Tissue response formation and maturation after cochlear implantation

The tissue response to cochlear implantation is thought to be involved in the loss of residual hearing, and its extent has been found to affect speech perception. This study investigated tissue response formation and maturation, focusing on both wound contraction using immunofluorescence markers and collagen deposition by multiphoton microscopy, in the implanted guinea pig cochlea.

Cochlear implantation was undertaken in a total of thirty-five guinea pigs, and the cochleae were harvested at four time-points: 1-, 14-, 28- and 84-days post-implantation. Ten animals were designated as controls. The tissue response morphology and collagen deposition were investigated by multiphoton microscopy. The wound contraction was studied using immunofluorescence markers of SMA and vimentin.

Tissue response was located in the scala tympani's basal-turn, between the lateral wall and basilar membrane. Its area didn't change; however, its morphology and contents changed overtime after cochlear implantation within the sampled basal-turn field. At the proliferative phase of wound healing (14-days), an increased SMA was observed, with a "bubble-like" space formed between the basilar membrane and tissue response. During the early remodelling phase (28-days), there was increased vimentin expression and collagen deposition within the middle of the tissue response. By the later remodelling phase (84-days), vimentin expression reduced, but collagen density continued to increase.

Cochlear implantation triggers proliferation of the fibroblasts involved in wound contraction; this process is completed by three months. In contrast, collagen density continued to increase during the three-month window indicative of scar formation which may precede bone growth.