Recently, the team of Professor Haiyue Jiang at the Plastic Surgery Hospital of Chinese Academy of Medical Sciences, in collaboration with the team of Professor Y. Shrike Zhang at Harvard Medical School, published a research article online in Nature Biomedical Engineering, entitled "4D-printed adaptive hydrogel tissue expanders for ear and breast reconstruction." Based on a polyelectrolyte poly(acrylic acid) photocurable hydrogel system, with systematic optimization of formulation and processing combined with digital light processing (DLP) 4D printing technology, the study successfully developed a novel tissue expander (AEH-TEs) capable of environment-adaptive expansion, excellent mechanical performance, and highly personalized geometric structures, providing a complete paradigm reference for the design, fabrication, and clinical translation of next-generation surface organ reconstruction devices.

Soft tissue expansion is one of the most important techniques in plastic surgery, enabling the acquisition of additional covering tissue through gradual expansion for the repair of surface organ defects caused by congenital malformations, tumor resection, burns, or large-area skin loss. Silicone tissue expanders, as a landmark invention, have benefited countless patients worldwide, yet remain challenged by complications including pain from repeated percutaneous saline injections, haematoma, expander migration, injection port turnover, connector tube kinking, imprecise expansion shape control, and the need for flap trimming surgery due to over-expansion. Early self-inflating hydrogels were explored as alternatives but failed to meet clinical demands due to overly rapid expansion, insufficient mechanical strength, and limited geometric versatility. Moreover, the geometry of an expander directly determines the morphology of the expanded flap — a long-standing unresolved challenge. By precisely tuning the ionization degree (α) and crosslinking density of the hydrogel, and establishing a synthesis–swelling coupling model based on Flory–Rehner theory, the research team achieved 10–30-fold volumetric expansion in a rabbit model while maintaining excellent mechanical performance to resist skin tension. More importantly, by converting patient 3D scan data into personalized templates for DLP printing, AEH-TEs can be fabricated into complex three-dimensional structures closely matching the target tissue or organ anatomy, fundamentally overcoming the limitations of conventional expanders in shape simplicity and poor expansion controllability.

The study indicates that AEH-TEs are not simply "automatically swelling hydrogels," but rather a new class of clinical devices that achieve programmable control over geometry, mechanics, and expansion kinetics in an integrated manner. In simulated rabbit ear reconstruction surgery, AEH-e-TEs required no injection at any point, with expansion morphology closely matching the target auricle; following implantation of the auricular prosthesis, a stable and natural ear shape was achieved without trimming. Compared with silicone expanders, AEH-e-TEs effectively avoided complications including device migration, injection port turnover, and flap over-expansion, eliminating the need for a third-stage trimming surgery, substantially shortening total operative time, and reducing both incision length and discarded tissue volume. Of particular note, in a surgically constructed haematoma model, AEH-e-TEs autonomously absorbed the accumulating blood and continued to expand normally, offering a new approach to preventing haematoma — one of the most serious complications following tissue expander surgery. In simulated breast reconstruction, AEH-b-TEs successfully expanded to the average adult female breast size (base diameter approximately 10 cm) in vivo, with satisfactory morphology, no tissue necrosis, and a clearly visible neovascular network in the subcutaneous expanded layer.

Future Outlook: This study demonstrates the potential of 4D-printed adaptive expanders across multiple surface organ reconstruction applications. Future work will focus on long-term in vivo performance, device refinement and performance optimization, scalable manufacturing, and regulatory pathways. Professor Jiang's team will conduct systematic studies on iterative device improvement, long-term in vivo safety and efficacy evaluation, and regulatory advancement, while extending the same 4D printing platform to intelligent implantable devices for additional clinical scenarios — including nasal, eyelid, and large-area skin defect reconstruction, post-excision coverage of scars and keloids, and aesthetic surgery applications — with the goal of advancing 4D printing technology from conceptual demonstration in materials and engineering science toward genuine clinical translation, ultimately benefiting more patients in need of surface organ reconstruction and aesthetic restoration.

Professor Haiyue Jiang of the Plastic Surgery Hospital of Chinese Academy of Medical Sciences and Professor Y. Shrike Zhang of Harvard Medical School are co-corresponding authors. Co-first authors are Dr. Di Wang, Attending Surgeon at the Plastic Surgery Hospital of Chinese Academy of Medical Sciences and Postdoctoral Fellow at Harvard Medical School; Associate Professor Jiaqi Lü of the Center for Advanced Laser Technology, Hebei University of Technology; and Assistant Professor Xiao Kuang of the Department of Mechanical Engineering, University of Wisconsin–Madison, and Postdoctoral Fellow at Harvard Medical School.

Corresponding Author:

Haiyue Jiang is a Chief Physician at the Plastic Surgery Hospital of Chinese Academy of Medical Sciences, a National Distinguished Physician, recipient of the Bethune Medal, and Principal Investigator of a National Key R&D Program Project under the 14th Five-Year Plan, enjoying Special Government Allowances of the State Council. He currently serves as President and Deputy Party Secretary of the Plastic Surgery Hospital of Chinese Academy of Medical Sciences, Professor of Clinical Medicine and Doctoral Supervisor at Peking Union Medical College, and holds concurrent positions including Standing Member of the Chinese Medical Association Council, Presidentof the Chinese Society of Plastic Surgery, Standing Member of the Beijing Medical Association Council, Chairman of the Beijing Society of Plastic Surgery, and Editor-in-Chief of the Chinese Journal of Plastic Surgery. With over 30 years of clinical, research, and educational experience in plastic surgery, he has long been dedicated to the clinical treatment and basic research of external ear reconstruction, positioning China at the international forefront in complex auricular malformations, challenging ear reconstruction, and functional restoration. He has received numerous awards including the Soong Ching Ling Pediatric Medicine Award, the Beijing Science and Technology Progress Award, and the National Health Commission Outstanding Young and Middle-Aged Expert Award.

First Author:

Di Wang is an Attending Surgeon in Plastic Surgery at the Plastic Surgery Hospital of Chinese Academy of Medical Sciences, a Clinical Master's/Doctoral graduate from Peking Union Medical College (supervised by Professor Haiyue Jiang and Professor Wen Chen), a Postdoctoral Fellow and Joint-training Doctoral candidate at Harvard Medical School (under Professor Y. Shrike Zhang), a member of the International Society of Aesthetic Plastic Surgery (ISAPS), and a healthcare technology manager. His research focuses on the clinical practice, materials development, and technology innovation in surface tissue and organ reconstruction and aesthetic medicine. He has published over 20 peer-reviewed research articles as thefirst author in journals including Nature Biomedical Engineering, Science Advances, Plastic and Reconstructive Surgery, and Aggregate, and serves as Principal Investigator on projects including the National Natural Science Foundation of China.