Patient-specific 3D implants

Lisa Ernst · 21.11.2025 · Health · 10 min

When a surgeon from a Swiss hospital calls us because a piece of skull is missing after an accident and the surgery is planned for two weeks from now, the clock immediately starts ticking in our workshop. In such situations, you quickly realize whether your workflow for patient-specific 3D implants really works or if everyone is still sending emails and DICOM files back and forth in chaos. Within a few days, a clean 3D model is created from a CT dataset, and from that, an implant or an anatomical model that fits this specific patient exactly. In practice, we repeatedly experience how much more relaxed a team goes into surgery when they have literally had the anatomy in their hands beforehand.

This is exactly what hospitals, practices, and medtech SMEs use patient-specific 3D implants for: planning complex procedures, reducing the risk of surprises in the OR, and being able to show patients very concretely what will happen. At the same time, there are some pitfalls along the way – incorrect scan parameters, unclear responsibilities, overly optimistic assumptions about desktop printers. Further down, you'll find our typical workflow from inquiry to the finished part, including specific settings and the mistakes we made ourselves at the beginning.

Quelle: Own representation

Basics

When we talk about patient-specific 3D printed implants, we mean components that fit exactly to the anatomy of an individual person and are based on CT or MRI data. Typical examples include cranial plates after trauma or tumor, plates and drilling templates in orthopedics, dental implants with drilling guides, as well as orthoses and masks for positioning or radiation therapy. The general process is always the same: you start with imaging data from radiology, segment the relevant structures, create a 3D surface model from it (e.g., in STL format), and prepare it for 3D printing of an implant or a test model.

A patient-specific implant is always intended for one specific person – for example, a cranial plate that exactly closes the defect in the CT and must be neither larger nor smaller. In regulation, we also speak of Custom-Made Devices (CMD): these are medical devices manufactured according to a written order with patient-specific design features for exactly one patient and not produced in series. Patient-Matched Devices are somewhere in between: they are produced in validated series processes but are adapted to a patient's anatomy, for example, patient-specific plates from a large implant manufacturer. As soon as a part ends up in the body or is used directly for diagnosis or therapy, we legally speak of a medical device. Then you automatically play by the rules of EU-MDR, national laws and relevant standards, for example, in quality management. The Swiss regulatory authority Swissmedic summarizes this concisely in a fact sheet on 3D printers and medical devices – including references to relevant norms and standards ( (ISO-Standards). Models printed purely for training or demonstration purposes are significantly simpler from a regulatory standpoint, as long as it is clearly documented that they are not used for direct treatment decisions.

Preparation

Before you print the first layer, you should know quite precisely what should be on the table in the end. Is it a patient-specific implant, a surgical guide, an anatomical training model for students, or a demonstration object for patient conversations? The clearer the purpose, the easier the material selection, software decisions, and coordination with the hospital or client.

In projects involving implants or surgical guides, you cannot avoid a clean setup with clear roles. Typically, you need a responsible physician, radiology for the imaging, a medical technology team or manufacturer with an approved quality management system, and documented assignment to EU-MDR oder nationalen Vorgaben. For purely anatomical models, you can plan a bit more loosely, for example, in cooperation between a clinic, a university laboratory, and the maker scene – the only important thing is that it is documented in writing that the model is not a medical device.

Technically, as a basis, you need imaging data in DICOM-Format, , usually CT with slice thicknesses of 0.5 to 1 millimeter. Coarser scanned datasets quickly look blocky in the 3D model and unnecessarily complicate things in design. For sensitive areas such as the skull base or spine, a maximum slice thickness of 1 millimeter has proven effective in our projects. For segmentation, many teams use open-source software like 3D Slicer or commercial solutions like Materialise Mimics; ; at 33d.ch, we see both variants regularly in customer projects.

