Abstract

Whispering gallery mode (WGM) resonators are compact and ultrasensitive devices, which enable label-free sensing at the single-molecule level. Despite their high sensitivity, WGM resonators have not been thoroughly investigated for use in dynamic biochemical processes including molecular diffusion and polymerization. In this work, the first report of using WGM sensors to continuously monitor a chemical reaction (i.e. gelation) in situ in a hydrogel is described. Specifically, we monitor and quantify the gelation dynamics of polyacrylamide hydrogels using WGM resonators and compare the results to an established measurement method based on rheology. Rheology measures changes in viscoelasticity, while WGM resonators measure changes in refractive index. Different gelation conditions were studied by varying the total monomer concentration and crosslinker concentration of the hydrogel precursor solution, and the resulting similarities and differences in the signal from the WGM resonator and rheology are elucidated. This work demonstrates that WGM alone or in combination with rheology can be used to investigate the gelation dynamics of hydrogels to provide insights into their gelation mechanisms.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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References

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2016 (8)

M. D. Baaske and F. Vollmer, “Optical observation of single atomic ions interacting with plasmonic nanorods in aqueous solution,” Nat. Photonics 10(11), 733–739 (2016).

K. D. Heylman, N. Thakkar, E. H. Horak, S. C. Quillin, C. Cherqui, K. A. Knapper, D. J. Masiello, and R. H. Goldsmith, “Optical microresonators as single-particle absorption spectrometers,” Nat. Photonics 10(12), 788–795 (2016).

J. Su, A. F. Goldberg, and B. M. Stoltz, “Label-free detection of single nanoparticles and biological molecules using microtoroid optical resonators,” Light Sci. Appl. 5(1), e16001 (2016).

F. Ordikhani, S. P. Zustiak, and A. Simchi, “Surface Modifications of Titanium Implants by Multilayer Bioactive Coatings with Drug Delivery Potential: Antimicrobial, Biological, and Drug Release Studies,” JOM 68(4), 1100–1108 (2016).

M. Asano, Y. Takeuchi, W. Chen, Ş. K. Özdemir, R. Ikuta, N. Imoto, L. Yang, and T. Yamamoto, “Observation of optomechanical coupling in a microbottle resonator,” Laser Photonics Rev. 10(4), 603–611 (2016).

G. Nemova and R. Kashyap, “Silica bottle resonator sensor for refractive index and temperature measurements,” Sensors (Basel) 16(1), 87 (2016).
[PubMed]

A. K. Denisin and B. L. Pruitt, “Tuning the range of polyacrylamide gel stiffness for mechanobiology applications,” ACS Appl. Mater. Interfaces 8(34), 21893–21902 (2016).
[PubMed]

Y. Wang, K. Zhang, S. Zhou, Y.-H. Wu, M.-B. Chi, and P. Hao, “Coupled-mode induced transparency in a bottle whispering-gallery-mode resonator,” Opt. Lett. 41(8), 1825–1828 (2016).
[PubMed]

2015 (1)

M. R. Foreman and F. Vollmer, “Optical tracking of anomalous diffusion kinetics in polymer microspheres,” Phys. Rev. Lett. 114(11), 118001 (2015).
[PubMed]

2014 (6)

M. D. Baaske, M. R. Foreman, and F. Vollmer, “Single-molecule nucleic acid interactions monitored on a label-free microcavity biosensor platform,” Nat. Nanotechnol. 9(11), 933–939 (2014).
[PubMed]

S. Zustiak, R. Nossal, and D. L. Sackett, “Multiwell stiffness assay for the study of cell responsiveness to cytotoxic drugs,” Biotechnol. Bioeng. 111(2), 396–403 (2014).
[PubMed]

A. K. Higham, C. A. Bonino, S. R. Raghavan, and S. A. Khan, “Photo-activated ionic gelation of alginate hydrogel: real-time rheological monitoring of the two-step crosslinking mechanism,” Soft Matter 10(27), 4990–5002 (2014).
[PubMed]

J. H. Wen, L. G. Vincent, A. Fuhrmann, Y. S. Choi, K. C. Hribar, H. Taylor-Weiner, S. Chen, and A. J. Engler, “Interplay of matrix stiffness and protein tethering in stem cell differentiation,” Nat. Mater. 13(10), 979–987 (2014).
[PubMed]

Y. Luo and Q. Wang, “Zein-based micro-and nano-particles for drug and nutrient delivery: A review,” J. Appl. Polym. Sci. 131(16), 1–12 (2014).

