Polymeric Struts Research Articles

Thermally induced deformations in multi-layered polymeric struts

Stimulus activated structures that deform from a reference to target configurations are used in various fields such as soft robotics, smart materials, and actuators. Examples of stimuli include electric and magnetic fields, swelling, and temperature. The design of stimulus activated structures requires a comprehensive understanding of the relations between geometry, material properties, structure composition, and the influence of the chosen stimulus. With the aim of better understanding these relations, this work employs moderate rotations theory to model the thermo-mechanical response of multi-layered polymeric struts in a wide range of temperatures. In particular, the transition from a glassy to a rubbery state is explicitly discussed. Implicit equations that relate the material properties and the geometry to the thermally-induced deformation are developed. To illustrate the merit of the model, we investigate the thermo-mechanical behavior of homogeneous and heterogeneous multi-layered struts under two boundary conditions - free-standing and pinned. We show that multi-layered beams with a mismatch in the thermal and elastic properties bend as a result of temperature change. Interestingly, the glass-transition temperature can result in the reversal of bending direction. We follow with simulations of thermally-activated polymer-based bi-layer struts with typical properties to demonstrate the applicability of the proposed design. This framework can be used as a guideline and an inverse design tool for the selection of materials and geometries for thermally-activated shape-morphing lattice-based structures that are capable of achieving multiple shape-shifts with a single stimulus. Additionally, this work can be readily extended to other stimuli and thus serves as a foundation for the effective design of stimulus activated structures capable of polymorphism.

Polymeric endovascular strut and lumen detection algorithm for intracoronary optical coherence tomography images.

Polymeric endovascular implants are the next step in minimally invasive vascular interventions. As an alternative to traditional metallic drug-eluting stents, these often-erodible scaffolds present opportunities and challenges for patients and clinicians. Theoretically, as they resorb and are absorbed over time, they obviate the long-term complications of permanent implants, but in the short-term visualization and therefore positioning is problematic. Polymeric scaffolds can only be fully imaged using optical coherence tomography (OCT) imaging-they are relatively invisible via angiography-and segmentation of polymeric struts in OCT images is performed manually, a laborious and intractable procedure for large datasets. Traditional lumen detection methods using implant struts as boundary limits fail in images with polymeric implants. Therefore, it is necessary to develop an automated method to detect polymeric struts and luminal borders in OCT images; we present such a fully automated algorithm. Accuracy was validated using expert annotations on 1140 OCT images with a positive predictive value of 0.93 for strut detection and an R2 correlation coefficient of 0.94 between detected and expert-annotated lumen areas. The proposed algorithm allows for rapid, accurate, and automated detection of polymeric struts and the luminal border in OCT images.

Bioresorbable scaffolds in the treatment of coronary artery disease. Expert consensus statement of the Association of Cardiovascular Interventions of the Polish Cardiac Society (ACVI PCS)

Bioresorbable scaffold coated with antimitotic drug is the latest development in the coronary stents technology. The concept of temporary scaffolding and natural vessel healing after angioplasty is a very attractive alternative to conventional metal stents. The results of the first observational studies have confirmed their ultimate biodegradation. Newest results of randomised trials and registries in broader clinical and anatomical indications also revealed the limitations of the first generation of scaffolds. The relatively thick polymeric struts and compliance with specific implantation protocol may influence the results. In this document, the group of experts presents the current state of knowledge, with a particular focus on the advantages and limitations of the new technology; it presents practical guidelines for optimal implantation techniques and clarifies documented indications for patients and lesions selection.

Late Self-Apposition With One-Year Persisting Uncoverage of Malapposed Bioresorbable Polymeric Struts

Late Self-Apposition With One-Year Persisting Uncoverage of Malapposed Bioresorbable Polymeric Struts

Quantitative assessment of the stent/scaffold strut embedment analysis by optical coherence tomography.

