Learning Dogfish Shark Anatomy Using 3D-Printed Models: A Feasibility Study

Abstract

3D-printed models (3DPMs) are being increasingly utilized as learning aids in medical and comparative anatomy education. Research suggests that 3DPMs can significantly improve students’ accuracy in recognizing important anatomical landmarks and provide a low-cost alternative to expensive or fragile specimens. The use of 3DPMs can also alleviate conservation concerns for certain endangered species. Additionally, 3DPMs provide a unique interactive experience in viewing structures that may otherwise be difficult to observe or handle directly by students. A novel 3DPM has been developed to help biology students learn the anatomy of the Squalus acanthias (S. acanthias), or dogfish shark, chondrocranium and brain. This feasibility study evaluated the perceived utility of these new 3DPMs in an undergraduate-level comparative chordate anatomy lab (BIOL 351) at Iowa State University in Spring 2023. Students responded to a questionnaire comprising Likert and open-ended long-form questions that uncovered their perceptions of and experience interacting with the 3DPMs. Two separate surveys were administered, one for the chondrocranium (29 responses) and one for the brain (16 responses). Students indicated a strong preference for using the 3DPMs as compared to the dissected and preserved specimens, citing the 3DPMs’ size, durability, and the ability to handle and rotate them as beneficial for understanding relevant anatomy. Further investigation is required to understand how the 3DPM improves students’ learning outcomes; however, this study confirms the model’s utility and biology students’ desire to have access to additional 3DPMs in the comparative chordate anatomy lab.

1. Introduction

The species Squalus acanthias (S. acanthias), commonly known as the spiny dogfish or dogfish shark, has long been used in the anatomy lab to explore comparative chordate anatomy. As a model organism, S. acanthias helps students understand the body plan of chondrichthyans, the class of jawed, cartilaginous fish that includes sharks, rays, and skates. S. acanthias also serves as an important character in understanding the evolutionary relationships between chordates; its chondrocranium (cartilaginous skull) and brain allow students to better understand the evolution of the bony skull and brain regions in vertebrates [1]. However, dissected or preserved specimens of the dogfish shark may be hard to visualize: the chondrocranium is prone to desiccation and can be difficult to dissect out fully to view from all angles; similarly, the brain is fragile and easily damaged during dissection. Specimens preserved in resin blocks and formaldehyde solution may be old and worn, rendering it difficult to view small, detailed anatomic structures.

Though popular in the biology dissection lab, dogfish sharks are slow to mature, and certain populations require careful management. The last 5–10 years have seen a decline due to overfishing, and the S. acanthias was listed as vulnerable according to the International Union for Conservation of Nature (IUCN) in 2023 [2,3]. Although animal dissections are required by many biology degree programs, the animals used for these educational needs are typically caught in the wild, disrupting the ecosystems in which they reside [4]. To mitigate the ecological damage of collecting live specimens, and to provide a better means of visualizing and interacting with dogfish shark neuroanatomy, we propose 3D-printed models as an effective supplement.

The interactive 3DPMs of the dogfish shark chondrocranium and brain aimed to achieve three learning objectives within the comparative chordate anatomy lab: (1) external anatomy of the dogfish chondrocranium, including foramina and other anatomical landmarks; (2) cranial nerves of the S. acanthias brain; and (3) distinct regions of the S. acanthias brain (see Supplementary Materials for specifics, as they are provided in Figures S1 and S2).

The neuroanatomy of the dogfish shark requires the observation of structures that are particularly fragile and difficult to view, given their thin, cartilaginous nature and proclivity for desiccation—namely, the chondrocranium itself and specific structures of the brain, including the cranial nerves and olfactory bulbs. Specific design choices in the development of the dogfish shark 3DPMs were made to provide students with tangible, interactive models of the fragile brain and chondrocranium which still aim to facilitate the understanding of the three learning objectives listed previously.

3D-Printed Models Support Learning

3D-printed models (3DPM) are becoming increasingly utilized as learning aids in medical and comparative anatomy education and offer several benefits [5,6,7]. They allow students to handle otherwise fragile or precious specimens without the risk of damage [6]. Additionally, 3DPMs can be printed at a larger-than-life scale, allowing for smaller or more detailed structures to be observed with greater ease [8,9]. Furthermore, 3DPMs, referred to by Krontiris-Litowitz as “manipulatives” [10], also offer a tactile, interactive experience since students can hold, rotate, and view them from multiple angles, take them apart and piece them back together, and directly feel the topology of specific anatomic landmarks and structures as a whole. Students, therefore, can develop a better visuospatial understanding of anatomic structures and morphology and even visualize structures that are otherwise difficult or impossible to observe directly in a real specimen [10,11].