V. R. Machavaram, L. Wang, S. D. Pandita, S. Hellmann, F. N. Bogonez, and G. F. Fernando, “Multi-point monitoring of cross-linking reactions,” J. Appl. Polym. Sci. 131(22), 41088 (2014).

2013 (3)

C. Junge, D. O’Shea, J. Volz, and A. Rauschenbeutel, “Strong coupling between single atoms and nontransversal photons,” Phys. Rev. Lett. 110(21), 213604 (2013).
[PubMed]

G. W. Ashley, J. Henise, R. Reid, and D. V. Santi, “Hydrogel drug delivery system with predictable and tunable drug release and degradation rates,” Proc. Natl. Acad. Sci. U.S.A. 110(6), 2318–2323 (2013).
[PubMed]

L. Shao, X. F. Jiang, X. C. Yu, B. B. Li, W. R. Clements, F. Vollmer, W. Wang, Y. F. Xiao, and Q. Gong, “Detection of single nanoparticles and lentiviruses using microcavity resonance broadening,” Adv. Mater. 25(39), 5616–5620 (2013).
[PubMed]

2012 (4)

F. Vollmer and L. Yang, “Review Label-free detection with high-Q microcavities: a review of biosensing mechanisms for integrated devices,” Nanophotonics 1(3-4), 267–291 (2012).
[PubMed]

M. S. Luchansky and R. C. Bailey, “High-Q optical sensors for chemical and biological analysis,” Anal. Chem. 84(2), 793–821 (2012).
[PubMed]

N. Parker and M. Povey, “Ultrasonic study of the gelation of gelatin: phase diagram, hysteresis and kinetics,” Food Hydrocoll. 26(1), 99–107 (2012).

Y. H. Kim, S. J. Park, S.-W. Jeon, S. Ju, C.-S. Park, W.-T. Han, and B. H. Lee, “Thermo-optic coefficient measurement of liquids based on simultaneous temperature and refractive index sensing capability of a two-mode fiber interferometric probe,” Opt. Express 20(21), 23744–23754 (2012).
[PubMed]

2011 (3)

B.-B. Li, Y.-F. Xiao, C.-L. Zou, Y.-C. Liu, X.-F. Jiang, Y.-L. Chen, Y. Li, and Q. Gong, “Experimental observation of Fano resonance in a single whispering-gallery microresonator,” Appl. Phys. Lett. 98(2), 021116 (2011).

S. P. Zustiak and J. B. Leach, “Characterization of protein release from hydrolytically degradable poly(ethylene glycol) hydrogels,” Biotechnol. Bioeng. 108(1), 197–206 (2011).
[PubMed]

S. M. Shamah and B. T. Cunningham, “Label-free cell-based assays using photonic crystal optical biosensors,” Analyst (Lond.) 136(6), 1090–1102 (2011).
[PubMed]

2010 (3)

H. K. Hunt and A. M. Armani, “Label-free biological and chemical sensors,” Nanoscale 2(9), 1544–1559 (2010).
[PubMed]

N. Bhattarai, J. Gunn, and M. Zhang, “Chitosan-based hydrogels for controlled, localized drug delivery,” Adv. Drug Deliv. Rev. 62(1), 83–99 (2010).
[PubMed]

B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96(25), 251109 (2010).

2009 (4)

B. W. Garner, T. Cai, S. Ghosh, Z. Hu, and A. Neogi, “Refractive index change due to volume-phase transition in polyacrylamide gel nanospheres for optoelectronics and bio-photonics,” Appl. Phys. Express 2(5), 057001 (2009).

M. Pöllinger, D. O’Shea, F. Warken, and A. Rauschenbeutel, “Ultrahigh-Q tunable whispering-gallery-mode microresonator,” Phys. Rev. Lett. 103(5), 053901 (2009).
[PubMed]

M. W. Tibbitt and K. S. Anseth, “Hydrogels as extracellular matrix mimics for 3D cell culture,” Biotechnol. Bioeng. 103(4), 655–663 (2009).
[PubMed]

K. M. Schultz, A. D. Baldwin, K. L. Kiick, and E. M. Furst, “Gelation of covalently cross-linked PEG–heparin hydrogels,” Macromolecules 42(14), 5310–5316 (2009).
[PubMed]

2008 (4)

