Penetration Force, Geometry, and Cutting Profile of the Novel and Old Ozurdex Needle: The MONO Study

Abstract

PURPOSE: To investigate the geometry, penetration force, and cutting profile of the novel and old needle of the drug delivery system (DDS) for Ozurdex injections in a standardized laboratory setting. METHODS: In this experimental study, the normative geometrical data of the DDS needle were systematically analyzed according to nomenclature DIN 13097 (ISO 7864) and ISO 9626. The force to penetrate a standardized 0.4-mm-thick polyurethane foil was measured by a penetrometer, when the needle was piercing, cutting, and sliding through the foil and plotted as a load-displacement diagram. Magnified images of the consecutive cut were taken after the entire penetration through the foil. RESULTS: In this experimental study, the mean point length was equal to 3.34 mm (3.28-3.36 mm) for the old DDS needle versus 3.33 mm (3.30-3.36 mm) for the new DDS needle. The secondary bevel length was 1.64 mm (1.42-1.73 mm) for the new and 1.66 mm (1.62-1.69 mm) for the old needle. The primary angle was 9.2° (9.0°-9.5°) for the old and 8.9° (8.5°-9.0°) for the new needle, respectively. The secondary bevel angle was 117.2° (116°-118°) for the old and 111.4° (110°-113°) for the new needle. The mean penetration force of the old DDS needles was significantly higher at all phases of the penetration experiment: The mean piercing force was 0.7 Newton (N) with the old and 0.47 N with the new DDS needle. The mean cutting force was remarkable higher with 1.1 N for the old DDS needle versus 0.78 N for the new DDS needle. The dilatation phase was not statistically significant between 0.94 and 0.99 N in both DDS needles. The friction phase was maintained at significantly higher levels with the old DDS needle of 0.47 N, whereas it returned to the lowest measurements of 0.11 N with the new DDS needle. Both DDS systems induced a characteristic chevron-shaped incision. CONCLUSION: A comparison of the old and new DDS needles demonstrated a reduced penetration force with the modified new DDS needle, which may help to achieve a smooth penetration through the human sclera.