In Vitro Hydrodynamic, Transient, and Overtime Performance of a Miniaturized Valve for Hydrocephalus

Abstract

Reliable cerebrospinal fluid (CSF) draining methods are needed to treat hydrocephalus, a chronic debilitating brain disorder. Current shunt implant treatments are characterized by high failure rates that are to some extent attributed to their length and multiple components. The designed valve, made of hydrogel, steers away from such protracted schemes and intends to provide a direct substitute for faulty arachnoid granulations, the brain's natural CSF draining valves, and restore CSF draining operations within the cranium. The valve relies on innate hydrogel swelling phenomena to strengthen reverse flow sealing at idle and negative pressures thereby alleviating common valve failure mechanisms. In vitro measurements display operation in range of natural CSF draining (cracking pressure, PT ~ 1-110 mmH2O and outflow hydraulic resistance, Rh ~ 24-152 mmH2O/mL/min), with negligible reverse flow leakage (flow, QO > -10 µL/min). Hydrodynamic measurements and over-time tests under physically relevant conditions further demonstrate the valve's operationally-reproducible properties and strengthen its validity for use as a chronic implant.

Three-Dimensionally Printed Microelectromechanical-System Hydrogel Valve for Communicating Hydrocephalus

“…Thus, the total yield is 27%, which was significantly higher than our previous work, having less than 1% yield. 24,25 The failed devices were analyzed to determine the cause of the malfunction. First, the 3D-printed molds have finite surface roughness.…”

“…Based on measurements on the benchtop model, the valve demonstrated the target hydrostatic characteristics for the CSF drainage mechanism with nonzero P T and negligible leakage. Long-term functional tests and a realistic in vitro experiment using a sheep brain build on earlier work in our group 24,25 and validate the valve's potential for treating HCP.…”

“…The hydrogel solution was prepared by mixing the base (2hydroxyethyl methacrylate, Sigma Aldrich), cross-linker (ethylene glycol dimethacrylate, Sigma Aldrich), and photoinitiator (2,2- dimethoxy-2-phenylacetophenone, Sigma Aldrich) at the ratio of 1:0.04:0.1. 24,25 3D-Printed Molds. The tapered hydrogel structure was fabricated using 3D-printed molds (Figure S1).…”

“…Resistive pressure sensors (PX26-001DV, Omega) have 1 mmH 2 O resolution, which were calibrated for the actual experiments by a customized setting. 24,25 All data were recorded by a data acquisition board (NI USB 6216, National Instruments) and Signal express.…”

“…Our earlier work demonstrated reasonable fluid draining and showed its feasibility as an alternative CSF drainage path. 24,25 However, the previous work suffered from low reproducibility and durability due to the manufacturing complexity, deficiency of the accurate measure of fluid pressure across the valve inside of the setup, and lack of verification of the valve in realistic environments. This work adopts 3Dprinted molds to significantly simplify the manufacturing complexity and utilizes swollen hydrogels to create nonzero cracking pressure and achieve negligible reverse leakage.…”