Biocompatibility of different biopolymers after being implanted into the rat cochlea

To assess the biocompatibility of different biopolymers with cochlea implant.

Six bioabsorbable polymers and biostable silicone were used for testing histologic reactions in the cochlea of the rat. The samples were prepared from three 50/50 poly(DL-lactide-co-glycolide) PDLLGA having different inherent viscosity (IV) values and 75/25 poly(DL-lactide-co-epsilon-caprolactone) P(DLLA/CL), poly-epsilon-caprolactone PCL, silicone, and chitosan by extruding the biomaterial as a rod using melt molding (for 50/50 PDLLGAs and 75/25 P(DLLA/CL) and PCL), blending (for silicone), and solving (for chitosan). The rods were cut into samples of diameter of 0.5 mm and length of 2 mm. All the samples were packed and sterilized by gamma irradiation (18 kGy, less than 42 degrees C). Twenty-two male and female Sprague-Dawley rats were used in the study. Four months after the implantation, the animals were killed for histologic observation.

Chitosan does not degrade in the cochlea 4 months after implantation and, therefore, stimulates very weak inflammatory reaction. The 50/50 PDLLGA (IV, 0.83 dL/g) degrades in the cochlea 4 months after implantation and does not stimulate inflammatory reaction. The 50/50 PDLLGA (IV, 0.41 dL/g; IV, 0.37 dL/g), 75/25 P(DLLA/CL), PCL, and silicone might induce strong inflammatory reaction in the cochlea.

Different degradation property of biomaterials in the cochlea indicates diverse drug releasing time in a controlled way. Chitosan is suitable for long-lasting drug delivery, whereas 50/50 PDLLGA (IV, 0.83 dL/g) favors quicker releasing. Both chitosan and 50/50 PDLLGA (IV, 0.83 dL/g) are ideal materials for cochlear drug delivery.