Simulation of resistance forces acting on surgical needles

In-Plane Si Microneedles: Fabrication, Characterization, Modeling and Applications

Microneedles are getting more and more attention in research and commercialization since their advancement in the 1990s due to the advantages over traditional hypodermic needles such as minimum invasiveness, low material and fabrication cost, and precise needle geometry control, etc. The design and fabrication of microneedles depend on various factors such as the type of materials used, fabrication planes and techniques, needle structures, etc. In the past years, in-plane and out-of-plane microneedle technologies made by silicon (Si), polymer, metal, and other materials have been developed for numerous biomedical applications including drug delivery, sample collections, medical diagnostics, and bio-sensing. Among these microneedle technologies, in-plane Si microneedles excel by the inherent properties of Si such as mechanical strength, wear resistance, biocompatibility, and structural advantages of in-plane configuration such as a wide range of length, readiness of integration with other supporting components, and complementary metal-oxide-semiconductor (CMOS) compatible fabrication. This article aims to provide a review of in-plane Si microneedles with a focus on fabrication techniques, theoretical and numerical analysis, experimental characterization of structural and fluidic behaviors, major applications, potential challenges, and future prospects.

Fracture behaviour of human skin in deep needle insertion can be captured using validated cohesive zone finite-element method

Medical needles have shown an appreciable contribution to the development of novel medical devices and surgical technologies. A better understanding of needle-skin interactions can advance the design of medical needles, modern surgical robots, and haptic devices. This study employed finite element (FE) modelling to explore the effect of different mechanical and geometrical parameters on the needle's force-displacement relationship, the required force for the skin puncture, and generated mechanical stress around the cutting zone. To this end, we established a cohesive FE model, and identified its parameters by a three-stage parameter identification algorithm to closely replicate the experimental data of needle insertion into the human skin available in the literature. We showed that a bilinear cohesive model with initial stiffness of 5000 MPa/mm, failure traction of 2 MPa, and separation length of 1.6 mm can lead to a model that can closely replicate experimental results. The FE results indicated that while the coefficient of friction between the needle and skin substantially changes the needle reaction force, the insertion velocity does not have a noticeable effect on the reaction force. Regarding the geometrical parameters, needle cutting angle is the prominent factor in terms of stress fields generated in the skin tissue. However, the needle diameter is more influential on the needle reaction force. We also presented an energy study on the frictional dissipation, damage dissipation, and strain energy throughout the insertion process.

A highly robust approach to fabricate the mass-customizable mold of sharp-tipped biodegradable polymer microneedles for drug delivery

A skin-perforable dissolving microneedle is a promising mediator for painlessly delivering active pharmaceutical compounds across the skin. All the microneedle manufacturing processes so far, however, are much sensitive to input variation and unfavorable for make-to-order approach. Here, a robust method for fabricating mass-customizable master molds is developed to prepare sharp-tipped biodegradable polymer microneedles. Our approach combines the predrying and chip casting (PCC) of an ultrathick photoresist layer with a substrateless, inclined, and rotational exposure (SIR exposure). The PCC achieves the uniform reduction of solvent across the photoresist thickness which is critically required for the formation of a sharp tip; the SIR exposure creates master molds whose geometry is easily customizable and virtually insensitive to a variation in ultraviolet (UV) exposure dose. A theoretical model for the spatiotemporal distribution of UV dose under SIR exposure is established to show the technological superiority of our method. Next, our method's applicability is proven by fabricating a set of poly(lactic-co-glycolic) acid (PLGA) microneedles and performing both porcine skin penetration test and their in vitro degradation test. Our approach is verified to be robust in manufacturing mass-customizable molds for skin-perforable dissolving microneedles and to have high compatibility with almost all existing biodegradable polymers. The findings of this study lead to both a significant growth of dissolving microneedle-mediated drug delivery and better understanding of drug release kinetics.

Variation of the Penetration Effort in an Artificial Tissue by Hypodermic Needles