X. Fan, I. M. White, S. I. Shopova, H. Zhu, J. D. Suter, and Y. Sun, “Sensitive optical biosensors for unlabeled targets: A review,” Anal. Chim. Acta 620(1-2), 8–26 (2008).
[PubMed]

F. Vollmer and S. Arnold, “Whispering-gallery-mode biosensing: label-free detection down to single molecules,” Nat. Methods 5(7), 591–596 (2008).
[PubMed]

P. B. Sutar, R. K. Mishra, K. Pal, and A. K. Banthia, “Development of pH sensitive polyacrylamide grafted pectin hydrogel for controlled drug delivery system,” J. Mater. Sci. Mater. Med. 19(6), 2247–2253 (2008).
[PubMed]

T.-H. Yang, “Recent applications of polyacrylamide as biomaterials,” Recent Patents Mater. Sci. 1(1), 29–40 (2008).

2007 (3)

S. J. Buggy, E. Chehura, S. W. James, and R. P. Tatam, “Optical fibre grating refractometers for resin cure monitoring,” J. Opt. A, Pure Appl. Opt. 9(6), S60 (2007).

J. Solon, I. Levental, K. Sengupta, P. C. Georges, and P. A. Janmey, “Fibroblast adaptation and stiffness matching to soft elastic substrates,” Biophys. J. 93(12), 4453–4461 (2007).
[PubMed]

J. Topolancik and F. Vollmer, “Photoinduced transformations in bacteriorhodopsin membrane monitored with optical microcavities,” Biophys. J. 92(6), 2223–2229 (2007).
[PubMed]

2006 (1)

J. M. Ward, D. G. O’Shea, B. J. Shortt, M. J. Morrissey, K. Deasy, and S. G. Nic Chormaic, “Heat-and-pull rig for fiber taper fabrication,” Rev. Sci. Instrum. 77(8), 083105 (2006).

2005 (2)

A. Armani, D. Armani, B. Min, K. Vahala, and S. Spillane, “Ultra-high-Q microcavity operation in H2O and D2O,” Appl. Phys. Lett. 87(15), 151118 (2005).

T. Yeung, P. C. Georges, L. A. Flanagan, B. Marg, M. Ortiz, M. Funaki, N. Zahir, W. Ming, V. Weaver, and P. A. Janmey, “Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesion,” Cell Motil. Cytoskeleton 60(1), 24–34 (2005).
[PubMed]

2004 (2)

M. Sumetsky, “Whispering-gallery-bottle microcavities: the three-dimensional etalon,” Opt. Lett. 29(1), 8–10 (2004).
[PubMed]

D. Calvet, J. Y. Wong, and S. Giasson, “Rheological monitoring of polyacrylamide gelation: Importance of cross-link density and temperature,” Macromolecules 37(20), 7762–7771 (2004).

2002 (1)

L. Weng, X. Zhou, X. Zhang, J. Xu, and L. Zhang, “In situ monitoring gelation process of N, N-dimethylacrylamide by refractive index technique,” Polymer (Guildf.) 43(25), 6761–6765 (2002).

2000 (3)

M. Giordano, L. Nicolais, A. M. Calabrò, S. Cantoni, A. Cusano, G. Breglio, and A. Cutolo, “A fiber optic thermoset cure monitoring sensor,” Polym. Compos. 21(4), 523–530 (2000).

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
[PubMed]

F.-L. Mi, C.-Y. Kuan, S.-S. Shyu, S.-T. Lee, and S.-F. Chang, “The study of gelation kinetics and chain-relaxation properties of glutaraldehyde-cross-linked chitosan gel and their effects on microspheres preparation and drug release,” Carbohydr. Polym. 41(4), 389–396 (2000).

1999 (2)

N. A. Peppas, K. B. Keys, M. Torres-Lugo, and A. M. Lowman, “Poly(ethylene glycol)-containing hydrogels in drug delivery,” J. Control. Release 62(1-2), 81–87 (1999).
[PubMed]

B. Zhang, D. Wang, S. Du, and Y. Song, “An investigation of a fiber optic sensor in the composite cure process,” Smart Mater. Struct. 8(4), 515 (1999).

