Strut Thickness Research Articles

Multi-objective crashworthiness optimization for a newly developed 3D re-entrant auxetic structure using response surface method and MOPSO algorithm

With the quick advancement of the vehicle industry, attention to automobile safety has increased. Crash boxes, which are placed in front of the side rails, play an essential role in preventing much damage to the front part of the car and also protecting passengers. Improving and optimizing these crash boxes’ energy absorption properties is necessary. In this study, a new structure of three-dimensional re-entrant auxetic has been presented for use as a crash box. Quasi-static uniaxial loading has been investigated experimentally and numerically. With the validation of the numerical simulation, the response surface method was implemented to investigate the value and type of different parameters’ effect on peak load and specific absorbed energy. Variables of the base and re-entrant strut thicknesses ( t1) and ( t2), the length of the base to re-entrant strut ( L/H), and the re-entrant angle ( θ) were considered in three levels. Through ANOVA analysis in Design-Expert software, it was found that the parameters t2 and θ had the highest effect on the peak load, energy absorption, specific energy absorption, and mean crashing force responses. With the increasing of t2 and θ, all responses increase and decrease, respectively. Also, multi-objective optimization based on minimum peak load and maximum specific energy absorption was performed by the desirability function method in Design-Expert software and the Multi-Objective Particle Swarm Optimization (MOPSO) algorithm. The proposed optimized structure exhibits enhanced energy absorption when compared to the optimized cylindrical auxetic structure and the thin-walled circular structure within the peak load range below 80 kN. Therefore, the proposed structure due to low peak load, uniformity collapse in the force-displacement diagrams, and stability of the structure during compression loading, can be used as the crash box.

Build parameter influence on strut thickness and mechanical performance in additively manufactured titanium lattice structures

Additively manufactured lattices have been adopted in applications ranging from medical implants to aerospace components. For solid AM components, the effect of build parameters has been well studied but comparably little attention has been paid to the influence of build parameters on lattice performance. For this project, the main aim was to evaluate static compressive mechanical performance of regular and stochastic lattices as a function of build parameters. The second aim was to compare strut dimensions of the metal lattice structures as build parameters were changed. Both regular and stochastic lattices were fabricated with a designed strut diameter of either 200 μm or 300 μm on a laser powder bed fusion machine. A range of laser power (140–180 W), scan speed (1700–2100 mm/s), and laser offset (0–45 μm) were used in fabricating each lattice. Compression tests were performed following the ISO 13314 (2011) standard to measure modulus, yield strength, and ultimate compressive strength values. Laser power adjustments produced the most significant effect on lattice performance. A change of 50 W resulted in roughly a 2X increase in maximum load and modulus for both regular and stochastic lattice structures. Regular lattice structures had a higher mechanical response during the mechanical evaluation. Internal strut diameters varied between build parameters as well, with laser offset adjustments producing the most noticeable change in strut geometry between lattice samples. These findings suggest that build parameter optimization, in lieu of using OEM parameters developed for solid structures, is necessary to ensure the optimum mechanical performance of AM lattice structures.

