Mechanical Response Properties Research Articles

Enhancement of protein mechanical stability: Correlated deformations are handcuffed by ligand binding.

As revealed by previous experiments, protein mechanical stability can be effectively regulated by ligand binding with the binding site distant from the force-bearing region. However, the mechanism for such long-range allosteric control of protein mechanics is still largely unknown. In this work, we use protein topology-based elastic network model (ENM) and all-atomic steered molecular dynamics (SMD) simulations to study the impact of ligand binding on protein mechanical stability in two systems, i.e., GB1 and CheY-binding P2-domain of CheA (CBDCheA). Both ENM and SMD results show that the ligand binding has considerable and negligible effects on the mechanical stability of these two proteins, respectively. These results are consistent with the experimental observations. A physical mechanism for the enhancement of protein mechanical stability was then proposed: the correlated deformations of the force-bearing region and the binding site are handcuffed by the binding of ligand. The handcuff effect suppresses the propagation of internal force in the force-bearing region, thus improving the resistance to the loading force. Our study indicates that ENM method can effectively identify the structure motifs allosterically related to the deformation in the force bearing region, as well as the force propagation pathway within the structure of the studied proteins. Hence, it should be helpful to understand the molecular origin of the different mechanical properties in response to ligand binding for GB1 and CBDCheA.

Nano-additive reinforcement of mixture epoxy syntactic foams

Carbon nanofibers (CNFs) and halloysite nanotubes (HNTs) were incorporated in syntactic foams containing a 90% by volume homogeneous mixture of (20/80 wt%) glass/thermoplastic microballoons to enhance the mechanical and impact response properties. Tensile, compressive, and impact tests were employed to comparatively characterize the effect of nano-additive reinforcement on mechanical response properties. Compressive strength and modulus enhancements as large as 39% and 18%, respectively, were achieved with a 0.125 wt% addition of CNF and increases of 61% and 7%, respectively, were achieved with a 0.125 wt% addition of HNT. Tensile strength and modulus enhancements as large as 107% and 68%, respectively, were achieved with a 0.125 wt% addition of CNF and increases of 104% and 70%, respectively, were achieved with a 0.125 wt% addition of HNT. Impact analysis data were used to show that measured peak force increased and build-up time to peak force decreased with increasing CNF or HNT weight percentage due to stiffening of the matrix. The smallest increase observed in peak force was 20% for a 0.125 wt% addition of CNF and 17% for a 0.125 wt% addition of HNT.

Abstract P5-07-13: Conceptual model of transdisciplinary science - Advocacy collaboration for the physical sciences and oncology: A case study focusing on breast density, biomarker discovery, and emerging therapeutics

Abstract BACKGROUND: What happens when you mix the foundations of tissue mechanics with advocacy? In a shared quest for exciting scientific frontiers, Bay Area physical scientists, clinical researchers, and advocates work in dynamic symbiotic relationships to integrate concepts drawn from their respective fields. Focusing on the mechanobiology of tumor progression in breast cancer, researchers and advocates are co-creating system change interventions for revamping convergent research processes. METHODS:As vital catalysts of transdisciplinary innovation, advocates affiliated with the National Cancer Institute (NCI) Physical Sciences and Oncology Network (PS-ON) applied core principles that synergize with the evolving disciplines of Implementation Science (IS) and the Science of Team Science (STS). Diverse methodologies to describe the intersections of physical sciences, breast density, biomarker discovery, emerging therapeutics and advocacy are presented. Additionally, we introduce a theoretical framework and conceptual puzzle illustrating multimethod science advocacy engagement strategies, a typology of contextual factors influencing collaboration, as well as the antecedents, processes, strategic priorities, and overall potential impacts of collaborative transdisciplinary science advocacy exchanges. RESULTS:Through proactive participation in four areas: 1) research and programmatic support, 2) education and outreach, 3) policy and strategy, and 4) representation and advisory, advocates, representing patient/consumer perspectives, worked toward a common set of goals with researchers and clinicians in determining how tumor microenvironments regulate cancer initiation and behavior through interactions among cell types (e.g., initiated cells, activated stromal cells, and components of the extracellular matrix). Applying NCI Office of Advocacy Relations (OAR) and NCI PS-ON Advocacy Working Group goals for strategic innovation, collaborative execution, and ethical codes of conduct, researchers and advocates codeveloped guiding conceptual frameworks based on organizational foundations, systems readiness, leadership commitment to change, and transdisciplinary levers to promote shared governance, bidirectional collaboration, advocacy inclusion, and the prioritization of research addressing questions of importance to patients. DISCUSSION: Embedding advocate patient/consumer evidentiary and experiential insights/perspectives regarding mechanics-directed research priorities and clinical interventions in the early phase of convergent research efforts contributes to our understanding of the important role of the physical organization in cell-to-cell contacts, tissue architecture, tumor microenviroments, and mechanical properties in response to therapy. Notably, catalyzing and leveraging advocate engagement across the research continuum provides novel opportunities for advancing institutional changes, spurring unique training/mentoring exchanges, and fostering innovative research and translational opportunities. Citation Format: Samson S, Northey JJ, Baas C, Weaver VM. Conceptual model of transdisciplinary science - Advocacy collaboration for the physical sciences and oncology: A case study focusing on breast density, biomarker discovery, and emerging therapeutics [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-07-13.