Fear of injection-related pain is a drawback to injectable therapy. Hypodermic injections are a cause for great anxiety and reduced adherence to the subcutaneous application of insulin for glycemic control in diabetics or in the treatment of multiple sclerosis, increasing the risk of complications and mortality. Injured or sick people have to undergo several daily injections, forcing them to rotate the veins and regions used to recover from the trauma caused by the perforation of the skin, tissue, muscles, veins, and arteries. People who suffer from type 1 diabetes mellitus (DM1) need to have their glycemic control 3 to 5 times a day and to take insulin up to 3 times a day. In both cases, the patient needs to perforate the skin. To quantify the pain perceived by the patients depends on the evaluation of each patient and therefore is subjective. This study aims to understand the application and self-application of hypodermic injections and decrease pain during its application and the phobia of the patient, following the reasoning that the lower the effort to penetrate the needle, the less trauma in the tissue and therefore the pain provoked. For that, it was analyzed how some of the characteristics of the needle can influence the sensation of pain in the injection. The needle penetration effort was measured in an artificial tissue (substitute skin model) for different cannula diameters, roughness, depth of penetration, lubrication, and angles of the perforating tip bevel. This study aimed to find alternatives to facilitate the application and self-application of hypodermic injections, increase safety and comfort, and reduce the pain intensity perceived by the patient. To do this, the bevel of needles used repeatedly was analyzed in the profile projector and SEM to verify the loss of the profile or the formation of burrs that could hamper the penetration or traumatize the tissue during the reuse of needles. It has also been mechanically analyzed, which can be done to prevent that the needles used in the subcutaneous application do not inadvertently reach the muscle. The greater penetration effort observed in the needles with greater angle of the bevel is responsible for the patient's perception of pain.

Characterization of tissue properties in epidural needle insertion on human specimen and synthetic materials

The force experienced while inserting an 18-gauge Tuohy needle into the epidural space or dura is one of only two feedback components perceived by an anaesthesiologist to deduce the needle tip position in a patient's spine. To the best of the authors knowledge, no x-ray validated measurements of these forces are currently available to the public. A needle insertion force recording during an automated insertion of an 18-gauge Tuohy needle into human vertebral segments of four female donors was conducted. During the measurements, x-ray images were recorded simultaneously. The force peaks due to the penetration of the ligamentum supraspinale and ligamentum flavum were measured and compared to the measurements of an artificial patient phantom for a hybrid patient simulator. Based on these force peaks and the slope of the ligamentum interspinale, a mathematical model was developed. The model parameters were used to compare human specimens and artificial patient phantom haptics. The force peaks for the ligamenta supraspinale and flavum were 7.55 ± 3.63 N and 15.18 ± 5.71 N, respectively. No significant differences were found between the patient phantom and the human specimens for the force peaks and four of six physical model parameters. The patient phantom mimics the same resistive force against the insertion of an 18-gauge Tuohy needle. However, there was a highly significant (p < 0.001, eff_size = 0.949 and p < 0.001, eff_size = 0.896) statistical difference observed in the insertion depth where the force peaks of the ligamenta supraspinale and flavum were detected between the measurements on the human specimens and the patient phantom. Within this work, biomechanical evidence was identified for the needle insertion force into human specimens. The comparison of the measured values of the human vertebral segments and the artificial patient phantom showed promising results.

Guidelines for designing a realistic peripheral venous catheter insertion simulator: A literature review

A literature review was conducted to develop more realistic medical simulators that better prepare aspiring health professionals to perform a medical procedure in vivo. Thus, this review proposes an approach that might assist researchers design improved medical simulators, particularly new materials that would enhance the sensation of touch for skin substitutes. By targeting the current needs in the field of simulation learning, we concluded that peripheral venous catheter insertion simulators lack realistic haptic feedback. Enhanced peripheral venous catheter insertion simulators will accelerate the mastery of the medical procedure, thus decreasing the number of failures in patients and costs related to this procedure.

Optimized needle shape reconstruction using experimentally based strain sensors positioning

Needles are tools that are used daily during minimally invasive procedures. During the insertions, needles may be affected by deformations which may threaten the success of the procedure. To tackle this problem, needles with embedded strain sensors have been developed and associated with navigation systems. The localization of the needle in the tissues is then obtained in real time by reconstruction from the strain measurements, allowing the physician to optimize its gesture. As the number of strain sensors embedded is limited in number, their positions on the needle have a great impact on the accuracy of the shape reconstruction. The main contribution of this paper is a novel strain sensor positioning method to improve the reconstruction accuracy. A notable feature of our method is the use of experimental needle insertion data, which increases the relevancy of the resulting sensor optimal locations. To the best of the author's knowledge, no experimentally based needle sensor positioning method has been presented yet. Reconstruction validations from clinical data show that the localization accuracy of the needle tip is improved by almost 40% with optimal locations compared with equidistant locations when reconstructing with two sensor triplets or more. Graphical Abstract Improvement of the reconstruction accuracy of a deformed needle shape by using experimental data to position strain sensors.

Face and construct validity of TU-Delft epidural simulator and the value of real-time visualization

Background and objectives

Learning epidural anesthesia traditionally involves bedside teaching. Visualization aids or a simulator can help in acquiring motor skills, increasing patient safety and steepening the learning curve. We evaluated the face and construct validity of the TU-Delft Epidural Simulator and the effect of needle visualization.