The degree of stent/scaffold embedment could be a surrogate parameter of the vessel wall-stent/scaffold interaction and could have biological implications in the vascular response. We have developed a new specific software for the quantitative evaluation of embedment of struts by optical coherence tomography (OCT). In the present study, we described the algorithm of the embedment analysis and its reproducibility. The degree of embedment was evaluated as the ratio of the embedded part versus the whole strut height and subdivided into quartiles. The agreement and the inter- and intra-observer reproducibility were evaluated using the kappa and the interclass correlation coefficient (ICC). A total of 4 pullbacks of OCT images in 4 randomly selected coronary lesions with 3.0 × 18 mm devices [2 lesions with Absorb BVS and 2 lesions with XIENCE (both from Abbott Vascular, Santa Clara, CA, USA)] from Absorb Japan trial were evaluated by two investigators with QCU-CMS software version 4.69 (Leiden University Medical Center, Leiden, The Netherlands). Finally, 1481 polymeric struts in 174 cross-sections and 1415 metallic struts in 161 cross-sections were analyzed. Inter- and intra-observer reproducibility of quantitative measurements of embedment ratio and categorical assessment of embedment in Absorb BVS and XIENCE had excellent agreement with ICC ranging from 0.958 to 0.999 and kappa ranging from 0.850 to 0.980. The newly developed embedment software showed excellent reproducibility. Computer-assisted embedment analysis could be a feasible tool to assess the strut penetration into the vessel wall that could be a surrogate of acute injury caused by implantation of devices.

Determination of highly porous plastic foam structural characteristics by processing light microscopy images data

ABSTRACTMathematical modelling of physical and mechanical properties of plastic foam as well as numerous practical applications requires knowledge of foam structural characteristics. A necessity exists to determine the characteristics of the spatial structure of inhomogeneous materials comprising inclusions of other material, e.g., polyurethane foam without destructing the material and analysis of each element. A methodology is elaborated for preparing highly porous plastic foam specimens and investigation of foam strut‐like structure with light microscopy (LM) by taking images in three mutually perpendicular planes. A mathematical model is developed for highly porous plastic foam for the determination of probability density functions of its building elements—polymeric struts': (a) length and (b) angles, using LM images in three mutually perpendicular planes. Computer codes are created and parameters of distribution functions for strut's length and angles are calculated using experimental data for verification. A good correspondence of the modelling results with experimental data is proved to exist. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39477.

Head to head comparison of optical coherence tomography, intravascular ultrasound echogenicity and virtual histology for the detection of changes in polymeric struts over time: insights from the ABSORB trial

To analyse and to compare the changes in the various optical coherence tomography (OCT), echogenicity and intravascular ultrasound virtual histology (VH) of the everolimus-eluting bioresorbable scaffold (ABSORB) degradation parameters during the first 12 months after ABSORB implantation. In the ABSORB study, changes in the appearance of the ABSORB scaffold were monitored over time using various intracoronary imaging modalities. The scaffold struts exhibited a progressive change in their black core area by OCT, in their ultrasound derived grey level intensity quantified by echogenicity, and in their backscattering ultrasound signal, identified as "pseudo dense-calcium" (DC) by VH. From the ABSORB Cohort B trial 35 patients had paired OCT, echogenicity and VH assessment at baseline and at six- (n=18) or 12-months follow-up (n=17). Changes in OCT strut core area, hyperechogenicity and VH-derived DC were analysed and compared at the various time points. At six months, the change (median[IQR]) in OCT strut core area was -7.2% (-14.0-+0.9) (p=0.053), in hyperechogenicity -12.7% (-33.7-+1.4) (p=0.048) and VH-DC 22.1% (-10.8-+48.8) (p=0.102). At 12 months, all the imaging modalities showed a decrease in the various parameters considered (OCT: -12.2% [-17.5--1.9], p=0.093; hyperechogenicity -24.64% [-36.6--16.5], p=0.001; VH-DC: -24.66% [-32.0--7.0], p=0.071). However, the correlation between the relative changes in these parameters was statistically poor (Spearman's rho <0.4). OCT, echogenicity and VH were able to detect changes in the ABSORB scaffold struts, although the correlation between those changes was poor. This is likely due to the fact that each imaging modality interrogates different material properties on different length scales. Further studies are needed to explore these hypotheses.

