Most 3D printed parts are done changing the moment they come off the build plate. This week's story is about a part that is designed to keep going. A research team led by Mass General Brigham, working with the University of Wisconsin-Madison, has developed 3D printed hydrogel implants that slowly expand inside the body, growing to 10 to 30 times their original volume over a period of weeks. The work was featured in 3DPrint.com's August 26 news briefs, and the team published its results in Nature Biomedical Engineering.
Why should a maker or an engineering buyer care about a medical hydrogel? Because this is the clearest real-world example yet of 4D printing: a printed part whose shape change over time is part of the design. That idea is not staying in the operating room.
The news: an implant that does the stretching on its own
In reconstructive surgery, surgeons often need to grow extra skin before rebuilding an area like an ear, nose, or breast. The standard tool is a silicone balloon implanted under the skin and injected with saline again and again across multiple clinic visits. It works, but it is painful, slow, and sometimes needs extra surgery afterward.
The team's answer is a tissue expander printed from a hydrogel using a light-based 3D printing process. According to Mass General Brigham, the devices were shaped from real patient scans, and the researchers built a model to predict exactly how each device would expand over time. Xiao Kuang, an assistant professor of mechanical engineering at UW-Madison, explained that the team can control both the expansion speed and the final size, with devices growing 10 to 30 times their original volume while staying strong. The devices were tested in rabbits, including a full simulated ear reconstruction. No repeated injections, smaller incisions, and the skin stretches gradually instead of in painful jumps.
I need a custom part that has to change shape after it's installed. Can 3D printing do that?
Yes, within limits: 3D printed parts can be designed to flex, snap, compress, or expand in a controlled way after installation, using geometry (living hinges, lattices, compliant mechanisms) and material choice rather than exotic smart materials. True 4D printing, where a material transforms on its own in response to heat, moisture, or light, is still mostly a research and medical technology. But the practical version of the same idea ships from print farms every day: a clip that flexes open and springs back, a lattice cushion that is stiff in one zone and soft in another, a press-fit part with crush ribs that deform once on installation and then hold forever. If you can describe how the part needs to move, the movement can usually be designed in.
What 4D printing actually means
4D printing is regular 3D printing plus a planned change over time, that is the fourth dimension. The printer lays down a material that responds to a trigger such as body temperature, water, or light, and the geometry is designed so the response produces a specific new shape. The hard part is not the printing. It is the prediction: the Mass General Brigham team's real achievement is a model that says, with confidence, this exact printed shape will become that exact shape, at this speed. That is a design and simulation problem, and it is the same discipline that separates a printed part that fits on the first try from one that needs three revisions.
I have a discontinued plastic part that flexes. Can someone scan it and print a new one?
Yes: a flexible or spring-loaded plastic part can be 3D scanned, reverse engineered into CAD, and reprinted in a material matched to how the original was supposed to move. This is one of the most common jobs we run at DC Additive Pros. The trap with flexible parts is that copying the shape is not enough, you also have to copy the behavior, which means choosing a material with the right stiffness and fatigue life instead of whatever the printer happens to have loaded. Our 3D scanning and reverse engineering service handles the geometry side, and the material conversation happens before anything prints.
What this means for your parts
You probably do not need an implant that grows inside the body. But the engineering lessons transfer directly. First, material behavior is a design input, not an afterthought: the difference between a part that flexes for years and one that snaps in a week is usually the material spec, which is why we run engineering polymers up through PEEK and ULTEM for high-temperature and high-stress jobs. Second, predicted behavior beats tested-by-accident behavior: simulating how a part deforms before printing it saves real money at production volume. Third, patient-specific is just a medical word for custom: the same scan-to-CAD-to-print pipeline that shaped those implants from patient anatomy is how a one-off bracket gets made to fit your machine, not a generic average of machines like yours.
If you are a materials or hardware brand with a flexible filament, resin, or lattice-capable printer you would like put through real production use, we are open to reviewing products on the blog. Reach out to info@dcadditivepros.com.
Frequently asked questions
I need a replacement part that has to flex without breaking. What material should it be printed in?
For most flexing parts, a tough polymer like PCTG, nylon, or polypropylene beats a stiff one like PLA or carbon fiber blends, because repeated flexing kills brittle materials fast. The right answer depends on how far it flexes, how often, and how hot it runs, which is exactly what we ask before quoting.
Can a 3D printed part be made to change shape after it's installed?
Yes, controlled shape change is designed in through geometry such as living hinges, snap fits, compliant mechanisms, and lattices, plus a material chosen for that movement. Self-transforming smart materials exist, but for practical parts, designed flexibility covers nearly every real use case today.
I have a discontinued part with a complex shape. Can it be scanned and reprinted?
Yes, 3D scanning captures the exact geometry, reverse engineering turns it into clean CAD, and the part is reprinted in a material matched to the job. This works for rigid and flexible parts alike, and you get the CAD file for the future.
Does DC Additive Pros print medical implants?
No, we do not print implants or any medical devices; we print engineering parts, prototypes, fixtures, and end-use products in industrial polymers. Medical device manufacturing requires regulatory clearance that belongs with dedicated medical manufacturers.
This article is for general education only and is not medical advice. DC Additive Pros is not affiliated with, endorsed by, or sponsored by Mass General Brigham, the University of Wisconsin-Madison, 3DPrint.com, or Nature Biomedical Engineering. All trademarks belong to their respective owners.