Magnetorheology of alginate ferrogels

Magnetorheological (MR) effect is a phenomenon typical of suspensions of magnetizable particles in a liquid carrier, characterized by strong changes of their mechanical properties in response to applied magnetic fields. Its origin is on the migration of magnetized particles and their aggregation into chain-like structures. However, for ferrogels, consisting of dispersions of magnetic particles in a polymer matrix, migration of particles is hindered by the elastic forces of the polymer network, preventing from strong MR effect. Interestingly, in this manuscript, we demonstrate that strong MR effect in robustly cross-linked polymer ferrogels is still possible. Experimental results showed enhancement of the storage modulus of more than one order of magnitude for alginate ferrogels containing less than about 10 vol% of iron particles under moderate magnetic fields. The differential feature of these ferrogels is that, instead of individual particles, the disperse phase consisted of large clusters of iron microparticles homogeneously distributed within the polymer networks. These clusters of magnetic particles were formed at the stage of the preparation of the ferrogels and their presence within the polymer networks had two main consequences. First, the volume fraction of clusters was considerably larger than this of individual particles, resulting in a larger effective volume fraction of solids. Second, since the force of magnetic attraction between magnetic bodies is roughly proportional to the cube of the body size, the existence of such clusters favored inter-cluster interaction under a magnetic field and the appearance of strong MR effect. On this basis, we demonstrated by theoretical modeling that the strong MR effect displayed by the alginate ferrogels of the present work can be quantitatively explained by assuming the existence of large, roughly spherical particle aggregates formed at the stage of the preparation of the ferrogels. Our theoretical model provides a reasonable quantitative prediction of the experimental results.

Loss of the PTH/PTHrP receptor along the osteoblast lineage limits the anabolic response to exercise.

Exercise and physical activity are critical to maintain bone mass and strength throughout life. Both exercise and physical activity subject bone to a unique combination of stimuli in the forms of dynamic loading and a systemic increase in parathyroid hormone (PTH). Although dynamic loading is considered to be the primary osteogenic stimuli, the influence of increasing PTH levels remains unclear. We hypothesize that activation of the PTH/PTH-related peptide type 1 receptor (PPR) along the osteoblast lineage facilitates bone formation and improved mechanical properties in response to exercise. To test this hypothesis, conditional PPR-knockout mice (PPRcKO) were generated in which PPR expression was deleted along the osteoblast lineage under the osterix promoter. At 8-weeks of age, both PPRfl/fl and PPRcKO mice were subjected to treadmill running or sedentary conditions for 5-weeks. Under sedentary conditions, PPRcKO mice displayed significantly less bone mass as well as smaller structural-level strength (yield-load and ultimate load), while tissue level properties were largely unaffected. However, PPRcKO mice exposed to exercise displayed significantly less structural-level and tissue-level mechanical properties when compared to exercised PPRfl/fl mice. Overall, these data demonstrate that PPR expression along the osteoblast lineage is essential for exercise to improve the mechanical properties of cortical bone. Furthermore, the influence of PPR activation on material properties is unique to exercise and not during normal growth and development.

