Multiple media outlets have recently reported that Chinese researchers have made an important advance in functional hydrogel materials, developing a new type of hydrogel capable of autonomously changing shape and sustaining continuous growth. Throughout the growth process, the material retains strong cytocompatibility and does not harm surrounding living cells, which researchers say gives it broad potential for biomedical applications. The work was led by a research team at South China University of Technology in collaboration with Xijing Hospital. The resulting paper, titled "Non-Equilibrium Hydrogel Demonstrates Cytocompatible and Seamless Heterotrophic Self-Growth," was published in the materials science journal Advanced Functional Materials. The paper has nine authors from four institutions, including South China University of Technology and Xijing Hospital, with corresponding authors including Changjiang Scholar Professor Bian Liming and Zhang Kai of the university.

For a long time, getting synthetic materials to "grow" the way living tissue does has been a major challenge in biomaterials research. Natural tissue continuously expands through cell division and matrix deposition, but once a conventional hydrogel is fabricated, its shape and volume are essentially fixed, making it difficult to accommodate the constantly changing spatial demands of a growing body or a healing tissue site. This "size mismatch" problem is especially acute in tissue repair for infant, child and adolescent patients: if an implanted material cannot expand in step with the patient's own growth, it often has to be replaced through repeated surgeries with progressively larger substitutes, which raises both surgical and infection risk and significantly increases medical costs.

Earlier research teams had tried to make hydrogels "self-grow" through covalent chemical reactions — having the material continuously take up external monomers and polymerize them internally to expand its volume — or by using double-network hydrogels that strengthen and expand under repeated mechanical loading. But these covalent- or mechanical-stimulus-based self-growing systems typically require initiators, ultraviolet light, specific ionic strengths, or repeated mechanical loading, conditions that are not friendly to living cells and have limited the direct use of such materials in living tissue or cell-culture environments. In other words, earlier self-growing hydrogels, even when they could "grow," struggled to safely host living cells while doing so.

To address this bottleneck, the South China University of Technology team proposed a new design: using mild coordination bonding between calcium ions and bisphosphonate-modified pectin molecules to build a non-equilibrium self-growing hydrogel system. Pectin is a polysaccharide naturally found in plant cell walls, known for good biocompatibility and biodegradability; after modifying it with bisphosphonate groups, the researchers enabled it to form reversible coordination crosslinks with calcium ions. In the experiments, the team first prepared a shaped "seed" hydrogel, then placed it in a solution containing soluble, pectin-derived polymer. The seed gel then continuously took up new polymer material from the surrounding solution, and calcium-ion coordination crosslinking seamlessly integrated this newly absorbed polymer into the existing network, driving a sustained increase in the gel's overall volume and mass. The team likened this process of "taking in raw material from the surrounding environment to grow" to the biological phenomenon of "heterotrophy," in which an organism obtains the substances it needs for growth by consuming external organic matter rather than synthesizing it internally, and accordingly named the material a "heterotrophic self-growing hydrogel." Because the calcium-coordination reaction proceeds under mild conditions, without relying on strong acids, strong bases, ultraviolet light or toxic initiators, the entire growth process can take place under conditions close to physiological ones, which the researchers say is key to achieving "cytocompatible self-growth."

The team emphasized that, during growth, new and old material within the hydrogel bond seamlessly, leaving no structural defects or weak points at the growth boundary — meaning the material retains good mechanical integrity even after repeated growth or long-term use, and is less prone to fracturing at the interface between old and new material under stress. More importantly, because the growth conditions are mild, living cells can be pre-encapsulated inside the seed gel and continue to survive and proliferate as the material grows, offering a feasible route toward composite biomaterials that contain living cells internally and can autonomously adjust their shape and volume as needed, moving the concept of "materials growing in concert with cells" a step closer from idea to experimental demonstration.

In terms of applications, a hydrogel material that can grow together with cells while retaining mechanical stability is seen as holding significant potential in tissue engineering, regenerative medicine and soft medical devices. For example, when repairing tissue defects in infants or adolescents, fixed-size implants often fail to keep pace with a patient's changing tissue dimensions as they grow, whereas a hydrogel with autonomous growth capability could, in theory, "grow" in step with surrounding tissue, reducing the need for repeated surgeries to replace materials. Such materials could also be used to build scaffolds for lab-grown organoids, drug-delivery carriers, or substrates for flexible wearable bioelectronic devices. The research team acknowledged, however, that the work remains at the laboratory stage, and further animal studies and long-term safety assessments are needed before its suitability for actual human tissue repair can be determined.

It is worth noting that self-growing, shape-morphing hydrogels have in recent years become a frontier area pursued by multiple Chinese research teams, and are also a hot topic internationally in materials science. The University of Science and Technology of China, for instance, has previously reported a photoresponsive hydrogel whose three-dimensional shape can rapidly and dramatically expand and reconfigure under light, and which has been used to drive miniature rotary soft-robotic structures; a team at the Beijing Institute of Technology has also reported a method for producing bioinspired self-growing hydrogels through interfacial polymerization. Internationally, researchers at Nanyang Technological University in Singapore and Carnegie Mellon University in the United States have likewise reported that controlling oxygen concentration within a system can guide hydrogels to grow along preset paths, forming complex three-dimensional shapes resembling those of natural plant and animal tissue. These different research paths emphasize different things: some focus on rapid shape change under external fields such as light or magnetism, others on long-term co-growth between a material and living tissue, together forming a diverse picture of current research into smart hydrogel materials, and underscoring the sustained effort and international competitiveness of Chinese research teams in this emerging interdisciplinary field.

The researchers said their next steps will focus on verifying the growth stability and long-term biosafety of the hydrogel system in animal models, as well as how well it integrates with real tissue interfaces, in order to move the material system from the laboratory toward preclinical research. Although practical medical application remains a considerable distance away, the achievement demonstrates the possibility of using molecular design to give synthetic materials a "growth" capability that mimics living organisms, providing an important scientific foundation and design model for the next generation of biomedical materials that can grow, adapt, and co-evolve with human tissue.