Integrin-Mimetic Mechanosensory Elastomer with Fluorescence Probe for Monitoring Chain Deformation in Situ

Open AccessCCS ChemistryRESEARCH ARTICLE10 May 2021Integrin-Mimetic Mechanosensory Elastomer with Fluorescence Probe for Monitoring Chain Deformation in Situ Chao Li, Xiqi Zhang, Longfei Luo, Lei Jiang and Longcheng Gao Chao Li Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, Key Laboratory of Beijing Energy, School of Chemistry, Beihang University, Beijing 100191 , Xiqi Zhang Key Laboratory of Bio-Inspired Materials and Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 , Longfei Luo Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 , Lei Jiang Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, Key Laboratory of Beijing Energy, School of Chemistry, Beihang University, Beijing 100191 Key Laboratory of Bio-Inspired Materials and Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 and Longcheng Gao *Corresponding author: E-mail Address: [email protected] Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, Key Laboratory of Beijing Energy, School of Chemistry, Beihang University, Beijing 100191 https://doi.org/10.31635/ccschem.021.202100793 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail Mechanosensory elastomers attract intense interests in the academic and industrial fields. However, molecular insight of macroscopic properties remains a significant challenge. Herein, we build up a correlation between the microscopic and macroscopic level by designing a mechanosensory elastomer with aggregation-induced emission luminogens (AIEgens) that monitors chain deformation in situ. The key constituents are the mechanosensory units, which are dynamic dimers bonded by ureidopyrimidinone (UPy) groups and tetraphenylethylene (TPE) for the fluorescence signal output. The photoluminescence (PL) technique successfully monitors elastomer chain deformation under external forces. The PL intensity increases linearly at low elongation, in excellent agreement with Hooke's law for ideal chains. Strong deviation from linear PL intensity is measured at high elongation, which can be theoretically described by the Langevin function. A correlation between the microscopic and the macroscopic level is then built. Download figure Download PowerPoint Introduction Soft materials that are fluorescent, mechanosensory, and self-healing play crucial roles in fields such as wearable electronics, clinical therapy, dynamic camouflage, and anticounterfeiting.1 By incorporating chromophores, many mechanosensory polymers have been exploited to realize force-induced color-change properties.2–8 The mechanochromic fluorescent process can be divided into two steps. First, external stimuli are transmitted from macroscopic scales down to individual chains, leading to the polymer chains deformation. Second, the polymer chain movements trigger the chromophores luminescence transition. Extensive research has focused on the mutual relationship between the external stimuli and fluorescence properties. The essential correlation between the movements of the polymer chains and the luminescence signals of the chromophores is generally neglected. Actually, there has been some research focusing on the movements of polymer chains by atomic force microscopy (AFM)9 and optical tweezers,10 which is expensive and difficult to operate. Designing a material system to reflect the movements of polymer chains with a convenient method [like a photoluminescence (PL) technique] would provide an opportunity to build a bridge between the macroscopic and microscopic regions. However, approaching such intelligent artificial materials remains a big challenge. Nature inspires us to overcome this challenge. There are numerous biological structures with various smart functions with over millions of years of evolution. Integrins, existing in all animals, are transmembrane proteins that facilitate