Methods

Sixty-eight anesthesiologists, anesthesia residents, and final-year medical students tested the epidural simulator. Participants performed six epidural simulations with and six without needle visualization. We tested face validity on a Likert scale questionnaire. We collected data with the simulator software (spinal taps, dura contacts, bone contacts, attempts, and time) and tested for correlation with the performer’s experience (construct validity). A visualization aid was tested in a randomized crossover design.

Results

Face validity as rated by the participants was above average, with a mean of 3.7 (2.0–4.8) on a 5-point scale. Construct validity was indicated by significantly more spinal taps (0.4 [0–4) vs 0.07 [0–2], p=0.04) and more dura contacts (0.58 [0–6] vs 0.37 [0–3], p=0.002) by the inexperienced group compared with the expert group. The visualization aid improved performance by reducing the number of bone contacts and the number of attempts, and by decreasing the procedure time. Prior visualization training reduced the total procedure time from 279 s (69–574) to 180 s (53–605) (p=0.01) for the “blind” procedure.

Conclusions

The TU-Delft Epidural Simulator is a useful tool for teaching motor skills during epidural needle placement. Prior use of a visualization tool improves performance even without visual support during consequent simulations.

A hybrid, low-cost tissue-like epidural needle insertion simulator

Epidural and spinal anesthesia are mostly performed "blind" without any medical imaging. Currently, training of these procedures is performed on human specimens, virtual reality systems, manikins and mostly in clinical practice supervised by a professional. In this study a novel hybrid, low-cost patient simulator for the training of needle insertion into the epidural space was designed. The patient phantom provides a realistic force feedback comparable with biological tissue and enables sensing of the needle tip position during insertion. A display delivers the trainee a real-time feedback of the needle tip position.

Novel design of honeybee-inspired needles for percutaneous procedure

The focus of this paper is to present new designs of innovative bioinspired needles to be used during percutaneous procedures. Insect stingers have been known to easily penetrate soft tissues. Bioinspired needles mimicking the barbs in a honeybee stinger were developed for a smaller insertion force, which can provide a less invasive procedure. Decreasing the insertion force will decrease the tissue deformation, which is essential for more accurate targeting. In this study, some design parameters, in particular, barb shape and geometry (i.e. front angle, back angle, and height) were defined, and their effects on the insertion force were investigated. Three-dimensional printing technology was used to manufacture bioinspired needles. A specially-designed insertion test setup using tissue mimicking polyvinyl chloride (PVC) gels was developed to measure the insertion and extraction forces. The barb design parameters were then experimentally modified through detailed experimental procedures to further reduce the insertion force. Different scales of the barbed needles were designed and used to explore the size-scale effect on the insertion force. To further investigate the efficacy of the proposed needle design in real surgeries, preliminary ex vivo insertion tests into bovine liver tissue were performed. Our results show that the insertion force of the needles in different scales decreased by 21-35% in PVC gel insertion tests, and by 46% in bovine liver tissue insertion tests.

Haptic Feedback in Needle Insertion Modeling and Simulation

Needle insertion is the most basic skill in medical care, and training has to be imparted not only for physicians but also for nurses and paramedics. In most needle insertion procedures, haptic feedback from the needle is the main stimulus in which novices need training. For better patient safety, the classical methods of training the haptic skills have to be replaced with simulators based on new robotic and graphics technologies. This paper reviews the current advances in needle insertion modeling, classified into three sections: needle insertion models, tissue deformation models, and needle-tissue interaction models. Although understated in the literature, the classical and dynamic friction models, which are critical for needle insertion modeling, are also discussed. The experimental setup or the needle simulators that have been developed to validate the models are described. The need of psychophysics for needle simulators and psychophysical parameter analysis of human perception in needle insertion are discussed, which are completely ignored in the literature.

Development of artificial tissue-like structures for a hybrid epidural anesthesia simulator

Puncturing the epidural space and lumbar puncture are common procedures in anesthesia. They are carried out blind, where a needle is advanced from posterior between two adjacent vertebrae. Two different approaches are common practice for this technique, the midline and the paramedian one. The learning curve characteristics of both approaches significantly depends on the number of punctures carried out by a medical novice. For the training of these blind procedures a hybrid simulator requires artificial structures imitating the tissues which are penetrated by the needle. Within this work a patient phantom for spinal needle insertion procedures was developed and validated successfully against literature as well as by a study carried out with medical experts.

