapitel wird auf die verschiedenen Prüfstände sowie auf die mit ihnen durchgeführte For-schung im Einzelnen eingegangen um somit einen Einblick in die praktischen Arbeiten des Instituts zu geben
Medizinische Simulationsmodelle stellen reale Gegebenheiten der menschlichen oder tierischen Anatomie mithilfe von physischen Komponenten nach.
Abdominal aortic aneurysm (AAA) is a permanent, irreversible dilation of the distal region of the aorta. Recent efforts have focused on improved AAA screening and biomechanics-based failure prediction. Idealized and patient - specific AAA phantoms are often employed to validate numerical models and imaging modalities. To produce such phantoms, the investment casting process is frequently used, reconstructing the 3D vessel geometry from computed tomography patient scans. In this study the alternative use of 3D printing to produce phantoms is investigated. The mechanical properties of flexible 3D - printed materials are benchmarked against proven elastomers. We demonstrate the utility of this process with particular application to the emerging imaging modality of ultrasound - based pulse wave imaging, a noninvasive diagnostic methodology being developed to obtain regional vascular wall stiffness properties, differentiating normal and pathologic tissue in vivo. Phantom wall displacements under pulsatile loading conditions were observed, showing good correlation to fluid – structure interaction simulations and regions of peak wall stress predicted by finite element analysis. 3D - printed phantoms show a strong potential to improve medical imaging and computational analysis, potentially helping bridge the gap between experimental and clinical diagnostic tools.
Minimally invasive endovascular image-guided interventions (EIGIs) are the preferred procedures for treatment of a wide range of vascular disorders. Despite benefits including reduced trauma and recovery time, EIGIs have their own challenges. Remote catheter actuation and challenging anatomical morphology may lead to erroneous endovascular device selections, delays or even complications such as vessel injury. EIGI planning using 3D phantoms would allow interventionists to become familiarized with the patient vessel anatomy by first performing the planned treatment on a phantom under standard operating protocols. In this study the optimal workflow to obtain such phantoms from 3D data for interventionist to practice on prior to an actual procedure was investigated. Patientspecific phantoms and phantoms presenting a wide range of challenging geometries were created. Computed Tomographic Angiography (CTA) data was uploaded into a Vitrea 3D station which allows segmentation and resulting stereo-lithographic files to be exported. The files were uploaded using processing software where preloaded vessel structures were included to create a closed-flow vasculature having structural support. The final file was printed, cleaned, connected to a flow loop and placed in an angiographic room for EIGI practice. Various Circle of Willis and cardiac arterial geometries were used. The phantoms were tested for ischemic stroke treatment, distal catheter navigation, aneurysm stenting and cardiac imaging under angiographic guidance. This method should allow for adjustments to treatment plans to be made before the patient is actually in the procedure room and enabling reduced risk of peri-operative complications or delays.
Additive manufacturing allows new applications due to the layer-based production without tools. Components with a high degree of individualization or with complex geometry can be produced efficiently. The advantages can be used in medical applications for the reproduction of patient data, e.g. for intracranial aneurysms. The treatment of intracranial aneurysms requires highly experienced medical staff and individual planning. Physical reproduc-tions of the complex geometry of the vessels support the treatment of intra-cranial aneurysms. In this paper a development of additive manufactured vessel models is presented. Based on the patient geometry a model of the aneurysm and the affected vessel is constructed. After the FDM-fabrication and sealing, the model is applicable in medical research.
Background:
Recent clinical studies have shown that recanalization rates are lower in stent-assisted coil embolization than in coiling alone in the treatment of cerebral aneurysms.
Objective:
This study aimed to assess and compare the hemodynamic effect of stent struts and straightening of vessels by stent placement on reducing flow velocity in sidewall aneurysms, with the goal of reducing recanalization rates.
Methods:
We evaluated 16 sidewall aneurysms treated with Enterprise stents. We performed computational fluid dynamics simulations using patient-specific geometries before and after treatment, with or without stent struts.
Results:
Stent placement straightened vessels by a mean (±standard deviation) of 12.9° ± 13.1° 6 months after treatment. Placement of stent struts in the initial vessel geometries reduced flow velocity in aneurysms by 23.1% ± 6.3%. Straightening of vessels without stent struts reduced flow velocity by 9.6% ± 12.6%. Stent struts had significantly stronger effects on reducing flow velocity than straightening (P = 0.004, Wilcoxon test). Deviation of the effects was larger by straightening than by stent struts (P = 0.01, F-test). The combination of stent struts and straightening reduced flow velocity by 32.6% ± 12.2%. There was a trend that larger inflow angles produced a larger reduction in flow velocity by straightening of vessels (P = 0.16).
Conclusion:
In sidewall aneurysms, stent struts have stronger effects (approximately 2 times) on reduction in flow velocity than straightening of vessels. Hemodynamic effects by straightening vary in each case and can be predicted by inflow angles of pre-operative vessel geometry. These results may be useful to design a treatment strategy for reducing recanalization rates.
As part of a multicenter cooperation (Aneurysm-Like Synthetic bodies for Testing Endovascular devices in 3D Reality) with focus on implementation of additive manufacturing in neuroradiologic practice, we systematically assessed the technical feasibility and accuracy of several additive manufacturing techniques. We evaluated the method of fused deposition modeling for the production of aneurysm models replicating patient-specific anatomy.
3D rotational angiographic data from 10 aneurysms were processed to obtain volumetric models suitable for fused deposition modeling. A hollow aneurysm model with connectors for silicone tubes was fabricated by using acrylonitrile butadiene styrene. Support material was dissolved, and surfaces were finished by using NanoSeal. The resulting models were filled with iodinated contrast media. 3D rotational angiography of the models was acquired, and aneurysm geometry was compared with the original patient data.
Reproduction of hollow aneurysm models was technically feasible in 8 of 10 cases, with aneurysm sizes ranging from 41 to 2928 mm(3) (aneurysm diameter, 3-19 mm). A high level of anatomic accuracy was observed, with a mean Dice index of 93.6% ± 2.4%. Obstructions were encountered in vessel segments of <1 mm.
Fused deposition modeling is a promising technique, which allows rapid and precise replication of cerebral aneurysms. The porosity of the models can be overcome by surface finishing. Models produced with fused deposition modeling may serve as educational and research tools and could be used to individualize treatment planning.
© 2016 American Society of Neuroradiology.
Opportunities for developing procedural skills are progressively rare. Therefore, sophisticated educational tools are highly warranted.
This study compared stereolithography and 3-dimensional printing for simulating cerebral aneurysm surgery. The latter jets multiple materials simultaneously and thus has the ability to print assemblies of multiple materials with different features. The authors created the solid skull and the cerebral vessels in different materials to simulate the real aneurysm when clipped.
Precise plastic replicas of complex anatomical data provide intuitive tactile views that can be scrutinized from any perspective. Hollowed out vessel sections allow serial clipping efforts, evaluation of different clips, and clip positions. The models can be used for accurate prediction of vascular anatomy, for optimization of teaching surgical skills, for advanced procedural competency training, and for patient counseling.
Simultaneous 3-dimensional printing is the most promising rapid prototyping technique to produce biomodels that meet the high demands of neurovascular surgery.
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