Background: Scoliosis is a three-dimensional abnormal curvature of the spine, with Adolescent Idiopathic Scoliosis (AIS) being the most common type. Current fusion treatment is highly invasive and removes all mobility of the fused spinal segments. To tackle this problem, non-fusion techniques were developed, that try to correct the abnormal spinal curvature while maintaining healthy spinal mobility. The state of the art of non-fusion treatment includes techniques that have highly inefficient methods of correction, contain long and hefty structures leading to large surgical scars, or cause the need for revision surgery. Most importantly though, all of the current techniques have high complication rates. It was therefore deemed necessary to design a mechanism that facilitates minimal invasive and local, non-fusion correction in a mechanically effective way, by applying constant force in the appropriate direction.

Methods: The anatomy and mechanics of a thoracic spinal segment were analyzed, showing the challenges that are at hand. From there, lists of requirements and wishes were generated that initiated the conceptualization process. Concepts were then generated, categorized, and selected after which it was shown that the concept of a single buckled leaf spring with joints was the most suitable. Future vision figures were made showing how an implant could look like that contains this mechanism. The mechanism was then further developed and an experimental setup was designed and built. This setup was used to carry out four proof of principle experiments that examined the viability of the buckled leaf spring as functional mechanism. The relation between thickness and buckling force was tested, as well as the hysteresis of the mechanism. Furthermore, the effect of misaligning
the mechanism both translationally and rotationally has been examined. Finally, the mechanism was placed inside soft tissue phantoms to examine the effect of the presence of surrounding soft tissues.

Results: A buckled leaf spring that fits the size and material requirements was manufactured and the results of the proof of principle experiments show that it manages to create a constant buckling force of desired magnitude for correction. However, misaligning the implant did show effects on the force profile, with the effects of translational misalignment being the most significant. Finally, little hysteresis was perceived, which significantly increased when the leaf spring was placed within a soft tissue phantom.

Discussion and Conclusion: The mechanism is as of yet not suitable for clinical implementation. Further design steps must be conducted and an extensive analysis of the anatomical and mechanical effects of placing the implant against the spinous processes must be carried out. Further recommendations have been made to improve the design and functioning of the mechanism. This study has demonstrated the potential that the mechanism of a buckled leaf spring has in the constant force correction of scoliosis.

Treatment of prostate cancer can be done by performing brachytherapy, where radioactive seeds are transperineally implanted in the prostate via needles. A known problem during treatments with needles is the risk of targeting errors caused by the deviation of the needle from the planned path in the prostate. One of the main sources of this error is the displacement of the prostate due to insertion of the needle. Often, stabilisation needles are used to stabilise the prostate, however, stabilisation needles alter prostate properties, damage tissue, and do not fully reduce prostate displacement. Therefore, in this study, we propose and evaluate an alternative solution that stabilises the prostate without additional tissue damage. The stabilisation solution is a modular suction cup referred as the ProSTATIC, which can be transperineally inserted via a 5 mm incision to attach to the prostate within the rectoprostatic space. The ProSTATIC has a multi-holed design consisting of three structural layers with their functionality; (1) the top to maintain the pressure inside of the suction cup and provide for structural stability, (2) the footprint to adapt and form a closed seal with the prostate surface, and (3) the self-regulating valves to increase the attachment reliability on irregular surface textures. For the footprint, we experimented with micro-patterns and suction hole sizes to increase the overall grip force. The prototype was completely fabricated out of biocompatible and ultrasound-compatible silicone rubber using mould casting. An experimental evaluation showed that the self-regulating valves work only on healthy prostate phantom. On healthy-tumorous and full tumorous tissue phantoms the suction holes deform, hindering the optimal working of the valves and leading to air leaks. Furthermore, only the prototype with the base footprint with enlarged suction holes (from 2 mm to 3.2 mm diameter) and radial ridges was able to generate a maximum grip force higher than the required 5 N for stabilisation and demonstrated that prostate displacement was reduced by 75% during needle insertion without the use of the ProSTATIC. The prototype proposed in this study forms an initial breakthrough in safe and reliable volumetric stabilisation of the prostate during brachytherapy.

