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Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis

Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203116 Valeria Khaimov*, Fabian Frost, Volkmar Senz, Klaus-Peter Schmitz, Niels Grabow and Markus M. Lerch Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis Abstract: Pancreatic fluid collections (PFCs) are a 1 Introduction common complication associated with pancreatic injury. Drainage of a PFC is usually indicated if a patient becomes Pancreatitis is an inflammatory condition of the pancreas symptomatic with complications such as bacterial mainly caused by gallstones or alcohol consumption [1]. Its superinfection, septicaemia, fistulas, biliary obstruction or severe, acute variety is burdened with a high mortality. gastric outlet obstruction. Endoscopic ultrasound guided Physiologically the disease arises from a premature activation drainage is a well-established minimally invasive procedure of digestive [2] and lysosomal [3, 4] proteases but vascular to insert stents into a fluid collection, most prominently factors greatly contribute to its severity [5]. Pancreatic fluid plastic double pigtail stents (DPSs) and lumen-apposing collections (PFCs) are a common complication of acute metal stents (LAMS). Both, DPSs and LAMSs have pancreatitis that may result in bacterial superinfection with advantages and disadvantages that need to be considered septicaemia, fistulas, biliary obstruction or gastric outlet before treatment. However, the main factors leading to obstruction. PFCs comprise, not exclusively, pseudocysts and failure of currently available stent systems are the relatively walled-off necrosis (WON). While a pseudocyst is composed short patency period and bacterial superinfection. of fluid enclosed by a wall of fibrous tissue, a WON also In this study, we subjected two broadly used pancreatic contains solid necrotic debris and has a significantly lower stents, a DPS and a LAMS Hot AXIOS stent, which were treatment success [6]. When complications or symptoms, retrieved from the same patient, to a systematic such as severe abdominal pain or inflammation appear, PFCs morphological analysis by scanning electron microscopy in need to be drained. Endoscopic ultrasound (EUS) guided order to identify factors related to stent topography and management is currently the gold standard for the drainage of geometry and potentially involved in stent failure. Results of PFCs [1]. A large number of different stents were developed this work will provide essential information for future that facilitate EUS-based drainage [7]. Each stent type has its innovations regarding the stent design for drainage of PFCs. own advantages and disadvantages that need to be considered when selecting the treatment. DPS are inexpensive, but stent Keywords: pancreatic fluid collections, pancreatic necrosis, patency is very low due to its small diameter. On the other metal stent, plastic stent, double pigtail stent. hand, LAMS create a larger lumen, but are much more expensive, more prone to migration, may cause late bleeding https://doi.org/10.1515/cdbme-2020-3116 complications and do not prevent food reflux [8, 9]. The variety of different stents available for PFC drainage and complications associated with stent placement suggests that there is a strong need for novel stent concepts. In order to develop new stent concepts for PFCs we aim ______ to identify the most critical factors leading to stent failure. To *Corresponding author: Valeria Khaimov: Institute for this end, we are currently performing a systematic scanning ImplantTechnology and Biomaterials e. V., Institute for Biomedical electron microscopy (SEM) analysis on the most frequently Engineering, Rostock University Medical Center, Friedrich- Barnewitz-Str. 4, Rostock, Germany, e-mail: used stents in clinical practise for PFC drainage. Here, we valeria.khaimov@uni-rostock.de present our findings from a case study of a retrieved Hot Fabian Frost, Markus M. Lerch: University Medicine Greifswald, AXIOS stent (Boston Scientific) together with a later placed Department of Medicine A, Greifswald, Germany DPS across the Hot AXIOS stent from a patient with WON Volkmar Senz, Niels Grabow: Institute for Biomedical resulting from necrotizing pancreatitis. Engineering, Rostock, Germany Klaus-Peter Schmitz: Institute for ImplantTechnology