Med-Tech Innovation Smart materials


and intensive care (Figure 1). More than 1 million procedures are performed annually in the UK.1


Intubation


which can involve anything from successful management after several attempts with multiple devices to complete failure.


Patients in these situations are at risk of reduced


blood oxygen levels and potential brain damage. In response, additional equipment is often used to guide tube placement and improve procedure success rates. In the majority of cases, a bougie is used to assist correct placement. This is a long, flexible rod, with a degree of shape memory retention that can be more easily manipulated into the airway and the tube then guided over the top of the rod. The advantage of the bougie is that it can be used without needing to “pre-load” the tube for an unexpectedly difficult patient; however, the disadvantage is that shape retention is generally poor and it must be removed to be reshaped. To address more difficult cases a wider range of expensive devices with various functionality are available, including video laryngoscopes and flexible, controllable fibre-optic bronchoscopes (Figure 2). These devices offer a high degree of control, but are expensive to purchase and maintain and require considerable time to set up in an emergency.


In association with anaesthetists at Queens Medical Centre, Nottingham, a brief was set to develop a mid-tier product that is as accessible and flexible in application as the standard bougie whilst incorporating the steerable tip functionality that is included in high tier products. This device needed to be compatible with conventional intubation devices as well as the more recent image-assisted equipment. Initial research focused on a range of potential methods of actuation including, fixed mechanical linkages (as are used in current fibre-scope technology), air pressure, magnetic fittings and smart materials. The result of this research was the identification of Flexinol (DynAlloy Inc., www.dynalloy.com), a shape memory alloy (SMA) as an ideal basis for a new and innovative device. Flexinol is a nickel-titanium alloy that belongs in the


SMA group of smart materials/actuators. Application of heat to the material, typically by application of an electrical current, triggers a conformational change resulting in a shortening of the wire of between 4–10%. If a Flexinol wire is inserted into the body of a hollow tube and attached at each end, heating the wire will result in bending or flexing of the tube. When the tube is made more rigid down the majority of its length, the flexing will occur only at the distal end, which will allow for it to be guided in the desired direction. Inserting two Flexinol wires longitudinally into the body of the bougie allows a


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involves placing a breathing tube into the windpipe of a sleeping patient; however, it is not always straightforward. Up to 11% of patients have an airway that is difficult to secure,2


Figure 1:


Endotracheal intubation procedure


Figure 2: Fibre-optic bronchoscope


high degree of flexibility of the tip of the device, combined with a fast and appropriate level of control (Figure 3). The two wires functioned in opposition to each other, giving a range of movement greater than 120 degrees in a single plane of movement, with a response time for maximum angulation of approximately 1 second. This functionality is more than adequate for the proposed clinical setting. The more rigid, proximal end of the device allows for a degree of shape pre-forming before insertion into the airway, and the controllable portion gives the fine control needed to guide the device into the airway rapidly and safely. The controls for the Flexinol part of the bougie are housed in an ergonomically designed, two-button hand- piece that can be clipped onto the airway-opening device in the operator’s left hand. This is then attached to the bougie section via an adaptor at the proximal end of the bougie. This setup enables efficient single operator control of the whole device, which is essential in the clinical setting of a difficult airway. Using Flexinol, it has been possible to produce a highly


cost-effective design that achieves an equal degree of tip controllability and maintains the benefits of the existing bougie. Optimised for use in the NHS, the final design incorporates a separate reusable control unit to house


Figure 3: Steerable endotracheal bougie, first stage prototype (Hughes 2013)


September/October 2014 ¦ 13


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