Skin of sea cucumbers: the smart connective tissue that alters mechanical properties in response to external stimuli

Skin of sea cucumbers: the smart connective tissue that alters mechanical properties in response to external stimuli

Obesity alters the in vivo mechanical response and biochemical properties of cartilage as measured by MRI

BackgroundObesity is a primary risk factor for the development of knee osteoarthritis (OA). However, there remains a lack of in vivo data on the influence of obesity on knee cartilage mechanics and composition. The purpose of this study was to determine the relationship between obesity and tibiofemoral cartilage properties.MethodsMagnetic resonance images (3T) of cartilage geometry (double-echo steady-state) and T1rho relaxation of the knee were obtained in healthy subjects with a normal (n = 8) or high (n = 7) body mass index (BMI) before and immediately after treadmill walking. Subjects had no history of lower limb injury or surgery. Bone and cartilage surfaces were segmented and three-dimensional models were created to measure cartilage thickness and strain. T1rho relaxation times were measured before exercise in both the tibial and femoral cartilage in order to characterize biochemical composition. Body fat composition was also measured.ResultsSubjects with a high BMI exhibited significantly increased tibiofemoral cartilage strain and T1rho relaxation times (P <0.05). Tibial pre-exercise cartilage thickness was also affected by BMI (P <0.05). Correlational analyses revealed that pre-exercise tibial cartilage thickness decreased with increasing BMI (R2 = 0.43, P <0.01) and body fat percentage (R2 = 0.58, P <0.01). Tibial and femoral cartilage strain increased with increasing BMI (R2 = 0.45, P <0.01; R2 = 0.51, P <0.01, respectively) and increasing body fat percentage (R2 = 0.40, P <0.05; R2 = 0.38, P <0.05, respectively). Additionally, tibial T1rho was positively correlated with BMI (R2 = 0.39, P <0.05) and body fat percentage (R2 = 0.47, P <0.01).ConclusionsStrains and T1rho relaxation times in the tibiofemoral cartilage were increased in high BMI subjects compared with normal BMI subjects. Additionally, pre-exercise tibial cartilage thickness decreased with obesity. Reduced proteoglycan content may be indicative of pre-symptomatic osteoarthritic degeneration, resulting in reduced cartilage thickness and increased deformation of cartilage in response to loading.

Can fluorine and chlorine functionalization stabilize the graphene like borophene?

During the last couple of years, borophene, novel two-dimensional materials made from boron atoms have attracted remarkable attentions. As an exciting experimental achievement, most recently graphene like borophene has been realized (arXiv:1712.08770), which however suffers from dynamical instability because of its electron-deficiency. Nevertheless, as it was theoretically confirmed, hydrogenated graphene like borophene structures are stable which were surprisingly very recently experimentally synthesized. Halogenated graphene like borophene is also expected to form B−Halogen bonds and thus form energetically favorable structures. The effects of halogenations for varying levels of coverage (B1X1, B2X1 and B4X1; X is F and Cl) on the properties of graphene like borophene such as the geometric structures, thermal stability, mechanical response, electronic structure and optical properties are systematically investigated by the first-principles methods. The stability of these structures is tested by phonon spectrum analyses and ab initio molecular dynamics (AIMD) simulations. The investigation of mechanical properties demonstrates their high in-plane stiffness and outstanding stretchability as well. Notably, B1F1 and B1Cl1 were found to present direct band gaps of 2.15 and 2.47 eV, respectively, according to the HSE06 functional results, which can be further finely tuned by applying mechanical strains. In contrast, B2F1 and B2Cl1 have metallic character. The optical calculations illustrate that applying different tensile strains on these monolayers result in blue and red shift in optical spectra, suggesting that they are potentially promising for the applications in optoelectronics and nanoelectronics. Interestingly, the in-plane optical anisotropy of these novel 2D materials is highly desirable for the design of polarization-sensitive photodetectors.

Mechanical Response and Shear-Induced Initiation Properties of PTFE/Al/MoO₃ Reactive Composites.