A combination of experimental and finite element analyses of needle-tissue interaction to compute the stresses and deformations during injection at different angles

One of the main clinical applications of the needles is its practical usage in the femoral vein catheterization. Annually more than two million peoples in the United States are exposed to femoral vein catheterization. How to use the input needles into the femoral vein has a key role in the sense of pain in post-injection and possible injuries, such as tissue damage and bleeding. It has been shown that there might be a correlation between the stresses and deformations due to femoral injection to the tissue and the sense of pain and, consequently, injuries caused by needles. In this study, the stresses and deformations induced by the needle to the femoral tissue were experimentally and numerically investigated in response to an input needle at four different angles, i.e., 30°, 45°, 60°, and 90°, via finite element method. In addition, a set of experimental injections at different angles were carried out to compare the numerical results with that of the experimental ones, namely pain score. The results revealed that by increasing the angle of injection up to 60°, the strain at the interaction site of the needle-tissue is increased accordingly while a significant falling is observed at the angle of 90°. In contrast, the stress due to injection was decreased at the region of needle-tissue interaction with showing the lowest one at the angle of 90°. Experimental results were also well confirmed the numerical observations since the lowest pain score was seen at the angle of 90°. The results suggest that the most effective angle of injection would be 90° due to a lower amount of stresses and deformations compared to the other angles of injection. These findings may have implications not only for understating the stresses and deformations induced during injection around the needle-tissue interaction, but also to give an outlook to the doctors to implement the most suitable angle of injection in order to reduce the pain as well as post injury of the patients.

Nonholonomic Modeling of Needle Steering

As a flexible needle with a bevel tip is pushed through soft tissue, the asymmetry of the tip causes the needle to bend. We propose that, by using nonholonomic kinematics, control, and path planning, an appropriately designed needle can be steered through tissue to reach a specified 3D target. Such steering capability could enhance targeting accuracy and may improve outcomes for percutaneous therapies, facilitate research on therapy effectiveness, and eventually enable new minimally invasive techniques. In this paper, we consider a first step toward active needle steering: design and experimental validation of a nonholonomic model for steering flexible needles with bevel tips. The model generalizes the standard three degree-of-freedom (DOF) nonholonomic unicycle and bicycle models to 6 DOF using Lie group theory. Model parameters are fit using experimental data, acquired via a robotic device designed for the specific purpose of inserting and steering a flexible needle. The experiments quantitatively validate the bevel-tip needle steering model, enabling future research in flexible needle path planning, control, and simulation.

Multicenter, prospective, crossover trial comparing the door-knocking method with the conventional method for EUS-FNA of solid pancreatic masses (with videos)

BACKGROUND AND AIMS

There are currently no prospective, controlled trials of needle puncture speed in EUS-guided FNA (EUS-FNA). In this study, we prospectively evaluated the accuracy of histological diagnosis and the tissue acquisition rate of EUS-FNA by using the door-knocking method (DKM) with a standard 22-gauge needle.

METHODS

From November 2013 to August 2014, 82 patients who had solid pancreatic masses underwent EUS-FNA in which the conventional method (CM) and DKM with 2 respective passes in turn were used. The primary outcomes of this study were the accuracy of histological diagnosis and the rates of tissue acquisition in 2 FNA procedures by using these 2 methods.

RESULTS

Although the successful tissue acquisition rate for histology was not significantly different with the DKM and CM (91.5% vs 89.0%, P = .37), the high cellularity tissue acquisition rate for histology with the DKM was significantly superior to that with the CM (54.9% vs 41.5%, P = .03). However, adequate quality rate and accuracy were not different in the DKM and CM (78.0% vs 80.5%, P = .42 and 76.8% vs 78.0%, P = .50, respectively). In the transgastric puncture group, although the adequate quality rate and accuracy were similar in the DKM and CM (84.1% vs 79.4%, P = .30 and 84.1% vs 76.2%, P = .11, respectively), the tissue acquisition rate tended to be higher with the DKM than the CM (93.7% vs 85.7%, P = .06). Moreover, the high cellularity tissue acquisition rate was significantly better with the DKM than the CM (63.5% vs 39.7%, P = .002). On the other hand, in the transduodenal puncture group, although the tissue acquisition rate was similar with the DKM and CM (84.2% vs 100%, P = .13), the adequate quality rate and accuracy were significantly lower with the DKM than with the CM (57.9% vs 84.2%, P = .03 and 52.6% vs 84.2%, P = .02, respectively).

CONCLUSION

EUS-FNA by using a 22-gauge needle with the DKM did not improve the accuracy of histological diagnosis, but enabled acquisition of a larger amount of tissue specimen by using transgastric puncture. (

TRIAL REGISTRATION

http://www.umin.ac.jp/english/: UMIN000012127.).

