The meniscus is crucial in maintaining the knee function and protecting the joint from secondary pathologies, including osteoarthritis. Although most of the mechanical properties of human menisci ...have been characterized, to our knowledge, its dynamic shear properties have never been reported. Moreover, little is known about meniscal shear properties in relation to tissue structure and composition. This is crucial to understand mechanisms of meniscal injury, as well as, in regenerative medicine, for the design and development of tissue engineered scaffolds mimicking the native tissue. Hence, the objective of this study was to characterize the dynamic and equilibrium shear properties of human meniscus in relation to its anisotropy and composition.
Specimens were prepared from the axial and the circumferential anatomical planes of medial and lateral menisci. Frequency sweeps and stress relaxation tests yielded storage (G′) and loss moduli (G″), and equilibrium shear modulus (G). Correlations of moduli with water, glycosaminoglycans (GAGs), and collagen content were investigated.
The meniscus exhibited viscoelastic behavior. Dynamic shear properties were related to tissue composition: negative correlations were found between G′, G″ and G, and meniscal water content; positive correlations were found for G′ and G″ with GAG and collagen (only in circumferential samples). Circumferential samples, with collagen fibers orthogonal to the shear plane, exhibited superior dynamic mechanical properties, with G′ ~70 kPa and G″ ~10 kPa, compared to those of the axial plane ~15 kPa and ~1 kPa, respectively. Fiber orientation did not affect the values of G, which ranged from ~50 to ~100 kPa.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
A fully bio‐based plastic composite comprising a polylactic acid (PLA) matrix with untreated bamboo filler (BF) was manufactured by a simple method. PLA and crushed bamboo flakes were compounded in a ...kneader and then injection molded without pretreatment of BF. The composites containing PLA and BF at 50:50 (PLA50/BF50) and 60:40 mass ratios (PLA60/BF40) were obtained. The PLA60/BF40 and PLA50/BF50 products were evaluated by thermal analysis (TG/DTA, DSC, and DMA), Fourier transform infrared (FTIR) spectroscopy analysis, and abrasive wear test. From the results, the composite of PLA and untreated BF was fabricated under high temperature and high‐pressure conditions, in kneading at 180°C and injection molding at 150–175°C and 95 MPa for 1.5 s. FTIR analysis indicated that changes in the functional groups of the composite products were dependent on the proportion of BF. Unfortunately, the BF did not improve the stiffness, viscoelasticity, and wear resistance of the PLA. However, the PLA50/BF50 product had a storage modulus comparable to that of the pure PLA product, and of which a 30% cost reduction was achieved by using abundant bamboo and reducing the amount of PLA.
The composite of PLA and untreated bamboo filler was fabricated in kneading at 180°C and injection molding at 150–175°C and 95 MPa for 1.5 s. The composite products containing PLA/BF at 50:50 and 60:40 were obtained. FTIR analysis indicated that changes in the functional groups of the composite products were dependent on the proportion of BF. Possible reactions between the PLA and BF during kneading and injection molding (a) PLA60/BF40‐IM (b) PLA50/BF50‐IM.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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•Successful fabrication of interconnected pores via spun sugar leaching.•Prominent increment of swelling capacity with the presence of PAAc chains.•Improvement in strength with the ...incorporation of nano-clay and PAAc chains.•Properties adaptation to the desired tissue is a requisite for an ideal cell scaffold.
In this study, a three-dimensional porous structure of poly(glycerol sebacate urethane) (PGSU) comprising nano-clay and polyacrylic acid (PAAc) was synthesized through a two-step synthesis route. Particulate leaching technique by introducing spun sugar as porogen was also performed as a fabrication method. It was hypothesized that the introduction of spun sugar with its filamentous shape would create interrelated pores required for cell adhesion and proliferation. Polarity, stiffness, and swelling capacity of PGSU would be enhanced by eco-friendly in-situ polymerization of PAAc and the contribution of biocompatible nanoclay. After characterizing the synthesis of PGSU-based scaffolds, viscoelastic behavior, hydrophilicity, and biocompatibility of scaffolds were evaluated. Doubling of swelling capacity in dry state and decrement of water contact angle (WCA) approved the effect of polar carboxyl groups of PAAc in the improvement of polarity and hydrophilicity of PGSU. DMTA results in dry and wet states demonstrated that increasing the concentration of nanoclay and the presence of PAAc chains led to the increase in the storage modulus while the elastic behavior at body temperature was preserved. Eventually, the feasibility of the porous structure of PGSU-based scaffolds in tissue engineering became clear by in vitro biocompatibility test and significant cell adhesion in plasma-treated PGSU/PAAC/nanoclay. Accordingly, introducing clay nanoparticles and in-situ polymerization of acrylic acid, together with porous structure, make PGSU a suitable substrate for cellular interactions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
To investigate the effect of short carbon fibre on the tribological behavior of phenolic resin-based friction materials, a reference friction composite holding various ingredients without short ...carbon fibre, and three friction composites holding 1, 2 and 4 vol% carbon fibre were formulated. The dynamic-mechanical and thermogravimetric analyses showed the increase of storage modulus and reduction of thermal stability, respectively, with incorporation of carbon fibre into the brake composites. The tribological characterizations revealed that the coefficient of friction (COF) and specific wear rate of the friction composites dropped with addition of carbon fibre into the composites. Carbon fibre also aggravated the fade behavior, reduction of COF with temperature increase. The SEM imaging of the composites revealed the formation of primary and secondary plateaus in the friction composites after addition of carbon fibre. The results obtained from dynamic-mechanical analysis, thermogravimetric analysis and SEM imaging were employed to investigate the worn surface of the samples and justify the aforementioned tribological behavior.
