Design of a mechanical clutch-based needle-insertion device

Abstract

Insertion of trocars, needles, and catheters into unintended tissues or tissue compartments results in hundreds of thousands of complications annually. Current methods for blood vessel cannulation or epidural, chest tube, and initial trocar placement often involve the blind pass of a needle through several layers of tissue and generally rely on distinguishable anatomic landmarks and a high degree of clinical skill. To address this simply and without the use of electronics, a purely mechanical clutch system was developed for use in medical devices that access tissue and tissue compartments. This clutch utilizes the surface contact of a buckled filament inside an S-shaped tube to transmit force from the filament (catheter/guide wire) to the tube (needle). Upon encountering sufficient resistance at the tip, such as dense tissue, the catheter buckles and locks within the tube, causing the filament and needle to advance as one. When the needle reaches the target tissue or fluid-filled cavity, the filament unlocks and slides freely into the target region while the needle remains stationary. A similar locking phenomenon has long been observed in drill strings inside drill shafts used by the oil-drilling industry, and oil industry models were adapted to describe the motion of this clutch system. A predictive analytical model was generated and validated with empirical data and used to develop prototypes of a complete device then tested in vitro on muscle tissue and in vivo on a porcine laparoscopic model with promising results.

Fig. 1.

Unbuckled and buckled flexible filaments within an S-shaped and straight tube. (A and B) The segments of filament contacting the tube (contact length) that experience sliding resistance for an uncompressed (A) and compressed (B) filament are shown in red. (C) Negligible sliding resistance is experienced within a straight tube in an uncompressed state. (D) Under compression, the filament rapidly buckles into a helix within the straight tube (or straight extension of the S-tube). In the compressed buckled state, the contact length and sliding resistance increase. With sufficient friction, the filament locks or jams inside the tube when compressed. (E) Incorporation of these principles into a clutch-based medical device for accessing a tissue compartment. (Ei) The physician positions the needle tip at the desired point of entry/trajectory and applies force to a hand piece. (Eii) The blunt-ended filament, unable to penetrate the firm tissue, buckles and locks inside the needle (as shown in C and D). (Eiii) Additional force is transferred from the filament to the needle wall resulting in advancement of the needle (including the locked filament). (Eiv) Upon entering the target compartment, the filament automatically unbuckles and advances, and simultaneously the needle stop advancing.

Fig. 2.

Empirical compression test results (solid lines) with prediction (dashed lines). F_in is the applied compressive force to the filament, whereas F_out is the measured force after passing through the tube. (A and B) Compressive forces in nylon filament for a single-bend S-tube with a long straight segment (A) and shortened straight segment (B). (C and D) Compressive forces in PTFE filament for a two-bend S-tube with a long straight segment (C) and shortened straight segment (D). (E) Compressive forces in a PTFE filament for a single-bend glass tube. The PTFE, being stiffer and having a lower friction coefficient, transmitted more force through the tube than the nylon. The locked regime (flat section of curves where F_out remains constant) for the nylon is visible in both the prediction and measured values in A and B.

Fig. 3.

A helically buckled filament (white) is visible inside a glass tube filled with blue dye. Regions where the filament touches the wall can be distinguished by its white appearance given a minimal amount of blue dye that exists between the filament and wall at points of contact.

Fig. 4.

Successful deployment of the filament in a muscle tissue model. The needle tip is observed at the interface of the muscle tissue, having stopped while the filament deployed as expected. The input portion of the prototype device is observed in the background.

Fig. 5.

Image showing the automatic deployment of the clutch from inside an insufflated porcine abdomen. The needle stops and the filament deploys simultaneously. In this particular image, the clutch has prevented the needle from puncturing the underlying viscera.