Spatially resolved micromechanical characterisation of human testis tissue reveals distinct signatures across developing, adult and pathological tissue states

Male reproductive health is in a state of decline that is characterised, in part, by an apparent global decrease in sperm concentrations. A functional preclinical model of the testis would provide an increased understanding of male reproductive health and facilitate the development of effective treatments for the rising incidence of male infertility. However, current preclinical models of the human testis have yet to successfully replicate the process of spermatogenesis, one of the primary functions of the testis. Understanding the micromechanical environment of the human testis could provide insights into overcoming the challenge of mimicking human spermatogenesis in vitro and aid in the development of representative material substrates for use in testicular models. This study characterised the mechanical properties of human testis tissue obtained from three cohorts, including adults undergoing microsurgical testicular sperm extraction (n = 6) and gender affirmation surgery (n = 24), and developmental tissues (foetal and adolescence) (n = 7). A nanoindentation technique, combined with histological investigation, was used to spatially characterise the elastic (Young's modulus) and viscoelastic properties (storage and loss moduli and Tan(δ)) of testis tissue across numerous morphological states. The tissue exhibited Young's modulus values between 0.1 and 1 kPa, while seminiferous tubules exhibited significantly higher Young's and storage moduli compared to interstitial space. Tan(δ) exhibited a significant negative correlation with spermatogenesis status in adult cohorts. This study informs the development of improved diagnostics for male infertility and facilitates the fabrication of mechanically representative material substrates for use in systems that aim to achieve in vitro spermatogenesis using human testicular cells.