Mechano-responsive Properties Research Articles

Development of an alginate–chitosan biopolymer composite with dECM bioink additive for organ-on-a-chip articular cartilage

In vitro use of articular cartilage on an organ-on-a-chip (OOAC) via microfluidics is challenging owing to the dense extracellular matrix (ECM) composed of numerous protein moieties and few chondrocytes, which has limited proliferation potential and microscale translation. Hence, this study proposes a novel approach for using a combination of biopolymers and decellularised ECM (dECM) as a bioink additive in the development of scalable OOAC using a microfluidic platform. The bioink was tested with native chondrocytes and mesenchymal stem cell-induced chondrocytes using biopolymers of alginate and chitosan composite hydrogels. Two-dimensional (2D) and three-dimensional (3D) biomimetic tissue construction approaches have been used to characterise the morphology and cellular marker expression (by histology and confocal laser scanning microscopy), viability (cell viability dye using flow cytometry), and genotypic expression of ECM-specific markers (by quantitative PCR). The results demonstrated that the bioink had a significant impact on the increase in phenotypic and genotypic expression, with a statistical significance level of p < 0.05 according to Student’s t-test. The use of a cell-laden biopolymer as a bioink optimised the niche conditions for obtaining hyaline-type cartilage under culture conditions, paving the way for testing mechano-responsive properties and translating these findings to a cartilage-on-a-chip microfluidics system.

Reversible mechanoresponsive luminescence based on an unsymmetrical D-π-A type phenanthroimidazole derivative

Abstract A kind of D-π-A mechanoresponsive luminescent molecule 2- (4- (1H-phenanthro[9,10-d] imidazol) benzylidene) malononitrile (ANPPI) was synthesized and characterized by UV absorption, photoluminescence, and other techniques. The obvious mechanoresponsive properties of ANPPI were reversible upon grinding and fuming, and were demonstrated by X-ray diffraction, scanning electron microscopy, and differential scanning calorimetry.

Regulable high-contrast mechanofluorochromic enhancement behaviour based on substituent effects.

Herein, a facile strategy was established to build mechanoresponsive luminogens with high sensitivity to substituents and positional effects. Even in slightly different structures, distinct optical phenomena, including fluorescence efficiency and mechano-responsive properties, were clearly present. Outstanding mechanical-induced emission enhancement (5-100 times) properties and reversibility makes for promising applications in pressure sensors and OLEDs.

Compressive forces stabilize microtubules in living cells.

Microtubules are cytoskeleton components with unique mechanical and dynamic properties. They are rigid polymers that alternate phases of growth and shrinkage. Nonetheless, the cells can display a subset of stable microtubules, but it is unclear whether microtubule dynamics and mechanical properties are related. Recent in vitro studies suggest that microtubules have mechano-responsive properties, being able to stabilize their lattice by self-repair on physical damage. Here we study how microtubules respond to cycles of compressive forces in living cells and find that microtubules become distorted, less dynamic and more stable. This mechano-stabilization depends on CLASP2, which relocates from the end to the deformed shaft of microtubules. This process seems to be instrumental for cell migration in confined spaces. Overall, these results demonstrate that microtubules in living cells have mechano-responsive properties that allow them to resist and even counteract the forces to which they are subjected, being a central mediator of cellular mechano-responses.

Rational design of spiro[fluorene-9,9′-xanthene] based molecule for aggregation induced emission (AIE) and mechanochromism (MC): synthesis and theoretical investigation

A novel highly luminescent material with donor–spacer–acceptor spiroxanthene core integrated with triphenylamine designed and synthesized for aggregation induced emission (AIE) and mechano-responsive properties.

Tough, Self-Recoverable, Spiropyran (SP3) Bearing Polymer Beads Incorporated PAM Hydrogels with Sole Mechanochromic Behavior.

Spiropyran-containing hydrogels that can respond to external stimuli such as temperature, light, and stress have attracted extensive attention in recent years. However, most of them are generally dual or multiple stimuli-responsive to external stimuli, and the interplay of different stimulus responses is harmful to their sensitivity. Herein, spiropyran bearing polymer beads incorporated PAM (poly(AM–co–MA/DMSP3)) hydrogels with sole mechanochromic properties were synthesized by emulsion polymerization of acrylamide (AM) and methyl acrylate (MA) in the presence of spiropyran dimethacrylate mechanophore (DMSP3) crosslinker. Due to the hydrophobic nature of MA and DMSP3, the resultant hydrogel afforded a rosary structure with DMSP3 bearing polymer beads incorporated in the PAM network. It is found that the chemical component (e.g., AM, MA, and DMSP3 concentrations) significantly affect the mechanical and mechanoresponsive properties of the as-obtained poly(AM–co–MA/DMSP3) hydrogel. Under optimal conditions, poly(AM–co–MA/DMSP3) hydrogel displayed high mechanical properties (tensile stress of 1.91 MPa, a tensile strain of 815%, an elastic modulus of 0.67 MPa, and tearing energy of 3920 J/m2), and a good self-recovery feature. Owing to the mechanoresponsive of SP3, the hydrogels exhibited reversible color changes under force-induced deformation and relaxed recovery states. More impressive, the poly(AM–co–MA/DMSP3) hydrogel showed a linear correlation between tensile strain and chromaticity (x, y) as well as a stain and resting time-dependent color recovery rate. This kind of hydrogel is believed to have great potential in the application of outdoor strain sensors.

