Strut Thickness Research Articles

Fabrication of Porous TiO2 with Aligned Pores Using Tert-Butyl Alcohol Based Freeze Casting

The effect of freezing conditions on the pore structure of porous TiO2 fabricated using a freeze casting process with tert-butyl alcohol slurry was investigated. The raw powder was heat treated to manufacture a porous body with stable shape by suppressing volume change induced by the phase transformation of TiO2 powder. The XRD analysis result indicated that the anatase phase fraction in the raw powder could be converted to 98.6% rutile phase by heating it at 800°C for 30 min. Porous TiO2 ceramics with unidirectionally aligned pore channels were prepared by freezing tert-butyl alcohol slurry containing 10 vol% TiO2 powder under different freezing temperatures of -20, -30 and -40°C, respectively. After removing the frozen tert-butyl alcohol by sublimation in vacuum, the green samples were sintered at 1100°C for 4 h in air. The porous body contains directional pores with a size of approximately 30 µm, and a hexagonal pore shape corresponding to the crystal structure of tert-butyl alcohol was observed in the cross-section of the pores. Small pores were observed at the bottom part of the porous body near the Cu plate where the solidification heat was released, but relatively large pores were present at the upper part. Both microstructure observation and pore size distribution indicated that the pore size and the strut thickness increased significantly with increasing freezing temperature. The change in pore characteristics was explained as being mainly due to the difference in the solidification behavior of the slurry and the rearrangement of the solid powder.

Comprehensive Geometric Parameterization and Computationally Efficient 3D Shape Matching Optimization of Realistic Stents

Abstract Flexible and compact shape representation schemes are essential for design optimization problems. Current shape representation schemes for coronary stent designs concern predominantly idealized or independent ring (IR) designs, which are outdated and only consider a small number of core design variables (such as strut width, height, and thickness) and ignore clinically critical design characteristics such as the number of connectors. No reports exist on the geometry parameterization of the latest helical stents (HS) that have more complex geometric designs than IR stents. Here, we present two new shape parameterization schemes to fully capture the 3D designs of contemporary IR and double-helix HS stents. We developed a 3D stent geometry builder based on 17 (IR) and 18 (HS) design variables, including strut width, thickness, height, number of connectors and rings, stent length, and strut centerline shape. The shape of the strut centerline was derived via a combination of NURBS, PARSEC, quarter circle, and straight line segments. Shape matching for complex 3D geometries, such as the contemporary stents within limited function evaluations, is not trivial and requires efficient parameterization and optimization algorithms. We used shape matching optimization with a limited function evaluation budget to test the proposed parameterization and two surrogate-assisted optimization algorithms relying on predictor believer and an expected improvement maximization formulation. The performance of these algorithms is objectively compared with a gradient-based optimization method to highlight their strengths. Our work paves the way for more realistic, full-fledged stent design optimization with structural and hemodynamic objectives in the future.

Additive manufactured 3D re-entrant auxetic structures for enhanced impact resistance

Abstract This study presents a novel exploration of the geometric parameters within a 3D re-entrant auxetic lattice structure, specifically focusing on their unique impact energy absorption properties, which were systematically evaluated through drop weight impactor testing. Each lattice configuration was additively manufactured using stereolithography, allowing for precise control over strut thickness (t), re-entrant angle (θ), and the aspect ratio (h/l) of unit cells during both low and high energy impact scenarios. This study found that the overall auxetic behavior is predominantly controlled by the aspect ratio of the cell ribs, while the modulus is governed by rib thickness. A finite element model was subsequently developed to simulate the experimental impact loading conditions and was used to examine a wider range of parameters that were not experimentally tested. The simulated dynamic test results displayed the deformation trends and changes to the Poisson's ratio. Among the studied parameters, experimental results highlighted that a lattice structure with t = 1.6 mm, θ = 65°, and a h/l ratio = 1.8 exhibited the highest specific energy absorption (SEA) under uniaxial impact deformation with 5 Joules of impact energy. Conversely, when employing 20 Joules of impact energy revealed the greatest SEA at t = 1.0 mm, θ = 65°, and an h/l ratio of 2.2. The results demonstrate unique deformation mechanism of auxetic structures under impact loading and the capacity to adapt the 3D re-entrant lattice structure for applications requiring tailored impact energy absorption.