Polytetrafluoroethylene/aluminum/molybdenum oxide (PTFE/Al/MoO3) reactive composites of a volume ratio of 60:16:24 were studied in this research. Quasi-static compression, dynamic compression and drop-weight experiments were performed to explore the mechanical response and the shear-induced initiation properties of the composites. Mesoscale images of the specimens after sintering demonstrate that PTFE, Al and MoO3 powders were evenly mixed and no chemical reaction occurred after the materials were stirred, pressed and sintered. The yield stress and compressive strength of PTFE/Al/MoO3 specimens are sensitive to strain rate within the range of 10−3~3 × 103 s−1, and the yield stress shows a bilinear dependence on the logarithm values of strain rate. The established Johnson-Cook constitutive model based on the experimental data can describe the mechanical response of PTFE/Al/MoO3 material well. Drop-weight tests show that the PTFE/Al/MoO3 specimens can react violently when impacted, with the characteristic drop height (H50) calculated as 51.57 cm. The recovered specimens show that the reaction started from the outer edge of the specimen with the largest shear force and the most concentrated shear deformation, indicating a shear-induced initiation mechanism. The reaction products of PTFE/Al/MoO3 specimens were AlF3, Al2O3, Mo and C, demonstrating that redox reaction occurred between PTFE and Al, and between Al and MoO3.

Body stiffness and damping depend sensitively on the timing of muscle activation in lampreys.

Unlike most manmade machines, animals move through their world using flexible bodies and appendages, which bend due to internal muscle and body forces, and also due to forces from the environment. Fishes in particular must cope with fluid dynamic forces that not only resist their overall swimming movements but also may have unsteady flow patterns, vortices, and turbulence, many of which occur more rapidly than what the nervous system can process. Has natural selection led to mechanical properties of fish bodies and their component tissues that can respond very quickly to environmental perturbations? Here, we focus on the mechanical properties of isolated muscle tissue and of the entire intact body in the silver lamprey, Ichthyomyzon unicuspis. We developed two modified work loop protocols to determine the effect of small perturbations on the whole body and on isolated segments of muscle as a function of muscle activation and phase within the swimming cycle. First, we examined how the mechanical properties of the whole lamprey body change depending on the timing of muscle activity. Relative to passive muscle, muscle activation can modulate the effective stiffness by about two-fold and modulate the effective damping by >10-fold depending on the activation phase. Next, we performed a standard work loop test on small sections of axial musculature while adding low-amplitude sinusoidal perturbations at specific frequencies. We modeled the data using a new system identification technique based on time-periodic system analysis and harmonic transfer functions (HTFs) and used the resulting models to predict muscle function under novel conditions. We found that the effective stiffness and damping of muscle varies during the swimming cycle, and that the timing of activation can alter both the magnitude and timing of peak stiffness and damping. Moreover, the response of the isolated muscle was highly nonlinear and length dependent, but the body's response was much more linear. We applied the resulting HTFs from our experiments to explore the effect of pairs of antagonistic muscles. The results suggest that when muscles work against each other as antagonists, the combined system has weaker nonlinearities than either muscle segment alone. Together, these results begin to provide an integrative understanding of how activation timing can tune the mechanical response properties of muscles, enabling fish to swim effectively in their complex and unpredictable environment.

Porosity and wave velocity evolution of granite after high-temperature treatment: a review

The evolution of porosity and changes in wave velocity in granite after high-temperature treatment has been experimentally investigated in different studies. Statistical analysis of the test results shows that there is a temperature threshold value that leads to variations in porosity and wave velocity. At a temperature that is less than 200 °C, the porosity of granite slowly increases with increases in temperature, while the wave velocity decreases. When the temperature is greater than 200 °C (especially between 400 and 600 °C), the porosity quickly increases, while the wave velocity substantially decreases. The temperature ranges of room temperature to 200 and 200–400 °C correspond to the undamaged state and the micro-damage state, respectively. The results confirm that there is an important link between the variations of physical and mechanical properties in response to thermal treatment. By studying the relationships among rock porosity, wave velocity and temperature, this provides the basis for solving multi-variable coupling problems under high temperatures for the thermal exploitation of petroleum and safe disposal of nuclear waste.

Fabrication and evaluation of a nerve guidance conduit capable of Ca2+ ion release to accelerate axon extension in peripheral nerve regeneration.