COMMERCIALLY PURE (CP-TI) TITANIUM MEDICAL IMPLANT PRODUCTION USING LASER POWDER BED FUSION (L-PBF) TECHNOLOGY

Decreasing the bulk weight without losing the biomechanical properties of commercial pure titanium (Cp-Ti) medical implants is now possible by using Laser Powder Bed Fusion (L-PBF) technology. Gyroid lattice structures that have precious mechanical and biological advantages because of similarity to trabecular bone. The aim of the study was to design and develop L-PBF process parameter optimization for manufacturing gyroid lattice Cp-Ti structures. The cleaning process was then optimized to remove the non-melted powder from the gyroid surface without mechanical loss.Gyroid cubic designs were created with various relative densities by nTopology. L-PBF process parameter optimization was progressed using with Cp-Ti (EOS TiCP Grade2) powder in the EOS M290 machine to achieve parts that have almost full dense and dimensional accuracy. The metallography method was made for density. Dimensional accuracy at gyroid wall thicknesses was investigated between designed and manufactured via stereomicroscope, also mechanical tests were applied with real time experiment and numerical analysis (ANSYS). Mass loss and strut thickness loss were investigated for chemical etching cleaning process.Gyroid parts had 99,5% density. High dimensional accuracy was achieved during L-PBF process parameters optimization. Final L-PBF parameters gave the highest 19% elongation and 427 MPa yield strength values at tensile test. Mechanical properties of gyroid were controlled with changing relative density. A minute chemical etching provided to remove non-melted powders.Compression test results of gyroids at numerical and real-time analysis gave unrelated while deformation behaviors were compatible with each other. Gyroid Cp-Ti osteosynthesis mini plates will be produced with final L-PBF process parameters. MTT cytotoxicity test will be characterized for cell viability.Acknowledgements This project is granted by TUBITAK (120N943). Feza Korkusuz MD is a member of the Turkish Academy of Sciences (TÜBA).

A process chain study for manufacturing nitinol stents

Nitinol is a commonly used alloy for manufacturing medical devices (i.e., stents). This study examines the process chain for manufacturing nitinol stents, focusing on the effects of laser cutting, heat treatment, and electropolishing processes on the stent’s final surface roughness, strut thickness, weight, and recoil. The laser cutting’s experimental results showed an optimal surface roughness (Ra) under 1.20 μm at 65% and 95% spot overlap, corresponding to feed rates of 300 mm/min and 749 mm/min, respectively. Heat treatment experiments on expanded stent samples revealed the lowest recoil of 0.78 mm achieved at 550°C for 720 s for 0.2 mm strut thickness. Electropolishing using 18V for 20 s provided the greatest reduction in surface roughness (Ra and Rz), along with a decrease in the weight and wall thickness. The results highlight the importance of optimizing process parameters to obtain desired surface quality, shape setting, and dimensional characteristics for functional nitinol stents. The research provides insights into enhancing the manufacturing of self-expanding nitinol stents for improved clinical outcomes.

Foam stability and thermo-mechanical properties of micro/nano filler loaded castor oil based flexible polyurethane foam

Use of fillers in polymers is to improve thermo-mechanical properties of the resulting material. Fillers are also used in polymeric foam as cell openers. Flexible polyurethane (PU) foams undergo major loss in structural stability when synthetic polyol is replaced with castor oil in the formulation as an alternate polyol. This study probes the effect of various micro and nano-fillers on PU foams prepared using blend polyol containing castor oil and synthetic polyol at a ratio of 1:1. Physical and cellular properties such as foam height, cell diameter, strut thickness and cell number density were evaluated to probe the structural stability of the foam. All foams prepared were found stable while it was found that the densities of the PU foams synthesized were greater than that of the conventional PU foams. Addition of fillers found to enhance thermal and mechanical properties of the foam. Moreover, all foam samples were found to observe thermal stability over and above 258 °C. Minimum glass transition temperature was recorded for 15% HG samples (i.e., −35.5 °C). Highest tensile strength was observed for 15% Si samples whereas, highest elongation was observed for 10% NC.

Comparison of the “Late Catch-Up” Phenomenon Between BuMA Supreme and XIENCE Stents Through Serial Optical Coherence Tomography at 1–2 Month and 2 Year Follow-Ups: A Multicenter Study

