Annals of 3D Printed Medicine 18 (2025) 100201 Contents lists available at ScienceDirect Annals of 3D Printed Medicine journal homepage: www.elsevier.com/locate/stlm Research paper Affordable multicolor 3D printing solution for biomedical education in lowand middle-income countries Dat Minh Lu a,b,** , Phong Van Dong c, Hien Bui Thu Hoang d , Dang Ngoc Tran e,b, Khiem Tran Dang f,g, Linh Thanh Duy Tran a,h , An Le Pham a,b,i,*,** a Family Medicine Center, Faculty of Medicine, University of Medicine and Pharmacy at Ho Chi Minh city, 217 Hong Bang St, Ward 11, District 5, Ho Chi Minh city, 700000, Vietnam Grants and Innovation Center, University of Medicine and Pharmacy at Ho Chi Minh city, 217 Hong Bang St, Ward 11, District 5, Ho Chi Minh city, 700000, Vietnam c Faculty of Mechanical Engineering, Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet St, Ward 14, District 10, Ho Chi Minh city, 700000, Vietnam d Department of Radiology, Cho Ray Hospital, 201B Nguyen Chi Thanh St, Ward 12, District 5, Ho Chi Minh City, 700000, Vietnam e Department of Environmental Health, Faculty of Public Health, University of Medicine and Pharmacy at Ho Chi Minh city, 217 Hong Bang St, Ward 11, District 5, Ho Chi Minh city, 700000, Vietnam f Department of Surgery, University of Medicine and Pharmacy at Ho Chi Minh city, 217 Hong Bang St, Ward 11, District 5, Ho Chi Minh city, 700000 Vietnam g Dept of Gastrointestinal Surgery, Nguyen Tri Phuong Hospital, 700000, Vietnam h College of Medicine, Taipei Medical University, Taipei, 110, Taiwan i Child Health Research Centre, The University of Queensland, Sir Fred Schonell Drive, Brisbane, Queensland, 4072, Australia b A R T I C L E I N F O A B S T R A C T Keywords: Three-dimensional Fused deposition filament Water-soluble Multicolor Education anatomy 3D printing for biomedical education in universities remains largely inaccessible in low- and middle-income countries (LMICs) due to the high cost of commercial material jetting and powder bed fusion 3D printers. To address this barrier, we have developed an affordable multicolor fused deposition modeling (FDM) 3D printer capable of producing biomedical models with intricate geometries. The key innovation of our printer is the novel integration of two distinct hybrid printhead configurations to enable simultaneous multicolor printing and watersoluble support material deposition. Positioned along the same X-axis, the first printhead employs a filament cutting, retracting, and purging mechanism to print in seven colors, while the second printhead is dedicated to printing water-soluble support material. The printer utilizes a hybrid CoreXY kinematic system and offers a 30 × 30 × 30 cm print volume. Its operations are controlled by two MKS Monster8 V2.0 boards and an MKS Pi V1.1 running Klipper firmware, with Orca Slicer software converting 3D model data into printer-readable instructions. Our printer successfully operated for up to 45 h, producing four detailed heart models (18 × 15 × 10 cm) and a multicolor DNA polymerase model from online databases and CT scan images. Support structures were removed by immersing the prints in warm water for 24 h, ensuring precise structural integrity for complex models. By combining multicolor printing with water-soluble support material, our cost-effective, frugal innovation allows the fabrication of intricate, vibrant biomedical models, making 3D printing more feasible for biomedical edu­ cation and research in LMICs. 1. Introduction 1.1. Application of biomedical models Biomedical models are usually used for teaching, learning, and practicing in health science fields such as medicine, biology, and ge­ netics. Healthcare practitioners can enhance their ability to strategize and implement intricate surgical operations, hence mitigating the like­ lihood of complications and enhancing patient outcomes through the development of precise and tailored models designed for individual * Corresponding author at: Child Health Research Centre, The University of Queensland, Sir Fred Schonell Drive, Brisbane, Queensland, 4072, Australia. ** Corresponding author at: Family Medicine Center, Faculty of Medicine, Grants and Innovation Center, University of Medicine and Pharmacy Ho Chi Minh city, 217 Hong Bang St, Ward 11, District 5, Ho Chi Minh city, 700000, Vietnam. E-mail addresses: luminhdat@ump.edu.vn (D.M. Lu), dongvanphong1908@mail.com (P. Van Dong), hoangbuithuhien@gmail.com (H.B.T. Hoang), tranngocdang@ump.edu.vn (D.N. Tran), khiemdangtran@yahoo.com (K.T. Dang), tranthanhduylinh@ump.edu.vn (L.T.D. Tran), phamlean@ump.edu.vn (A.L. Pham). https://doi.org/10.1016/j.stlm.2025.100201 Received 31 October 2024; Received in revised form 19 February 2025; Accepted 17 March 2025 Available online 3 April 2025 2666-9641/© 2025 The Authors. Published by Elsevier Masson SAS. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 patients [1]. Moreover, medical education is significantly influenced by the utilization of 3D printing. Traditionally, learning and teaching have relied on materials such as atlases, screen visualizations, 3D models created using the casting process, and cadavers. Nevertheless, the scarcity of cadavers and the use of hazardous chemicals in their pres­ ervation process may render them unsuitable for medical instruction. The presence of these compounds has the potential to cause health problems, including irritation of the skin and airways, and an increased risk of infection [2,3]. Furthermore, the current accessibility of 3D models produced by injection molding methods is limited in terms of both design and quantity, thus falling short of achieving desired educational objectives. Anatomical 3D printing allows for the creation of precise 3D models of patient-specific anatomies in a flexible manner which are applied for educational purposes, surgical planning (visuali­ zation, practicing intervention), external parts, surgical instruments, and internal implants [4]. A systematic review has revealed that seven research studies employing 3D printed anatomical models in surgical procedures demonstrated a mean time saving of 62 min per case. This translates to a cost saving of $3720 per case due to reduced operating time. Based on these findings, it was estimated that a minimum of 63 3D printed models or guides per year, equivalent to 1.2 per week, would be necessary to offset the annual fixed costs of utilizing this technology [1]. A review of the literature on medical education found that students who learned using 3D printing models had better test performance, found the 3D models more useful, achieved higher test accuracy, and expressed greater satisfaction with their learning compared to a con­ ventional group that studied using cadaver and 2D models [5]. 