Modelling needle forces during insertion into soft tissue

Robot-assisted needle-based surgeries are sought to improve many operations, from brain surgery to spine and urological procedures. Force feedback from a needle can provide important guidance during needle insertion. This paper presents a new modelling method of needle force during insertion into soft tissue based on finite element simulation. This is achieved by analysing the results of a series of needle inserting experiments with different insertion velocities. The forces acting on the needle are then modelled based on the experimental results. A simulation is implemented to verify the designed model.

Structures, properties, and functions of the stings of honey bees and paper wasps: a comparative study

Through natural selection, many animal organs with similar functions have evolved different macroscopic morphologies and microscopic structures. Here, we comparatively investigate the structures, properties and functions of honey bee stings and paper wasp stings. Their elegant structures were systematically observed. To examine their behaviors of penetrating into different materials, we performed penetration-extraction tests and slow motion analyses of their insertion process. In comparison, the barbed stings of honey bees are relatively difficult to be withdrawn from fibrous tissues (e.g. skin), while the removal of paper wasp stings is easier due to their different structures and insertion skills. The similarities and differences of the two kinds of stings are summarized on the basis of the experiments and observations.

Fractional Skin Harvesting: Device Operational Principles and Deployment Evaluation

As an alternative method to conventional split-thickness skin grafts (STSGs), we recently proposed fractional skin grafting (FSG), which consists in harvesting hundreds of microscopic skin tissue columns (MSTCs) to place them directly into the skin wound (Tam et al., 2013, “Fractional Skin Harvesting: Autologous Skin Graft Without Donor Site Morbidity,” Plast. Reconstructive Surgery–Global Open, 1(6)). This paper (i) introduces the concept and operational principles of a simple but robust fractional skin harvesting (FSH) device and (ii) presents the quantitative evaluation of the deployment of the FSH device with respect to different harvesting-needle sizes. The device utilizes a hypodermic needle with a specific cutting-geometry to core skin tissue mechanically. The tissue core is removed from the donor site into a collecting basket by air and fluid flows. The air flow transports the tissue core, while the fluid flow serves the purpose of lubrication for tissue transport and wetting for tissue preservation. The design and functionality of the device were validated in an animal study conducted to establish preclinical feasibility, safety and efficacy of the proposed FSH device and FSG method. The FSH device, operating at 55.16 kPa (8 psi) gauge pressure and 208 ml/min saline flow rate, cored 800 μm diameter × 2.5 mm length skin columns using a 1.05/0.81 mm outer/inner diameter needle. The MSTC harvesting rate was established by the user at 1 column/sec. For this columns size, about 50 MSTCs are required to cover a 1.5 cm × 1.5 cm wound. In comparison to STSGs, the proposed FSG method results in superior healing outcomes on the donor and wound sites. Most important, the donor site heals without morbidity by remodeling tissue, as opposed to scarring. The FSH device has the capability of extracting full-thickness skin columns while preserving its viability and eliminating the donor site morbidity associated with skin grafting.

Needle-tissue interaction forces--a survey of experimental data

The development of needles, needle-insertion simulators, and needle-wielding robots for use in a clinical environment depends on a thorough understanding of the mechanics of needle-tissue interaction. It stands to reason that the forces arising from this interaction are influenced by numerous factors, such as needle type, insertion speed, and tissue characteristics. However, exactly how these factors influence the force is not clear. For this reason, the influence of various factors on needle insertion-force was investigated by searching literature for experimental data. This resulted in a comprehensive overview of experimental insertion-force data available in the literature, grouped by factor for quick reference. In total, 99 papers presenting such force data were found, with typical peak forces in the order of 1-10N. The data suggest, for example, that higher velocity tends to decrease puncture force and increase friction. Furthermore, increased needle diameter was found to increase peak forces, and conical needles were found to create higher peak forces than beveled needles. However, many questions remain open for investigation, especially those concerning the influence of tissue characteristics.

Prestress as an optimal biomechanical parameter for needle penetration

Drug delivery requires precise intradermal and subcutaneous injections of formulations to clinically relevant penetration depths. However, penetration depth is confounded by skin deflection, which occurs prior to and during penetration as the skin surface deforms axially with the needle, and which varies profoundly due to differing intrinsic mechanical (e.g. viscoelastic) tissue properties, disease state, aging, and ethnicity. Herein, an ex vivo model was utilized to study factors that affect skin deflection and the efficacy of injection, including prestress applied at the tissue surface, needle gauge, velocity, and actuation depth. The application of prestress minimized skin deflection during needle penetration and allowed for needle actuation to the targeted penetration depths with minimum variability. The force required to achieve target penetration depths was found to increase with prestress and decrease with needle gauge. Our findings emphasize the need for prestress applied to the skin surface to minimize variation in skin properties and administer formulations for intradermal and subcutaneous treatments with maximum precision.

