Kompetenzzentrum für Medizintechnik Mecklenburg-Vorpommern

Ausgewählte Forschungsarbeiten

Schmidt W, Lanzer P, Behrens P, Brandt-Wunderlich C, Öner A, Ince H, Schmitz K-P, Grabow N. Direct comparison of coronary bare metal vs. drug-eluting stents. Same platform, different mechanics? EurJ Med Res 23 (2). 2018

doi: 10.1186/s40001-017-0300-y.

Abstract:

BACKGROUND/PURPOSE: Drug-eluting stents (DES) compared to bare-metal (BMS) have shown superior clinical performance, but are considered less suitable in complex cases. Most studies do not distinguish between DES and BMS with respect to their mechanical performance.  The objective was to obtain mechanical parameters for direct comparison of BMS and DES.

METHODS/MATERIALS: In vitro bench tests evaluated crimped stent profiles, crossability in stenosis models, elastic recoil, bending stiffness (crimped and expanded), and scaffolding properties. The study included five pairs of BMS and DES each with the same stent platforms (all n=5; PRO-Kinetic Energy, Orsiro: BIOTRONIK AG, Bülach, Switzerland; MULTI-LINK 8, XIENCE Xpedition: Abbott Vascular, Temecula, CA; REBEL Monorail, Promus PREMIER, Boston Scientific, Marlborough, MA; Integrity, Resolute Integrity, Medtronic, Minneapolis, MN; Kaname, Ultimaster: Terumo Corporation, Tokyo, Japan). Statistical analysis used pooled variance t-tests for pairwise comparison of BMS with DES.

RESULTS: Crimped profiles in BMS groups ranged from 0.97±0.01mm (PRO-Kinetic Energy) to 1.13±0.01mm (Kaname) and in DES groups from 1.02±0.01mm (Orsiro) to 1.13±0.01mm (Ultimaster). Crossability was best for low profile stent systems. Elastic recoil ranged from 4.07±0.22 % (Orsiro) to 5.87±0.54% (REBEL Monorail) including both, BMS and DES. The bending stiffness of crimped and expanded stents showed no systematic differences between BMS and DES neither did the scaffolding. 

CONCLUSIONS: Based on in vitro measurements BMS appear superior to DES in some aspects of mechanical performance, yet the differences are small and not class uniform. The data provide assistance in selecting the optimal system for treatment and assessment of new generations of bioresorbable scaffolds.

EurJ Med Res. 2018; 23 (2)

 

 

Schmidt W, Schmitz K-P, Behrens P, Grabow N, Ince H, Öner A. Expansion characteristics of coronary stents in focal stenoses. Current Directions in Biomedical Engineering 3 (2) 139-142. 2017

doi: 10.1515/cdbme-2017-0029.

Abstract:

The presented experimental in vitro approach was designed to assess the expansion behavior of stent systems in a resistant focal stenosis model with respect to a potential dog-boning effect. Five different stent systems (nominal diameter 3.0 mm) were investigated. The focal stenosis was simulated by a stainless steel tube (ID ? 1.20 mm). Stent expansion was performed using a proprietary test device consisting of a test chamber with 37 °C water, 2-axis laser scanner and a pressure controller.

All stents could be properly expanded up to recommended maximum pressure (RBP). At nominal pressure (NP) maximum diameters ranged from 2.923 to 3.560 mm while at RBP the maximum diameters were 3.391 to 3.984 mm. Only minimal flaring of stent struts from the expanded balloon was observed. None of the stent systems failed under the extremely high stress at the edges of the focal stenosis.

Current Directions in Biomedical Engineering. 2017; 3 (2):139-142.

Wissgott C, Schmidt W, Brandt-Wunderlich C, Behrens P, Andresen R. Clinical Results and Mechanical Properties of the Carotid CGUARD Double-Layered Embolic Prevention Stent. Journal of endovascular therapy, 24 (1), S. 130–137. 2017

doi: 10.1177/1526602816671134.

PMID: 27733689

Abstract:

BACKGROUND/PURPOSE: To report early clinical outcomes with a novel double-layer stent for the internal carotid artery (ICA) and the in vitro investigation of the stent’s mechanical properties.

