Freeze drying and Lugol staining of human menisci reveal circumferential fibre volumes to guide meniscus implant design and virtual simulation.

The knee menisci are essential for maintaining joint stability and load distribution, with circumferential collagen fibres playing a critical biomechanical role. Degenerative or traumatic injuries to the meniscus can require implants to restore function. This study aimed to develop a 3D-printable meniscus implant that could be virtually tested prior to production. A novel staining and preparation protocol using Lugol's solution and freeze-drying was applied to six intact human menisci, enabling high-resolution micro-CT imaging. Quantitative analysis revealed that approximately 48% of the meniscal volume consists of circumferential fibres. Based on this, a two-volumetric printable stereolithography (STL) model was created, with an inner volume representing 48% of the total structure. A custom Python script was developed to translate the G-code from this model into a two-volumetric finite element (FE) model -overcoming the limitations of conventional software. The two-volumetric implant was then evaluated in a virtual knee joint using thermoplastic polyurethane materials with elastic moduli of 54 MPa and 205 MPa. The results confirmed the feasibility of simulating and optimizing patient-specific meniscal implants prior to fabrication.