1
INTRODUCTION
In this chapter it will rst introduced the work's case of study, then it will discuss the founding principles on which it is based.
1.1 Minimally Invasive Surgery
Minimally Invasive Surgery (MIS) has been introduced in 1987 with the rst laparoscopic cholecystectomy. Since then, the list of procedures performed laparo-scopically has grown together with improvements in technology and the technical skill of surgeons [Lanfranco et al., 2004]. A minimally invasive procedure is less invasive than open surgery used for the same purpose. It involves the use of la-paroscopic devices and remote-control manipulation of instruments with indirect observation of the surgical eld through an endoscope or large scale display panel, and is carried out through the skin (Figure 1.1). The main challenges of this pro-cedure are due to the fact that all surgical instruments enter the patient's body through one or more cannulae or trocars. These are small, straw-like tubes that form entry ports into the abdomen through the skin. These ports are impor-tant because the abdomen must be lled with carbon dioxide to create room to move around and visualize the operative area. The ports create four fundamental challenges for the surgeon:
1. limited range of motion and access; 2. limited visualization;
3. eye-hand separation; 4. limited tactile feedback.
Figure 1.1: Schematics of laparoscopic appendectomy.
Evolution of technology has enabled to reduce these disadvantages, allowing a better vision and dexterity of the instruments, even if the procedure requires a high level of training for surgeons. The main advantages of this modern technique (reduction of trauma, reduction of the risk of infection and a faster recovery) are all for the bene t of the patient. For the surgeon, however, the method is less favorable. Due to the loss of good visual and proprioceptive perception of the operation zone, the operation becomes more di cult and time-consuming. A straightforward solution for these problems can be found in the eld of robotics since robot-assisted surgery can overcome most of the obstacles of laparoscopic surgery. They increase dexterity, restore proper hand-eye coordination and er-gonomic position, and improve visualization. In addition, these systems make procedures that were technically di cult or unfeasible previously, now possible. Instruments with increased degrees of freedom greatly enhance the surgeon's abil-ity to manipulate instruments and thus the tissues. These systems are designed in such a way that the surgeons' tremor can be compensated on the end-eector motion through appropriate hardware and software lters and strategies. In ad-dition, these systems can scale movements so that large movements of the control grips on the surgeon side can be transformed into micromotions inside the patient. These robotic systems eliminate the fulcrum eect, making instrument manipula-tion more intuitive. With the surgeon's sitting at a remote, ergonomically designed
workstation, current systems also eliminate the need to twist and turn in awkward positions to move the instruments and visualize the monitor [Vitiello et al., 2013]. A paradigmatic example is the Eye Robot, a cooperatively-controlled microsurgery robot for retinal microsurgery. The surgeon and the robot share control of a tool attached to the robot through a force sensor. The robot controller senses forces exerted by the operator on the tool and uses this information in various control modes to provide smooth, tremor-free, precise positional control and force scaling [Uneri et al., 2010]. In the past few years, novel surgical techniques have been progressing from research to clinical practice with the aim of further reducing invasiveness and access trauma. One of these is Single-Port Laparoscopy.
1.1.1 Single-Port Laparoscopy
Single-Port Laparoscopy (SPL) rather than using multiple ports positioned strategically around the surgical site, is based on the use of a single port placed through the navel. The primary advantage to this approach is that it leaves no cosmetic scar. However, SPL has more limitations than the laparoscopic approach, because it does not allow triangulation from two dierent points, thus severely lim-iting the dexterity of the surgeon, although several ad hoc instruments have been developed and are already on the market. SPL includes any minimally invasive procedure:
• performed through a single entry port (Figure 1.2);
• applicable to multiple locations (abdomen, pelvis, thorax); • utilizing laparoscopic, endoscopic or robotic instrumentation.
The major bene ts in SPL are the same cited for MIS plus a better cosmetics, be-cause the only scar occur at the navel. However, it shows remarkable drawbacks. In fact, surgical instruments are inserted parallel through the single hole, thus hindering instrument triangulation, needed for proper tissue manipulation, and reducing the dexterity of the operator. In addition, clashing of the instruments often occurs inside and outside the abdomen. Furthermore, retraction of the or-gans is hampered, and this is another issue that led to research and development of novel devices and retraction techniques. Much work has been done to develop multi-degree of freedom forceps. However they are still inadequate to grasp, ma-nipulate or push aside internal organs. Moreover, the risk of complication due to traumatization of soft tissue while trying to securely grip to them is still an
unresolved issue in MIS. Strong but gentle grip to soft, wet and delicate tissues is an imperative need during MIS and still an unresolved challenge.
Figure 1.2: A port for SPL on the market: SILS Port.