1998 (2)

H. A. von Recum, S. W. Kim, A. Kikuchi, M. Okuhara, Y. Sakurai, and T. Okano, “Novel thermally reversible hydrogel as detachable cell culture substrate,” J. Biomed. Mater. Res. 40(4), 631–639 (1998).
[PubMed]

T. Koyano, N. Minoura, M. Nagura, and K. Kobayashi, “Attachment and growth of cultured fibroblast cells on PVA/chitosan-blended hydrogels,” J. Biomed. Mater. Res. 39(3), 486–490 (1998).
[PubMed]

1996 (3)

A. M. Mathur and A. B. Scranton, “Characterization of hydrogels using nuclear magnetic resonance spectroscopy,” Biomaterials 17(6), 547–557 (1996).
[PubMed]

A.-L. Kjøniksen and B. Nyström, “Effects of polymer concentration and cross-linking density on rheology of chemically cross-linked poly (vinyl alcohol) near the gelation threshold,” Macromolecules 29(15), 5215–5222 (1996).

H. J. Naghash and O. Okay, “Formation and structure of polyacrylamide gels,” J. Appl. Polym. Sci. 60(7), 971–979 (1996).

1994 (2)

J. P. Baker, L. H. Hong, H. W. Blanch, and J. M. Prausnitz, “Effect of initial total monomer concentration on the swelling behavior of cationic acrylamide-based hydrogels,” Macromolecules 27(6), 1446 (1994).

S. Hvidt, E. B. Joergensen, W. Brown, and K. Schillen, “Micellization and gelation of aqueous solutions of a triblock copolymer studied by rheological techniques and scanning calorimetry,” J. Phys. Chem. 98(47), 12320–12328 (1994).

1993 (1)

E. Betzig and R. J. Chichester, “Single molecules observed by near-field scanning optical microscopy,” Science 262(5138), 1422–1425 (1993).
[PubMed]

1990 (2)

R. S. Wallis, M. Amir-Tahmasseb, and J. J. Ellner, “Induction of interleukin 1 and tumor necrosis factor by mycobacterial proteins: the monocyte western blot,” Proc. Natl. Acad. Sci. U.S.A. 87(9), 3348–3352 (1990).
[PubMed]

N. W. Cheetham and E. N. Mashimba, “Conformational aspects of xanthan—Galactomannan gelation. Further evidence from optical-rotation studies,” Carbohydr. Polym. 14(1), 17–27 (1990).

1988 (1)

M. Djabourov, J. Leblond, and P. Papon, “Gelation of aqueous gelatin solutions. I. Structural investigation,” J. Phys. 49(2), 319–332 (1988).

1987 (1)

H. Schägger and G. von Jagow, “Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the separation of proteins in the range from 1 to 100 kDa,” Anal. Biochem. 166(2), 368–379 (1987).
[PubMed]

1982 (1)

C. Y. M. Tung and P. J. Dynes, “Relationship between viscoelastic properties and gelation in thermosetting systems,” J. Appl. Polym. Sci. 27(2), 569–574 (1982).

1981 (2)

J. Acton, M. Hanna, and L. Satterlee, “Heat-induced gelation and protein-protein interaction of actomyosin,” J. Food Biochem. 5(2), 101–113 (1981).

S. Sathe and D. Salunkhe, “Functional properties of the great northern bean (Phaseolus vulgaris L.) proteins: emulsion, foaming, viscosity, and gelation properties,” J. Food Sci. 46(1), 71–81 (1981).

1977 (1)

C. Coffmann and V. Garcia, “Functional properties and amino acid content of a protein isolate from mung bean flour,” J. Food Technol. 12(5), 473–484 (1977).

1976 (2)

W. A. Eaton, J. Hofrichter, P. D. Ross, R. G. Tschudin, and E. D. Becker, “Comparison of sickle cell hemoglobin gelation kinetics measured by NMR and optical methods,” Biochem. Biophys. Res. Commun. 69(2), 538–547 (1976).
[PubMed]

P.-O. Larsson and K. Mosbach, “Immobilization and steroid-transforming microorganisms in polyacrylamide,” Methods Enzymol. 44, 183–190 (1976).
[PubMed]

Acton, J.

J. Acton, M. Hanna, and L. Satterlee, “Heat-induced gelation and protein-protein interaction of actomyosin,” J. Food Biochem. 5(2), 101–113 (1981).

Amir-Tahmasseb, M.

R. S. Wallis, M. Amir-Tahmasseb, and J. J. Ellner, “Induction of interleukin 1 and tumor necrosis factor by mycobacterial proteins: the monocyte western blot,” Proc. Natl. Acad. Sci. U.S.A. 87(9), 3348–3352 (1990).
[PubMed]

Anseth, K. S.