METHODS/MATERIALS: A prospective single-center study enrolled 30 consecutive patients (mean age 73.1±6.3 years; 21 men) with symptomatic (n=25) or high-grade (n=5) ICA stenosis treated with the new double-layer carotid CGUARD Embolic Prevention System (EPS) stent, which has an inner opencell nitinol design with an outer closed-cell polyethylene terephthalate layer. The average stenosis of the treated arteries was 84.1%±7.9% with a mean lesion length of 16.6±2.1 mm. In the laboratory, 8×40-mm stents where tested in vitro with respect to their radial force during expansion, the bending stiffness of the stent system and the expanded stent, as well as the collapse pressure in a thin and flexible sheath. The wall adaptation was assessed using fluoroscopy after stent release in step and curved vessel models.

RESULTS: The stent was successfully implanted in all patients. No peri- or postprocedural complications occurred; no minor or major stroke was observed in the 6-month follow-up. The bending stiffness of the expanded stent was 63.1 N·mm2 and (not unexpectedly) was clearly lower than that of the stent system (601.5 N·mm2). The normalized radial force during expansion of the stent to 7.0 mm, consistent with in vivo sizing, was relatively high (0.056 N/mm), which correlates well with the collapse pressure of 0.17 bars. Vessel wall adaptation was harmonic and caused no straightening of the vessel after clinical application.

CONCLUSIONS: Because of its structure, the novel CGUARD EPS stent is characterized by a high flexibility combined with a high radial force and very good plaque coverage. These first clinical results demonstrate a very safe implantation behavior without any stroke up to 6 months after the procedure.

Journal of endovascular therapy. 2017; 24 (1): 130–137

Schmidt W, Behrens P, Brandt-Wunderlich C, Siewert S, Grabow N, Schmitz KP. In vitro performance investigation of bioresorbable scaffolds – standard tests for vascular stents and beyond. Cardiovasc Revasc Med. 2016

doi: 10.1016/j.carrev.2016.05.001

PMID: 27266902

Abstract:

BACKGROUND/PURPOSE: Biodegradable polymers are the main materials for coronary scaffolds. Magnesium has been investigated as a potential alternative and was successfully tested in human clinical trials. However, it is still challenging to achieve mechanical parameters comparative to permanent bare metal (BMS) and drug-eluting stents (DES). As such, in vitro tests are required to assess mechanical parameters correlated to the safety and efficacy of the device.

METHODS/MATERIALS: In vitro bench tests evaluate scaffold profiles, length, deliverability, expansion behavior including acute elastic and time-dependent recoil, bending stiffness and radial strength. The Absorb GT1 (Abbott Vascular, Temecula, CA), DESolve (Elixir Medical Corporation, Sunnyvale, CA) and the Magmaris (BIOTRONIK AG, Bülach, Switzerland) that was previously tested in the BIOSOLVE II study, were tested.

RESULTS: Crimped profiles were 1.38±0.01mm (Absorb GT1), 1.39±0.01mm (DESolve) and 1.44±0.00mm (Magmaris) enabling 6F compatibility. Trackability was measured depending on stiffness and force transmission (pushability). Acute elastic recoil was measured at free expansion and within a mock vessel, respectively, yielding results of 5.86±0.76 and 5.22±0.38% (Absorb), 7.85±3.45 and 9.42±0.21% (DESolve) and 5.57±0.72 and 4.94±0.31% (Magmaris). Time-dependent recoil (after 1h) was observed for the Absorb and DESolve scaffolds but not for the Magmaris. The self-correcting wall apposition behavior of the DESolve did not prevent time-dependent recoil under vessel loading.

CONCLUSIONS: The results of the suggested test methods allow assessment of technical feasibility based on objective mechanical data and highlight the main differences between polymeric and metallic bioresorbable scaffolds.

Cardiovasc Revasc Med. 2016 Sep;17(6):375-83

Schmidt W, Hubmann P, Behrens P, Behrend D, Schmitz K-P: Biomechanics of optimum stent implantation strategy considering Vessel wall contact and vessel trauma. Biomed Tech (Berl), 2013

doi:  /j/bmte.2013.58.issue-s1-C/bmt-2013-4113/bmt-2013-4113.xml.

