Background Periprosthetic osteolysis is the most common long-term complication of a total joint arthroplasty, often resulting in aseptic loosening of the implant. As we aim at developing a safe and minimally invasive implant refixation procedure, thorough characterisation of the properties of the periprosthetic tissue is needed. Methods In this pilot study, the periprosthetic tissue of eleven patients undergoing hip revision surgery due to aseptic loosening was obtained. Histology, confocal microscopy, atomic force microscopy (AFM) and nanoindentation were performed to structurally and mechanically characterise the tissue. The study was approved by the Medical Ethical Committee of the Leiden University Medical Center. Results Using a Sirius Red staining and Movat staining, samples were shown to contain collagen fibers and a ground substance consisting of glycosoaminoglycans and mucopolysaccharides. However, the relative proportions of these tissue components differed between as well as within samples. Confocal microscopy revealed differences in collagen fiber orientation and thickness between tissues. Certain samples showed increased collagen staining intensity as well as increased fiber directionality, indicating higher degrees of tissue maturation. Using AFM and nanoindentation, the Young's modulus of the tissue was determined, which is a measure of tissue stiffness. The ranges of Young's moduli observed (generally 0–250 kPa) were relatively low when compared to other collagen-rich soft tissues (e.g. 500 kPa in skin and even 25 MPa in pericardium). Since the periprosthetic tissue develops at a site of friction, cells at the bone-implant interface seem not able to produce a matrix with optimal strength and properties. Conclusions This study provides new insights on the structural organization and mechanical properties of the periprosthetic tissue. Large inter-patient as well as intra-patient variations in tissue characteristics at all levels studied were observed, which strengthens the need for further research and underscores the need for tailored solutions in the field of treating aseptic loosening.@en