Objectives: This study was aimed at comparing the “late catch-up” phenomenon between the BuMA Supreme bioresorbable polymer sirolimus-eluting stent and the XIENCE stent through serial optical coherence tomography (OCT) at within 2 months and 2 year follow-ups. Methods: A total of 49 of 75 patients from the PIONEER-II study were enrolled in a 2 year OCT follow-up study; 44 patients with 50 lesions were included in the statistical analysis. The primary endpoints were neointimal thickness and late luminal loss (LLL) after stent implantation. Results: The stenosis diameter, and minimum in-stent or in-segment diameter, did not significantly differ between the BuMA Supreme and XIENCE arms at within 2 months and 2 year follow-ups. The strut neointimal coverage and thickness were greater in the BuMA group than the XIENCE group at the 1 and 2 month follow-ups (P = 0.044 and P = 0.010, respectively) but not at the 2 year OCT follow-up. Neither early luminal loss at the within 2 months follow-up (P = 0.849) nor LLL at the 2 year OCT follow-up (P = 0.613) showed differences between device arms. No significant differences in imaging and clinical endpoints were observed between device arms at follow-up. Conclusions: The BuMA Supreme stent’s faster re-endothelization with no “late catch-up” phenomenon has potential advantages over the XIECE stent for patients with coronary artery disease and high bleeding risk because it decreases the duration of dual antiplatelet therapy.

Long-term outcomes following ultrathin vs thin-strut drug-eluting stents for percutaneous coronary intervention: an updated systematic review and meta-analysis of randomized control trials.

Current thin-strut 2nd generation drug eluting stents (DES) are considered as optimal standard of care for revascularization of coronary artery disease (CAD) patients undergoing percutaneous coronary intervention (PCI). Ultrathin (≤ 70 μm strut thickness) strut DES have recently been shown to reduce target lesion failure (TLF) compared to thin-strut DES. Therefore, in order to assess the validity of improved outcomes associated with ultrathin-strut DES, we conducted an updated meta-analysis that includes recently published follow-ups of previously conducted randomized controlled trials (RCTs). MEDLINE and Scopus were queried from their inception to May 2024 to identify studies comparing outcomes between ultrathin and current thin-strut 2nd generation DES groups. A random-effects meta-analysis was conducted to derive risk ratios (RR) from dichotomous data. The primary endpoint was long-term TLF defined as a composite of cardiac death, target vessel myocardial infarction (TV-MI) and clinically driven target lesion revascularization (CD-TLR). The secondary outcome was target-vessel failure (TVF) defined as a composite of cardiac death, TV-MI and clinically driven target-vessel revascularization (CD-TVR). A total of 17 RCTs (n=22141) with a mean follow-up of 34 months were included. The risk of TLF was significantly lowered in the ultrathin DES group in comparison to thin-strut DES. A significant decrease was also noted in rates of TVF, CD-TLR and CD-TVR in the ultrathin DES vs thin-strut DES group. The results of our analysis demonstrate a significantly reduced risk of TLF in the ultrathin DES group in comparison with thin-strut DES. Ultrathin DES was also associated with a significantly decreased risk of TVF, CD-TLR and CD-TVR.

First-in-Human Evaluation of a Polymer-Free Everolimus-Eluting Stent Using a Titanium Dioxide Film.

In patients with coronary artery disease treated with permanent polymer-coated drug-eluting stents (DES), the persistent presence of a less biocompatible polymer might delay arterial healing. Thin strut polymer-free DES have the potential to improve clinical outcomes and reduce the duration of dual antiplatelet therapy (DAPT). The purpose of this first-in-human study was to assess the safety and effectiveness of a novel polymer-free DES in patients with de novo coronary lesions. The TIGERevolutioN® stent (CG Bio Co., Ltd., Seoul, Korea) consists of a cobalt chromium platform with a strut thickness of 70 μm and a surface treated with titanium dioxide onto which everolimus-eluting stent (EES) is applied abluminally (6 µg/mm of stent length) without utilization of a polymer. A total of 20 patients were enrolled, with de novo coronary lesions (stable or unstable angina) and > 50% diameter stenosis in a vessel 2.25 to 4.00 mm in diameter and ≤ 40 mm in length for angiographic, optical coherence tomography (OCT), and clinical assessment at 8 months. All patients received DAPT after stent implantation. The primary endpoint was angiographic in-stent late lumen loss (LLL) at 8 months. Twenty patients with 20 lesions were treated with TIGERevolutioN®. At 8 months, in-stent LLL was 0.7 ± 0.4 mm. On OCT, percent area stenosis was 29.2 ± 9.4% and stent strut coverage was complete in all lesions. No adverse cardiovascular event occurred at 8 months. The new polymer-free EES was safe and effective with low LLL and excellent strut coverage at 8 months of follow-up. Trial Registration: Clinical Research Information Service Identifier: KCT0005699.