PMID: 24042755

Abstract:

An optimum stent implantation strategy is assumed to depend on stent diameter and implantation pressure.
However, which consequences are expected in case of mismatch? The presented study investigated stent implantation in native porcine arteries and measured acute lumen gain, vessel injury and wall contact area between stent struts and surrounding vessel. Biomechanical aspects of stent recoil and expansion diameter were included to assess the results. Maximum overexpansion will lead to severe vessel injury but not maximum wall contact. It is concluded that the goal should be proper diameter match. It is barely affected by the implantation pressure.

Biomed Tech (Berl), 2013. 58 (Suppl. 1) 867-868

Schmidt W, Lanzer P: Instrumentation, in: P. Lanzer (ed.), Catheter-Based Cardiovascular Interventions 2013

doi: 10.1007/978-3-642-27676-7_27

Abstract:

Selection of the optimum instrumentation in individual cases represents an important part of interventional decision making. To date, the majority of these decisions are based on personal experience, evidence-based clinical data, availability, and costs. Decisions based on objective performance criteria are relatively rare due to the lack of a more detailed technical documentation of individual products. Although it is true that even the best technical description of a specific product may not fully capture the behavior of the product in clinical settings, the availability of technical data has a direct impact on the ability of the operators to weight advantages and drawbacks of interventional instrumentation and make informed and better choices between similar and dissimilar products. Given the wealth of products reaching the growing markets, such ability shall likely become even more important in the future. To realize better choices for instrumentation, four basic steps should be considered. First, standard methodology of measurements of biomechanical properties of stents and SDS must be improved; examples and some proposals have been provided in this paper. Second, industry needs to adopt these methods and market their stent products along with the disclosure of the relevant nonproprietary biomechanical data. Third, biomechanical interactions between stents and lesions need to be better studied and understood. Fourth, the results of steps 1–3 need to be clinically applied. Further advancements of the state of the practice and art of intracoronary stenting are an important future goal of the interventional community. This goal will require an ongoing strong interdisciplinary cooperation of physicians, medical engineers, and natural scientists.

In: P. Lanzer (ed.), Catheter-Based Cardiovascular Interventions, DOI 10.1007/978-3-642-27676-7_27, Springer-Verlag Berlin Heidelberg 2013, p. 445-472

Brandt C, Schmidt W, Behrens P, Schmitz KP. The effect of different guide wires on the trackability of coronary stent delivery systems, Biomed Tech 2012

doi: 10.1515/bmt-2012-4300

PMID: 22962176

Abstract:

The trackability is an essential property for determining the handling characteristics of coronary stent systems. It depends on the friction properties and flexibility of the stent system, the constitution of the vessel, but also on the properties of the guide wire used for the intervention. The influence of five commercially available coronary workhorse guide wires of different manufactures (Abbott, BIOTRONIK, Boston Scientific, Medtronic, Terumo) on trackability of two different stent systems was tested. Proximal shaft force was measured while moving a stent system over the guide wire to be tested into an in vitro vessel model. The trackability of the stent systems was best with BIOTRONIK Galeo Hydro and worst with Boston Scientific Luge™. The trackability of stent systems does not only depend on the properties of the stent system itself, but also on the guide wire used. The trackability properties could be improved by using an appropriate combination of stent system and guide wire.

Biomed Tech 2012; 57 (Suppl. 1) 880-881, © 2012 by Walter de Gruyter · Berlin · Boston.

Schmidt W, Schmitt L, Behrens P, Martin H, Röhr U, Schmitz K-P : Fatigue testing of stents for peripheral vasculature with axial, bending and torsion loading, Biomed Tech 2011

doi: 10.1515/BMT.2011.364

Abstract:

Introduction: Vascular implants for peripheral vessels in particular femoro-popliteal regions are exposed to severe loading and deformation. Radiological findings in clinical practice provide evidence of partially serious strut fractures. Thus, fatigue testing of stents with relevant deformation is required for product approval of stents. In this context the verification of actually applied deformations compared to physiological conditions becomes highly important.
Method: A test setup was developed and built which enables the loading of self-expanding stents with cyclic axial compression or tension, with bending at a defined radius on a curved disc and torsion around the longitudinal axis of the stent. The load can be applied simultaneously by a synchronous control of linear drives. The verification of the applied deformations was statically obtained by measurements of elongations and dynamically by calibrated high-speed camera recordings (CamRecord CR600x2, Optronis). The long-term loading occurs in contact with a test medium at 37°C. Visual inspections are performed from outside through the transparent test tube as well as from inside using an endoscope (Mini Boreskop X-25-25-000- 70, Olympus). The inspections allow assessments of the state of the stents at specific test intervals without removing them before test conclusion.
Results: The programmed travel distances of the linear drives were achieved with high accuracy. Due to the fact of stent fixation within an elastic tube the stiffness relation between stent and tube has direct impact on achieved stent deformation. This influence can be precisely compensated by the experimental determination of relevant stiffness values of stent and tubing. Examination of stent deformation by the high-speed camera confirmed the accuracy of loading (< 5% of measured value).
Conclusion: The developed test setup meets the requirements of accuracy of stent deformation. Compared to other commercially available test machines we realized well defined deformations for all load modes. This is a clear improvement with respect to reproducibility of testing. Long-term testing of available stents was performed successfully.

Biomed Tech 2011; 56 (Suppl. 1), DOI 10.1515/BMT.2011.364

Schmidt W, Wissgott C, Andresen R, Behrens P, Schmitz K-P. Performance characteristics of modern self-expanding nitinol stents indicated for SFA, Fortschr. Röntgenstr., 2011

doi: 10.1055/s-0031-1273445

PMID: 21751121

Abstract:

Ziel: Bestimmung von Leistungsparametern aktueller Stents für die AFS und ihrer Kathetersysteme (SDS).
Material und Methoden: Sechs 7 mm/ 80 mm-Stentsysteme wurden untersucht: BIOTRONIK Astron Pulsar (4F), EDWARDS LifeStent FlexStar, ev3 PROTÉGÉ Everflex, CORDIS Smart Control, BARD E-Luminexx, GUIDANT Absolute (alle 6F). Die SDS wurden hinsichtlich Profil, Flexibilität im Stentbereich, Führbarkeit und Schiebbarkeit durch ein gewundenes Gefäßmodell sowie der Freisetzkraft der Stents vermessen. Von den Stents wurden die Flexibilität, die Radialkraft bei Aufweitung und Kompression und die Längenänderung ermittelt.
Ergebnisse: Das 4F-System hatte ein Profil von 1,45 mm. Bei den 6F-Stentsystemen betrug es 1,96 - 2,10 mm. Der Astron Pulsar war am flexibelsten (195 Nmm²) verglichen mit 334 - 972 Nmm² der 6F-Systeme. Die Schubkraft des steifsten Systems (FlexStar, 0,314N) war höher als die des Astron Pulsar (0,273N), aber niedriger als die der anderen Systeme (0,387 - 0,579N). Die Freisetzkräfte betrugen 1,69N (Absolute), 2,05N (Astron Pulsar) bis 13,00N (FlexStar). Die Radialkraft bei der Aufweitung betrug bei einen Stentdurchmesser von 6 mm 3,95N (Absolute) und 3,99N (Astron Pulsar) bis 7,22N (FlexStar) und war bei Kompression höher.
Schlussfolgerung: Das 4F-System hatte die beste Flexibilität und Führbarkeit. Die Freisetzkraft war bei den meisten Systemen mit Freisetzvorrichtungen hoch. Die Radialkraft der Stents erstreckt sich über einen großen Bereich. Die Ergebnisse könnten hilfreich sein, um für verschiedene Läsionen den besten Stent zu wählen.