For 3D printing itself, depending on the goal, you choose between in-house production and a certified partner. For purely training and anatomical models, a cleanly calibrated FDM or resin printer is often sufficient. For implants or high-stress templates, metals like titanium, high-performance polymers like PEEK or PEKK, and special medical resins are usually used – typically by a service provider precisely tailored to these materials and standards.

Practical checklist from our workshop

In practice, we have found the following sequence to be beneficial before we even think about the slicer:

• Document the use case in writing together with the clinical team (purpose, region, desired product).
• Clarify responsibilities: who is medically responsible, who is the manufacturer, who segments, who prints.
• Define the scan protocol (modality, slice thickness, field of view) and agree with radiology.
• Determine the software stack (e.g., DICOM viewer, segmentation, CAD, slicer) and check access.
• Decide early whether you are creating a medical device or a pure model and document this in the project brief.

If all of this is clearly established, the actual design and printing steps run much more smoothly – and you have to improvise less later.

Step-by-step guide

The production of patient-specific 3D printed implants and models follows almost the same pattern for us. The details change depending on the specialty, but the logic remains the same.

Step 1: Define clinical use case and product type

Together with surgery and radiology, we first clarify what the model or implant will be used for – for example, a patient-specific cranial plate after an accident, a drilling template for dental implants, or a heart model for surgery planning. At the same time, we determine whether it is an implant, a surgical guide, or a pure anatomical model, as this affects its classification as a Custom-Made Device, Patient-Matched Device, or Non-Medical Device. A good test: you can write the use case in one sentence and all parties involved nod in agreement.

Step 2: Plan and perform imaging

For bony structures, we usually plan a CT scan, and for certain soft tissue applications, a high-resolution MRI. The parameters are important: slice thickness of a maximum of 1 millimeter, suitable reconstruction kernels, and a field of view that completely covers the relevant region. In practice, we repeatedly see datasets where half the mandible is missing – that's annoying because you then have to rescan everything. Therefore, in the DICOM viewer, we consistently check whether the dataset is complete and free of artifacts.

Step 3: Segmentation and creation of a 3D surface model

The DICOM data then lands in segmentation software like 3D Slicer oder Mimics. . There, the target structures are marked – for example, skull cap, alveolar ridge, or vertebral body – and exported as a 3D mesh, usually in STL format. We are well aware of typical pitfalls: holes in the mesh after strong metal artifact reduction, cut-off tips due to too small a field of view, or stair-step artifacts due to too large a slice thickness. Therefore, we always perform a brief visual check by overlaying the 3D model with the original images and comparing edges and contours.

Quelle: 3dprintingindustry.com

Schematic workflow for the production of a patient-specific 3D printed bone implant with an optimized lattice structure.

Step 4: Construct implant or model

Based on the segmented anatomy, the actual design is created. For complex cases, we like to use medical design software like Materialise 3-matic Medical, , which allows for very precise control of lattice structures, screw holes, and transitions. For a cranial plate, for example, we define the contour along the defect boundaries, the plate thickness, and the position of the fixation points; for drilling templates, we position sleeves so that the angle and depth of the drilling are precisely guided. Mistakes we ourselves have made: too thin struts that break when removing supports, or geometries that are difficult to place in the OR. Today, we therefore work with clear minimum thicknesses and edge distances, which we refine with each project.

Step 5: Choose printing strategy and material

For actual implants, we consistently rely on certified partners who manufacture titanium or PEEK implants in validated processes. For anatomical models and training objects, we print a lot ourselves – often with FDM or resin. Layer heights of 0.1 to 0.2 millimeters have proven effective for us, as the balance between detail and printing time is good. A simple check is a reference measurement in the model, for example, a 50-millimeter strut, which we measure after printing. If the deviation is less than one millimeter, that is more than sufficient for most planning purposes.

