Di Wang, PhD, and Y. Shrike Zhang, PhD, of the Division of Engineering in the Mass General Brigham Department of Medicine, are the lead and senior authors of a paper published in Nature Biomedical Engineering, "4D-printed adaptive hydrogel tissue expanders for ear and breast reconstruction."
Q: What challenges or unmet needs make this study important?
Tissue expansion is a common technique used in reconstructive surgery. Surgeons slowly stretch nearby skin to grow extra tissue that can be used to rebuild areas such as the ear, breast or nose.
The most used device today is a silicone balloon that is gradually filled with saltwater over several weeks or months. While this approach has helped many patients, it has downsides. The repeated injections can be painful and require frequent clinic visits. Complications can also occur, such as bleeding, device shifting or problems with the injection port. In many cases, patients also need an extra surgery to remove excess stretched skin.
Researchers have explored self-inflating materials as an alternative, but earlier versions expanded too quickly, were not strong enough, and could only be made in simple shapes. Because the shape of the device determines the final shape of the stretched skin, this has limited how well surgeons can match a patient's needs.
Q: What central question(s) were you investigating?
We wanted to see if a new type of 4D-printed device could solve these challenges all at once.
These devices are made using a special material that can change over time once inside the body. In this case, the device slowly expands on its own without needing injections.
We asked whether these devices could: expand on their own without injections, hold their shape under skin tension, and be customized to match a patient's exact anatomy.
We also wanted to know if they could perform better than current devices, both in how well they work and in reducing complications.
Q: What methods or approach did you use?
We developed a special gel-like material whose expansion speed and final size can be carefully controlled.
Using a light-based 3D printing method, we created devices shaped like a human ear or breast based on real patient scans. We also built a model to predict how each device would expand over time.
We tested the devices in rabbits, including a full simulation of ear reconstruction surgery. This included placing the device, allowing it to expand inside the body, removing it, and then inserting an ear implant.
We compared our devices to standard silicone expanders that require daily injections, looking at how easy they were to use in surgery and what complications occurred.
Q: What did you find?
The new devices expanded to 10 to 30 times their original volume while staying strong. The expansion happened slowly and steadily, allowing the skin to stretch naturally.
We saw clear signs that the skin adapted, including increased surface area, healthy thinning of the skin, and growth of new blood vessels.
Compared with standard silicone expanders, these devices had several advantages. They did not require repeated injections and eliminated the need for an additional surgery to trim excess skin. They also reduced overall surgery time and incision size, while staying in place better.
Q: What are the real-world implications, particularly for patients?
These devices can be customized to match each patient's body, helping surgeons create more precise results for procedures such as ear and breast reconstruction.
One major benefit is that patients would no longer need repeated injections over several weeks or months. Instead, the device is implanted once and then expands on its own.
This could mean fewer clinic visits, less discomfort, fewer surgeries, and lower risk of complications.
The technology could also be used for many types of reconstructive procedures and potentially for cosmetic surgery.
More broadly, this work shows how 4D printing could be used in real medical care, opening the door to more personalized treatments.
Q: Were you surprised by any of the findings?
One unexpected finding was that the device could absorb small amounts of bleeding.
Bleeding, known as a hematoma, is a serious complication in these surgeries because it can increase pressure on the tissue and reduce blood flow, which may damage the skin.
Currently, surgeons often place drains to remove excess blood, but these can increase the risk of infection.
In our study, the device absorbed the blood on its own while continuing to expand normally. This suggests it could help reduce one of the most common and serious complications without needing additional tools like drains.
Authorship: In addition to Zhang and Wang, Mass General Brigham authors include Xiao Kuang, Liming Lian, Sili Yi, Hossein Ravanbakhsh, Guosheng Tang, Maobin Xie, Carlos Ezio Garciamendez-Mijares, Prajwal Agrawal, Zixuan Wang, and Sushila Maharjan.
Paper cited: Wang, D, et al. "4D-printed adaptive hydrogel tissue expanders for ear and breast reconstruction," Nature Biomedical Engineering, DOI: https://www.nature.com/articles/s41551-026-01681-z
Funding: Support from the Brigham Research Institute is acknowledged.
Disclosures: Zhang consulted for Allevi by 3D Systems; consults for PepGel; cofounded, consults for and holds options of Linton Lifesciences and Criocore; and sits on the scientific advisory board and holds options of Xellar Biosystems. The relevant interests are managed by the Brigham and Women's Hospital. The other authors declare no competing interests.