cell-extracellular matrix (ECM) adhesion.11 Integrin-mediated mechanosensing is involved in many physiological processes, such as the sense of touch,12 vascular homeostasis,13 and the growth and remodeling of tissue.14 Integrins are composed of non-covalently bonded dimers (α and β subunits), which act as mechanosensory linkages in the cytoskeletal network (Figure 1a). When mechanical stimuli are applied, force is transduced across the interfaces to each integrin via hydrogen bonding. Conformational activation of the integrins is triggered, and then chemical signals are stimulated. High sensitivity to the peptide chain conformation is the key factor.15–18 Figure 1 | The mechanosensory integrin is composed of α and β subunits, bonded by noncovalent interaction. (a) An external force is transduced across the interface between the α and β subunits, triggering a conformational transition and stimulating chemical signals. (b) The concept of fabricating a biomimetic mechanosensory elastomer. The mechanosensory units contain UPy dimers with quadruple hydrogen bonding and TPE groups with conformation-dependence fluorescence. Download figure Download PowerPoint We get inspiration from the molecular structure of integrins to design the mechanosensory elastomer and provide a convenient way to monitor the polymer chain deformation under external force. The crucial part of the structure is a dynamic mechanosensory unit, which acts as the functional junction of polybutadiene (PB) rubber. The unit is composed of ureidopyrimidinone (UPy) dimers for chain extension and mechanophores for fluorescent signal output (Figure 1b). UPy groups form self-complementary quadruple hydrogen bonding, providing sufficient mechanical connection for the polymer chains.19 The dynamic connection endows the system with self-healable properties,20 which are remarkable features of biosystems. Tetraphenylethylene (TPE), a typical aggregation-induced emission (AIE) luminogen,21–23 is introduced because of its excellent microenvironment sensitivity.24–26 When external mechanical stimuli are applied, the polymer chains undergo conformational changes. Thus, the internal force is transduced to the TPE groups, and the TPE intramolecular motions are restricted.27,28 As a result, TPE fluorescence emission is enhanced. The mechanosensory elastomer exhibits healing properties, and the procedure is visualized in situ. Furthermore, deformation of the elastomer chain is reflected by the actuated fluorescence enhancement. For the first time, we utilize the PL technique to monitor elastomer chain deformation under an external force. Based on the mechanosensory phenomenon, we demonstrate the application toward erasable optical data storage media. Experimental Methods Synthesis of PB-(TPE-NH2)2 Carboxyl-terminated polybutadiene (PB-COOH) (5.0 g, 1 mmol) was dissolved in 50 mL of CH2Cl2, then added TPE-(NH2)2 (3.62 g, 0.01 mol), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI) (0.58 g, 3 mmol), and 4-dimethylaminopyridine (DMAP) (0.12 g, 1 mmol). The mixture was stirred at room temperature overnight. Then excess CH2Cl2 was removed by rotary evaporation, and the mixture was precipitated into methanol to obtain the product PB-(TPE-NH2)2 (4.8 g glassy solid, yielding 84%). 1H NMR result: δ (ppm) = 6.7–7.2 (m, 36H, TPE), 6.4 (d, 4H, Ar-NH2), 5.5–5.7 (m, 36H, 1,2-C H=CH2), 5.3–5.5 (m, 300H, 1,4-CH2-C H=C H-CH2-), 4.8–5.0 (m, 74H, 1,2-CH=C H2), 1.8–2.2 (m, 652H, 1,4-C H2-CH=CH-C H2-), 1.0–1.7 (m, 120H, 1,2-C H-C H2-) ( Supporting Information Figure S3b). The molecular weight was measured by gel permeation chromatography (GPC) [Mn = 14,400, polymer dispersity index (PDI) = 2.44] ( Supporting Information Figure S2). Synthesis of PB-(TPE-UPy)2 PB-(TPE-NH2)2 (1.5 g, 0.1 mmol) was dissolved in 10 mL dimethylformamide (DMF), then 2-(1-imidazolylcarbonylamino)-6-methyl-4-[1H]-pyrimidinone (IPy) (0.22 g, 1 mmol) was added. The mixture was heated to 100 °C under N2 atmosphere and stirred overnight. Then excess DMF was removed by rotary evaporation, and the mixture was precipitated into methanol to obtain the product PB-(TPE-UPy)2 (1.12 g solid, yielding 73%). 