Biocompatibility and healing process of polyester meshes in the brain: in vivo examination in rats.

OBJECTIVES: To analyze the biocompatibility of multifilament polyester (PET) meshes used for the implantation of auditory brainstem implants in a standardized Wistar rat model (n=29). METHODS: The physical properties of the meshes were examined during surgery. Using a modified plastic embedding, the local tissue reaction and the stability of mesh position in the region of the fourth ventricle were evaluated in section series from day 3 to 64. The cellular reaction was further differentiated using transmission and scanning electron microscopy. RESULTS: PET meshes were stable for handling. However, sharp edges inevitably led to brainstem and cerebellar penetration in some cases. The meshes were preserved in situ in all section series. Positioning was stable with one exception. A sufficient fibroblast and collagen fiber encasement was reached after 14 days. In all cases, no further change was observed through day 64. The host-defense reaction was persistent and characterized by numerous macrophages and foreign-body giant cells. Bacterial infection occurred in three cases. CONCLUSIONS: PET meshes proved to have an acceptable biocompatibility regarding local-tissue reaction in the brain. Modified polymer structures should be developed to reduce risk of injury. Anti-inflammatory surface treatments and monofilament meshes could reduce the infection rate.

Optimization of glycol methacrylate embedding of large specimens in neurological research. Study of rat skull-brain specimens after implantation of polyester meshes.

Advances in neuroscience require better anatomical knowledge of neuronal architecture and structural details. Optimal embedding techniques are the basis for precise morphometric studies in section series as well as for the evaluation of tissue specimens or implants of differing hardness. There are very few methods for preparing large specimens by resin embedding, although resins such as polyethylene glycol (PEG) and methyl methacrylate (MMA) are presently in use. However, these methods have proven to be laborious and sometimes unsatisfactory for serial sectioning. While glycol methacrylate embedding (GMA) is suitable for smaller specimens, it results in inadequate infiltration and polymerization in blocks larger than 1 x 1 x 0.2 cm. We present an improved technique using GMA, which permits both standardized embedding of 4 x 2 x 2 cm blocks and preparation of section series. This method was developed for preserving skull-brain specimens from rats with polyester-mesh implants. The excellent preservation of cellular details allowed the assessment of local tissue reaction to foreign-body material in situ. Advantages of this method are: (1) No toxic catalysts or solvents are used (as opposed to MMA and current GMA processes); (2) Laborious routines in stretching and mounting of sections are not necessary (in contrast to PEG and MMA); (3) No deplastination is required before staining (in contrast to PEG and MMA); (4) Excellent morphologic preservation of various tissue is achieved.

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.