Coring and Fragmentation of Elastomeric Needle Shield in a Pre-Filled Syringe

Elastomeric components such as closures and stoppers play key roles in providing container closure integrity (CCI), supporting a portfolio of injectable combination products and primary containers including needle shields (NSs) in prefilled syringes (PFSs). Upon piercing through the elastomeric (i.e., synthetic rubber) components, the physical interaction between the needle and the deformable elastomer could result in the formation of small, random-shaped particles fragmented and dislodged from the NS material due to cutting processes. This phenomenon, called coring, poses a major risk in drug product contamination, as elastomer particle fragments can potentially be aspirated with the medication and injected into a patient or prevent injection. Here, we present a combined computational and experimental approach to assess the incidence of coring. In particular, we first experimentally characterized the nonlinear finite deformation behavior of five commonly used NS elastomers and calibrated constitutive models. Then, we performed finite element simulations validated with needle insertion experiments to compare the coring behavior of the NS elastomers. We demonstrated that higher maximum failure strain under tension and higher deformation-stiffening properties of the elastomer are contributing factors that attenuate coring and fragmentation. The experimental-numerical framework presented is suitable for quantifying broad correlative and discovering relationships between device properties governing the incidence of coring and fragmentation.