M. W. Tibbitt and K. S. Anseth, “Hydrogels as extracellular matrix mimics for 3D cell culture,” Biotechnol. Bioeng. 103(4), 655–663 (2009).
[PubMed]

Armani, A.

A. Armani, D. Armani, B. Min, K. Vahala, and S. Spillane, “Ultra-high-Q microcavity operation in H2O and D2O,” Appl. Phys. Lett. 87(15), 151118 (2005).

Armani, A. M.

H. K. Hunt and A. M. Armani, “Label-free biological and chemical sensors,” Nanoscale 2(9), 1544–1559 (2010).
[PubMed]

Armani, D.

A. Armani, D. Armani, B. Min, K. Vahala, and S. Spillane, “Ultra-high-Q microcavity operation in H2O and D2O,” Appl. Phys. Lett. 87(15), 151118 (2005).

Arnold, S.

F. Vollmer and S. Arnold, “Whispering-gallery-mode biosensing: label-free detection down to single molecules,” Nat. Methods 5(7), 591–596 (2008).
[PubMed]

Asano, M.

M. Asano, Y. Takeuchi, W. Chen, Ş. K. Özdemir, R. Ikuta, N. Imoto, L. Yang, and T. Yamamoto, “Observation of optomechanical coupling in a microbottle resonator,” Laser Photonics Rev. 10(4), 603–611 (2016).

Ashley, G. W.

G. W. Ashley, J. Henise, R. Reid, and D. V. Santi, “Hydrogel drug delivery system with predictable and tunable drug release and degradation rates,” Proc. Natl. Acad. Sci. U.S.A. 110(6), 2318–2323 (2013).
[PubMed]

Baaske, M. D.

M. D. Baaske and F. Vollmer, “Optical observation of single atomic ions interacting with plasmonic nanorods in aqueous solution,” Nat. Photonics 10(11), 733–739 (2016).

M. D. Baaske, M. R. Foreman, and F. Vollmer, “Single-molecule nucleic acid interactions monitored on a label-free microcavity biosensor platform,” Nat. Nanotechnol. 9(11), 933–939 (2014).
[PubMed]

Bailey, R. C.

M. S. Luchansky and R. C. Bailey, “High-Q optical sensors for chemical and biological analysis,” Anal. Chem. 84(2), 793–821 (2012).
[PubMed]

Baker, J. P.

J. P. Baker, L. H. Hong, H. W. Blanch, and J. M. Prausnitz, “Effect of initial total monomer concentration on the swelling behavior of cationic acrylamide-based hydrogels,” Macromolecules 27(6), 1446 (1994).

Baldwin, A. D.

K. M. Schultz, A. D. Baldwin, K. L. Kiick, and E. M. Furst, “Gelation of covalently cross-linked PEG–heparin hydrogels,” Macromolecules 42(14), 5310–5316 (2009).
[PubMed]

Banthia, A. K.

P. B. Sutar, R. K. Mishra, K. Pal, and A. K. Banthia, “Development of pH sensitive polyacrylamide grafted pectin hydrogel for controlled drug delivery system,” J. Mater. Sci. Mater. Med. 19(6), 2247–2253 (2008).
[PubMed]

Becker, E. D.

W. A. Eaton, J. Hofrichter, P. D. Ross, R. G. Tschudin, and E. D. Becker, “Comparison of sickle cell hemoglobin gelation kinetics measured by NMR and optical methods,” Biochem. Biophys. Res. Commun. 69(2), 538–547 (1976).
[PubMed]

Betzig, E.

E. Betzig and R. J. Chichester, “Single molecules observed by near-field scanning optical microscopy,” Science 262(5138), 1422–1425 (1993).
[PubMed]

Bhattarai, N.

N. Bhattarai, J. Gunn, and M. Zhang, “Chitosan-based hydrogels for controlled, localized drug delivery,” Adv. Drug Deliv. Rev. 62(1), 83–99 (2010).
[PubMed]

Blanch, H. W.

J. P. Baker, L. H. Hong, H. W. Blanch, and J. M. Prausnitz, “Effect of initial total monomer concentration on the swelling behavior of cationic acrylamide-based hydrogels,” Macromolecules 27(6), 1446 (1994).

Bogonez, F. N.

V. R. Machavaram, L. Wang, S. D. Pandita, S. Hellmann, F. N. Bogonez, and G. F. Fernando, “Multi-point monitoring of cross-linking reactions,” J. Appl. Polym. Sci. 131(22), 41088 (2014).

