High Fracture Stress Research Articles

Self‐Healing Poly(acrylic acid) Hydrogels: Effect of Surfactant

SummaryPhysical poly(acrylic acid) gels were prepared by micellar copolymerization of hydrophilic monomer acrylic acid with large hydrophobic monomer stearyl methacrylate (C18) in solutions of worm‐like anionic surfactant (sodium dodecyl sulfate, SDS) and cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) micelles. Hydrophobe content of the monomer mixtures was 2 mol.% and total monomer concentration in gels was 20 w/v%. Gelation reactions were monitored by rheometry using oscillatory deformation tests. Hydrogel samples were also subjected to uniaxial elongation and compression tests after preparation and swelling. The physical gels with SDS and CTAB showed similar properties as long as they are at the state of preparation, such as insoluble in water and exhibit time‐dependent dynamic moduli, high Young's modulus, high fracture stress, high elongation ratios at break. Also self‐healing was evidenced by mechanical measurements. Physical gels formed in SDS solution were stable, exhibited high equilibrium swelling ratios and SDS progressively extracted from the network in water. On the other hand, gels with CTAB formed a complex and resulted in shrinkage after gels were immersed in a large excess of water because both electrostatic interactions between the charged components and hydrophobic interactions between the polymer backbone and the alkyl chains of the surfactant are important in driving the self‐assembly of molecules to form ordered structures. These structures of the polyelectrolyte surfactant complexes have unusual mechanical properties. Also, the hydrogel samples with CTAB self‐healed via heating and surfactant treatment of the damaged areas withstand up to 1.05 MPa stresses and rupture at a stretch of 800%.

Thermo-mechanical property of shape memory polymer/carbon fibre composites

The shape memory polymer composites with trans-1,4-polyisoprene matrix and chopped carbon fibre reinforcement are developed to improve the mechanical weakness of pure trans-1, 4-polyisoprene in this study. The specimens are fabricated with carbon fibre weight fraction of 5%, 10% and 15%, and the average length of short chopped carbon fibre is 2 mm. The influences of various carbon fibre weight fractions on mechanical behaviour are characterised, and the thermodynamic properties of the developed SMP composites are investigated. The results show that there exists an optimum carbon fibre weight fraction between 0% and 10% to have a highest fracture stress and an extremely low residual strain. The fracture strain gets larger with the increment of temperature, and the value of the residual strain becomes relatively stable with the increase of the number of cycles.

Phase-Separation-Induced Anomalous Stiffening, Toughening, and Self-Healing of Polyacrylamide Gels.

Novel, tough, strong, and self-healable poly-acrylamide (PAAm) gels are fabricated by inducing an appropriate phase-separation structure using a poor solvent. The phase separation induces a gel-glass-like transition of the PAAm gels, providing the gels an anomalously high modulus (211 MPa), fracture stress (7.13 MPa), and fracture energy (4.16 × 10(4) J m(-2)), while keeping a high solvent content (≈60 vol%).

Characteristics of the bulk hydrogels made of the citric acid cross-linked whey protein microgels

A non-toxic, biocompatible and generally recognized as safe (GRAS) chemical, citric acid, was employed for pH adjustment and cross-linking of whey proteins either before or after their microgelification by heat. A conventionally-made microgel sample was also fabricated by using hydrochloric acid for pH adjustment on 5.8 and subsequent heating at 85 °C. Size approximation of microgel particles from atomic force microscopy images indicated that chemical cross-linking resulted in smaller particles (80–130 nm and 100–150 nm for post- and pre-microgelification cross-linked samples, respectively) compared with conventional counterpart (150–300 nm). Based on Fourier transform infrared spectroscopy results, it was concluded that prolonged citric acid cross-linking of whey proteins prior to microgelification caused extensive cross-linking of protein units and preserved proteins α-helical structure. The pre-cross-linked microgels formed firmer (higher fracture stress and complex modulus) calcium-induced cold-set bulk gel with higher water-holding capacity and denser microstructure compared with conventional and post-cross-linked microgels. These superiorities were attributed to existence of higher number of carboxyl residues in the structure of the pre-cross-linked microgels. The alteration in the properties of the final bulk hydrogels via cross-linking of the microgel building-units can be exploited for modulating and controlling the release behavior of loaded cargo within hydrogel, resulting in a more tuned application of gels as edible delivery systems.

Treating Atypical Femoral Fractures Related to Bisphosphonates.

