The research, published in the journal 3D Printing in Medicine, was conducted by a team from the Regional Hospital in Liberec, the Motol Faculty Hospital in Prague, the Faculty of Medicine in Hradec Kralove and the Technical University of Liberec in the Czech Republic. Led by Lukas Capek of the Department of Clinical Biomechanics, the group set out to answer a deceptively simple question: how well do the materials commonly fed into desktop fused deposition modeling printers actually mimic the mechanical behavior of pediatric cranial bone? The answer, distilled through mechanical testing and computer simulation, is that most of them do not, and that even the best candidate carries trade-offs that anyone building surgical training models needs to understand.

The team compared six widely available fused deposition modeling materials: polylactic acid, better known as PLA; acrylonitrile styrene acrylate, or ASA; PET-G; a commercial filament marketed under the name Simu Bone specifically for anatomical models; polypropylene, or PP; and thermoplastic polyurethane, or TPU. These were benchmarked against genuine ex vivo specimens of pediatric calvarial bone, the skull cap bone harvested with ethical approval from Motol University Hospital. The mechanical yardstick was the three-point bending test, a standard technique in which a sample is supported at both ends and loaded in the middle until it deflects, allowing researchers to extract the Young’s modulus, a measure of stiffness that describes how much a material resists elastic deformation.

The numbers revealed a striking spread. Native pediatric cranial bone exhibited a mean Young’s modulus of 375 plus or minus 204 megapascals, a value that reflects both the intrinsic softness of infant skull bone and considerable biological variability between specimens. Simu Bone, the filament explicitly designed to imitate bone, turned out to be dramatically too stiff, measuring 3380 plus or minus 14 megapascals, roughly nine times stiffer than the real tissue it is meant to emulate. At the opposite extreme, TPU was far too compliant at just 61 plus or minus 11 megapascals, behaving more like a flexible rubber than a cranial plate. Polypropylene emerged as the closest match to native bone mechanics, although the researchers note that printing with it posed practical challenges, since PP is notoriously prone to warping and poor bed adhesion on consumer printers.

Between those extremes sat the everyday workhorse filaments. PLA, ASA and PET-G, the materials most hobbyists and hospital makerspaces reach for first, all landed well above the stiffness of pediatric calvarial bone, meaning models printed from them will feel rigid and unyielding where a real infant skull would flex and give under surgical instruments. That discrepancy matters more than it might appear. In craniosynostosis procedures, surgeons rely on tactile feedback, feeling how bone bends, springs and fractures as it is cut, contoured and reshaped. A model that is nine times too stiff invites the trainee to apply far more force than would ever be safe in the operating room, while one that is too soft fails to convey the resistance that guides instrument handling.

The researchers also explored a popular workaround: tuning the infill density of the print. Fused deposition modeling builds parts as hollow shells filled with internal lattice patterns, and reducing the infill percentage is the easiest way to soften a printed part without changing material. The experiments showed that infill reduction does modestly decrease stiffness, offering a degree of tunability. But the effect is limited and gradual, and it cannot bridge the enormous gap between, say, a 3380 megapascal filament and 375 megapascal bone. Infill tuning, in other words, is a fine adjustment tool, not a substitute for choosing the right polymer in the first place.

Perhaps the most conceptually important finding came from the finite element analysis, the computational half of the study. The team built numerical simulations of the bending tests to explore whether matching a single global property such as overall elasticity is enough to make a printed model behave like bone. The simulations indicated that it is not. Regional deformation patterns, the way strain distributes across the geometry of a skull segment during loading, are critical for realistic simulation, and a material can match the average stiffness of bone while still deforming in the wrong places and in the wrong way. This finding pushes the field beyond the naive goal of hitting one target number and toward the harder challenge of replicating the spatial mechanical behavior of layered, heterogeneous cranial bone.

The implications reach well beyond the laboratory. Patient-specific three-dimensional printed models have become a mainstay of preoperative planning and surgical rehearsal for complex craniofacial cases, and they are increasingly central to training the next generation of neurosurgeons and craniofacial surgeons. Hospitals around the world have installed banks of desktop printers precisely because printed skulls are cheap, fast to produce and anatomically faithful, derived directly from patient imaging. This study adds a crucial caveat to that enthusiasm: anatomical accuracy without mechanical fidelity produces a model that looks right but feels wrong, and in surgery, feel is often what counts. The authors emphasize that anyone selecting materials for cranial training models must balance mechanical fidelity against printability, since the most mechanically faithful option, polypropylene, is also among the most difficult to print reliably.

There are also broader lessons for the growing field of medical simulation. The wide scatter in the native bone measurements, with a standard deviation of more than half the mean modulus, is a reminder that pediatric cranial bone is not a single well-defined material but a biological structure whose properties vary with donor age, skull location and the layered architecture of inner and outer cortical tables separated by diploë. Any single polymer, however well tuned, will be an approximation. The Czech team’s work, supported by the Ministry of Health of the Czech Republic under grant NW25-08-00228, provides the quantitative baseline that material scientists and biomedical engineers will need as they develop next-generation bone-mimicking filaments, and it gives surgical educators an evidence-based ranking for the materials they can buy today. For now, the practical takeaway is clear: if the goal is to rehearse surgery on an infant skull, polypropylene is the closest thing to bone that a standard fused deposition modeling printer can deliver, provided the printer operator is prepared to wrestle with its temperamental printing behavior.

