A biomechanical model of Peyronie's disease

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

Peyronie's disease affects penile mechanics, but published research lacks biomechanical characterization of affected tunica albuginea. This work aims to establish mechanical testing methodology and characterize pathological tissue mechanics of Peyronie's disease. Tunica albuginea was obtained from patients (n = 5) undergoing reconstructive surgery for Peyronie's disease, sectioned into test specimens (n = 12), stored frozen at -20 °C, and imaged with micro-computed tomography (µCT). A tensile testing protocol was developed based on similar soft tissues. Correlation of mechanical summary variables (force, displacement, stiffness, work, Young's modulus, ultimate tensile stress, strain at ultimate tensile stress, and toughness) and µCT features were assessed with linear regression. Specimens empirically grouped into hard or soft stress-strain behavior were compared using a Student's t-test. Surface strain and failure patterns were described qualitatively. Specimens displayed high inter- and intra-subject variability. Mineralization volume was not correlated with mechanical parameters. Empirically hard tissue had higher ultimate tensile stress. Failure mechanisms and strain patterns differed between mineralized and non-mineralized specimens. Size, shape, and quantity of mineralization may be more important in determining Peyronie's disease plaque behavior than presence of mineralization alone, and single summary variables like modulus may not fully describe mechanical behavior.

Biomechanical Simulation of Peyronie's Disease

A pathological disorder of human penile function, known as Peyronie's disease, is characterized by the formation of plaque particles within the tunica albuginea. The plagues in the shape of rigid plate form in the scars as a result of the imperfect healing process. Due to high stiffness, plagues are the source of pain and anomalous deformations during erectile penis function. The authors simulate the biomechanical behavior of the penile structure by a 3D finite element model. The numerical model is based on the real geometrical shape and the tissue structure with consideration of large nonlinear deformations. The penile erection is modeled by the initial strains imposed on the corpus cavernosa. The stress analysis is performed in a case study of various plague locations. The Peyronie's syndrome manifested by the penis angular deviation simulated by the analysis is compared with the clinical data. The computational simulations provide a rational explanation for the clinical observations on patients. The objective is to apply the proposed modeling approach for the development and validation of treatment methods based on the application of shock waves.

Sonic hedgehog delivery from self-assembled nanofiber hydrogels reduces the fibrotic response in models of erectile dysfunction

Erectile dysfunction (ED) is a serious medical condition in which current treatments are ineffective in prostatectomy and diabetic patients, due to injury to the cavernous nerve (CN), which causes irreversible remodeling of the penis (decreased smooth muscle and increased collagen), through a largely undefined mechanism. We propose that sonic hedgehog (SHH) and neural innervation, are indispensable regulators of collagen in the penis, with decreased SHH protein being an integral component of the fibrotic response to loss of innervation. We examined collagen abundance and morphology in control (Peyronie's), prostatectomy and diabetic patients, and in rat models of penile development, CN injury, SHH inhibition and under regenerative conditions, utilizing self-assembling peptide amphiphile (PA) nanofiber hydrogels for SHH delivery. Collagen abundance increased in penis of ED patients. In rats, collagen increased with CN injury in a defined time frame independent of injury severity. An inverse relationship between SHH and collagen abundance was identified; SHH inhibition increased and SHH treatment decreased penile collagen. SHH signaling in the pelvic ganglia (PG)/CN is important to maintain CN integrity and when inhibited, downstream collagen induction occurs. Collagen increased throughout penile development and with age, which is important when considering how to treat fibrosis clinically. These studies show that SHH PA treatment reduces collagen under regenerative post-prostatectomy conditions, indicating broad application for ED prevention in prostatectomy, diabetic and aging patients and in other peripheral nerve injuries. The PA nanofiber protein vehicle may be widely applicable as an in vivo delivery tool.

STATEMENT OF SIGNIFICANCE

We use self-assembling peptide amphiphiles (PA) as biological delivery vehicles to prevent cavernous nerve (CN) injury induced erectile dysfunction (ED). These versatile hydrogels were molecularly pre-programmed for sonic hedgehog (SHH) protein delivery, either from an injectable solution with fast, in situ assembly into a soft hydrogel, or by highly aligned monodomain nanofiber bundles. We used PAs to examine a novel neuronal component to collagen regulation and the role of SHH in the fibrotic response to CN injury. SHH perturbation in the penis or the CN, selectively impacts collagen, with SHH inhibition increasing and SHH treatment suppressing collagen. These results suggest that SHH treatment by PA has translational potential to suppress collagen induction and remodelling, an irreversible component of ED development.

