A Pilot Study to Establish a Penetrating Traumatic Brain Injury Rat Model for Implantation of a 3D Printed Scaffold

IntroductionTraumatic brain injuries (TBIs) are the leading cause of death and disability, with penetrating TBIs being the most lethal form. As the primary injury involves a foreign object breaking the skull, disrupting the blood brain barrier (BBB), and damaging the brain tissue, the secondary injury that follows is further damaging with persistent inflammation leading to tissue atrophy. While no TBI treatments currently exist, ongoing investigations are developing biomaterial scaffolds and cellular therapies to improve upon the poor outcomes from this disease. This pilot study sets out to establish a TBI rat model that maintains focal damage to the cerebral cortex, while manually disrupting the BBB. Injuries disrupting this barrier need to be managed differently than those that do not, allowing us to develop a specific, therapeutic treatment for this type of injury. We hypothesize that our method of BBB disruption will indicate behavioral, physical, and histological evidence of a TBI. Our TBI model will also create a cranial opening in which we can ensure surgical feasibility of implantation of a scaffold. We hypothesize the implantation of FDA-approved synthetic polymer, poly (lactic-co-glycolic acid) (PLGA), and carbon-based nanomaterial, reduced graphene oxide (rGO), will not show evidence of a foreign body rejection at 30 days after surgery. MethodsFour Sprague Dawley rats underwent a stereotaxic surgery with a 5-mm craniotomy. The dura and brain tissue were disrupted using a beaver blade. The PLGA/rGO scaffold was gently placed onto the brain tissue. Neurological function was evaluated for the first three days, then weekly throughout the 30-day study. At 30 days, brains were dissected, paraffin embedded, and sectioned for H&E and Prussian blue staining, and immunohistochemistry (IHC). ResultsNeurological function assessments indicated no change in rat behavior and normal wound healing over the 30 day study. H&E and Prussian blue staining indicated mild leptomeningeal thickening and evidence of hemosiderin in 3 rats. One rat had foreign body giant cells and an abscess around the implanted material with evidence of more severe leptomeningeal thickening and hemosiderin. IHC indicated normal anatomic structures with no changes in 5 of the 6 markers at 30 days after surgery. Neural marker, NeuN, had a significant decrease in expression for all four rats. DiscussionWhile there was no behavioral or symptomatic evidence of a TBI, histology showed evidence of a mild, focal TBI in 3 of the 4 rats, and evidence of a foreign body response and a severe, focal TBI in 1 rat. Future studies will perform IHC at earlier timepoints to confirm additional biomarkers, and will implant a scaffold that is more mechanically aligned with the brain tissue to further evaluate the biocompatibility of graphene nanoparticles in brain tissue, and the effectiveness of a therapeutic scaffold.