ORIGINAL ARTICLE Nitinol actuated soft structures towards transnasal drug delivery: a pilot cadaver study Manivannan Sivaperuman Kalairaj 1 & Bok Seng Yeow 1 & Chwee Ming Lim 2,3 & Hongliang Ren 1 Received: 25 June 2019 /Accepted: 16 December 2019 # International Federation for Medical and Biological Engineering 2020 Abstract Sudden hearing loss can be treated noninvasively by administering drugs to the middle ear (≈1 ml) via the eustachian tube. The nasopharyngeal cavity requires high dexterity manipulation as it is restricted by the nasal vestibule, and precise drug delivery through the small cavity can allow previously unreachable areas to be reconsidered for localized delivery. Nitinol has shape memory capabilities and can be used for distal actuation accessed from small lumen and a tortuous path. The drug delivery device (DDD) is a soft and needle-sized (2 mm) and comprises of Nitinol, ribbon spring, and a drug delivery tube. By controlling the input voltage to the Nitinol, bending of the device at different angles could be achieved, and the ribbon spring works antago- nistically to the Nitinol to revert to the initial position once deactivated. The actuation of the device and its corresponding bending are calculated in vitro and found to have a bending angle ranging between 36.2 and 66.8° for applied voltages of 1.2–2.0 V, with surface temperature of 45.6–154 °C. The DDD is able to actuate 200 cycles with ≈91–76% retention of bending performance, with a temperature increase of ≈8.5–9% when 1.2–2.0 V is applied. Addition of soft insulating material shows ≈34–62% reduction in the surface temperature in the first cycle and ≈37–59% over 200 cycles when actuated at 1.2–2.0 V. The active steering and navigation capabilities of the DDD are demonstrated in simulated environments (based on the eustachian tube dimensions of adult and infant). Preclinical testing in human cadavers is demonstrated and suggests the developed DDD controlled by varying the input voltages for bending, and mechanically varied drug delivery may be a feasible option for localized drug delivery in eustachian tube. Keywords Actuator . Drug delivery . Eustachian tube . Nasopharyngeal cavity . Shape memory alloy 1 Introduction Surgical procedures are marching towards the improvements upon current medical practices and instrumentation by the implementation of robotic solutions. One common aspect is the manipulator, a flexible and elongated body, which finds applications in key-hole surgery, natural orifice transluminal endoscopic surgery (NOTES), and endoscopic procedures [1]. Such surgeries traverse the narrow vasculature and lumens of the patient, which applies a restriction to the device size where tools are designed on the millimeter scale. The small scale of the device and the distal location of the actuation make con- trolling such instruments challenging [2]. Traditional actuators are tendon driven, such as endoscopes, laparoscopic instru- ments, and guide wires. They are however difficult to control when the conducting trajectories are too tortuous [1, 3–5]. Poor distal control is a safety concern as injuries can occur when excessive forces are applied to deflect or dislodge the equipment. Alternatives to the tendon-driven mechanism in- clude electromagnetics, piezoelectrics, and pneumatics [6], each having limitations to improve upon the distal control of surgical actuators such as inability to downscale, minimal ac- tuation range, and bulky. Shape memory actuators (SMAs) [7], which can be alloys or polymers [8], are small and have excellent strength to weight ratio [9]; Nitinol is one example of an SMA. Nitinol wires are joule heated by a controlled voltage, which allows for an electronic control system, and the actuation signals, unlike tendon-driven systems, are transmitted through the * Hongliang Ren ren@nus.edu.sg 1 Department of Biomedical Engineering, National University of Singapore, Singapore 117583, Singapore 2 Department of Otorhinolaryngology – Head and Neck Surgery, Singapore General Hospital, Singapore 169856, Singapore 3 Duke–NUS Graduate Medical School, Singapore 169857, Singapore Medical & Biological Engineering & Computing https://doi.org/10.1007/s11517-019-02102-x