Artificial arachnoid granulation: sub-mmduckbill valve for hydrocephalus treatment

Abstract

Purpose: Hydrocephalus is characterized by the accumulation of excess cerebrospinal fluid (CSF) in the cranium due to an imbalance between production and absorption of CSF. The standard treatment involves the implantation of a shunt to divert excess CSF into the peritoneal cavity, but these shunts exhibit high failure rates over time. In pursuit of improved reliability and performance, this study proposes a miniaturized valve designed to mimic the natural one-way valve function of the arachnoid granulations and thereby replace the shunts. Methods: A benchtop testing setup was employed to characterize the behavior of the fabricated valve. Additionally, an animal study was conducted to assess the valve's in vivo: performance. This involved the injection of saline into the lateral ventricle to elevate intracranial pressure (ICP), followed by the drainage of the saline through the valve inserted into the cisterna magna (CM) to reduce pressure. Results: Our prototype features a silicone duckbill valve design combined with a silicone tube as an inlet. Through benchtop testing, the valve exhibited unidirectional flow with negligible reverse leakage, revealing that critical parameters such as the width of the fluid channel (W) and bill length (L) could be controlled to optimize valve performance. Notably, the valve configuration with W = 0.8 mm and L $<$0.5 mm achieved the lowest cracking pressure (2.22 $\pm$ 0.07 mmHg) and outflow resistance (22.00 $\pm$ 0.70 mmHg/mL/min) within the low cracking pressure range of conventional shunts. Our observations demonstrated that when the valve was closed, pressure differences from baseline to peak exceeded 20 mmHg due to the absence of drainage, resulting in sustained pressure elevation. Conversely, upon opening the valve by removing the clamp, pressure differences from baseline to peak remained below 5 mmHg, indicating effective drainage of injected saline through the valve. Conclusion: These promising results highlight the potential of the miniaturized duckbill valve as an alternative for ICP management in hydrocephalus, offering improved control and reliability compared to conventional shunting systems. Further research is required to evaluate the valve’s performance as a chronic implant.