and Biomaterials e.V., Rostock, Germany Open Access. © 2020 Valeria Khaimov et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. Valeria Khaimov et al., Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis — 2 2 Methods 2.1 Scanning electron microscopy Retrieved stents were briefly rinsed with 0.1 M sodium phosphate buffer (pH 7.4) and fixed with 2.5% glutaraldehyde/2% formaldehyde over night at 4°C. After fixation the samples were briefly rinsed with phosphate buffer before dehydration in an ascending ethanol series (70% - 80% - 96% - 100%) followed by a chemical drying procedure with hexamethyldisilazane. SEM was performed on a Quanta FEG 250 (FEI Company, Germany). The Hot AXIOS stent was first analysed in total before it was cut longitudinally revealing the luminal side of the scaffold. Same strategy was chosen for the DPS with the exception that the stent had first to be cut transversely in order to fit into the SEM chamber. Samples were mounted on carriers and sputter coated with gold prior to measurement. Any manipulations on stent samples led to release of some deposits from the sample. Loosely attached debris were gently removed by compressed air. Figure 1: SEM micrographs of the retrieved Hot Axis stent. Abluminal view. 3 Results A Hot AXIOS stent with an electrocautery-enhanced delivery system was used for transgastric drainage of a PFC resulting from pancreatic necrosis. The stent remained for 43 days in the patient in the position it was originally inserted. By the end of this period a double pig tail plastic stent was placed inside the Hot AXIOS stent. In total 9 endoscopic necrosectomies were performed before both stents were retrieved from the patient. 3.1 Morphological and morphometric analysis of retrieved stent samples SEM micrographs of the abluminal side of the Hot AXIOS stent revealed struts of 80-90 µm in size. The Figure 2: SEM micrographs of the retrieved Hot Axis stent. Luminal polymeric coating within stent cells was rough in the centre view. with characteristic bubbles probably resulting from the struts at the flanged ends resulted in more deposits (Fig. 1 E manufacturing process. Most of the stent area was free of and F). The luminal side of the Hot AXIOS stent was deposits. However, rough areas of the stent cells seem to be relatively smooth with no struts visible due to uniform prone to deposition of cell debris (Fig. 1 A and B). In polymeric coverage of the scaffold. A few narrow cracks in addition, some struts were only partially covered by the the coating were observed and some irregularly shaped debris polymer coating and these spots were associated with multi- were distributed throughout this side of the stent (Fig. 2 A layered agglomerates containing cell-like round-shaped and B). In contrast, clearly more deposits were detected at the structures (Fig. 1 C and D). Smaller distance between the luminal side of the flanged ends of the stent (Fig. 2 C and D). Valeria Khaimov et al., Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis — 3 The Hot AXIOS stent and electrocautery-enhanced system is indicated for use to facilitate transgastric or transduodenal endoscopic drainage of a pancreatic pseudocyst or the biliary tract [6]. The stent is composed of a braided nitinol framework fully covered by silicone with wide flanges at the ends to ensure accurate anchorage of the stent within the PFCs area. Its wide diameter provides a conduit for direct endoscopic necrosectomy which improves drainage and reduces the need for repeated endoscopies [10]. Plastic DPS have coiled ends usually with additional side holes that should support stent patency even if the stent becomes occluded. These stents are extremely cheap, but are also limited by the small diameter leading to rapid stent occlusion. Recent reports suggest that placement of plastic DPSs across LAMSs reduces the incidence of cavity infections due to better stent patency and is meanwhile a well-established treatment for PFCs [11]. In this study we have subjected such a stent pair retrieved from the same patient, after repeated necrosectomies to a systematic SEM analysis. Although materials chosen for stents usually prevent any deposits of biological origin, we have observed various agglomerates of cell-like objects on the stent surface. Our data provide a profound basis for the identification of stent Figure 3: SEM micrographs