I also find those studies to be interesting.
The above links are all related to collagen. There are many different types of collagen and I am wondering of what type of collagen the tunica albuginea is primarily composed and of what type(s) regulate penile girth. I found them as I was trying to answer these questions. Some of what is linked above is contradictory.
The tunica is a type of fascia. Does anyone know of what collagen type fascia and more specifically the tunica albuginea is composed and the roles played by the various tunica types?