Suvranu De

Haptics in minimally invasive surgical simulation and training

Haptics is a valuable tool in minimally invasive surgical simulation and training. We discuss important aspects of haptics in MISST, such as haptic rendering and haptic recording and playback. Minimally invasive surgery has revolutionized many surgical procedures over the last few decades. MIS is performed using a small video camera, a video display, and a few customized surgical tools. In procedures such as gall bladder removal (laparoscopic cholesystectomy), surgeons insert a camera and long slender tools into the abdomen through small skin incisions to explore the internal cavity and manipulate organs from outside the body as they view their actions on a video display. Because the development of minimally invasive techniques has reduced the sense of touch compared to open surgery, surgeons must rely more on the feeling of net forces resulting from tool-tissue interactions and need more training to successfully operate on patients.

Effects of insertion conditions on tissue strain and vascular damage during neuroprosthetic device insertion

Long-term integration of neuroprosthetic devices is challenged by reactive responses that compromise the brain-device interface. The contribution of physical insertion parameters to immediate damage is not well described. We have developed an ex vivo preparation to capture real-time images of tissue deformation during device insertion using thick tissue slices from rat brains prepared with fluorescently labeled vasculature. Qualitative and quantitative assessments of damage were made for insertions using devices with different tip shapes inserted at different speeds. Direct damage to the vasculature included severing, rupturing and dragging, and was often observed several hundred micrometers from the insertion site. Slower insertions generally resulted in more vascular damage. Cortical surface features greatly affected insertion success; insertions attempted through pial blood vessels resulted in severe tissue compression. Automated image analysis techniques were developed to quantify tissue deformation and calculate mean effective strain. Quantitative measures demonstrated that, within the range of experimental conditions studied, faster insertion of sharp devices resulted in lower mean effective strain. Variability within each insertion condition indicates that multiple biological factors may influence insertion success. Multiple biological factors may contribute to tissue distortion, thus a wide variability was observed among insertions made under the same conditions.

Mechanical properties of the hexagonal boron nitride monolayer: Ab initio study

Abstract Using density functional theory (DFT) calculations we found that hexagonal boron nitride monolayer (h-BN) shows a non-linear elastic deformation up to an ultimate strength followed by a strain softening to the failure. To develop a continuum based model for such non-linear behavior, we proposed a method to study high order elastic constants of the 2D hexagonal structures. The continuum description of the elastic properties of monolayer h-BN is obtained using this method through ab initio density functional theory. This rigorous continuum description of the elastic response is formulated by expanding the elastic strain energy density in a Taylor series in strain truncated after the fifth-order term. we obtained a total of fourteen non-zero independent elastic constants for up to tenth-order tensor.

The method of finite spheres with improved numerical integration

Abstract The method of finite spheres was introduced as a truly meshless technique with the goal of achieving computational efficiency in a mesh-free procedure. In this paper we report several new numerical integration rules that result in a significant reduction in computational cost.

New materials graphyne, graphdiyne, graphone, and graphane: review of properties, synthesis, and application in nanotechnology

Plenty of new two-dimensional materials including graphyne, graphdiyne, graphone, and graphane have been proposed and unveiled after the discovery of the “wonder material” graphene. Graphyne and graphdiyne are two-dimensional carbon allotropes of graphene with honeycomb structures. Graphone and graphane are hydrogenated derivatives of graphene. The advanced and unique properties of these new materials make them highly promising for applications in next generation nanoelectronics. Here, we briefly review their properties, including structural, mechanical, physical, and chemical properties, as well as their synthesis and applications in nanotechnology. Graphyne is better than graphene in directional electronic properties and charge carriers. With a band gap and magnetism, graphone and graphane show important applications in nanoelectronics and spintronics. Because these materials are close to graphene and will play important roles in carbon-based electronic devices, they deserve further, careful, and thorough studies for nanotechnology applications.

Mechanical stabilities of silicene

The mechanical stabilities of planar (g) and low-buckled (b) honeycomb monolayer structures of silicon under various large strains are investigated using density functional theory (DFT). The mechanical properties, including the ultimate stresses, ultimate strains, and high order elastic constants of silicene are predicted, as well as the structure evolutions. Both g-Si and b-Si can sustain large strains (η ≥ 0.15) for armchair, zigzag, and biaxial deformation. The third, fourth, and fifth order elastic constants are indispensable for accurate modeling of the mechanical properties under strains larger than 0.03, 0.06, and 0.08 respectively. The second order elastic constants, including in-plane stiffness, are predicted to monotonically increase with pressure while the Poisson ratio monotonically decreases with increasing pressure. Our results on the positive ultimate strengths and strains, second order elastic constants, and the in-plane Youngs modulus indicate that both g-Si and b-Si are mechanically stable.

