What are the key factors of success in the relationship between an academic institution and a resulting spin-off?

Networking opportunities, use of laboratories and research cooperation are key resources universities can provide to their spin-offs in their further development. How can these ventures make their academic institution of origin a long-term partner? Which benefits do universities have when continuing to provide the start-up with the support required? Are there some ideal routines and guidelines to create a profitable and long-lasting collaboration for both?