3D printing a universal knee meniscus using a custom collagen ink

Tears of the meniscus are among the most commonly diagnosed knee injuries. Because most of the meniscus lacks the ability to self-heal due to its low vascularity, surgical intervention is needed in more than 85% of cases. Tissue-engineered meniscal implants may provide a treatment strategy that better supports healing and long-term health and mobility benefits. We used three-dimensional printing to develop a “universal” human meniscal tissue repair device that can be trimmed to match the corresponding area of damage debrided during the patient's surgical repair. Computer aided design software was used to design an adult meniscus of average shape based on published physical dimensions. To reproduce the natural fiber arrangement found in the meniscus, the tool path for 3D bioprinting was structured to use alternating layers of circumferential and radial extrusions. We also developed extrudable, shear thinning bioinks based on meniscus biochemical components, including collagen I methacrylate, collagen II, and chondroitin sulfate methacrylate. The combination of this tissue-specific bioink and the deposition pattern to build the meniscus are novel. Ink formulations were evaluated with rheology to assess the viscosity and post-gelling stiffness. Inks retained shape fidelity when thermally gelled after printing into a support bath, and the fabricated menisci maintained stable dimensions for up to 4 weeks post printing. Bioprinted menisci containing human mesenchymal stem cells were also dimensionally stable, and viable cells were present up to 4 weeks post printing. Increased glycosaminoglycan deposition was noted in the bioprinted meniscus over 21 days, and decorin and collagen type I gene expression increased. Compression testing demonstrated that Young's modulus approaches 100 kPa when molded as a solid object and 45 kPa when extruded into the meniscus shape. This 3D printed, anisotropic meniscus emulates the natural architecture and biochemical composition of the natural human meniscus and has potential to be developed into a device for use in treatment of meniscal injuries.