Doctors widely prescribe osteoclast-inhibiting bisphosphonate drugs to treat osteoporosis, but long-term bisphosphonate use has been linked to an increased risk of atypical subtrochanteric femoral fractures. According to an updated task force report from the American Society for Bone and Mineral Research, the features that distinguish these atypical subtrochanteric fractures include transverse orientation, general lack of comminution, and localized cortical thickening at the fracture site. In addition, the prolonged healing times of these fractures challenge orthopaedists to obtain strong and stable fixation that outlasts the extended period required for fracture union. Intramedullary nailing is often used to treat these fractures, but related characteristics such as canal narrowing can make this fixation approach unfeasible. This month’s “Case Connections” looks at various techniques for repairing bisphosphonate-associated atypical femoral fractures. In the January 14, 2015, JBJS Case Connecto r , Yuasa et al. reported on the case of a sixty-nine-year-old woman who, one month prior to scheduled right hip arthroplasty to treat osteoarthritis, presented with severe right thigh pain after a low-trauma fall. History-taking revealed four-plus years of treatment with alendronate (Fosamax), and radiographs showed a noncomminuted transverse subtrochanteric fracture below an arthritic hip joint. During a single operation, the patient underwent cementless total hip arthroplasty using a modular stem/neck, followed by fracture reduction and fixation using a cable-and-plate system (Fig. 1). The patient was switched from alendronate to a …

Gelling properties of protein fractions and protein isolate extracted from Australian canola meal

Gelling properties of canola albumin and globulin fractions, and canola protein isolate (CPI) were examined in this study. The effects of pH and salt concentration on canola protein gelling properties were studied primarily by means of dynamic oscillatory rheology and gel texture analysis. The findings were supported by confocal laser scanning microscopy (CLSM) images of the gels, isoelectric point, and solubility measurement data. All canola proteins showed typical heat-set gel protein profiles. Gels formed at higher pH had better gelling properties including higher overall resistance to deformation (G*), higher gel elasticity (low tan δ ), higher fracture stress and firmness, and denser gel microstructure. Isoelectric points of canola proteins used in this study were in the range of pH3.0–4.7 where low protein solubility was observed. The albumin fraction was able to form a very weak gel at pH4, whereas the globulin fraction and CPI precipitated due to loss of protein surface charge. The effects of NaCl on gelling were protein sample dependent. The presence of NaCl negatively affected gelling properties of albumin and globulin fractions, with decreases in overall resistance to deformation (G*), and fracture stress and firmness, but positively affected CPI gels in the same aspects. The elasticity (tan δ) of all canola protein gels remained constant in the presence of NaCl. Frequency sweep analysis revealed that the albumin fraction and CPI formed weak gels, whereas the globulin fraction formed a strong gel. Strain sweep analysis further confirmed that the globulin fraction formed a stronger gel with a critical strain of at least 10%. This study demonstrates the high potential of canola proteins, particularly the globulin fraction, as a prospective gelling agent.

Novel candidate genes putatively involved in stress fracture predisposition detected by whole-exome sequencing.

While genetic factors in all likelihood contribute to stress fracture (SF) pathogenesis, a few studies focusing on candidate genes have previously been reported. The objective of this study is to gain better understanding on the genetic basis of SF in a gene-naive manner. Exome sequence capture followed by massive parallel sequencing of two pooled DNA samples from Israeli combat soldiers was employed: cases with high grade SF and ethnically matched healthy controls. The resulting sequence variants were individually verified using the Sequenom™ platform and the contribution of the genetic alterations was validated in a second cohort of cases and controls. In the discovery set that included DNA pool of cases (n = 34) and controls (n = 60), a total of 1174 variants with >600 reads/variant/DNA pool were identified, and 146 (in 127 genes) of these exhibited statistically significant (P < 0·05) different rates between SF cases and controls after multiple comparisons correction. Subsequent validation of these 146 sequence variants individually in a total of 136 SF cases and 127 controls using the Sequenom™ platform validated 20/146 variants. Of these, three missense mutations (rs7426114, rs4073918, rs3752135 in the NEB, SLC6A18 and SIGLEC12 genes, respectively) and three synonymous mutations (rs2071856, rs2515941, rs716745 in the ELFN2, GRK4, LRRC55 genes) displayed significant different rates in SF cases compared with controls. Exome sequencing seemingly unravelled novel candidate genes as involved in SF pathogenesis and predisposition.