1H NMR results: δ (ppm) = 13 (s, 2H, UPy), 12.2 (d, 4H, UPy), 6.7–7.1 (m, 36H, TPE), 5.5–5.6 (m, 1,2-C H=CH2), 5.0–5.4 (m, 1,4-CH2-C H=C H-CH2-), 4.8–5.0 (m, 1,2-CH=C H2), 1.7–2.4 (m, 1,4-C H2-CH=CH-C H2-), 0.9–1.6 (m, 1,2-C H-C H2-) ( Supporting Information Figure S3c). The molecular weight was measured by GPC (Mn = 16,000, PDI = 1.96, Supporting Information Figure S2). Preparation of films of PB-(TPE-UPy)2 and PS/PB-(TPE-UPy)2 PB-(TPE-UPy)2 (100 mg) was dissolved in 2 mL CHCl3, then the solution was added into 2-cm diameter polytetrafluoroethylene molds. After the solvent evaporated, the sample was taken into a vacuum oven at 40 °C overnight, and the complete film could be easily removed from the template. Polystyrene (PS) (1.0 g) and PB-(TPE-UPy)2 (50 mg) were dissolved in 10 mL CHCl3, then the solution was droppered on polytetrafluoroethylene molds of different sizes. After the solution evaporated, the sample was taken into vacuum oven at 40 °C. Then the complete film was stuck to A4 paper, and different patterns were printed by a wire printer. Results and Discussion Preparation of the mechanosensory elastomer The mechanosensory units containing TPE and UPy groups are modified to the PB ends by a two-step amidation reaction ( Supporting Information Figure S1). The polymer structure was confirmed by a molecular weight increase in the GPC curves and the appearance of typical chemical shifts in the 1H NMR spectrum ( Supporting Information Figures S2 and S3). The disappearance of chemical shifts of –COOH after TPE modification indicated complete conversion. The integration ratios of UPy and TPE after UPy modification indicate that the molar ratio of UPy/TPE is close to 1:1. From the terminal groups analysis based on NMR results, the PB chains were quantitatively functionalized, and each PB chain mostly contained two UPy groups. Thus, the PB chains are telechelic and exclusively form dimers through an UPy quadruple hydrogen bond.29,30 The supramolecular dimers act as physical chain-extending moieties, forming long chains with alternating structures of hard and soft segments. The elastomer presents excellent thermal stability, where the 5% loss temperature was above 270 °C ( Supporting Information Figure S4). Dynamic linkers between polymer chains Although there is no chemical cross-link point for the telechelic polymer, the association strength of the terminal UPys is sufficiently strong. The PB chains extend and form an entanglement network. The mechanosensory units could also act as the physical crosslink points which enhance the mechanical strength of the sample. In appearance, the original state of the PB is liquid-like and becomes solid after grafting the mechanosensory units ( Supporting Information Figure S1). From the AFM image (Figure 2a), we can see fiber-like structures that appear bright. They are related to the stacks of hard segments. The stacks are likely in the lateral direction of the TPE-UPy association plane, making the PB chains difficult to disentangle. The TPE-UPy stacks were verified by the X-ray scattering technique (Figure 2b). At a higher scattering factor, a wide halo with a size of approximately 0.45 nm is observed, corresponding to the stack distance of TPE-UPy. From the small-angle X-ray scattering results, we can see that phase separation occurred with a feature size of approximately 10 nm, although the scattering peak is wide and no higher-order scattering peak is seen. Figure 2 | The structural characterizations. (a) AFM image of the elastomer surface. (b) X-ray scattering curves indicating that the mechanosensory units assemble into the microphase separation structure. The two-dimensional (2D) small-angle X-ray scattering profile (I) shows a halo without higher order, indicating the structure lacks long-range order. The 2D wide-angle X-ray scattering profile (II) indicates the lateral stacks of the mechanosensory units. (c) FTIR spectra of the elastomer at 3200–3500 cm−1 obtained by heating the sample between 30 and 150 °C. (d) FTIR spectra of the elastomer at 3200–3500 cm−1 obtained cooling the sample between 30 and 150 °C. The data are recorded every 10 °C. The peak at 3440 cm−1 indicates the association and dissociation of hydrogen bonding of the UPy groups in the mechanosensory units. Download figure Download PowerPoint Dynamic hydrogen bonding of the UPy groups in the mechanosensory units is confirmed by in situ variable temperature Fourier transform infrared (FTIR) spectroscopy. Figure 2c shows the spectra in the region of 3200–3500 cm−1 from 30 to 150 °C. The band at approximately 3300 cm−1 is related to hydrogen-bonded N–H stretching. As temperature increases, the hydrogen-bonded N–H stretching band shifts to higher frequency and exhibits a steady decrease in intensity and increase in bandwidth, indicating that the H-bond strength becomes weaker. Meanwhile, a small broad peak starts to be detected at 3440 cm−1 at 60 °C, implying the presence of free N–H groups.31 In addition, the cooling procedure shows reversibility of the transition (Figure 2d). Meanwhile, the shoulder changes (around 1530 cm−1) also confirm the association/dissociation of hydrogen bonding of the UPy groups ( Supporting Information Figure S5). AIE property of mechanosensory elastomer TPE-containing elastomer exhibits typical AIE phenomena.23 The polymer is virtually nonfluorescent when dissolved in a good solvent. The PL intensity dramatically increases with increased water content (Figures 3a and 3b). In addition, the elastomer also presents temperature-dependent responsiveness to fluorescence intensity ( Supporting Information Figure S6), and the fluorescence intensity of the maximum emission wavelength drops dramatically with increasing temperature. The higher temperature means increased intramolecular motions of the benzene ring, which leads to more dissipation of the excited-state energy in the form of nonradiative transition. The transition of fluorescence intensity matches the glass transition temperature (Tg) of PB-(TPE-UPy)2 ( Supporting Information Figure S7).32 It is worth noting that there is also a transition around 60 °C, corresponding to the hydrogen-bonding dissociation. That is to say that the intramolecular motions of TPE were additionally activated by the hydrogen-bonding dissociation, which could cause extra decreases of fluorescent intensity. Figure 3 | AIE property of the elastomer. (a) The fluorescence spectra of the mechanosensory elastomer in tetrahydrofuran (THF)/water mixtures with different water fractions. (b) The plots of PL intensity as a function of water content exhibit features of AIE. The inset shows the digital images of the sample in THF/water mixtures with increasing water fraction upon UV exposure. Download figure Download PowerPoint Self-healing property of mechanosensory elastomer The aggregation of mechanosensory units serves as the dynamic physical crosslink points, due to the noncovalent interactions. By reversible association/dissociation, the cross-link points can be built/rebuilt. In this way, the materials can self-heal after damage. Fluorescent elements enable the elastomer to visualize the damage/heal process. Recoverability from damages has become the crucial factor that determines the service life of materials. For integrins, the dynamic hydrogen-bonding network plays an important role in wound healing.33 The supramolecular polymer has intrinsic self-healing ability as a result of the UPy hydrogen-bonding interaction and low Tg. Furthermore, the damage and recovery processes are able to be monitored by PL