Vascular Response of the Segments Adjacent to the Proximal and Distal Edges of the ABSORB Everolimus-Eluting Bioresorbable Vascular Scaffold: 6-Month and 1-Year Follow-Up Assessment: A Virtual Histology Intravascular Ultrasound Study From the First-in-Man ABSORB Cohort B Trial

This study sought to investigate in vivo the vascular response at the proximal and distal edges of the second-generation ABSORB everolimus-eluting bioresorbable vascular scaffold (BVS). The edge vascular response after implantation of the BVS has not been previously investigated. The ABSORB Cohort B trial enrolled 101 patients and was divided into B(1) (n = 45) and B(2) (n = 56) subgroups. The adjacent (5-mm) proximal and distal vessel segments to the implanted ABSORB BVS were investigated at either 6 months (B(1)) or 1 year (B(2)) with virtual histology intravascular ultrasound (VH-IVUS) imaging. At the 5-mm proximal edge, the only significant change was modest constrictive remodeling at 6 months (Δ vessel cross-sectional area: -1.80% [-3.18; 1.30], p < 0.05), with a tendency to regress at 1 year (Δ vessel cross-sectional area: -1.53% [-7.74; 2.48], p = 0.06). The relative change of the fibrotic and fibrofatty (FF) tissue areas at this segment were not statistically significant at either time point. At the 5-mm distal edge, a significant increase in the FF tissue of 43.32% [-19.90; 244.28], (p < 0.05) 1-year post-implantation was evident. The changes in dense calcium need to be interpreted with caution since the polymeric struts are detected as "pseudo" dense calcium structures with the VH-IVUS imaging modality. The vascular response up to 1 year after implantation of the ABSORB BVS demonstrated some degree of proximal edge constrictive remodeling and distal edge increase in FF tissue resulting in nonsignificant plaque progression with adaptive expansive remodeling. This morphological and tissue composition behavior appears to not significantly differ from the behavior of metallic drug-eluting stents at the same observational time points.

Evaluation of the Second Generation of a Bioresorbable Everolimus-Eluting Vascular Scaffold for the Treatment of De Novo Coronary Artery Stenosis: 12-Month Clinical and Imaging Outcomes

The first generation of the bioresorbable everolimus drug-eluting vascular scaffold showed signs of shrinkage at 6 months, which largely contributed to late luminal loss. Nevertheless, late luminal loss was less than that observed with bare metal stents. To maintain the mechanical integrity of the device up to 6 months, the scaffold design and manufacturing process of its polymer were modified.Quantitative coronary angiography, intravascular ultrasound with analysis of radiofrequency backscattering, and as an optional assessment, optical coherence tomography (OCT) were performed at baseline and at a 6-month follow-up. Forty-five patients successfully received a single bioresorbable everolimus drug-eluting vascular scaffold. One patient had postprocedural release of myocardial enzyme without Q-wave occurrence; 1 patient with OCT-diagnosed disruption of the scaffold caused by excessive postdilatation was treated 1 month later with a metallic drug-eluting stent. At follow-up, 3 patients declined recatheterization, 42 patients had quantitative coronary angiography, 37 had quantitative intravascular ultrasound, and 25 had OCT. Quantitative coronary angiography disclosed 1 edge restenosis (1 of 42; in-segment binary restenosis, 2.4%). At variance with the ultrasonic changes seen with the first generation of bioresorbable everolimus drug-eluting vascular scaffold at 6 months, the backscattering of the polymeric struts did not decrease over time, the scaffold area was reduced by only 2.0% with intravascular ultrasound, and no change was noted with OCT. On an intention-to-treat basis, the late lumen loss amounted to 0.19±0.18 mm with a limited relative decrease in minimal luminal area of 5.4% on intravascular ultrasound. OCT showed at follow-up that 96.8% of the struts were covered and that malapposition of at least 1 strut, initially observed in 12 scaffolds, was detected at follow-up in only 3 scaffolds. Mean neointimal growth measured by OCT between and on top of the polymeric struts equaled 1.25 mm(2), or 16.6% of the scaffold area.Modified manufacturing process of the polymer and geometric changes in the polymeric platform have substantially improved the medium-term performance of this new generation of drug-eluting scaffold to become comparable to those of current drug eluting stents.URL: http://clinicaltrials.gov. Unique identifier: NCT00856856.