Kinetic grain growth, shape memory and corrosion behavior of two Cu-based shape memory alloys after thermomechanical treatment

Metallurgical and mechanical properties along with shape memory and corrosion behavior of Cu-11.8% Al-3.7% Ni- 1%Mn and Cu-11% Al-5.6% Mn shape memory alloys (SMAs) were comparatively studied. The influence of grain refinement on the properties was studied by optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), potentiodynamic polarizations and bend and tensile tests. Static recrystallization and kinetic grain growth show a rapid recrystallization in the first 15 s of annealing at 800 °C followed by grain growths. The minimum grain sizes obtained after 15 s are 90 and 260 μm for Cu-Al-Ni-Mn and Cu-Al-Mn, respectively. Tensile tests show typical three-stage curves for both alloys, and it is seen that alloys exhibit high fracture stress and strain after grain refinement. Microstructural observations show zig-zag morphology of β′1 martensite in the Cu-Al-Ni-Mn and coexistence of β′1 and γ′1 in the Cu-Al-Mn, which were confirmed by differential scanning calorimetry results. The shape memory ratios (η) of the alloys before thermomechanical treatment, and after thermomechanical annealing at 800 °C for different time up to 15 min followed by water quenching, were evaluated. In addition, corrosion behavior of alloys after grain refinement was analyzed by means of potentiodynamic polarization measurements. The results showed that the anodic reactions were dominated by dissolution of copper, and Cu-Al-Ni-Mn alloy exhibits a better corrosion resistance than Cu-Al-Mn alloy.

Synthesis and characterization of mechanically flexible and tough cellulose nanocrystals–polyacrylamide nanocomposite hydrogels

The unique combinations of hard and soft components with core/shell structures were proposed to synthesize high strength nanocomposite hydrogels. The elastomeric hydrogels containing rod-like cellulose nanocrystals (CNCs) core and polyacrylamide shell were made from aqueous solutions via free radical polymerization in the absence of chemical cross-links. The obtained hydrogels possessed greater tensile strength and elongation ratio when compared with chemically cross-linked counterparts. Oscillatory shear experiments indicated that CNCs interacted with polymer matrix via both chemical and physical interactions and contributed to the rubbery elasticity of the hydrogels. The nanocomposite hydrogels were more viscous than the chemical hydrogels, suggesting the addition of CNC led to the increase of energy dissipating and viscoelastic properties. The network structure model was proposed and it suggested that the high extensibilities and fracture stresses were related to the well-defined network structures with low cross-linking density and lack of noncovalent interactions among polymer chains, which may promote the rearrangements of network structure at high deformations.

Self-healing polyacrylic acid hydrogels

pH responsive physical gels were prepared by micellar copolymerization of acrylic acid with 2 mol% stearyl methacrylate (C18) in a solution of worm-like sodium dodecyl sulfate micelles. The physical gels are insoluble in water and exhibit time-dependent dynamic moduli, high Young's modulus (6–53 kPa), high fracture stress (41–173 kPa), high elongation ratios at break (1800–5000%), and self-healing, as evidenced by rheological and mechanical measurements. Cyclic elongation tests show significant hysteresis due to the existence of reversibly breakable bonds (up to 25%) within the gel network. As the polymer concentration is increased, both the lifetime of hydrophobic associations and the mechanical strength of gels increase while the elongation ratio at break decreases. As compared to the polyacrylamide gels formed under identical conditions, the present hydrogels exhibit a much stronger self-healing effect, which is attributed to the cooperative hydrogen bonding between the carboxyl groups stabilizing the hydrophobic domains. The efficiency of self-healing significantly increases with increasing temperature due to the decrease of the lifetime of hydrophobic associations.

Influences of Strain Rates on Fracture Mechanism and Phase Separation in Hf-Based Bulk Metallic Glass

Abstract The uniaxial compressive fracture behavior of a Hf44.5Cu27Ni13.5Ti5Al10 bulk metallic glass (BMG) was investigated at different strain rates (10−4∼103 s−1) by an INSTRON-5569 testing machine and Split Hopkinson Pressure Bar. The results show that the Hf44.5Cu27Ni13.5Ti5Al10 bulk metallic glass isn't sensitive to strain rate under the quasi-static compression condition. The fracture strength is 2400 MPa. The fracture strength is 2840 MPa under the dynamic compression. The dimple structure and periodical corrugation formed at the fracture surface were observed. The fracture mechanism attributed to ductile fracture in the range of micro-scale. In addition, interaction of elastic waves and the dynamic crack front plays an important role during the formation of periodic corrugations. The higher fracture stress and adiabatic temperature are caused by the higher dynamic compressive strain rate. Phase separation was formed by segregation and diffusion at the interface during compression and affected the formation of shear cracks/bands.

