Clinical Results and Mechanical Properties of the Carotid CGUARD Double-Layered Embolic Prevention Stent

2016 ◽  
Vol 24 (1) ◽  
pp. 130-137 ◽  
Author(s):  
Christian Wissgott ◽  
Wolfram Schmidt ◽  
Christoph Brandt-Wunderlich ◽  
Peter Behrens ◽  
Reimer Andresen
Keyword(s):  
Mechanical Properties ◽  
Double Layer ◽  
Clinical Results ◽  
Radial Force ◽  
Bending Stiffness ◽  
Lesion Length ◽  
Collapse Pressure ◽  
Stent System ◽  
In Vitro Investigation

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: 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 open-cell 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. Conclusion: 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.

Revision characteristics of cement-augmented, cannulatedfenestrated pedicle screws in the osteoporotic vertebral body: a biomechanical in vitro investigation

2009 ◽  
Vol 11 (1) ◽  
pp. 23-27 ◽  
Author(s):  
Thomas R. Blattert ◽  
Stefan Glasmacher ◽  
Hans-Joachim Riesner ◽  
Christoph Josten
Keyword(s):  
Bone Tissue ◽  
Vertebral Body ◽  
Pedicle Screws ◽  
Clinical Results ◽  
Mineral Density ◽  
In Vitro Investigation ◽  
Human Cadaver Model ◽  
Surrounding Bone ◽  
Severe Grade

In generalized osteoporosis, instrumentation with cement-augmented pedicle screws is an amplification of the therapeutic spectrum. Early clinical results are promising for both solid and cannulated screws; however, there are concerns regarding the revision characteristics of these screws, especially for the cannulated-fenestrated type with its continuous cement interconnection from the core of the screw to surrounding bone tissue. In a human cadaver model, bone mineral density (BMD) was assessed radiographically. Spinal levels T9–L4 were instrumented left unilaterally, transpedicularly by using cannulated-fenestrated pedicle screws with the dimensions 6.5 × 45 mm. Polymethylmethacrylate cement (1.5 ml) was injected through the screws into each vertebra. After polymerization of the cement, the extraction torque was recorded. For both implantation and explantation of the screws, a fluoroscope was used to guarantee correct screw and cement positioning and to observe possible co-movements—that is, any movement of the cement mass within the vertebral body upon removal of the screw. For comparison, the extraction torque of same-dimension pedicle screws was recorded in a nonosteoporotic, non–cement-augmented instrumentation. The BMD was 0.60 g/cm2, a level that corresponds to a severe grade of osteoporosis. For removal of the screws, the median and mean extraction torques were 34 and 49 ± 44 Ncm, respectively. No co-movements of the cement mass occurred within the vertebral body. In the nonosteoporotic control, BMD was 1.38 g/cm2. The median and mean extraction torques were 123 and 124 ± 12 Ncm, respectively. Thus, the revision characteristics of cement-augmented, cannulated-fenestrated pedicle screws are not problematic, even in cases of severe osteoporosis. The winglike cement interconnection between the screw core and surrounding bone tissue is fragile enough to break off in the event of an extraction torque and to release the screw. There is no proof to support the theoretical fear that while trying to remove a screw, the composite of screw and cement would not break but instead would rotate as a whole in the osteoporotic vertebral body.

scholarly journals Degradation and erosion mechanisms of bioresorbable porous acellular vascular grafts: an in vitro investigation

2017 ◽  
Vol 14 (132) ◽  
pp. 20170102 ◽  
Author(s):  
Piyusha S. Gade ◽  
Keewon Lee ◽  
Blaise N. Pfaff ◽  
Yadong Wang ◽  
Anne M. Robertson
Keyword(s):  
Mechanical Properties ◽  
Mass Loss ◽  
Mechanistic Model ◽  
Vascular Grafts ◽  
Damage Function ◽  
Surface Erosion ◽  
Outer Diameter ◽  
In Vitro Investigation