Mechanical, electrochemical and permeability behaviour of Ti6Al–4V scaffolds fabricated by electron beam powder bed fusion for orthopedic implant applications: The role of cell type and cell size

Ti–6Al–4V scaffolds have attracted much attention for biomedical applications owing to their bone-mimicking mechanical properties and better bone tissue in-growth and additive manufacturing can be employed to fabricate complex geometry scaffolds. The present study aimed to investigate the effects of scaffold architecture on the mechanical, electrochemical, and permeability behaviour of Ti–6Al–4V scaffolds fabricated by electron beam powder bed fusion (EB-PBF). For this, scaffolds with diamond and rhombic dodecahedron cell types, having various cell sizes, were designed and successfully fabricated. Chemical etching minimized the surface defects and improved the geometric fidelity of the scaffolds compared to the original designs. The larger the cell size, the coarser the dual α/β phase microstructure due to the higher heat accumulation in thicker struts. The scaffold architecture proved significant effects on the mechanical properties, where all scaffolds were mechanically comparable with human bone. Short/long-term electrochemical corrosion tests indicated that the corrosion performance significantly improved with an increase in cell size, irrespective of the cell type; this was attributed to the lower exposure of surface area to the electrolyte, coarse microstructure and a higher fraction of β phase. This study recommended that the EB-PBF Ti–6Al–4V scaffolds are promising candidates for orthopaedic implant applications from mechanical and electrochemical points of view.

Mechanical analysis of radial performance in biodegradable polymeric vascular stents manufactured using micro-injection molding

Micro-injection molding (MiM) is a promising technique for manufacturing biodegradable polymeric vascular stents (BPVSs) at scale, in which a trapezoidal strut cross section is needed to ensure high-quality de-molding. However, there is a lack of research on the influence of the strut cross-sectional shape on its mechanical properties, posing a challenge in determining the key geometries of the strut when using MiM to produce BPVSs. Hence, this work has investigated the relationships between the geometry parameters, including the de-molding angle, and the radial support property of BPVSs using the finite element method. The results reveal that the radial stiffness of BPVSs is significantly affected by the de-molding angle, which can be counteracted by adjusting strut height, bending radius, and strut thickness. Stress distribution analysis underscores the crucial role of the curved portion of the support ring during compression, with the inner side of the curved region experiencing stress concentration. A mathematical model has been established to describe the relationships between the geometry parameters and the radial support property of the BPVSs. Notably, the radius of the neutral layer emerges as a key determinant of radial stiffness. This study is expected to serve as a guideline for the development of BPVSs that can be manufactured using MiM.

Framework for additive manufacturing of porous Inconel 718 for electrochemical applications

Porous electrodes were developed using laser powder bed fusion of Inconel 718 lattice structures and electrodeposition of a porous nickel catalytic layer. Laser energy densities of ∼83–333 J/m were used to fabricate ∼ 500 µm thick electrodes made of body centered cubic unit cells of 200–500 µm and strut thicknesses of 100–200 µm. Unit cells of 500 µm and strut thickness of 200 µm were identified as optimum. Despite small changes in feature sizes by the energy input, the porosity of >50 % and pore size of ∼ 100 µm did not change. In a subsequent step, we used nickel electrodeposition to create smaller scale pores on the electrode. The electrochemical performance of the electrodes for hydrogen/oxygen evolution reaction (HER/OER) was evaluated in a three-electrode setup. For HER, a much larger maximum current density of ∼−372 mA/cm2 at a less negative potential of ∼−0.4 V vs RHE (potential against reversible hydrogen electrode) was obtained in the nickel-coated samples, as compared to −240 mA/cm2 at ∼−0.6 V in the bare ones, indicating superior performance of the coated samples. Conversely, OER exhibited minor performance differences upon application of the coating, indicating insignificant dependence of OER to surface composition and available surface.

