Emerging 3D printing technology permits innovative approaches to manufacture cartilage scaffolds associated with layer-by-layer mechanical property adaptation. However, information about gradients of mechanical properties in human articular cartilage is limited. In this study, we quantified a zone-dependent change of local elastic modulus of human femoral condyle cartilage by using an instrumented indentation technique. From the cartilage superficial zone towards the calcified layer, a gradient of elastic modulus values between 0.020 ± 0.003 MPa and 6.44 ± 1.02 MPa was measured. To validate the tissue quality, the histological tissue composition was visualized by glycosaminoglycan and collagen staining. This work aims to introduce a new protocol to investigate the zone-dependent mechanical properties of graded structures, such as human articular cartilage. From this knowledge, better cartilage repair strategies could be tailored in the future.

Despite active development over the past 15 years, contemporary nanoindentation methods still suffer serious drawbacks, particularly long thermal stabilization and thermal drift, which limit the duration of the measurements to only a short period of time. The presented work introduces a novel ultra nanoindentation method that uses loads from the mN range up to 50 mN, is capable of performing long-term stable measurements, and has negligible frame compliance. The method is based on a novel patented design, which uses an active top referencing system. Several materials were used to demonstrate the performance of the method. The measurements with hold at maximum load confirm extremely low levels of instrument thermal drift. The presented Ultra Nanoindentation Tester opens new possibilities for testing thin films and long-term testing, including creep of polymers at high resolution without the need of long thermal stabilization.

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