Instruments based on shape-memory alloy properties for minimal access surgery, interventional radiology and flexible endoscopy

Abstract

Instrumental manipulations during minimal access surgery (MAS) are limited by the four degrees of freedom (d.o.f.) possible when long instruments are introduced into the peritoneal cavity through access ports. This is in sharp contrast to an equivalent instrument held in the hand by the surgeon during open conventional surgery, where six d.o.f. are available. Steerable motorised endo-effectors are one engineering option to overcome this intrinsic limitation of MAS. However, it is difficult to meet the torque requirements of such instruments using existing electric motor technology. We have sought a different, though not mutually-exclusive approach to the design and development of more effective instrumentation for MAS, based on shape-memory alloy (SMA). SMA formed from nickel-titanium (NiTi) has unique superelastic and shape-recovery properties, and are therefore an advantageous construction material for instrument components and devices within the limited size constraints imposed by the ports used in MAS. In general, novel MAS instrumentation based on SMA components falls into two categories, depending on whether superelastic, or shape recovery properties are utilised for a particular instrument design. This paper is based on research and development carried out in Dundee during the past 15 years on NiTi-SMA based instrumentation for MAS.