When a bone breaks, the body can often repair the damage on its own. In many cases, the broken pieces slowly grow back together as new bone forms. However, some injuries are too serious for the body to fix without medical help. Surgeons may also need to remove part of a bone if a tumor is present. In situations like these, doctors usually place an implant inside the body to support the healing process and help the bone grow again.
Many implants today use the patient’s own bone, called autografts. In some cases, surgeons use metal or ceramic implants. While these methods can be effective, they also present certain challenges. Autografts require another surgery to remove bone from the body. This method can cause more pain and raise the risk of infection. Metal implants are very stiff and may become loose over time. Researchers think better solutions should work more like natural bone.
Bone is not a simple, solid structure. Instead, it is a very complex tissue filled with tiny tunnels and cavities. According to Professor Xiao-Hua Qin, a biomaterials engineer at ETH Zurich, successful bone repair depends on many types of cells working together.
These cells must move into the implant and start building new bone tissue. If the implant does not allow this process to happen, healing may not occur properly. To address this challenge, Qin and her research team, together with Professor Ralph Müller, have developed a new type of material that could be used for bone implants in the future. Their work was recently published in the scientific journal Advanced Materials. The team created a special hydrogel that is soft and flexible, similar to jelly.
This material can slowly dissolve in the body as natural bone replaces it. The idea for this material comes from the body’s natural way of healing a broken bone. When a bone breaks, the body does not form hard bones immediately. First, it creates a soft structure that helps the bone start healing.
During the first few days, a blood clot or bruise appears at the injury site. They enter the damaged part and begin the repair process. Nutrients can also move through the area to support healing. Inside this early structure, a network made of fibrin holds the cells together. Over time, this soft tissue slowly changes into strong, rigid bone.
The hydrogel created by the researchers copies this early stage of bone healing. It contains about 97 percent water and only 3 percent of a special polymer that is safe for the body. To control how the material solidifies, the scientists added two special molecules. One molecule connects the polymer chains together. The other reacts when it is exposed to light and starts the chemical process that forms a solid structure.
A former doctoral student in the research group, Wanwan Qiu, designed the connecting molecule specifically for this project. When a laser beam with a certain wavelength shines on the hydrogel, the polymer chains link together immediately. The laser hardens the parts it touches. The remaining material stays in liquid form. It can be rinsed away later. This makes it easier for scientists to shape the hydrogel.
The method also allows them to create very precise structures inside it. Some of the structures are as small as 500 nanometers. This level of detail is important because natural bone also contains tiny internal features. Qin says shaping hydrogels is normally difficult because they behave like soft jelly. However, the new connecting molecule allows the material to be formed quickly and accurately. The laser system can work at speeds of up to 400 millimeters per second, which the researchers say is a record for this type of technology.
In their experiments, the scientists produced hydrogel structures that closely resemble real bone. They used medical imaging data as a guide to create designs similar to bone trabeculae, the tiny internal supports inside bone. Natural bone contains a huge network of channels filled with fluid. According to Qin, a small cube of bone about the size of a die contains around 74 kilometers of microscopic tunnels. For comparison, the famous Gotthard Base Tunnel is about 54 kilometers long.
So far, the hydrogel has only been tested in laboratory conditions. In these tests, bone-forming cells quickly moved into the material and began producing collagen, an essential substance in bone tissue. The experiments also showed that the hydrogel is biocompatible and does not harm the cells.
The research team has already filed a patent for the base material and anticipates its eventual use in medicine. More studies are necessary before that can happen. Qin is planning animal tests with scientists from the AO Research Institute Davos. Researchers will test whether the hydrogel implant helps broken bones heal. They will also see if the bone becomes strong again. If the results are satisfactory, this method could give doctors a more natural way to treat serious bone injuries.