techniques due to the incorporation of TPE. After scraping the sample, a bright scratch is observed by the fluorescence microscope. The scraping can self-heal in 6 h at room temperature ( Supporting Information Figure S8). The healing process can also be accelerated by heating. The scratch is totally recovered within 10 min at 60 °C (Figure 4a). The elastomer film is cut into two pieces and links together again at 60 °C. The separate fragments reconnect by healing and maintain original mechanical strength (Figure 4b). The stress–strain curves of the original and healed film are shown in Figure 4c. The mechanical properties are well recovered after healing. The rubber, with easy and efficient healing ability, can serve as an airtight material, which has promise in the extension of product lifetime. Figure 4 | The mechanosensory elastomer healed after damage, and the process is visualized by PL methods. (a) The fluorescence microscopy images of the scraping sample after heating in 60 °C with different times: 0, 5, and 10 min. (b) The fluorescent digital images of the elastomer film before and after healing. (c) The stress–strain curves of the sample at the original state and after healing for 5 and 10 min, indicating excellent self-healing ability. Download figure Download PowerPoint In situ chain deformation monitoring Adherens junctions experience changes in mechanical tension and can serve as mechanotransducers. We measured the PL spectrum in situ as the sample film was stretched. During stretching, the fluorescence intensity clearly increases despite the decreasing surface density of AIE probes (Figure 5a). Stretch-enhanced fluorescence results from the restriction of intramolecular motions during deformation. Due to the low Tg and flexibility of PB, at the original state, the polymer chains are unperturbed, providing sufficient free volume for the motion of PB-linked benzene rings. At the onset of stress, the chain segments are forced to move out of their preferred positions. The external tension changes the chain conformation from a nearly undeformed state to an extended state. With external tension, the chains undergo segmental orientation, leading to a retractive force along the chains. As a result, the motions of benzene rings that are connected to the PB chains are greatly limited, causing dramatic increases in fluorescence intensity. Furthermore, the stretching-induced chain orientation can be confirmed by the polarizing microscopy (POM) observation. From Figure 5b, we can see banded textures after mechanical stretching, indicating that the PB chains adopt parallel conformation. On the contrast, there is no birefringence because the polymer chains are isotropic chains without stretching ( Supporting Information Figure S9). Figure 5 | PL technique monitors the chains deformation in situ. (a) The PL curves of the elastomer at different elongations exhibit elongation-dependent fluorescence. (b) Banded texture of PB-(TPE-UPy)2 under stretching, indicating that the chains are parallelized. (c and d) The PL intensity increases linearly with strain in the low-elongation regime and becomes strongly nonlinear at higher elongation. Download figure Download PowerPoint The PL intensity exhibits a linear increase with strain in the low-elongation regime (Figure 5c). As described above, the PB-(TPE-UPy)2 forms a physically cross-linked network, with the aggregated UPy dimers acting as the physical cross-linkers. When strain is applied to the networks, the chains between the cross-linkers lose conformational entropy when stretched from the original coil state. At small strain, the entropic elasticity of the chain obeys Hooke's law since the polymer chain satisfies ideal chain statistics in the melt state. Each chain experiences a force proportional to its end-to-end distance R via f = 3 k T R / ( N b 2 ) (1)where N is monomer number and b is monomer size.34 