Monofilament handgrip set and holder

Monofilaments (MFs) are used for sensory function testing of hands and feet in for instance diabetic or leprosy patients. MF test sets are well available and affordable in high resource contexts. However, in low resource contexts these are not well available or too expensive. Some clinical staff in LMIC have access to alternatively sourced MFs that come without a handgrip, and that are used either without handgrip, or with a DIY handgrip that limits usability. 

This project developed a set of MF handgrips to improve the use of these alternatively sourced MFs. The design has a handgrip and a foldable head that allows the MF to fold away when not in use to protect the integrity of the MF when not in use. The foldable head will lock in both positions (folded and unfolded). The foldable head that holds the MF is coded with a letter H or F (Hand or Foot) and a number  2, 3, 4, 5 for the corresponding MF size. A simple holder to store the set of handgrips is also included.

This set was successfully printed and used in both PLA and PETG material. Pictures added here are the PLA version. It is advised to use different filament colors for the hand or foot set so they can be easily identified. After printing and mild post-processing the ‘head’ can be assembled into the handgrip by sliding it in from the bottom side of the handgrip. Next, the corresponding MF can be inserted and glued in place using a low-strength glue (white glue/crafting glue) to allow change of the monofilament in a later stage. The length of the monofilament extending from the handgrip should be 38mm exactly. The forces required for buckling of the filament can be checked against the reference value  documented in literature for each particular monofilament size/color (given in milligrams or grams):

If your monofilament after assembly at around 38mm protruding length reaches lower forces then it is too long. If it reaches higher forces it is too short. One strategy is to cut the MF generously long, then measure the buckling force, cut a tiny piece of, measure again, until the buckling force is close to the target force. Please be aware that the cut edge might be sharp, so make sure to glue that end of the MF into the handpiece, and the neat uncut edge will be the edge in contact with the patient.

All necessary files are shared here, including SolidWorks files for making changes to the design if needed.