Experimental Investigation of the Effect of Bleed on the Aerodynamics of a Low-Pressure Compressor Stage in a Turbofan Engine

Abstract The compression system in modern turbofan engines is split into stages linked by transition ducts. Downstream of the low-pressure system, a handling bleed is often required and, in conjunction with structural vanes, can introduce component interactions, which compromise aerodynamic performance. In this paper, a fully annular, low-speed test facility incorporating a 1½ stage axial compressor is used to examine the flow in the last stage of a low-pressure compressor and the downstream transition duct. The transition duct incorporated load-bearing struts, including a so-called king strut with twice the thickness of the regular struts. The bleed utilized a 360-deg annular slot located on the casing immediately downstream of the low-pressure rotor and upstream of the outlet guide vane. The results showed that both the regular and king strut caused a similar flow distortion in the vane row but overall imposed a negligible effect on overall performance. The addition of bleed had a larger effect, generating an increasing outboard bias at the rotor exit as the bleed flow migrated toward the offtake. At the design operating point, the outlet guide vanes were relatively insensitive to this until the highest bleed rate (18%) where evidence of stall was observed. At a lower operating point, a modification to the rotor swirl caused additional incidence onto the vanes, resulting in an earlier onset of the stall; a full stall was observed above 10% bleed. Increasing bleed caused a gradual increase in duct loss up to stall when losses increased rapidly.

Improvement of Work-Hardening Behavior of Co-Cr-W-Ni Alloy by Adding Mn/Fe for Balloon-Expandable Stents

The Co-20Cr-15W-10Ni (CCWN, mass%) alloy, registered as American society of testing and materials (ASTM) F90, has been widely used as a balloon-expandable stent because of its excellent balance between its mechanical properties and corrosion resistance. To realize a less invasive stent placement, the stent diameter must be reduced, which implies that the stent strut thickness must be reduced. As such, the CCWN alloy must be high in strength and ductility while maintaining a low yield stress to facilitate the expansion and suppression of stent recoil. In this study, we focus on the effects of the adding Mn/Fe on the microstructure, mechanical properties, and corrosive properties of CCWN alloys. A 6 mass% Mn-added CCWN alloy with a grain size of approximately 20 μm prepared in this study exhibits excellent balance between tensile strength and ductility. In addition, it exhibits a lower yield stress while maintaining a high tensile strength compared with the ASTM F90 alloy. Meanwhile, a 6 mass% Fe-added CCWN alloy exhibits a higher ductility compared with the ASTM F90 alloy. The addition of Mn or Fe to the CCWN alloy increases the stacking fault energy of the alloy and suppresses strain-induced martensitic transformation during plastic deformation, thus improving the ductility of the alloy. Results of polarization tests show that the 6 mass% Mn-or Fe-added CCWN alloys exhibit the same corrosion current density as the ASTM F90 alloy. Mn-added Co-Cr-W-Ni alloys are suitable for use in balloon-expandable stents.

The effect of nodal connectivity and strut density within stochastic titanium scaffolds on osteogenesis.

Modern orthopaedic implants use lattice structures that act as 3D scaffolds to enhance bone growth into and around implants. Stochastic scaffolds are of particular interest as they mimic the architecture of trabecular bone and can combine isotropic properties and adjustable structure. The existing research mainly concentrates on controlling the mechanical and biological performance of periodic lattices by adjusting pore size and shape. Still, less is known on how we can control the performance of stochastic lattices through their design parameters: nodal connectivity, strut density and strut thickness. To elucidate this, four lattice structures were evaluated with varied strut densities and connectivity, hence different local geometry and mechanical properties: low apparent modulus, high apparent modulus, and two with near-identical modulus. Pre-osteoblast murine cells were seeded on scaffolds and cultured in vitro for 28days. Cell adhesion, proliferation and differentiation were evaluated. Additionally, the expression levels of key osteogenic biomarkers were used to assess the effect of each design parameter on the quality of newly formed tissue. The main finding was that increasing connectivity increased the rate of osteoblast maturation, tissue formation and mineralisation. In detail, doubling the connectivity, over fixed strut density, increased collagen type-I by 140%, increased osteopontin by 130% and osteocalcin by 110%. This was attributed to the increased number of acute angles formed by the numerous connected struts, which facilitated the organization of cells and accelerated the cell cycle. Overall, increasing connectivity and adjusting strut density is a novel technique to design stochastic structures which combine a broad range of biomimetic properties and rapid ossification.