Bonino, C. A.

A. K. Higham, C. A. Bonino, S. R. Raghavan, and S. A. Khan, “Photo-activated ionic gelation of alginate hydrogel: real-time rheological monitoring of the two-step crosslinking mechanism,” Soft Matter 10(27), 4990–5002 (2014).
[PubMed]

Breglio, G.

M. Giordano, L. Nicolais, A. M. Calabrò, S. Cantoni, A. Cusano, G. Breglio, and A. Cutolo, “A fiber optic thermoset cure monitoring sensor,” Polym. Compos. 21(4), 523–530 (2000).

Brown, W.

S. Hvidt, E. B. Joergensen, W. Brown, and K. Schillen, “Micellization and gelation of aqueous solutions of a triblock copolymer studied by rheological techniques and scanning calorimetry,” J. Phys. Chem. 98(47), 12320–12328 (1994).

Buggy, S. J.

S. J. Buggy, E. Chehura, S. W. James, and R. P. Tatam, “Optical fibre grating refractometers for resin cure monitoring,” J. Opt. A, Pure Appl. Opt. 9(6), S60 (2007).

Cai, K.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
[PubMed]

Cai, T.

B. W. Garner, T. Cai, S. Ghosh, Z. Hu, and A. Neogi, “Refractive index change due to volume-phase transition in polyacrylamide gel nanospheres for optoelectronics and bio-photonics,” Appl. Phys. Express 2(5), 057001 (2009).

Calabrò, A. M.

M. Giordano, L. Nicolais, A. M. Calabrò, S. Cantoni, A. Cusano, G. Breglio, and A. Cutolo, “A fiber optic thermoset cure monitoring sensor,” Polym. Compos. 21(4), 523–530 (2000).

Calvet, D.

D. Calvet, J. Y. Wong, and S. Giasson, “Rheological monitoring of polyacrylamide gelation: Importance of cross-link density and temperature,” Macromolecules 37(20), 7762–7771 (2004).

Cantoni, S.

M. Giordano, L. Nicolais, A. M. Calabrò, S. Cantoni, A. Cusano, G. Breglio, and A. Cutolo, “A fiber optic thermoset cure monitoring sensor,” Polym. Compos. 21(4), 523–530 (2000).

Chang, S.-F.

F.-L. Mi, C.-Y. Kuan, S.-S. Shyu, S.-T. Lee, and S.-F. Chang, “The study of gelation kinetics and chain-relaxation properties of glutaraldehyde-cross-linked chitosan gel and their effects on microspheres preparation and drug release,” Carbohydr. Polym. 41(4), 389–396 (2000).

Cheetham, N. W.

N. W. Cheetham and E. N. Mashimba, “Conformational aspects of xanthan—Galactomannan gelation. Further evidence from optical-rotation studies,” Carbohydr. Polym. 14(1), 17–27 (1990).

Chehura, E.

S. J. Buggy, E. Chehura, S. W. James, and R. P. Tatam, “Optical fibre grating refractometers for resin cure monitoring,” J. Opt. A, Pure Appl. Opt. 9(6), S60 (2007).

Chen, S.

J. H. Wen, L. G. Vincent, A. Fuhrmann, Y. S. Choi, K. C. Hribar, H. Taylor-Weiner, S. Chen, and A. J. Engler, “Interplay of matrix stiffness and protein tethering in stem cell differentiation,” Nat. Mater. 13(10), 979–987 (2014).
[PubMed]

Chen, W.

M. Asano, Y. Takeuchi, W. Chen, Ş. K. Özdemir, R. Ikuta, N. Imoto, L. Yang, and T. Yamamoto, “Observation of optomechanical coupling in a microbottle resonator,” Laser Photonics Rev. 10(4), 603–611 (2016).

Chen, Y.-L.

B.-B. Li, Y.-F. Xiao, C.-L. Zou, Y.-C. Liu, X.-F. Jiang, Y.-L. Chen, Y. Li, and Q. Gong, “Experimental observation of Fano resonance in a single whispering-gallery microresonator,” Appl. Phys. Lett. 98(2), 021116 (2011).

Cherqui, C.

K. D. Heylman, N. Thakkar, E. H. Horak, S. C. Quillin, C. Cherqui, K. A. Knapper, D. J. Masiello, and R. H. Goldsmith, “Optical microresonators as single-particle absorption spectrometers,” Nat. Photonics 10(12), 788–795 (2016).