A fundamental mechanism of in situ tissue regeneration from biodegradable synthetic acellular vascular grafts is the effective interplay between graft degradation, erosion and the production of extracellular matrix. In order to understand this crucial process of graft erosion and degradation, we conducted an in vitro investigation of grafts ( n = 4 at days 1, 4, 7, 10 each) exposed to enzymatic degradation. Herein, we provide constitutive relationships for mass loss and mechanical properties based on much-needed experimental data. Furthermore, we formulate a mathematical model to provide a physics-based framework for understanding graft erosion. A novel finding is that despite their porous nature, grafts lost mass exponentially via surface erosion demonstrating a 20% reduction in outer diameter and no significant change in apparent density. A diffusion based, concentration gradient-driven mechanistic model of mass loss through surface erosion was introduced which can be extended to an in vivo setting through the use of two degradation parameters. Furthermore, notably, mechanical properties of degrading grafts did not scale with mass loss. Thus, we introduced a damage function scaling a neo-Hookean model to describe mechanical properties of the degrading graft; a refinement to existing mass-dependent growth and remodelling (G&R) models. This framework can be used to improve accuracy of well-established G&R theories in biomechanics; tools that predict evolving structure–function relationships of neotissues and guide graft design.

scholarly journals In Vitro Degradation Behaviours of PDO Monofilament and Its Intravascular Stents with Braided Structure

2016 ◽  
Vol 16 (2) ◽  
pp. 80-89 ◽  
Author(s):  
Cong-er Wang ◽  
Pei-hua Zhang
Keyword(s):  
Mechanical Properties ◽  
Vascular Wall ◽  
Radial Force ◽  
Temporary Increase ◽  
Crystalline Region ◽  
Bending Rigidity ◽  
Intravascular Stents ◽  
Braided Structure ◽  
Intravascular Stent

Abstract Biodegradable intravascular stent has attracted more and more focus in recent years as an effective solution for angiostenosis. Ideal stents were expected to exhibit sufficient radial force to support the vascular wall, while suitable flexibility for the angioplasty. After vascular remodeling, stents should be degraded into small molecular and be eliminated from human body, causing no potential risk. In this paper, poly-p-dioxanone (PDO) monofilament was braided into net structure with four different braiding density, two of which exhibited sufficient radial force larger than 30 kPa, and three of which showed the bending rigidity within 11.7–88.1 N•mm2. The degradation behaviors of monofilaments and stents have been observed for 16 weeks. The findings obtained indicate that degradation first occurred in morphology region, which induced temporary increase of crystallinity, monofilament bending rigidity and stent mechanical properties. During this period, monofilament tends to be hard and brittle and lost its tensile properties. Then the crystalline region was degraded and stent mechanical properties decreased. All the results reveal that the PDO intravascular stents with braided structure were able to afford at least 10 weeks of sufficient support to the vascular wall.

scholarly journals Design and evaluation of nano-hydroxyapatite/poly(vinyl alcohol) hydrogels coated with poly(lactic-co-glycolic acid)/nano-hydroxyapatite/poly(vinyl alcohol) scaffolds for cartilage repair

2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Weiping Su ◽  
Yihe Hu ◽  
Min Zeng ◽  
Mingqing Li ◽  
Shaoru Lin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Double Layer ◽  
Cartilage Repair ◽  
Vinyl Alcohol ◽  
Glycolic Acid ◽  
Mechanical Load ◽  
Poly Vinyl Alcohol ◽  
Primary Role ◽  
Pva Hydrogel

Abstract Background Poly(vinyl alcohol) (PVA) hydrogels have been widely used in synthetic cartilage materials. However, limitations of PVA hydrogels such as poor biomechanics and limited cell ingrowth remain challenges in this field. Methods This work aimed to design novel nano-hydroxyapatite (nano-HA)/poly(vinyl alcohol) (PVA) hydrogels coated with a poly(lactic-co-glycolic acid) (PLGA)/nano-HA/PVA scaffold to counter the limitations of PVA hydrogels. The core, comprising nano-HA/PVA hydrogel, had the primary role of bearing the mechanical load. The peripheral structure, composed of PLGA/nano-HA/PVA, was designed to favor interaction with surrounding cartilage. Results The double-layer HA/PVA hydrogel coated with PLGA/HA/PVA scaffold was successfully prepared using a two-step molding method, and the mechanical properties and biocompatibility were characterized. The mechanical properties of the novel PLGA/HA/PVA scaffold modified HA/PVA hydrogel were similar to those of native cartilage and showed greater sensitivity to compressive stress than to tensile stress. Rabbit chondrocytes were seeded in the composites to assess the biocompatibility and practicability in vitro. The results showed that the peripheral component comprising 30 wt% PLGA/5 wt% HA/15 wt% PVA was most conducive to rabbit chondrocyte adhesion and proliferation. Conclusions The study indicated that the double-layer HA/PVA hydrogel coated with PLGA/HA/PVA scaffold has the potential for cartilage repair.

