Introduction: This study was one more step of a systematic approach for the development of a poly-L-lactic biodegradable support matrix incorporating a therapeutically releasable amount of ampicillin. In vitro studies (3 months) documented the sustained release of therapeutic levels of antimicrobial.¹ In vivo efficacy was demonstrated in otitis media-induced chinchillas (S. pneumoniae) and cats (Eustachian tube obstruction).² Histopathological studies in cats documented a lack of inflammatory reaction from the device itself, and its capacity of being biodegradable.² Aims and objectives: This step evaluates potential hair damage to this device. Materials and methods: Morphometry of the organ of Corti (hair cell count) was done in 14 chinchillas exposed to these devices for 3 weeks (7 with and 7 without ampicillin). Results: There were no qualitative changes in the stereocilia nor in the cell bodies of hair cells. The morphology of hair cells in the control sides and the sides with the experimental devices is the same. Conclusion: Poly-L-lactic acid biodegradable support matrix incorporating a therapeutically releasable amount of ampicillin does not cause hair cell morphological damage when inserted in the middle ear of chinchillas.