Strain Recovery Research Articles

Amoeba plate test with Acanthamoeba castellanii as an innovative tool for Nocardia recovery from sputum samples: a proof-of-concept study.

The culture-proven diagnosis of Nocardiosis is challenging due to the difficulties in recovering Nocardia colonies from respiratory samples containing a complex polymicrobial flora. However, the isolation of Nocardia strains remains necessary to perform antibiotic susceptibility testing and adapt the antibiotic regimen of the patients. This study provides an innovative culture method based on a solid medium amoebic coculture, the amoeba plate test (APT), to cultivate Nocardia strains from clinical sputa samples. Nocardia grew across the APT amoebic monolayer. Moreover, the APT, which is already used in a reference center for the recovery of Legionella strains, exhibited good performances for Nocardia recovery and decontamination of interfering flora, thereby representing a promising second line tool to improve Nocardia culture.

Improving shape memory effect in Fe-Mn-Si-based alloys by reducing annealing twin boundaries through trace boron doping

Previous work has shown that the shape memory effect (SME) exhibited a strong negative dependence on the density of annealing twin boundaries (ATBs) in Fe-Mn-Si-based alloys. Reducing the density of ATBs has thus been an effective way to improve the SME of Fe-Mn-Si-based alloys. This study investigated the effects of trace B doping on the density of ATBs and the resultant SME in solution-treated Fe-Mn-Si-based alloys. Results indicated that doping 89 ppm B effectively reduced the density of ATBs in the solution-treated Fe-Mn-Si-based alloy. Consequently, its SME was remarkably improved. The maximum shape recovery strain reached 2.7 % in the B-doped alloy, 1.3 % higher than in the alloy without B doping. This work demonstrates a new avenue to improve the SME by doping trace B, which is of significance for the fabrication of Fe-Mn-Si-based shape memory alloys in a more cost-effective manner.

Minimally Invasive Transthoracic Intramyocardial Cellular Transplantation Under Echocardiographic Guidance for Myocardial Impairment

Abstract Objective: To explore the approach of minimally invasive transthoracic intramyocardial cellular transplantation under echocardiographic guidance to promote ischemic myocardial repair in a preclinical big-animal study. Methods: Female Guangxi Bama miniature pigs (weight: 25–30 kg) were randomly allocated into the sham group, untreated myocardial infarction (MI) group (MI group), the MI and surgical intramyocardial injection (SIM) group (MI-SIM group), and the MI and transthoracic echocardiography-guided percutaneous intramyocardial injection (TTEPIM) group (MI-TTEPIM group) (n = 4 each) using a lottery method. A swine MI model was established in the 3 groups excluding the sham group, and human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CM) labeled with the herpes simplex virus type-1 thymidine kinase reporter gene (hiPS-CMTK+) were transplanted by SIM in MI-SIM group and TTEPIM in MI-TTEPIM group. The operation time, postoperative recovery time of animals and volume of blood loss were collected for comparison between MI-SIM group and MI-TTEPIM group. 9-(4-[18F] fluoro-3-(hydroxymethyl) butyl) guanine positron emission tomography/computed tomography imaging was performed to track the hiPS-CMTK+ in vivo. Cardiac function and morphology were evaluated by echocardiography. Results: The operation time and postoperative recovery time of MI-TTEPIM group were significantly shorter than those of MI-SIM group ((28.3 ± 3.6) min vs. (97.0 ± 6.7) min, P < 0.001; (1.3 ± 0.3) d vs. (7.5 ± 0.9) d, P < 0.001). MI-TTEPIM also showed significantly lesser volume of blood loss during cell transplantation than MI-SIM group ((4.3 ± 0.8) mL vs. (47.0 ± 4.1) mL, P < 0.001). The transplanted cells could be traced more accurately in vivo in MI-TTEPIM than in MI-SIM. The circumferential strain of intervention region in the MI-TTEPIM group (–25.07% ± 0.27%) was significantly higher than that of the MI-SIM (–20.39% ± 0.67%) and MI groups (–19.68% ± 0.67%), respectively (P < 0.01). Conclusion: A minimally invasive TTEPIM protocol with stem cells for treating the ischemic myocardium was established in this study. Transplantation of hiPS-CMTK+ with this method could promote the recovery of the circumferential strain of the ischemic myocardium. The findings of this study lay a foundation for the clinical transformation of this auxiliary means of treatment in the future.