3D printing of biomolecular models can also aid research and pedagogy fields. A survey showed that 3D printing helps improve stu­ dent engagement in class as well as overall grade of biochemistry course [6]. Biomolecular models help connect abstract or invisible structures to human comprehension by offering tangible representations at a scale that is perceivable to humans [7]. Therefore, the integration of 3D printing technology into health science education is of utmost impor­ tance in the 21st century. required, which is impractical for intricate models with deep cavities and risks structural damage. These constraints limit its suitability for multi-color biomedical models with complex internal geometries, where both structural integrity and accurate anatomical representation are essential. FDM, in contrast, is an affordable and widely accessible technology that has been extensively used in LMICs for biomedical education and surgical planning [9]. In FDM 3D printing, thermoplastic filament is heated and extruded through a nozzle to build models and support structures layer by layer. To enhance its suitability for biomedical model production, an ideal FDM 3D printer must meet two critical requirements: 1. Multicolor printing – The ability to print in at least seven distinct colors is necessary to differentiate intricate anatomical and biochemical structures using a single material, typically polylactic acid (PLA). 2. Water-soluble support material printing – The capability to print support structures using polyvinyl alcohol (PVA), which dissolves in water post-printing, ensuring the integrity of models with complex geometries. FDM technology can be optimized to meet these requirements, of­ fering a cost-effective and practical solution for biomedical education and research. 1.3. Limitations of existing FDM 3D printing technology for biomedical model printing Most commercially available FDM 3D printers offer either multicolor printing or water-soluble support material printing, but few efficiently integrate both in a single system. Some printers, like the Bambu Lab X1Carbon and A1 Mini, achieve multicolor printing by switching filaments through a single extruder, but they cannot reliably print with watersoluble materials. Other printers, such as the Sovol SV04 (SPIXI ENT., Shenzhen, China), utilize two independent extruders (IDEX), while models like the Ultimaker S5 (Ultimaker Co., Zaltbommel, The Netherlands) employ two direct extruders mounted on the same car­ riage. These configurations allow PLA and PVA printing within a single job, but color capability is typically limited to two or fewer. Such limi­ tations pose significant challenges when attempting to combine both multicolor printing and water-soluble support materials in biomedical 3D printing, where color differentiation and soluble supports are crucial for complex geometry models. A single-extruder setup, while capable of switching colors, is un­ suitable for printing both polylactic acid (PLA) and polyvinyl alcohol (PVA) together. This approach requires excessive purging during ma­ terial transitions, leading to high PVA wastage and increasing the risk of nozzle clogging due to the heterogeneity of materials, which reduces printing reliability. On the other hand, independent dual extruders systems can print PLA with PVA separately, but they often lack multi­ color capabilities. A tool-changing 3D printer, such as the Original Prusa XL, allows multiple printheads to switch using a docking mechanism, enabling the printing of up to four colors and water-soluble support material. However, this design requires a larger physical footprint, limits the number of printheads (typically to fewer than six), and demands precise calibration and increased hardware complexity, thus raising labor, maintenance time, and operating costs. Several studies have explored biomedical 3D printing using either multicolor printing or water-soluble support materials, but rarely in combination. For example, a two-color prostate cancer model was pro­ duced using dual extruders FDM 3D printing with no water-soluble support material for just $20 [10]. Other studies have demonstrated the printing of single-color abdominal aortic aneurysms and heart models with water-soluble support materials, but at the expense of multicolor capability [11,12]. Additionally, Eduardo [7] developed a 1.2. Low-cost 3D printing solutions for biomedical models 3D printing, also known as additive manufacturing, enables the creation of three-dimensional objects by depositing material layer by layer, allowing for the production of complex geometries with minimal waste. Several 3D printing technologies exist, ranging from low-cost methods, such as fused deposition modeling (FDM) and vat photo­ polymerization, to high-cost, advanced systems, such as material jetting and powder bed fusion. Material jetting uses a printhead to dispense photopolymer materials that are cured by UV light while also incorpo­ rating water-soluble support material, allowing for full-color, high-res­ olution prints with varied mechanical properties. Powder bed fusion selectively fuses powdered materials, such as metals or plastics, using a heat source like a laser or electron beam. This technology can incorpo­ rate an inkjet printhead to enable full-color printing, and the powder bed acts as a support structure, eliminating the need for cutting off the support pilars [8]. However, the acquisition and maintenance costs of these printers are high, making them impractical for use in LMICs. Vat photopolymerization 3D printing technology is a widely employed in medical applications, valued for its high resolution and precision. This process utilizes ultraviolet (UV) light to selectively cure liquid photopolymer resin, enabling the layer-by-layer fabrication of complex geometries. The technology is available across a broad price spectrum, with entry-level systems such as the Elegoo series costing a few hundred USD, while industrial systems such as Formlabs can exceed several thousand USD. Despite its advantages in surgical guide fabrica­ tion, vat photopolymerization has significant limitations for biomedical model production. It is monochromatic, lacks water-soluble support materials, and requires labor-intensive post-processing. Support struc­ tures must be manually removed, and post-printing colorization is 2 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 protocol for printing biomolecules using