Evaluation with in vivo optical coherence tomography and histology of the vascular effects of the everolimus-eluting bioresorbable vascular scaffold at two years following implantation in a healthy porcine coronary artery model: implications of pilot results for future pre-clinical studies

To quantify with in vivo OCT and histology, the device/vessel interaction after implantation of the bioresorbable vascular scaffold (BVS). We evaluated the area and thickness of the strut voids previously occupied by the polymeric struts, and the neointimal hyperplasia (NIH) area covering the endoluminal surface of the strut voids (NIHEV), as well as the NIH area occupying the space between the strut voids (NIHBV), in healthy porcine coronary arteries at 2, 3 and 4 years after implantation of the device. Twenty-two polymeric BVS were implanted in the coronary arteries of 11 healthy Yucatan minipigs that underwent OCT at 2, 3 and 4 years after implantation, immediately followed by euthanasia. The areas and thicknesses of 60 corresponding strut voids previously occupied by the polymeric struts and the size of 60 corresponding NIHEV and 49 NIHBV were evaluated with both OCT and histology by 2 independent observers, using a single quantitative analysis software for both techniques. At 3 and 4 years after implantation, the strut voids were no longer detectable by OCT or histology due to complete polymer resorption. However, analysis performed at 2 years still provided clear delineation of these structures, by both techniques. The median [ranges] areas of these strut voids were 0.04 [0.03–0.16] and 0.02 [0.01–0.07] mm2 by histology and OCT, respectively. The mean (±SD) thickness by histology and OCT was 220 ± 40 and 120 ± 20 μm, respectively. The median [ranges] NIHEV by histology and OCT was 0.07 [0.04–0.20] and 0.03 [0.01–0.08] mm2, while the mean (±SD) NIHBV by histology and OCT was 0.13 ± 0.07 and 0.10 ± 0.06 mm2. Our study indicates that in vivo OCT of the BVS provides correlated measurements of the same order of magnitude as histomorphometry, and is reproducible for the evaluation of certain vascular and device-related characteristics. However, histology systematically gives larger values for all the measured structures compared to OCT, at 2 years post implantation.

Preparation of the reticulated hydroxyapatite ceramics using carbon-coated polymeric sponge with elongated pores as a novel template

This paper proposes a novel, simple way to improve the compressive strength of reticulated porous hydroxyapatite (HA) ceramics using carbon-coated polymeric sponges with elongated pores as a novel template. This template allowed samples to have two interconnected pore networks with a preferential orientation, in which an addition pore network was newly formed by removing the carbon-coated polymeric struts, while preserving the pre-existing pore network. The compressive strength of the sample was as high as 2.9 ± 0.3 MPa with a porosity of 76% when tested parallel to the direction of pore elongation. In addition, the in vitro cell test using a pre-osteoblast cell line revealed the samples to have good biocompatibility.

Comparison between the first and second generation bioresorbable vascular scaffolds: a six month virtual histology study

To compare the intravascular ultrasound virtual histology (IVUS-VH) appearance of the polymeric struts of the first (Revision 1.0) and the second (Revision 1.1) generation bioresorbable vascular scaffold (BVS). IVUS-VH misrepresents polymeric struts as dense calcium (DC) and necrotic core (NC) so that their presence and disappearance could be used as potential artifactual surrogate of bioresorption. DC and NC were assessed in both revisions of the BVS by analysing IVUS-VH from all patients in the ABSORB cohort A (Revision 1.0) and cohort B (Revision 1.1) study who had an IVUS-VH post-treatment and at 6-month follow-up. Post-treatment and 6-month follow-up IVUS-VH results, available in 60 patients (BVS 1.0 n=28; BVS 1.1 n=32), indicated an insignificant rise in DC+NC area compared to baseline with Revision 1.1 (0.10 ± 0.46 mm2, p=0.2), whilst a significant reduction was seen with Revision 1.0 (-0.57 ± 1.3 mm2, p=0.02). A significant correlation has been found between the change in the DC+NC area and the change in external elastic membrane area (y=0.68x-0.1; r=0.58, p=0.03). Based on 6-months IVUS-VH analysis, the BVS 1.1 appears to have a different backscattering signal compared to the BVS 1.0, which may reflect differences in the speed of chemical and structural alteration.