Dynamic covalent polymer networks with mechanical and mechanoresponsive properties reinforced by strong hydrogen bonding

Mechanoresponsive dynamic covalent networks were designed and synthesized by embedding radical mechanophores into the polymer backbone as crosslinkers. The mechanical properties and mechanoresponsiveness of the polymers were reinforced by hydrogen bonds.

PG-150 distearate-PVA self-healing hydrogel: Potential application in tissue engineering

Today, the proposal for self-healing biomaterials suitable for application in engineering for soft tissues with low mechanical stress such as in brain, adipose tissue or thyroid has prominently increased. In this study, a self-healing PG-150 distearate-PVA hydrogel was developed through the freezing/thawing method and characterized. The developed hydrogel proved higher crystallinity than the control hydrogel (without freezing/thawing cycle). Furthermore, the hydrogel presented adequate chemical and mechano-responsive properties, allowing it to maintain its structure when sudden impact was subjected. In addition, the hydrogel was capable of deforming under low levels of mechanical stress, making it an excellent option as tissue engineering material.

Functional flexible molecular crystals: intrinsic and mechanoresponsive properties

Flexible molecular crystals have attracted much attention to unique optoelectronic applications and stimuli-responsive chemistry, resulting in various functional molecular crystals for controlling photons, phonons, electrons, and magnons.

Thermomechanically controlled fluorescence anisotropy in thin films of InP/ZnS quantum dots.

Macroscopic scale sources of polarized light play a fundamental role in designing light-emitting devices. In this communication we report the formation of nano- and macro-scale ordered, layered assemblies of InP/ZnS quantum dots (QDs) exhibiting fluorescence anisotropy (FA), as well as thermo- and mechano-responsive properties. The long-range organization of small, quasi-isotropic nanoparticles was achieved by introducing liquid crystal molecules to the surface of QDs, without the need to use an organic matrix. Melting/crystallization of the ligand at 95 deg. C translated to a reversible reconfiguration of QDs thin film between 2D layered and body-centered cubic structures, characteristic for a temperature range below and above the melting point, respectively. The low-temperature, layered structure exhibited mechano-responsiveness which was key to introduce and control the sample alignment. Interestingly, transverse and parallel alignment modes of QDs layers were achieved, depending on the temperature of mechanical shearing. As prepared QD samples exhibited fluorescence anisotropy strongly correlated to the macroscopic orientation of the layers. Correlated small-angle X-ray diffraction (SAXRD) and fluorescence spectroscopy studies confirmed the mm-scale alignment of the thin films of QDs. Such films may be advantageous for developing efficient, densely packed, and uniform macro-scale FA sources.

3D Printed, Microgroove Pattern-Driven Generation of Oriented Ligamentous Architectures.

Specific orientations of regenerated ligaments are crucially required for mechanoresponsive properties and various biomechanical adaptations, which are the key interplay to support mineralized tissues. Although various 2D platforms or 3D printing systems can guide cellular activities or aligned organizations, it remains a challenge to develop ligament-guided, 3D architectures with the angular controllability for parallel, oblique or perpendicular orientations of cells required for biomechanical support of organs. Here, we show the use of scaffold design by additive manufacturing for specific topographies or angulated microgroove patterns to control cell orientations such as parallel (0°), oblique (45°) and perpendicular (90°) angulations. These results demonstrate that ligament cells displayed highly predictable and controllable orientations along microgroove patterns on 3D biopolymeric scaffolds. Our findings demonstrate that 3D printed topographical approaches can regulate spatiotemporal cell organizations that offer strong potential for adaptation to complex tissue defects to regenerate ligament-bone complexes.

Polymorphism, Mechanofluorochromism, and Photophysical Characterization of a Carbonyl Substituted Difluoroboron-β-Diketone Derivative

Difluoroboron-β-diketones are known to exhibit very promising mechanochromic luminescence but a greater understanding of these materials and their mechanoresponsive properties is still desirable. Here we demonstrate that a combination of spectroscopic and physicochemical techniques is necessary to understand the variation of solid-state fluorescence observed under mechanical stress and thermal annealing. For this study, we decided to focus on a new fluorescent compound showing a polymorphic behavior. Our investigation on the mechanofluorochromic properties is based on a thorough spectroscopic study (steady-state and time-resolved) on powder samples and thin films deposited on paper and coverglass substrates. Three different states were identified: two crystalline states (a stable green-emissive and a metastable yellow-emissive one) and an amorphous phase (yellow orange emission). The detailed photophysical properties highlight the dynamic excimer formation processes, which can take place in the yellow-emi...