Performance assessment of an electrostatic filter-diverter stent cerebrovascular protection device. Is it possible not to use anticoagulants in atrial fibrilation elderly patients?

Stroke is the second leading cause of death worldwide. Nearly two-thirds of strokes are produced by cardioembolisms, and half of cardioembolic strokes are triggered by Atrial Fibrillation (AF), the most common type of arrhythmia. A more recent cause of cardioembolisms is Transcatheter Aortic Valve Replacements (TAVRs), which may onset post-procedural adverse events such as stroke and Silent Brain Infarcts (SBIs), for which no definitive treatment exists, and which will only get worse as TAVRs are implanted in younger and lower risk patients. It is well known that some specific characteristics of elderly patients may lower the safety and efficacy of anticoagulation therapy, making it a real urgency to find alternative therapies. We propose a device consisting of a strut structure placed at the base of the treated artery to model the potential risk of cerebral embolisms caused by dislodged debris of varying sizes. This work analyzes a design based on a patented medical device, intended to block cardioembolisms from entering the cerebrovascular system, with a particular focus on AF, and potentially TAVR patients. The study has been carried out in two stages. Both of them based on computational fluid dynamics (CFD) coupled with Lagrangian particle tracking method. The first stage of the work evaluates a variety of strut thicknesses and inter-strut spacings, contrasting with the device-free baseline geometry. The analysis is carried out by imposing flowrate waveforms characteristic of both healthy and AF patients. Boundary conditions are calibrated to reproduce physiological flowrates and pressures in a patient's aortic arch. In the second stage, the optimal geometric design from the first stage was employed, with the addition of lateral struts to prevent the filtration of particles and electronegatively charged strut surfaces, studying the effect of electrical forces on the clots if they are considered charged. Flowrate boundary conditions were used to emulate both healthy and AF conditions. Results from numerical simulations coming form the first stage indicate that the device blocks particles of sizes larger than the inter-strut spacing. It was found that lateral strut space had the highest impact on efficacy. Based on the results of the second stage, deploying the electronegatively charged device in all three aortic arch arteries, the number of particles entering these arteries was reduced on average by 62.6% and 51.2%, for the healthy and diseased models respectively, matching or surpassing current oral anticoagulant efficacy. In conclusion, the device demonstrated a two-fold mechanism for filtering emboli: while the smallest particles are deflected by electrostatic repulsion, avoiding microembolisms, which could lead to cognitive impairment, the largest ones are mechanically filtered since they cannot fit in between the struts, effectively blocking the full range of particle sizes analyzed in this study. The device presented in this manuscript offers an anticoagulant-free method to prevent stroke and SBIs, imperative given the growing population of AF and elderly patients.

Comparison of endothelial shear stress between ultrathin strut bioresorbable polymer drug-eluting stent vs durable-polymer drug-eluting stent post-stent implantation: An optical coherence tomography substudy from BIOFLOW II