High Fracture Efficiency and Stress Concentration Phenomenon for Microgel-Reinforced Hydrogels Based on Double-Network Principle

Double-network hydrogels (DN gels) have aroused considerable interest because of their excellent mechanical strength and toughness, low sliding friction, good biocompatibility, as well as wide tuna...

Characterization of Piezoresistive-Si-Nanowire-Based Pressure Sensors by Dynamic Cycling Test With Extralarge Compressive Strain

A novel pressure sensor using piezoresistive silicon nanowires (SiNWs) embedded in a suspended multilayered diaphragm is investigated by a probe-based dynamic cycling test combining the standard bulge testing setup. By utilizing the high fracture stress of the SiN <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> film, we explored the behavior of the SiNW under a level of extralarge compressive strain for the first time, including strain levels of more than 2.1% under the static testing and 1.5% under the dynamic testing. Drift of the initial resistances of the SiNW was observed at different time intervals during the dynamic testing under a compressive strain of higher than 1.3%, while the sensitivity of the pressure sensor basically keeps unchanged. However, there was almost no drift or degradation observed in the sensor characteristics when an equivalent point loading within the application working range is applied to the pressure sensor during the dynamic testing.

Poly(vinyl alcohol) Hydrogel Can Autonomously Self-Heal.

It is discovered that poly(vinyl alcohol) (PVA) hydrogel prepared using the freezing/thawing method can self-repair at room temperature without the need for any stimulus or healing agent. The autonomous self-healing process can be fast for mechanically strong PVA hydrogel yielding a high fracture stress. Investigation on the effect of the hydrogel preparation conditions points out that hydrogen bonding between PVA chains across the interface of the cut surfaces is at the origin of the phenomenon. The key for an effective self-healing is to have an appropriate balance between high concentration of free hydroxyl groups on PVA chains on the cut surfaces prior to contact and sufficient PVA chain mobility in the hydrogel.

Influence of Milk, Corn Starch, and Baking Conditions on the Starch Digestibility, Gelatinization, and Fracture Stress of Biscuits

ABSTRACTDough for nontraditional semisweet biscuits—prepared with wheat flour or replacing part of the wheat flour with corn starch, with or without skim milk—was baked at two oven temperatures, 120 or 170°C, until reaching moisture content and water activity lower than 6% and 0.5, respectively. Assays of fracture stress, differential scanning calorimetry, X‐ray diffraction, and starch digestibility were performed. Results showed that biscuits containing milk had the highest fracture stress, and biscuits baked at low temperature were harder than biscuits baked at high temperature. The degree of starch gelatinization during baking was higher when dough was baked at 170°C, compared with dough baked at 120°C. The decrease in gelatinization coincides with the decrease in the height and surface of peaks at 15 and 23° in the X‐ray diffraction patterns. Milk and corn starch did not affect the starch digestibility of biscuits, but biscuits baked at 170°C presented lower fracture stress and higher starch digestibility than biscuits baked at 120°C.

Characterization of Silicon Nanowire Embedded in a MEMS Diaphragm Structure Within Large Compressive Strain Range

The characteristics of piezoresistive silicon nanowires (SiNWs) under compressive strain as large as 1.7% are reported. The SiNW is embedded in a multilayered diaphragm structure consisting of silicon nitride and silicon oxide. After leveraging the high fracture stress and intrinsic tensile stress of silicon nitride layer to produce a flat diaphragm, we can create large compressive strain to the SiNW without damaging the diaphragm. The relationship between SiNW resistance change and applied strain is measured and investigated with 2-μm and 5-μm SiNWs for both scientific and practical points of view. This approach demonstrates the validity to reveal the SiNW properties under large strain, and the exploration provides good reference for future SiNW-based MEMS sensor design.

