The boundary conditions included 4 constraints on the lateral and dorsal-plantar aspects of the penis, allowing its expansion as a result of inflation by an equivalent erectile pressure Ρe = Ρa- σcc. The erectile pressure, Ρe, reflected the resistance stress σcc of the spongy corpus cavernosa tissue to inflation pressure Ρa = 100 mmHg caused by arterial blood flow into the cavities of the penis. As the penis becomes erect, blood is supplied to the corpus cavernosa until the full erection corporal volume reaches VE which is the total corporal capacity (TCC). When blood drains and the penis becomes flaccid, the corporal volume reduces up to VF = 35% TCC. Assuming that the corpus cavernosal tissue is unstressed at VF, the characteristic stretch ratio λmax from flaccid to full erection is given by the generally accepted relationship λ= (VE/VF)1/3 and equals 1.42. It is further assumed that the mechanical characteristics of the corpus cavernosal tissue is similar to those of the lung parenchyma, hence, σcc=7 KPa at λmax=1.42. The penile soft tissues were assumed to be homogenous, isotropic, and linear elastic materials.