•The composite brake friction materials containing carbon fibre at various concentrations were prepared.•Carbon fibre reduced the wear rate of phenolic-resin based composite friction materials.•Carbon fibre reduced the friction coefficient and suppressed the fade at high content (4 vol%).•The formation of primary and secondary plateaus promoted by incorporation of carbon fibre.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
A novel trifluorovinyl-ether (-OCF&z.dbd;CF
2
, TFVE) functionalized diamine (
DA-TFVE
) with a triarylmethane structure was successfully obtained from renewable vanillin through a Brønsted acidic ...ionic liquid catalyzed Friedel-Crafts reaction. Subsequently, traditional two-step condensations between
DA-TFVE
and dianhydride (6FDA and CBDA) were used to prepare two linear polyimides (
PI-1
and
PI-2
, respectively) containing TFVE side groups. Both polyimides exhibited excellent film-forming ability and good solubility in common organic solvents. Upon heating, the linear polyimides could be transformed into cross-linked polyimides (
c
PI-1
and
c
PI-2
) with perfluorocyclobutyl (PFCB) ether linkers through thermal 2π + 2π post-polymerization of TFVE groups. Surprisingly, both
c
PI-1
and
c
PI-2
exhibited high mechanical strength with a storage modulus of more than 2.0 GPa at room temperature, as well as outstanding thermal stability with glass transition temperatures of 402 °C and 374 °C, respectively. The polymer films before and after thermal crosslinking showed high transparency. In particular, a transmittance of 73% at 450 nm and 81% at 500 nm was observed for the colorless polyimide
PI-2
with aliphatic segments. X-ray diffraction results of the obtained PIs showed that the average inter-chain distances (
d
-spacing) were 0.44-0.59 nm, indicating the hindered chain packing caused by PFCB linkers between the polymer chains. All these results suggested their potential application as candidate materials in high-performance packaging and flexible electronics.
Soluble polyimides with -OCF&z.dbd;CF
2
side groups were successfully prepared from a vanillin-derived aromatic diamine. After crosslinking, fluorinated polyimide networks were obtained with high thermal resistance, transparency and mechanical strength.
In this research the thermal, crystallization, and mechanical properties of branched poly (butylene succinate) (PBS) copolymers, which were synthesized through a two-stage esterification and ...condensation polymerization from 1,4-butanediol, 1,2-decanediol, and succinic acid and abbreviated as PBDS, were systematically investigated and compared with those of PBS homopolymer. Both PBS and PBDS copolymers showed relatively high and similar molecular weights, with the weight average molecular weights of 6.89 × 104 g/mol and above. PBDS copolymers showed the similar high thermal stability as PBS. With an increase in 1,2-decene succinate (DS) content, the glass transition temperature, melting point temperature, and equilibrium melting point temperature of PBDS copolymers gradually decreased. At the same cooling rate, the melt crystallization temperature of PBDS copolymers decreased, while at the same degree of supercooling, the crystallization half-time increased. The branching did not modify the crystallization mechanism and crystal structure of PBDS copolymers. Both the storage modulus and the glass transition temperature of PBDS copolymers gradually decreased with increasing the DS content. Compared with PBS, increasing the DS content obviously improved the elongation at break and accordingly decreased the Young's modulus and tensile strength of PBDS copolymers. In brief, the thermal, crystallization, and mechanical properties of PBS may be conveniently tuned by a copolymerization method via the introduction of branching.
