3D-Printed Research Immobilization Cast.

Overview

This project involved the design and fabrication of a custom 3D-printed immobilization cast for a mouse hindlimb research model. The objective was to develop a device capable of maintaining controlled knee and ankle positioning while providing an anatomically appropriate fit and allowing continuous visual monitoring of the underlying limb.

The project was conceptually based on a previously published mouse hindlimb contracture model. However, the original researchers’ CAD files were unavailable, so I developed the entire design independently using Onshape, referencing the published research as a starting point.

My primary responsibility was the complete CAD development, prototyping, and refinement of the cast. The project combined mechanical design, anatomical constraints, and resin additive manufacturing to produce a functional biomedical research device.

Design process

The design process began with an examination of the published mouse cast model. I used the original research as a conceptual reference, preserving its target knee flexion and ankle dorsiflexion positions while independently developing the complete geometry in Onshape.

Rather than simply scaling an existing model, I designed the shell geometry, internal contours, curvature, and clamping features to accommodate the target mouse hindlimb anatomy.

One of the most significant design challenges was determining the optimal separation geometry for the two halves of the cast. Early versions used a vertical split, but this made installation difficult because the limb could shift as the cast was positioned. I redesigned the separation to follow the curvature of the skeletal structure, improving how the cast accommodated the limb during installation.

The design underwent five major iterations. Each iteration addressed specific problems identified during prototyping, including limb clearance, clamp groove depth, segment length, internal radii, and overall print quality.

Prototyping

All prototypes were manufactured using resin 3D printing. Initial versions used standard photopolymer resin, but this material proved insufficiently durable and was susceptible to chewing damage.

I transitioned to an ABS-like photopolymer resin to improve toughness and resistance to wear. Transparency was another major engineering consideration. Although the resin itself was clear, the initial printed results did not provide sufficient visibility through the cast.

I experimented with the printing and post-processing approach until I achieved a much clearer, glass-like finish. This was important because the cast needed to allow visual monitoring of the underlying limb without requiring repeated removal.

Final casts were fabricated using an Elegoo Mars 5 Ultra resin printer, selected for its high resolution and dimensional accuracy. The printer was able to reproduce fine geometric features, including hinge recesses and detailed internal contours.

Post-processing included washing, UV curing, and surface finishing to remove support artifacts and produce smooth internal contact surfaces.

Prototypes were evaluated for anatomical fit, joint positioning, skin contact, and potential pressure points or slippage. Feedback from these evaluations informed subsequent geometric modifications.

Results

Five major design iterations resulted in a refined and functional immobilization cast. The final design incorporated an improved shell separation, revised internal geometry, and a more durable clamping system.

The transition to ABS-like resin addressed the durability limitations of earlier prototypes, while experimentation with print finishing produced the high level of transparency needed for visual monitoring.

The final cast was successfully fabricated and used in the research project. It provided a reproducible physical device for maintaining the intended hindlimb positioning while allowing the underlying limb to remain visible.

The project demonstrated the ability to independently translate an existing scientific concept into a functional engineering design through CAD development, iterative prototyping, and material experimentation.

What I learned

This project gave me the opportunity to independently translate a biomedical research requirement into a physical engineering solution. It challenged me to consider much more than the dimensions and appearance of a CAD model. Anatomical constraints, installation, material durability, optical clarity, and manufacturing limitations all influenced the final design.

One of my biggest takeaways was the importance of iterative prototyping. The initial design was far from the final product, and each revision required identifying a specific limitation and developing an engineering solution. The transparency experiments were particularly interesting because they demonstrated how manufacturing and post-processing decisions can be just as important as the CAD geometry itself.

Working alongside a biomedical research team also gave me a better understanding of how engineering contributes to scientific research. I gained experience connecting mechanical design, digital modeling, and additive manufacturing to solve a problem outside the traditional scope of mechanical engineering.

Ultimately, this experience strengthened my interest in interdisciplinary engineering, particularly mechanical design, biomedical technology, and rapid prototyping.