Evidence that the spatial, tactile, and interactive learning afforded by 3DPMs can significantly improve students’ learning outcomes, while providing a low-cost alternative to more expensive or difficult-to-obtain specimens, has furthered their prevalence in the classroom [5,7,11,12]. Students who used 3DPMs were able to more quickly and accurately identify anatomic structures, receiving higher test scores [5,10,13], and they self-reported increased satisfaction while learning content-heavy material as compared to students who used traditional visual aids such as static diagrams [5,7]. Similar findings have been documented in other science-subject areas, including molecular biology [14,15], chemistry, and neurophysiology [10].

Student satisfaction and engagement in a content-heavy course can be difficult to foster, yet these are important factors for improving learning and the overall student experience [16,17,18]. Thus, 3DPMs can offer students a novel and fun way of visualizing, interacting with, and learning anatomy. We approach student satisfaction in this study as indicated by: perceived utility of 3DPMs, perceived learnability of the relevant anatomy using the models, and increased engagement during the lab session while exploring and learning about chordate anatomy.

This feasibility study sought to understand the utility of a novel, interactive, 3D-printed model of the S. acanthias chondrocranium and brain to improve student learning in the comparative chordate anatomy lab. The following research questions (RQ) guided this study:

RQ1: 

Are 3D-printed models a viable supplement to standard learning aids, including dissected specimens, in the chordate anatomy lab?

RQ2: 

a. What design features of a 3D-printed anatomical model do students perceive as effective for learning and understanding anatomy?

b. How can a 3D-printed model of the dogfish shark chondrocranium and brain be designed to be interactive while retaining accurate representation of anatomy?

RQ3: 

Do students enjoy using tangible 3D models to learn chordate anatomy and find them useful additions to the lab?

2. Materials and Methods

This project was conducted in two phases. Phase 1: production (including 3D modeling and fabrication), and phase 2: study design (including data collection and analysis). The overall methods are represented in the flowchart below (Figure 1).

2.1. Production

2.1.1. 3D Modeling

Photogrammetry data of the dogfish shark chondrocranium were obtained from Thomas et al. (2016) as an STL file [12] (see Figure 1). The scan was reconstructed and refined in Maxon’s ZBrush using real specimen dissections in the chordate lab and The Dissection of Vertebrates by De Iuliis and Pulerà (2019) as additional reference material [1]. Several structures required reconstruction that were not visible or resolved in the initial scan, specifically the nasal capsules, the endolymphatic fossa, various foramina (i.e., glosso-pharyngeal, hyomandibular, epiphyseal, trigemino-facial, trochlear), and internal spaces indicating the location of the semicircular canals. The digital 3D model was scaled up to twice the size of the scanned specimen (roughly 98 mm in length and 46 mm wide) to allow for better visibility of small anatomical landmarks. The 3D model was then cut in half transversely to create a superior and inferior chondrocranium piece. A 3.8 mm × 2 mm cylindrical depression was modeled at opposing corners on each half of the bisected chondrocranium (four in total on each half) for later insertion of 3.2 mm × 1.6 mm Magcraft rare-earth magnets in the fabrication stage; these paired magnets hold the two halves of the 3D-printed chondrocranium together. Boolean operations in Maxon ZBrush were used to create the chondrocranium’s cranial cavity, where the brain resides. Additional tolerance was modeled into this cavity to allow the brain model to fit between the two chondrocranium halves when put together.

The 3D model of the brain was created “from scratch”: preliminary sketches of the brain and cranial nerves (see Figure 1) were drawn based on references from lab dissections and preserved specimens, as well as the same anatomical text by De Iuliis and Pulerà (2019) [1]. The size of the 3D-modeled brain was scaled to fit the chondrocranium 3D model, and, therefore, was also twice the size of a typical S. acanthias brain.

Close collaboration with instructors in the comparative chordate anatomy course at Iowa State University ensured model accuracy and inclusion of all important anatomical features and landmarks of the chondrocranium and brain to meet the learning objectives for the lab.