1.1.2 State of art
Current Tools
A complete surgery is accompanied with the use of various tools. Scissors, grippers, clamps, knifes etc. The MIS operation begins with inserting the tools from a trocar which has a typical range diameter of 5 − 15 mm. Usually a camera together with a cutting tool and a gripper is inserted. An important fact is the use of appropriate gripper for dexterous manipulation of the surgery. The maximum goal value for the force at the tip of the gripper is considered to be 4 N which is enough large for most of the micro surgeries such as cardiovascular stents, tissues etc. while the diameter of the gripper is restricted to 3 mm [Adldoost et al., 2012]. Traditional tools present:
• sharp edges;
• no compliant properties.
A large technical dierence between the handling of tissue by minimally invasive or by open surgery is the introduction of the force on the tissue. In the case of a colon resection done by conventional open surgery, the surgeon uses his ngers to displace the bowels, where the force is exerted on the backside of the bowel. The endoscopic gripper will pull the bowel at the front side, where the force is introduced on a much smaller area of the tissue and thus the stresses are much
higher [Lazeroms et al., 1996]. The small incision through which the instruments must be inserted is the main problem occurring during the design of the gripper. For the new design of a gripper to be used in laparoscopy, a better resemblance to the nger of a surgeon is pursued. The basic idea is to make a gripper which bends around the tissue (bowel).
Safe interaction with tissues
The main di culty of applying robots to minimally invasive surgery is the han-dling of soft tissues. Manipulation of large abdominal organs, e.g., spleen, kidney, and liver, is a di cult task using conventional laparoscopic instruments. Usually, surgeons have to use fan retractors to push aside and hold the organ or to grasp its ligaments. These methods, however, are often inadequate to provide an ac-ceptable and stable manipulation capability with a su ciently large maneuvering space. This troublesome limitation has persuaded some surgeons to use a so called "Hand Assisted Laparoscopic Surgery" approach in some laparoscopic operations, e.g., splenectomy and nephrectomy, in which a 7−8 cm incision is made on the wall of abdominal cavity to pass the surgeon's hand and manipulate the large organs. Obviously, this approach causes a considerable trauma on the patient's body and is not compatible with the minimally invasive nature of the laparoscopic surgery [Mirbagheri and Farahmand, 2010]. Although much work has been done to develop multi-degree of freedom forceps, they are still inadequate to grasp, manipulate or push aside internal organs. Force feedback or touch sensation is limited in the currently available MIS tools, creating the potential for excessive force application during surgery and unintended tissue injury. Among other things, although it is known that the amount of stress to cause damage is dierent between the tissues [De et al., 2007], the same tools are used for all the procedures .The risk of compli-cation due to traumatization of soft tissues while trying to securely grasp to them is still an unresolved issue using conventional instruments, often characterized by sharp edges and no compliant properties. Current research is focused on improve-ment of traditional tools, adding compliant constructive strategies [Bhargav et al., 2012] or implementing force-feedback controlled forceps, to limit the force exerted, preventing damages on the tissues[Puangmali et al., 2008]. Alternatively, a smart-designed instrument made up of intrinsically compliant materials would avoid the use of complex force-feedback control. Developing exible instruments for medi-cal applications is thus a miniaturization challenge. Most of the existing valuable examples of "Continuum Robots" which usually have a large number of redun-dant Degrees of Freedom (DOFs), typically exible and deformable, are still not
directly applied to the medical eld and only a few number of pioneering works for soft instruments applied in surgery can be found in literature. In [Jiang et al., 2012] an octopus-inspired manipulation device of 10 mm diameter that can al-ter its body stiness from being exible to rigid via granular jamming, that can exhibit can exhibit 0.20 N of force in soft state and 0.42 N in rigid state, while in [Cianchetti et al., 2013] a modular manipulator for minimal access surgery is obtained from combination of exible uidic actuators enabling omnidirectional bending and elongation capability and the granular jamming phenomenon to im-plement a selective stiness changing. In [Webster et al., 2006] a continuously exible snake-like robots, called active cannulas, is presented, that consist of sev-eral telescoping pre-curved superelastic tubes, exible and shapable to navigate through bends traversing the natural oriï¬ces, lumens, and other anatomical spaces of the human body. Their compliance makes active cannulas safer than existing MIS tools. Indeed, if inadvertent tissue contact along the shaft occurs, the device will bend rather than damage the tissue. Until now no one has ventured into the design of a totally soft gripping tool for surgery.
