Polyester meshes and adhesive materials in the brain: comparative research in rats to optimize surgical strategy

Object. The goal of this study was to determine the biocompatibility of polyester mesh electrode carriers for auditory brainstem implants with and without adhesives in a rat model. Methods. Physical properties of the meshes were evaluated within the fourth ventricle region, both without (Group A) and with adhesives (muscle, Group B; oxidized regenerated cellulose [ORC], Group C; and fibrin glue, Group D). The stability of the mesh position, the healing process, and host defense reaction after 2 to 60 days were examined in series of tissue sections in which meshes were preserved in situ. The cellular reaction was further evaluated using electron microscopy. Although otherwise pliable, polyester meshes were too rigid when used with adhesives, especially fibrin glue or muscle. Also, the sharp edges of the meshes presented a risk of brainstem and cerebellar lesions. Regardless of the material, meshes induced persistent inflammatory tissue reactions characterized by numerous macrophages and foreign-body giant cells. After 14 days, the cellular response had resulted in sufficient fibroblast and collagen fiber encapsulation of the meshes and remained essentially unchanged thereafter. No influence of adhesives on the healing process was observed, and, unexpectedly, these substances did not reduce the risk of dislocation prior to adequate cellular encasement. In some rats in Groups A and C, purulent inflammation, in part with Gram-positive bacteria, occurred after 2 to 14 days. The ORC exhibited persistent swelling, introducing the risk of occlusive hydrocephalus and/or brainstem compression. Conclusions. Polyester meshes and various adhesives exhibited acceptable biocompatibility in terms of local tissue reaction. Adhesives reduced pliability of the meshes, however, and were ineffective in reducing the risk of dislocation. Handling characteristics could be improved by better mesh designs, and risk of infection could be reduced by both improved designs and surface treatment of the meshes with antibacterial agents.