2.1.2. 3D-Printing and Fabrication

Initial prototypes of the chondrocranium halves and brain were printed on Ultimaker S5 3D printers using 2.5 mm clear Polylactic Acid (PLA) 3D-printing filament. The 3D model STL files were uploaded to Ultimaker Cura, a 3D-printing (3DP) prep software, and set up to print with a 10% infill and a resolution of 0.1 mm; supports were automatically generated by Cura. The 3D-printed prototypes were reviewed by comparative chordate anatomy instructors to ensure all necessary structures were visible and clear. Additional issues related to model size and fit were addressed at this stage before final printing. The final, corrected models were printed on Formlabs 3+ SLA printers using Formlabs Clear V4 resin. The STL files were uploaded to Formlabs PreForm software for print preparation, set up to print at a resolution of 0.1 mm with automatically-generated scaffolding. The size of the models was decreased by 5% (therefore printed at a 1.95:1 scale relative to life-size) due to sizing constraints of the available Formlabs 3+ build plate. After printing, these models were washed with 95% isopropyl alcohol for 10 min in the Formlabs Form Wash and cured with the Formlabs Form Cure for 10–12 min. Four 3.2 mm × 1.6 mm Magcraft rare-earth magnets were glued into each of the depressions on each chondrocranium half using super glue. The resin-printed brain models were color-coded using acrylic paint pens and sealed with a clear coat of Krylon spray varnish.

2.1.3. Design Considerations

Specific design features were taken into account in the development of the educational dogfish chondrocranium and brain 3DPMs. We hypothesized that these design features would increase the perceived utility of the 3DPMs as tools for learning dogfish shark neuroanatomy by biology students. These design feature include the (1) size of the models, (2) interactivity of brain and chondrocranium, (3) material of final models, and (4) color coding. The inclusion of these design features aimed to ensure that the user achieved the three learning objectives.

The chondrocranium and brain were printed at approximately 2× the size of an average S. acanthias specimen. Though they can vary in size, dissected and preserved specimens are often less than 100 mm across, which can make it difficult to view small landmarks. Increasing the size of the 3DPMs allows the user to more easily view very small features, including the cranial nerve foramina externally visible in the chondrocranium, which was one of the required learning objectives. By increasing the size, students would be able to view small structures more easily but still be able to hold the 3DPMs in their hands. By not over-enlarging the 3DPMs, students may be more easily able to make associations between the model and the actual appearance of a dissected or preserved specimen.

The interactivity of the 3DPMs of the brain and chondrocranium aimed to allow users to physically handle the two structures, which is difficult or impossible due to the fragility of the dissected or preserved specimens. Similar studies found students preferred physically interacting with anatomical models, and it led to improved learning outcomes [19,20]; this informed the design of the dogfish shark chondrocranium and brain. Allowing the brain to fit within the chondrocranium halves further solidified the association of certain chondrocranium features with brain structures, including cranial nerves to relevant foramina in the chondrocranium.

The material nature of the models was another important design consideration aimed to increase the perceived utility of the 3DPMs; resin was chosen as the final printing material because of its higher-resolution capability, smooth texture once cured, and material quality which imitates the semi-transparent cartilaginous chondrocranium, allowing the brain within to be partially visible. The higher resolution allows for more surface detail, and, therefore, more fully resolved modeling of small and difficult-to-view anatomical structures, namely, the chondrocranium foramina and cranial nerves. The visibility of the brain through the chondrocranium was intended to allow students to understand brain regions and their associated locations within the chondrocranium as viewed in situ; for example, the opaque olfactory bulbs are visible through the semi-transparent nasal capsules of the chondrocranium.

Color coding has been established as an effective means to differentiate anatomical structures in 3D models [21]. Relevant brain regions were assigned a color and painted accordingly on the resin brain model, aiming to improve discernability between brain regions and increase the utility of the models. Additionally, the opaque color coding of the brain model allowed it to be viewed through the semi-transparent chondrocranium; as mentioned above, we posited this visibility would increase perceived student utility.

2.2. Study Design

2.2.1. Study Demographic

Students who were enrolled in the Spring 2023 comparative chordate anatomy lab course were invited to participate in this study. No students had taken this lab course previously or had familiarity with the material. No additional demographic information about participants was collected or used in this study.

2.2.2. Data Collection: Questionnaires

Two separate, anonymous questionnaires, one regarding the chondrocranium (Table S1) and one regarding the brain (Table S2), were administered during the classroom labs in which the 3DPMs were introduced; as the lesson plans for the chondrocranium and brain were delivered in separate lab sessions over a period of two weeks, the questionnaires were likewise administered separately. Quantitative and qualitative user feedback was collected to gauge various aspects of perceived utility and student satisfaction with the 3DPMs as learning aids. Quantitative feedback was collected through a series of Likert questions (seven questions related to the chondrocranium and eight questions related to the brain). All Likert questions were presented on a five-point scale: 1 = strongly disagree, 2 = disagree, 3 = neutral, 4 = agree, and 5 = strongly agree. Three open-form questions included in both questionnaires gave participants the opportunity to write qualitative responses and feedback regarding the strengths and weaknesses of the interactive models as learning tools.

