Biomechanics of a parasitic wasp ovipositor : Probing for answers

Insects such as mosquitoes, true bugs, and parasitic wasps, probe for resources hidden in various substrates. The resources are often, located deep within the substrate and can only be reached with long and thin (slender) probes. Such probes can, however, easily bend or break (buckle) when pushed inside the substrate, which makes probing a challenging task. Nevertheless, the mentioned insects use their probes repeatedly throughout their lifetime without apparent damage. Furthermore, the probes are also used for sensing the targets, can be steered during insertion, and can transport both fluids (e.g. blood, phloem sap) and eggs. Insect probes seem highly versatile structures that satisfy many functional requirements, including buckling avoidance, steering, sensing, and transport. Similar requirements also hold for minimally invasive medical procedures, where slender tools are used to minimize damage to the patient. Understanding the probing process in insects can bring insights in the insect ecology and evolution and it may also help in the development of novel surgical tools. In this thesis, I focus on the mechanical and motor adaptations of insect probing, while other aspects are only briefly discussed. In chapter 2, we review the literature on the probing structures and their operating principles across mosquitoes, parasitic wasps, and hemipterans. Probes are either modified mouthparts (mosquitoes, true bugs) or special tubular outgrowths of the abdomen (parasitic wasps). Despite having different developmental origins, the probes share three major morphological characteristics, which may reflect the shared functional requirements of buckling avoidance and steering: (i) the probes consist of multiple, interconnected elements that can slide along each other, (ii) the probe diameters are very small, which leaves no space for internal musculature, and (iii) the distal ends (tips) of the probe elements are asymmetric and often bear various serrations, hooks, bulges, or notches. How such slender multi-element probes avoid buckling during insertion has been hypothesized in the so-called push–pull mechanism. According to this mechanism, the probe is inserted into the substrate by reciprocal movements of the elements. The insects therefore simultaneously push on some of the probe elements, while pulling on the others. The tip serrations are directed such, that they primarily increase the friction upon pulling of the elements. This puts the pulled elements under tension and makes them effectively stiffer in bending (like when pulling a rope). The elements under tension can serve as guides along which the other elements are pushed inside the substrate without the risk of buckling. The insect alternates the pushing and pulling between the elements to incrementally insert the probe in the substrate. This mechanism has, however, never been quantified in insects and it was hitherto unknown whether the animals rely on it during probing. The probe tip asymmetry presumably facilitates steering. The asymmetric tip geometry leads to asymmetric reaction forces from the substrate on the tip during insertion, which push the probe tip sideways into a curved path. Controlling the tip geometry therefore allows for control of probing direction. Although offsetting the elements by sliding already changes the shape of the probe tip, these changes might be too small to induce the necessary change of probing direction. A number of mechanisms that enhance the tip asymmetry during the sliding of the elements have been suggested. However, few mechanisms have been observed or studied in vivo, so it is not completely clear how insects steer with their probes. Additionally, the effect of the substrate on both the steering and insertion mechanisms is unknown. To understand the biomechanics of insect probing, we investigated the probing behaviour of the braconid parasitic wasp Diachasmimorpha longicaudata. This is an ideal species for studying the buckling avoidance and steering, because it: (i) possess a slender ovipositor several millimetres in length, (ii) probes into solid material (e.g. citrus fruits), and (iii) attack fruit-fly larvae that are freely moving within the substrate (i.e. steering can be expected). The ovipositor of D. longicaudata is similar to other hymenopterans and consists of three interconnected elements (valves), one dorsal and two ventral ones. The interconnection is a tongue-and-groove mechanism, which allows for sliding of the valves, but prevents their separation. The ovipositor has an asymmetric tip—the distal end of the dorsal valve is enlarged (bulge), while the ventral valve tips have harpoon-like serrations. Additionally, just proximal to the bulge of the dorsal valve, the ovipositor is characteristically bent in an S-shape. This seems to be a feature present only in D. longicaudata and closely related species. The wasps also possess a pair of sheaths that envelop the ovipositor at rest and throughout most of the probing process, but do not penetrate into the substrate. In chapter 3, we studied the kinematics of ovipositor insertion into translucent, artificial substrates of various stiffnesses. Ovipositor insertion was filmed in a three camera setup, which allowed us to reconstruct the ovipositor insertion in 3D, while also monitoring the orientation of the insect’s body. We discovered that the wasps can explore a wide range of the substrate by probing in any direction with respect to their body orientation from a single puncture point. Probing range and speed decreased with increasing substrate stiffness. Wasps used two strategies of ovipositor insertion. In soft substrates, all ovipositor valves were pushed inside the substrate at the same time. In stiff substrates, wasps always moved the valves alternatively, presumably employing the hypothesized push–pull mechanism. We observed that ovipositors can follow curved trajectories inside the substrate. Detailed kinematic analysis revealed that the ovipositors followed a curved path during probing with protracted ventral valve(s). In contrast, probing with protracted dorsal valve resulted in straight trajectories. We linked the changes in the probing direction to the shape changes in the ovipositor tip. When the ventral valves were protracted, they curved towards the dorsal valve, resulting in an enhanced bevel which presumably