Predicting water vapor egress rate through elastomeric needle shields of prefilled syringes

Prefilled syringes (PFSs) with staked-in-needles are widely used for high-concentration biologics but are vulnerable to needle clogging driven by water evaporation of trapped liquid in the needle lumen. This study quantitatively links trapped liquid volume, water vapor egress, and drying dynamics to inform device- and condition-dependent clogging risk. Commercial staked-in-needle PFSs with three rigid needle shield (RNS) elastomer formulations were characterized by X-ray computed tomography (XRCT). Elastomer water vapor permeabilities measured under controlled temperature and humidity were utilized. These data parameterized a steady-state Fickian diffusion model in COMSOL Multiphysics ® to compute water vapor concentration fields and water egress rates as functions of temperature, relative humidity, and needle/RNS design. A closed-form expression for egress rate and a Pareto sensitivity analysis were derived. Simulations showed water egress rates ranged from 0 to 0.7 nL/day, increasing with temperature and elastomer permeability and decreasing with ambient humidity, accompanied by minor influence of needle geometry within the tested range of 0.275 and 0.300 mm inner diameter and needle insertion depth shifts (± 1 mm). Estimated evaporation times for 4.5–13.3 nL liquid droplets can span days to months depending on storage conditions. This integrated experimental–computational framework quantitatively relates nanoliter-scale liquid retention to vapor-driven drying in staked-in-needle PFSs and identifies temperature, humidity, and elastomer permeability as key levers to mitigate needle-clogging risk at the device level.