Chi, M.-B.

Chichester, R. J.

E. Betzig and R. J. Chichester, “Single molecules observed by near-field scanning optical microscopy,” Science 262(5138), 1422–1425 (1993).
[PubMed]

Choi, Y. S.

J. H. Wen, L. G. Vincent, A. Fuhrmann, Y. S. Choi, K. C. Hribar, H. Taylor-Weiner, S. Chen, and A. J. Engler, “Interplay of matrix stiffness and protein tethering in stem cell differentiation,” Nat. Mater. 13(10), 979–987 (2014).
[PubMed]

Clements, W. R.

L. Shao, X. F. Jiang, X. C. Yu, B. B. Li, W. R. Clements, F. Vollmer, W. Wang, Y. F. Xiao, and Q. Gong, “Detection of single nanoparticles and lentiviruses using microcavity resonance broadening,” Adv. Mater. 25(39), 5616–5620 (2013).
[PubMed]

Coffmann, C.

C. Coffmann and V. Garcia, “Functional properties and amino acid content of a protein isolate from mung bean flour,” J. Food Technol. 12(5), 473–484 (1977).

Cunningham, B. T.

S. M. Shamah and B. T. Cunningham, “Label-free cell-based assays using photonic crystal optical biosensors,” Analyst (Lond.) 136(6), 1090–1102 (2011).
[PubMed]

Cusano, A.

M. Giordano, L. Nicolais, A. M. Calabrò, S. Cantoni, A. Cusano, G. Breglio, and A. Cutolo, “A fiber optic thermoset cure monitoring sensor,” Polym. Compos. 21(4), 523–530 (2000).

Cutolo, A.

M. Giordano, L. Nicolais, A. M. Calabrò, S. Cantoni, A. Cusano, G. Breglio, and A. Cutolo, “A fiber optic thermoset cure monitoring sensor,” Polym. Compos. 21(4), 523–530 (2000).

Deasy, K.

J. M. Ward, D. G. O’Shea, B. J. Shortt, M. J. Morrissey, K. Deasy, and S. G. Nic Chormaic, “Heat-and-pull rig for fiber taper fabrication,” Rev. Sci. Instrum. 77(8), 083105 (2006).

Denisin, A. K.

A. K. Denisin and B. L. Pruitt, “Tuning the range of polyacrylamide gel stiffness for mechanobiology applications,” ACS Appl. Mater. Interfaces 8(34), 21893–21902 (2016).
[PubMed]

Djabourov, M.

M. Djabourov, J. Leblond, and P. Papon, “Gelation of aqueous gelatin solutions. I. Structural investigation,” J. Phys. 49(2), 319–332 (1988).

Du, S.

B. Zhang, D. Wang, S. Du, and Y. Song, “An investigation of a fiber optic sensor in the composite cure process,” Smart Mater. Struct. 8(4), 515 (1999).

Dynes, P. J.

C. Y. M. Tung and P. J. Dynes, “Relationship between viscoelastic properties and gelation in thermosetting systems,” J. Appl. Polym. Sci. 27(2), 569–574 (1982).

Eaton, W. A.

W. A. Eaton, J. Hofrichter, P. D. Ross, R. G. Tschudin, and E. D. Becker, “Comparison of sickle cell hemoglobin gelation kinetics measured by NMR and optical methods,” Biochem. Biophys. Res. Commun. 69(2), 538–547 (1976).
[PubMed]

Ellner, J. J.

R. S. Wallis, M. Amir-Tahmasseb, and J. J. Ellner, “Induction of interleukin 1 and tumor necrosis factor by mycobacterial proteins: the monocyte western blot,” Proc. Natl. Acad. Sci. U.S.A. 87(9), 3348–3352 (1990).
[PubMed]

Engler, A. J.

J. H. Wen, L. G. Vincent, A. Fuhrmann, Y. S. Choi, K. C. Hribar, H. Taylor-Weiner, S. Chen, and A. J. Engler, “Interplay of matrix stiffness and protein tethering in stem cell differentiation,” Nat. Mater. 13(10), 979–987 (2014).
[PubMed]

Fan, X.

X. Fan, I. M. White, S. I. Shopova, H. Zhu, J. D. Suter, and Y. Sun, “Sensitive optical biosensors for unlabeled targets: A review,” Anal. Chim. Acta 620(1-2), 8–26 (2008).
[PubMed]

Fernando, G. F.