LABORATORY STUDY ON NEEDLE–TISSUE INTERACTION: TOWARDS THE DEVELOPMENT OF AN INSTRUMENT FOR AUTOMATIC VENIPUNCTURE

Although venipuncture is one of the most common clinical procedures and is performed by trained medical staff, difficulties arise in 5% of insertion procedures. An instrument that guarantees the insertion of a needle into a vein in a single approach is expected to be beneficial to both medical staff and patients. The next step towards automatic venipuncture is to determine if insertion force feedback can be used, irrespective of insertion speed, insertion angle, or vein depth and diameter. Needle insertion experiments are performed on phantom and porcine tissues to study the interaction between the needle and tissue. A prototype instrument is developed to perform automatic venipuncture on the phantom. From the experiments, we conclude that an increased insertion speed of the needle leads to an increase in insertion force and tissue deformation. Furthermore, distinct force peaks are observed at the penetration of phantom skin and vein, thus enabling automatic detection of phantom vein puncture.

A virtual reality simulator for ultrasound-guided biopsy training

A VR-based training system for practicing biopsies simulates ultrasound imagery by stitching multiple ultrasound volumes on the basis of a 3D scale-invariant feature transform algorithm. In addition, a six-degree-of-freedom force model delivers a realistic haptic rendering of needle insertion.

A novel actuator for simulation of epidural anesthesia and other needle insertion procedures

INTRODUCTION

When navigating a needle from skin to epidural space, a skilled clinician maintains a mental model of the anatomy and uses the various forms of haptic and visual feedback to track the location of the needle tip. Simulating the procedure requires an actuator that can produce the feel of tissue layers even as the needle direction changes from the ideal path.

METHODS

A new actuator and algorithm architecture simulate forces associated with passing a needle through varying tissue layers. The actuator uses a set of cables to suspend a needle holder. The cables are wound onto spools controlled by brushless motors. An electromagnetic tracker is used to monitor the position of the needle tip.

RESULTS

Novice and expert clinicians simulated epidural insertion with the simulator. Preliminary depth-time curves show that the user responds to changes in tissue properties as the needle is advanced. Some discrepancy in clinician response indicates that the feel of the simulator is sensitive to technique, thus perfect tissue property simulation has not been achieved.

CONCLUSIONS

The new simulator is able to approximately reproduce properties of complex multilayer tissue structures, including fine-scale texture. Methods for improving fidelity of the simulation are identified.

The Role of Haptics in Medical Training Simulators: A Survey of the State of the Art

This review paper discusses the role of haptics within virtual medical training applications, particularly, where it can be used to aid a practitioner to learn and practice a task. The review summarizes aspects to be considered in the deployment of haptics technologies in medical training. First, both force/torque and tactile feedback hardware solutions that are currently produced commercially and in academia are reviewed, followed by the available haptics-related software and then an in-depth analysis of medical training simulations that include haptic feedback. The review is summarized with scrutiny of emerging technologies and discusses future directions in the field.

Experimental model for analyzing cutting resistance by various knives for cataract surgery

BACKGROUND

The trend in current cataract surgery towards clear corneal incision and sutureless procedures makes us realize the importance of wound construction. For optimal surgical outcomes, we need good surgical instruments. In this study, we employed a resistance recording system to analyze the characteristics of seven commercially available disposable cataract knives and to find clues for the future development of 'good' cataract knives.

METHODS

The cutting resistance was recorded during perpendicular penetrations of porcine scleral tissues by cataract knives. This data was processed and analysed mathematically with MATLAB software (The MathWorks, Inc, Natick, MA, USA) to see the resistance wave shapes and their derivatives to show the products' differing characteristics.

RESULTS

The wave shapes demonstrated product-dependent characteristics. The average maximum penetration resistance varied from 86.4 to 233 mN. The first order time derivatives also showed distinctive wave shapes.

CONCLUSION

We used an experimental model to analyze one aspect of a knife's character. This model can help give clues for future developments, although this is the initial step.

Mechanics of dynamic needle insertion into a biological material

During needle-based procedures, transitions between tissue layers often lead to rupture events that involve large forces and tissue deformations and produce uncontrollable crack extensions. In this paper, the mechanics of these rupture events is described, and the effect of insertion velocity on needle force, tissue deformation, and needle work is analyzed. Using the J integral method from fracture mechanics, rupture events are modeled as sudden crack extensions that occur when the release rate J of strain energy concentrated at the tip of the crack exceeds the fracture toughness of the material. It is shown that increasing the velocity of needle insertion will reduce the force of the rupture event when it increases the energy release rate. A nonlinear viscoelastic Kelvin model is then used to predict the relationship between the deformation of tissue and the rupture force at different velocities. The model predicts that rupture deformation and work asymptotically approach minimum values as needle velocity increases. Consequently, most of the benefit of using a higher needle velocity can be achieved using a finite velocity that is inversely proportional to the relaxation time of the tissue. Experiments confirm the analytical predictions with multilayered porcine cardiac tissue.

