Peripheral nerve-on-a-chip
Description
Bringing a newly formulated drug used for neurological applications to the market is a highly time and labor-intensive process. The current pathway of bringing a drug to market requires extensive drug testing on animal models at the pre-clinical stage. Live animal models are expensive, low-throughput and increasingly recognized to be poor predictors of clinical outcomes in the process of drug development. An in vitro testing platform would address these above stated problems by providing a pre-screening process that could improve the high attrition rates of novel pharmaceutical compounds and also reduce the demand for the number of animals used for testing. This dissertation presents the progress of studies that were conducted to create a three-dimensional myelinated in vitro peripheral nerve-on-a-chip model that could be subject to electrophysiological and histological testing to be used as a tool for drug screening. In the first study, our model utilized an ultra-violet light cured methacrylated heparin hydrogel as the growth permissive substrate and a polyethylene glycol gel as a growth restrictive boundary that contained three-dimensional neural growth from an embryonic rat’s dorsal root ganglion explant. The model enabled electrophysiological field recording testing to measure metrics such as compound action potential amplitude and nerve conduction velocity. However, the heparin hydrogel presented issues with immunohistochemistry and histological studies leading us to recreate the model with a different growth permissive substrate. The second study utilized a methacrylated gelatin hydrogel in place of the heparin as the growth substrate. The dense neural growth was rapider than heparin while the gel allowed electrophysiological and histological testing to conclusively show the presence of myelin. Data from the histological testing was used to tabulate structural measurement such as percentage of myelinated axons and g-ratios which were then correlated with the electrophysiological data. This study paved way to use this model to simulate a demyelinating physiology and assess the effectiveness of a possible neuroprotective agent. The third and final study investigated the usage of the peripheral nerve-on-a-chip as model of demyelination by using forskolin and twitcher mouse serum, adapted from the established in vivo model of Krabbe’s disease. The effects of demyelination were observed using electrophysiological, immunohistochemistry, and histological studies. The corticosteroid dexamethasone was also included in the demyelination models to assess its extent of neuroprotection against the demyelinating agents. The results established a novel myelinated peripheral nerve-on-a-chip model which could be subject to electrophysiological, immunohistochemistry, and histological studies. The model has the potential to be used to simulate various pathologies and evaluate the efficacy of drugs before animal testing could be conducted.