a low-cost FDM 3D printer with only one color and no water-soluble support material. To the best of our knowledge, there is a significant gap in the liter­ ature on FDM 3D printing that combines multicolor printing with watersoluble support material in a single process. This limitation restricts the ability to create detailed, high-fidelity biomedical models essential for educational and research applications. Thus, our primary objective is to modify the FDM 3D printing process to enable the simultaneous printing of up to seven colors along with water-soluble support material, over­ coming the constraints of existing technologies. PVA, a secondary printhead is added on the same gantry. Each printhead can independently move along the X-axis. This setup is known as inde­ pendent extruder (IDEX) (Fig. 2B). The integration of a multicolor printhead and IDEX creates a novel configuration, which we call DAPHybrid-IDEX (Fig. 2A). Each printhead is equipped with two CR-10 hotends (Shenzhen Creality 3D Technology Co., Shenzhen, China), which have a nozzle diameter of 0.4 mm. 2.1.2. The integration of both direct drive extruder and Bowden extruders: hybrid extrusion Our constructed printer, the DAP V1, features a multicolor printhead equipped with one direct drive extruder and seven Bowden extruders. We call this configuration “Hybrid extrusion”. A direct drive extruder is a stepper motor attached to a extruder kit located right above the printhead that regulates the process of introducing filament into the nozzle (Fig. 1A). A Bowden extruder, on the other hand, involves a stepper motor that drives the filament through a plastic tube, known as a Bowden tube (Fig. 1B). Seven Bowden extruders (NEMA 17 42CM04, Leadshine Technology Co., Shenzhen City, Guangdong Province, China) propel seven filaments through the filament splitter into the direct drive extruder, and subsequently into the nozzle. After each color change, the direct drive extruder synchronizes its rotational motion with the cor­ responding activated Bowden extruder. In other words, the Bowden extruders are responsible for filament transition, while the direct extruder is responsible for precise control of material flow during the printing process (Fig. 1C). On the other hand, the secondary printhead responsible for printing water-soluble support material is equipped with only a direct drive extruder. Two direct extruders are dual drive stepper motors (NEMA 14 36HS2418CL16, GIBOH, NBLINGKAI Manufacturer). 2. Method 2.1. Two innovative approaches of our DAP V1 multicolor 3D printer system 2.1.1. The integration of ten-inlets-one-outlet multicolor printhead and independent extruders (IDEX) technology To enable printing in multiple colors using a single material (PLA), a single nozzle printhead is mounted on a mobile gantry equipped with a filament changing mechanism. Filaments are driven into the filament splitter, which has ten inlets and one outlet. This configuration allows for printing in a maximum of ten colors (Fig. 1C). When the filament change sequence is initiated, the printhead moves to the stationary sharp blade positioned on the front gantry of the printer, to sever the molten filament before withdrawal (Fig. 4C). Retracting molten filament into the filament splitter without trimming may lead to potential fila­ ment jamming. The subsequent filament is propelled through the fila­ ment splitter and directed into the hot nozzle. A small section of filament is purged out to prevent color contamination from the preceding filament. To enable the printing of water-soluble support material, specifically Fig. 1. Types of extrusion system. Footnotes: A. Direct extrusion. B. Bowden extrusion. C. Our DAP printer with “Hybrid extrusion”. 3 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 Fig. 2. Multi-color, multi-materials nozzle configuration. Footnotes: A: Our “DAP-Hybrid-IDEX”, B: IDEX, C: tools changer, D: single nozzle with filament splitter, E: Fixed multiple nozzles on a printhead. 2.2. Printer kinematics and electronics source [13]). The movement of the build platform in the Z-axis direction is also driven by two stepper motors. The model of all stepper motors that drive the X, Y, Z axes is NEMA 17 42CM04 (Leadshine Technology Co., Shenzhen City, Guangdong Province, China). Two MKS Monster 8 V2 controller boards, along with a MKS Pi V1.1 (Makerbase, Guangzhou, Guangdong, China) loaded with an open-source firmware Klipper V0.12.0, are used to control the printer. A web-based application, Mainsail (BIGTREETECH, Shenzhen, China) acts as a control interface The hybrid CoreXY kinematic is chosen for the motion mechanism of the printer’s components. Four closed-loop stepper motors were set up by wiring four MKS-SERVO42C-V1.0 drivers (Makerbase, Guangzhou, Guangdong, China) to four stepper motors, which are used to operate the mobile gantry along the Y-axis direction and to move the two printheads along the X-axis direction on the mobile gantry (Fig. 3, Fig. 3. Hybrid CoreXY kinematics. Footnotes: Y1, Y2: stepper motors for moving the printheads-carriage gantry along Y-axis direction. X1, X2: stepper motors for moving two printheads along X-axis direction on the moving gantry. P1: Multicolor printhead (PLA). P2: Printhead printing water-soluble support material (PVA). (Source [14]). 4 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 for the printer. After assembly, the two printheads may not be properly aligned in terms of their printing positions. To achieve precise alignment of the printhead positions in relation to each other, the printer must undergo printhead offset calibration. Finally, our innovative multicolor 3D printer prototype, named DAP V1 (Fig. 4), has been completed. The breakdown of machine cost is shown in Table 1. was subjected to a thickness of 2 mm. The outer boundary of the left ventricular myocardium and the interventricular septum were segmented using “Surface cut” tool. This allowed us to segment the entire block of the left ventricle and myocardium. "Logical operators" were used to segment the left myocardium by subtracting the left ventricle from the entire block. The segmentation of coronary arteries was performed using the “Paint” tool, with a threshold range of 300 to 870 HU. Subsequently, the arteries’ diameter was augmented by 1 mm using the ’Margin - Grow’ tool to replicate the artery wall. The cardiac valves were segmented by using the “Paint” tool, with intensities ranging from 100 to 400 HU (Fig. 5). The 3D model was partitioned into the upper and lower parts. The cut plane is positioned slightly below the plane that encompasses the mitral annulus. The magnetic joints were ultimately designed for assembling the two components of the model within the Meshmixer V3.5 software (Autodesk Inc., CA 94105 USA). 