of the retrieved DPS. A-D: abluminal hot spots that promote deposition of cells or debris view, E and F: luminal view. responsible for stent failure and will contribute to a better SEM examination of the retrieved DPS revealed a treatment and outcome of patients with PFCs. relatively thin layer of deposits on its surface with large areas barely covered by debris. In the middle part irregularly Author Statement shaped debris, but no adherent cells were detected on the The authors acknowledge technical assistance of Katja Hahn stent surface (Fig. 3 A and B). Analysis of both coiled ends and Babette Hummel. Research funding: Partial financial revealed several multilayered cell agglomerates partially support by the Federal Ministry of Education and Research reaching into or entirely covering the holes of the DPS (Fig. (BMBF) within RESPONSE “Partnership for Innovation in 3 C and D). The size of the cells in such regions was around Implant Technology” and by the European Social Fund 8-10 µm. (ESF) within the excellence research program of the state At the luminal side of the DPS the same type of cell Mecklenburg-Vorpommern. Conflict of interest: Authors agglomerates was observed, in some part loosely packed with state no conflict of interest. The study was conducted under grooves in between, but also including areas entirely ethics approval of Greifswald University Medicine on non- occluded. human material otherwise discarded. 4 Summary and Conclusion References [1] Mayerle J, Hoffmeister A; Werner J; Witt H; Lerch MM, The variety of currently available metal stents for the Mössner J. Chronic pancreatitis--definition, etiology, treatment of PFCs and numerous complications resulting in investigation and treatment. Dtsch Arztebl Int. stent failure show that there is a strong need for the 2013;110(22):387-93. [2] Halangk W, Krüger B, Ruthenbürger M, Stürzebecher J, development of a superior stent system. Albrecht E, Lippert HE, Lippert H, Lerch MM. Trypsin SEM analysis of the surface upon retrieval from the patient activity is not involved in premature, intrapancreatic will provide valuable insights into stent-tissue interactions trypsinogen activation. Am J Physiol Gastrointest Liver and new impulses for the development of the next generation Physiol. 2002;282(2):G367-74. stents used for PFCs drainage. Valeria Khaimov et al., Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis — 4 [3] Lerch MM, Saluja AK; Dawra R, Saluja M, Steer ML. The effect of chloroquine administration on two experimental models of acute pancreatitis. Gastroenterology. 1993;104(6):1768-79. [4] Wartmann T, Mayerle J, Kähne T, Sahin-Tóth M, Ruthenbürger M, Matthias R et al. Cathepsin L inactivates human trypsinogen, whereas cathepsin L- deletion reduces the severity of pancreatitis in mice. Gastroenterology. 2010;138(2):726-37. [5] Weidenbach H, Lerch MM, Gress TM, Pfaff D, Turi S, Adler G. Vasoactive mediators and the progression from oedematous to necrotising experimental acute pancreatitis. Gut. 1995;37(3):434-40. [6] Alali A, Mosko J, May G, Teshima C. Endoscopic Ultrasound-Guided Management of Pancreatic Fluid Collections: Update and Review of the Literature. Clinical endosc. 2017;50(2):117–125. [7] Mangiavillano B, Pagano N, Baron TH; Arena M, Iabichino G, Consolo P, Opocher E, Luigiano C. Biliary and pancreatic stenting: Devices and insertion techniques in therapeutic endoscopic retrograde cholangiopancreatography and endoscopic ultrasonography. World J Gastrointest Endosc. 2016;8(3):143-56. [8] Kwon CI, Ko, Kwang Hyun; Hahm, Ki Baik; Kang, Dae Hwan (2013): Functional self-expandable metal stents in biliary obstruction. Clin endosc. 2013;46(5):515–521. [9] Lee PJ, Papachristou GI. New insights into acute pancreatitis. Nat Rev Gastroenterol Hepatol. 2019;16(8):479–496. [10] Weilert F, Binmoeller KF. Specially designed stents for translumenal drainage. Gastrointest Interv. 2015;4(1):40–45. [11] Wang Z, Wu X, Zhao S, Li Z, Bai Y; Wang D. The role of co-axially placed double-pigtail stents within lumen- apposing metal stents in draining pancreatic fluid collections. Gastrointest endosc. 2018;88(2):409–410. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Current Directions in Biomedical Engineering de Gruyter

Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis

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10.1515/cdbme-2020-3116