Effect of Compressive Strain Rates on Viscoelasticity and Water Content in Intact Porcine Stomach Wall Tissues.

Laparoscopic staplers are used extensively to seal and transect tissue. These devices compress tissue between the stapler jaws to achieve a desired compressed tissue thickness in preparation for stapling. The extent and rate of compression are dependent on surgeon technique, tissue characteristics, and stapler type, all of which can impact stapling outcomes such as bleeding, staple line leaks, and tissue healing. Historically, surgeons have relied on their experience, training, and tactile feedback from the device to optimize stapling. In recent years, the transition to electromechanical and robotic staplers has greatly impacted the tactile feedback available to the surgeon. This raises new questions about the optimal rates of tissue compression and the resultant tissue forces. This study quantifies the transmural biomechanics of the porcine stomach wall. Multi-rate indentation tests were used to observe the effects of indentation rate on the viscoelastic behavior of the stomach tissue during indentation, stress relaxation, and unconstrained recovery. Results show that the stomach wall demonstrates higher stress relaxation (88% vs 80%) and greater strain recovery (52% vs 47%) when indented at high rates (37.5%/s) vs slow rates (7.5%/s). Additionally, water content analysis was used to study fluid flow away from indented regions. Unindented regions were found to have greater water content compared to indented regions (78% compared to 75%). This data generated in this study may be used to enable the development of constitutive models of stomach tissue, which in turn may inform the control algorithms that drive compressive surgical devices.

Stereochemical Shape Morphing in Diels-Alder Polymer Networks.

The intrinsic reversibility of dynamic covalent bonding, such as the furan-maleimide Diels-Alder (DA) cycloaddition reactions, enables reprocessable, self-healing polymer materials that can be reconfigured via the mechanism of solid-state plasticity. In this work, the temperature-dependent exchange rates of stereochemically distinct endo and exo DA bonds are leveraged to achieve tunable, temperature- and stress-activated shape morphing in Diels-Alder polymer (DAP) networks. Through thermal annealing, ≈35% of endo DA isomers are converted in neat DAP networks to the thermodynamically favored exo form, achieving ≈97% exo after complete annealing at 60°C. This conversion results in a ≈1.7 fold increase in elastic modulus, from 1.7 to 3.0MPa, and significantly alters the stress relaxation and shape recovery behavior. Spatially resolved annealing, is further showcased enabling the precise control of spatial distributions of endo and exo DA bonds across planar geometries. The locally distinct concentrations of endo/exo isomers, achieved by temperature-induced conversion of endo DA isomers to the thermodynamically stable exo DA isomers, gave rise to the spatial distributions of stress relaxation rates and elastic strain recovery mismatch to enable controlled stereochemical shape morphing. This approach provides a simplified, thermally driven method for shape morphing, with potential applications in soft robotics and flexible electronics.

Natural cellulose reinforced multifunctional eutectogels for wearable sensors and epidermal electrodes

Wearable electronics significantly impact health monitoring, clinical care, and human-machine interfaces. Eutectogels, which utilize deep eutectic solvents (DES) address the drawbacks of hydrogels, such as weight loss and poor temperature tolerance, as well as the high costs and toxicities associated with ionogels. Despite these advances, most eutectogels serve only as sensors or epidermal electrodes and rarely fulfill both functions simultaneously. In this study, we present a multifunctional eutectogel designed to function in both ways. Incorporating natural cotton cellulose nanofibers as nanofillers reinforced the tensile strength of the resultant eutectogel by 7.47 times compared to that of the pure eutectogel, reaching 4.93 MPa. This eutectogel exhibited high ionic conductivity (1.22 S m−1), strong adhesion (1562.2 kPa to iron), self-healing ability (80.37% strain recovery and 80.53% tensile strength recovery), a broad temperature tolerance (−40 to 80 °C), and antibacterial properties. It demonstrates high sensitivity for the real-time strain detection of human activities and accurately captures electrophysiological signals, enabling the control of a small car. This versatile eutectogel has excellent potential for use in flexible wearable electronics.