Abstract 4120583: Long term Safety and Efficacy of Ultrathin Bioabsorbable polymer sirolimus eluting Stents Versus Thin Durable polymer everolimus eluting Stents in Patients Undergoing Percutaneous Coronary Intervention: A systematic review and meta analysis

Background: First generation drug eluting stents (DES) with thick polymers may contribute to local vascular inflammation and late stent thrombosis. Thinner-strut DES (ultrathin), particularly those with biodegradable polymers, aim to reduce this risk by minimizing flow disturbance and vascular injury. However, the long-term safety and efficacy of ultrathin biodegradable polymer sirolimus eluting stents (BP-SES) compared to durable polymer everolimus eluting stents (DP-EES) are still uncertain. Thus, we performed a meta analysis to compare outcomes of these two stents. Methods: Inclusion criteria comprised randomized controlled trials comparing ultrathin BP SES and thin DP EES in patients undergoing percutaneous coronary interventions with long term follow-up of at least 3 years. We excluded cohort studies, case reports, editorials, conference abstracts, and animal studies. Primary outcomes were target lesion failure (TLF), cardiac death (CD), target-vessel myocardial infarction (TV-MI), and clinically indicated target lesion revascularization (CI-TLR). We systematically searched PubMed, Cochrane CENTRAL, and Scopus. Cochrane’s ROB 2.0 tool assessed trial quality, and RevMan software (5.4) performed the meta-analysis. Results: Our analysis included ten RCTs, totaling 16,216 patients, with 9,108 in the BP SES group and 7,108 in the DP EES group. TLF occurred in 905 patients (9.94%) in the BP-SES group and 821 patients (11.55%) in the DP-EES group, with no statistically significant differences between the groups (RR = 0.92, 95% CI = 0.85 to 1.01, p = 0.08). Additionally, there were no significant differences in cardiac death (RR = 1.00, 95% CI = 0.84 to 1.19, p = 1.00), TV-MI (RR = 0.91, 95% CI = 0.78 to 1.05, p = 0.19), and CI-TLR (RR = 0.88, 95% CI = 0.78 to 1.01, p = 0.06) between the two groups. Conclusion: The use of BP-SES did not result in higher rates of TLF, CD, TV-MI, or CI-TLR compared to DP-DES. These findings suggest that both BP-SES and DP-DES are viable options for PCI procedures, with comparable long-term safety profiles. However, some trials used strut thicknesses exceeding 70µm in cases requiring wider diameters, similar to the strut thickness in the DP-EES group. This makes it challenging to assess whether, in addition to biodegradable polymers, lower strut thickness contributes to reducing target lesion-related events. Further research may be needed to explore other relevant outcomes and to confirm these findings in diverse patient populations.

Performance Assessment of an Electrostatic Filter-Diverter Stent Cerebrovascular Protection Device: Evaluation of a Range of Potential Electrostatic Fields Focusing on Small Particles.