In this study, biodegradable nanocomposites consisting of poly (glycerol sebacate) (PGS) elastomeric matrix and the reinforcing phase of calcium titanate (CaTiO3 ) nanoparticles were fabricated as a nerve guidance conduit (NGC) for peripheral nerve regeneration. CaTiO3 nanoparticles were synthesized via the sol-gel method and calcined at 800°C for 60 min. PGS elastomer was synthesized via the polycondensation reaction of glycerol and sebacate (1:1) and 2.5 and 5 wt. percentages of the synthesized CaTiO3 nanoparticles were added to the PGS prepolymer solution. The composites obtained were heated in order to make crosslinks in the pre-polymer. CaTiO3 nanoparticles, PGS elastomer, and the composites fabricated were characterized in terms of their structural, chemical, physical, mechanical, and cell response properties to evaluate the feasibility of using the nanocomposite for NGC applications. The results indicated that CaTiO3 nanoparticles were 50 nm in size. When the nanoparticles were added to the PGS, the elastic modulus and tensile strength of the nanocomposite reached values of about 1 and 0.5 MPa, respectively that are near those of natural nerves. The degradation behavior and swelling of the nanocomposites, as compared with those of the PGS elastomer, were controlled by introducing CaTiO3 into the PGS, which swelling limitation could prevent nerve compression. It was observed that Ca2+ ions established chemical bonds with PGS, which led to high crosslink densities that, in turn, contribute to improved mechanical properties of the composite. The Ca2+ ions released from the nanocomposite samples were in the nontoxic range. The PC12 cell line on the surface of the nanocomposite specimens showed good cell adhesion and proliferation with improved axon outgrowth and extension. Based on the results obtained the fabricated PGS/CaTiO3 nanocomposite may be recommended as a suitable NGC with desirable effects on peripheral nerve regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2181-2189, 2018.

Tuning Self-Healing Property of Stiff Supramolecular Polymer for Flexible Electronics

Organic electronics are receiving increasing attention for the development of flexible devices, due to the generally easier processability and higher flexibility of organic, compared to inorganic, materials. However, although many suitable organic materials possess some measure of elasticity, flexible electronic devices are often prone to cracking or breaking over time, resulting in poor durability and reliability. As a result, the burgeoning field of self-healing materials for electrochemical devices has begun to attract attention. Self-healing polymers can be designed to recover their original mechanical properties after physical damage, increasing their useful lifetime. Therefore, development of self-healing polymers is highly desirable to accommodate increasing demand for flexible devices. For decades, soft gels, elastomers, and hybrid organic-inorganic systems with self-healing properties have been designed based on reversible interactions and dynamic covalent bonds. However, previous approaches typically sacrifice stiffness to achieve self-healing properties, mostly resulting in materials with tensile moduli less than 1 MPa. These soft and deformable materials are less likely to maintain reliable and stable pathways for electron or ion movement in devices. Additionally, considering different application conditions, how to modulate these self-healing and mechanical properties in response to various environment cues, such as temperature, pH, or light is vital for improving long-term mechanical integrity as well. In particularly, tunability based on temperature is widely useful for initiating self-healing ability and controlling stiffness for flexible electronics, which will widen their ultimate potential applications. Herein, we report a supramolecular polymer system based on pi-pi interaction between naphthalenediimide (NDI) and pyrene (Py) derivatives, which possesses high stiffness (Young’s modulus > 69 MPa) while also retaining mild self-healing temperature (< 50oC) and inherent ionic conductivity (> 10-6 S/cm at 50°C when doped with LiTFSI). Additionally, we demonstrate the tunability of the pi-pi interaction modes by doping small molecule additives into the polymer, which can modulate the interaction strength and crosslinking density in the system. The self-healing temperature and Young’s modulus are tunable in a wide range (30-60oC, 69-219 MPa) to satisfy different potential applications, such as artificial skin and wearable batteries. We demonstrate our polymer possesses decent stretchability (100% strain without cracking), flexibility, and ability to heal cracking at human body temperature, which shows application potential for wearable electronics. Compared to softer self-healing polymers reported previously, our system not only transcends the currently-available regime of mechanical properties in self-healing systems, but also provides a general strategy for tuning self-healing and mechanical properties in supramolecular polymers.

Alterations in Leg Extensor Muscle-Tendon Unit Biomechanical Properties With Ageing and Mechanical Loading.

