This chapter explores the theoretical implications of co-authorship with living systems in the context of bio-digital fabrication. It presents a body of work focused on 3D printing and robotic deposition techniques that integrate living systems such as fungi, lichens, algae, and bacteria. These microorganisms are embedded into bioreceptive, hydrogel-based substrates, forming hybrid material systems that grow, adapt, and eventually decompose—challenging traditional design notions of form, function, permanence, and authorship. Grounded in the concept of bioreceptivity, the research investigates how computational design, microbiology, and digital fabrication can converge to develop living materials that function as active ecological interfaces. These materials are not static but evolve through time and environmental interaction, becoming carbon-positive structures that heal, grow, and regenerate. The methodologies combine generative modeling, environmental simulation tools, and machine learning with lab-based protocols for cultivating and manipulating living cells. These living materials operate within circular economies, utilizing local, renewable resources and upcycled waste, while reducing energy and carbon footprints. By treating biological systems as collaborators rather than passive materials, this research proposes new frameworks for regenerative design practice. It emphasizes low-energy, toxin-free, biodegradable lifecycles, offering alternatives to extractive, high-waste industrial processes. Ultimately, the work repositions fabrication as an act of cultivation and care, where the designer engages in a dynamic, symbiotic relationship with material life. This approach contributes to the growing discourse on biodesign and living systems thinking, promoting a shift toward ecologically responsive and regenerative design strategies embedded in both scientific rigor and creative experimentation.