Assessment of drug-eluting stents and bioresorbable stents by grayscale IVUS and IVUS-based imaging modalities

Grayscale IVUS and IVUS-based imaging modalities during the last years have become useful in the assessment not only of drug eluting stent, but also of new bioresorbable vascular scaffolds. Although IVUS resolution is not sufficient for determining stent coverage (optical coherence tomography is the gold standard), serial IVUS can measure intimal hyperplasia, assess acute and late incomplete stent apposition, detect the presence and persistence of edge dissections, study edge effects and look for causes of restenosis and thrombosis. In addition other IVUS-based imaging modalities, such as IVUS-VH, iMAP or palpography, can be used to study the serial compositional and mechanical changes of the plaque behind stent struts and also to follow the bioresorption of the new bioresorbable scaffolds, analyzing the backscattering signal coming from the polymeric struts. This review details and evaluates grayscale IVUS and IVUS-based techniques findings in clinical trials, highlighting the usefulness of these imaging modalities in the study of drug eluting stents and bioresorbable vascular scaffold.

Intracoronary Optical Coherence Tomography and Histology at 1 Month and 2, 3, and 4 Years After Implantation of Everolimus-Eluting Bioresorbable Vascular Scaffolds in a Porcine Coronary Artery Model

Background— With the use of optical coherence tomography (OCT), alterations of the reflectance characteristics of everolimus-eluting bioresorbable vascular scaffold (BVS) struts have been reported in humans. In the absence of histology, the interpretation of the appearances of the struts by OCT remains speculative. We therefore report OCT findings with corresponding histology in the porcine coronary artery model immediately after and at 28 days and 2, 3, and 4 years after BVS implantation. Methods and Results— Thirty-five polymeric BVS (3.0×12.0 mm) were singly implanted in the main coronary arteries of 17 pigs that underwent OCT and were then euthanized immediately (n=2), at 28 days (n=2), at 2 years (n=3), at 3 years (n=5), or at 4 years (n=5) after implantation. All BVS-implanted arteries in these animals were evaluated by histology except for 5 arteries examined at 2 years with gel permeation chromatography to assess the biodegradation of the polymeric device. Fourteen arteries with BVS from an additional 6 pigs were examined by gel permeation chromatography at 1 (n=1), 1.5 (n=2), and 3 (n=2) years. Corresponding OCT and histology images were selected with the distal and proximal radiopaque markers used as landmarks. At 28 days, by OCT, 82% of struts showed sharply defined, bright reflection borders, best described as a box-shaped appearance. Histologically, all struts appeared intact with no evidence of resorption. At 2 years, by OCT, 60±20 struts were discernible per BVS with 80.4% of the strut sites as a box-shaped appearance. Despite their defined appearance by OCT, by histology, these structures appeared to be composed of proteoglycan, with polymeric material being at such low level as to be no longer quantifiable by chromatography. At 3 years, by OCT, recognizable struts decreased to 28±9 struts per BVS: 43.7% showed dissolved black box; 34.8%, dissolved bright box; 16.1%, open box; and 5.4%, preserved box appearance. Histology shows that connective tissue cells within a proteoglycan-rich matrix replaced the areas previously occupied by the polymeric struts and coalesced into the arterial wall. At 4 years, by OCT, 10±6 struts were recognizable as either dissolved black or dissolved bright box. In histology, these struts are minimally discernible as foci of low-cellular-density connective tissue. Relative to the prediction of histological type by OCT appearance, the preserved box appearance of OCT corresponds well with 2-year histology (86.4%), whereas the dissolved bright and black box appearances correspond to 3-year histology (88.0% and 90.7%, respectively). Struts indiscernible by OCT correspond to the integrated strut footprints seen at 4 years (100%). Conclusions— Struts that are still discernible by OCT at 2 years are compatible with largely bioresorbed struts, as demonstrated by histological and gel permeation chromatography analysis. At 3 and 4 years, both OCT and histology confirm complete integration of the struts into the arterial wall.

