Computational Analysis of Surgical Tool-Brain Tissue Interaction

This paper presents new surgical tool-brain tissue interactions models in three directional format considering the linear elastic, hyperelastic and viscoelastic properties of a brain tissue which are characterized by conducting stress-strain simulation on brain model. Brain tissues properties like a Neo-Hookean, Mooney-Rivlin Model and Prony Series are considered. Effects of adopting non-linear properties are discussed. After optimizing models in COMSOL Muiltiphysics 4.0, the models show that the brain tissues contain non-linear characteristic and the coefficients of the models are available to Open Inventor in order to initiate a visio-haptic simulation which will be used for doctors and surgical operation manipulators

Realistic tool-tissue interaction models for surgical simulation and planning

Surgical simulators present a safe and potentially effective method for surgical training, and can also be used in pre- and intra-operative surgical planning. Realistic modeling of medical interventions involving tool-tissue interactions has been considered to be a key requirement in the development of high-fidelity simulators and planners. The soft-tissue constitutive laws, organ geometry and boundary conditions imposed by the connective tissues surrounding the organ, and the shape of the surgical tool interacting with the organ are some of the factors that govern the accuracy of medical intervention planning.\ud \ud This thesis is divided into three parts. First, we compare the accuracy of linear and nonlinear constitutive laws for tissue. An important consequence of nonlinear models is the Poynting effect, in which shearing of tissue results in normal force; this effect is not seen in a linear elastic model. The magnitude of the normal force for myocardial tissue is shown to be larger than the human contact force discrimination threshold. Further, in order to investigate and quantify the role of the Poynting effect on material discrimination, we perform a multidimensional scaling study. Second, we consider the effects of organ geometry and boundary constraints in needle path planning. Using medical images and tissue mechanical properties, we develop a model of the prostate and surrounding organs. We show that, for needle procedures such as biopsy or brachytherapy, organ geometry and boundary constraints have more impact on target motion than tissue material parameters. Finally, we investigate the effects surgical tool shape on the accuracy of medical intervention planning. We consider the specific case of robotic needle steering, in which asymmetry of a bevel-tip needle results in the needle naturally bending when it is inserted into soft tissue. We present an analytical and finite element (FE) model for the loads developed at the bevel tip during needle-tissue interaction. The analytical model explains trends observed in the experiments. We incorporated physical parameters (rupture toughness and nonlinear material elasticity) into the FE model that included both contact and cohesive zone models to simulate tissue cleavage. The model shows that the tip forces are sensitive to the rupture toughness. In order to model the mechanics of deflection of the needle, we use an energy-based formulation that incorporates tissue-specific parameters such as rupture toughness, nonlinear material elasticity, and interaction stiffness, and needle geometric and material properties. Simulation results follow similar trends (deflection and radius of curvature) to those observed in macroscopic experimental studies of a robot-driven needle interacting with gels

A FEEDBACK-BASED DYNAMIC INSTRUMENT FOR MEASURING THE MECHANICAL PROPERTIES OF SOFT TISSUES

In this paper, a novel feedback-based dynamic instrument integrated into a Minimally- Invasive-Surgery (MIS) tool to evaluate the mechanical impedance of soft tissues is presented. This instrument is capable of measuring viscoelasticity of tissues if specific boundary conditions are known. Some important advantages of the proposed instrument are that it is robust and simple in comparison to other similar instruments as it does not require magnitude information of plant’s displacement output and no force sensor is used. The precision and accuracy of the measurements of the proposed instrument for soft tissues is noticeably higher than similar instruments, which are not optimized to work with soft tissues. The proposed dynamic instrument is designed to detect the frequency shifts caused by contacting a soft tissue using an improved phase-locked loop feedback system (closed loop). These frequency shifts can then be used to evaluate the mechanical properties of the tissue. The closed-loop method works fast (with an approximate resonance-frequency-shift rate of 15 Hz per second), and is capable of measuring dy­ namic mechanical properties of viscoelastic tissues, while previous focus was mostly on static/quasi-static elastic modulus. The instrument is used to evaluate the equivalent stiffness of several springs and cantilever beams, mass of reference samples, and also the frequency shifts of several phantoms with injected tumors, noting that these frequency shifts can be used to measure the viscoelasticity of the tissues. It is also shown that the instrument can be used for tumor localization in these phantoms

Force Measurement Methods in Telerobotic Surgery: Implications for End-Effector Manufacture

Haptic feedback in telesurgical applications refers to the relaying of position and force information from a remote surgical site to the surgeon in real-time during a surgical procedure. This feedback, coupled with visual information via microscopic cameras, has the potential to provide the surgeon with additional ‘feel’ for the manipulations being performed at the instrument-biological tissue interface. This increased sensitivity has many associated benefits which include, but are not limited to; minimal tissue damage, reduced recuperation periods, and less patient trauma. The inclusion of haptic feedback leads to reduction in surgeon fatigue which contributes to enhanced performance during operation. Commercially available Minimally Invasive Robotic Surgical (MIRS) systems are being widely used, the best-known examples being from the daVinci® by Intuitive Surgical Inc. However, currently these systems do not possess force feedback capability which therefore restricts their use during many delicate and complex procedures. The ideal system would consist of a multi-degree-of-freedom framework which includes end-effector instruments with embedded force sensing included. A force sensing characterisation platform has been developed by this group which facilitates the evaluation of force sensing technologies. Surgical scissors have been chosen as the instrument and biological tissue phantom specimens have been used during testing. This test-bed provides accurate, repeatable measurements of the forces produced at the interface between the tissue and the scissor blades during cutting using conventional sensing technologies. The primary focus of this paper is to provide a review of the traditional and developing force sensing technologies with a view to establishing the most appropriate solution for this application. The impact that an appropriate sensing technology has on the manufacturability of the instrument end-effector is considered. Particular attention is given to the issues of embedding the force sensing transducer into the instrument tip

