Effective treatment of bone defects requires innovative materials that support bone regeneration, are easy to apply, and adapt easily to the defect site. Injectable hydrogels offer a minimally invasive solution, but often lack mechanical integrity and biological functionality. Traditional methods that combine bone grafts with adhesive materials often fail to achieve simultaneous bone regeneration and adhesion. To help advance bone tissue engineering, a research team at Pohang University of Science and Technology (POSTECH) developed an injectable, adhesive hydrogel that achieves photocrosslinking and mineralization simultaneously, without the need for bone grafts, when it is irradiated with light that is safe for the human body. When the hydrogel is activated by visible light, its primary components form bonds and harden, and bone-building minerals like calcium and phosphate begin to form within the hydrogel. These minerals function as bone graft material, eliminating the need for separate bone grafts and adhesives. Through synergistic photocrosslinking and mineralization, the hydrogel can provide both bone regeneration and adhesion. Together, these processes also enhance the mechanical and bioactive properties of the hydrogel, allowing for rapid, controlled customization, even for irregular defects. POSTECH researchers have developed an injectable adhesive hydrogel to support bone regeneration. Irradiating the hydrogel with visible light simultaneously induces crosslinking and mineralization. Courtesy of Pohang University of Science and Technology. To formulate the hydrogel, the researchers integrated a photoreactive agent with calcium ions and phosphonodiol, a photodegradable material that facilitates rapid formation of calcium under irradiation. The team integrated these materials in a matrix of tyramine-conjugated alginate and arginine-glycine-aspartate (RGD) peptide-fused, bioengineered mussel adhesive protein (MAP-RGD). The gel-forming capability of alginate is improved by tyramine conjugation, allowing rapid visible light crosslinking. MAP-RGD facilitates adhesion and bioactive RGD peptides promote cell attachment and proliferation. The hydrogel is coacervate-based, which helps it retain its shape and position after being injected into the body. It does not dissolve in or mix with water and exhibits superior mechanical properties, including enhanced underwater tissue adhesive strength and compressive resistance. The researchers evaluated the ability of the adhesive hydrogel system to accelerate bone regeneration in vivo in rat models with femoral bone defects. The hydrogel was successfully injected into the irregularly shaped defects. It adhered accurately to the defect sites and effectively delivered components essential for bone regeneration, without the need for bone grafts. Earlier studies also explored the use of light for treating bone defects, but encountered issues such as requiring separate preparation and mixing of bone grafts and adhesive materials, and weak bonding of the main components of the gel, which often degraded over time. The new adhesive hydrogel has the potential to improve bone tissue engineering for resolving defects caused by trauma, infections, and other conditions. It could provide a versatile, efficient, biofriendly alternative to conventional bone repair methodologies. “The injectable hydrogel system for bone regeneration developed by our research team represents an innovative alternative to conventional complex treatments for bone diseases and will greatly advance bone tissue regeneration technology,” professor Hyung Joon Cha said. The research was published in Biomaterials (www.doi.org/10.1016/j.biomaterials.2024.122948).