2.2.3. Chordate Lab Lesson Plan

The typical set-up in the lab for learning the neuroanatomy of the S. acanthias includes specimens that are pre-dissected by teaching assistants, preserved specimens in resin and formaldehyde, and lab manuals with labeled diagrams and dissection photos. Students are provided with a list of terms they are required to know and spend the lab session exploring the anatomy using these references. The sessions during which this study ran introduced the 3DPMs by placing one model at each of the four lab benches, along with a printed copy of the visual diagram/key specifically designed for the models (see Supplementary Materials). The 3DPMs were provided in parallel to the preserved and dissected specimens of the dogfish shark available to students. The complete interactive model of the chondrocranium and brain was given to students regardless of the topic focus being reviewed in a given lab session (i.e., chondrocranium in week 1 or brain in week 2). Students were encouraged to interact with the models and use them to understand the relevant anatomical landmarks and features of the S. acanthias chondrocranium and brain before completing the questionnaire. No further training in the use of the models was provided.

Voluntary questionnaires were distributed to students inthe Comparative Chordate Anatomy lab at Iowa State University in February 2023. Students who were interested in participating in the study completed and returned the questionnaires at the end of the lab period. Consent was obtained at the time of questionnaire completion; these questionnaires were anonymous, and responses cannot be traced back to any individual student. Ethics was approved through an expedited review by the Institutional Review Board at Iowa State University (IRB ID #22-130).

2.2.4. Data Analysis

Students were assigned a de-identifying participant code to correlate responses between the two questionnaires (e.g., p# for the first and p#b for the second) if completed and returned. Quantitative and qualitative responses from each returned questionnaire were transcribed electronically and organized in a spreadsheet. Average Likert scores and standard deviation for each of the quantitative questions were calculated. Although related, the long-form responses for each questionnaire (i.e., chondrocranium and brain) were analyzed separately.

Qualitative responses were transcribed as written. Basic thematic analysis and keyword clustering were performed to group responses according to the strengths or weaknesses of various design characteristics of the 3DPMs, as well as general comments.

3. Results

3.1. 3D Models

Four identical 3D-printed models of the interactive chondrocranium and brain were fabricated in clear resin (Figure 2).

The chondrocranium measured 110.5 mm by 97.25 mm by 174.4 mm, while the brain measured 83.5 mm by 74 mm by 134.4 mm. The majority of the production timeline was dedicated to modeling the brain and chondrocranium in Maxon ZBrush. The 3D reconstruction represents an “idealized” version of the exterior chondrocranium, allowing for greater clarity of structures that were not previously resolved or visible based on the photogrammetry data from Thomas et al. (2016) [12], and the interior was modeled to allow for easy interaction with the 3D-printed brain. Additional supplementary visual materials were created, including a labeled 3D render of the chondrocranium model from the left lateral, dorsal, and posterior views (Figure S1), and a labeled color key for the brain model showing the left lateral, dorsal, and ventral views (Figure S2). These one-page guides were printed and distributed to students along with the 3DPMs in the lab.

3.2. Study Demographic

A total of 32 undergraduate students were enrolled in the Spring 2023 comparative chordate anatomy lab course; no students had taken this lab course previously or had familiarity with the material. No additional demographic information about participants was collected or used in this study. In week 1 (chondrocranium), 29 students returned the questionnaire (90% response rate); in week 2 (brain), 16 students returned completed questionnaires (50% response rate).

3.3. Student Responses Regarding Utility of the Chondrocranium 3DPM

Results from the chondrocranium questionnaire are shown in

Table 1. Summary of questionnaire responses regarding chondrocranium 3DPM utility.