A Stimuli-Responsive Metallohydrogel Exhibiting Cyclohexane-Like Hydrophobicity.

Silver(I) forms a hydrogel in the presence of cholate with unusual properties, which are not observed with other cations. Polarity-sensitive probes have shown that the spherical aggregates observed in the gel have 'pockets' with hydrophobicity comparable to that of degassed cyclohexane. The gel exhibited thermo- and mechanoresponsive properties. Color tunability from blue to cyan and green was observed with prodan. The two sol phases of the gel formed by applying stress and temperature showed very different properties.

N‐Cadherin, a novel and rapidly remodelling site involved in vasoregulation of small cerebral arteries

N-cadherin formed punctate adherens junctions (AJ) along the borders between vascular smooth muscle cells (VSMCs) in the pressurized rat superior cerebellar artery. The formation of N-cadherin AJs in the vessel wall depends on the intraluminal pressure and was responsive to treatment with phenylephrine (PE) (10-5 m) and ACh (10-5 m). N-cadherin-coated beads were able to induce clustering of N-cadherin-enhanced green fluorescent protein (EGFP) on the plasma membrane of isolated VSMCs, whereas treatment with PE (10-5 m) or sodium nitroprusside (10-5 m) induced a significant increase or decrease in the N-cadherin-EGFP clustering, respectively. Application of pulling force (∼1nN) to the N-cadherin-coated beads via an atomic force microscope induced a localized mechanical response from the VSMCs that opposed the pulling. N-cadherin is the major cell-cell adhesion molecule in vascular smooth muscle cells (VSMCs). We tested the hypothesis that N-cadherin is part of a novel mechanosensory mechanism in VSMCs and plays an active role in both the arteriolar myogenic response and during changes in vascular tone induced by vasomotor agonists. Intact and pressurized rat superior cerebellar arteries were labelled for confocal immunofluorescence imaging. N-cadherin formed punctate adherens junctions (AJ) along the borders between VSMCs. When the lumen pressure was raised from 50 to 90mmHg, both the density and the average size of N-cadherin AJs increased significantly. Similarly, arteriolar constriction with phenylephrine (PE) (10-5 m) induced a significant increase of N-cadherin AJ density at 50mmHg, whereas vasodilatation induced by ACh (10-5 m) was accompanied by a significant decrease in density and size of N-cadherin AJs. An atomic force microscope (AFM) was employed to further examine the mechano-responsive properties of N-cadherin adhesion sites in isolated VSMCs. AFM probes with an attached N-cadherin-coated microbead (5μm) induced a progressive clustering of N-cadherin-enhanced green fluorescent protein (EGFP) on the VSMC surface. Application of pulling force (∼1nN) to the N-cadherin-coated-beads with the AFM induced a localized mechanical response from the VSMCs that opposed the pulling. Treatment with PE (10-5 m) or sodium nitroprusside (10-5 m) induced a significant increase or decrease of the N-cadherin-EGFP clustering, respectively. These observations provide compelling evidence that N-cadherin AJs are sensitive to pressure and vasomotor agonists in VSMCs and support a functional role of N-cadherin AJs in vasomotor regulation.

Hydrogen bonding-assisted loosely packed crystals of a diaminomaleonitrile-modified tetraphenylethene compound and their photo- and mechano-responsive properties

Loosely packed crystals: Intermolecular-hydrogen-bonding assisted loosely packed crystals were constructed as multi-responsive materials with turn-on emission properties.

Controlling solid-state optical properties of stimuli responsive dimethylamino-substituted dibenzoylmethane materials

Dimethylamino β-diketones with electron donating and withdrawing substituents displayed solvatochromism and aggregation induced emission. In the solid state, a blue to orange color range and thermal and mechanoresponsive properties were achieved.

Two‐Step Mechanochromic Luminescence of N,N′‐Bis‐Boc‐3,3′‐di(pyren‐1‐yl)‐2,2′‐biindole

Despite recent advances in the development of mechanochromic luminescent organic molecules, the mechano-responsive properties of intramolecularly stacked fluorophores are not well documented. Herein, the synthesis and emission properties of three N,N'-bis-Boc-3,3'-diaryl-2,2'-biindole (Boc=tert-butoxycarbonyl) derivatives as a new class of solid-state emissive fluorophores are described. For a 3,3'-dipyrenyl derivative in the crystalline state, partial intramolecular stacking of the dipyrenyl groups was observed, which results in a two-step mechanochromic luminescence from blue (λem =462 nm) to green (λem =516 nm) and yellow (λem =535 nm).