caused a change in insertion direction. In chapter 4, we investigated the above described steering mechanism by quantifying the bending stiffness (three point bend test) and the geometry (high-resolution computer tomography) of the ovipositor in D. longicaudata. Additionally, we qualitatively assessed the material composition of the valves using fluorescence imaging. The thick dorsal valve bulge might be stiff and could straighten the S-shaped region of the ovipositor during the valve offset, causing bending of the tip. We discovered that the S-shaped region of the ovipositor is significantly softer than its neighbouring regions, which is mostly due to the presence of resilin in the S-shaped region of the ventral valve. Resilin is a rubber-like protein and reduces the stiffness of the otherwise heavily sclerotized valves. Additionally, we showed that the ventral valves have a higher bending stiffness than the dorsal valve along most of their length. The exception is presumably the bulge on the dorsal valve—although we could not directly measure its bending stiffness, its geometrical properties show that it is the thickest (and therefore stiffest) region in the distal end of the ovipositor. Outside the substrate, offsetting of the valves in any direction (i.e. pro- or retraction of the ventral valves) caused a straightening of the S-shaped region of the ovipositor and a curving towards the dorsal side. However, during probing in a substrate, such curving was only observed upon protraction of the ventral valves. We hypothesize this is due to the interaction of the ovipositor with the substrate. Namely, the bevelled ventral valve tips generate substrate reaction forces that promote dorsal curving, while the bevelled tip of the dorsal valve generates substrate forces that promote ventral bending. The interaction between the ventral and dorsal valves straightens the S-shaped region of the ovipositor and enhances dorsal curving. This therefore facilitates strong shape changes of the tip only upon protraction of the ventral valves, while counteracting the ventral curving of the dorsal valve. These opposing mechanisms presumably result in an approximately straight protraction of the dorsal valve. In chapters 2 and 3 we describe how the wasps use the reciprocal valve movements when probing in stiff substrates. As such substrates presumably require strong forces during insertion, the reciprocal valve movements may indeed serve to avoid buckling. However, how the valves are actuated or the forces generated during probing have never been quantified. In chapter 5, we therefore investigated the ovipositor base and the muscles driving the movements of the valves. At the base, the valves attach to plate-like structures that are interconnected with a series of linkages. The muscles attach to these plates and can move them with respect to each other. Such movements also result in the movements of the valves. To analyse the mechanics of this linked system, we performed high-resolution computer tomography scans of wasps in different stages of the probing cycle. This allowed us to compare the configurational changes of the basal plates to the valve offset, and measure the muscle cross-sections and attachment sites. We also calculated the muscle moment arms and estimated the forces and moments of the most relevant musculature actuating the ovipositor movements, by assuming a tensile muscle stress previously reported for insect muscles. For the ventral valves only, we also calculated the forces the valves can exert onto the substrate. The dorsal valve can only be moved by moving the base that is linked inside the abdomen, and therefore force estimation could not be made. The displacement magnitude of the basal plates corresponded to the valve offset, indicating that the valves are indeed moved due to the changes in the arrangement of the basal plates. We also showed that the ventral valve plates move most during the probing cycle, while the magnitude of the dorsal valve plate movements is much smaller. This suggests that the ventral valves move along the dorsal valve, while the dorsal valve moves together with the abdomen during probing. Additionally, in the situation where the animal keeps its abdomen stationary, we estimated the maximal forces actuating the ventral valves. The estimated maximal pushing forces can be higher than the estimated buckling load of the unsupported ovipositor outside the substrate. Assuming the maximal pushing forces are required during probing, antibuckling mechanisms are needed to avoid damaging the ovipositor. Buckling can be limited (prevented) by either supporting the ovipositor outside the substrate with additional sheaths, employing the push–pull mechanism, or both. Subtracting the maximal estimated pushing and pulling forces on the ventral valves, results in a net pushing force that is very close to the buckling threshold of the ovipositor, albeit still slightly higher. The sheaths, although being flexible, might provide the additional support if needed. In this thesis, I show that multi-element probes are inserted into the substrate using reciprocal movements of the individual elements. These movements appear to be necessary in stiff substrates, which presumably require high pushing forces on a single element during probing. This is in accordance with the hypothesis that reciprocal valve movements serve as an anti-buckling mechanism. Additionally, such valve movements are also important for steering of the probe during insertion. The valve offset controls the shape of the probe tip and therefore the net substrate reaction forces that result in bending of the probe. Wasps evolved special structures that enhance the shape changes of their ovipositor tips and facilitate steering. Our findings may be interesting for a broad range of audiences. Entomologists, evolutionary biologists, and ecologists may find them useful when studying the diversification of probing insects, their evolutionary success, or their ecological interactions (e.g. insect–plant, parasite–host). The anti-buckling and steering mechanisms may be helpful when developing novel, man-made probes. These mechanisms allow for minimization of the probe thickness and accurate steering control, which minimizes substrate damage during probing. Our findings may be particularly useful in the development of slender, steerable needles for minimally invasive surgery.</p