Statement	Average (±SD)	Example Qualitative Responses
The 3D models accurately depict the anatomical features I need to know.	4.62 (±0.62)	“It was detailed enough to see, but not overwhelmingly detailed” (p21) “The first visceral arch could be added so that the user knows which side is ventral and dorsal” (p7)
The interaction between the 3D chondrocranium and brain was helpful in understanding the anatomy of the chondrocranium.	4.79 (±0.41)	“The ability to take it apart is helpful to visualize structures you otherwise couldn’t see as well” (p16) “Being able to take it apart and see how and where everything fits into place” (p23) “It’s magnetic, pretty cool.” (p18b)
The ability to physically handle the chondrocranium was helpful in understanding its anatomical features.	4.83 (±0.38)	“being able to handle it is very helpful in remembering the different parts in relation to each other” (p18) “I love how you can take it apart and rotate it to see all the structures” (p3)
The size of the model was appropriate for identifying all the necessary structures.	4.66 (±0.48)	“It gives students a closer look at the different anatomical features.” (p14) “good size; might be interesting to print @ real size”(p11) “It’s a little small” (p13)
Compared to the preserved specimen, I am less worried about damaging or breaking the 3D model.	4.86 (±0.44)	“Material is sturdy and easy to handle” (p8) “The magnets make me feel less likely to break it, as I’m not worrying about clasps or anything (also good for accessibility)” (p27)
Using the 3D model improved my learning experience.	4.75 (±0.52)	“It’s very cool!” (p18) “It was very helpful!” (p6)
Compared to viewing the preserved specimen for understanding anatomical relationships, the 3D model was:	4.45 (±0.74)	“The 3D model guarantees that you will be able to observe all the needed structures. Whereas the preserved specimen does not do so to the same effect.” (p10) “Being able to take it apart, rotate it to see it from different angles, and actually being able to hold it” (p28) “I don’t think it can completely replace looking at a preserved specimen just because of the amount of information and structures we have to learn & the nature of everyone’s learning style but it is a great resource esp [sic] because you can take it apart” (p1)

Seven Likert questions of agreement on a 5-point scale (1 = strongly disagree; 5 = strongly agree) indicating students’ perceptions of utility of the brain 3DPM. Select qualitative responses that thematically correspond to each question are displayed in the right-side column.

. Overall, students responded strongly to the physical nature of the 3D-printed chondrocranium model in helping them understand the anatomy. A total of 24 out of 29 students (83%) strongly agreed that “the ability to physically handle the chondrocranium was helpful in understanding its anatomical features” (mean score 4.62 ± 0.38). Similarly, 23 students (79%) strongly agreed with the statements, “the interaction between the 3D-printed chondrocranium and brain was helpful in understanding the chondrocranium anatomy” and “compared to the preserved specimen, I am less worried about damaging or breaking the 3D model”.

A total of 26 students included written qualitative responses on their questionnaires. In these long-form responses, 13 students (50%) highlighted the ability to “handle”, “rotate”, and/or “take apart” the model as being particularly effective. The magnetic closure of the two chondrocranium halves was also indicated as effective in the model, with 6 out of 26 students mentioning this feature in their responses. Six students also commented on the surface quality of the 3D-printed chondrocranium, identifying the semi-translucent material and/or the sturdiness as particularly effective, as exemplified by one student’s response: “The translucent outside is really nice because you can see how the interior structures align with the skull” (p3).

A total of 18 out of 26 (69%) students provided qualitative written responses regarding what could be improved with the chondrocranium 3DPM. While most students indicated that the “3D of the model accurately depicts the anatomical features I need to know” in the Likert questionnaire (mean score 4.62 ± 0.62), seven students (27%) indicated issues with the size of the model, with statements such as “It’s a little small” (p13) and “Accurately show size of the 3D model in real life” (p17), or they identified particular structures that could be further resolved or added to the print, e.g., “The semicircular canals were a little difficult to identify” (p6). Though six students, as previously mentioned, liked the resin transparency quality, four students thought it made it “hard to see” (p13, p23) with one student elaborating, “If it were made out of a different material it might be easier to recognize structures, depth perception was difficult, hard to see distinct parts” (p12). Finally, confusion about how the model was oriented (distinguishing between top vs. bottom) was mentioned by three students.

Students were also able to provide additional general comments or questions about the chondrocranium model. A total of 10 responses (34% of total survey participants) were received; of these, four students indicated that they would like to see more 3D models in the course or further development of the 3D chondrocranium model. One student wrote, “It would be amazing to see the continuation of this project, possibly and a full Squamus [sic] skeleton model” (p4). Another expressed, “I wish there were more of these for other specimens” (p2). Others included statements such as “I love it!” (p6) and “It is very cool! You should make more models!” (p5).

Notably, one student pointed out in their written response the positive environmental and ethical impact of using 3DPMs for this species, stating “I think this could save a lot of animals from being farmed just to dissect” (p3).