A blood sampling microsystem for pharmacokinetic applications: design, fabrication, and initial results

This paper describes a microsystem for automated blood sampling from laboratory mice used in pharmacokinetic studies. Intended to be mounted as a "backpack" on a mouse, it uses a microneedle, reservoir, and an actuator to instantaneously prick the animal for a time-point sample, eliminating the need for a tethered catheter with large dead volume. The blood is collected by capillary effect through a 31-33 gauge microneedle (250-210 microm OD) into a approximately 1 microL micromachined steel reservoir. The voice coil actuator provides a peak force of approximately 300 mN, which amply exceeds the measured piercing force of mouse skin (i.e., 60-85 mN for a 31-gauge needle with 12 degrees bevel). The sampling system was tested in vitro using a mock vessel with adjustable pressure; the reservoir was filled in <0.15 s by a combination of the capillary effect and blood pressure. The system may also be used to sample interstitial fluid, but the absence of blood pressure makes it necessary to enhance the capillary effect of the needle. This is accomplished by either electropolishing the inner surface to make it more hydrophilic or using a polymer wire insert to increase the surface area. The steel surface of the reservoir is also coated with silicon oxynitride by plasma-enhanced chemical vapor deposition to improve its hydrophilicity. Blood from fresh bovine tissue was collected into the reservoir to simulate interstitial fluid sampling. In vivo tests on live, anesthetized mice resulted in successful collection of blood into the reservoir. The possible integration of the device in microanalytical systems and the device scalability for multisampling are discussed.

A real-time prostate cancer detection technique using needle insertion force and patient-specific criteria during percutaneous intervention

In this article, the authors present a novel real-time cancer detection technique by using needle insertion forces in conjunction with patient-specific criteria during percutaneous interventions. Needle insertion experiments and pathological analysis were performed for developing a computer-aided detection (CAD) model. Backward stepwise regression method was performed to identify the statistically significant patient-specific factors. A baseline force model was then developed using these significant factors. The threshold force model that estimated the lower bound of the cancerous tissue forces was formulated by adding an adjustable classifier to the baseline force model. Tradeoff between sensitivity and specificity was obtained by varying the threshold value of the classifier, from which the receiver-operating characteristic (ROC) curve was generated. Sequential quadratic programming was used to optimize the CAD model by maximizing the area under the ROC curve (AUC) using a set of model-training patient data. When the CAD model was evaluated using an independent set of model-validation patient data, an AUC of 0.90 was achieved. The feasibility of cancer detection in real time during percutaneous interventions was established.

A real-time prostate cancer detection technique using needle insertion force and patient-specific criteria during percutaneous intervention

In this article, the authors present a novel real-time cancer detection technique by using needle insertion forces in conjunction with patient-specific criteria during percutaneous interventions. Needle insertion experiments and pathological analysis were performed for developing a computer-aided detection (CAD) model. Backward stepwise regression method was performed to identify the statistically significant patient-specific factors. A baseline force model was then developed using these significant factors. The threshold force model that estimated the lower bound of the cancerous tissue forces was formulated by adding an adjustable classifier to the baseline force model. Trade-off between sensitivity and specificity was obtained by varying the threshold value of the classifier, from which the receiver-operating characteristic (ROC) curve was generated. Sequential quadratic programming was used to optimize the CAD model by maximizing the area under the ROC curve (AUC) using a set of model-training patient data. When the CAD model was evaluated using an independent set of model-validation patient data, an AUC of 0.90 was achieved. The feasibility of cancer detection in real time during percutaneous interventions was established.

Design principles for the use of simulation as an aid in interventional cardiology training

Learning complex skills through simulation is a goal for training physicians in specialties such as interventional cardiology, where traditional training puts patients at risk. Intuitively, interactive simulation of anatomy, pathology and therapeutic actions should lead to shortening of the learning curve for novice or inexperienced physicians. An accurate recreation of the interactions among anatomy, pathology and therapeutic actions is a necessary, but not sufficient, condition for the development of a simulation-based training system. In addition to real-time graphic interactivity coupled with haptic response, a successful training tool will require features of a 'learning system' such as: an embedded curriculum, functionality that allows rehearsal and practice, hypertext links to educational information, personal archiving, and instructor review and testing capabilities. We describe how such a system might look for the field of interventional cardiology, and suggest that designing a simulation with both technical and pedagogical fidelity is essential in developing simulation-based training systems in any field of medicine.