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Abstract

DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203116 Valeria Khaimov*, Fabian Frost, Volkmar Senz, Klaus-Peter Schmitz, Niels Grabow and Markus M. Lerch Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis Abstract: Pancreatic fluid collections (PFCs) are a 1 Introduction common complication associated with pancreatic injury. Drainage of a PFC is usually indicated if a patient becomes Pancreatitis is an inflammatory condition of the pancreas symptomatic with complications such as bacterial mainly caused by gallstones or alcohol consumption [1]. Its superinfection, septicaemia, fistulas, biliary obstruction or severe, acute variety is burdened with a high mortality. gastric outlet obstruction. Endoscopic ultrasound guided Physiologically the disease arises from a premature activation drainage is a well-established minimally invasive procedure of digestive [2] and lysosomal [3, 4] proteases but vascular to insert stents into a fluid collection, most prominently factors greatly contribute to its severity [5]. Pancreatic fluid plastic double pigtail stents (DPSs) and lumen-apposing collections (PFCs) are a common complication of acute metal stents (LAMS). Both, DPSs and LAMSs have pancreatitis that may result in bacterial superinfection with advantages and disadvantages that need to be considered septicaemia, fistulas, biliary obstruction or gastric outlet before treatment. However, the main factors leading to obstruction. PFCs comprise, not exclusively, pseudocysts and failure of currently available stent systems are the relatively walled-off necrosis (WON). While a pseudocyst is composed short patency period and bacterial superinfection. of fluid enclosed by a wall of fibrous tissue, a WON also In this study, we subjected two broadly used pancreatic contains solid necrotic debris and has a significantly lower stents, a DPS and a LAMS Hot AXIOS stent, which were treatment success [6]. When complications or symptoms, retrieved from the same patient, to a systematic such as severe abdominal pain or inflammation appear, PFCs morphological analysis by scanning electron microscopy in need to be drained. Endoscopic ultrasound (EUS) guided order to identify factors related to stent topography and management is currently the gold standard for the drainage of geometry and potentially involved in stent failure. Results of PFCs [1]. A large number of different stents were developed this work will provide essential information for future that facilitate EUS-based drainage [7]. Each stent type has its innovations regarding the stent design for drainage of PFCs. own advantages and disadvantages that need to be considered when selecting the treatment. DPS are inexpensive, but stent Keywords: pancreatic fluid collections, pancreatic necrosis, patency is very low due to its small diameter. On the other metal stent, plastic stent, double pigtail stent. hand, LAMS create a larger lumen, but are much more expensive, more prone to migration, may cause late bleeding https://doi.org/10.1515/cdbme-2020-3116 complications and do not prevent food reflux [8, 9]. The variety of different stents available for PFC drainage and complications associated with stent placement suggests that there is a strong need for novel stent concepts. In order to develop new stent concepts for PFCs we aim ______ to identify the most critical factors leading to stent failure. To *Corresponding author: Valeria Khaimov: Institute for this end, we are currently performing a systematic scanning ImplantTechnology and Biomaterials e. V., Institute for Biomedical electron microscopy (SEM) analysis on the most frequently Engineering, Rostock University Medical Center, Friedrich- Barnewitz-Str. 4, Rostock, Germany, e-mail: used stents in clinical practise for PFC drainage. Here, we valeria.khaimov@uni-rostock.de present our findings from a case study of a retrieved Hot Fabian Frost, Markus M. Lerch: University Medicine Greifswald, AXIOS stent (Boston Scientific) together with a later placed Department of Medicine A, Greifswald, Germany DPS across the Hot AXIOS stent from a patient with WON Volkmar Senz, Niels Grabow: Institute for Biomedical resulting from necrotizing pancreatitis. Engineering, Rostock, Germany Klaus-Peter Schmitz: Institute for ImplantTechnology and Biomaterials e.V., Rostock, Germany Open