BackgroundRecent clinical data indicate a different performance of biodegradable polymer (BP)-drug eluting stent (DES) compared to durable polymer (DP)-DES. Whether this can be explained by a beneficial impact of BP-DES stent design on the local hemodynamic forces distribution remains unclear. ObjectivesTo compare endothelial shear stress (ESS) distribution after implantation of ultrathin (us) BP-DES and DP-DES and examine the association between ESS and neointimal thickness (NIT) distribution in the two devices at 9 months follow up. Methods and resultsWe retrospectively identified patients from the BIOFLOW II trial that had undergone OCT imaging. OCT data were utilized to reconstruct the surface of the stented segment at baseline and 9 months follow-up, simulate blood flow, and measure ESS and NIT in the stented segment. The patients were divided into 3 groups depending on whether DP-DES (N = 8, n = 56,160 sectors), BP-DES with a stent diameter of >3 mm (strut thickness of 80 μm, N = 6, n = 36,504 sectors), or BP-DES with a stent diameter of ≤3 mm (strut thickness of 60 μm, N = 8, n = 50,040 sectors) were used for treatment. The ESS, and NIT distribution and the association of these two variables were estimated and compared among the 3 groups. ResultsIn the DP-DES group mean NIT was 0.18 ± 0.17 mm and ESS 1.68 ± 1.66 Pa; for the BP-DES ≤3 mm group the NIT was 0.17 ± 0.11 mm and ESS 1.49 ± 1.24 Pa and for the BP-DES >3 mm group 0.20 ± 0.23 mm and 1.42 ± 1.24 Pa respectively (p < 0.001 for both NIT and ESS comparisons across groups). A negative correlation between NIT and baseline ESS was found, the correlation coefficient for all the stented segments was −0.33, p < 0.001. ConclusionIn this OCT sub-study of the BIOFLOW II trial, the NIT was statistically different between groups of patients treated with BP-DES and DP-DES. In addition, regions of low ESS were associated with increased NIT in all studied devices.

Optimal mechanical properties of Hydroxyapatite gradient Voronoi porous scaffolds for bone applications — A numerical study

Irregular Voronoi-based lattice (IVL) structures in tissue engineering (TE) have significant potential for bone regeneration. These scaffolds can mimic natural human bone interconnectivity by gradually altering strut thickness (ST) and seed point space (PS), which affects both mechanical and biological characteristics. This paper investigates the impact of design parameters, ST and PS, on Hydroxyapatite (HA) ILV structures’ mechanical properties (elastic modulus (E) and maximum compressive strength (MCS)) and geometrical characteristics (pore number, size, and distribution, surface area (SA), and surface area-to-volume ratio (SA/VR)). Four types of IVL scaffolds were designed; PC-TC (Constant PS-Constant ST), PC-TG (Constant PS-Gradient ST), PG-TC (Gradient PS-Constant ST), and PG-TG (Gradient PS-Gradient ST). The study, conducted through linear static structural finite element analysis (FEA) with maximum stress criteria, underscores the profound impact of irregularity and morphology on mechanical performance and geometrical features. Regarding SA and SA/VR, a comparison between PC-TC with other proposed scaffolds showed a minor improvement for PC-TG, while higher significant improvements were found for both PG-TG and PG-TC. In terms of pores distribution and number, no noticeable improvement was observed for the PC-TG scaffold compared to PC-TC. In contrast, PG-TC and PG-TG lattices demonstrated a variety of pore distributions and approximately doubled pore numbers. Studying mechanical properties, considering E and MCS, showcases substantial gains for PG-TC. It, however, revealed that for the rest of the scaffolds, no enhancement was observed regarding E. Based on these results, gradient PS proved to be more effective than gradient ST in enhancing mechanical performance and geometrical properties. Due to these improvements, this study holds promise for expediting bone regeneration and reducing postoperative complications in bone replacement applications.