The influence of plasticizer on the mechanical, structural, thermal and strain recovery properties following stress-relaxation process of silk fibroin/sodium alginate biocomposites for biomedical applications

The influence of plasticizer glycerol (GLY) on the mechanical, structural, and thermal properties of silk fibroin (SF)/sodium alginate (SA) biocomposite films was investigated in detail. As the SF/SA ratio increased up to 65%, the SF content significantly improved the Tensile strength (σT), Young's modulus (Ey) but reduced the elongation at break (εb). To modify and enhance the elasticity and flexibility of the biocomposite films, the GLY as a plasticizer was used at different ratio from 20 to 50% for each SF/SA biocomposite films. Although the extensibility of the films was improved greatly with increasing GLY ratio, σT and Ey reduced significantly. The effect was observed more apparently for the GLY ratio starting from 35%. It was also shown that crystallinity index in the Amide I region increased as the SF/SA ratio increased to 65%. Increasing SF content improved the thermal stability of the SF/SA biocomposites. The XRD results showed that crystallinity was increased as SF/SA ratio increased. Stress-relaxation of SF/SA (30%) biocomposite films plasticized with GLY revealed that each kind of plasticized films showed a viscoelastic behavior and a fast relaxation in the first stage (1–2 min) of the processes and then continued slowly. The GLY increased the extensibility and elasticity limit of the SF/SA (30%) composite films. During the strain recovery processes, the plasticized composite films recovered completely in a quite shorter time than that of unplasticized films. It was observed higher the GLY content, the recovery times became shorter.

Microstructure and properties of superelastic Ti-18Zr-15Nb alloy subjected to combination of moderate/severe cold drawing and post-deformation annealing

Ti-18Zr-15Nb (at%) shape memory alloy was subjected to a thermomechanical treatment (TMT), combining cold drawing (CD) with moderate (e = 0.5/1.1), and severe (e = 1.9/3.3) true strains, and post-deformation annealing (PDA) at 500–600 °C to fabricate a wire for medical application. The phase composition, microstructure, crystallographic texture, mechanical and functional properties were studied. The combination of cold drawing with true strain e = 0.5 and PDA at 550 °C for 5 min showed remnants of the original deformed grains, inside of which there is apparently a polygonized substructure, and a partially recrystallized structure of β-phase with a low amount of α-phase (grain size of D≈8 μm). With an increase in true strain, annealing temperature and holding time, a fully recrystallized structure and grain growth were observed. After TMT including the moderate cold drawing, a crystallographic texture with preferable orientation in the <101>β direction was formed. As true strain increases to e = 1.9/3.3, the preferable orientation changes to the <210>β direction; the intensity of this crystallographic texture increases as the true strain increases. Maximum difference between the dislocation and transformation yield stresses was observed after CD with true strain e = 1.1 and PDA at 550 °C for 30 min (Δσ ≈ 405 MPa). Elongation to failure about 20 % was observed after CD with a true strain of e = 0.5 and PDА at 600 °C for 30 min (D≈15 μm). During superelastic cyclic testing with 4 % applied strain after CD (e = 1.9–3.3) and PDA at 550 °C for 5–15 min (D≈1–3 μm) the alloy exhibits high values of superelastic (εrse ≈ 1,8–2,1 %) and total elastic+superelastic (εrel+se ≈ 3,3–3,5 %) recovery strains as well as sufficient maximum tensile stress (σmax ≈ 441–472 MPa), and accumulated residual strain (εacc ≈ 0.4–0.7 %).

Cohesive Living Bacterial Films with Tunable Mechanical Properties from Cell Surface Protein Display.

