The anterior cruciate ligament (ACL) is the primary stabilizer of the knee joint, and ACL injuries are highly prevalent, particularly among physically active and athletic individuals. Although ACL reconstruction is a well-established orthopedic procedure, significant challenges remain regarding biological integration between the graft and bone, which may negatively affect clinical outcomes.

In recent years, advanced biomaterials and regenerative medicine approaches have gained increasing attention as potential strategies to enhance osteointegration and promote more physiological tissue healing. Before clinical application, these materials must undergo rigorous in vitro biological evaluation in accordance with international standards, particularly ISO 10993-5 for cytotoxicity assessment.

The study will investigate cytotoxicity, cell viability, inflammatory responses, pro-fibrotic effects, and osteogenic potential using relevant human cell models. The regenerative effects of platelet-rich plasma (PRP), a source of growth factors, will also be evaluated.

The biomaterials under investigation include a titanium alloy and polylactic acid (PLA), both widely used in orthopedic applications. The main objective is to demonstrate their biocompatibility, absence of cytotoxic, inflammatory, and pro-fibrotic effects, and their ability to support osteogenic processes and tissue integration. The findings will provide essential evidence for subsequent preclinical in vivo studies and future clinical translation.

Femoral condyle, tibial plateau and synovial membrane samples

Patients undergoing primary total knee arthroplasty at the Orthopaedic and Trauma Clinic II of the IRCCS Istituto Ortopedico Rizzoli (Bologna, Italy), in whom collection of tibial plateau, femoral condyles and/or synovial tissue is planned.

Inclusion criteria:

Age 18-80 years, male or female Primary tricompartmental osteoarthritis Body Mass Index (BMI) < 35 Kellgren-Lawrence grade III-IV osteoarthritis Written informed consent

Exclusion criteria:

Previous partial knee arthroplasty or cartilage repair/regenerative procedures Rheumatoid arthritis or chronic corticosteroid/immunosuppressive therapy Positive testing for HIV, HBV or HCV infection Concentrated bone marrow (BMC) samples

Patients of both sexes providing written informed consent and presenting with the following characteristics:

Inclusion criteria:

Age 18-70 years Medial compartment knee osteoarthritis (Kellgren-Lawrence grade II-III for >4 months) Failure of ≥6 months of conservative treatment (NSAIDs/analgesics, hyaluronic acid, corticosteroid or PRP injections) Written informed consent

Exclusion criteria:

Inability to provide informed consent Knee trauma within the previous 6 months Malignancy, rheumatic disease, uncontrolled diabetes, uncontrolled thyroid disorders Alcohol or drug abuse BMI > 35 Intra-articular injections within the previous 6 months Knee surgery within the previous 12 months HIV, HBV or HCV positivity Platelet-rich plasma (PRP) samples

Patients of both sexes with degenerative cartilage disease of the knee.

Inclusion criteria:

Age 18-65 years Clinical signs and symptoms of knee cartilage degeneration Radiographic or MRI evidence of degeneration (Kellgren-Lawrence grade II-IV) Hemoglobin > 11 g/dL Platelet count > 150,000/mm³ No clinically relevant ECG abnormalities Written informed consent

Exclusion criteria:

Rheumatoid arthritis or chronic corticosteroid/immunosuppressive therapy Uncontrolled diabetes Hematological disorders or anticoagulant/antiplatelet therapy Thyroid metabolic disorders Alcohol, drug or medication abuse NSAID use within 3 days prior to blood draw Cardiovascular disease contraindicating a 150 mL blood draw HIV, HBV or HCV positivity

Subjects will be recruited among patients admitted to the IRCCS Istituto Ortopedico Rizzoli and scheduled for total knee arthroplasty for the treatment of chondral defects and/or undergoing regenerative infiltrative therapies with BMC and PRP.

For the study, biological material obtained during the surgical removal of femoral condyles, tibial plateaus and synovial membranes, as well as during implantation of the prosthetic components, will be used. For BMC and PRP, only waste material not required for the surgical procedures will be collected.

The recovery of such material will be performed during routine clinical practice by the medical staff of the Orthopaedic and Trauma Clinic II.