3.4. Student Responses Regarding Utility of the Brain 3DPM

A total of 16 out of 32 comparative chordate anatomy students returned a completed questionnaire about their experience using the brain 3D model as a learning tool (50% response rate). The questionnaire regarding the brain included the same seven questions in the first questionnaire, and one additional question asking about the value of the color-coding. Results and sample quotations are shown in

Table 2. Summary of questionnaire responses regarding brain 3DPM utility.

Statement	Average (±SD)	Example Qualitative Responses
The 3D models accurately depict the anatomical features I need to know.	4.5 (±0.52)	“I really like the clarity of the printed structures” (p8b) “Some of the nerves are hard to see” (p4b)
The interaction between the 3D chondrocranium and brain was helpful in understanding the anatomy of the brain.	4.63 (±0.5)	“It’s very easy to see the relation between the different structures.” (p2b) “I was slightly confused as to which side was dorsal or ventral when it wasn’t in the cranium” (p3b) “The brain/cranium also fitting in one way helps with anatomical positioning as well” (p5)
The ability to physically handle the brain was helpful in understanding its anatomical features.	4.81 (±0.40)	“I like that you can rotate the brain to look at all structures” (p4b) “the ability to hold, rotate, and point out structures helps me learn these” (p12b)
The size of the model was appropriate for identifying all the necessary structures.	4.31 (±0.60)	“it could be a bit bigger to make smaller structures more visible” (p11b) “it would be easier if it were slightly larger, but practicing on an accurate size was good as well” (p21b)
Compared to the preserved specimen, I am less worried about damaging or breaking the 3D model.	4.13 (±1.2)	“thinner pieces could be a little thicker to prevent breaking the model; we broke one of the thinner pieces off of the model accidentally” (p12b) “Sturdier material, maybe?” (p2b)
Using the 3D model improved my learning experience.	4.6 (±0.63)	“overall very helpful to seeing complex structures!” (p23b) “perhaps [make] more [models] so they can be shared a little easier” (p5b)
The color-coding of the brain was helpful in identifying structures.	4.69 (±0.60)	“The color coding does work well with identifying certain structures” (p12b) “The color coordination with key works very well” (p23b)
Compared to viewing the preserved specimen for understanding anatomical relationships, the 3D model was:	4.5 (±0.52)	“overall very helpful to see complex structures” (p23b) “The dorsal and ventral sides could be easier to distinguish.” (p1b)

Eight Likert questions of agreement on a 5-point scale (1 = strongly disagree; 5 = strongly agree) indicating students’ perceptions of utility of the brain 3DPM. Sample qualitative responses that thematically correspond to each question are displayed in the right-side column.

.

As with the chondrocranium, a majority of the students (13 out of 16, or 81%) strongly agreed with the statement indicating the ability to physically handle the 3D-printed brain model as helpful in learning its anatomy (average score 4.81 ± 0.4); 4 students addressed this aspect of the models in their qualitative responses as being beneficial for learning. Correspondingly, nearly half (44%) of the qualitative responses mentioned the ability to “rotate” or “handle” the 3D brain as beneficial. A total of 12 students (75%) also strongly agreed that the color-coding of the 3D brain model and the associated printed color key were helpful (average score 4.69 ± 0.60), with 9 students commenting on this aspect in their written feedback.

The brain scored lower than the chondrocranium, however, in terms of students’ worry about damaging the model as compared to the preserved specimen, and there was greater variability in students’ responses (average score 4.13 ± 1.2). The structure of concern was the long, thin olfactory tract, which is brittle due to the hard resin material, and broke during one lab session (a student addressed this in their written feedback). Students also somewhat agreed (avg. score 4.31 ± 0.60) that the size of the 3D brain model was appropriate for identifying anatomical structures; five written responses indicated that a larger scale would help with observing smaller structures on the brain. Finally, two students had difficulty orienting the brain when removed from the chondrocranium, stating in their written responses that the dorsal and ventral sides were confusing to identify.

General comments about the model expressed enjoyment (50% of written responses) in using it to learn and the desire to see additional 3D models for the lab, with statements such as “I love it!” (p3b), “It is very cool! You should make more models!” (p5), and “I wish there were more of these for other specimens” (p2).

