# Review of Advanced Medical Telerobots
## 2 Medical Telerobotic Topologies
### Single-Leader Single-Follower Topology (SL/SF)
#### 2.1.1 Sensory Augmentation through SL/SF Telerobotic Surgery
Regarding haptics-based augmentation it can be mentioned that despite two decades of research and existing evidence of a significant benefit of haptic feedback in surgical operations [122, 100, 123], the commercialized surgical robotics systems are not equipped with haptic feedback [35, 36, 55, 101, 109, 122, 124]. The reason for this absence is explained later in this section. However, before investigating the corresponding reasons, the importance of haptic feedback in surgery should be discussed, as given in the following. In the literature, it has been shown that haptic sensation provides critical information during manual surgery regarding (a) the mechanical characteristics of tissue (such as texture, stiffness, size, and location of tumors) [125], (b) the amount of force which may cause damage on the tissue [122, 126, 127], and (c) quality of tool manipulation to avoid issues such as suture breakage and needle slippage [40, 99]. It is also known that haptic information is very critical for reducing surgical errors [35, 36], and tissue damage [122, 126, 127], besides operating times [1]. The mentioned knowledge has been achieved by systematic studies conducted in many cases on manual surgeries due to the conventional concerns related to degraded haptic sensation in manual MIS caused by the following factors:  
* friction inside the cable-driven tools [128, 129, 130, 131, 132, 133, 134], also between the tool and the tro-car [125, 135],
* the disturbing forces at the trocar and abdominal wall, the disturbing forces on the tool by nearby organs [136],
* the small point of contact between the tool and tissue causing low signal to noise ratio, and the long mechanical distance between the point of contact with tissue and the hand of the surgeons [36, 136, 137]. Despite the benefits of minimally invasive surgeries, such as reduced blood loss [30], reduced damage to the tissues [31], reduced risk of infection [32], reduced recovery time [33], and cosmetic benefits [34], the limited sensory awareness (caused by factors mentioned in the above) has been a conventional bottleneck for manual MIS [35, 36]. The mentioned challenge has called for extensive and specialized sensorimotor training for manual MIS surgeons and has raised excessive concerns about the ability of surgeons to perceive the status of the surgical site even for experienced surgeons [1, 20, 40, 41]. Thus, in many complex surgical cases, MIS is known to be excessively challenging for surgeons to conduct, putting a significant amount of mental and physical burden on them [37, 38, 39]. The situation is more challenging for microsurgeries, as the amount of force is much lower than the ability of human perception, which has made those surgeries visually heavy and cognitively complex [66, 138, 139, 140, 141, 142, 143, 144]. However, the above-mentioned restrictions on haptic sensation can be addressed using robotic surgical systems. In theory, small arrays of tactile sensors can be mounted on surgical tools which can detect the interactional forces during the surgery [7, 122, 125, 136, 145, 146]. The measured force signals can then be filtered, processed, amplified, and sent to the force control loop of the actuated leader robot, which can then replicate the resulting force for the surgeon, increasing the haptic awareness during surgeries [101, 102, 147]. It should also be noted that the measured force can also be visualized and sonified for the surgeon indirectly increasing the haptic awareness in the absence of direct feedback. This technique is known in the literature as a sensory substitution [40, 99, 100, 145, 146] and is usually suggested as a replacement for direct force feedback when the stability of closed-loop force feedback cannot be guaranteed. Besides, to address the issue of the small amplitude of force during micro-robotic surgery, such as retinal surgery, ultra-small, and accurate force sensors have been suggested in the literature which can measure micro- to milli-Newton forces, and be magnified for the surgeons for better awareness [66; 138; 139].