Additive Manufacturing via Direct Ink Writing: Printing Functional Hydrogels and Ceramics for Medical Applications

Additive manufacturing (AM) also known as 3D printing is a highly versatile set of techniques for processing polymers, metals as well as ceramics into complex shapes. Among all AM techniques Direct Ink Writing (DIW) is the most versatile in terms applicable materials by employing a simple extrusion-based approach. Soft hydrogels, e.g., have been processed for biomedical applications using DIW. These polymeric materials offer not only tunable printing properties but also often show great biocompatibility. In combination with functional particles like ZnO these materials will exhibit advanced functionalities like antibacterial properties. This work presents an ink system for active wound dressings consisting of sodium alginate hydrogel as carrier and ZnO particles in the shape of micrometer sized crystals (t-ZnO) with a tetrapod geometry. While the sodium alginate adjusts the inks rheological properties, the individual ZnO tetrapod arms penetrate through the hydrogels surface and have direct contact with the wound. This is due to the unique geometry of the t-ZnO as well as the selection of suitable concentrations for the alginate hydrogel and the particles. The penetration of t-ZnO enables to utilize the tetrapod’s antibacterial properties. Additionally, rheological investigations have been performed improving the printing the results. The sodium alginate shows a high yield point as well as a shear thinning behavior, which is highly desirable for a 3D printing process. These properties enable to print openly porous wound dressings with an oxygen access directly at wounds surface while the at same time the damaged tissue stays protected from contaminations. In order to improve the wound healing even further the t-ZnO particles can be decorated with a variety of functional proteins. These characteristics have been proven using cell and ex-vivo skin tests.<br/>In contrast to these soft materials, DIW allows also to process hard ceramic biomaterials like zirconia. In combination with water soluble polymers like polyethylene oxide, pastes with high shape retention and strong shear thinning properties can be produced. These pastes are utilized in this work for the 3D printing of dental implant materials. The rheological properties have been tailored by changing the inks pH value allowing to process yttrium stabilized zirconia and reaching a high mechanical strength. In summary, this works presents an AM approach, which allows to manufacture soft hydrogels and polymers in combination with hard ceramic particles enabling the versatility of DIW and showing their great potential for biomedical applications.