Tunica albuginea allograft: a new model of LaPeyronie's disease with penile curvature and subtunical ossification

The pathophysiology of LaPeyronie's disease (PD) is considered to be multifactorial, involving genetic predisposition, trauma, inflammation and altered wound healing. However, these factors have not yet been validated using animal models. In this study, we have presented a new model obtained by tunica albuginea allograft. A total of 40, 16-week-old male rats were used. Of these, 8 rats served as controls and underwent a 10 × 2-mm-wide tunical excision with subsequent autografting, whereas the remaining 32 underwent the same excision with grafting of the defect with another rat's tunica. Morphological and functional testing was performed at 1, 3, 7 and 12 weeks after grafting. Intracavernous pressure, the degree of penile curvature and elastic fiber length were evaluated for comparison between the allograft and control groups. The tissues were obtained for histological examination. The penile curvature was significantly greater in the allografted rats as compared with the control rats. The erectile function was maintained in all rats, except in those assessed at 12 weeks. The elastin fiber length was decreased in the allografted tunica as compared to control. SMAD2 expression was detected in the inner part of the allograft, and both collagen-II- and osteocalcin-positive cells were also noted. Tunica albuginea (TA) allograft in rats is an excellent model of PD. The persistence of curvature beyond 12 weeks and the presence of ossification in the inner layer of the TA were similar to those observed in men with PD. Validation studies using this animal model would aid understanding of the PD pathophysiology for effective therapeutic interventions.

Sonic hedgehog protein is decreased and penile morphology is altered in prostatectomy and diabetic patients

Erectile dysfunction (ED) is a debilitating medical condition and current treatments are ineffective in patients with cavernous nerve (CN) injury, due to penile remodeling and apoptosis. A critical regulator of penile smooth muscle and apoptosis is the secreted protein sonic hedgehog (SHH). SHH protein is decreased in rat prostatectomy and diabetic ED models, SHH inhibition in the penis induces apoptosis and ED, and SHH treatment at the time of CN injury suppresses smooth muscle apoptosis and promotes regeneration of erectile function. Thus SHH treatment has significant translational potential as an ED therapy if similar mechanisms underlie ED development in patients. In this study we quantify SHH protein and morphological changes in corpora cavernosal tissue of control, prostatectomy and diabetic patients and hypothesize that decreased SHH protein is an underlying cause of ED development in prostatectomy and diabetic patients. Our results show significantly decreased SHH protein in prostatectomy and diabetic penis. Morphological remodelling of the penis, including significantly increased apoptotic index and decreased smooth muscle/collagen ratio, accompanies declining SHH. SHH signaling is active in human penis and is altered in a parallel manner to previous observations in the rat. These results suggest that SHH has significant potential to be developed as an ED therapy in prostatectomy and diabetic patients. The increased apoptotic index long after initial injury is suggestive of ongoing remodeling that may be clinically manipulatable.

The biomechanics of erections: two- versus one-compartment pressurized vessel modeling of the penis

Previous biomechanical models of the penis simulated penile erections utilizing 2D geometry, simplified 3D geometry or made inaccurate assumptions altogether. These models designed the shaft of the penis as a one-compartment pressurized vessel fixed at one end when in reality it is a two-compartment pressurized vessel in which the compartments diverge as they enter the body and are fixed at two separate anatomic sites. This study utilizes the more anatomically correct two-compartment penile model to investigate erectile function. Simplified 2D and 3D models of the erect penis were developed using the finite element method with varying anatomical considerations for analyzing structural stresses, axial buckling, and lateral deformation. This study then validated the results by building and testing corresponding physical models. Finally, a more complex and anatomically accurate model of the penis was designed and analyzed. When subject to a lateral force of 0.5 N, the peak equivalent von Mises (EVM) stress in the two-compartment model increased by about 31.62%, while in the one-compartment model, the peak EVM stress increased by as high as 70.11%. The peak EVM stress was 149 kPa in the more complex and anatomically accurate penile model. When the perforated septum was removed, the peak EVM stress increased to 455 kPa. This study verified that there is significant difference between modeling the penis as a two- versus a one-compartment pressurized vessel. When subjected to external forces, a significant advantage was exhibited by two corporal based cavernosal bodies separated by a perforated septum as opposed to one corporal body. This is due to better structural integrity of the tunica albuginea when subjected to external forces.

