An investigation of the force-time characteristics of needle insertions into Isobutene-Isoprene (Butyl) rubber bungs used in the pharmaceutical industry

Abstract

For reasons of hygiene, the preparation and parenteral administration of drugs utilises a fresh sterile needle for each injection. Automated systems, where the drug is prepared for later administration, are not likely to suffer from biological cross-contamination and thus needles may be utilised for multiple insertions, providing enhanced cost efficiency. In order to assess the optimum needle life, an experiment was conducted to investigate the change in the force required to effect penetration, into isobutene-isoprene rubber bungs, over a number of insertions.

Similarities between the injection process and that of metal die blanking have been noted, extending to the design of the needle. The experiments were conducted in an automated manner; a traversing mechanism provided the means of needle insertion and resultant forces were measured using a load cell. Force-time signatures, captured on a Digital Storage Oscilloscope, were transmitted to a microcomputer for incorporation into result documentation and disk storage. The characteristic signatures have been shown to demonstrate similarities to those of die blanking, thus vindicating the chosen model. Analysis of the insertion impulse, or change in momentum, as it varied with the number of insertions was expected to provide a measure of 'bluntness'. This is confirmed in the analysis of the initial small scale test results.