Journal of Mechanical Science and Technology 27 (3) (2013) 805~811 www.springerlink.com/content/1738-494x
DOI 10.1007/s12206-013-0129-4
Mechanism design and dynamic analysis of a multi-functional endoscopic clipping device† Jong-Jin Bae, Seung-Han Yang and Namcheol Kang* School of Mechanical Engineering, Kyungpook National University, 1370, Sankyuk-dong, Buk-gu, Daegu, 702-701, Korea (Manuscript Received May 10, 2012; Revised August 23, 2012; Accepted October 24, 2012) ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Abstract Minimal invasive surgery using endoscopic clipping devices is widely used in the treatment of hemorrhages and perforations in the gastro-intestinal tract. Although endoscopic clipping devices have been used for over 30 years and have undergone continuous development, there is still a need to improve their functions. In response to this, new mechanisms for multi-functional endoscopic clipping devices have been developed in this study. Dynamic simulation is performed to analyze the mechanical behavior of the developed clipping device. Optimization of the clip spring location to maximize clipping forces is also achieved by finite element analysis. Keywords: Mechanism design; Endoscopic clipping device; Dynamic simulation; Optimization ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1. Introduction Minimal invasive surgery (MIS) is a surgical procedure, in which a minimal incision is made on the body for the insertion of cameras and various tools [1, 2]. MIS incisions are smaller than those of traditional open surgery, are less painful, and require only a short hospital stay. Such advantages have led to the wide use of MIS. Natural orifice transluminal endoscopic surgery (NOTES), one field of MIS, is also actively applied nowadays. NOTES is a surgical operation, in which an endoscope is inserted inside the human body through natural openings (i.e., oral or anal) [3]. NOTES is used for stopping spontaneous hemorrhages in the gastro-intestinal tract, which are caused by such conditions as gastroesophageal reflux disease and gastric ulcers. Furthermore, NOTES is used for removing gallstone via gastrointestinal endoscopy. Perforation refers to the condition, in which a hole forms within the gastro-intestinal tract as a result of foreign substances, drug overuse, or chronic ulcers [4]. Such cases are considered serious emergency conditions and require rapid treatment as they may lead to death if left untreated. Perforation and hemorrhage treatment methods include thermal methods [5, 6], injections [7, 8], and methods using an endoscopic clipping device. Thermal methods have the disadvantage of damaging the surrounding tissues, while injection therapy may lead to perforations by causing ulcers. In comparison, using endoscopic clipping devices is applicable for directly *
Corresponding author. Tel.: +82 53 950 7545, Fax.: +82 53 950 6550 E-mail address:
[email protected] † Recommended by Associate Editor Yoon Hyuk Kim © KSME & Springer 2013
(a)
(b)
(c)
Fig. 1. Endoscopic view of (a) perforation; (b) perforations closed with 5 clips; (c) 4 weeks after closure with clips [14].
controlling hemorrhage at blood vessels, and only causes low levels of damage to surrounding tissues [9, 10]. In addition, hemostasis using clipping devices decreases the likelihood of rehemorrhage compared with the thermal method and injection [8, 11-13]. Fig. 1 shows the perforation and the resulting condition 4 weeks after using an endoscopic clipping device [14]. Endoscopic clipping devices have been used for around 30 years, and during this period, technological enhancements have led to the creation of various clip types [14, 15]. Currently, different endoscopic clipping devices have been developed for use in hemostasis and treatments within the gastrointestinal tract [16-18]. Such devices vary in form and size depending on the manufacturer, although their functions are similar. The endoscopic clipping devices manufactured by Olympus and Boston Scientific have been examined in a previous work, which looked into the main functions of these clipping devices [6]. The two clipping devices are similar in their overall shape and size, but differ in their mechanisms.
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Fig. 4. Schematics of the designed multi-functional clip.
Fig. 2. Sketch of the endoscopic clipping device.
(a) Olympus®
(b) Boston ScientificTM
Fig. 3. Endoscopic clipping device products.