Silent Brain Infarction (SBI) is increasingly recognized in patients with cardiac conditions, particularly Atrial Fibrillation (AF) in elderly patients and those undergoing Transcatheter Aortic Valve Implantation (TAVI). While these infarcts often go unnoticed due to a lack of acute symptoms, they are associated with a threefold increase in stroke risk and are considered a precursor to ischemic stroke. Moreover, accumulating evidence suggests that SBI may contribute to the development of dementia, depression, and cognitive decline, particularly in the elderly population. The burden of SBI is substantial, with studies showing that up to 11 million Americans may experience a silent stroke annually. In AF patients, silent brain infarcts are common and can lead to progressive brain damage, even in those receiving anticoagulation therapy. The use of cerebral embolic protection devices (CEPDs) during TAVI has been explored to mitigate the risk of stroke; however, their efficacy remains under debate. Despite advancements in TAVI technology, cerebrovascular events, including silent brain lesions, continue to pose significant challenges, underscoring the need for improved preventive strategies and therapeutic approaches. 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 atrial fibrillation, thromboembolism, or dislodged debris of varying potential TAVI patients. The study has been carried out in two stages. Both are based on computational fluid dynamics (CFD) coupled with the 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 flow rate waveforms characteristic of healthy and AF patients. Boundary conditions are calibrated to reproduce physiological flow rates 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 from 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: (1) while the smallest particles are deflected by electrostatic repulsion, avoiding micro embolisms, 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.

Diagnostic performance of CCTA and CTP imaging for clinically suspected in-stent restenosis: A meta-analysis

AimsThe objective of this study is to conduct a meta-analysis to assess the diagnostic performance of Coronary Computed Tomography Angiography (CCTA) and a hybrid approach that incorporates Computed Tomography Perfusion (CTP) in addition to CCTA (CCTA ​+ ​CTP) for the detection of in-stent restenosis (ISR), as defined by angiography. MethodsA comprehensive search of articles identified 18,513 studies. After removing duplicates, title/abstract screening, and full-text review, 17 CCTA and 3 CCTA ​+ ​CTP studies were included. Only studies using ≥64-slices multidetector computed tomography (CT) were considered eligible. ResultsThe per-patient ISR prevalence was 43 ​%, with 92 ​% of stents fully interpretable with CCTA. Meta-analysis exhibited a per-stent CCTA (n ​= ​2674) sensitivity of 90 ​% (95 ​% CI; 84–94 ​%), specificity of 89 ​% (95 ​% CI; 86–92 ​%), positive likelihood ratio of 7.17 (95 ​% CI; 5.24–9.61), negative likelihood ratio of 0.17 (95 ​% CI; 0.10–0.25), and diagnostic odds ratio of 45.7 (95 ​% CI; 22.71–82.43). Additional sensitivity analyses revealed no influence of stent diameter or strut thickness on the diagnostic yield of CCTA. The per-stent diagnostic performance of CCTA ​+ ​CTP (n ​= ​752) did not show differences compared to CCTA. ConclusionsWith currently utilized scanners, CCTA and CCTA ​+ ​CTP demonstrated high diagnostic performance for in-stent restenosis evaluation. Consequently, a history of previous stent implantation should not be an argument to preclude using these methods in clinically suspected patients.

Design method for individualised 3D printed lattice shoe midsoles

Additive manufacturing has enabled the production of individualised 3D printed shoe soles with improved properties. A promising approach is to use lattice structures that have high energy absorption properties and low weight. A design method of a cellular shoe midsole with optimised strut diameters of lattice structures is proposed. The shoe sole model is obtained by re-modelling a 3D scan of a foot to ensure a customised fit. The optimisation of strut thicknesses is based on a simplified stress distribution acting on the shoe sole during walking or running, using finite element simulations. Therefore, the optimal strut thickness for each region of the sole can be determined and adjusted. Two types of lattice structures with different topology and thus significant variations in stiffness are chosen, resulting in a wide range of required strut thicknesses. The developed design process allowed for the creation of a 3D printed shoe sole with improved strut thicknesses and a customised fit. The resulting cellular shoe soles are additively manufactured and experimental compressive tests are conducted to investigate the mechanical behaviour and differences between the shoe soles with the corresponding lattice types. The results show that both shoe soles have a similar behaviour under compression. The design tool developed has the potential to improve foot health and comfort, especially for people with foot problems, as all parameters affecting the performance of a shoe sole can be adjusted. However, more research is needed to fully understand the durability and performance of these shoe soles in real-world conditions.