Material selection in quick comparison

Step 6: Postprocessing, quality assurance, and documentation

After printing, we remove support structures, clean the part, and prepare it for sterilization depending on the intended use. For implants, the manufacturer must include mechanical testing, dimensional checks, and formal release in the quality management system; nothing works here without a solid system behind the scenes. Manufacturers of Custom-Made Devices must prove a complete quality management according to EU-MDR For training and anatomical models, documented visual inspection, a comparison of selected dimensions against specifications, and brief feedback from users after use are often sufficient.

Step 7: Clinical application, feedback, and iteration

The most exciting moment is always the first use: does the plate really fit as well as the virtual model promised? Is the drilling guide used intuitively, or does it jam at an unexpected point? After such cases, we actively collect feedback from the OR and document the fit, handling, and any peculiarities. This gradually leads to in-house design rules and checklists, making subsequent projects significantly faster and safer. At 33d.ch, our current standard workflow for patient-specific projects has emerged precisely from this feedback process.

Common mistakes & solutions

Many difficulties repeat themselves in projects again and again – whether it's about cranial plates, dental guides, or orthoses. We see three typical pitfalls particularly often.

Mistake 1: Regulation comes into play too late. At the beginning, an implant project often seems like an exciting technical case, and suddenly the question arises: who is actually the manufacturer in the sense of EU-MDR? If no one has a clear answer to this, it's a warning sign. Our solution: right from the start of the project, we define which partner acts as the manufacturer, how the release process works, and which documents must end up in the technical dossier at the end.

Mistake 2: CT data is too coarse or incomplete. This happened to us at the beginning too: we had a nice dataset with 2-millimeter slices – until we rotated the model in the viewer and saw stair-step artifacts everywhere. Such data is hardly suitable as a basis for precise plates or guides. Today, we consistently require slice thicknesses of a maximum of 1 millimeter and briefly check each series in the viewer before anyone starts segmentation.

Mistake 3: Desktop printers are overestimated. For prototypes and training objects, we love our workshop printers, but they don't replace a qualified implant manufacturer with tested materials and validated processes. When someone says: "We'll quickly print this in titanium in the basement," we know that a conversation about roles and responsibilities is due first. Our rule of thumb: design and test models gladly in-house, anything that goes into the body belongs in a strictly regulated manufacturing process.

A nice example from practice: in an ENT project, 3D printed sinus models were initially used solely as training objects. However, the material was so soft that the milling feel had little to do with reality – this is frustrating, especially for experienced surgeons. After a material change and adjusted wall thicknesses, the handling was significantly more realistic, and in a study, the models could even be meaningfully compared with cadavers. Such feedback loops are invaluable because they directly lead to better designs and material decisions.

Variations & adaptations

The process described above can be adapted to very different goals – as long as you know where you can be creative and where the regulations set clear boundaries. For patient-specific metal implants, many teams work with specialized manufacturers who produce a titanium or PEEK solution from the design and provide the regulatory documentation. For orthoses or positioning aids, for example, in radiation therapy, you can also handle individual steps in-house, as long as the overall process is embedded in a certified quality management system.

3D printed anatomical models as a supplement or replacement for cadavers in education are very exciting. Studies show that such models enable comparable or even better knowledge transfer in certain scenarios – and are much easier to scale because you can reprint them as many times as needed. For us, they are particularly useful when rare pathologies or complex variations are to be trained that are hardly found on a "standard cadaver."

For technology fans and makers who want to try their hand at anatomical models without immediately diving into the medical device world, it's worth taking a look at open platforms like the NIH 3D Print Exchange. . There you will find validated anatomical models, molecular structures, and teaching models that are deliberately provided for education and research. The only important thing is that it remains clear: these files are not automatically approved as implants or surgical guides – but they provide you with an excellent basis for learning, experimenting, and for your first own projects.

There is also a lot of activity in materials. In clinical practice, metals like titanium, biocompatible polymers like PEEK and PEKK, technical plastics, as well as silicones and resins, currently dominate. In parallel, the community is researching hydrogel-based bioinks with living cells, which could potentially be used for tissue or organ structures. In our daily work, this is more of an exciting outlook – most projects still revolve around "classic" plastics and metals that can be reliably printed, cleaned, and documented.