Comparison among ultra-thin coronary stents: a network metanalysis

Abstract Background Ultrathin-struts drug eluting stents (DESs) have been related to potential improvement in stent-related outcomes compared to thicker-struts DES. However, comparison among different ultrathin devices are lacking. Methods All Randomized Controlled Trials (RCTs) comparing ultrathin (strut thickness &amp;lt; 70 µm) vs thicker struts DES in an all-comers population were included. Target lesion failure (TLF), as defined by included trials, at one year follow up was the primary endpoint. Cardiovascular (CV) death, myocardial infarction (MI), target lesion revascularization (TLR) and stent thrombosis (ST) were the secondary ones. Arms of included trials were compared by means of Network Meta Analysis (NMA). Results Nine studies encompassing 20081 patients were included: Orsiro DESs were evaluated in 7 arms with 8086 patients, MiStent in one arm (703 patients) and Supraflex in one arm with 720 patients. At one year follow up, no significant differences were noted for TLF. In particular, Orsiro was associated with similar risk of TLF compared with Supraflex (RR 1.7; CI 0.59 - 1.78) and with Xience (RR 0.98; CI 0.71 - 1.35), being the one with the highest probability of performing best. Orsiro stent was the one with the highest probability of performing best also for MI and TLR. Conclusions Ultrathin DES are all associated with a comparable risk of TLF as compared with second generation, thicker struts DES. As for the risk of repeat revascularization and of TLF, Orsiro was the one with the highest probability of performing best, either compared with other ultrathin DES or with thicker-struts devices.TLR: RRs among different devices

In-plane quasi-static compression deformation of Ti6Al4V double arrow-headed lattice structures fabricated by electron beam powder bed fusion process: Build orientation, scan speed and failure mechanism

The 2D double arrow-headed (DAH) lattice structures, which are promising cellular structures for impact mitigation, remain relatively unexplored in terms of their compression response when manufactured using the powder bed fusion process with Ti6Al4V (Ti64) alloy. This study aims to investigate the effects of build orientation and beam scan speed of Electron Beam Powder Bed Fusion (PBF-EB) process on the energy absorption of 2D Ti64 DAH lattice structures. Additionally, potential microstructural variations due to adjusted process parameters can be linked to different levels of energy absorption. For the compressions, the lattice structures were manufactured at two build orientations (0° and 45°), using three different beam scan speeds: speed function (SF), low speed (LS), high speed (HS). In micro-characterizations, the unit cells of 0deg-LS exhibited the lowest micro-porosity level at 0.12 %. Based on KAM values, thin struts at unit cells had higher residual stresses than thick struts, contributing to the initiation of failure locations. The compressions revealed that the 0deg-LS group absorbed 21.6 % and 24 % more energy than 0deg-SF and 0deg-HS groups, respectively, at compressions of 33 %. 45° samples absorbed approximately 10 % more energy than 0° samples except HS groups. The lowest micro-porosity of 0deg-LS contributed to having the highest energy absorption among 0deg samples. As the residual stresses in KAM values did not differ strongly with varying beam speed, varied energy absorptions were not linked to them. An optimization of the numerical compressions helped obtain designs with higher energy absorption and less relative volume. This study provides valuable insights into Ti64 cellular applications constrained with 2D-type designs.

An Innovative Stereolithography 3D Tubular Method for Ultrathin Polymeric Stent Manufacture: The Effect of Process Parameters.

In the last decades, researchers have been developing bioresorbable stents (BRS) to overcome the long-term complications of drug-eluting stents (DES). However, BRS technology still presents challenging limitations in terms of manufacturing, materials, or mechanical properties. At this juncture, companies have developed ultrathin DES that may further improve the efficacy and safety profile of traditional DES by reducing the risk of target-lesion and target-vessel failures until BRS are developed. Nonetheless, the metallic platform of ultrathin DES still presents problems related to their cellular response. The use of polymers as a permanent platform in DES has not previously been studied due to the limitations of current manufacturing technologies. In this work, an innovative manufacturing method for polymeric stent production using tubular stereolithography (SLA) technology is proposed both for BRS and for ultrathin polymeric DES. The effects of manufacturing process parameters were studied by modelling the outcomes (stent thickness and strut width) with the key manufacturing variables (exposure, resin volume, and number of layers). Two different laser setups were used to compare the results. Microscopy results proved the merit of this novel tubular SLA process, which was able to obtain stents with 70 μm strut width and thickness in barely 4 min using only 0.2 mL of resin. Differential Scanning Calorimetry (DSC) results showed the stability of the manufacturing method. The results obtained with this innovative technology are promising and overcome the limitations of other previously used and available technologies.