Epidural insertion simulator of higher insertion resistance & drop rate after puncture

Accidents such as dural puncture remain one of the problems of epidural anesthesia, and unskilled doctors can repeat such accidents. The purpose of the current research was to provide a new simulator for epidural insertion training. No reference data regarding the resistance force used when inserting a needle into patients have been reported. A comparative study was conducted to aid in the development of a new simulator. Pork loin (n=5) were employed as a substitute for patients. Thickness was set at 2 cm so as to improve the reproducibility. The authors took the conventional simulator apart, and picked a block as an analogue of muscle and ligamentum flavum. A new simulator was made of a melamine foam resin block and a latex rubber sheet. An epidural needle fixed on a motorized stage was inserted at the speed of 2 mm per second. The reaction force was measured while the needle was inserted into each specimen. Waveform of the pork loin exhibited two slopes of different inclines up to peaks and then falls after puncture. The conventional simulator showed a simple increase up to peak and a slow fall after puncture. In contrast, the new simulator showed two slopes up to peak and then a sudden fall after puncture. The insertion resistances were 2.5 N/s for the porcine, 0.8 N/s for the conventional and 2.1 N/s for the new simulator. The drop rates were 5 N/s for the porcine, 0.6 N/s for the conventional and 24 N/s for the new simulator. The higher insertion resistance and drop rate for the new simulator than the conventional simulator will be suitable for epidural insertion training.

Modeling of Tool-Tissue Interactions for Computer-Based Surgical Simulation: A Literature Review

Surgical simulators present a safe and potentially effective method for surgical training, and can also be used in robot-assisted surgery for pre- and intra-operative planning. Accurate modeling of the interaction between surgical instruments and organs has been recognized as a key requirement in the development of high-fidelity surgical simulators. Researchers have attempted to model tool-tissue interactions in a wide variety of ways, which can be broadly classified as (1) linear elasticity-based, (2) nonlinear (hyperelastic) elasticity-based finite element (FE) methods, and (3) other techniques that not based on FE methods or continuum mechanics. Realistic modeling of organ deformation requires populating the model with real tissue data (which are difficult to acquire in vivo) and simulating organ response in real time (which is computationally expensive). Further, it is challenging to account for connective tissue supporting the organ, friction, and topological changes resulting from tool-tissue interactions during invasive surgical procedures. Overcoming such obstacles will not only help us to model tool-tissue interactions in real time, but also enable realistic force feedback to the user during surgical simulation. This review paper classifies the existing research on tool-tissue interactions for surgical simulators specifically based on the modeling techniques employed and the kind of surgical operation being simulated, in order to inform and motivate future research on improved tool-tissue interaction models.

An ultrasound-guided organ biopsy simulation with 6DOF haptic feedback

Ultrasound-guided biopsy is one of the most fundamental, but difficult, skills to acquire in interventional radiology. Intensive training, especially in the needle insertion, is required for trainee radiologists to perform safe procedures. In this paper, we propose a virtual reality simulation system to facilitate the training of radiologists and physicians in this procedures. Key issues addressed include a 3D anatomical model reconstruction, data fusion of multiple ultrasound volumes and computed tomography (CT), realistic rendering, interactive navigation, and haptic feedbacks in six degrees of freedom (DOF). Simulated ultrasound imagery based on real ultrasound data is presented to users, in real-time, while performing an examination on the needle placement into a virtual anatomical model. Our system delivers a realistic haptic feeling for trainees throughout the simulated needle insertion procedure, permitting repeated practices with no danger to patients.

'Smart' needle for percutaneous surgery: influential factor investigation

Precise needle insertion is important for a number of percutaneous interventions. Yet it is difficult to achieve in practice due to target movement and needle deflection. Preliminary design and simulation of 'Smart Needle' are presented in this paper for active needle steering. This smart needle is designed to use piezoelectric actuators to adjust the needle tip position. Some simulations have been carried out to investigate the influences of the factors, such as input voltage, the length and thickness of the piezoelectric actuators etc. on the produced needle tip deflection. This information is useful in designing an effective smart needle that will need less electrical input in order to achieve certain needle displacement.

Subject-specific biomechanical simulation of brain indentation using a meshless method

We develop a meshless method for simulating soft organ deformation. The method is motivated by simple, automatic model creation for real-time simulation. Our method is meshless in the sense that deformation is calculated at nodes that are not part of an element mesh. Node placement is almost arbitrary. Fully geometrically nonlinear total Lagrangian formulation is used. Geometric integration is performed over a regular background grid that does not conform to the simulation geometry. Explicit time integration is used via the central difference method. To validate the method we simulate indentation of a swine brain and compare the results to experimental data.