4. Discussion

This feasibility study sought to understand students’ perceived utility of a novel 3D-printed model of the S. acanthias chondrocranium and brain as a tangible, interactive visual learning aid in an undergraduate comparative chordate lab course. Students self-reported high levels of satisfaction in using the 3DPMs by rating the models’ utility for better understanding dogfish shark neuroanatomy as compared to preserved and dissected specimens. This has been documented by other studies which found that students expressed preference for or higher satisfaction in using 3DPMs over traditional methods of learning [5,11,15,20]. In the following sections, we discuss specific design features of the dogfish shark 3DPMs that students perceived to be helpful or not in their learning.

4.1. Interactivity and Color-Coding Are Useful Design Features

The ability to physically handle the 3DPMs was found to be one of the most valuable features. Unlike the dissected specimens, which cannot be manipulated in space, the 3D models offered students a unique tactile and interactive experience to better visualize the anatomy, since they could view structures from multiple angles and see structures that may otherwise be obstructed from one view, e.g., the ventral view of the chondrocranium. Evidence that such physical experience can improve learning outcomes is documented in Preece et al. (2013), in which students who utilized 3D models of horse foot anatomy scored significantly higher than students using computer models or textbook illustrations [19]. Pandya et al. (2021) similarly found that students studying otolaryngology preferred using a tactile model of the airway; students rated the tangible models as superior in improving their anatomical knowledge, which further supports the findings of this study that students value and prefer the tangible and manipulable aspects of 3DPMs [20].

The interactivity of the model, made possible by having the chondrocranium cut in two and adhered using magnets, was another design feature students enjoyed and found useful. The ability to take apart the chondrocranium and examine the brain inside allows students to better understand the relationship between these two structures, since they can locate specific landmarks on one and “fit” them into the corresponding landmark in the other; for example, the olfactory sac at the coronal end of the brain and corresponding nasal capsule in the chondrocranium. Moreover, the magnet feature was seen as “cool”, allows for easier handling and contributes to the sleek design, and was even described as “accessible” in one response, since the two halves easily snap together and do not use a more complex mechanism such as a clasp or hook.

The color-coding of the 3D brain, along with an accompanying labeled color key print-out, proved to be useful for identifying relevant anatomical features. Color-coding is well established as a useful visual cue for learning complex 3D structures and can aid in retention [21]. However, it has been found that some students can find color-coding confusing when they later try to identify anatomic structures on the specimen [22]. We, therefore, suggest providing a non-color-coded version of the 3DPM so students can correlate color-labeled anatomic structures with the corresponding structures in a neutral or natural-toned specimen.

4.2. Material and Size of the Models Can Be Improved

The design of these 3D-printed models aimed to address the fragility and size of the actual dogfish brain and chondrocranium. However, students expressed varying satisfaction with the material nature of the models, in both their sturdiness and appearance, as well as the model size.

Issues arose regarding the material of the 3D prints. The chondrocranium resin print was not painted and remained transparent, mimicking the semi-transparent quality of a real chondrocranium, which also allowed students to view the color-coded brain inside. Although some students appreciated this unique aspect of the 3DPMs, others expressed difficulty in viewing some structures on the chondrocranium due to the semi-transparency reducing depth cues and not being able to see the topology as clearly.

The stiff resin material was also less conducive to handling than anticipated. The olfactory tract of the dogfish shark is a very thin structure and was printed as such to retain the anatomic accuracy of the real specimen. Although printed resin is relatively durable, very thin structures may be prone to shattering. During the lab period, one of the 3D-printed brain models was dropped and broke at the olfactory tract (and it was subsequently noted, with regret, in the student’s questionnaire response). Student questionnaire responses reflected this fabrication flaw regarding the fragility of the thinner areas of resin. However, 3D models may be comparatively cheaper to (re)produce than to obtain another animal for dissection or preservation, and students were still generally less concerned about damaging the 3D-printed brain model than the preserved or dissected specimens, which we reassert is a benefit of using 3D models in the lab.

Students had varying levels of agreement about whether the size of the models was appropriate for viewing and learning the anatomy. Though students on average agreed that the size of the chondrocranium and brain were appropriate, various long-form responses indicated interest in altering their size; one student requested larger models, one preferred smaller, and one expressed interest in a model that was accurate to life size. Conversely, five students provided written feedback that the brain model could be scaled up to make smaller structures more visible and clearer to see. Though only one size scale was provided to students in the study, the ease of scalability of 3D models is highlighted in both McMenamin et al. (2014) and O’Reilly et al. (2015) as a particularly effective feature [8,9], with the possibility of providing a variety of model sizes. Therefore, it would be possible to 3D-print a series of models that allow students to understand and compare the anatomic structures at different scales.