Evaluation of the Second Generation of a Bioresorbable Everolimus Drug-Eluting Vascular Scaffold for Treatment of De Novo Coronary Artery Stenosis

Background— The first generation of the bioresorbable everolimus drug-eluting vascular scaffold showed signs of shrinkage at 6 months, which largely contributed to late luminal loss. Nevertheless, late luminal loss was less than that observed with bare metal stents. To maintain the mechanical integrity of the device up to 6 months, the scaffold design and manufacturing process of its polymer were modified. Methods and Results— Quantitative coronary angiography, intravascular ultrasound with analysis of radiofrequency backscattering, and as an optional assessment, optical coherence tomography (OCT) were performed at baseline and at a 6-month follow-up. Forty-five patients successfully received a single bioresorbable everolimus drug-eluting vascular scaffold. One patient had postprocedural release of myocardial enzyme without Q-wave occurrence; 1 patient with OCT-diagnosed disruption of the scaffold caused by excessive postdilatation was treated 1 month later with a metallic drug-eluting stent. At follow-up, 3 patients declined recatheterization, 42 patients had quantitative coronary angiography, 37 had quantitative intravascular ultrasound, and 25 had OCT. Quantitative coronary angiography disclosed 1 edge restenosis (1 of 42; in-segment binary restenosis, 2.4%). At variance with the ultrasonic changes seen with the first generation of bioresorbable everolimus drug-eluting vascular scaffold at 6 months, the backscattering of the polymeric struts did not decrease over time, the scaffold area was reduced by only 2.0% with intravascular ultrasound, and no change was noted with OCT. On an intention-to-treat basis, the late lumen loss amounted to 0.19±0.18 mm with a limited relative decrease in minimal luminal area of 5.4% on intravascular ultrasound. OCT showed at follow-up that 96.8% of the struts were covered and that malapposition of at least 1 strut, initially observed in 12 scaffolds, was detected at follow-up in only 3 scaffolds. Mean neointimal growth measured by OCT between and on top of the polymeric struts equaled 1.25 mm 2 , or 16.6% of the scaffold area. Conclusion— Modified manufacturing process of the polymer and geometric changes in the polymeric platform have substantially improved the medium-term performance of this new generation of drug-eluting scaffold to become comparable to those of current drug eluting stents. Clinical Trial Registration— URL: http://clinicaltrials.gov . Unique identifier: NCT00856856.

IVUS radiofrequency analysis in the evaluation of the polymeric struts of the bioabsorbable everolimus‐eluting device during the bioabsorption process

In the ABSORB study cohort A the changes in the amount of dense calcium and necrotic core have not been reported in comparison to the prestenting phase; this evaluation could be useful to better clarify the bioabsorption process. Aim of this study was therefore to evaluate the dynamic changes in plaque size and plaque tissue composition observed between 6 months and 2 years follow-up, and to compare these findings to the prestenting phase. Angiography, intravascular ultrasound and derived parameters (virtual histology, palpography, and echogenicity) were serially assessed postprocedure, at 6 months and at 2 years in 20 patients. In a subset of 8 patients the same measurements were also recorded in the prestenting phase. In the total population a reduction of 18% in the plaque area was observed between 6 month and 2 year follow-up (7.56 +/- 2.32 mm2 at 6 months vs. 6.16 +/- 2.10 mm2 at 2 year follow-up; P < 0.01). In the subgroup of eight patients who underwent IVUS during the pre-stenting phase, the plaque area at 2 year follow-up was not significantly different when compared to the prestenting plaque area (7.29 +/- 2.29 mm2 at prestenting vs. 7.48 +/- 1.45 mm2 at 2 year follow-up, P = NS). Necrotic core area was reduced by 24% between the 6 month and 2 year follow-up (0.97 +/- 0.66 mm2 at 6 months vs. 0.74 +/- 0.53 mm2 at 2 year follow-up; P = NS), whilst dense calcium was reduced by 14% from 6 month to 2 year follow-up (0.83 +/- 0.50 mm2 at 6 months vs 0.72 +/- 0.64 mm2 at 2 year follow-up; P = NS). Whilst the necrotic core at 2 years follow-up was not significantly different when compared to the pre-stenting phase (0.62 +/- 0.42 mm2 prestenting vs 1.07 +/- 0.56 mm2 at 2 year follow-up; P = NS), the area of dense calcium was significantly higher at follow-up compared to prestenting (0.35 +/- 0.35 mm2 pre-stenting vs. 0.84 +/- 0.66 mm2 at 2 year follow-up; P < 0.05). The reduction in the necrotic core component between 6 month and two year follow-up could be related to a synergistic effect of the bio-absorption process and the anti-inflammatory action of everolimus.

