Mechanics and mechanisms of puncture by medical needles

Resistance to puncture is a critical property for several applications, in particular for elastomer materials used in protective clothing. To evaluate the puncture resistance of membranes, some methods have been proposed as standard tests. However, the rounded puncture probes used in these tests are very different from real pointed objects like medical needles, and may not measure the level of material resistance that correspond to them. In fact, puncture by medical needles is shown to proceed gradually as the needle cuts into the membrane. This behavior is highly different from puncture by rounded probes which occurs suddenly when the strain at the probe tip reaches the failure value. In addition, maximum force values are observed to be much smaller with medical needles. A method has been developed based on the change in strain energy with the puncture depth to evaluate the fracture energy associated to puncture. The results show that the phenomenon of puncture by medical needles involves contributions both from friction and fracture energy, in a similar way as for cutting. Prestrained samples must be used to determine the material puncture energy.