Development of Kagome-based functionally graded beams optimized for flexural loadings

This study is concerned with the development of an innovative beam geometry based on a tessellation of Kagome unit cells and the improvement of its geometry with the aim of increasing its flexural properties. This aspect was achieved by generating a functionally graded metamaterial structure based on a novel approach that considers the well-established analytical beam theory models as the basis of for the optimization of the structural parameters of the unit cells at an individual level. The starting premise is that the optimal strut thickness variation with the height of the beam will cause the material to yield uniformly in the critical cross-section. Preliminary studies were conducted in order to numerically determine the variation of the stiffness and the strength of the Kagome structure with the thickness of its struts. Considering the equivalent stress distribution during bending in the critical cross-section, an optimal variation of the stiffness with the height of the beam was evaluated. Based on these results, different values for the strut diameter were imposed at corresponding coordinates relative to the neutral axis, assuring a continuous transition across the height of the beam. The flexural properties of the developed functionally graded structure were evaluated using finite element analyses and determined superior characteristics when compared with the data obtained from simulations performed on an uniform Kagome beam with of the same mass. The investigated structures were manufactured through stereolithography and subjected to three-point bending tests, the results being in agreement with the numerical data, thus validating the design.

Understanding the impact of nickel coating on the mechanical and corrosion behaviour of copper foams

ABSTRACT This study used a sponge replication technique to fabricate open-cell copper (Cu) foams with varying pore sizes. Nickel coating was applied via electrolysis to produce nickel-copper (NiCu) foams to enhance the Cu foams' energy absorption efficiency and corrosion resistance. The foams were characterized under static conditions to assess their compressive and corrosion properties. The nickel coating improved compressive strength by increasing foam strut thickness and reducing defects, as observed via scanning electron microscopy (SEM). The 10 Pores per inch (PPI) NiCu foam shows a substantial increase in compressive strength, close to 17.7%, compared to the 10 PPI Cu foam, resulting in a maximum compressive strength of 11.3 MPa. Similarly, 20PPI NiCu foam shows an increase of compressive strength of 20% when compared to 20 PPI Cu foam. NiCu foams significantly reduced corrosion current density compared to uncoated Cu foams, indicating enhanced corrosion protection from the nickel coating.

Numerical Analysis of Strut Thickness and Placement Effects on H-Darrieus Vertical-Axis Water Turbine

Numerical Analysis of Strut Thickness and Placement Effects on H-Darrieus Vertical-Axis Water Turbine

Effect of geometric defects on the mechanical properties of additive manufactured Ti6Al4V lattice structures

Lattice structures realized by additive manufacturing (AM) have the great potential for a broad range of engineering applications. However, the lattice structures are involved in geometric defects. This paper focuses the effect of geometric defects on the mechanical properties of Ti6Al4V lattice structures manufactured by laser powder bed fusion (L-PBF), three cell topologies, i.e., body centered cubic with vertical struts (BCCZ), face centered cubic with vertical struts (FCCZ), and face and body centered cubic with vertical struts (FBCCZ) were studied. X-ray computed tomography was used to extract the shape and the distribution of process-induced geometric defects of these three kinds of samples. Probability density distributions of geometric defects in each layer were also established to analyze the effect of the printing sequence on geometric defects. Then these distributions of geometric defects were inputted into Abaqus to build the modified statistical models to study the effect of geometric defects on mechanical properties. It is shown that the deviation of the cross-section radius exhibits normal distribution and the deviation of the center axis offset exhibits logarithmic distribution. And the middle layer of the sample has a better manufacturing precision. The modified statistical model can predict the mechanical properties within an error of 5 %. The strut thickness deviation had a more significant effect on the mechanical properties than the strut waviness.

