A Radial Clutch Needle for Facile and Safe Tissue Compartment Access

Abstract

Efficient and safe access to targeted therapeutic sites is a universal challenge in minimally invasive medical intervention. Percutaneous and transluminal needle insertion is often performed blindly and requires significant user skill and experience to avoid complications associated with the damage of underlying tissues or organs. Here, we report on the advancement of a safer needle with a radial mechanical clutch, which is designed to prevent overshoot injuries through the automatic stopping of the needle once a target cavity is reached. The stylet-mounted clutch system is inexpensive to manufacture and compatible with standard hypodermic or endoscopic needles, and therefore can be adapted to achieve safe access in a myriad of minimally invasive procedures, including targeted drug delivery, at-home and in-hospital intravenous access, laparoscopic and endo- and trans-luminal interventions. Here, we demonstrate the clutch needle design optimization and illustrate its potential for rapid and safe minimally invasive cannulation.

Keywords: bioinspiration; cannulation; medical devices; minimally invasive; safety needles.

Figure 1:

Device Concept (a) An overview of the principle of placing the needle in a target site using a radial clutch-based mechanism. (1) The mechanical clutch needle assembly comprises a braid mounted to a blunt rounded-tip stylet to form the radial clutch and a standard double-beveled needle. When the assembly in unloaded there is no friction between the stylet and the needle; (2a) Once the needle tip is approximated against the tissue surface, only the stylet is pushed. As the stylet is blunt it does not penetrate the tissue and thus axial force translates to radial expansion of the braid until it creates a frictional interlock with the needle; (2b) Once sufficient force has been transferred to the needle, the stylet and needle are coupled and advance as one; (3) When a drop off in resistance occurs on entering the target cavity, the stylet-mounted clutch disengages from the needle and only the blunt stylet continues to advance; (4) At this point the stylet can be retract or a guidewire inserted prior to safe needle removal. (b) A representative image of the braid-based radial clutch being deployed in a transparent tube for ease of visualization. When axial compression is applied to stylet (1 -> 2), the initial braid angle β₁ becomes more acute as the braid expands radial until the helical-wound wires come into contact with the needle body β₂. When axial compression is released (3), β₂ returns to β₁ and the stylet is free to move without friction inside the needle body.

Figure 2:

Device assembly (a) Braid preparation. A flat-wire stainless steel biaxial braid with a low number of crossings per inch (~30 – 40 PPI) is rough cut to ~55mm length, to provide excess material for a final target clutch length of 40.5mm. The braided wire segments are stretched in a rig so that the ends can be annealed and cinched to prevent the wire unravelling and to aid insertion into the stylet body. Annealing is performed locally using an open flame for ~ 10 seconds until it glows red and the braid is cut to its final length at the annealed points’ (b) The braid is inserted at either end into two halves of a stylet from a disassembled Veress Needle. An alignment fixture in combination with a hand crimping tool (DMC AF8) is used to control the point of crimping. Care is taken to ensure that the crimp location does not increase the profile of the stylet; (c) The stylet is inserted into a matching standard double-bevel needle. Optionally, a Tuohy-Borst adapter (which contains an adjustable hemostatic valve), can be adhered to the proximal end of the needle and the valve tightened onto the needle to lock the relative position of the stylet and needle until the mechanical clutch system is ready for use.

Figure 3:

Design Optimization (a) Theoretical prediction, adapted from Jedwab et al. [32], of the relative behaviour of radial clutches (initial angle β specified in legend) as they expand from their initial outside diameter (OD) until they contact the inner diameter (ID) of the needle, in response to the application of axial force to the stylet; (b) Experimental demonstration of tunability of the radial clutch. A radial clutch stylet is inverted, its proximal end fixed and its distal end attached to free hanging weights (equivalent force value recorded on x-axis as ‘Force Applied’). A load cell is used to record the corresponding force transferred to the needle for increasingly dense braid samples, from ~30 PPI to ~50 PPI; (c) Experimental set-up, adapted from Bassett et al. [29], demonstrating the elasticity and repeatability of the clutch engagement mechanism through cyclic loading. The needle is fixed in position and the proximal end of the stylet is connected to one load cell. The input force (F_in) upon simulating pushing of the stylet is compared to the output force (F_out) measured by a second load cell at the distal end of the stylet through 10 cycles; (d) Benchtop comparison against Veress needle, gold-standard for closed laparoscopic access, where an inflated latex balloon represents an underlying organ and Syndaver is used to represent skin. The proximal end of the needle or stylet is attached to a uniaxial mechanical tester with the distal end approximating the synthetic skin. The needle mechanisms are lowered by 40mm at 8.33 mm/s and the peak force of insertion recorded. The balloons are inspected for signs of puncture.

Figure 4:

Proof-of-Concept Pre-clinical assessment of radial clutch needle (a) Laparoscopic Access achieved in a human cadaver with a pre-insufflated abdomen to aid visualization; (b) Tracheal access demonstrated as a means of achieve safe airway access in a porcine model; (c) Vascular access achieved in a porcine ear vein. Still images in each case show (i) tissue tenting prior to needle perforation, (ii) disengagement of radial clutch of blunt stylet (iii) stylet is removed and safe insertion of the needle into target cavity demonstrated. In the case of (a) laparoscopic access, (iv) the overshoot distance was estimated from 12 repeat insertions (line represents mean value).