2.3. 3D data preparation 2.3.1. Heart failure model generated from a CT scan of a real patient An anonymous female patient diagnosed with heart failure and ischemic heart disease underwent an ECG-gated computed tomography coronary angiography with intravenous contrast using a 128-detectorrow CT scanner (Siemens Healthineers Inc., Leipzig, Germany), with a 120 kV voltage and 0.5 mm slice thickness. Images of the diastolic phase were captured and stored in DICOM format, then imported into the 3D Slicer software. 3D Slicer is an open-source medical imaging software, with many advanced visualization features used in biomedical fields worldwide [14]. The process of 3D image segmentation is employed to demarcate anatomical structures within medical scans such as magnetic resonance imaging (MRI) or computed tomography (CT) images to form 3D digital models. Seed points were placed on the images of right and left atria, ventricles, the ascending aorta, superior vena cava, and pul­ monary artery. “Grow from seed” automatic segmentation tool was then applied. This tool expands the seed points to encompass regions char­ acterized by comparable Hounsfield unit (HU) intensity. The segmen­ tations subsequently underwent manual revision and refinement, employing several tools like “Scissor”, “Paint”, “Erase”, and “Island”’ by an experienced radiologist. A 1.5 mm thick aorta wall was constructed using the “Hollow - Inside Surface” tool. The superior vena cava, pul­ monary artery, pulmonary vein, right atrium, and left atrium were subjected to a wall thickness of 1 mm. The right ventricular myocardium 2.3.2. Other heart models and DNA polymerase molecule model from existing online database The 3D models of healthy heart, congenital heart diseases including Tetralogy of Fallot and Transposition of the great arteries were the creation of University Medical Center Groningen, The Netherlands [15]. The models are copyrighted under Attribution-Non-Commercial-Share Alike 4.0 International (CC BY-NC-SA 4.0). The anterior walls of both the right and left ventricles are incised to enable visualization of the mitral and tricuspid valves (Fig. 6). An intricate biomolecular model such as polymerase-DNA complex was chosen as a test print (Fig. 6). The model was retrieved from Na­ tional Institutes of Health (NIH 3D), which serves as an open, community-driven platform for accessing, sharing, and generating bioscientific and medical 3D models tailored for 3D printing and inter­ active visualization, encompassing virtual and augmented reality ap­ plications [16]. Fig. 4. DAP V1 multicolor 3D printer. Footnotes: A: Filaments are propelled by seven stepper motors, which are known as Bowden extruders, mounted on top of the printer. B: Multicolor printhead on the left and water-soluble support material printhead on the right. Filament splitter containing ten inlets, and one outlet sits on top of the left printhead. C: Prior to each color change, multicolor printhead moves to the blade position to trim the molten filament before retraction. 5 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 × 10 cm. The construction of the four models necessitated a total of 750 g of PLA, 320 g of PVA for the support structures, and 410 g of PLA for the purging process during color alteration. Each heart is outlined with precise anatomical characteristics (Fig. 8). Despite its stringing print, polyvinyl alcohol does not compromise the print quality as it readily dissolves in water. Each heart model incurs a total manufacturing cost of 30 USD, which encompasses materials, electricity, printer depreciation, and manpower. The second test is to evaluate the printer’s capability to produce intricate and detailed prints, specifically those pertaining to biomole­ cular models. The resulting model showcases the precise execution of large number of filament retractions and complex printer movements to accurately print biopolymer chains, links, and struts between them. Fig. 9A depicts the DNA polymerase molecule model within a watersoluble support block, whereas Fig. 9B and C illustrate the model after the disintegration of the support structures in water, hence preserving the integrity of the model. The total amount of PLA required for printing the model was 53 g, with an additional 123 g allocated for purging during color transitions, and 51 g for PVA. The printing process took a total of 16 h to finish. The aggregate expenditure associated with the production process, encompassing materials, electricity, printer depre­ ciation, and labor, amounts to $20 USD per biomolecular model. Table 1 Pricing of mechanical and electrical components of DAP V1 3D printer. Components 3030 Aluminum Extrusion 15 mm Linear Guide Rail 12 mm Lead Screw 12 mm Linear Shaft LMK12LUU Linear Bearing Laser-cut steel parts GT2 Pulley 20 Teeth, 5 mm Bore GT2 Idler Pulley 20 Teeth, 5 mm Bore GT2 Timing Belt GT2 Closed Loop Timing Belt 200mm KFL001 Pillow Block Bearing SFH12 Shaft Support Block Support Wheel 3030 Corner Bracket Bolts and Nuts Total for Mechanical components Electronic MKS Monster V2 Controller Board components MKS Pi V1.1 Board TMC 2209 Stepper Driver BMG Extruder Kit Creality CR10 Hotend Assembled MK8 NEMA 17 Stepper Motor + MKSSERVO42C-V1.0 Driver NEMA 17 42CM04 Stepper Motor NEMA 14 36HS2418CL16 Stepper Motor 24 V 20A Power Supply 300 mm Aluminum Print Bed 220 V Silicone Heated Bed SSR MOSFET for Heated Bed Textured Glass Bed Mechanical Endstop Acrylic Enclosure Panels Electrical Wire and Connectors Total for Electric components TOTAL Price (USD) 15 m 3 2 4 4 16 6 12 $ 65 $ 47 $ 16 $ 10 $8 $ 118 $3 $ 10 6m 2 $7 $3 4 8 4 30 2 1 16 8 2 $5 $8 $4 $5 $ 40 $ 349 $ 66 $ 48 $ 51 $ 44 $ 48 6 $ 66 7 2 $ 39 $ 13 2 1 1 1 1 4 1 $ 20 $ 12 $ 18 $4 $8 $1 $ 40 $ 20 $ 498 $ 847 Mechanical components Quantity 4. Discussion 4.1. The integration of both direct drive extruder and Bowden extruders: hybrid extrusion The use of either a Bowden extruder or a direct extruder is common in conventional FDM 3D printers, though their combination is rare. The Bowden extruder configuration involves the attachment of the extruder to the printer frame, enabling the passage of filament through a plastic tube known as a Bowden tube. This configuration decreases the print­ head’s weight and allows for multicolor 3D printing. However, it leads to limited control over the filament when printing intricate and minute features, as there is a slight