Impact of Surface Finishing on Ti6Al4V Voronoi Additively Manufactured Structures: Morphology, Dimensional Deviation, and Mechanical Behavior

Additively manufactured medical devices require proper surface finishing before their use to remove partially adhered particles and provide adequate surface roughness. The literature widely investigates regular lattice structures—mainly scaffolds with small pores to enhance osseointegration; however, only a few studies have addressed the impact of surface finishing on the dimensional deviation and the global and local mechanical responses of lattice samples. Therefore, the current research investigates the impact of biomedical surface finishing (i.e., corundum sandblasting and zirconia sandblasting) on Voronoi lattice structures produced by laser powder bed fusion (LPBF) with large pores and different thicknesses on the surface morphology and global and local mechanical behaviors. MicroCT and SEM are performed for the assessment of dimensional mismatch and surface evaluation. The mechanical properties are investigated with 2D digital image correlation (DIC) in quasi-static compression tests to estimate the impact of surface finishes on local maps of strain. In the quasi-static tests, both the global mechanical performances, as expected, and local 2D DIC strain maps were mainly affected by the strut thickness, and the impact of different surface finishings was irrelevant; on the contrary, different surface finishing processes led to differences in the dimensional deviation depending on the strut thickness. These results are relevant for designing lattice structures with thin struts that are integrated into medical prostheses that undergo AM.

Experimental characterization of acoustic damping materials

AbstractDue to their ease of use and low cost, passive damping methods are a preferred mean for the reduction of noise in many engineering applications. This applies in particular to foam materials, which exhibit good acoustic and mechanical damping properties. The selection of suitable materials is usually carried out experimentally and can be very labor‐intensive and time‐consuming. For this reason, it is helpful to develop qualified numerical methodsthat can be used for material design and selection. Hence, foam materials must be characterized experimentally in order to enable a later comparison with vibroacoustic simulations. This contribution, therefore, aims at providing suitable parameters for the use in numerical analyses and their validation. Firstly, the microstructure of a foam specimen is captured by means of a CT scan. In addition to providing the geometry for the multi‐physics simulations, this measurement is also used to determine characteristic foam features, for example, strut thickness and pore size distribution. In the second step, the frequency‐dependent stiffness and damping properties of the material are determined by a special experimental setup utilizing an electrodynamic shaker. Here, the dynamic system is approximated as a single‐mass oscillator, which is sufficiently accurate for low frequencies. These properties will later be used in the numerical model to evaluate different parameter identification approaches. In the third and last step of the experimental campaign, measurements with an impedance tube are conducted to obtain the coefficient of absorption. This material parameter is particularly suitable for comparing experiments and simulations. Finally, the correlation between the experimental results is examined to provide a deeper understanding of the foam materials.

On the mechanical behavior of polymeric lattice structures fabricated by stereolithography 3D printing

AbstractThe utilization of 3D printing technology has transformed the possibilities for design adaptability and manufacturability. This study delves into the mechanical response and energy absorptivity of resin‐based lattice structures when subjected to compression, specifically examining structures fabricated from Tough 2000 (ductile) and Rigid 10K (brittle) resin materials using a stereolithography 3D printer. The analysis encompasses various types of lattice designs (such as cubic‐primitive, circular, triangular, and hexagonal), gradient structures, and combined shape configurations with varying strut dimensions. The primary objective is to provide significant findings regarding the compressive performance of these resin lattice structures produced through 3D printing. Analysis results show that graded and combined lattice designs have better compressive behavior compared to regular shapes with the same strut thickness. In addition, and for strut thickness of 0.5 mm, combined lattice designs show better energy absorption capabilities compared to regular shapes.

