Sterilization just means "the process of making something free from bacteria or other living microorganisms", the only "processing" besides that is adding glycerol which is a lubricant/moisturizer, perhaps also helps to "glue" it all up. At the end it is still raw fish skin being implanted over healing wounds, it just needs to be clean as heck because healing wounds are very pron to acute infections (and the worst of them require the amputation of the limb).