Fortschr. Röntgenstr., 2011; 183: 818–825

Wiemer M, Butz T, Schmidt W, Schmitz K-P, Horstkotte D, Langer C. Scanning electron microscopic analysis of different drug-eluting stents after failed implantation: From nearly undamaged to major ..., Catheterization and Cardiovascular Interv 2010

doi: 10.1002/ccd.22347

PMID: 20088011

Abstract:

Background: Implantation of drug eluting stents (DES) in tortuous and/or calcified vessels is much more demanding compared with implantation of bare metal stents (BMS) due to their larger diameters. It is unknown whether drug eluting stent coatings get damaged while crossing these lesions.
Methods: In 42 patients (34 male, 68.1 ± 10 years) with 45 calcified lesions (15.9 mm ± 7.9 mm), DES could not be implanted, even after predilatation. Diabetes was present in 19 patients (45 %). Sixty-one stents were used; 19 Cypher select™, 18 Taxus Liberté™, 10 CoStar™, 5 Endeavor RX™, 4 Xience V™. 3 Janus Carbostent™, 1 Yukon Choice S™, and 1 Axxion™ DES. The entire accessible surface area of these stents, in either the unexpanded and expanded state, were examined with an environmental scanning electron microscope (XL30 ESEM, Philips) to evaluate polymer or surface damage.
Results: The polymers of Taxus Liberte, Cypher Select, Xience V, CoStar, and Janus DES were only slightly damaged (less than 3% of surface area), whereas the Endeavor RX Stents showed up to 20% damaged surface area. In DES without a polymer (Yukon and Axxion), it could be shown that most of the stent surface (up to 40%) were without any layer of drug.
Conclusion: Placement of drug eluting stents in tortuous vessels and/or calcified lesions could cause major surface damage by scratching and scraping of the polymer or drug by the arterial wall, even before implantation. There were remarkable differences among the stents examined, only minor damage with the Cypher, Taxus Costar, Janus, and Xience V, whereas the Endeavor, the Yukon, and the Janus DES showed large areas of surface injury.

Catheterization and Cardiovascular Interventions 75:905–911 (2010)

Schmidt W, Behrens P, Schmitz K-P. Biomechanical Aspects of Potential Stent Malapposition at Coronary Stent Implantation, in: IFMBE Proceedings 2009

Abstract:

Despite of the clearly improved restenosis rates with drug-eluting stents (DES), optimization of stent deployment is still important for favourable immediate and longterm results. This requirement is fed by the recently reported potential risk of late stent thrombosis which is among other factors assumed to be caused by stent malapposition. Stent malapposition appears frequently in clinical practice for DES as well as bare-metal stents (BMS).
Our study investigated the biomechanical process of stent implantation by measuring stent/balloon profile during stent expansion, the remaining profile after balloon removal (elastic recoil), stent systems pressure-diameter characteristics (compliance) as well as the radial strength and stiffness of nine different modern BMS.
It was found that the elastic recoil (3.60 to 6.87%) and stent system compliance (0.95 to 2.29%/bar) were the most critical parameters with regard to stent malapposition. The stent profiles at nominal pressure varied within a range of -0.097 to +0.294 mm.
It is concluded that an accurate measurement of target vessel diameter as a basic criterion for selection of stent system is necessary as well as considering the compliance and elastic recoil data of the individual stent systems. Semi-compliant systems may cover a broader range of target diameters.

In: O Dössel, WC Schlegel (eds.): WC2009, IFMBE proceedings 25/XI, pp. 136 – 139, 2009.

W. Schmidt, P. Lanzer, P. Behrens, LD Topoleski, K.-P. Schmitz: A comparison of the mechanical performance characteristics of seven drug-eluting stent systems, Catheterization and Cardiovascular Intervention 2009

doi: 10.1002/ccd.21832

PMID: 19085917

Abstract:

Objectives: Mechanical properties of drug eluting stents (DES) will be measured to provide comparable numerical data to assess deliverability, and thus clinical performance.
Background: DES are routinely used in coronary interventions to reduce the rates of restenosis and target vessel revascularizations. Current research is primarily concerned with issues related to late stent thrombosis. However, mechanical properties of DES are a critical determinant of deliverability, and consequently the ultimate arbiter of their clinical performance.
Methods: Mechanical properties (pushability, trackability, crossability) were measured under standardized in-vitro conditions. The vessel models were derived from typical vessel anatomy but adapted to the individual tests. Additionally, profile and bending forces of the stent segment of the delivery system were measured. Seven different commercially available balloon-expandable coronary DES systems were included. All stents were 3.0 mm diameter with a stent length from 14 to 18 mm.
Results: The pushability expressed as the ratio of distal force at a specific proximal push force (4N) ranged between 38.66 and 18.53%. The trackability as the mean track-forces ranged from 0.551 N to 1.137 N. One stent system could not pass this test. The mean crossing forces at a 1.4 mm stenosis model ranged from 0.038 N up to 0.103 N. The mean crimped stent profiles ranged from 1.055 mm to 1.198 mm and the bending stiffness of the crimped stent was 17.22 to 47.20 Nmm².
Conclusion: Better understanding of mechanical properties of DES shall improve tactile skills of the interventionists during PCI and to improve criteria for DES selection in specific clinical settings.