Vat photopolymerization of ultra-porous bioactive glass foams

The introduction of additive manufacturing technologies in the field of biomaterials science has opened new horizons for regenerative medicine. In this work, we pushed the potential of vat polymerization to the limit for fabricating ultra-porous bioactive SiO2-CaO-MgO-P2O5-CaF2-Na2O glass scaffolds with bone-like architectural characteristics. The tomographic reconstruction of an open-cell foam was used as input file to the printing system and reliably reproduced in all its exquisite details, as assessed by morphological analyses of sintered scaffolds (thickness of single struts 35 μm, exceptionally high porosity around 94 vol%, most pores with size from 500 to 900 μm). Immersion studies in simulated body fluid (SBF) revealed the apatite-forming ability (i.e., in vitro bioactivity) of the scaffolds, the surface of which started being coated by calcium phosphate after just 3 days from the beginning of the experiments. Taken together, these results show great promise for application of such scaffolds in bone defect repair.

Biocompatibility and Haemocompatibility Assessments of RBC with Polymeric Coated Cardiac Stent.

The current investigation was conducted to evaluate the biocompatibility and hemocompatibility of polymeric-coated cardiac stents. Coronary stents are typically small wire mesh tubes that are used to open arteries that are obstructed over time as a result of the buildup of fat, cholesterol, or other materials. A 10 milliliter isolated blood red blood cell was obtained using the Prozeta cobalt chromium coronary stent, which had the following specifications: stent length = 18 mm, strut thickness = 0.065 mm, expansion range = 2.25 mm to 4.00 mm, and burst pressure = 6ATM. Using an R&D coating equipment, polyethylene glycol (PEG) polymers were applied to the coronary stent. Assessments of the polymeric-coated cardiac stent’s biocompatibility and hemocompatibility were conducted using various evaluation criteria. CAD software has been used to help with the stent’s modeling. According to the supplied catalog, the strut’s thickness and width are calculated to be 0.065 mm and its length is 18 mm. The histology of RBC in an isolated sample (polymer coated on stent) found at 2000 Rx was examined using a motic microscope. Using a UV-visible spectrophotometer set to 414 wave length, a 10µg/ml solution of RBC in distilled water was scanned at 200–500 nm to measure the UV absorption maximum. The absorbance was found to be 0.8312 nm. An FTIR analysis of RBC reveals absorptions that include bending and stretching vibrations. Peak Position was discovered at wave numbers 3661.76, 1684.62, 1547.98, 1472.07, 1278.06, and 841.98. Using SEM the surface morphology of RBC was study and it was found the measurements 6.1, 4.2, 3.3, 3.2, 3.1, and 2.2 µm in diameter with standard error 0.548584. It has been determined that PEG-coated material demonstrated significant outcomes that resulted in coronary stent that was both biocompatible and hemocompatible of polymeric-coated cardiac stent, which is a step towards altering the treatment regimen.

Stochastic or deterministic: Duality of fatigue behaviour of 3D-printed meta-biomaterials

The two deformation modes of meta-biomaterials during cyclic loading have been revealed: stochastic and deterministic strut failure processes. Biomimetic Voronoi structures with a range of strut thicknesses and number of cells per unit volume are printed. We show that when the strut thickness is 200 μm or above, the fatigue fracture process of the lattice is deterministic and the fatigue scatters are below 15%. As the strut is thinned to 150 μm, the local failures occur randomly within the structure, which may lead to a high fatigue scatter (>30%). The two distinct behaviours result from the processing limit of the laser powder bed fusion technique. We demonstrate that the fatigue scatter and the location of the failure process within the lattice are related to the probability that a cluster of unconnected struts larger than a critical value can exist within the lattice. Unlike solid parts, porosity hardly triggers any damage in metallic lattices during cyclic deformation. The discovery of the Janus-like failure process opens up our understanding of meta-biomaterials and defines the pathway towards the design of mechanically durable intricate implants.

