Penetration force and cannula sliding profiles of different pen needles: the PICASSO study

PURPOSE: Pen needles used for insulin injections can have different characteristics that affect a patient’s injection experience. The aim of the study was to investigate in a standardized laboratory setting the penetration force and sliding force of different 31/32/33/34 gauge pen needles available in 3.5/4/5/8 mm length and 3/5 bevel tips for subcutaneous injection through pen needles and injection pens. METHODS: Eight different commercially available pen needles were tested in this experimental study. The needle was inserted into a polyurethane substrate at a specific constant speed and the force for insertion was recorded as a function of penetration depth. A load cell was utilized to measure force during the different stages of insertion. RESULTS: Maximum load was lower with the PiC G32×4 when compared with the G32×4 5-bevel needle (p<0.0001), while it was not significantly lower with the PiC G32×4 when compared to the G32×4 3-bevel needle (p=0.064). The comparison of G33×4 PiC and G34×3.5 PiC needles with G32 needles demonstrated significantly lower maximum loads with G33 and G34 (p<0.0001). No difference between needles emerged for sliding results. CONCLUSION: Newer pen needles represent a significant improvement in insulin delivery, reducing the amount of force required to penetrate tissues. Needle tip sharpness and other factors that can reduce the force of insertion such as lubrication are important parameters that can be optimized to increase patient acceptance.