variation in filament movement within the tube. The magnitude of the filament play increases proportionally with the length of the Bowden tube. Therefore, Bowden extruders are not suitable for fabricating biomolecular models that require extensive fine control over filament retractions and extrusions. In contrast, a direct drive extruder is positioned directly above the printhead, enabling more precise control over filament movement. However, this design increases the printhead’s mass, thus limiting the number of direct extruders that can be incorporated on the printhead. The increased weight of the printhead results in decreased print speed and quality. Consequently, a direct drive extruder is frequently employed for the purpose of printing a single color and a single material. With direct drive extruder in “Hybrid extrusion” system, it is possible to exert precise control over the extru­ sion and retraction of the filament within the nozzle, thereby facilitating the printing process of an intricate DNA polymerase model. Addition­ ally, the utilization of Bowden extruders with filament splitter in “Hybrid extrusion” system allows for smooth filament transition, thereby enabling the printing of numerous colors (Fig. 1C). 2.4. Printing tests with our innovative multicolor DAP V1 3D printer All digital models were imported into Orca Slicer V1.9.1 software (SoftFever). Slicing process provides the 3D printer with exact in­ structions, known as G-code, to deposit material in order to create each layer. Orca Slicer is open-source software that offers extensive custom­ ization for users. Polylactic acid (Kingroon, Shenzhen Kingroon Tech Co., Kowloon, Hong Kong) was used to print all models at a temperature of 200 ◦ C. Polyvinyl alcohol (eSUN, Shenzhen Esun Industrial Co., Nanshan Dis­ trict, Shenzhen, China), acting as the water-soluble support material, is printed at a temperature of 190 ◦ C. The layer height is 0.3 mm, and the infill is 10 percent. Following this, the completed prints are immersed in warm water at a temperature range of 40–50 ◦ Celsius, with continuous water circulation, for a duration of 24 h, until all supporting structures have completely disintegrated. Fig. 7 and the two videos below illustrate the printing process of the heart models and the polymerase-DNA complex. 4.2. Innovative DAP-Hybrid-IDEX configuration in DAP V1 multicolor 3D printer 3. Results In the realm of multicolor or multi-material 3D printing, there exist two primary configurations: single nozzle and multiple nozzles. Regarding multiple nozzle designs, there are three types of configura­ tions: IDEX (two independent extruders or printheads), fixed multiple nozzles on a printhead, and tool changer 3D printers. Presently, the X1-C (Bambu Lab Co., Shenzhen, China), the most sophisticated FDM printer, employs a solitary nozzle equipped with a retract and purge system to produce prints in a maximum of 16 colors. The device is outfitted with advanced sensors and lightweight components, facilitating The printing of all tests with our DAP V1 multicolor 3D printer has been successfully completed. The first test is to evaluate the printer’s endurance and its capacity to reproduce various macroscopic-scale anatomical details, such as the heart. Two distinct print jobs were used to print the four heart models. The simultaneous printing of two models required an estimated duration of 45 h per print job. The heart models exhibit an appropriate size, with dimensions of roughly 18 × 15 6 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 Fig. 5. 3D segmentation. Footnotes: Segmentation of the heart chambers and the great vessels on CT images (A) and on 3D reconstruction (B). Segmentation of the vessel walls and heart chambers in anterior view (C) and in posterior view (D). Fig. 6. Test prints. Footnotes: From left to right: Healthy heart, Tetralogy of Fallot, Transposition of the great arteries and DNA polymerase models. exceptionally rapid printing speeds. Nevertheless, the current system lacks the capability to incorporate a second printhead, hence impeding the printing of PVA material in conjunction with other materials. The ultimate goal of our research is to find an affordable and sustainable solution to print biomedical models in multiple colors with intricate geometry, which requires water-soluble support material. FDM tech­ nology offers the potential for printing in multiple colors and different materials at a low cost; however, there is still a lack of an efficient and robust system on the market that can address our needs. We successfully combined multicolor 3D printing with single nozzle and IDEX technol­ ogy, which we call "DAP-Hybrid-IDEX” in our DAP V1 printer. Table 2 and Fig. 2 [17,18] show a direct comparison between our "DAP-Hy­ brid-IDEX" and other multiple nozzle configurations. Table 3 compares our DAP V1 printer with the Bambu Lab X1C Combo and A1 Mini Combo. Of course, the DAP-Hybrid-IDEX system is not perfect in terms of color transition duration, material waste, and the number of printable materials. Nevertheless, we consider it the most advantageous solution to meet our requirements. Using the DAP-Hybrid-IDEX configuration enables simultaneous printing with two materials, eliminating the need to purge expensive PVA during material transitions. Additionally, it reduces the likelihood of nozzle jamming compared to concurrent 7 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 Fig. 7. The printing process of the heart models. Footnotes: A: The multicolor printhead is active, B: The water-soluble support material printhead is active. The water-soluble support structures are yellowish and in zigzag pattern. Fig. 8. Finished test prints of heart models. Footnotes: From left to right: Healthy heart, Tetralogy of Fallot, Transposition of the great arteries and heart failure from CT scan. A: front view, B: left side view, C: back view. 8 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 Fig. 9. Finished test print of DNA polymerase molecule model. Footnotes: A: model with water-soluble support structures. B,C: model after dissolving support structures in water. Table 2 Comparison of different FDM 3D printing with multiple nozzle configurations. Print head configuration DAP-Hybrid-IDEX IDEX Fixed multiple nozzles on a printhead Tools changer Typical printer DAP V1 Ultimaker S5 Original Prusa XL Number of colors Quality of color Up to 10 May cause color bleeding due to insufficient purging 30 s 0.09 to 0.12 g per color transition 2 Low Higher Sovol SV04 2 High Up to 4 Oozing unwanted color Up to 6 High 10 s No 2 Low Higher 10 s No