Background: Minimally invasive cancellous bone biopsy is a common medical procedure in which a needle is used to extract a piece of cancellous bone for examination. Unfortunately, this procedure is not always successful, as sometimes the biopsy can slip partially or completely, necessitating a new biopsy. The occurrence of these errors is not well documented, but the main causes are believed to be an inadequate grip on the biopsy by the current golden standard or improper use of the additional instrument of the golden standard. This study aimed to design a novel mechanism for use in a biopsy needle, with the goal of combating the causes of the errors by providing an integrated design that guarantees the extraction of a biopsy.
Methods: The design process was explored by plotting the potential variations onto a design tree. This resulted in four distinct concepts. Criteria were established to evaluate the concepts. The Cam-follower concept was chosen as the final design. This mechanism was then constructed into a functioning prototype. This prototype was tested in a visual experiment and in a material experiment using gelatin and artificial bone tissue phantoms.
Results: The cam-follower mechanism was able to close off 89% of the end of the needle prototype. It was successful in extracting complete biopsies from the gelatin tissue phantom. The analysis of the softest bone was challenging due to the lengthwise compression of the biopsies. The needle prototype had difficulty penetrating the medium hard artificial bone and broke beyond use during these tests. The needle prototype was not put through its paces on the most difficult artificial bone type prepared for the experiment because of the harm it had sustained.
Discussion and conclusion: The Cam-follower mechanism is an integrated instrument that is intended to improve the efficacy of minimally invasive bone biopsy instruments. The current needle prototype was able to extract biopsies of higher quality and size from the gelatin tissue phantom compared to the golden standard. However, it failed to extract a viable biopsy from the artificial bone tissue phantoms, meaning that the design did not meet its goal. It is possible that the tissue phantoms used in this study did not accurately replicate real bone tissue, which could have impacted the results. Additionally, the main focus of the design was on the mechanism when the bone was already penetrated, so any issues that arose during penetration were not addressed before the material test. It is recommended to further refine the design with these results in mind. Small changes, such as incorporating elements from the golden standard like the tapered end and the sharpened cutting edge of the outer needle, could have a positive effect and enable the cam-follower to guarantee extraction of a biopsy, which would open the door to a clinical application.

An improvement for pedicle screws would be if the screws can directly transfer their forces to the strong cortical bone of the vertebra, rather than through the softer cancellous bone. This approach requires the creation of a curved trajectory through cancellous bone. The goal of this project is to adapt the flexible oscillating drill design of Müller to a steerable drill that can create a curved hole in artificial cancellous bone.
The oscillating drill tip is a cylinder which oscillates rotationally around its centre axis. The cutting direction is radial. This drill design constantly produces a sideways force since the cutters produce a friction force tangential to the cylindrical wall. The friction force on the forward stroke is currently cancelled out by an equal and opposite force during the reversed stroke. Introducing a difference in phase or amplitude between the two translationally oscillating inputs to the drill head can create a force difference between the forward and reverse stroke, which provides a net sideways steering force over many repetitions.
A prototype drill and accompanying oscillator have been designed and built to further research the effects of the amplitude and phase difference on the drill motion and drilling performance. The oscillator outputs two oscillations that can be individually adjusted in stroke length and their relative phase angle. The output stroke lengths can be set to 0.75, 0.50 and 0.25 mm. The phase difference can be adjusted in 18° increments between 0° and 360°. The drill consists of the cylindrical drill head and two parallel leaf springs that slide longitudinally and thereby transfer the motion of the oscillator to the drill head.
The results showed that the drill got embedded in the drilled hole which is insufficient for measuring a steering effect. Therefore, two alternative drill designs were proposed and evaluated to increase the drilling depth. The design adaptation that provides the most promising result, is to drastically lower the stiffness of the connection between the drill head and the leaf springs. An amplitude or phase difference applied by the oscillator causes the drill head to produce a different motion pattern. The pattern from the amplitude difference shows a decrease in the deviation distance which is expected to have a diminishing effect on the effectiveness of the drill. A phase difference of 144° between the two oscillations, causes the drill to produce an oval motion pattern which is expected to be the most effective in generating a steering effect.
This project provides a great basis for the future development of a drill that can steer without a steering actuator. The next step forward with this design should be to incorporate hinges between the leaf springs and the drill head, to maximise the rotational motion of the drill head.

Loosening of pedicle screws after spinal fusion surgery can lead to serious complications and may prevent fusion between vertebrae. This problem, which has increased in recent years, is a more frequent problem in patients with osteoporosis. In this study, we explore the possibility to use an expanding in‐pedicle anchor with the goal of increasing the contact area of the in‐pedicle anchor with the pedicle cortex to reduce toggling. Toggling is the rocking motion that can occur when an in‐pedicle anchor is subjected to lateral forces that can occur during the patient’s daily activities. A stainless steel scaled‐up 2D proof‐of‐principe prototype was developed and manufactured consisting of a central bolt with flattened sides, a nut, and ten sliding wedges. The wedges expand by applying a compression force by tightening the nut. In order for the prototype to reach the pedicle cortex, it needs to compress the surrounding cancellous bone first. It was shown in experiments that the proof‐of‐principle prototype was able to compress 5 and 10 PCF Sawbones solid foam, which corresponds to osteoporotic human cancellous bone. The proof‐of‐principle prototype was able to make contact with the top and bottom of a custom‐made 2D pedicle model where a conventional screw would have been limited to contact on the two flanks. The proof‐op‐principle prototype showed a better resistance
to lateral loads than an unexpanded model with the same dimensions. The proposed in‐pedicle anchor shows potential for improved resistance to caudocranial toggling by increasing the number of contact points with the pedicle cortex. The use of an in‐pedicle expansion to prevent toggling holds a promising future for possible clinical applications.