scholarly journals Structural Design of Mechanical Property for Biodegradable Polymeric Stent

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Yunbo Wei ◽  
Minjie Wang ◽  
Danyang Zhao ◽  
Hongxia Li ◽  
Yifei Jin
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Design Method ◽  
Ring Structure ◽  
Mechanical Tests ◽  
Radial Force ◽  
Element Analysis ◽  
Stent Expansion ◽  
Supporting Ring

How to improve stent mechanical properties is a key issue for designing biodegradable polymeric stents (BPSs). In this study, a new design method of BPS was proposed based on the force analysis of supporting rings and bridges during stent implantation, and a novel BPS called open C-shaped stent (OCS) with superior comprehensive mechanical properties was developed accordingly. The key mechanical properties including radial force, radial recoil, and axial foreshortening of the OCS have been comprehensively studied and compared with those of the Abbott BVS using finite element analysis (FEA). In addition, the effects of the stent geometries on these mechanical properties have also been discussed in detail. Besides, in vitro mechanical tests including stent expansion and planar compression experiments have been performed to verify the simulation results. Based on the FEA results, it is found that the radial force and radial recoil of the designed OCS are 30% higher and 24% lower than those of the BVS, respectively. Meanwhile, the OCS is not shortened during expansion. Radial force and radial recoil are mainly dependent on the supporting ring structure, and the utilization of designed unequal-height supporting ring (UHSR) can effectively improve these two properties. Axial foreshortening is mainly determined by the bridge geometry as well as the connecting position of the bridge with the adjacent supporting rings. It is feasible to improve the axial foreshortening by using the bridges with a curved structure and locating the connecting position in the middle of the straight section of the supporting elements. The rationality of the proposed OCS and the effectiveness of the finite element method have been verified by in vitro experiments.

scholarly journals Experimental evaluation of stent retrievers’ mechanical properties and effectiveness

2016 ◽  
Vol 9 (3) ◽  
pp. 257-263 ◽  
Author(s):  
Paolo Machi ◽  
Franck Jourdan ◽  
Dominique Ambard ◽  
Cedric Reynaud ◽  
Kyriakos Lobotesis ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Vessel Wall ◽  
Large Diameter ◽  
Mechanical Tests ◽  
Radial Force ◽  
Functional Tests ◽  
Clot Removal ◽  
Stent Retrievers ◽  
Thrombus Removal

BackgroundFive randomized controlled trials recently appeared in the literature demonstrating that early mechanical thrombectomy in patients with acute ischemic stroke is significantly related to an improved outcome. Stent retrievers are accepted as the most effective devices for intracranial thrombectomy.ObjectiveTo analyze the mechanical properties of stent retrievers, their behavior during retrieval, and interaction with different clots and to identify device features that might correlate with the effectiveness of thrombus removal.Materials and methodsAll stent retrievers available in France up to June 2015 were evaluated by mechanical and functional tests aimed at investigating the variation of their radial force and their behavior during retrieval. Devices were also tested during in vitro thrombectomies using white and red experimental thrombi produced with human blood. Functional tests and in vitro thrombectomies were conducted using a rigid 3D printed vascular model.ResultsMechanical tests showed a variation in radial force during retrieval for each stent. A constant radial force during retrieval was related to continuous cohesion over the vessel wall and a higher rate of clot removal efficacy. All stent retrievers failed when interacting with white large thrombi (diameter ≥6 mm).ConclusionsNone of the tested devices were effective in removing white clots of large diameter (≥6 mm). Constant radial force during retrieval allows constant cohesion to the vessel wall and pressure over the clot; such features allow for a higher rate of clot removal.

scholarly journals A realistic way to investigate the design, and mechanical properties of flow diverter stents