The authors of that work found problems with these devices, such as lengthy surgical times (because the devices cannot be reopened) and difficulty in approaching the area of surgery (because their rotational functions are limited). Endoscopic clipping devices consist of a handle, sheath, and a clip on the tip of the sheath (Fig. 2). The slider is attached to the handle so that the opening and closing of the clip can be adjusted. The sheath prevents the breakaway and damage of the clip during the insertion of the clip into the body. The sheath also covers the endoscopic clipping device to ease the insertion into the blood vessels, which have a narrow diameter. Furthermore, the clip, located at the sheath end tip, captures the surgery area. The Olympus product is one of the most widely used clipping devices in the world (Fig. 3(a)) [6]. This product is relatively cost effective, because the clip is used while being attached to the cartridge where the clip is kept, making reuse possible [16]. Partial rotation is also possible, thereby allowing different procedures using a range of clips with varying opening angles and length. However, this product suffers from a low success rate because re-opening and the repetitive opening and closing the clip during procedure are not possible. Meanwhile, the Boston scientific device allows up to five re-openings, thereby ensuring a higher success rate [6]. Furthermore, the clip is pre-installed to the sheath to enable emergent uses. However, the device is relatively costly because it cannot be reused (i.e., the clipping device must be disposed after use). In addition, it also has difficulty in approaching the
area of surgery because rotation is not possible (Fig. 3(b)). Although a wide variety of endoscopic clipping devices is available in the market, few studies on the effectiveness and reliability of each product have been conducted. For example, Shin et al. studied the retention rates of HX-5L (Olympus), resolution clip (Boston scientific), and TriClip (Wilson Cook) and compared the respective durations of the clips’ attachment through tests made on animals [17]. Jensen et al. compared the performances of QuickClip (Olympus), Resolution clip, and TriClip [19, 20]. The retention rates and healing times were compared after performing endoclip treatments for 7 adult dogs with artificially generated gastric ulcers. However these studies are not clinical trials, but have been performed using animal models. Thus, the experimental results are insufficient in terms of the number of the endoscopic clips as well as the situations considered. Nevertheless, they found that the rotation and reopening functions are essential in ensuring high treatment success rates. In the current study, we develop a new mechanism to overcome such difficulties by benchmarking two types of endoscopic clipping devices currently being used. Furthermore, based on the developed mechanism, we perform the dynamic and the optimization analysis of the clipping device.
2. Mechanism design According to the benchmarking of current devices, there are a few necessary functions of a multi-functional endoscopic clipping device. First, it must have a re-opening function, which increases success rate, and a rotation function, which enables easier approach to the area of surgery. Second, surgeons should be able to adjust the opening and closing angles. Finally, the clip should be reusable. Therefore, in this study, we developed a new endoscopic clipping device, which has all of the abovementioned functions. The clip we developed includes an upper board, lower board, and springs (Fig. 4). The design of the multi-functional endoscopic clipping device is such that it is kept inside the cartridge, which consists of a double cone, a sheath tip, and a stopper (Fig. 5). Stoppers allow the clipping device to move to the left, but restrict movement to the right. Furthermore, the upper cone of the double cone adjusts the opening and closing angles of the clip, while the lower cone locks the clip after capture.
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(a) Capturing
(b) Detachment Fig. 5. Designed clipping device in the cartridge.
Fig. 8. Capturing and detachment mechanisms of the clipping device.
Fig. 9. Rotation mechanism of the designed clipping device. Fig. 6. Installation mechanism of the designed clipping device.
(a) Open configuration
(b) Closed configuration Fig. 7. Opening and closing mechanisms of the designed clipping device.
Fig. 6 shows the configuration after installation to the cartridge—all prepared for surgery. The groove at the female socket of the double cone and the male socket of the wire attached to the handle are connected tightly. Simultaneously, the sheath tip and sheath are connected to allow the rotational motion of the clip and wire, whereas the sheath does not rotate. Re-opening is configured through the process described here. First, the handle is pushed to the left, opening the clip as the forces of the spring between the upper and the lower boards are restored (Fig. 7(a)). Then, the handle is pulled to the right, restricting the movement of the double cone to the right due to the action of the stopper. Continuously pulling the handle locks the double cone, and the right end of the clip continues to move along the inclined plane of the double cone (Fig. 7(b)). The clip continues to move to the right and the clip closes. At this point, clip reopens when the handle is pushed
again to the left. Repeating this step leads to the opening and closing of the clip, thus guaranteeing the re-opening function. Next, with the clip located at the lesion, the slide is moved to the right, locking the right-end of the clip at the double cone, thus completing the capturing process (Fig. 8(a)). Furthermore, continuously pulling the slider to the right leads to the detachment of the separable wire, leaving only the clip and the double cone in the body (Fig. 8(b)). After detachment, the sheath can be removed from the body to replace a new clip from the cartridge, allowing the reuse of the clipping device. Finally, to achieve the rotation of the multi-functional clip, the handle is rotated so as to rotate the connected wire, the movement of which is transferred onto the separable wire connected to the clip, causing the clip to rotate (Fig. 9). The clip can be rotated 360° in both clockwise and counterclockwise directions. The clipping device we developed can be detached through the separation of the separable wire, and not by removing the connection between the male and female sockets. The socket and the wire are connected tightly, thus carrying sufficient torque to the clip. Comparisons between the benchmarking products and the new design developed in this study are summarized in Table 1. The new design allows the three main functions of re-opening, reusability and rotation, whereas the other two products are limited in terms of certain functional aspects. Both the Olympus product and the new design use cartridges to install new clips, whereas the Boston scientific product is manufactured with the clip already loaded. The Boston scientific clipping device is also initially closed when the clip is exposed inside the body, thereby requiring an opening procedure. Meanwhile, both the initially opened shape of the Olympus product and that of the new clip allow immediate capture upon approaching the area of surgery. Longer retention ensures a continuous hemostatic effect [17]; thus, the Boston scientific clipping device and the new design have an advantage in this aspect. Meanwhile, the Olympus clipping device has an ini-
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Table 1. Comparisons of the current and new clipping devices. Olympus
Boston
Open/Close
X
O
New design O
Reusability
O
X
O
Rotation
△
X
O
Installation
Easy
Pre-loaded
Easy
Initial shape
Opened
Closed
Opened
Retention
Short
Long
Long*
Remainders
Medium
Large
Small
(a) Displacement of point A
* indicates expectation.
