Ovipositing the Prostate

Abstract

Prostate cancer is one of the most common types of cancer in men, especially as they get older. The primary treatments involve radical prostatectomy or radiotherapy, which target the entire prostate gland but often lead to side effects that impair urinary, sexual, or bowel function. The good news is that prostate cancer usually grows slowly and is often detected at an early stage, opening the door for more localized treatments with fewer side effects, such as TransPerineal Laser Ablation (TPLA). TPLA is based on light-tissue interaction. The tissue absorbs the light and converts it into heat, which induces irreversible thermal damage to the tissue, resulting in local cell death. The light is delivered via a laser fiber inside a needle positioned near the tumor under ultrasound guidance. In the future, Magnetic Resonance Imaging (MRI) is expected to replace ultrasound as the preferred imaging guidance option.

For TPLA, control of the needle path is of utmost importance to accurately reach the target region. Commonly used needles are rigid and bound to straight trajectories, which might lead to restricted access because of Pubic Arch Interference (PAI) or targeting errors because of needle deflection caused by needle-tissue interaction. Therefore, using current needles makes it hard to control the needle trajectory and reach the target region.

In nature, needle-like structures exist that allow for trajectory control. Specifically, certain species of parasitic wasps possess a slender and steerable needle-like structure called the ovipositor, of which they can control the trajectory. These wasps not only advance their ovipositors through often stiff substrates without suffering damage by using a so-called self-propelled motion, but they can also steer their ovipositors in order to reach their desired targets. Wasp-inspired mechanisms might address current challenges in TPLA needles. Therefore, the main purpose of this thesis is to present and evaluate innovative wasp-inspired needle designs developed to enhance needle trajectory control for TPLA treatment.

In Part 1, Chapter 2 reviews challenges in needle positioning for therapeutic prostate cancer interventions, including (1) access restrictions to the prostate gland caused by the pubic arch, known as PAI, and (2) needle positioning errors. Current clinical guidelines addressing PAI and needle positioning errors are ambiguous, and clinical compliance varies, complicating the assessment of acceptable levels of PAI and needle positioning errors.

Chapter 3 reviews the state-of-the-art in bioinspired medical needles, categorizing the strategies for needle-tissue interaction (i.e., reduce or enlarge grip) and propulsion (i.e., external or internal strategies) of the needle.

To identify future directions of the technologies applied by instruments for localized cancer treatment, Chapter 4 reviews the patent literature on minimally- and non-invasive focal therapy instruments to treat localized cancer, categorizing the patented instruments based on their treatment target, treatment purpose, and treatment means.

Part 2 presents two designs of wasp-inspired needles. Parasitic wasps can self-propel their ovipositors and transport eggs through them. Chapter 5 combines these mechanisms into a 3-mm outer diameter needle comprising six parallel nitinol rods interconnected by an internal ring. The prototype demonstrated self-propulsion through and transport of tissue-mimicking phantoms.
In addition to self-propulsion and transport, the parasitic wasp can curve and steer its ovipositor to reach the desired target location. Chapter 6 presents the design of a steerable self-propelled 0.89-mm outer diameter needle containing a central needle segment with a bevel-shaped prebent tip. The prototype was able to self-propel and steer in tissue-mimicking phantoms without buckling.

Part 3 explores novel actuation mechanisms for wasp-inspired needles, enabling MRI guidance. Chapter 7 presents a manual MRI-compatible actuation system for a 0.84-mm outer diameter self-propelled needle. The manual actuation system was inspired by the click pen and solely consists of MR-safe 3D-printed parts. The evaluation showed that the needle was visible in MR images and self-propelled through ex vivo human prostate tissue. Chapter 8 enhances this system by integrating a steering mechanism into the actuation system and accommodating an optical fiber for TPLA procedures, enabling discrete bevel-shaped tip steering in tissue-mimicking phantoms.
Chapter 9 investigates MRI-compatible pneumatic actuation for wasp-inspired needles, which alleviates the need for urologists to operate the needle manually within the confined space of the MRI bore. The prototype demonstrated that it was able to actuate the self-propelled needle in ex vivo porcine liver tissue under MRI guidance.

In addition to MRI compatibility, TPLA requires decoupling the needle from the actuation system, which is explored in Part 4. Chapter 10 presents a user-friendly design, allowing the actuation system to be stationary as it drives the needle forward in a self-propelled sequence. In this design, the low-friction ball spline facilitates needle propulsion into tissue while preventing buckling, which was exemplified in experiments in tissue-mimicking phantoms.

Chapter 11 explores a modular actuation system that enables a theoretically infinite needle length inspired by mechanical pencils. By clamping, advancing, and releasing the needle segments sequentially, the needle achieved self-propulsion through tissue-mimicking phantoms and fruits with differing stiffnesses and inhomogeneous anatomies.

This thesis shows the value of translating biological into engineering mechanisms to tackle design challenges in medical instruments. The needle and actuation system designs presented in this thesis contribute to a new generation of needles that enhance needle trajectory control for TPLA treatment. The proposed wasp-inspired needle designs and actuation systems pave the way for improving percutaneous interventions, particularly TPLA for prostate cancer treatment.