Engineered living materials (ELMs) constitute a novel class of functional materials that contain living organisms. The mechanical properties of many such systems are dominated by the polymeric matrices used to encapsulate the cellular components of the material, making it hard to tune the mechanical behavior through genetic manipulation. To address this issue, we have developed living materials in which mechanical properties are controlled by the cell-surface display of engineered proteins. Here, we show that engineered Esherichia coli cells outfitted with surface-displayed elastin-like proteins (ELPs, designated E6) grow into soft, cohesive bacterial films with biaxial moduli around 14 kPa. When subjected to bulge-testing, such films yielded at strains of approximately 10%. Introduction of a single cysteine residue near the exposed N-terminus of the ELP (to afford a protein designated CE6) increases the film modulus 3-fold to 44 kPa and eliminates the yielding behavior. When subjected to oscillatory stress, films prepared from E. coli strains bearing CE6 exhibit modest hysteresis and full strain recovery; in E6 films much more significant hysteresis and substantial plastic deformation are observed. CE6 films heal autonomously after damage, with the biaxial modulus fully restored after a few hours. This work establishes an approach to living materials with genetically programmable mechanical properties and a capacity for self-healing. Such materials may find application in biomanufacturing, biosensing, and bioremediation.

Mechanical Behaviors of Orthogonal Spiral Metal Skeleton–Polyurethane Elastomer Composites under Complex Loading Modes

Herein, a novel material design strategy is proposed: an interpenetrating composite composed of a woven orthogonal spiral metal skeleton and polyurethane (PU) elastomer. This interpenetrating composite combines rigidity and flexibility, exhibiting excellent elasticity and deformation recovery. The deformation behavior and mechanical properties of the composites under various loading conditions are investigated through experiments and numerical simulations. Different degrees of warping behaviors occur in composites with various structural parameters under uniaxial tension. Alternating rotations and double spiral arrangements can significantly limit the warping phenomenon, with a maximum reduction of 78%. The bending load capacity is regularly increased by increasing the wire diameter and decreasing the pitch. Increasing the number of loaded spiral wires enhances the bending load capacity of the composites. Uniaxial compression tests demonstrate that the composites have excellent load‐carrying capacity and strain recovery, with compressive strength 1.5 times that of pure PU. Cyclic compression tests further illustrate the excellent energy consumption capacity and stability of the composites. Overall, the introduction of orthogonal spiral skeletons into the composites demonstrates the potential to achieve enhanced load‐carrying capacity and large strain recovery simultaneously.

Preparation and Mechanical Properties Analysis of Rare Earth Filling Ethylene‐Allene Monomer Rubber Composite

AbstractEthylene propylene diene monomer (EPDM) rubber is used in critical sectors such as national defense, military, and aerospace. However, it has performance limitations under high temperatures, affecting its dynamic mechanical properties, creep, and stress relaxation. To overcome these limitations, rare earth cerium oxide (CeO2) was incorporated as a filler into EPDM in this study, which enhances its properties and makes it suitable for the demanding applications. It could be seen that the CeO2‐enriched EPDM has significantly improved mechanical characteristics at elevated temperatures. The Young's modulus of CeO2‐enriched EPDM increased by about 100 %, while the energy storage modulus reaches a maximum increase of around 140 % at 165 °C. The addition of CeO2 improves its damping properties, provides better creep and stress relaxation resistance, and results in greater residual strain recovery. At room temperature, the impact on the stress relaxation rate at 50 % strain is minimal for the material EPDM, and it is almost negligible for the material EPDM/CeO2.These findings demonstrate that CeO2‐enriched EPDM has enhanced performance under high‐temperature conditions. Under elevated temperature conditions, EPDM enriched with CeO2 exhibits enhanced mechanical properties, superior creep resistance, and stable stress relaxation behavior, rendering it more adept at withstanding the rigorous conditions encountered in aerospace applications.

Distinct interactions with pentaalanine tuned by terminal structures of polyisoprene that determine their mechanical properties

The terminal aggregates of natural rubber exhibit multi-scale reinforcing effects, but the synthetic counterpart still lacks of readily available terminal functionalized polymers, and the corresponding terminal structure-function correlation remains obscure. In this work, by utilizing commercial raw materials, four kinds of polyisoprene (PIP) derivatives with different terminal structures (PEO, ene-PEO, COOH, H) were prepared and blended with pentaalanine to investigated the change of terminal structures and impact on rubber performance. It is revealed that the tight hydrogen-bonded β-sheet in the terminal nanoconfinements is correlated to the overall performance of the elastomers. As the polarity of the terminal group of the main chain increases, the content of the β-sheet formed with 5A also increases, and the corresponding properties such as tensile strength, dimensional stability, strain recovery, apparent activation energy and cross-linking density are all enhanced. Among them, two elastomers (PIP-PEO, PIP-ene-PEO) have high tensile strength and great dimensional stability, which are comparable to Malaysian natural rubber. These results present the multi-scale reinforcement process of terminal H-bonding aggregates due to the synergistic changes and stable co-assembly of polar main chains and peptide, giving an inspiration for the development of large-scale, high strength and creep resistant synthetic elastomers.