(a) 3D view
(b) Side view
Fig. 10. Clip device model used in RecurDyn simulation.
(b) Distance between the upper and lower boards of the clip tips Fig. 11. Simulation results of the clip motion.
tially opened static equilibrium configuration, which tends to re-open as it returns to its original state. However, despite its initially opened shape, our clipping device is expected to have long clipping duration due to the action of the double cone. Finally, among the three devices, the amounts of remaining components in the body after the detachment show slight differences, and these depend on the original size of the clips.
3. Results 3.1 Dynamic simulation A dynamic analysis of the clipping device developed in this study was performed. In the design step, the motion of the designed clipping device behaves correctly, and unexpected problems may occur or not. RecurDyn V7R5 [21] was used for the dynamic analysis (Fig. 10). The clip, stopper, double cone, sheath tip, and separable wire were modeled as a rigid body, while the connections between the upper and lower boards, clip and separable wire, and stopper and sheath were modeled as revolute joints. In addition, torsional springs were used to model the clip spring and the connection between the stopper and the sheath. In this analysis, several contact conditions between the clip and double cone, double cone and stoppers, and separable wire and double cone were considered, with the values of 0.25 and 0.2 for the static and dynamic coefficients of friction, respectively. For simplicity, gravitational force was ignored, and the handle and the slider were not included in this simulation. In this simulation, the sheath moves only in the horizontal direction; input motion was applied to the separable wire so that the clip can capture the lesion after the rotating, closing, and opening motions (Fig. 11(a)). The output motion, which is
the distance between the upper and lower boards of the clip tips, is shown in Fig. 11(b). The multi-functions of the clip device are described according to each step. The initial step is the process of pushing the separable wire outside the sheath tip to expose the clip in the body and assessing the proper functioning of the stopper and the spring. The clip was properly opened by the action of the clip spring when the separable wire was moved to the left for about 9 seconds. Rotation was realized after the clip was exposed in the body. The position of point A did not change, because 180° rotational motion was applied without translational movement. In this step, rotational function was appropriately performed although the distance of the clip tips changed slightly due to centrifugal forces. Re-opening was made by the closing and opening motions, after which the roles of the double cone and the stopper were examined. In the close step, the distance between the upper and lower boards of the clip tips was decreased by the action of the double cone upon pulling the separable wire to the right. In this step, the stopper, which restricts the right-direction movement of the double cone, was confirmed to function properly. When the separable wire was pushed again, the clip returned to its original open configuration due to the clip spring. When the separable wire was continuously pulled again to capture lesion, the distance of the clip tips decreased and the clip was locked at the groove of the double cone. The results of dynamic simulation show proper realization of the multi-functions of the endoscopic clipping device developed in this study. Furthermore, the intended functions of the stopper and double cone were confirmed.
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(a) Illustration of the stopper before bending (a) Opened shape with sheath and clip
(b) Closed shape
(b) Illustration of the stopper after bending Fig. 13. Schematics of the stopper mechanism. (c) Rotated shape Fig. 12. Photos showing major mechanisms of the multi-functional endoscopic clipping device prototype.