Efficient Motion and Inspection Planning for Medical Robots with Theoretical Guarantees

Medical robots enable faster and safer patient care. Continuum medical robots (e.g., steerable needles) have great potential to accomplish procedures with less damage to patients compared to conventional instruments (e.g., reducing puncturing and cutting of tissues). Due to their complexity and degrees of freedom, such robots are often harder and less intuitive for physicians to operate directly. Automating robot-assisted medical procedures can enable physicians and patients to harness the full potential of medical robots in terms of safety, efficiency, accuracy, and precision.Motion planning methods compute motions for a robot that satisfy various constraints and accomplish a specific task, e.g., plan motions for a mobile robot to move to a target spot while avoiding obstacles. Inspection planning is the task of planning motions for a robot to inspect a set of points of interest, and it has applications in domains such as industrial, field, and medical robotics. With motion and inspection planning, medical robots would be able to automatically accomplish tasks like biopsy and endoscopy while minimizing safety risks and damage to the patient. Computing a motion or inspection plan can be computationally hard since we have to consider application-specific constraints, which come from the robotic system due to the mechanical properties of the robot or come from the environment, such as the requirement to avoid critical anatomical structures during the procedure.I develop motion and inspection planning algorithms that focus on efficiency and effectiveness. Given the same computing power, higher efficiency would shorten the procedure time, thus reducing costs and improving patient outcomes. Additionally, for the automation of medical procedures to be clinically accepted, it is critical from a patient care, safety, and regulatory perspective to certify the correctness and effectiveness of the algorithms involved in procedure automation. Therefore, I focus on providing theoretical guarantees to certify the performance of planners. More specifically, it is important to certify if a planner is able to find a plan if one exists (i.e., completeness) and if a planner is able to find a globally optimal plan according to a given metric (i.e., optimality).Doctor of Philosoph

A Textbook of Advanced Oral and Maxillofacial Surgery

The scope of OMF surgery has expanded; encompassing treatment of diseases, disorders, defects and injuries of the head, face, jaws and oral cavity. This internationally-recognized specialty is evolving with advancements in technology and instrumentation. Specialists of this discipline treat patients with impacted teeth, facial pain, misaligned jaws, facial trauma, oral cancer, cysts and tumors; they also perform facial cosmetic surgery and place dental implants. The contents of this volume essentially complements the volume 1; with chapters that cover both basic and advanced concepts on complex topics in oral and maxillofacial surgery

Applications of micro-CT in the Criminal Justice System of England and Wales: an impact assessment