Aurophilicity in Action: Fine-Tuning the Gold(I)-Gold(I) Distance in the Excited State To Modulate the Emission in a Series of Dinuclear Homoleptic Gold(I)-NHC Complexes.

The solution-state emission profiles of a series of dinuclear Au(I) complexes 4-6 of the general formula Au2(NHC-(CH2)n-NHC)2Br2, where NHC = N-benzylbenzimidazol-2-ylidene and n = 1-3, were found to be markedly different from each other and dependent on the presence of excess bromide. The addition of excess bromide to the solutions of 4 and 6 leads to red shifts of ca. 60 nm, and in the case of 5, which is nonemissive when neat, green luminescence emerges. A detailed computational study undertaken to rationalize the observed behavior revealed the determining role aurophilicity plays in the photophysics of these compounds, and the formation of exciplexes between the complex cations and solvent molecules or counterions was demonstrated to significantly decrease the Au-Au distance in the triplet excited state. A direct dependence of the emission wavelength on the strength of the intracationic aurophilic contact allows for a controlled manipulation of the emission energy by varying the linker length of a diNHC ligand and by judicial choice of counterions or solvent. Such unique stimuli-responsive solution-state behavior is of interest to prospective applications in medical diagnostics, bioimaging, and sensing. In the solid, the investigated complexes are intensely phosphorescent and, notably, 5 and 6 exhibit reversible luminescent mechanochromism arising from amorphization accompanied by the loss of co-crystallized methanol molecules. The mechano-responsive properties are also likely to be related to changes in bromide coordination and the ensuing alterations of intramolecular aurophilic interactions. Somewhat surprisingly, the photophysics of NHC ligand precursors 2 and 3 is related to the formation of ground-state associates with bromide counterions through hydrogen bonding, whereas 1 does not appear to bind its counterions.

Mechanoresponsive Properties of the Periodontal Ligament

The periodontal ligament (PDL) functions as an enthesis, a connective tissue attachment that dissipates strains created by mechanical loading. Entheses are mechanoresponsive structures that rapidly adapt to changes in their mechanical loading; here we asked which features of the PDL are sensitive to such in vivo loading. We evaluated the PDL in 4 physiologically relevant mechanical environments, focusing on mitotic activity, cell density, collagen content, osteogenic protein expression, and organization of the tissue. In addition to examining PDLs that supported teeth under masticatory loading and eruptive forces, 2 additional mechanical conditions were created and analyzed: hypoloading and experimental tooth movement. Collectively, these data revealed that the adult PDL is a remarkably quiescent tissue and that only when it is subjected to increased loads—such as those associated with mastication, eruption, and orthodontic tooth movement—does the tissue increase its rate of cell proliferation and collagen production. These data have relevance in clinical scenarios where PDL acclimatization can be exploited to optimize tooth movement.

Structural bases for mechano-responsive properties in molecular gels of (R)-12-hydroxy-N-(ω-hydroxyalkyl)octadecanamides. Rates of formation and responses to destructive strain.

The self-assembly and gelation behavior of a series of (R)-12-hydroxy-N-(ω-hydroxyalkyl)octadecanamides (HS-n-OH, where n = 2, 3, 4 and 5 is the length of the alkyl chain on nitrogen), as well as those of two ‘model’ compounds, N-(3-hydroxypropyl)octadecanamide (S-3-OH) and (R)-12-hydroxy-N-propyloctadecanamide (HS-3), have been investigated in a wide range of liquids. A unique aspect of some of the HS-n-OH gels is the degree and velocity of their recovery of viscoelasticity after the cessation of destructive shear. The recovery times vary from less than one second to hundreds of seconds, depending on the length of the ω-hydroxyalkyl group on nitrogen. The data indicate that the modes and dynamics of aggregation of the gelator molecules from incubation of a sol phase below the gel melting temperature, as analyzed by Avrami and fractal equations, cannot be used to explain the degree and dynamics of the thixotropy: sol-to-gel transformations involve assembly of 0-dimensional objects (i.e., individual gelator molecules) into 1-dimensional fibrils and then into 3-dimensional networks; recovery after mechano-destruction of gels requires only 1-dimensional to 3-dimensional re-assembly or re-association of 3-dimensional spherulitic objects. A model to understand the extreme sensitivity of the thixotropy on the length of the ω-hydroxyalkyl group in the HS-n-OH (which is based upon detailed comparisons among the dynamic properties of the gels, the morphologies of the neat gelators, and the fibrillar networks of the gels) invokes the importance of the cleavage and reformation of H-bonds between fibers at ‘junction zones’ or between spherulitic objects.