Evaluation and comparison for higher temperature performance index of emulsified asphalt mastic using coal gangue powder

In order to investigate the rheological behavior and the influence of solid waste coal gangue powder on the high-temperature performance of cold recycled Emulsified Asphalt Mastics (EAM), Dynamic Shear Rheometer (DSR) and Multiple Stress Creep Recovery (MSCR) tests were conducted using three different fillers and four powder-to-binder ratios of EAM. Evaluation indexes such as rutting factor (G*/sinδ), improved rutting factor (G*/1−1/sinδ∙tanδ), Unrecoverable Creep Compliance (Jnr), Cumulative Strain (CS) and Creep Recovery Ratio (R) were used to analyze the influence of filler type and dosage on high temperature of EAM, and the effectiveness of these indexes to evaluate high temperature is considered. Moreover, atomic force microscopy experiments were carried out to study on interaction mechanism between the fillers and emulsified asphalt. Finally, grey relational analysis method was used for quantitative assessment of these indexes for EAM. The results indicate that all three fillers effectively improve the high-temperature performance, with a larger improvement observed as the filler dosage increases, among which the tunneling coal gangue powder is the most significant. Under a stress level of 0.1 KPa, the coal gangue filler mastic appears the best deformation recovery ability, whereas under a stress level of 3.2 KPa, the cement filler mastics appears the best deformation recovery ability. The additional fillers significantly influence the nano-scale surface morphology of the residues, and the tunneling coal gangue powder appears a stronger adsorption capacity for free polar components compared to the cement and limestone mineral powder. It is suggested that the Jnr and CS can be used as evaluation indexes of high temperature evaluation index of EAM, instead of G*/1−1/sinδ∙tanδ or G*/sinδ or R.

Microstructure, mechanical properties, and shape memory behavior of laser-directed energy deposited Co–20Fe–18Cr–19Mn high-entropy alloy

Laser additive manufacturing has become a powerful tool in modern production processes, and the additive manufacturing of Cantor-type high-entropy alloys has attracted considerable attention owing to its unique properties. In this study, we successfully utilized a laser-directed energy deposition (L-DED) process to fabricate a Co–20Fe–18Cr–19Mn, wt.% (Co40Fe20Cr20Mn20, at.%) alloy and analyzed its microstructure, room temperature mechanical properties, and shape memory effect. Microstructural analysis revealed a dense microstructure of the alloy. Before heat treatment, the alloy exhibited a microstructure consisting of both columnar and equiaxed dendrites with a hexagonal close-packed structure (HCP). However, post-treatment led to a completely different microstructure owing to recrystallization with a face-centered cubic (FCC) structure. Tensile testing results indicated a subtle anisotropy in the yielding, and after heat treatment, a significant enhancement in ductility was observed. A study of the shape memory effect demonstrated that the as-printed samples exhibited an FCC-HCP dual-phase structure, which transformed into an FCC single-phase structure after heat treatment. The application of external loading induced reformation of the HCP phase, successfully demonstrating the shape memory effect in the alloy, with a maximum recovery strain of 0.79 %.

Dual effects of pre-deformation and shape recovery process on martensitic transformation behavior in NiTi-Nb composite wire

The martensitic transformation behavior of NiTi-Nb composite wire following the pre-deformation and shape recovery (PD&SR) process was investigated. The wire drawing process significantly decreased the martensitic transformation start temperature (Ms) of NiTiNb alloy. Interestingly, the PD&SR process exhibited dual effects on the initial Ms temperature, depending on the annealing temperature. When the composite wire was annealed at higher temperature, the PD&SR process decreased the Ms temperature. In contrast, when the composite wire was annealed at lower temperature, the PD&SR process raised the Ms temperature. These dual effects can be attributed to the competition between the hindering effect of deformation dislocation and the promoting effect of stress coupling near the interface between the β-Nb phase and the NiTi matrix. At lower annealing temperature, the stress coupling generated by the β-Nb nanowires and the NiTi matrix is stronger, leading to an increase in the Ms temperature. Furthermore, the pre-deformation strain and shape recovery temperature influenced the dislocation density and the strength of stress coupling, thereby regulating the Ms temperature within a certain range.