An investigation of PLLA hybrid stent design to overcome thick strut problems

Biodegradable polymer-based stents simultaneously provide scaffolding, drug release, and biodegradation to eliminate chronic inflammation. The most important factors hindering the wide use of these stents are thick struts, low radial strength, and large footprints formed on the inner wall of the artery as a result of stent expansion. Negative Poisson’s Ratio (NPR), also known as the Auxetic design, has shown great potential to provide radial strength with less strut thickness. However, a detailed mechanical evaluation proving improvement in stent performance parameters is not available in the literature. In this study, the performance parameters of two stent designs based on the Auxetic geometry with PLLA were analyzed under in-vivo conditions using an in-silico model consisting of the artery, crimper, and expander FE model. For this purpose, one design utilizes Auxetic unit cell, which is already available in the literature, while the other uses a newly proposed Hybrid design combining Auxetic and Chevron type geometries. Additionally, a specially heated coaxial balloon-catheter system was considered as a deployment tool between glass transition and body temperature, and carried out for thin-strut stent simulations. The Hybrid design is shown to resolve the foreshortening problem of Auxetic design and collapse pressure of commercial PLLA stents. In this present study validates the potential of Hybrid design to overcome problems for polymer-based biodegradable stents.

Methodology for Liquid Foam Templating of Hydrogel Foams: A Rheological and Tomographic Characterization

AbstractHydrogel foams are widely used in many applications such as biomaterials, cosmetics, foods, or agriculture. However, controlling precisely foam morphology (bubble size or shape, connectivity, wall and strut thicknesses, homogeneity) is required to optimize their properties. Therefore, a method is proposed here for generating, controlling, and characterizing the morphology of hydrogel foams from liquid foam templates: Using the example of Alginate‐CaHPO4‐based hydrogel foams, a highly controllable foaming process is provided by bubbling nitrogen through nozzles into the solution, which produces hydrogel foams with millimeter‐sized bubbles. A rheological characterization protocol of the foam's constituent material is first implemented and highlights the impact of the initial liquid foam properties and of the competition between the solidification kinetics and the foam aging mechanisms on the resulting morphology. X‐ray tomographic characterization performed on solidifying and solidified samples then demonstrates that by controlling the temporal evolution of the foam via its formulation, it is possible to tune the final morphology of the alginate foams. This method can be adapted to other hydrogel or polymer formulations, foam characteristics and length scales, as soon as solidification processes happen on timescales shorter than foam destabilization mechanisms.

Distribution and propagation of stress and strain in cube honeycombs as trabecular bone substitutes: Finite element model analysis

For designing trabecular (Tb) bone substitutes suffering from osteoporosis, finite element model (FEM) simulations were conducted on honeycombs (HCs) of 8 × 8 × 1 (2D) and 8 × 8 × 8 (3D) assemblies of cube cellular units consisting of 0.9 mm long Nylon® 66 (PA, Young's modulus E: 2.83 GPa) and polyethylene (PE, E: 1.1 GPa) right square prisms. Osteoporotic damage to the Tb bone was simulated by removing the inner vertical struts (pillars; the number of removed pillars: Δn ≤ 300) and by thinning the strut (thickness, d: 0.4–0.1 mm), while the six facade lattices were kept flawless. Uniform and uniaxial compressive loads on the HCs induced elastic deformation of the struts. The pillars held almost all the load, while the horizontal struts (beams) shared little. E for PA 3D HCs of all d smoothly decreased with Δn. PA 3D HCs of 0.2 mm struts deserved to be the substitutes for Tb bone, while PE 3D HCs of 0.05 mm struts were only for the Tb bone of the poorest bone quality. For the PA 3D HCs, the maximum von Mises stress (σM) first rapidly increased with Δn and showed a break at Δñ50, then gradually approached the yield stress of PA (50 MPa). Moreover, small portions of the stress were transferred from the façade pillars to the adjacent inner beams, especially those near the lost-pillar sites, denoted as X defects. The floor beams of thinner struts associated with the X-defects were lifted, and similar lifting effects in smaller amounts were propagated to the other floors. The 3DHCs of the thicker struts showed no such flexural deformations. The concept of force percolation through the remaining struts was proposed to interpret those mechanical behaviors of the HCs.