4.3. Novelty and Enjoyment Using 3DPMs Increase Student Engagement

Students responded with excitement about the models and expressed enjoyment in using them for learning dogfish shark anatomy. Written qualitative responses indicate increased student engagement and a desire to see additional 3DPMs in the chordate lab. We posit that the novelty of the 3DPMs fostered students’ curiosity and engagement with the course material during these lab sessions; introducing innovative course materials that are learner-centered and encourage better understanding through active learning can be a benefit for students in the classroom [23]. Furthermore, 3D printing has become increasingly popular in medical/clinical contexts and other STEM fields; exposing students earlier on may spark interest in learning how to use this technology for their future academic and professional pathways [23].

One student highlighted the conservation value of using 3DPMs as supplements or replacements for dissected and preserved specimens. The environmental and ethical impacts of the use of 3DPMs is another benefit over the use of wild-caught or harvested specimens for classroom dissections. Students sensitive to the ethical and conservation concerns surrounding dissections may be more incentivized and interested in interacting with 3DPMs than preserved or dissected specimens.

4.4. Limitations and Future Research Opportunities

The 3DPMs will need to undergo another round of iteration, both in digital modeling and fabrication, to improve on the design based on students’ feedback. Improvements to the resolution of some structures, such as the cranial nerves on the brain, will allow for easier viewing. Similarly, the separate structure of the semicircular canal was not included in the model as it is not technically part of the neuroanatomy, but students are required to identify and know this structure. It may therefore be beneficial to 3D-model and include the semicircular canal for context, as learning about its anatomy and location within the chondrocranium may support overall understanding of morphological interrelationships and anatomic functions. The fragility of the olfactory tract can be addressed by 3D printing with flexible resin; a prototype of the dogfish shark brain was, in fact, printed using flexible resin, however it was not used as part of the lab. We see this as a potential solution for durability and extended use of this model in the classroom.

Furthermore, a challenge with anatomic 3DPMs remains in accurately showing the relationship between the cranial nerves and corresponding foramina of the chondrocranium or skull, a technical aspect that requires further experimentation with 3D printing and materials to see how these structures can best be visualized.

A limitation of this feasibility study is that it did not measure learning outcomes. Therefore, this newly iterated 3DPM should be evaluated with students in the lab using more experimental methods, such as a pre-test/post-test, comparing a control group’s performance when using only traditional learning materials (i.e., dissected specimens and static illustrations) with that of an experimental group using only the 3DPMs. A goal would be to evaluate whether or not the 3DPM is an alternative to dissected specimens, or at least an augmentation that would reduce the number of animals needed for dissection. Another potential study could investigate how students interact with the physical 3D model as compared to a digital 3D model on an interactive screen, and measure aspects such as ease and speed of identifying key structures, or understanding the spatial relationships between the chondrocranium and brain.

Other cognitive abilities relevant for learning anatomy, such as spatial ability, could be explored in relation to the use of the dogfish shark 3DPMs. Several previous studies have established a connection between spatial ability (SA) and students’ ease with using 3D models in STEM learning (including anatomy), where 3D models appear to benefit students with high SA and are less beneficial for students with low SA [24,25,26]. Interestingly, a majority of students in our study appreciated the ability to handle and freely rotate the models to view them from multiple angles and cited this as helpful in their learning. We are therefore curious to investigate whether there is an inclination for high SA students in this field and to develop new teaching and learning methods to help students with low SA develop this skill and benefit from the use of 3DPMs.

Finally, another limitation was the population for this study, which included students in the comparative chordate anatomy lab course at one university. In addition to gathering more student feedback in subsequent semesters of this course, future studies may include multiple institutions with a similar course offering and similar student demographics to evaluate the potential benefits of using this 3DPM. Moreover, as students in our study indicated in their written responses, additional 3DPMs for other model organisms would be of value to introduce in the lab.

5. Conclusions

This study developed the first interactive, 3D-printed model of the dogfish shark chondrocranium and brain. Students who used this model indicated preference for the 3DPM over dissected and preserved specimens, noting the tactile and interactive features as particularly useful for understanding S. acanthias neuroanatomy. The findings of this feasibility study support the use of a 3PDM of the S. acanthias chondrocranium and brain to augment learning in the comparative chordate anatomy classroom. We believe sharing this added benefit with students and educators alike will foster appreciation for alternative visual learning aids in the comparative chordate anatomy course and reduce reliance on caught animals for biology education. The S. acanthias 3DPM shows the potential of 3D-printed models in comparative anatomy education.