If you want to see the workflow from CT data to the finished 3D model step by step, it's worth taking a look at the embedded video. There you can see very well how DICOM import, segmentation, and model preparation interlock – precisely the steps we go through in our projects every day.

FAQ: Questions we repeatedly encounter in projects

Finally, we answer a few questions that we are regularly asked in our daily work at 33d.ch – whether it's on the phone, in the meeting room, or directly at the machine.

Question 1: Can I easily produce patient-specific implants with a good desktop 3D printer?

Short answer: no. Medical device requirements apply to implants and surgical guides – i.e., quality assurance, material certifications, risk management, and often clinical evaluation. A desktop printer is great for prototypes, test parts, or training models, but it doesn't replace a certified manufacturing process with validated parameters and documented traceability. A sensible approach is: you develop the design and test it with your own printers, but have the actual implant produced and released by an authorized manufacturer.

Question 2: How fine do CT or MRI data need to be for 3D models to be meaningfully printable?

For bone, slice thicknesses of 0.5 to 1 millimeter have proven effective in our practice. Coarser slices create visible steps and cost you a lot of time in post-processing. Many teams manage well with 1 millimeter for surgical guides, while 1.25 millimeters are often already borderline. For very complex structures – such as the skull base or fine joint surfaces – a special 3D printing protocol in radiology, precisely tailored to your project, is worthwhile.

Question 3: What are the advantages of 3D printed anatomical models in education compared to cadavers?

3D models are infinitely reproducible, do not require cooling, and can be specifically designed to highlight certain pathologies or variations. You can color-code them, label them, saw them, drill them – and then simply reprint the model. Especially for large cohorts in training or for recurring simulation training, such models are therefore very attractive. Our impression from projects with universities: students often dare to do more with printed models and repeat critical steps more frequently than with cadavers.

Question 4: What is bioprinting and biofilaments all about – is it already everyday practice?

Bioprinting works with so-called bioinks, mostly hydrogel-based carrier materials in which living cells are embedded. These can be used in the lab to produce tissue structures, tumor models, or test systems for medications. In clinical practice, we have hardly encountered this yet; titanium, PEEK, and various plastics still dominate there. If you want to start with patient-specific implants, it makes sense to focus on these established materials first and view bioprinting more as an exciting future topic.

Question 5: Where can I find reputable 3D models for training and patient education?

A very good starting point is the NIH 3D Print Exchange. . There you will find thousands of biomedical models – from organs to bones to molecules – as well as tools to create your own files. In parallel, many university libraries and medical technology laboratories maintain their own curated collections of 3D print resources specifically created for teaching and simulation. This allows you to work relatively quickly with high-quality datasets without building everything from scratch.

Mini-conclusion for your everyday work with patient-specific 3D implants

• Without a clearly defined use case and role distribution, every implant project becomes unnecessarily complicated – take deliberate time for this at the beginning.
• Good imaging data is half the battle: clean DICOM scans with appropriate slice thickness save hours in segmentation and design later.
• Use your workshop printers for prototypes and training models, but rely on regulated manufacturing processes for actual implants.
• Feedback from surgery and education is not a "nice-to-have" but the engine for better designs, material decisions, and workflows.

If you keep this in mind, your first patient-specific project will not be an experiment, but the start of a repeatable process.

Also fits well (as next topics in the blog):

• Understanding 3D printing tolerances
• Storing filament and resins correctly
• 3D scanning for medicine and SMEs
• Checklist: From DICOM to printable STL
• Material comparison for medical 3D printing applications

The second video shows how clinics and industry collaborate to implement patient-specific implants on a larger scale. If you want to see how your own workflow can be professionalized in the long term, this is a good source of inspiration.