Catheterization and Cardiovascular Intervention, 73 (2009), 350-360

Wissgott C, Schmidt W, Behrens P, Schmitz K-P, Andresen R: Vergleich mechanischer Eigenschaften von selbst expandierenden peripheren Stents, Fortschr. Röntgenstr., 2009

doi: 10.1055/s-0028-1109108

PMID: 19353486

Abstract:

Ziel: Es wurden selbst expandierende Nitinolstents untersucht, um deren Wandanpassung, Flexibilität und Radialfestigkeit zu vergleichen und Kennwerte für ihre Eignung in speziellen Gefäßprovinzen zu überprüfen.
Material und Methoden: Die In-vitro-Messungen wurden durchgeführt an Acculink, Zilverstent, Philon, Precise, Luminexx, SelfX und Sinus Super-Flex. Alle Stents hatten einen Durchmesser von 8 mm, waren 38 - 44 mm lang. Gemessen wurde Schiebbarkeit und Profil, die Radialkraft, die Biegesteifigkeit im expandierten Zustand sowie die Röntgensichtbarkeit. Die Wandanpassung wurde in einem s-förmig gekrümmten Gefäßmodell und einem Modell mit einer Durchmesseränderung von 5 auf 7 mm fotografisch dokumentiert. Bewertet wurde in der Krümmung der Wandabstand und die Durchmesserreduktion und im Stufenmodell der schnelle und harmonische Übergang.
Ergebnisse: Bei 7 mm Stentdurchmesser wurden radiale Kräfte von 1,09 (Sinus Super-Flex) bis zu 2,59 N (Philon) gemessen. Die Biegesteifigkeit der Stents betrug 11,7 (Acculink) bis 88,1 Nmm² (Luminexx). Eine gute Wandanpassung zeigten der Precise und Philon Stents, wobei der SelfX und Sinus Super-Flex Stent mit einer Durchmesserreduktion und größtem Wandabstand in der Gefäßkrümmung auffielen. Starke Änderungen des Gefäßquerschnittes wurden durch Stents mit kurzen Segmenten am schnellsten adaptiert (Acculink, Precise).
Schlussfolgerung: Die Anpassung eines Stents an ein gekrümmtes Gefäß oder Stufen im Gefäßquerschnitt ist vor allem von der Stentstruktur und nicht durch deren radiale Kräfte oder Steifigkeit bestimmt. Die festgestellten Unterschiede bei den untersuchten Stents können dem Anwender zur Auswahl des geeigneten Stents für bestimmte Gefäßregionen dienen.

Fortschr. Röntgenstr., 2009, DOI 10.1055/s-0028-1109108

Schmidt W., Schmitz, K.-P.: Devices. In: Mastering of Endovascular Techniques – A guide to excellence

In: Mastering of Endovascular Techniques – A guide to excellence (ed. P. Lanzer); Lippincott William & Wilkins; Philadelphia, 2006, 114 - 135

Ausgewählte Patente

Röhr U, Schmitz K-P, Schmidt W, Behrend D. Vorrichtung und Verfahren zum Prüfen der Dauerfestigkeit eines Medizinprodukts

Patent DE 10 2009 050 576 B4, 12.09.2013, erteilt

Schmitz KP, Behrens P, Schmidt W, Behrend D, Kaminsky J, Lootz D, Enzenross P: Anordnung und Verfahren zur Prüfung von Gefäßimplantaten

Patent DE 19903476.1

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