1.2 Soft Robotics
1.2.1 A Bio-inspired starting point
Since ancient times, man has always tried to study and emulate the perfect complexity of Nature systems, continuous source of inspiration for all elds of hu-man creation. The process of biomimicry carries innovation inspired by Nature. It looks at Nature as a model, measure and mentor. For instance, it studies Nature's models and then imitates or takes inspiration from these designs and processes to solve human problems (Figure 1.3). In a society accustomed to dominate or 'im-proving' Nature, on 'what we can extract from the natural world' or 'how we can better exploit it', this respectful imitation is based instead on 'what we can learn from it'. [Benyus, 2009]. Animals represent the main source of inspiration. They have a wide variety of continuous structures: arms, tails, tentacles, and various other appendages are used improving balance/stability, exploration/sensing and obstacle removal/grasping tasks. Octopus arms, which are formidable weapons as well as eective manipulators, appear to be similarly directed in the direction of objects of interest rather than having their shapes closely controlled. Elephants also simplify control of their trunks by moving them within a plane oriented to-wards objects they desire to grasp. Brittle stars manipulate objects in a similar manner as octopuses, but unlike them they do not have strong suction cups on
Figure 1.3: Some examples of biomimicry.
their arms. Each arm is like a snake's tail and can be used to wrap around objects. They can slither or crawl depending on the terrain. Their arms are quite dexterous and can be used to grab food and move it to the star's central mouth. Observing these biological examples motivate a new look at soft continuum robots [Cowan and Walker, 2008].
Figure 1.4: Octopus, elephant and brittle star.
There are many examples in Nature of mobile structures made from soft materi-als. The fundamental understanding of the morphology and functionality of soft structures in Nature increases insight and can lead to new design concepts in soft robotics. The natural world demonstrates the potential capabilities of soft robots. Although robotic systems are usually made of rigid materials such as steel and aluminum, biological systems are rarely composed only of rigid mechanical compo-nents, but they generally make use of soft, elastic, and exible materials in order
to survive in complex unstructured environments [Iida and Laschi, 2011]. Ani-mals exploit soft structures to move eectively in complex natural environments. Studying how animals exploit soft materials to move in complex, unpredictable environments can provide invaluable insights for emerging robotic applications in medicine, search and rescue, disaster response, and human assistance. These ca-pabilities have inspired robotic engineers to incorporate soft technologies into their designs. The goal is to endow robots with new, bio-inspired capabilities that permit adaptive exible interactions with unpredictable environments [Kim et al., 2013]. Biological inspiration does not imply that we attempt to copy nature. Rather, the goal is to understand the principles underlying the behavior of animals and humans and transfer them to the development of robots [Pfeifer et al., 2012]. In conclusion, our duty towards nature is to protect it and safeguard each creature, to transmit this immense living cultural heritage to future generations, who will in their turn observe, be fascinated and draw inspiration.
1.2.2 Embodied Intelligence
The growing need for soft robots in service tasks, in unstructured environments, in contact with humans, is leading to release the basic assumption of rigid parts in currently robotics. Robots are made up of materials that are literally thousands of times more rigid than the soft tissue in our body and this is ne for what robots are designed and used for today, but the rigidity of materials and machines used in current robotics de nitely limit their compatibility with humans [Hicks, 2012]. There has been an increasing interest in the use of soft and deformable structures in the robotic systems. Soft and deformable structures are crucial in the systems that deal with uncertain and dynamic task-environments, e.g. grasping and ma-nipulation of unknown objects, locomotion in rough terrains, and physical contacts with living cells and human bodies. Soft robotics aims to equip robots for the un-predictable needs of such situations by endowing them with capabilities that are based not in control systems but in the material properties and morphology of their bodies. It focuses on these mechanical qualities and on the integration of materials, structures, and software. In the same way that animal movements are based on the tight integration of neural and mechanical controls, soft robotics aims to achieve better and simpler mechanisms by exploiting the 'mechanical intelligence' of soft materials. A key point for soft continuum structures is adaptability: compliance to environmental constraints via an enhanced con guration- or shape-space. The role of soft body parts appears clear in natural organisms, to increase adaptability and robustness. Moreover, unlike industrial robots that are programmed to
exe-cute limited number of tasks, bio-inspired robots are expected to display a wide range of behaviors in unpredictable environments, as well as to interact safely and smoothly with human co-workers.
1.2.3 Soft Robotics and MIS
The application of soft robotics in the surgery eld is a challenge, especially for precision grasping, because of its intrinsically uncertainty in positioning due to the absence of rigid links. This study proposes to explain how this issue can be exploited as a point of strength. The idea at the base of this proposal is to study the feasibility to grasp soft tissues by using a soft instrument based on the 'embodied intelligence' concept. The advantages are all related to the intrinsically compliant property of the elastomeric material chosen to fabricate this kind of tool, which would allow safely getting closer to soft tissues inside the unstructured workspace of abdominal cavity, without the risk of damaging blood vessels or delicate organs during the manipulating procedures. This rede nes the concept itself of open-loop control which can be based on the material property as a 'sensing element' of environmental stimuli. It lays the groundwork for the realization of a powerful instrument equipped with a kind of low-level intelligence su cient to ensure a safe but stable approach, without the need of a real force-feedback. The intertwined concepts of biomimicry, soft robotics and embodied intelligence have driven the designed of a bioinspired highly-compliant, under-actuated and scalable manipulator.