Subject of Research: Comparative mechanical assessment of 3D printed skull materials versus pediatric cranial bone for craniosynostosis surgical training

Article Title: Comparative assessment of 3D printed skull materials and ex vivo bone for craniosynostosis training: a finite element analysis

Article References: Capek, L., Celisova, S., Taborsky, J., Vitvar, J., Benes, V., & Solfronk, P. (2026). Comparative assessment of 3D printed skull materials and ex vivo bone for craniosynostosis training: a finite element analysis. 3D Printing in Medicine. https://doi.org/10.1186/s41205-026-00347-5

Image Credits: AI Generated

DOI: 10.1186/s41205-026-00347-5

Keywords: craniosynostosis, 3D printing, fused deposition modeling, surgical training, finite element analysis, Young's modulus, pediatric cranial bone, polypropylene, Simu Bone, three-point bending, patient-specific models, surgical simulation

The research, led by Kaitlin Pardue and colleagues in the Department of Surgery, was published in Global Surgical Education, the Journal of the Association for Surgical Education. The team set out to test a simple but urgent premise: because sternotomy is a high-risk procedure that general surgery residents encounter infrequently, simulation may be the most practical way to close the experience gap without compromising patient safety.

The procedural stakes are considerable. Opening the sternum requires precise midline division of the bone with a sternal saw, and deviations can damage underlying structures, complicate closure and increase the risk of postoperative wound complications. Prior surveys of general surgery residency program directors have documented limited cardiac surgery exposure during training, and many trainees report low comfort levels with the procedure — a pattern the Oklahoma group sought to address directly.

In the study, 25 learners consented and completed a baseline sternotomy on the training model before receiving any instruction. The majority of participants were resident trainees, making up 72 percent of the cohort, and 60 percent were male. Notably, none of the participants had ever performed a sternotomy prior to the simulation, and the group reported strikingly low baseline preparedness, averaging just 1.2 on a 5-point scale.

The training protocol was deliberately straightforward. After the baseline attempt, participants viewed a standardized instructional video demonstrating proper technique, then repeated the procedure on the simulator. Surveys administered before and after the initial sternotomy, and again at the completion of the simulation, measured self-assessed preparedness and anxiety using a 5-point Likert scale.

Objective scoring was built into the simulator itself. Artificial sternums were marked with a colored grading scale that allowed a 30-point accuracy assessment, capturing how closely trainees adhered to the ideal midline path. In addition, de-identified video recordings of each attempt were scored by blinded faculty reviewers on a 4-point technique scale, adding an independent, human evaluation of procedural skill alongside the anatomical accuracy measure.

The results were unambiguous. Accuracy scores on the sternum model rose from an average of 15.64 at baseline to 22.36 after training on the 30-point scale, a statistically significant improvement (p=0.006). Blinded faculty technique scores climbed from 2.08 to 3.48 on the 4-point scale (p<0.0001), indicating that the gains were visible not just in the cut itself but in the overall quality of the trainees’ operative technique.

The psychological benefits were just as striking. Ninety-six percent of participants reported improvement in preparedness following the simulation exercise, with an average increase of 1.3 points on the preparedness scale. Self-reported anxiety scores also fell significantly, dropping from 3.72 before the exercise to 2.76 afterward (p=0.001). The authors note that reducing anxiety in a controlled, nonthreatening environment may be a key mechanism by which simulation prepares trainees for real clinical scenarios.

The research was supported in part by a grant from the OUHSC College of Medicine’s Jerry Vannatta, MD Academy of Teaching Scholars, and the authors report no financial conflicts of interest. The study received ethical approval from the Human Investigation Committee of the University of Oklahoma (IRB# 15961), and informed consent was obtained from all participants.

The investigators conclude that, given the rare and high-risk nature of sternotomy, simulation offers an excellent opportunity to build both skill and confidence in surgical trainees — and may serve as a metric for assessing competence. While this was a pilot study and further work is needed to determine whether simulator gains translate into durable clinical competency, the findings suggest that a relatively simple, reproducible model combined with directed teaching could become a standard part of preparing the next generation of surgeons for one of the most demanding openings in the operating room.

The educational challenge at the heart of this study reflects a broader shift in how surgical training is conceived. Traditional apprenticeship models, in which residents learn by graduated exposure to real operations, assume that trainees will encounter each critical procedure often enough to progress from observation to supervised performance to independence. For procedures like median sternotomy, that assumption increasingly fails. Cardiac surgery volumes are concentrated in specialized centers, general surgery residents rotate through cardiothoracic services for limited periods, and the operation itself is often reserved for the most experienced members of the team because of the stakes involved. The result is a structural gap between what trainees are expected to be ready for and what they have actually practiced.