Mixed experimental and numerical approach for characterizing the biomechanical response of the human leg under elastic compression

Elastic compression is the process of applying an elastic garment around the leg, supposedly for enhancing the venous flow. However, the response of internal tissues to the external pressure is still partially unknown. In order to improve the scientific knowledge about this topic, a slice of a human leg wearing an elastic garment is modeled by the finite-element method. The elastic properties of the tissues inside the leg are identified thanks to a dedicated approach based on image processing. After calibrating the model with magnetic resonance imaging scans of a volunteer, the pressure transmitted through the internal tissues of the leg is computed. Discrepancies of more than 35% are found from one location to another, showing that the same compression garment cannot be applied for treating deficiencies of the deep venous system or deficiencies of the large superficial veins. Moreover, it is shown that the internal morphology of the human leg plays an important role. Accordingly, the approach presented in this paper may provide useful information for adapting compression garments to the specificity of each patient.

A three-dimensional model of the penis for analysis of tissue stresses during normal and abnormal erection

Approximately half of the males between the ages of 40 and 70 suffer erectile dysfunction. Because adequate mechanical interactions in the penis are necessary for functional erection it is important to analyze stresses in the erect penis. Previous penis models were limited to simplified or two-dimensional geometry. Here we developed a three-dimensional model for structural analysis of normal erection as well as erections of a penis with substantial asymmetry of the corporal bodies, and Peyronie's disease. The model was constructed based on anatomical images and included skin, tunica albuginea, corpus cavernosa, and spongiosum. The mechanical behavior of the tunica and skin were assumed to be three-dimensional-orthotropic, and other tissues as well as Peyronie's plaque was taken as linear elastic. Stresses and deformations during erection were analyzed using a commercial finite elements (FE) solver. Erection was simulated by raising blood pressure in the corporal bodies to 100 mmHg. The tunica was found to be the most highly loaded tissue in the erect penis. Peak von Mises stresses in the healthy tunica, tunica of the asymmetric corpora model, and tunica with Peyronie's disease were 114 kPa, 167 kPa, and 830 kPa, respectively. The angles of distortion of the penis with respect to the vertical axis were approximately 4.5 degrees and approximately 2 degrees , for the asymmetric and Peyronie's cases, respectively. The model's ability to determine internal stresses in the erect penis offers a new point of view on the mechanical factors involved with erection, and enables us to relate these data with different penile pathologies.

Biomechanical aspects of Peyronie's disease in development stages and following reconstructive surgeries

Peyronie's disease is a disorder of the penile connective tissues that leads to development of dense fibrous or ossified plaques in the tunica albuginea, causing penile deformity and painful erection. A biomechanical model of the penis was utilized for analyzing the mechanical stresses that develop within its soft tissues during erection in the presence of Peyronie's plaques. The model's simulations demonstrated stress concentrations around nerve roots and blood vessels due to the plaques. These stresses may irritate nerve endings or compress the vascular bed, and thus cause penile deformity and/or painful erection. The model was further used to elaborate the effects of different biological or artificial materials for reconstruction of the penis following plaque removal. Clinical applications of the present model can range from analysis of the etiology of the disease to assisting in the determination of optimal timing for therapeutic interventions and in the selection of patch material for penile reconstructions.

Computational tools in rehabilitation of erectile dysfunction

Erectile dysfunction (ED) is defined as the inability to achieve and maintain an erection adequate for satisfactory intercourse. It is a common problem among approximately 50% of men between the ages of 40 and 70. Erectile dysfunction is not only stressful to both the affected individual and his partner, but it can also negatively affect self-esteem. Biomechanical models have recently been developed to study both the structural and hemodynamic factors involved in normal and pathological erectile conditions. These computational models, which are reviewed in the present paper, allow for better understanding of the mechanisms acting in ED and provide a suitable basis for development of state-of-the-art interdisciplinary treatment approaches aimed to improve the quality of life for these men.