3.2 Prototype The prototype was constructed based on the results of the dynamic simulation. The clip spring was connected by welding a thin aluminum sheet to the upper and lower boards. The shape of the double cone was partially modified in order to ensure the smooth execution of the clip motions. Transparent acrylic was used to facilitate easy examination inside the sheath. The handle and the slider were not made in the prototype. The opened shape of the prototype is shown in Fig. 12(a), including the device’s components. The clip was closed when the wire moved to the right side after exposing the clip (Fig. 12(b)). The re-opening functions were realized by repeating the opening and closing motions. The rotational function of the endoscopic clip prototype was also checked, (Fig. 12(c)). The stopper was implemented using a metal strip (Fig. 13(a)). Suppose the clip moved to the left, the stopper moved upward while the metal strip was bent (Fig. 13(b)). As soon as the double cone passed the stopper completely, the stopper returned to its original position by restoring forces of the metal strip. The stopper limited the motion of the clip when the clip moves back to the right, thereby blocking the movement of the double cone. The mechanisms predicted in the dynamic simulation were confirmed according to several examinations. 3.3 Optimization Optimization was performed to determine the location of
Fig. 14. Design parameter of the clip.
the clip spring to maximize the clipping forces. The overall shape (with clip dimensions including the design parameter, Ls, which is the distance of the clip spring from hinge) is shown in Fig. 14, where, t is the thickness of the clip and L1 and L2 are the front and rear lengths of the clip, respectively. In addition, d is the diameter of the hinge, and θ is the angle between the front and rear parts of the clip. The clip spring formed an arc connected with the clip tangentially, and the thickness of the clip spring was measured to be ¼ that of the clip. The clip and clip spring used in the study were made of stainless steel, with elastic moduli of 193 and 210 GPa, respectively. First, the lengths of L1 and L2 were determined, considering geometric constraints. Suppose the clip was opened completely, the distance between the top and bottom tips, Lo, were calculated as follows:
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4. Discussion and conclusion
Fig. 15. Vertical deflection of the clip tips with respect to the location of the clip spring, LS.
(1) or
(2) In this study, the minimum value of L1 satisfying Eq. (2) was selected to leave small remainders in a human body once the clip is detached. Meanwhile, when the inner diameter of the sheath tip was DS, from the geometric relations, the length of L2 was calculated as follows: (3) or
(4) Similarly, the maximum value of L2 can be chosen to satisfy Eq. (4), thereby obtaining the longest stroke when surgeons operate with open and close functions. The location of the clip spring, Ls, was then determined, considering the deflection of the clip tips. When a clip captures a lesion, the reaction forces at C and D are the clipping forces between the top and bottom clip tips. In addition, based on the Maxwell reciprocal theorem, the condition of maximum clipping forces is equals that of minimum deflections at C and D for a given boundary condition at A and B [22]. Therefore, it is necessary to determine the location of the clip spring when the deflection at C or D is at a minimum. The hinge constrained all degrees of freedom, except the horizontal direction. Computations were carried out using finite element analysis. The optimum location of the clip spring was 4.5 mm from the hinge because this location generated maximum clipping forces that resulted in the longest retention time of the clip in a human body (Fig. 15).
In this study, a new mechanism for the multi-functional endoscopic clipping device was developed to complement the drawbacks of current designs. The new design allows the three main functions of re-opening, reusability, and rotation. Dynamic simulation was performed to analyze the dynamical behavior of the designed clip device. Based on the dynamic analysis, a prototype was made to verify the mechanisms of the developed endoscopic clipping device. Furthermore, finite element analysis was performed to optimize the location of the clip spring,, which resulted in the maximum clipping forces for the longest retention time. The new endoscopic clipping device developed in this study has several advantages. The dual cone allows opening, closing, and rotating functions through separable wires. This mechanism is superior to current devices in terms of multi-functional positioning and transmitting rotational torque. In addition, the new clipping device is cost effective, because the re-opening function increases the success rate of the treatment. Currently, endoclips have been used in the treatment of gastro-intestinal bleeding and perforation. In addition, the validity and reliability of the endoclips have been verified by the high rate of primary hemostasis and low rebleeding rate represented in the form of a variety of bleeding compared with other closure techniques. Similar primary hemostasis and recurrent bleeding rates have only been shown when comparing the endoclip with the thermal method in the treatment of bleeding Dieulafoy's lesion. However, theoretically, the endoclip has no additional tissue damage, and can have an important role as a marker [6]. Based on these results, it is expected that the new multi-functional endoscopic device can have the same performances. In the future, clipping devices should handle two or more clips at a time to skip the re-insertion procedure during treatment. Given that two or more endoclips are used in clinical treatments, endoscopic devices, in which several clips are installed, can help ensure the high success rate of future treatments [23].
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Jong-Jin Bae received his B.S. degree in School of Mechanical Engineering from KyungpookNational University, Korea, in 2011 and his M.S. in 2013. Currently he is a doctoral studentin the same school. His current research interests include the design of medical device such as a clip, a catheter and guide wires used in endoscopic device. Namcheol Kang received his B.S. degree in Mechanical Engineering from KAIST in 1992, M.S in Mechanical Design and Production Engineering from Seoul National University in 1994, and Ph. D in Mechanical Engineering from Purdue University in 2004. Currently he is a professor in School of Mechanical Engineering at Kyungpook National University, Korea. His primary research interestsare dynamics, vibration and stability analysis in structures.