Tendons transfer forces produced by muscle to the skeletal system and can therefore have a large influence on movement effectiveness and safety. Tendons are mechanosensitive, meaning that they adapt their material, morphological and hence their mechanical properties in response to mechanical loading. Therefore, unloading due to immobilization or inactivity could lead to changes in tendon mechanical properties. Additionally, ageing may influence tendon biomechanical properties directly, as a result of biological changes in the tendon, and indirectly, due to reduced muscle strength and physical activity. This review aimed to examine age-related differences in human leg extensor (triceps surae and quadriceps femoris) muscle-tendon unit biomechanical properties. Additionally, this review aimed to assess if, and to what extent mechanical loading interventions could counteract these changes in older adults. There appear to be consistent reductions in human triceps surae and quadriceps femoris muscle strength, accompanied by similar reductions in tendon stiffness and elastic modulus with ageing, whereas the effect on tendon cross sectional area is unclear. Therefore, the observed age-related changes in tendon stiffness are predominantly due to changes in tendon material rather than size with age. However, human tendons appear to retain their mechanosensitivity with age, as intervention studies report alterations in tendon biomechanical properties in older adults of similar magnitudes to younger adults over 12–14 weeks of training. Interventions should implement tendon strains corresponding to high mechanical loads (i.e., 80–90% MVC) with repetitive loading for up to 3–4 months to successfully counteract age-related changes in leg extensor muscle-tendon unit biomechanical properties.

Mechanical Metamaterials with Thermoresponsive Switching between Positive and Negative Poisson's Ratios

There have been many studies on smart mechanical materials that sensibly deform in response to external stimuli. However, most of the previous studies have focused on structure changes but largely neglected stimuli‐responsive and programmable mechanical properties. Here, we present a novel strategy of mechanical metamaterials, engineered materials with mechanical properties defined by their structure rather than their composition, to design smart materials that change their mechanical properties in response to external stimuli. The present work demonstrates mechanical metamaterials with thermoresponsive and reversible switching between positive and negative Poisson's ratios. In order to realize the thermoresponsive and reversible switching, a thermoresponsive rod with an extremely large thermal expansion coefficient is developed utilizing two‐way shape memory effects. As an application of our metamaterials, we propose soundproofing materials that selectively block sound waves in a specific frequency range depending on temperature.

Theoretical realization of Mo2P; a novel stable 2D material with superionic conductivity and attractive optical properties

Mo2P as a new member of the advancing two-dimensional (2D) materials family has been theoretically identified in this study. We conducted extensive density functional theory calculations to explore the crystal structure, dynamical stability, mechanical response, electronic structure and optical properties. Mo2P was found to be metallic with the Fermi energy locating at the d bands of transition metal Mo. A high reflectivity of ∼100% at low energies less than 1eV was observed, introducing Mo2P as a potential candidate for photonic and optoelectronic applications such as transmitting electromagnetic waves devices. Our calculations confirm that the novel 2D structure is dynamically stable and can withstand at high temperatures including 1000K. Mo2P was found to yield high tensile strength and elastic modulus of 12GPanm and 56GPanm, respectively. We particularly evaluated the application of Mo2P as an anode material for Li and Na-ion rechargeable batteries. The open-circuit voltages of 0.88–1.06V and 0.94–0.09V were predicted for Li and Na ions storages, respectively, which are desirable for commercial anodic materials. Interestingly, our calculations predict remarkably low diffusion energy barriers of 50meV and 17meV for Li and Na adatoms, respectively, promising to achieve ultrafast charging/discharging. The findings provided by this study can motivate further experimental and theoretical studies to probe new 2D crystals made from phosphor and transition metals with 2H and 1T atomic structures.

Design of biobased PLLA triblock copolymers for sustainable food packaging: Thermo-mechanical properties, gas barrier ability and compostability

Novel poly(lactic acid)-based chain extended triblock copolymers have been successfully synthesized in melt. The new polymers are characterized by a triblock ABA architecture, where A, is poly(lactic acid) and B is an ad hoc synthesized random biobased aliphatic copolyester poly(propylene/neopentyl glycol succinate). PLLA homopolymer has been also prepared for the sake of comparison. The samples under study were deeply characterized from the molecular, thermal and structural point of view. Mechanical and barrier properties and compostability were also investigated, in order to assess the potentiality of these materials in food packaging applications. The results obtained show that copolymerization leads to better mechanical response and barrier properties with respect to poly(lactic) acid homopolymer. Moreover, the presence of the central B block in the main polymer chain facilitates the process of compostability.