Up to 6 Low Lower if nozzles are not calibrated properly Complex Complex Higher Higher Color transition time Material for purging Number of materials Weight of printhead Printing accuracy Nozzles offset calibration Ease of use Cost of maintenance Energy consumption Simple Simple Instantly No Up to 4 High Lower if nozzles are not calibrated properly Complex Simple Lower Lower Simple Lower Lower Complex Higher Higher printing of PLA and PVA with the same printhead. Furthermore, DAPHybrid-IDEX enables multicolor printing, enhancing the versatility of our printing capabilities. Since the open-source Klipper firmware allows the connection of multiple MKS Monster 8 controller boards, the maximum number of colors is constrained only by the number of inlets on the filament splitter. The utilization of DAP-Hybrid-IDEX yields a reduced number of printheads, hence diminishing the intricacy of the printhead offset calibration procedure and the expenses associated with the operation and upkeep of the system in comparison to a tool changer 3D printer. On the other hand, a tool changer 3D printer necessitates a distinct printhead for every color and material. The operation of our DAP-Hybrid-IDEX in the DAP V1 printer is more straightforward and facilitates easier calibration of the printhead offset compared to a tool changer 3D printer. We also incorporate closed-loop motors into the X and Y axes, enabling the printer to autonomously correct the printhead’s position in the event of a collision with an obstruction along its trajec­ tory, thereby minimizing layer shifts. On a tool changer 3D printer, the procedure of adjusting the misalignment of five printheads can be a laborious and time-intensive task. Multiple nozzles design often lead to inaccuracies in printing. The maintenance expenses associated with a tool changer printer are elevated due to the increased number of mechanical components involved. A tool changer 3D printer is typically limited to only 6 print­ heads due to insufficient space on the printer frame. Conversely, this printer can be integrated with CoreXY kinematics, enabling extremely fast printing. A tool changer 3D printer alters color by changing the printheads, eliminating the need for filament purging. Each color change occurs within just 10 s, in contrast to the minimum of 30 s required by our DAP-Hybrid-IDEX. Our printer would require >8 h to change filaments for a print that had 1000 color transitions. To enhance efficiency, we can either decrease the length of the printhead or increase the filament retraction speed. It is important to acknowledge that the quantity of filament purging during color alterations is contingent only upon the number of colors employed in a particular printing task and the number of printed layers. This implies that, when considering an equal number of layers, the quantity of purge material and the duration required for color changes in a print job that prints many items concurrently and a print job that prints only one object are equivalent. Based on the aforementioned discovery, it is possible to achieve an in­ direct reduction in print time for each model by augmenting the quantity of models produced concurrently, hence resulting in a decrease in manufacturing costs. To achieve that, the printer must operate contin­ uously and dependably for several days. Minor faults, such as electronics overheating, unstable voltage, loose belt drives, loose extruder screws, or layer shifts, could cause significant damage and potentially ruin the entire print job throughout a lengthy printing process. Hence, it is imperative to incorporate sufficient cooling fans and an uninterruptible power supply unit. A time-lapse camera should also be incorporated to oversee the print work, enabling prompt intervention in the event of a possible print failure. Additionally, it aids in the identification of error during print job for later assessment and improvement. Lastly, akin to aviation, 3D printers necessitate regular maintenance and a thorough 9 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 Table 3 A direct comparison of our DAP V1 printer with the Bambu Lab X1C Combo and the A1 Mini Combo. Printer General Material and color Motion system Operating system Build volume Number of colors Quality of color Color transition time Material for purging Supported materials Print head and nozzles Sensors Number of materials in a single print Number of print head Offset calibration between nozzles Max speed of print head Max acceleration of tool head Camera Filament Run Out Sensor Filament Odometry Power Loss Recover Filament Tangle Sensor Suitability for Number of colors biomedical model Combination of multicolor and waterprinting soluble support material printing Print volume Maintenance (machine components) Pricing DAP V1 Bambu Lab X1C combo Bambu Lab A1 mini combo Hybrid CoreXY Klipper (open source) 300 × 300 × 300 mm 7 (upgradable to 10) Acceptable 30 s 0.09 to 0.12 g per color transition (adjustable) PLA, PETG, TPU, PVA CoreXY Bambu Lab (proprietary) 256 × 256 × 256 mm 4 (upgradable to 16) High 75 - 90 s 0.22 to 0.35 g per color transition (adjustable) PLA, PETG, TPU, ABS, ASA, PVA, PET, PA, PC, Carbon/ Glass Fiber Reinforced Polymer 1 1 No 500 mm/s 20 m/s² Up to 1080P, Timelapse supported Cartersian Bambu Lab (proprietary) 180 × 180 × 180 mm 4 (non-upgradable) High 75 - 90 s 0.22 to 0.35 g per color transition (adjustable) PLA, PETG, TPU, PVA 2 2 (independent extruders) Simple 200 mm/s 5 m/s² Up to 1080P, Timelapse supported Yes No Yes No Sufficient Suitable Yes Yes Yes Yes Sufficient Unsuitable Sufficient Flexible Barely sufficient Sourced from the manufacturer 847 USD with seven colors Combo with four colors: 1349 USD Plus 309 USD for each 4 colors added 1 1 No 500 mm/s 10 m/s² Up to 1080P, Timelapse supported Yes Yes Yes Yes Insufficient Unsuitable Insufficient Sourced from the manufacturer Combo with four colors: 349 USD would decrease the cost to $20.5 USD per model, with the print job lasting for 70 h. Similarly, printing 10 DNA polymerase models simul­ taneously would reduce the cost to $9.5 USD for each model, and the print job would last for 69 h. Eduardo used a single color, single material FDM 3D printer to print biomolecular models [7]. The efficacy of this approach is limited to models of relatively modest complexity, as the support structures necessitate manual trimming using cutting pliers. Furthermore, manually painting the biomolecular model requires sig­ nificant labor and may not always be practical for intricate molecular structures. checklist before any operation in order to optimize the success of prints. 