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•The thermal, crystallization and mechanical properties of branched PBS were studied.•With increasing DS content, the Tg, Tm and Tmo of PBDS copolymers decreased.•The crystallization of PBDS copolymers significantly was retarded by the branching.•The branching did not modify the crystallization mechanism and crystal structure.•The dynamic and tensile mechanical properties were clearly affected by the branching.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
As a class of thermosetting resins with exceptional overall performance, cyanate esters have not received sufficient attention for their potential applications in 3D printing. In this paper, ...polytetrafluoroethylene micropowder is used for the first time as a thixotropic agent to regulate the rheological properties of liquid bisphenol E cyanate monomer for direct ink writing of cyanate ester resins in 3D printing. Due to their appropriate compatibility, the mixed inks exhibit high storage modulus and shear-thinning behavior, enabling the printed structures to maintain their shape well during printing and subsequent curing processes. The printed samples have good mechanical strength and excellent thermal stability. At the same time, the presence of polytetrafluoroethylene endows the composite materials with low dielectric constant and hydrophobicity. The latter property leads to high hygrothermal stability of the composites. The cyanate ester-polytetrafluoroethylene composite developed here offers a reliable method for 3D printing high performance cyanate ester, efficiently enhances the processibility of the cyanate ester based materials.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Objective: The present study investigates viscoelastic properties of human autopsy brain tissue via nanoindentation to find feasible biomarkers for Alzheimer's disease (AD) in ex vivo condition and ...to understand the mechanics of the human brain better, especially on the difference before and after progression of AD. Methods: Viscoelastic properties of paraformaldehyde-fixed, paraffinembedded thin (8 μm) sectioned normal and AD affected human autopsy brain tissue samples are investigated via nanoindentation with a combined loading profile of a linear preloading and a sinusoidal loading at various loading frequencies from 0.01 to 10 Hz. In 1200 indentation tests for ten human autopsy brain tissue samples from ten different subjects (five AD cases and five normal controls), viscoelastic properties such as Young's modulus, storage modulus, loss modulus, and loss factor of both gray and white matter brain tissues samples from normal and AD affected tissues were measured experimentally. Results: We found that the normal brain tissues have higher Young's modulus values than the AD affected brain tissues by 23.5% and 27.9% on average for gray and white matter, respectively, with statistically significant differences (p <; 0.0001) between the normal and AD affected brain tissues. Additionally, the AD affected brain tissues have much higher loss factor than the normal brain tissues on lower loading frequencies. Significance: AD is one of the leading causes of death in America and continues to affect a growing population. The challenges of recognizing the early pathological changes in brain tissue due to AD and diagnosing a patient has led to much research focused on finding biomarkers for the disease. In this regard, understanding the mechanics of brain tissues is increasingly recognized to play an important role in diagnosing brain diseases.
In this study, carbon fiber (CF)/polyetherketoneketone (PEKK) composites with 5% void content, manufactured via an in situ consolidated automated fiber placement (AFP) lay‐up process, are aged in hot ...water at 70°C for 30 days. Firstly, a deep understanding of the deterioration in the mechanical performance is developed with a comprehensive and complementary set of material characterization strategies, including (i) microstructural characterization with Fourier‐transform infrared spectroscopy (FTIR), (ii) thermal characterization with differential scanning calorimetry (DSC), and (iii) dynamic mechanical analysis (DMA). The material characterization concurrently highlights the plasticization and post‐crystallization phenomena after aging with changes in the peak densities with FTIR, formation of second glass transition temperature (Tg) in DSC and DMA, and drop in storage modulus, loss modulus, and tan delta (δ) amplitudes. Then, acoustic emission (AE) is utilized as an inspection tool to identify the damage mechanisms regarding the 6.5%, 5.2%, and 4% decrease in tensile strength, strain at failure and modulus, respectively, in a comparative manner. The AE findings, remarking the weakening of the fiber–matrix interface after aging, are validated with scanning electron microscopy analysis. This study introduces an aging process‐induced damage mechanism triggered with inhomogeneous water absorption for AFP manufactured CF/PEKK composites with in situ consolidation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The research on the polymer silicate layer nanocomposites is currently focusing on maximizing the polymer‐filler interface interaction. This study aimed to elucidate the effect of two different types ...of montmorillonite (MMT), which were Cloisite sodium (CNa) and Cloisite 10A (C10A), on the thermal, water absorption, and mechanical performances of polylactide (PLA) nanocomposites. Nanocomposites with different clay loadings from 1 to 7 wt% were fabricated by melt intercalation in a twin‐screw extruder. XRD analysis showed an intercalated structure for PLA/C10A at 1 and 3 wt% loadings. From TGA analysis, the initial thermal degradation temperature for PLA/C10A at 1 and 3 wt% showed promising enhancement in thermal stability. DSC results also confirmed that both nanocomposites at clay loadings less than 5 wt% improved thermal properties and crystallinity compared to neat PLA. Storage modulus and tan δ for PLA/C10A shifted towards higher temperature. Water absorption intakes of PLA/C10A at 1 and 3 wt% loadings were reduced by 42% and 39%, respectively. For PLA/C10A at the optimum loading of 3 wt%, tensile strength improved by 21% and strain by 17%. This loading exhibited the finest morphological structure.
PLA/ 3 %wt Cloisite 10A nanocomposites prepared by melt blending produced finer structure compared to PLA/ 3 %wt Cloisite Na, may be contributed by better interfacial interaction between C10A in PLA matrix. The interaction improved tensile strength and strain at break by 21% and 17% than PLA alone. The highest shift of glass transition temperature in Dynamic Mechanical Analysis was found in PLA/3 %wt Cloisite 10A at 77.6 °C, which was improved by 19% compared to PLA.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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