Walking recovers cartilage compressive strain in vivo

BackgroundArticular cartilage is a fiber reinforced hydrated solid that serves a largely mechanical role of supporting load and enabling low friction joint articulation. Daily activities that load cartilage, lead to fluid exudation and compressive axial strain. To date, the only mechanism shown to recover this cartilage strain in vivo is unloading (e.g., lying supine). Based on recent work in cartilage explants, we hypothesized that loaded joint activity (walking) would also be capable of strain recovery in cartilage. MethodsEight asymptomatic young adults performed a fixed series of tasks, each of which was followed by magnetic resonance imaging to track changes in their knee cartilage thickness. The order of tasks was as follows: 1) stand for 30 ​min, 2) walk for 10 ​min, 3) stand for 30 ​min, and 4) lie supine for 50 ​min. The change in cartilage thickness was used to compute the axial cartilage strain. ResultsStanding produced an average axial strain of −5.1 ​% (compressive) in the tibiofemoral knee cartilage, while lying supine led to strain recovery. In agreement with our hypothesis, walking also led to cartilage strain recovery. Interestingly, the recovery rate during walking (0.19 ​% strain/min) was nearly 3-fold faster than lying supine (0.07 ​% strain/min). ConclusionsThis study represents the first in vivo demonstration that joint activity is capable of recovering compressive strain in cartilage. These findings indicate that joint activities such as walking may play a key role in maintaining and recovering cartilage strain, with implications for maintaining cartilage health and preventing or delaying cartilage degeneration.

Novel fracturing fluid made of low molecular weight polymer and surfactant achieves proppant full suspension and filling entire area of hydraulic fractures

In large-scale hydraulic fracturing of unconventional reservoirs, high viscosity friction reducers (HVFR) which employ high concentration polymers of high molecular weight can improve proppant suspension, but still lack long-distance and long-time proppant transport capability. Herein, for the first time, we report a fracturing fluid made of self- assembled low molecular weight polymer and a surfactant (LMPS). When using only 0.1 wt% of the polymer, LMPS has a viscosity of 29.6 mPa·s (170 s−1, 25 ℃) and can achieve full suspension of 40/70 mesh sand at 80 ℃. LMPS can form robust short molecular chain networks through numerous self-assembling association sites, rather than relying on entanglement. Notably, it achieves a minimum loss tangent as low as 0.1 in the viscoelastic response, demonstrating its strong elastic characteristics. According to the creep-recovery test, the strain recovery rate (87.9 %) of LMPS at 0.2 wt% polymer concentration far exceeds that of the HVFR with a concentration as high as 10.1 %. This indicates that LMPS has a stronger deformation-resisting ability, thereby preventing proppant settling. Taking advantage of LMPS’ superior proppant suspension capability, proppant can move with the slurry to the whole fracture for placement, while the HVFR provides only 48 % height support of the fractures in the form of dunes. A field trial shows that at a polymer concentration of 0.2 wt%, LMPS can stably transport 20/40 mesh quartz sand under a slurry rate of 2.8 m3/min and a proppant concentration of 635 kg/m3 during the fracturing process.

Comprehensive mapping of mechanical properties and martensitic transformation in Ti–Al–Mo standard ternary system: Integrating literature data and fabricating novel high-Al-content superelastic alloys