4.3. Printing quality of DAP V1 multicolor 3D printer The four printed heart models have a uniform size, measuring around 18 × 15 × 10 cm (Fig. 8). Fig. 9 depicts a DNA polymerase molecule model that is both visually appealing and affordable for health science education. These models meet the need for visual and tangible aids in biomedical education. 4.4. Economics and broader significance of our DAP V1 multicolor 3D printer 4.5. Limitations Our printer has several limitations. During color transitions, slight color bleeding from the preceding color is still present. This issue can be mitigated by increasing filament purging during each color change. For example, the Bambu Lab printer uses three times the purging amount compared to ours, resulting in better color quality, but this comes at the cost of longer print times. our printer has a slower print speed due to the heavier gantry carrying two printheads. Although the open-source Klipper firmware offers a resonance compensation feature to cancel machine vibrations at high print speeds, the printer itself lacks advanced sensors that could further optimize print quality and enhance overall performance. As mentioned above, our focus is solely on creating colorful and intricate biomedical models for visualization purposes in anatomy, biology courses, or surgery planning. Producing realistic models for medical procedures training, which require mimicking human tissue colors and properties, is not within the scope of this study. In developing countries, state-of-the-art printing technologies like PolyJet are often utilized in medical education, with a printer costing over $200,000 USD. For instance, in a study, the heart model printed with an Object 500 Connex3 PolyJet printer incurred costs exceeding $400 USD [19]. Another study employed a Stratasys J750 printer to produce a skull base model for teaching, which cost over $1600 USD [20], making it un­ suitable for LMICs. In contrast, the cost to build our DAP V1 printer is less than $1000 USD. For comparison, the Bambu Lab X1C costs $1658 for the 8-color upgrade version, while the A1 Mini costs $349 for the non-upgradable 4-color printing. Neither printer includes a second printhead for dissolvable support material. Our printer can be easily installed in any educational facility with minimal environmental impact. Our $30 USD heart models, despite some color bleeding, exhibit decent surface color quality and can to a certain extent fulfill the learning outcomes of our students. Given the same number of layers, since the amount of material used for purging remains constant regardless of the number of models printed at a time, we can further reduce manufacturing costs simply by increasing the number of models printed simultaneously. For instance, printing 4 hearts concurrently 5. Conclusions In this study, we successfully developed and tested the DAP V1 multicolor FDM 3D printer, a novel configuration designed for produc­ ing intricate biomedical and anatomical models with multicolor and water-soluble support material printing capability. The printed models from various input sources demonstrate the printer’s effectiveness, outperforming comparable FDM printers currently available on the market. While the print quality remains inferior to material jetting technol­ ogy, the results are sufficient for biomedical education. More impor­ tantly, our system provides significant economic advantages, with lower 10 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 (continued ) machine acquisition and operating expenses. The DAP-Hybrid-IDEX configuration becomes increasingly cost-efficient for larger batch pro­ duction, which is crucial in resource-limited settings. Future optimizations in printer frame, motion system, sensors, firmware, and software could further enhance performance, color quality, print speed and reliability, potentially elevating the system to an industrial-grade level. Our work presents a transformative solution to make biomedical 3D printing accessible, affordable, and customizable for most educational facilities. This frugal innovation facilitates wider adoption, allowing institutions to produce learning materials on demand and improve the quality of health science education in LMICs. Glossary Glossary Abbreviation Definition Low and middle-income countries LMICs Fused Deposition Filament FDM Hybrid CoreXY kinematics DAP-Hybrid-IDEX Independent extruders IDEX In 2023, low-income countries are defined as having a gross national income (GNI) per capita of $1145 or less, while lower-middle-income countries have a GNI per capita ranging from $1146 to $4515. A 3D printing process that uses thermoplastic filament, extruding it layer by layer onto a build plate to form a three-dimensional object. A variation of the CoreXY motion system commonly used in 3D printers. Our printer’s configuration combines multicolor 3D printing with a single nozzle and IDEX technology Independent extruders are a 3D printing system where two printheads operate separately on the same X axis, allowing for two materials printing, color changes, or simultaneous production of two objects. The integration of both direct drive extruder and Bowden drive extruder. A type of FDM 3D printer configuration that can transition between various printheads by magnetic grabbing and docking mechanism. Vat photopolymerization is a 3D printing process that uses light to cure liquid photopolymer resin in a vat, solidifying it layer by layer to form a three-dimensional object. Polylactic acid (PLA) is a biodegradable thermoplastic derived from renewable resources like corn starch or sugarcane, commonly used in 3D printing for its ease of use, low melting temperature, and eco-friendly properties. Polyvinyl alcohol (PVA) is a watersoluble synthetic polymer often used in 3D printing as a support material, allowing for easy removal by dissolving in water without affecting the main printed object. An organization established to develop technical standards for the manufacturing of electrical and medical imaging equipment. Stepper motors are electric motors that move in precise, fixed steps, allowing for accurate control of position and speed, commonly used in 3D printers and CNC machines. Hybrid-extrusion Tool-changer 3D printers Vat photopolymerization Polylactic acid PLA Polyvinyl alcohol PVA National Electrical Manufacturers Association NEMA Stepper motors Glossary Abbreviation Closed-loop stepper motors DAP V1 ECG-gated Digital Imaging and Communications in Medicine DICOM Hounsfield unit HU 3D image segmentation AttributionNonCommercialShareAlike 