Models of Mechanics and Growth in Developmental Biology: A Computational Morphodinamics approach

Recent evidence has revealed the role of mechanical cues in the development of shapes in organisms. This thesis is an effort to test some of the fundamental hypotheses about the relation between mechanics and patterning in plants. To do this, we develop mechanical models designed to include specific features of plant cell walls. These are heterogeneous stiffness and material anisotropy as well as rates and directions of growth, which we then relate to different domains of the plant tissue.In plant cell walls, anisotropic fiber deposition is the main controller of longitudinal growth. In our model, this is achieved spontaneously, by applying feedback from the maximal stress direction to the fiber orientation. We show that a stress feedback model is in fact an energy minimization process. This can be considered as an evolutionary motivation for the emergence of a stress feedback mechanism. Then we add continuous growth and cell division to the model and employ the strain signal directing large growth deformations. We show the advantages of strain-based growth model for emergence of plant-like organ shapes as well as for reproducing microtubular dynamics in hypocotyls and roots. We also investigate possibilities for describing microtubular patterns, at root hair outgrowth sites according to stress patterns. Altogether, the work described in this thesis, provides a new improved growth model for plant tissue, where mechanical properties are handled with appropriate care in the event of growth driven by either molecular or mechanical signals. The model unifies the patterning process for several different plant tissues, from shoot to single root hair cells, where it correctly predict microtubular dynamics and growth patterns. In a long-term perspective, this understanding can propagate to novel technologies for improvement of yield in agriculture and the forest industry

Biomechanical function of the periodontal ligament in biting and orthodontic tooth movement

Alveolar bone remodelling is vital for the success of dental implants and orthodontic treatments. However, the underlying biomechanical mechanisms, in particular the function of the periodontal ligament (PDL) in bone remodelling, are not well understood. The PDL is a soft fibrous connective tissue that joins the tooth root to the alveolar bone and plays a critical role in the transmission of loads from the teeth to the surrounding bone. However, due to its complex structure, small size and location within the tooth socket it is difficult to study in vivo. Finite element analysis (FEA) is an ideal tool with which to investigate the role of the PDL, but inclusion of the PDL in FE models is complex and time consuming and most FE models that include teeth do not consider the PDL. The aim of this study was to investigate the effects of including the PDL and its fibrous structure in mandibular finite element models.This research involved the development of a novel method to include the fibres of the PDL in FE models. A simplified single tooth model was developed to assess the effects of modelling fibrous PDL compared to the traditional approach of representing the PDL as a simple layer of solid material and to an absent PDL. The same study design was then applied to a high-resolution model of the human molar region, which is the first time that the fibrous structure of the PDL has been included in a model with realistic tooth and bone geometry. Finally, molar region models of five additional species (cat, cercocebus, pig, rabbit and sheep) were tested with and without a PDL.The results from the research showed that omission of the PDL creates a more rigid model, reducing the strains observed in the mandibular corpus for all six species studied. This suggests that the results obtained are not specific to the human molar region, but may be true for the mammalian mandible in general. Compared to a solid PDL, the fibrous PDL altered the strains in the models, in particular increasing the strains observed in the tooth socket. This may be important for the management of orthodontic treatment, as strains in this region are thought to play an important role in bone remodelling during orthodontic tooth movement

A Virtual-Based Haptic Endoscopic Sinus Surgery (ESS) Training System: from Development to Validation

Simulated training platforms offer a suitable avenue for surgical students and professionals to build and improve upon their skills, without the hassle of traditional training methods. To enhance the degree of realistic interaction paradigms of training simulators, great work has been done to both model simulated anatomy in more realistic fashion, as well as providing appropriate haptic feedback to the trainee. As such, this chapter seeks to discuss the ongoing research being conducted on haptic feedback-incorporated simulators specifically for Endoscopic Sinus Surgery (ESS). This chapter offers a brief comparative analysis of some EES simulators, in addition to a deeper quantitative and qualitative look into our approach to designing and prototyping a complete virtual-based haptic EES training platform

Strain stiffening universality in composite hydrogels and tissues

Soft biological tissues exhibit a remarkable resilience to large mechanical loads, a property which is associated with the strain stiffening capability of the biopolymer networks that structurally support the tissues. Yet, recent studies have shown that composite systems such as tissues and blood clots exhibit mechanical properties that contradict those of the polymer matrix - demonstrating stiffening in compression, but softening in shear and tension. The microscopic basis of this apparent paradox remains poorly understood. We show that composite hydrogels and tissues do indeed exhibit non-linear elastic stiffening in shear - which is governed by the stretching of the polymer chains in the matrix - and that it is driven by the same mechanism that drives compression stiffening. However, we show that the non-linear elastic stiffening in composite hydrogels and tissues is masked by mechanical dissipation arising from filler-polymer interactions known as the Mullins effect, and we introduce a method to characterize the non-linear elasticity of the composites in isolation from this overall strain softening response through large-amplitude oscillatory shear experiments. We present a comprehensive characterization of the non-linear elastic strain stiffening of composite hydrogels and soft tissues, and show that the strain stiffening in shear and compression are both governed by universal strain amplification factors that depend on essential properties of the composite system, such as the filler concentration and the filler-polymer interaction strength. These results elucidate the microscopic mechanisms governing the non-linear mechanics of tissues, which provides design principles for engineering tissue-mimetic soft materials, and have broad implications for cell-matrix mechanotransduction in living tissues