Towards an efficient meshless computational technique: the method of finite spheres

Computational efficiency and reliability are clearly the most important requirements for the success of a meshless numerical technique. While the basic ideas of meshless techniques are simple and well understood, an effective meshless method is very difficult to develop. The efficiency depends on the proper choice of the interpolation scheme, numerical integration procedures and techniques of imposing the boundary conditions. These issues in the context of the method of finite spheres are discussed.

Using the PhysX engine for Physics-based Virtual Surgery with Force Feedback

The development of modern surgical simulators is highly challenging, as they must support complex simulation environments. The demand for higher realism in such simulators has driven researchers to adopt physics‐based models, which are computationally very demanding. This poses a major problem, since real‐time interactions must permit graphical updates of 30 Hz and a much higher rate of 1 kHz for force feedback (haptics). Recently several physics engines have been developed which offer multi‐physics simulation capabilities, including rigid and deformable bodies, cloth and fluids. While such physics engines provide unique opportunities for the development of surgical simulators, their higher latencies, compared to what is necessary for real‐time graphics and haptics, offer significant barriers to their use in interactive simulation environments.

Common uses and cited complications of energy in surgery

BackgroundInstruments that apply energy to cut, coagulate, and dissect tissue with minimal bleeding facilitate surgery. The improper use of energy devices may increase patient morbidity and mortality. The current article reviews various energy sources in terms of their common uses and safe practices.MethodsFor the purpose of this review, a general search was conducted through NCBI, SpringerLink, and Google. Articles describing laparoscopic or minimally invasive surgeries using single or multiple energy sources are considered, as are articles comparing various commercial energy devices in laboratory settings. Keywords, such as laparoscopy, energy, laser, electrosurgery, monopolar, bipolar, harmonic, ultrasonic, cryosurgery, argon beam, laser, complications, and death were used in the search.ResultsA review of the literature shows that the performance of the energy devices depends upon the type of procedure. There is no consensus as to which device is optimal for a given procedure. The technical skill level of the surgeon and the knowledge about the devices are both important factors in deciding safe outcomes.ConclusionsAs new energy devices enter the market increases, surgeons should be aware of their indicated use in laparoscopic, endoscopic, and open surgery.

Predictive modeling of lung motion over the entire respiratory cycle using measured pressure-volume data, 4DCT images, and finite-element analysis.

PURPOSE Predicting complex patterns of respiration can benefit the management of the respiratory motion for radiation therapy of lung cancer. The purpose of the present work was to develop a patient-specific, physiologically relevant respiratory motion model which is capable of predicting lung tumor motion over a complete normal breathing cycle. METHODS Currently employed techniques for generating the lung geometry from four-dimensional computed tomography data tend to lose details of mesh topology due to excessive surface smoothening. Some of the existing models apply displacement boundary conditions instead of the intrapleural pressure as the actual motive force for respiration, while others ignore the nonlinearity of lung tissues or the mechanics of pleural sliding. An intermediate nonuniform rational basis spline surface representation is used to avoid multiple geometric smoothing procedures used in the computational mesh preparation. Measured chest pressure-volume relationships are used to simulate pressure loading on the surface of the model for a given lung volume, as in actual breathing. A hyperelastic model, developed from experimental observations, has been used to model the lung tissue material. Pleural sliding on the inside of the ribcage has also been considered. RESULTS The finite-element model has been validated using landmarks from four patient CT data sets over 34 breathing phases. The average differences of end-inspiration in position between the landmarks and those predicted by the model are observed to be 0.450 +/- 0.330 cm for Patient P1, 0.387 +/- 0.169 cm for Patient P2, 0.319 +/- 0.186 cm for Patient P3, and 0.204 +/- 0.102 cm for Patient P4 in the magnitude of error vector, respectively. The average errors of prediction at landmarks over multiple breathing phases in superior-inferior direction are less than 3 mm. CONCLUSIONS The prediction capability of pressure-volume curve driven nonlinear finite-element model is consistent over the entire breathing cycle. The biomechanical parameters in the model are physiologically measurable, so that the results can be extended to other patients and additional neighboring organs affected by respiratory motion.