4.0 International (CC BY-NC-SA 4.0) National Institutes of Health NIH Definition Closed-loop stepper motors use feedback from sensors to monitor and adjust their position in real time, providing higher accuracy, torque, and efficiency compared to open-loop stepper systems. The name of our constructed version 1 3D printer An ECG-gated CT scan is a type of computed tomography that synchronizes image acquisition with the heart’s electrical activity, reducing motion artifacts and providing clearer images of the heart and blood vessels. A standard protocol for processing, storing, and transmitting medical images across various medical imaging devices and systems. A measurement scale in CT imaging that quantifies radiodensity, which is essential for 3D segmentation. The process of demarcating anatomical structures within medical scans to form 3D digital models. Creative Commons license allowing others to remix, adapt, and build upon the work noncommercially, as long as they credit the creator and license their new creations under identical terms. The NIH 3D Print Exchange is a platform provided by the National Institutes of Health offering open 3D models related to biomedical science Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Declaration of generative AI and AI-assisted technologies in the writing process During the preparation of this work, we used ChatGPT 4 in the writing process to improve the readability and language of the manu­ script. After using this tool, we reviewed and edited the content as needed and took full responsibility for the content of the published article. Acknowledgements We gratefully acknowledge Prof. An Le Pham and Grants and Inno­ vation Center for their invaluable support and contributions to our study. Prof. An‘s generosity in providing both essential materials and devices was crucial in facilitating our research efforts. Funding sources This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. (continued on next column) 11 D.M. Lu et al. Annals of 3D Printed Medicine 18 (2025) 100201 Supplementary materials [10] Chen MY, Skewes J, Woodruff MA, Dasgupta P, Rukin NJ. Multi-colour extrusion fused deposition modelling: a low-cost 3D printing method for anatomical prostate cancer models. Sci Rep 2020;10(1):10004. https://doi.org/10.1038/s41598-02067082-7. [11] Chung M, Radacsi N, Robert C, McCarthy ED, Callanan A, Conlisk N, et al. On the optimization of low-cost FDM 3D printers for accurate replication of patientspecific abdominal aortic aneurysm geometry. 3D Print Med 2018;4(1):2. https:// doi.org/10.1186/s41205-017-0023-2. [12] Meyer-Szary J, Luis MS, Mikulski S, Patel A, Schulz F, Tretiakow D, et al. The role of 3D printing in planning complex medical procedures and training of medical professionals-cross-sectional multispecialty review. Int J Environ Res Public Health 2022;19(6). https://doi.org/10.3390/ijerph19063331. [13] Mixed corexy and hybrid-corexy kinematic for single toolhead [Available from: https://klipper.discourse.group/t/mixed-corexy-and-hybrid-corexy-kinematic-fo r-single-toolhead/4375. [14] Fedorov A, Beichel R, Kalpathy-Cramer J, Finet J, Fillion-Robin JC, Pujol S, et al. 3D Slicer as an image computing platform for the Quantitative Imaging Network. Magn Reson Imaging 2012;30(9):1323–41. https://doi.org/10.1016/j. mri.2012.05.001. [15] Groningen UMC. [Available from: https://sketchfab.com/3d-models/healthy-he art-and-lungs-5c62cd4d4ba04243be1062d2263d3ef0. [16] 3D N, (NIAID) NIoAaID. [Available from: https://3dnih.gov/entries/3D PX-015454. [17] Why you need independent dual extrusion for high-temp 3D printing [Available from: https://www.aon3d.com/hardware/independent-dual-extrusion-for-high-te mp-3d-printing/. [18] Original Prusa XL semi-assembled single-toolhead 3D printer [Available from: htt ps://www.prusa3d.com/en/product/original-prusa-xl-semi-assembled-single-too lhead-3d-printer/. [19] Radzi S, Tan HKJ, Tan GJS, Yeong WY, Ferenczi MA, Low-Beer N, et al. Development of a three-dimensional printed heart from computed tomography images of a plastinated specimen for learning anatomy. Anat Cell Biol 2020;53(1): 48–57. https://doi.org/10.5115/acb.19.153. [20] Saleh Y, Piper R, Richard M, Jeyaretna S, Cosker T. Designing a 3D printed model of the skull-base: a collaboration between clinicians and industry. J Med Educ Curricul Develop 2022;9. https://doi.org/10.1177/23821205221080703. 23821205221080703. Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.stlm.2025.100201. References [1] Ballard DH, Mills P, Duszak Jr R, Weisman JA, Rybicki FJ, Woodard PK. Medical 3D printing cost-savings in orthopedic and maxillofacial surgery: cost analysis of operating room time saved with 3D printed anatomic models and surgical guides. Acad Radiol 2020;27(8):1103–13. https://doi.org/10.1016/j.acra.2019.08.011. [2] Tiruneh C. Acute adverse effects of formaldehyde treated cadaver on new innovative medical students and anatomy staff members in the dissection hall at Wollo University, Northeast Ethiopia. Adv Med Educ Pract 2021;12:41–7. https:// doi.org/10.2147/amep.S291755. [3] Demiryürek D, Bayramoğlu A, Ustaçelebi S. Infective agents in fixed human cadavers: a brief review and suggested guidelines. Anat Rec 2002;269(4):194–7. https://doi.org/10.1002/ar.10143. [4] Tejo-Otero A, Buj-Corral I, Fenollosa-Artés F. 3D Printing in medicine for preoperative surgical planning: a review. Ann Biomed Eng 2020;48(2):536–55. https://doi.org/10.1007/s10439-019-02411-0. [5] Garcia J, Yang Z, Mongrain R, Leask RL, Lachapelle K. 3D printing materials and their use in medical education: a review of current technology and trends for the future. BMJ Simulat Technol Enhanc Learn 2018;4(1):27–40. https://doi.org/ 10.1136/bmjstel-2017-000234. [6] Lohning AE, Hall S, Dukie S. Enhancing understanding in biochemistry using 3D printing and cheminformatics technologies: a student perspective. J Chem Educ 2019;96(11):2497–502. https://doi.org/10.1021/acs.jchemed.8b00965. [7] Da Veiga Beltrame E, Tyrwhitt-Drake J, Roy I, Shalaby R, Suckale J, Pomeranz Krummel D. 3D Printing of biomolecular models for research and pedagogy. J Visualiz Exper: JoVE 2017;(121). 10.3791/55427. [8] Kim GB, Lee S, Kim H, Yang DH, Kim YH, Kyung YS, et al. Three-dimensional printing: basic principles and applications in medicine and radiology. Korea J Radiol 2016;17(2):182–97. 10.3348/kjr.2016.17.2.182. [9] Sun Z, Wong YH, Yeong CH. Patient-specific 3D-printed low-cost models in medical education and clinical practice. Micromach (Basel) 2023;14(2). 10.3390/ mi14020464. 12
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