Titanium alloys are increasingly used as structural and functional materials owing to their exceptional properties. This study aimed to develop β-Ti shape memory alloys by creating a compositional map of the phase constitution and mechanical properties of the Ti–Al–Mo ternary system at room temperature, particularly near the α″+β phase region. Data for 95 alloy compositions were collected from the literature, and the composition region of Ti–(7–14) mol% Al–(3–7) mol% Mo, which has rarely been reported, was experimentally investigated. The phase constitution of Ti–Al–Mo alloys primarily depends on the Mo concentration; however, at Al concentrations of 10 mol% or higher, the β phase region expands. The yield stress was found to be minimal around 6 mol% Mo on the low-Al side, and this minimum shifted to lower Mo concentrations as the Al content increased, corresponding to the β/(α″+β) boundary. The ultimate tensile strength increased marginally in low-Mo compositions because of the twinning-induced plasticity effect, with the optimal composition near Ti–11 mol% Al–4 mol% Mo. Superelasticity was observed in high-Al regions, particularly in the Ti–11 mol% Al–6 mol% Mo alloy, which exhibited a superelastic recovery strain of 3.2 % and a total shape recovery strain of 6 %. These findings highlight the potential for developing new room temperature superelastic alloys in the Ti–(10–14) mol% [Al]eq–(5–6) mol% [Mo]eq composition region.

Surface and bulk viscoelastic stability of solvent-stored bulk-fill resin-based composite

ObjectiveInvestigate the effect of solvent-storage on surface hardness and bulk creep of fast photo-cured bulk-fill resin-based composite (RBC) compared to conventionally irradiated bulk-fill RBCs. MethodsThree bulk-fill RBCs were studied: Tetric® PowerFill (fast photo-cured bulk-fill RBC) (TPF), Tetric EvoCeram® (EVO), and GrandioSO® x-tra (GSOx) (conventional). Disk-shaped specimens of clinically realistic thickness (4 mm) were prepared from each material for: Group A: surface measurements (18 mm diameter) and Group B: 4 mm diameter for bulk compressive creep measurements. Group A disks were light-cured from the upper ‘occlusal’ surface for either 3 s or 20 s according to the manufacturer’s recommendation. Martens hardness (HM) of both top and bottom surfaces of each specimen were measured. Group B: 4 × 4 mm cylindrical specimens were fully cured to measure bulk creep (CB). A 20 MPa static compressive stress was applied for 2 h, followed by 2 h of unloading. Strain deformation was recorded continuously for 4 h. Both Martens and bulk creep studies were performed under the following storage conditions at 37 °C: (i) dry at 24 h post curing (baseline), and (ii) after 7 and 30 d of storage in two different media: distilled water (DW) and 75 % ethanol/water (75 % E/W). ResultsAt baseline, HM for all materials ranged from 587 to 439 N/mm2 (top) and 398 to 342 N/mm2 (bottom). After 30 d of solvent-storage, more pronounced HM changes were observed, with the bottom surface being more affected. Normalised HM for TPF decreased by 44 % after 30 d in 75 % E/W. Maximum creep strain ranged from 1.1 % to 2.1 % at baseline, and after 30 d in 75 % E/W this increased from 1.9 % to 2.9 %. Depending on the material and storage condition, the percentage creep strain recovery after 30 d ranged between 65.2 % and 80 %. Increased filler loading in the bulk-fill RBCs decreased the creep strain magnitude and increased the surface hardness. SignificanceSolvent storage decreased the Martens hardness of both upper and lower surfaces and increased the bulk creep characteristics of bulk-fill RBCs. Nevertheless, there was a similar relative stability in surface hardness and viscoelastic stability of fast-cured PowerFill compared to conventionally irradiated RBCs.

Ag-S coordination strategy for high recovery driving stress in recyclable shape memory polymers

To address the issue of low strength and recovery stress in recyclable shape memory polymer (SMP) materials with dynamic covalent bonds in practical applications, we propose a method based on Ag-S coordination interactions to improve dynamic covalent bonds, thereby preparing recyclable SMP with high recovery stress and large recovery strain. The introduction of in situ reduced silver nanoparticles (AgNPs) in the SMP system play multiple roles, serving as additional physical crosslinking points at the microscale and coordinating with disulfide bonds in the system to construct a multi-level dynamic network structure. This endows the material with exceptional mechanical properties (tensile strength of 25.93 MPa and fracture strain of 1466.83 %) and recovery driving stress (5.59 MPa), while maintaining more than 99 % shape recovery and fixity rate. Furthermore, due to the outstanding photothermal performance of AgNPs, the composite material has acquired remote photothermal driving capabilities. The proposed Ag-S coordination enhancement offers a new approach for SMP materials that achieve both large actuation distance and high recovery stress, holding significant potential for applications in soft robotics and actuators.