The Criminal Justice System of England and Wales is currently facing major challenges. One is the financial pressure of government funding cuts, the other the increasing need for professionalisation and rigour within the system. This thesis presents the use of micro Computed Tomography, Additive Manufacturing, and 3D visualisation to address both challenges. By drawing on data from live murder investigations the project examines how these digital technologies can be used to improve the investigation of strangulation deaths, sharp force injuries, and fractures. Each of these categories was treated as a separate case in the overall multiple-case study research design. The increased detail enabled by micro-CT assisted pathologists in the diagnosis of strangulation as previously undetected injuries of the larynx could be identified. A validation study comparing injured to uninjured samples was conducted to increase the strength of the interpretations. For sharp force injuries analysis, micro-CT proved useful for providing the necessary injury characteristics and highly accurate measurements to allow weapon identification. The high resolution of micro-CT scanning also enabled the visualisation of trauma on the smallest of skeletal elements, often encountered in non-accidental injuries in children. The cross-case synthesis revealed the main themes of clarity, objectivity, and visualisation which were improved by using micro-CT irrespective of type of homicide. The significance of these themes further crystallised in semi-structured interviews conducted with various stakeholders of the Criminal Justice System. Management concepts proved suitable to assess the project’s success as the themes used in operations management such as quality, delivery, and cost apply to the delivery of justice as well. A good working relationship with West Midlands Police’s homicide investigators and researchers at WMG was crucial to providing the technology and expertise to address real-life problems whilst ultimately saving taxpayers’ money

