Hybrid hydrodynamic characteristic for hydrocephalus valve: A numerical investigation using electrical equivalent networks

International audienceNumerical simulations based on the classical Marmarou’s model have been carried out to analyse the dynamics of hydrocephalus valves. The evolution of the intracranial pressure in various case studies has been determined with a specific focus on flow control valves. It has been shown that their capability to prevent postural under- and over-drainage may be significantly altered by non-idealities of their hydrodynamic characteristics and by the inter-individual variability of the cerebrospinal fluid production rate. The use of microtechnology to improve the flow rate accuracy also enables the possibility to get original designs that are desirable to address specific restrictions of use associated with flow-control valves, in particular for patients exhibiting very high resistance to cerebrospinal fluid reabsorption. A new hybrid hydrodynamic characteristic of a hydrocephalus valve is proposed to stabilize the intracranial pressure. This new passive valve is equivalent to two pressure regulators at high and low relative pressures, corresponding respectively to upright and decubitus positions. The device is able to automatically switch from one configuration to the other as a function of the postural change. Numerical simulations suggest that this new hybrid valve should combine the advantages of both differential and flow control valves

Design of a Passive Flow Regulator Using a Genetic Algorithm

Passive flow regulators are usually intended to deliver or drain a fluid at a constant rate independently from pressure variations. Microfluidic devices made of a stack of two plates are considered here: the first plate comprises a flexible silicon membrane having through holes while the second plate is a rigid substrate with a cavity, an outlet hole and pillars aligned with the through holes of the membrane. The liquid flows through the holes etched in the membrane and through the small gap between the bottom of the membrane and the pillars: each hole can therefore be considered as a valve which progressively closes as the pressure increases, thus leading to a non-linear fluidic behaviour. FEM simulations have been performed to ensure a constant flow rate in the specified range of pressure. To make the design reliable, the device characteristics have been optimized using an evolutionary algorithm. The fitness function notably takes into account machining and alignment tolerances. Typical designs dedicated to drug delivery and hydrocephalus treatment are discussed

Passive flow control valve for protein delivery

Passive ow control valves are usually intended to deliver or drain a uid at a constant rate independently of pressure variations. Micro uidic devices made of a stack of two plates are considered here: the rst plate comprises a exible silicon membrane having through holes while the second plate is a rigid substrate with a cavity, an outlet hole and pillars aligned with the through holes of the membrane. The liquid ows through the holes etched in the membrane and through the gap be- tween the membrane and the pillars. Each gap can be considered as a valve which progressively closes as the pressure increases. Numerical modelling of the uid dynamics inside the device associated with FEM simulations of the membrane dis- tortion have been performed to design a device that exhibits a constant ow rate in a speci ed range of pressure. To make the design more reliable, the device charac- teristics have been optimized using a genetic algorithm, the tness function taking notably into account machining and alignment tolerances. This algorithm has been nally used to design ow control valves for wearable injectors dedicated to the in- fusion of viscous drug formulations (hyaluronic acid, adalimumab, golimumab ...) at high pressure. Prototypes have been characterized using solutions of 12 and 24 cP. It has been demonstrated experimentally that this technology is suitable to passively infuse biological products at ow rates up to 1 mL/min. The numerical model has then been re ned further so as to obtain a good correlation with experimental data