Access. © 2020 Valeria Khaimov et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. Valeria Khaimov et al., Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis — 2 2 Methods 2.1 Scanning electron microscopy Retrieved stents were briefly rinsed with 0.1 M sodium phosphate buffer (pH 7.4) and fixed with 2.5% glutaraldehyde/2% formaldehyde over night at 4°C. After fixation the samples were briefly rinsed with phosphate buffer before dehydration in an ascending ethanol series (70% - 80% - 96% - 100%) followed by a chemical drying procedure with hexamethyldisilazane. SEM was performed on a Quanta FEG 250 (FEI Company, Germany). The Hot AXIOS stent was first analysed in total before it was cut longitudinally revealing the luminal side of the scaffold. Same strategy was chosen for the DPS with the exception that the stent had first to be cut transversely in order to fit into the SEM chamber. Samples were mounted on carriers and sputter coated with gold prior to measurement. Any manipulations on stent samples led to release of some deposits from the sample. Loosely attached debris were gently removed by compressed air. Figure 1: SEM micrographs of the retrieved Hot Axis stent. Abluminal view. 3 Results A Hot AXIOS stent with an electrocautery-enhanced delivery system was used for transgastric drainage of a PFC resulting from pancreatic necrosis. The stent remained for 43 days in the patient in the position it was originally inserted. By the end of this period a double pig tail plastic stent was placed inside the Hot AXIOS stent. In total 9 endoscopic necrosectomies were performed before both stents were retrieved from the patient. 3.1 Morphological and morphometric analysis of retrieved stent samples SEM micrographs of the abluminal side of the Hot AXIOS stent revealed struts of 80-90 µm in size. The Figure 2: SEM micrographs of the retrieved Hot Axis stent. Luminal polymeric coating within stent cells was rough in the centre view. with characteristic bubbles probably resulting from the struts at the flanged ends resulted in more deposits (Fig. 1 E manufacturing process. Most of the stent area was free of and F). The luminal side of the Hot AXIOS stent was deposits. However, rough areas of the stent cells seem to be relatively smooth with no struts visible due to uniform prone to deposition of cell debris (Fig. 1 A and B). In polymeric coverage of the scaffold. A few narrow cracks in addition, some struts were only partially covered by the the coating were observed and some irregularly shaped debris polymer coating and these spots were associated with multi- were distributed throughout this side of the stent (Fig. 2 A layered agglomerates containing cell-like round-shaped and B). In contrast, clearly more deposits were detected at the structures (Fig. 1 C and D). Smaller distance between the luminal side of the flanged ends of the stent (Fig. 2 C and D). Valeria Khaimov et al., Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis — 3 The Hot AXIOS stent and electrocautery-enhanced system is indicated for use to facilitate transgastric or transduodenal endoscopic drainage of a pancreatic pseudocyst or the biliary tract [6]. The stent is composed of a braided nitinol framework fully covered by silicone with wide flanges at the ends to ensure accurate anchorage of the stent within the PFCs area. Its wide diameter provides a conduit for direct endoscopic necrosectomy which improves drainage and reduces the need for repeated endoscopies [10]. Plastic DPS have coiled ends usually with additional side holes that should support stent patency even if the stent becomes occluded. These stents are extremely cheap, but are also limited by the small diameter leading to rapid stent occlusion. Recent reports suggest that placement of plastic DPSs across LAMSs reduces the incidence of cavity infections due to better stent patency and is meanwhile a well-established treatment for PFCs [11]. In this study we have subjected such a stent pair retrieved from the same patient, after repeated necrosectomies to a systematic SEM analysis. Although materials chosen for stents usually prevent any deposits of biological origin, we have observed various agglomerates of cell-like objects on the stent surface. Our data provide a profound basis for the identification of stent Figure 3: SEM micrographs of the retrieved DPS. A-D: abluminal hot spots