Current trends in surgical intervention favour a minimally invasive (MI) approach,
in which complex procedures are performed through increasingly small incisions.
Specifically, in neurosurgery, there is a need for minimally invasive keyhole access,
which conflicts with the lack of maneuverability of conventional rigid instruments. In
an attempt to address this fundamental shortcoming, this thesis describes the concept
design, implementation and experimental validation of a novel flexible and steerable
probe, named “STING” (Soft Tissue Intervention and Neurosurgical Guide),
which is able to steer along curvilinear trajectories within a compliant medium.
The underlying mechanism of motion of the flexible probe, based on the reciprocal
movement of interlocked probe segments, is biologically inspired and was
designed around the unique features of the ovipositor of certain parasitic wasps.
Such insects are able to lay eggs by penetrating different kinds of “host” (e.g. wood,
larva) with a very thin and flexible multi-part channel, thanks to a micro-toothed
surface topography, coupled with a reciprocating “push and pull” motion of each segment.
This thesis starts by exploring these foundations, where the “microtexturing”
of the surface of a rigid probe prototype is shown to facilitate probe insertion into
soft tissue (porcine brain), while gaining tissue purchase when the probe is tensioned
outwards. Based on these findings, forward motion into soft tissue via a reciprocating
mechanism is then demonstrated through a focused set of experimental trials in
gelatine and agar gel. A flexible probe prototype (10 mm diameter), composed of
four interconnected segments, is then presented and shown to be able to steer in a
brain-like material along multiple curvilinear trajectories on a plane. The geometry
and certain key features of the probe are optimised through finite element models,
and a suitable actuation strategy is proposed, where the approach vector of the tip is
found to be a function of the offset between interlocked segments. This concept of a
“programmable bevel”, which enables the steering angle to be chosen with virtually
infinite resolution, represents a world-first in percutaneous soft tissue surgery.
The thesis concludes with a description of the integration and validation of a fully
functional prototype within a larger neurosurgical robotic suite (EU FP7 ROBOCAST),
which is followed by a summary of the corresponding implications for future
work
