BDNF and deafness: Gillespie et al. (2015) solved this problem by encapsulating fibroblasts into a non-biodegradable, biocompatible alginate matrix (ImmupelTM, Living Cell Technologies Limited). The same hydrogel was used to encapsulate Schwann cells genetically modified to overexpress the neurotrophins BDNF or neurotrophin 3 (NT-3). These entrapped cells supported SGN survival in an in vitro model of deafness (Pettingill et al., 2008) and, in the case of the BDNF-producing Schwann cells, protected SGNs in a guinea pig model (Pettingill et al., 2011).