Spinal fusion surgery is applied, amongst other reasons, to correct unwanted curves in a spine hampered by scoliosis. During spinal fusion surgery, holes in the vertebra must be drilled, after which pedicle screws are placed. Traditional drilling only allows for the formation of straight holes. Ill-placed trajectories cannot be course-corrected, leading to repositioning the drill and starting again in the, weakened by the first attempt, vertebra. This thesis aims to develop a drilling method that will allow for the application of trajectory control during operation. This will form the first step towards a new spinal surgical instrument that could be used for course-correcting during spinal drilling or form curved holes applicable for new state-of-the-art alternate bone anchors.
The proof-of-principle instrument designed and fabricated in this thesis consists of an impulse generation part, a bendable tube with a saline medium, and a working head, which will perform the impacts on the bone tissue. The method consists of drilling using the repetitive impact of a solid round tip with a diameter of 4 mm. Through the use of a bendable impulse transmission tube, the instrument allows for the application of steerable drilling. The impulse will be generated by a manual compressed and released compression spring. This impulse will be translated into a hydraulic pressure wave; whereafter it will travel through the liquid medium of the tube, ending at the working head, which translates it into an impact on the target tissue.
The method has been proven to work in every state of curvature of the transmitting tube, ranging from 0 degrees till 90 degrees. Furthermore, almost 20% of the desired impulse output found in this thesis, 0.077 Ns, that would allow for high-speed drilling, 0.3 mm per strike, was reached. A linear increase in impulse output was found, correlating with the linear input increase, suggesting plausible higher impulse output magnitudes could be possible. In the future, the instrument's efficiency should be increased, as a mean efficiency of 3.5% was achieved, caused mainly by leakage of the saline filler and high friction with the mechanisms in the tube. All in all, the method shows great potential to be utilised as a future trajectory controlled bone drilling instrument.

Abstract—Spinal fusion surgery is an operation in which two or more adjacent vertebrae are rigidly connected, with the goal to remedy spinal instability, deformation of the vertebrae, or a herniated intervertebral disc. Vertebrae are conventionally fixated by means of pedicle screws, the downsides of which are accidental cortical wall breaches during drilling and poor holding strength of the screw. The holding strength of the bone anchor may be improved by increasing its contact area with the hard cortical wall of the vertebral body. To accomplish this, a curved hole needs to be made along the inside of the cortical wall. This research presents the design, manufacturing, and testing of a bone drilling device, that is flexible in one plane. To this end, the drill was developed on the basis of the tsetse fly’s proboscis, which is a mechanism that uses a cutting surface with its axis of rotation perpendicular to the drilling direction. Implementing this cutting motion has several advantages over conventional drilling: It facilitates using leaf springs as a flexible transmission, and it is not limited to drilling round holes. A prototype was built and tested on Sawbones closed cell foam, which closely mimics the mechanical properties of the cancellous bone found in human vertebrae. The prototype was capable of effectively cutting through foam with densities up to 10 pounds per cubic foot (PCF) with a feed rate of 50 mm/min. The ability to deflect off and follow a simulated cortical wall was also tested, and proved to be effective up to an insertion angle of 15˚. The bio-inspired drilling device presented in this research opens up new possibilities in the development of flexible drilling for a wide variety of orthopaedic applications.

This report describes the design of a wire rope based grasper for a tissue transport mechanism based on friction including means for operation. The previous transport mechanism design had no mechanism to transfer tissue into the lumen to be transported. To create the grasper, the wire ropes were plastically deformed to bend outward, creating the open shape of the grasper. A sheath consisting of magnets, springs, and a shrink tube can be slid over the plastically deformed section, straightening the wire ropes. This closed the grasp to constrain tissue. Operation was done by four finger handles, two on the main device and two clamped on the slidable sheath with magnets. Springs were used to make the passively hold the grasper in closed position, making it voluntary opening. To maintain the shape of the grasper, wire ropes were soldered together at the grasper tip, constrained in the sliders of the transport mechanism and wire rope guides were placed to the side of the magnets. After constraining the tissue, transfer into the lumen was done by actuating the transport mechanism. Gelatin phantom tissue samples were used to test the functionality the of the grasper. Results show successful constraining of 3mm, 4mm, 5mm spheres as well as a cylinder of 4mm with a length of 6.5mm. The spherical samples were all successfully transferred into the transport mechanism. The cylindrical sample was successfully transferred when inserted in axial orientation, but three out of six samples failed when insertion was perpendicular to the transport mechanism. Tissue samples were successfully grasped from a surface in three different orientations and the grasper was tested with the transport mechanism in a bend to test if no original functionality was lost. This grasper allows for a step towards a new surgical instrument.