Simulation has emerged as the most widely endorsed response to this kind of exposure gap, and the evidence base supporting it has matured considerably over the past two decades. Systematic reviews of skills transfer after simulation-based surgical training have concluded that simulator-acquired skills do carry over to clinical settings, particularly when the training model reproduces the key perceptual and motor demands of the real procedure. For sternotomy, those demands include stabilizing the saw against a rigid, unforgiving structure; maintaining a strictly midline trajectory along the sternal symphysis; adjusting force as the saw traverses the denser manubrium and body of the bone; and halting the division at exactly the right moment to avoid plunging into the mediastinum. A model that lets trainees rehearse these elements repeatedly, without any risk to a patient, addresses precisely the components of the procedure where error is most costly.

The Oklahoma team’s simulator was not developed in a vacuum. Prior work in cardiac surgery education, including published efforts to build median sternotomy simulation models specifically for surgical training, has demonstrated growing interest in reproducing this single high-stakes step outside the operating room. What distinguishes the present study is its pairing of a physical, reproducible model with a structured instructional sequence and a dual scoring system. The combination matters because simulation alone, without deliberate instruction and objective feedback, tends to reinforce whatever habits a trainee brings to the task. The standardized video shown between the baseline and post-training attempts ensured that improvement reflected learning of correct technique rather than mere familiarity with the model.

The colored grading scale embedded in the artificial sternums deserves particular attention as a methodological feature. By scoring accuracy on a 30-point scale directly on the bone itself, the investigators created an assessment that is objective, inexpensive, and immediately interpretable. A deviated cut is visible in the artifact it leaves behind, which mirrors the clinical reality that a non-midline sternotomy is apparent to the operative team the moment the bone is divided. This kind of built-in assessment also points toward competency-based approaches to surgical education, in which progression is tied to demonstrated performance on defined tasks rather than to time served or case counts alone. A program director could, in principle, use a sternotomy simulator score as one element of a broader portfolio of procedural readiness.

The anxiety findings add a dimension that is often underemphasized in technical skills research. Self-reported anxiety fell from 3.72 to 2.76 on the five-point scale, a statistically significant decrease that accompanied the objective performance gains. The relationship between anxiety and surgical performance is well recognized: elevated stress degrades fine motor control, narrows attention, and impairs decision-making, particularly in trainees who are performing a procedure for the first time. Allowing a first attempt to occur in a low-stakes setting, where an imperfect cut has no consequence, may interrupt that cycle. By the time a trainee holds a sternal saw over a patient, the procedure is no longer a first exposure, and the psychological load of the moment is correspondingly reduced.

The clinical consequences of a poorly executed sternotomy help explain why this particular step merits dedicated training. Deviations from the midline can leave asymmetric bone edges that complicate wire closure and sternal reapproximation, and sternal wound complications, including dehiscence and mediastinitis, are among the most serious morbidities following cardiac operations. Off-midline cuts may also lacerate underlying pleura or vascular structures. Because these complications carry substantial morbidity and cost, investments in preclinical rehearsal of the incision are consistent with broader quality and safety priorities in cardiothoracic care.

As a pilot study, the work has limitations that the authors themselves acknowledge and that frame the agenda for future research. The cohort of 25 learners was small and drawn from a single institution, and the absence of any prior sternotomy experience among participants, while ideal for measuring learning curves, means the simulator’s value for more advanced trainees remains untested. The study measured immediate post-training performance rather than retention, leaving open the question of how durable the gains are over weeks or months. Most importantly, demonstrating improved simulator performance is not the same as demonstrating improved clinical competency, and translational studies linking simulator scores to supervised performance in actual operations would strengthen the case for widespread adoption.

Nevertheless, the pattern of results across three independent measures — anatomical accuracy, blinded technique scoring, and self-reported preparedness — converges on a consistent conclusion. The magnitude of the improvements, achieved with a single instructional session and a reproducible model, suggests an efficient educational intervention that could be implemented without elaborate resources. For a procedure that most general surgery residents will rarely, if ever, perform before being expected to assist with or perform it, that efficiency is the central argument for making sternotomy simulation a routine component of surgical preparation.

Subject of Research: A sternotomy simulation program to improve surgical trainees' performance and preparedness

Article Title: Splitting hairs: improving sternotomy performance and preparedness among trainees using a novel simulation program

Article References: Pardue, K., Davis, R., Trimble, J., Harter, M., Wood, F., Scott, R., & Lees, J. (2026). Splitting hairs: improving sternotomy performance and preparedness among trainees using a novel simulation program. Global Surgical Education – Journal of the Association for Surgical Education, 5(1), Article 174. https://doi.org/10.1007/s44186-026-00581-9

Image Credits: AI Generated

DOI: 10.1007/s44186-026-00581-9

Keywords: sternotomy, surgical simulation, surgical education, general surgery residency, trainee preparedness, technical skills, cardiothoracic surgery, pilot study, competency assessment, medical training, anxiety reduction, patient safety