INTRODUCTION: Erectile dysfunction (ED) affects to some degree approximately 52% of the male population aged 40-70 years. Many men do not respond to, or are precluded from using, pharmaceutical treatments for ED and are therefore advised to consider penile prostheses. Different types of penile prosthesis are available, such as inflatable penile prostheses (IPPs). IPPs consist of a pair of inflatable cylinders inserted into the corpora cavernosa (CC). During inflation/deflation of these cylinders, the CC and other surrounding tissues such as the tunica albuginea (TA) are highly impacted. Therefore, it is critical to understand the mechanics of penile tissues for successful implantation of IPPs and to reduce tissue damage induced by IPPs. OBJECTIVES: We explored the importance of the biomechanics of penile tissues for successful IPP function and reviewed and summarized the most significant studies on penile biomechanics that have been reported to date. METHODS: We performed an extensive literature review of publications on penile biomechanics and IPP implantation. RESULTS: Indenters have been used to characterize the mechanical behavior of whole penile tissue; however, this technique applied only local deformation, which limited insights into individual tissue components. Although one reported study addressed the mechanical behavior of TA, this investigation did not consider anisotropy, and there is a notable absence of biomechanical studies on CC and CS. This lack of understanding of penile tissue biomechanics has resulted in computational models that use linear-elastic materials, despite soft tissues generally exhibiting hyperelastic behavior. Furthermore, available benchtop/synthetic models do not have tissue properties matched to those of the human penis, limiting the scope of these models for use as preclinical testbeds for IPP testing. CONCLUSION: Improved understanding of penile tissue biomechanics would assist the development of realistic benchtop/synthetic and computational models enabling the long-term performance of IPPs to be better assessed.

This paper presents a computational study to investigate the mechanical properties of human penile tissues. Different experimental testing regimes, namely indentation and plate-compression tests, are compared to establish the most suitable testing regime for establishing the mechanical properties of the different penile tissues. An idealised MRI-based geometry of the penis, containing different tissue layers, is simulated using the finite element (FE) method to enable realistic predictions of the deformation of the penis. Unlike the linear elastic models used in the literature to-date, hyperelastic isotropic/anisotropic material models are used to capture material nonlinearity and anisotropy. The influence of material properties, morphological variations, material nonlinearity and anisotropy are investigated. Moreover, the implantation of an inflatable penile prosthesis (IPP) is simulated to assess the effects of the implantation procedure, material nonlinearity, and anisotropy on tissue stresses. The results indicate that the interior layers of the penis do not affect the overall stiffness of the penis in the indentation test, while the plate-compression test is able to capture the effects of these layers. Tunica Albuginea (TA) is found to have the most significant contribution to the total stiffness of the penis under load. It can also be observed that buckling occurs in the septum of the penis during the compression tests, and different morphologies dictate different compressive behaviours. There is a clear need for future experimental studies on penile tissues given the lack of relevant test data in the literature. Based on this study, plate-compression testing would offer the most insightful experimental data for such tissue characterisation.