Fibrous tissues growth and remodeling: Evolutionary micro-mechanical theory

Living fibrous tissues are composite materials having the unique ability to adapt their size, shape, structure and mechanical properties in response to external loading. This adaptation, termed growth and remodeling (G&R), occurs throughout life and is achieved via cell-induced turnover of tissue constituents where some are degraded and new ones are produced. Realistic mathematical modeling of G&R provides insight into the basic processes, allows for hypotheses testing, and constitutes an essential tool for establishing clinical thresholds of pathological remodeling and for the production of tissue substitutes aimed to achieve target structure and properties. In this study, a general 3D micro-mechanical multi-scale theory of G&R in fibrous tissue was developed which connects between the evolution of the tissue structure and properties, and the underlying mechano-biological turnover events of its constituents. This structural approach circumvents a fundamental obstacle in modeling growth mechanics since the growth motion is not bijective. The model was realized for a flat tissue under two biaxial external loadings using data-based parameter values. The predictions show close similarity to characteristics of remodeled adult tissue including its structure, anisotropic and non-linear mechanical properties, and the onset of in situ pre-strain and pre-stress. The results suggest that these important features of living fibrous tissues evolve as they grow.

Cellulose nanocrystals from Actinidia deliciosa pruning residues combined with carvacrol in PVA_CH films with antioxidant/antimicrobial properties for packaging applications

Kiwi Actinidia deliciosa pruning residues were here used for the first time as precursors for the extraction of high performing cellulose nanocrystals (CNC) by applying a bleaching treatment followed by an acidic hydrolysis. The resultant cellulosic nanostructures, obtained by an optimize extraction procedure (0.7% wt/v two times of sodium chlorite NaClO2) followed by an hydrolysis step, were then used as reinforcements phases in poly(vinyl alcohol) (PVA) blended with natural chitosan (CH) based films and also combined, for the first time, with carvacrol used here as active agent. Morphological and optical characteristics, mechanical response, thermal and migration properties, moisture content and antioxidant and antimicrobial assays were conducted. The morphological, optical and colorimetric results underlined that no particular alterations were induced on the transparency and color of PVA and PVA_CH blend by the presence of CNC and carvacrol, while they were able to modulate the mechanical responses, to induce antioxidant activities maintaining the migration levels below the permitted limits and suggesting the possible application in industrial sectors. Finally, inhibitions on bacterial development were detected for multifunctional systems, suggesting their protective function against microorganisms contamination.

Mechanical Adaptability of the MMP-Responsive Film Improves the Functionality of Endothelial Cell Monolayer.

Extracellular matrix and cells are inherent in coordinating and adapting to each other during all physiological and pathological processes. Synthetic materials, however, show rarely reciprocal and spatiotemporal responses to cells, and lacking self-adapting properties as well. Here, a mechanical adaptability based on the matrix metalloproteinase (MMPs) sensitive polyelectrolyte film is reported. Poly-lysine (PLL) and methacrylated hyaluronic acid (HA-MA) nanolayers are employed to build the thin film through the layer-by-layer assembly, and it is further crosslinked using MMP sensitive peptides, which endows the films with changeable mechanical properties in response to MMPs. It is demonstrated that stiffness of the (PLL/HA-MA) films increases with the crosslinking, and then decreases in response to a treatment of enzyme. Consequently, the crosslinked (PLL/HA-MA) films reveal effective growth of endothelial cells (ECs), leading to fast formation of EC monolayer. Importantly, significantly improved endothelial function of the EC monolayer, which is characterized by integrity, biomolecules release, expression of function related gene, and antithrombotic properties, is achieved along with the decrosslinking of the film because of EC-secreted MMPs. These results suggest that mechanical adaptability of substrate in Young's modulus plays a significant role in endothelial progression, which shows great application potential in tissue engineering, regenerative medicine, and organ-on-a-chip.