For a network, R should be proportional to strain. Therefore, the retractive force increases linearly. The force is transferred to the TPE, which raises the restriction on the intramolecular motion of TPE groups. As a result, the PL intensity is proportional to elongation. With further stretching, the dependence of PL intensity becomes strongly nonlinear, which is attributed to the finite chain extensibility at high elongations (Figure 5d). A strongly deformed chain satisfies non-Gaussian statistics, and the dependence of force f on chain elongation R can be given implicitly through the Langevin function34: R / N b = coth ( f b / k T ) − k T / f b(2)The retractive force transferred to TPE increases more rapidly with elongation. Consequently, the more constrained intramolecular rotation of TPE leads to stronger fluorescence emission. The variation tendency of PL intensity represents the stress state of the elastomer chain during stretching. AFM9 and optical tweezers10 have been used to measure the elongation dependence of force applied to single chains. These methods are rather complicated and require expensive equipment. Herein, we provide a more convenient method to monitor and further research on the polymer chain movement. For the first time, we use the PL technique to monitor the elastomer chain deformation under an external force. The deformation-dependent PL property shows excellent reversibility. By repeatedly measuring the PL of the elastomer at original and 100% strain ( Supporting Information Figure S10), we can see that the PL intensity is approximately recovered. Rewritable data storage The deformation-dependent PL property of the polymer has potential applications in fields such as data storage, chemosensing, and security labeling. We blend PB with PS to increase mechanical strength, which is a universal strategy in the industry. The resultant PS/PB blend retains the fluorescent responsiveness to pressure and strain ( Supporting Information Figure S11). The fluorescence intensity almost linearly increases with corresponding strain, similarly to PB-(TPE-UPy)2 at low deformations (Figure 5b). The blends bear enhanced mechanical properties. They could be processed into any desired shape. A thin film is made by solution casting. We use a commercial wire printer connected with a computer to print designed patterns. As seen in Figures 6a and 6b, we print a rose directly on the composite thin film. Under sunlight, the printed picture is nearly undetectable. Under a hand-held UV lamp, it is clearly visible, exhibiting a brighter blue fluorescence signal. Under the pressure from the needle tip, the PB chains underwent conformation change from the equilibrium state, resulting in restriction of TPE and fluorescence enhancement. The mechanosensory properties of the material can be used for optical data storage. More importantly, the data storage medium is rewritable due to the dynamic noncovalent interactions of the mechanosensory units. The rose disappears completely after annealing with a hot wind blower. In addition, the film is recyclable. Figure 6 | The mechanosensory elastomer enables application in rewritable data storage. (a) A rose was printed by a wire printer and (b) was erased completely by heating with a heat gun. Download figure Download PowerPoint Conclusions Inspired by integrins, we introduced TPE as a mechanosensory indicator that can monitor the change in tension along a polymer chain during deformation. We incorporated TPE into the backbone of UPy-terminated linear PB, and the polymers form an entangled physical network due to the hydrogen bonds and stacking of UPy dimers. The fluorescence of TPE increases in response to macroscopic deformation. The morphology-dependent PL of the elastomer agrees well with the entropy elasticity model of the elastomer, which provides a convenient approach for experimental research on polymer chain