Optimal design of polymer-based microneedle for improved collection of whole blood from human fingers

A highly applicable theoretical model and a simple, inexpensive mould-based method is introduced to design and fabricate the pyramid-shaped SU-8 microneedle. The main purpose is to be able to extract blood at point-of-care sites from up to 80% of typical nurse-home patients with a disorder of blood circulation in fingers and toes (Raynaud´s phenomenon). Geometry optimisation was conducted based on the study of fracture force, which can be accurately predicted by the proposed theoretical model. The accuracy of the proposed theoretical model was confirmed by the finite element study and practical measurement. For practical verification, measurement of fracture force was conducted on fabricated SU-8 microneedles, including a 1470 μm-tall pyramid-shaped microneedle and a 1515 μm-tall traditional-shaped microneedle. The measurement results confirmed the improved strength of the proposed pyramid-shaped microneedle, especially of the pyramidal tips, which can exhibit significantly higher applied force with 2.82 N compared with the 0.51 N bevel tip. Practical tests of skin penetrability on human fingers showed that the microneedles fabricated with the proposed geometry may be sharp and strong enough to safely puncture human skin and long enough to reach the blood vessels.