Combinatorial Search for Ni–Nb–Ti Thin Film Amorphous Alloys with High Corrosion Resistances

In this paper, we present a combinatorial search for novel Ni–Nb–Ti thin film amorphous alloys suitable for use in diaphragm-type microelectromechanical systems (MEMS) vacuum sensors. The corrosion resistances to ClF3 gas and heat resistances of the thin films were evaluated by a combinatorial method that enables efficient searching for candidate materials. The combinatorial evaluation revealed that Ni56Nb33Ti11 and Ni49Nb35Ti16 thin film amorphous alloys exhibit a high heat resistance and a high corrosion resistance to ClF3 gas. Moreover, both samples exhibited high fracture stresses of over 1.0 GPa. Both samples were assessed to be suitable diaphragm materials for diaphragm-type MEMS vacuum sensors. We also fabricated and evaluated a simple diaphragm-type MEMS vacuum sensor using a Ni49Nb35Ti16 thin film amorphous alloy; the results confirmed the suitability of this amorphous alloy as a diaphragm material.

Searching for noble Ni–Nb–Zr thin film amorphous alloys for optical glass device molding die materials

Abstract This paper presents a search for Ni–Nb–Zr thin film amorphous alloys for use as optical glass device molding die materials. To efficiently search for candidate materials, we used a combinatorial method to evaluate thermal stability. First, compositionally spread Ni–Nb–Zr libraries were fabricated by combinatorial arc plasma deposition (CAPD). To evaluate thermal stability, the Ni–Nb–Zr amorphous CAPD samples in the libraries were annealed in vacuum at 723 K, representing the molding temperature for glass devices, for various time periods. The phases of the annealed CAPD samples were identified using X-ray diffractometry (XRD). From XRD identification, candidate amorphous compositions with high thermal stabilities were screened. Sputter-deposited samples with the same candidate amorphous compositions were subsequently fabricated. Other desired properties for optical glass device molding die materials, including mechanical strength, linear expansion coefficient, oxidation resistance, machinability and anti-sticking properties to molten glass, were evaluated. The investigation revealed Ni 36 Nb 39 Zr 25 to be a suitable composition for a new glass lens molding die material. This material exhibited a high fracture stress, σ f , of 1.3 GPa, good heat resistance, good oxidation resistance, similar linear expansion coefficient as glass, good machinability, and excellent anti-sticking properties to molten glass.

The ductile to brittle transition for C–Mn steel with an ultrafine grain ferrite/cementite microstructure

The Charpy impact energy was measured as a function of temperature for plain C–Mn steel with an ultrafine grain ferrite/cementite (UGF/C) microstructure and with a coarse-grain ferrite/pearlite (CGF/P) microstructure. Instrumented Charpy impact tests were carried out at 273 K and 77 K for the UGF/C microstructure. The steel with the UGF/C microstructure exhibited an upper shelf energy lower than the steel with the CGF/P microstructure, a higher lower shelf energy and the transition in impact energy occurred more gradually at a lower temperature. The ductile to brittle transition in the steel with the UGF/C microstructure was caused by a decrease in energy absorbed by ductile fracture rather than a change of fracture mode from ductile fracture to cleavage as occurred for the CGF/P microstructure. The fracture surface of the UGF/C steel in the upper shelf region contained large dimples and numerous small dimples whereas the fracture surface in the lower shelf region contained small dimples and cleavage facets. A lower amount of energy was absorbed in the transition region and the lower shelf region due to the decrease of dimple diameter and depth. Nevertheless, some energy was absorbed in the lower shelf because there were some small dimples even at the liquid helium temperature. In contrast, essentially no energy was absorbed in the lower shelf for the CGF/P steel because of typical cleavage fracture. The UGF/C microstructure has a high cleavage fracture stress.

Water-Induced Brittle-Ductile Transition of Double Network Hydrogels

In the previous studies, we have developed double network hydrogels (DN gels) with extra-ordinarily high mechanical strength and toughness although the gels contain 90 wt % of water. In this study, we investigated the effect of water content on the mechanical behavior of the DN gel consists of poly(2-acrylamido-2-methylpropanesulfonic acid) gels (PAMPS gels) as the first network and polyacrylamide gels (PAAm gels) as the second network. When the DN gel was dried gradually from its equilibrium swelling state (90 wt % water content), it exhibited a ductile behavior with a very high fracture stress and strain at an intermediate water content c (65 wt % < c < 75%), and then became brittle upon further decreasing in water content (c < 60 wt %). The behavior of the DN gel was compared with the corresponding single network gels, PAMPS and PAAm. It is found that at the intermediate water content, the fracture stress and strain of PAAm gel reached maximum, and the brittle−ductile change of DN gel upon with the change in water content was the results of the change in the mechanical properties of PAAm network.