https://www.tie2-kinase.com/2016/08/18/in-order-to-verify-if-certainly-rgc-are-taken-care-of-andor-expanded-in-presence-of-shh-we-next-tested-the-prolonged-term-effect-of-shh-incubating-the-3-d-collagen-cultures-for-14-days-in-the-absence/