Assessment of the absorption process following bioabsorbable everolimus-eluting stent implantation: temporal changes in strain values and tissue composition using intravascular ultrasound radiofrequency data analysis A substudy of the ABSORB clinical trial

The main objective was to use IVUS-backscatter radiofrequency (IVUS-RF) to assess the degradation of a bioabsorbable stent by measuring serial changes in dense calcium (DC) and necrotic core (NC) as assessed by intravascular ultrasound-Virtual Histology (IVUS-VH) and in the strain as assessed by palpography. In the ABSORB trial, 27 patients treated with a single bioabsorbable everolimus-eluting stent (BVS, Abbott Vascular, Santa Clara, CA, USA) were all imaged with IVUS-RF post-stenting and at 6-month follow-up, and 13 and 12 patients were also investigated pre-stenting with IVUS-VH and palpography respectively. From pre- to post-stenting, with VH (n = 13), there was an increase in mean "DC" (9.8 vs. 25.4%, p = 0.0002) and "NC" (15.5 vs. 30.5%, p = 0.0002). In palpography (n = 12), the mean number of frames with Rotterdam Classification (ROC) III/IV per cm decreased from 1.22 +/- 1.91 to 0.12 +/- 0.31 (p = 0.0781) and the mean cumulative strain values (all frames with ROC I-IV scores) changed from 0.50 +/- 0.27 to 0.20 +/- 0.10% (p = 0.0034). Comparing post-stenting with follow-up (n = 27), VH showed a decrease in "DC" (29.7% vs. 21.1%, p = 0.0001). "NC" also decreased (26.9 vs. 21.5%, p = 0.0027). For palpography (n = 25 patients), an increase in the mean number of frames with ROC III/IV per cm was observed from 0.09 +/- 0.26 to 0.22 +/- 0.36 (p = -0.1563) while the mean cumulative strain values (all frames with ROC I-IV scores) changed from 0.15 +/- 0.10 to 0.26 +/- 0.12% (p < 0.0001). IVUS-VH changes at 6 months suggest alteration of the BVS with reduction of RF backscattering by polymeric struts. Strained plaques on the palpograms were almost abolished following stent implantation. However, strain values reappeared within 6 months suggesting an increase in endoluminal deformability of the stented vessel.

Improved compressive strength of reticulated porous zirconia using carbon coated polymeric sponge as novel template

Strong reticulated porous zirconia was fabricated using a carbon coated polymeric sponge as a novel template. In this technique, a polymeric sponge was first coated with a carbon black slurry, before coating it with the zirconia slurry. The introduction of the additional fugitive carbon coating layer was used to make the severely curved triangular polymeric struts more round, consequently producing large rounded triangular voids within the sintered zirconia struts. The fabricated sample showed a high compressive strength of 0.85 ± 0.13 MPa at 96% porosity, which was much higher than that of the sample fabricated without the carbon coating layer (0.47 ± 0.11 MPa). This enhancement was attributed not only to the elimination of the crack-like defects at the apices of the triangular voids, but also to the increased resistance against the strut bending caused by the larger voids within the zirconia struts.