Biomimetic adhesive for tissue and bone from the 3D printer

Researchers at the Fraunhofer Institute for Applied Polymer Research together with the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) and the Fraunhofer USA Center for Manufacturing Innovation have developed a tissue adhesive based on the model of the mussel. The printable dopamine-based tissue adhesive can even be printed on curved, uneven surfaces.

The researchers found the model for the tissue adhesive in nature: mussels. These adhere to a wide range of marine surfaces and are difficult to remove. The special adhesive effect is due to a protein that contains the amino acid dihydroxyphenylalanine - also known as DOPA.

"DOPA ensures extremely effective adhesion. We have transferred this property to our adhesive by synthesizing polymers that contain the building block dopamine, a chemical analogue of DOPA," reports Dr. Wolfdietrich Meyer, scientist at the Fraunhofer Institute for Applied Polymer Research (IAP). Various additives such as apatite particles, proteins and signaling molecules can also promote the growth of bone cells and can be used as a coating material for titanium implants, for example.

The newly developed printing process makes it possible to print titanium hip implants. "The synthetic imitation of the biochemical properties of mussel proteins, in particular the amino acid DOPA, enables an immediate and long-lasting bond between implant and bone," says Meyer.

This solves a problem that affects many patients with hip implants. Until now, hip implants have lost their hold in the bone after some time because the bone recedes. The new tissue adhesive should prevent premature replacement in future. "The adhesive is biocompatible and promotes the ingrowth of the implant into the bone, which minimizes the need for subsequent adjustments or revision surgery," says Meyer, describing the advantages of the biomimetic adhesive.

The functionality of the adhesive can be extended by chemical synthesis. One modification allows it to react to light, for example. "If it is irradiated with UV light, it hardens. This increases its adhesive effect," reports Meyer. In 3D printing, photoreactive materials can be processed under UV radiation. This allows complex structures for customized medical implants to be built.

The introduction of dopamine-like monomers into a polymer matrix creates a versatile adhesive. Biomedical applications include the promotion of bone adhesion through specific microtopography on the titanium surface and with DOPA acrylate. And hydroxyapatite nanoparticles in the ink improve the integration of the implant in the body. Hydrogels can be used to control the degree of hydration and water distribution, which is crucial for biomedical applications such as promoting cell adhesion and proliferation.

"We have virtually developed the printing material for 3D printing," says Meyer. This is because the research team at the Fraunhofer Institutes IAP and IGB has succeeded in making the adhesive printable by cross-linking the polymers. At the Fraunhofer Center for Manufacturing Innovation (CMI) in Boston, USA, the material was applied to a three-dimensional titanium hip joint using a bioprinter. This is clear evidence a precise and customized application is possible.