that promote deposition of cells or debris view, E and F: luminal view. responsible for stent failure and will contribute to a better SEM examination of the retrieved DPS revealed a treatment and outcome of patients with PFCs. relatively thin layer of deposits on its surface with large areas barely covered by debris. In the middle part irregularly Author Statement shaped debris, but no adherent cells were detected on the The authors acknowledge technical assistance of Katja Hahn stent surface (Fig. 3 A and B). Analysis of both coiled ends and Babette Hummel. Research funding: Partial financial revealed several multilayered cell agglomerates partially support by the Federal Ministry of Education and Research reaching into or entirely covering the holes of the DPS (Fig. (BMBF) within RESPONSE “Partnership for Innovation in 3 C and D). The size of the cells in such regions was around Implant Technology” and by the European Social Fund 8-10 µm. (ESF) within the excellence research program of the state At the luminal side of the DPS the same type of cell Mecklenburg-Vorpommern. Conflict of interest: Authors agglomerates was observed, in some part loosely packed with state no conflict of interest. The study was conducted under grooves in between, but also including areas entirely ethics approval of Greifswald University Medicine on non- occluded. human material otherwise discarded. 4 Summary and Conclusion References [1] Mayerle J, Hoffmeister A; Werner J; Witt H; Lerch MM, The variety of currently available metal stents for the Mössner J. Chronic pancreatitis--definition, etiology, treatment of PFCs and numerous complications resulting in investigation and treatment. Dtsch Arztebl Int. stent failure show that there is a strong need for the 2013;110(22):387-93. [2] Halangk W, Krüger B, Ruthenbürger M, Stürzebecher J, development of a superior stent system. Albrecht E, Lippert HE, Lippert H, Lerch MM. Trypsin SEM analysis of the surface upon retrieval from the patient activity is not involved in premature, intrapancreatic will provide valuable insights into stent-tissue interactions trypsinogen activation. Am J Physiol Gastrointest Liver and new impulses for the development of the next generation Physiol. 2002;282(2):G367-74. stents used for PFCs drainage. Valeria Khaimov et al., Systematic microscopic analysis of retrieved stents from a patient with pancreatic necrosis — 4 [3] Lerch MM, Saluja AK; Dawra R, Saluja M, Steer ML. The effect of chloroquine administration on two experimental models of acute pancreatitis. Gastroenterology. 1993;104(6):1768-79. [4] Wartmann T, Mayerle J, Kähne T, Sahin-Tóth M, Ruthenbürger M, Matthias R et al. Cathepsin L inactivates human trypsinogen, whereas cathepsin L- deletion reduces the severity of pancreatitis in mice. Gastroenterology. 2010;138(2):726-37. [5] Weidenbach H, Lerch MM, Gress TM, Pfaff D, Turi S, Adler G. Vasoactive mediators and the progression from oedematous to necrotising experimental acute pancreatitis. Gut. 1995;37(3):434-40. [6] Alali A, Mosko J, May G, Teshima C. Endoscopic Ultrasound-Guided Management of Pancreatic Fluid Collections: Update and Review of the Literature. Clinical endosc. 2017;50(2):117–125. [7] Mangiavillano B, Pagano N, Baron TH; Arena M, Iabichino G, Consolo P, Opocher E, Luigiano C. Biliary and pancreatic stenting: Devices and insertion techniques in therapeutic endoscopic retrograde cholangiopancreatography and endoscopic ultrasonography. World J Gastrointest Endosc. 2016;8(3):143-56. [8] Kwon CI, Ko, Kwang Hyun; Hahm, Ki Baik; Kang, Dae Hwan (2013): Functional self-expandable metal stents in biliary obstruction. Clin endosc. 2013;46(5):515–521. [9] Lee PJ, Papachristou GI. New insights into acute pancreatitis. Nat Rev Gastroenterol Hepatol. 2019;16(8):479–496. [10] Weilert F, Binmoeller KF. Specially designed stents for translumenal drainage. Gastrointest Interv. 2015;4(1):40–45. [11] Wang Z, Wu X, Zhao S, Li Z, Bai Y; Wang D. The role of co-axially placed double-pigtail stents within lumen- apposing metal stents in draining pancreatic fluid collections. Gastrointest endosc. 2018;88(2):409–410.

Journal

Current Directions in Biomedical Engineering – de Gruyter

Published: Sep 1, 2020

Keywords: pancreatic fluid collections; pancreatic necrosis; metal stent; plastic stent; double pigtail stent

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