conformation transition. The elastomer also shows self-healing ability and is visualized by the in situ observation of TPE fluorescence. Besides, the elastomer is capable of printing rewritable optical data. The biomimetic design concepts represent a general approach to the preparation of functional materials. Supporting Information Supporting Information is available and includes experimental details, measurements, and supporting databases. Conflict of Interest There is no conflict of interest to report. Author Contributions L.G. and L.J. conceived the project. C.L. completed the experimental section with help of X.Z. and L.L. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Information This work was supported by the National Natural Science Foundation of China (nos. 21875009 and 51973227), the National Key Research and Development Program of China (nos. 2017YFA0206904 and 2017YFA0206900), the Youth Innovation Promotion Association CAS (no. 2020028), and the Fundamental Research Funds for the Central Universities. Acknowledgments The authors are grateful for discussion with Prof. Yang Shuang from Peking University. References 1. Xu C.; Stiubianu G. T.; Gorodetsky A. A.Adaptive Infrared-Reflecting Systems Inspired by Cephalopods.Science2018, 359, 1495–1500. Google Scholar 2. Crenshaw B. R.; Weder C.Self-Assessing Photoluminescent Polyurethanes.Macromolecules2006, 39, 9581–9589. Google Scholar 3. Wang Q.; Gossweiler G. R.; Craig S. L.; Zhao X.Cephalopod-Inspired Design of Electro-Mechano-Chemically Responsive Elastomers for On-Demand Fluorescent Atterning.Nat. Commun.2014, 5, 4899. Google Scholar 4. Zhang H.; Chen Y.; Lin Y.; Fang X.; Xu Y.; Ruan Y.; Weng W.Spiropyran as a Mechanochromic Probe in Dual Cross-Linked Elastomers.Macromolecules2014, 47, 6783–6790. Google Scholar 5. Davis D. A.; Hamilton A.; Yang J.; Cremar L. D.; Van Gough D.; Potisek S. L.; Ong M. T.; Braun P. V.; Martínez T. J.; White S. R.; Moore J. S.; Sottos N. R.Force-Induced Activation of Covalent Bonds in Mechanoresponsive Polymeric Materials.Nature2009, 459, 68. Google Scholar 6. Potisek S. L.; Davis D. A.; Sottos N. R.; White S. R.; Moore J. S.Mechanophore-Linked Addition Polymers.J. Am. Chem. Soc.2007, 129, 13808–13809. Google Scholar 7. Mizoshita N.; Tani T.; Inagaki S.Isothermally Reversible Fluorescence Switching of a Mechanochromic Perylene Bisimide Dye.Adv. Mater.2012, 24, 3350–3355. Google Scholar 8. Calvino C.; Guha A.; Weder C.; Schrettl S.Self-Calibrating Mechanochromic Fluorescent Polymers Based on Encapsulated Excimer-Forming Dyes.Adv. Mater.2018, 30, 1704603. Google Scholar 9. Rief M.; Oesterhelt F.; Heymann B.; Gaub H. E.Single Molecule Force Spectroscopy on Polysaccharides by Atomic Force Microscopy.Science1997, 275, 1295–1297. Google Scholar 10. Perkins T.; Smith D.; Chu S.Direct Observation of Tube-like Motion of a Single Polymer Chain.Science1994, 264, 819–822. Google Scholar 11. Giancotti F. G.; Ruoslahti E.Integrin Signaling.Science1999, 285, 1028–1033. Google Scholar 12. Ju L.; McFadyen J. D.; Al-Daher S.; Alwis I.; Chen Y.; Tønnesen L. L.; Maiocchi S.; Coulter B.; Calkin A. C.; Felner E. I.; Cohen N.; Yuan Y.; Schoenwaelder S. M.; Cooper M. E.; Zhu C.; Jackson S. P.Compression Force Sensing Regulates Integrin αIIbβ3 Adhesive Function on Diabetic Platelets.Nat. Commun.2018, 9, 1087. Google Scholar 13. Bazzoni G.; Dejana E.Endothelial Cell-to-Cell Junctions: Molecular Organization and Role in Vascular Homeostasis.Physiol. Rev.2004, 84, 869–901. Google Scholar 14. Discher D. E.; Janmey P.; Wang Y.