Diagnosis with near infrared spectroscopy during minimally invasive procedures

The goal of this dissertation is to present the potential of diffuse optical spectroscopy technique to characterize and differentiate types of tissue, including dysplastic and cancerous tissues, when measuring the tissue spectra during a surgical or an interventional procedure under medical image guidance. This dissertation begins with a chapter that describes the different mathematical modeling of light transport in scattering media such as tissue. Each of the existing models used in literature is described including the way to extract the optical properties by applying it to the tissue measurements performed with fiber-optic handheld probes. An overview of the clinical applications investigated by the research groups is given as well as the performance of the diagnosis in discriminating different types of tissue based on the derived parameters. Chapter 2 and 3 corresponds to the validation of the diffusion theory model applied to optical spectroscopy measurements performed in a wide wavelength range as compared to what has been already presented in literature. In fact, chapter 2 presents the very first validation available in literature of the applicability of diffusion theory approximation model to measurements performed from 900 to 1600 nm. Water and lipid absorption coefficients were measured for different temperatures and used to in the model to derive the concentration of these chromophores. The validation was performed by recovering the actual water and lipid content in custom made emulsions with known lipid content. The validation of the reduced scattering estimation was performed by correlating the estimated parameters related to the reduced scattering with the particles size of the emulsions after blending and investigating the particle size distribution. Chapter 3 presents the advantage of extending the commonly-used wavelength range from 400 to 1000 nm up to 1600 nm. Although water and lipid can be estimated from diffuse optical spectroscopy measurements up to 1000 nm, this chapter shows that the extension of the wavelength significantly improves the accuracy of the optical properties extraction and that the lack of spectral feature of water and lipid when measuring up to 1000 nm can not only yield inaccurate water and lipid content but as well influence the estimated blood concentrations and reduced scattering parameters. Chapters 4 through 6 present the application of diffuse optical spectroscopy for diagnosis related to liver diseases. Chapter 4 is a benchmarking of optical spectroscopy with other techniques such as magnetic resonance spectroscopy (MRS), nuclear magnetic resonance spectroscopy (NMR), high performance thin layer chromatography (HPTLC) and histopathology for hepatic lipid quantification in mice. The derived hepatic fat fractions in the mice liver did not show any significant differences between the various techniques. Furthermore, it was shown that it was possible to clearly distinguish the group of mice on chow diet from the group of mice on high fat diet. The potential of diffuseoptical spectroscopy in quantifying hepatic lipid is of great interest for diagnosis of fatty liver disease where it is considered to be positive in patients for hepatic lipid fractions as low as 5%. Chapter 5 presents optical spectra acquired ex vivo on metastasis in liver and the surrounding healthy liver tissue in 14 patients. This chapter demonstrates the importance of including bile absorption coefficients to the model in addition to oxygenated-hemoglobin (HbO2), deoxygenated hemoglobin (Hb), water and lipid as livers are rich in bile ducts. This study shows that it is possible to discriminate tumors from the surrounding healthy liver tissue based on the amount of bile, water and the reduced scattering amplitude. Chapter 6 describes the diagnosis performance of diffuse optical spectroscopy in discriminating the tumors from the healthy liver samples with two different methods: classifying the types of tissues using the derived clinical parameters from fitting the diffusion theory mathematical model to the measurements as well as applying a statistical method to classify the raw optical measurements. In this chapter, in addition to discriminating tumors from healthy tissue, the lipid content estimated with diffuse optical spectroscopy showed a strong correlation with hepatic fat estimation from the histological slides. These findings ultimately have impact on detecting tumors when performing a biopsy as well as defining the steatosis level in liver. Chapter 7 demonstrates the capability of diffuse optical spectroscopy in discriminating tumor sites from the surrounding healthy lung tissues. An ex vivo study was conducted in samples excised from 10 patients with lung cancer. This study showed that hemoglobin volume fraction and the reduced scattering amplitude showed significant difference in both type of tissue by being lower in tumors as compared to the healthy lung sites. Additionally, the performance of diagnosis to discriminate the tumors from the healthy lung samples was evaluated and yielded sensitivity and specificity up to 86% and 85%, respectively. Chapters 8 and 9 demonstrate the potential of diffuse optical spectroscopy to classify several types of breast tissues including malignant types. Chapter 8 corresponds to an ex vivo study on 54 excised breast samples that were measured at 5 different sites, namely adipose, glandular, fibroadenoma, invasive carcinoma and ductal carcinoma in situ. From the various optical parameters that are derived from the measurements and the chromophores volume fractions, statistical tests were performed to investigate which parameter shows significant difference between pairwise types of tissue. Furthermore, the performance of diagnosis in discriminating the 5 types of tissue yielded area under receiver operator curve (AUC) ranging from 86% to 100%. Additionally, the performance of classifying benign and malignant samples was made with different types of classification methods that were already applied by various research groups that conducted optical spectroscopy measurements on breast samples. The different classification schemes were compared and it was shown that the performance of the diagnosis can vary a lot depending on the type of classification that is used. Therefore this chapter emphasizes the importance of being very critical when selecting the classification scheme. Chapter 9 shows the differences in investigating the difference in optical properties and measurements between malignant and non-malignant tissue by comparing optical spectroscopy in quantifying hepatic lipid is of great interest for diagnosis of fatty liver disease where it is considered to be positive in patients for hepatic lipid fractions as low as 5%. Chapter 5 presents optical spectra acquired ex vivo on metastasis in liver and the surrounding healthy liver tissue in 14 patients. This chapter demonstrates the importance of including bile absorption coefficients to the model in addition to oxygenated-hemoglobin (HbO2), deoxygenated hemoglobin (Hb), water and lipid as livers are rich in bile ducts. This study shows that it is possible to discriminate tumors from the surrounding healthy liver tissue based on the amount of bile, water and the reduced scattering amplitude. Chapter 6 describes the diagnosis performance of diffuse optical spectroscopy in discriminating the tumors from the healthy liver samples with two different methods: classifying the types of tissues using the derived clinical parameters from fitting the diffusion theory mathematical model to the measurements as well as applying a statistical method to classify the raw optical measurements. In this chapter, in addition to discriminating tumors from healthy tissue, the lipid content estimated with diffuse optical spectroscopy showed a strong correlation with hepatic fat estimation from the histological slides. These findings ultimately have impact on detecting tumors when performing a biopsy as well as defining the steatosis level in liver. Chapter 7 demonstrates the capability of diffuse optical spectroscopy in discriminating tumor sites from the surrounding healthy lung tissues. An ex vivo study was conducted in samples excised from 10 patients with lung cancer. This study showed that hemoglobin volume fraction and the reduced scattering amplitude showed significant difference in both type of tissue by being lower in tumors as compared to the healthy lung sites. Additionally, the performance of diagnosis to discriminate the tumors from the healthy lung samples was evaluated and yielded sensitivity and specificity up to 86% and 85%, respectively. Chapters 8 and 9 demonstrate the potential of diffuse optical spectroscopy to classify several types of breast tissues including malignant types. Chapter 8 corresponds to an ex vivo study on 54 excised breast samples that were measured at 5 different sites, namely adipose, glandular, fibroadenoma, invasive carcinoma and ductal carcinoma in situ. From the various optical parameters that are derived from the measurements and the chromophores volume fractions, statistical tests were performed to investigate which parameter shows significant difference between pairwise types of tissue. Furthermore, the performance of diagnosis in discriminating the 5 types of tissue yielded area under receiver operator curve (AUC) ranging from 86% to 100%. Additionally, the performance of classifying benign and malignant samples was made with different types of classification methods that were already applied by various research groups that conducted optical spectroscopy measurements on breast samples. The different classification schemes were compared and it was shown that the performance of the diagnosis can vary a lot depending on the type of classification that is used. Therefore this chapter emphasizes the importance of being very critical when selecting the classification scheme. Chapter 9 shows the differences in investigating the difference in optical properties and measurements between malignant and non-malignant tissue by comparing intra and inter-patients variations. It was concluded that the diagnosis performance is best when comparing the tissues within single patients as compared to when all data from all patients are compared. Chapter 10 presents the feasibility of real-time tissue characterization during needle insertions from healthy liver to hepatocellular carcinoma tumor where medical imaging such as 3D fluoroscopy and ultrasound were used as reference. Whereas in literature point measurements in healthy and in tumors are compared, this study shows that continuous diffuse reflectance measurements while advancing the needle enables the identification of the tumor boundaries based on the derived clinical parameter, namely blood oxygenation and volume fraction as well as the scattering amplitude