2021 ◽  
Author(s):  
Prasanth Velvaluri ◽  
Mariya Pravdivtseva ◽  
Johannes Hensler ◽  
Fritz Wodarg ◽  
Olav Jansen ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Flow Diverter ◽  
Radial Force ◽  
Cell Area ◽  
Flow Properties ◽  
4D Flow ◽  
Flow Mri ◽  
Mechanical Devices ◽  
First Time

Purpose: Braided flow diverters (FD) are highly sophisticated, delicate, and intricate mechanical devices used to treat intracranial aneurysms and thus saving lives. Testing such devices in vitro, however, remains an unsolved challenge. Here, we evaluate methods that access flow, design, and mechanical properties in vitro. Methods: Flow properties, cell porosity, and cell area were evaluated by placing FDs in patient-derived, 3D printed models of human vasculature. 4D flow MRI was used to measure fluid dynamics. Laser microscopy was used to measure porosity and cell area with the top of aneurysm sac cut off for the model. New testing methods were developed to investigate the bending, circumferential, and longitudinal radial force continuously over varying diameters. Results: The placement and flow properties of the FD in the vasculature models were successfully measured by MRI, although artifacts occurred. The setup to measure porosity and cell area inside of the model proved successful. The newly discussed methods allowed us to measure the indicated forces, to our knowledge for the first time, continuously. Conclusion: Modern and specifically tailored techniques, some of which were presented here for the first time, allow detailed insights into the flow and mechanical properties of braided flow diverter stents.

Initial Clinical Results and In Vitro Testing of the New CGuard MicroNet-Covered “One-Size-Fits-All” Carotid Stent

2019 ◽  
Vol 26 (4) ◽  
pp. 578-582 ◽  
Author(s):  
Christian Wissgott ◽  
Christoph Brandt-Wunderlich ◽  
Christoph Kopetsch ◽  
Wolfram Schmidt ◽  
Reimer Andresen
Keyword(s):  
Carotid Artery ◽  
Internal Carotid ◽  
Clinical Results ◽  
Covered Stent ◽  
Radial Force ◽  
Test Device ◽  
Maximum Expansion ◽  
Stent Length ◽  
The One

Purpose: To evaluate a MicroNet-covered stent designed for the carotid artery with the new ability to adjust to different vessel diameters. Materials and Methods: Thirty consecutive patients (mean age 72.1±7.7 years; 26 men) with symptomatic stenosis (86.3%±6.4%) of the internal carotid artery were treated with the new self-adjusting nitinol stent, which has a self-expanding, open-cell design covered by an outer conformable layer (MicroNet). The only stent used was the “One-Size-Fits-All” CGuard stent with lengths of 30 or 40 mm. In bench testing, the chronic outward force of the One-Size-Fits-All stent was determined with a segmented head radial force test device. The stent was deployed directly into the test device at a diameter of 5.0 mm, and the chronic outward force was measured up to 10.0 mm, the maximum expansion of the stent. Results: The stent was successfully implanted in all 30 patients without periprocedural complications, including no neurological events within 30 days. The chronic outward force normalized by stent length demonstrated a near-equivalent radial force outcome: The stent displayed only a minor difference between the minimal radial force at 9.0 mm (0.195 N/mm) and the maximal radial force at 5.5 mm (0.330 N/mm). Conclusion: The new self-adjusting, MicroNet-covered stent has high conformability combined with an almost equivalent radial force at expansion diameters ranging from 5.5 to 9.0 mm. The first clinical results demonstrate that the new One-Size-Fits-All stent can be safely implanted in internal carotid arteries with reference diameters within this range.

Mechanical Properties of a Biodegradable Balloon-expandable Stent From Poly(L-lactide) for Peripheral Vascular Applications

2006 ◽  
Vol 1 (1) ◽  
pp. 84-88 ◽  
Author(s):  
Niels Grabow ◽  
Carsten M. Bünger ◽  
Katrin Sternberg ◽  
Steffen Mews ◽  
Kathleen Schmohl ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Static Load ◽  
Buffer Solution ◽  
In Vitro Degradation ◽  
Collapse Pressure ◽  
Application Range ◽  
Solution Cast ◽  
Drug Incorporation