-L.Tissue Cells Feel and Respond to the Stiffness of Their Substrate.Science2005, 310, 1139–1143. Google Scholar 15. Tzima E.; Irani-Tehrani M.; Kiosses W. B.; Dejana E.; Schultz D. A.; Engelhardt B.; Cao G.; DeLisser H.; Schwartz M. A.A Mechanosensory Complex that Mediates the Endothelial Cell Response to Fluid Shear Dtress.Nature2005, 437, 426. Google Scholar 16. Kim M.; Carman C. V.; Springer T. A.Bidirectional Transmembrane Signaling by Cytoplasmic Domain Separation in Integrins.Science2003, 301, 1720–1725. Google Scholar 17. Ehrlicher A. J.; Nakamura F.; Hartwig J. H.; Weitz D. A.; Stossel T. P.Mechanical Strain in Actin Networks Regulates FilGAP and Integrin Binding to Filamin A.Nature2011, 478, 260. Google Scholar 18. Marszalek P. E.; Lu H.; Li H.; Carrion-Vazquez M.; Oberhauser A. F.; Schulten K.; Fernandez J. M.Mechanical Unfolding Intermediates in Titin Modules.Nature1999, 402, 100. Google Scholar 19. Beijer F. H.; Sijbesma R. P.; Kooijman H.; Spek A. L.; Meijer E. W.Strong Dimerization of Ureidopyrimidones via Quadruple Hydrogen Bonding.J. Am. Chem. Soc.1998, 120, 6761–6769. Google Scholar 20. Hentschel J.; Kushner A. M.; Ziller J.; Guan Z.Self-Healing Supramolecular Block Copolymers.Angew. Chem. Int. Ed.2012, 124, 10713–10717. Google Scholar 21. Hong Y.; Lam J. W.; Tang B. Z.Aggregation-Induced Emission.Chem. Soc. Rev.2011, 40, 5361–5388. Google Scholar 22. Mei J.; Leung N. L. C.; Kwok R. T. K.; Lam J. W. Y.; Tang B. Z.Aggregation-Induced Emission: Together We Shine, United We Soar!Chem. Rev.2015, 115, 11718–11940. Google Scholar 23. Luo J.; Xie Z.; Lam J. W. Y.; Cheng L.; Chen H.; Qiu C.; Kwok H. S.; Zhan X.; Liu Y.; Zhu D.; Tang B. Z.Aggregation-Induced Emission of 1-Methyl-1,2,3,4,5-Pentaphenylsilole.Chem. Commun.2001, 18, 1740–1741. Google Scholar 24. Shustova N. B.; McCarthy B. D.; Dincă M.Turn-On Fluorescence in Tetraphenylethylene-Based Metal–Organic Frameworks: An Alternative to Aggregation-Induced Emission.J. Am. Chem. Soc.2011, 133, 20126–20129. Google Scholar 25. Xu J.; Ji W.; Li C.; Lv Y.; Qiu Z.; Gao L.; Chen E.; Lam J. W. Y.; Tang B.; Jiang L.Reversible Thermal-Induced Fluorescence Color Change of Tetraphenylethylene-Labeled Nylon-6.Adv. Opt. Mater.2018, 6, 1701149. Google Scholar 26. Yang Y.; Zhang S.; Zhang X.; Gao L.; Wei Y.; Ji Y.Detecting Topology Freezing Transition Temperature of Vitrimers by AIE Luminogens.Nat. Commun.2019, 10, 3165. Google Scholar 27. Qian H.; Cousins M. E.; Horak E. H.; Wakefield A.; Liptak M. D.; Aprahamian I.Suppression of Kasha's Rule as a Mechanism for Fluorescent Molecular Rotors and Aggregation-Induced Emission.Nat. Chem.2016, 9, 83–87. Google Scholar 28. Mei J.; Hong Y.; Lam J. W. Y.; Qin A.; Tang Y.; Tang B. Z.Aggregation-Induced Emission: The Whole Is More Brilliant than the Parts.Adv. Mater.2014, 26, 5429–5479. Google Scholar 29. Hirschberg J. K.; Beijer F. H.; van Aert H. A.; Magusin P. C.; Sijbesma R. P.; Meijer E. W.Supramolecular Polymers from Linear Telechelic Siloxanes with Quadruple-Hydrogen-Bonded Units.Macromolecules1999, 32, 2696–2705. Google Scholar 30. Keizer H. M.; van Kessel R.; Sijbesma R. P.; Meijer E. W.Scale-Up of the Synthesis of Ureidopyrimidinone Functionalized Telechelic Poly(ethylenebutylene).Polymer2003, 44, 5505–5511. Google Scholar 31. Mes T.; Smulders M. M.; Palmans A. R.; Meijer E. W.Hydrogen-Bond Engineering in Supramolecular Polymers: Polarity Influence on the Self-Assembly of Benzene-1,3,5-Tricarboxamides.Macromolecules2010, 43, 1981–1991. Google Scholar 32. Song Z.; Lv X.; Gao L.; Jiang L.Dramatic Differences in the Fluorescence of AIEgen-Doped Micro- and Macrophase Separated Systems.J. Mater. Chem. C.2018, 6, 171–177. Google Scholar 33. Margadant C.; Sonnenberg A.Integrin-TGF-β Crosstalk in Fibrosis, Cancer and Wound Healing.EMBO Rep.2010, 11, 97–105. Google Scholar 34. Rubinstein M.; Colby R. H.Polymer Physics; Oxford University Press: New York, 2003. Google Scholar Previous articleNext article FiguresReferencesRelatedDetails Issue AssignmentNot Yet AssignedSupporting Information Copyright & Permissions© 2021 Chinese Chemical SocietyKeywordsconformationmechanosensorybiomimeticelastomerAIEAcknowledgmentsThe authors are grateful for discussion with Prof. Yang Shuang from Peking University. Downloaded 301 times Loading ...