Novel Applications and Refinements of Ultrasound Techniques in Perinatal and Infant Death Investigation

The decline in parental consent for perinatal autopsies has led to the development of less invasive autopsy techniques, primarily using imaging and in some cases acquiring tissue samples through laparoscopic techniques via small incisions. Whilst post-mortem MRI (PMMR) has been extensively tested, and shown to be a suitable modality for determining the cause of death/demise in the perinatal cohort, it is not widely available. This thesis explores the utility of a poorly explored, yet more accessible, cheaper, dynamic imaging modality widely used in ‘live’ paediatric imaging for the purposes of a less invasive autopsy – the perinatal post-mortem ultrasound (PMUS). I present a systematic review of the limited literature of PMUS diagnostic accuracy for perinatal death investigation encompassing 4 publications with 455 cases in total. This reveals an overall pooled whole body sensitivity rate of 73.3% [95% CI 59.9, 83.5] and specificity rate of 96.6% [95% CI 92.6, 98.4] . A comprehensive imaging protocol for whole body PMUS is also presented based on my own experience in scanning 272 perinatal deaths. An analysis in 130 of these cases with autopsy as a reference standard, showed that brain and abdominal diagnoses yielded the highest sensitivity rates (90.9% and 92.3% respectively), with spinal, cardiac and thoracic diagnoses yielding the lowest sensitivity rates (50%, 50% and 57.1% respectively). Imaging of the brain and heart however were the least likely to be of diagnostic quality (76.8% and 78.3% diagnostic cases respectively), particularly in macerated fetuses. In a subset of cases where PMUS and 1.5T PMMR were performed, there was no significant difference in whole body diagnostic accuracy rates (concordance rates for PMUS versus PMMR of 86.4% [95%CI 77.7, 92.0] versus 88.6% [95% CI 80.3, 93.7]), although PMMR yielded fewer non-diagnostic brain and cardiac examinations (2.9% and 2.9% non-diagnostic brain and cardiac PMMR cases versus 22.8% and 14.7% non-diagnostic PMUS cases). In the second part of my thesis, I describe the development of an ‘incisionless’ ultrasound guided biopsy method using a single entry site for the biopsy needle – the umbilical vein. This ‘INTACT’ biopsy method allowed for a ‘non-invasive’ autopsy with tissue sampling, with a biopsy success rate of 76.1% overall for all organs, with highest individual organ success rates >90% for heart and lungs. I conclude by discussing how best to incorporate PMUS into clinical practice and suggest areas for future researc