Background: Biodegradable polymeric stents represent a competitive approach to permanent and absorbable metallic stents for vascular applications. Despite major challenges resulting from the mechanical properties of polymeric biomaterials, these stent concepts gain their attraction from their intrinsic potential for controlled biodegradation and facile drug incorporation. This study demonstrates the mechanical properties of a novel balloon-expandable slotted tube stent from PLLA. Method of Approach: Polymeric balloon-expandable slotted tube stents (nominal dimensions: 6.0×25mm) were manufactured by laser machining of solution cast tubes (I.D.=2.8mm, d=270±20μm) from biodegradable (1) PLLA and (2) PLLA/PCL/TEC. The stents were tested in vitro for their mechanical properties: deployment, recoil, shortening, collapse, and creep behavior under a static load of 100mmHg. In vitro degradation was performed in Sørensen buffer solution at 37°C. After 0∕2∕4∕8∕12∕24 weeks the remaining collapse stability and molecular weight were assessed. Results: All stents could be deployed by balloon inflation to 8bar at 1bar∕min (PLLA) and 3bar∕min (PLLA/PCL/TEC). Recoil, shortening, and collapse pressure were: 2.4%∕3.4%∕0.67bar (PLLA), and 8.8%∕2.3%∕0.23bar (PLLA/PCL/TEC). A static load of 100mmHg induced pronounced creep processes in the PLLA/PCL/TEC stent. The PLLA stent remained patent and exhibited no creep propensity. During in vitro degradation an increase in collapse pressure was observed (maxima at 12w: 1.3bar (PLLA), 0.7bar (PLLA/PCL/TEC)). At 24 weeks, molecular weight was decreased by 28% (PLLA), and 52% (PLLA/PCL/TEC). Conclusions: Stents fabricated from pure PLLA exhibited adequate mechanical properties. The slow permissible deployment rate, however, limits their potential application range and demands further development.

scholarly journals Experimental in-vitro investigation on Epi-Off-Crosslinking on porcine corneas

PLoS ONE ◽  
2021 ◽  
Vol 16 (4) ◽  
pp. e0249949
Author(s):  
Federica Boschetti ◽  
Debora Conti ◽  
Elvira M. Soriano ◽  
Cosimo Mazzotta ◽  
Anna Pandolfi
Keyword(s):  
Exposure Time ◽  
Irradiation Dose ◽  
Shell Theory ◽  
Clinical Results ◽  
Quantitative Relation ◽  
Corneal Tissue ◽  
Pronounced Increase ◽  
In Vitro Investigation

Aim To evaluate quantitatively the effects of the Epi-Off-CXL irradiance dose on the stromal stiffening of pig corneas. Setting Laboratory of Biological structures (LaBS), Politecnico di Milano, Milano, Italy. Methods Inflation tests have been carried on 90 excised and de-epithelized pig corneas, monitoring the change of configuration of the corneal dome at specific pressures. Test have been carried out twice on each cornea, once before and once after Epi-Off-CXL performed at a constant irradiance of 9 mW/cm2 and variable UV-A exposure times. Corneas were grouped according to the exposure time (2.5, 5, 10, 15 and 20 min), proportional to the irradiation dose (1.35, 2.7, 5.4, 8.1, and 10.8 J/cm2). A theoretical model based on linearized shell theory has been used to estimate the increment of the corneal stiffness. Results The linearized shell theory allowed to establish a quantitative relation between the increment of the stiffness parameters and the irradiation dose. Relative to the pre-treatment values, in all experiments the post-treatment corneal stiffness revealed a pronounced increase. In general, the stiffness gain increased with the exposure time. No significant differences in stiffening was observed between tests conducted at 2.5, 5, and 10 min exposure. Conclusions Qualitatively, the effectiveness of accelerated CXL treatments observed in pig corneas complies very well with in-vivo clinical results in humans, suggesting that experimental data in pigs can be very useful for the design of the procedure in humans. A larger irradiation dose provides a larger increment of the corneal stiffness. Due to the biological variability of the tissues, however, it is difficult to distinguish quantitatively the level of the reinforcement induced by accelerated protocols (low doses with < = 10 min exposure), less prone to induce damage in the corneal tissue. Therefore, the definition of personalized treatments must be related to the actual biomechanics of the cornea.

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