Mechanical characterization of fibrotic and mineralized tissue in Peyronie's disease

Characterisation of human penile tissue properties using experimental testing combined with multi-target inverse finite element modelling

This paper presents an inverse finite element (FE) approach aimed at estimating multi-layered human penile tissues. The inverse FE approach integrates experimental force-displacement and boundary deformation data of penile tissues with a developed FE model and uses new experimental data on human penile tissue. The experimental study encompasses whole organ plate-compression tests and individual layer tensile and compression tests, providing comprehensive insights into the tissue's mechanical behaviour. The biomechanical characterisation of penile tissue is of crucial significance for understanding its mechanical behaviour under various physiological and pathological conditions. The FE model is constructed using the realistic geometry of the penile segment and appropriate constitutive models for each tissue layer to leverage the accuracy and consistency of the model. Through systematic variation of tissue parameters in the inverse FE algorithm, simulations achieve the best match with both force-displacement and deformed boundary results obtained from the whole organ plate-compression tests. Test results from individual tissue layers are also utilised to assess the estimated parameters. The proposed inverse FE approach allows for the estimation of penile tissue parameters with high precision and reliability, shedding light on the mechanical properties of this complex biological organ. This work has applications not only in urology but also for researchers in various disciplines of biomechanics. As a result, our study contributes to advancing the understanding of human penile tissue mechanics whilst the methodology could also be applied to a range of other soft biological tissues. STATEMENT OF SIGNIFICANCE: This research uses a multi-target inverse finite element (FE) approach for estimating the material parameters of human penile tissues. By integrating experimental data and a realistic FE model, this study achieves high-precision constitutive model parameter estimation, offering key insights into penile tissue mechanics under various loading conditions. The significance of this work lies in the use of this inverse FE approach for fresh-frozen human penile tissues, to identify the mechanical properties and constitutive models for both segregated tunica albuginea and corpus cavernosum as well as intact penile tissue segments. The study's scientific impact lies in its advancement of the understanding of human urological tissue mechanics, impacting researchers and clinicians alike.

Experimental testing combined with inverse-FE for mechanical characterisation of penile tissues

Erectile dysfunction (ED) predominantly affects men in their 40-70s and can lead to poor quality of life. One option for ED treatment is surgical implantation of an inflatable penile prosthesis (IPP). However, they can be associated with negative outcomes including infection, migration or fibrosis. To improve outcomes, the interaction between the IPP device and surrounding tissues needs further investigation and this could be achieved using pre-clinical testbeds, but they need to be informed by extensive tissue testing. In this study, an experimental approach is adopted to characterise the mechanics of horse penile tissue and establish a testing protocol for penile tissue. The whole penis segments were tested in plate compression tests to obtain whole penis behaviour which is necessary for validation of a pre-clinical testbed, whilst tensile and compression tests were performed on individual penile tissues, namely corpus cavernosa and tunica albuginea. The second part of the paper deals with the development of a computational model employing an inverse finite element approach to estimate the material parameters of each tissue layer. These material parameters are in good agreement with the experimental results obtained from the individual tissue layers and whole organ tissue tests. This paper presents the first study proposing realistic nonlinear elastic material parameters for penile tissues and offers a validated testbed for IPPs. STATEMENT OF SIGNIFICANCE: Erectile Dysfunction (ED) affects over half the male population aged 40-70 potentially leading to poor quality of life. Patients not responding to conventional treatments of ED, are advised to use penile prostheses which can create an erection using implanted inflatable cylinders. A significant drawback of such prostheses, however, is the substantial tissue damage they can induce during their usage. Preclinical testbeds, including computational and bench-top models, could offer an efficient means of improving device designs to mitigate this damage but such testbeds require extensive knowledge of penile tissue properties. In this study, the authors determine penile tissue mechanics and apply an inverse FE approach to characterise the penile material properties required to validate preclinical models of the penis.

A phase 2 randomized, placebo-controlled crossover trial to evaluate safety and efficacy of platelet-rich plasma injections for Peyronie's disease: clinical trial update

Peyronie's Disease (PD) is characterized by fibrotic plaques in the penile tunica albuginea, causing curvature and painful erections. Current treatments have limited established efficacy. Platelet-Rich Plasma (PRP), known for modulating inflammation, offers a potential alternative. This randomized, placebo-controlled, crossover study at the University of Miami assesses PRP's safety and efficacy for PD. Forty-one PD patients were randomized into PRP-placebo (Group A) and placebo-PRP (Group B) sequences, receiving two injections of each treatment over three months, with a crossover to receive two injections of alternate treatment over the next three months. Assessments include pain scale, goniometry, questionnaires, and curvature evaluations. Preliminary analysis of 28 patients shows that PRP is safe. There were no adverse events, including penile complications, during follow-up. Pain scores during treatments showed no significant difference between PRP and placebo (p = 0.52). Over six months, the PRP-Placebo group's median PDQ score decreased from 1.9 (IQR: 1.7-2.9) to 1.4 (IQR: 0.7-2.1). This change was not statistically significant (p = 0.098). In contrast, the Placebo-PRP group showed a significant reduction from 1.8 (IQR: 1.4-2.6) to 1.2 (IQR: 1.0-2.0) (p = 0.020). No significant changes in IIEF scores were observed. Both groups initially had a median penile curvature of 40 degrees. At 3 months, the PRP-Placebo group's curvature decreased to 38 degrees (IQR: 35-47.5), while the Placebo-PRP group decreased to 35 degrees (IQR: 30-60). At 6 months, the PRP-Placebo group showed a significant reduction to 25 degrees (IQR: 20-40, p = 0.047), while the Placebo-PRP group's reduction to 32.5 degrees (IQR: 20-50) was not significant (p = 0.490). These early results indicate a delayed PRP effect, prompting further investigation into its long-term impacts. Although limited by sample size, this study suggests PRP injections as a safe treatment for PD, with ongoing research aiming to clarify its therapeutic value.

Development of in silico models to guide the experimental characterisation of penile tissue and inform surgical treatment of erectile dysfunction

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.

A review of the experimental methods and results of testing the mechanical properties of Tunica Albuginea

The present work provides a comprehensive review of the literature on the mechanical properties and existing human tunica albuginea tissue testing methods. Assessments were completed on papers reporting experimental values of Young's modulus, tensile strength, puncture strength, stiffness, toughness, and strain at the ultimate tensile strength (UTS). A high degree of variability in the reported experimental values was found; Young's modulus ranged from 5 MPa to 118 MPa, and tensile strength went from 1.1 MPa to 6.1 MPa. A comparison of the variability of the reported experimental values for puncture strength, stiffness, toughness, and strain at the UTS could not be completed due to a lack of experimental results. This review discusses the pathophysiology and surgical treatment of erectile dysfunction and Peyronie's disease, variability in the existing reported mechanical properties, the impact of the variability of mechanical properties on in silico models and explores the absence of a standardised testing method as a possible reason for the variable in results. Finally, this work attempts to provide suggestions for standardising future mechanical testing of the tunica albuginea through minimising and reporting freeze/thaw cycling, noting the proximal/distal region of the cadaver tunica sample, reporting the orientation (o'clock position) of the cadaver tunica sample, and testing the cadaver tunica samples in bi-axial tension. Ultimately, standardising the testing methodologies of the tunica albuginea will provide higher confidence in reported mechanical property values.