In this work, we introduce biodegradation as a process of more-than-human unmaking. We begin by positioning biodegradation amongst related works in design research before presenting a circular process of making and unmaking biomaterials and living organisms through biodegradation. To exemplify this process, we detail two existing works - ReClaym and Biomenstrual - that exemplify how biodegradability can be explored in design through different biomaterials, methods, and contexts. By diffractively reading these projects through one another, we identify six themes and corresponding suggestions for researchers engaging with biodegradation. Lastly, we discuss the broader design implications and limitations, as well as the more-than-human values that emerge from designing for biodegradation via biomaterials. Through this, we aim to provide design researchers with practical tools and insights for engaging with biodegradation to unmake anthropocentric hierarchies between humans, non-humans, and biomaterials, which in turn can promote environmental sustainability and support more-than-human collaboration and care.