V. R. Machavaram, L. Wang, S. D. Pandita, S. Hellmann, F. N. Bogonez, and G. F. Fernando, “Multi-point monitoring of cross-linking reactions,” J. Appl. Polym. Sci. 131(22), 41088 (2014).

Flanagan, L. A.

T. Yeung, P. C. Georges, L. A. Flanagan, B. Marg, M. Ortiz, M. Funaki, N. Zahir, W. Ming, V. Weaver, and P. A. Janmey, “Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesion,” Cell Motil. Cytoskeleton 60(1), 24–34 (2005).
[PubMed]

Ford, E. K.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
[PubMed]

Foreman, M. R.

M. R. Foreman and F. Vollmer, “Optical tracking of anomalous diffusion kinetics in polymer microspheres,” Phys. Rev. Lett. 114(11), 118001 (2015).
[PubMed]

M. D. Baaske, M. R. Foreman, and F. Vollmer, “Single-molecule nucleic acid interactions monitored on a label-free microcavity biosensor platform,” Nat. Nanotechnol. 9(11), 933–939 (2014).
[PubMed]

Fournel, M.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
[PubMed]

Fuhrmann, A.

J. H. Wen, L. G. Vincent, A. Fuhrmann, Y. S. Choi, K. C. Hribar, H. Taylor-Weiner, S. Chen, and A. J. Engler, “Interplay of matrix stiffness and protein tethering in stem cell differentiation,” Nat. Mater. 13(10), 979–987 (2014).
[PubMed]

Funaki, M.

T. Yeung, P. C. Georges, L. A. Flanagan, B. Marg, M. Ortiz, M. Funaki, N. Zahir, W. Ming, V. Weaver, and P. A. Janmey, “Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesion,” Cell Motil. Cytoskeleton 60(1), 24–34 (2005).
[PubMed]

Furst, E. M.

K. M. Schultz, A. D. Baldwin, K. L. Kiick, and E. M. Furst, “Gelation of covalently cross-linked PEG–heparin hydrogels,” Macromolecules 42(14), 5310–5316 (2009).
[PubMed]

Garcia, V.

C. Coffmann and V. Garcia, “Functional properties and amino acid content of a protein isolate from mung bean flour,” J. Food Technol. 12(5), 473–484 (1977).

Garner, B. W.

B. W. Garner, T. Cai, S. Ghosh, Z. Hu, and A. Neogi, “Refractive index change due to volume-phase transition in polyacrylamide gel nanospheres for optoelectronics and bio-photonics,” Appl. Phys. Express 2(5), 057001 (2009).

Georges, P. C.

J. Solon, I. Levental, K. Sengupta, P. C. Georges, and P. A. Janmey, “Fibroblast adaptation and stiffness matching to soft elastic substrates,” Biophys. J. 93(12), 4453–4461 (2007).
[PubMed]

T. Yeung, P. C. Georges, L. A. Flanagan, B. Marg, M. Ortiz, M. Funaki, N. Zahir, W. Ming, V. Weaver, and P. A. Janmey, “Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesion,” Cell Motil. Cytoskeleton 60(1), 24–34 (2005).
[PubMed]

Ghosh, S.

B. W. Garner, T. Cai, S. Ghosh, Z. Hu, and A. Neogi, “Refractive index change due to volume-phase transition in polyacrylamide gel nanospheres for optoelectronics and bio-photonics,” Appl. Phys. Express 2(5), 057001 (2009).

Giasson, S.

D. Calvet, J. Y. Wong, and S. Giasson, “Rheological monitoring of polyacrylamide gelation: Importance of cross-link density and temperature,” Macromolecules 37(20), 7762–7771 (2004).

Gilligan, K. J.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
[PubMed]

Giordano, M.

M. Giordano, L. Nicolais, A. M. Calabrò, S. Cantoni, A. Cusano, G. Breglio, and A. Cutolo, “A fiber optic thermoset cure monitoring sensor,” Polym. Compos. 21(4), 523–530 (2000).

Goldberg, A. F.

J. Su, A. F. Goldberg, and B. M. Stoltz, “Label-free detection of single nanoparticles and biological molecules using microtoroid optical resonators,” Light Sci. Appl. 5(1), e16001 (2016).

Goldsmith, R. H.

K. D. Heylman, N. Thakkar, E. H. Horak, S. C. Quillin, C. Cherqui, K. A. Knapper, D. J. Masiello, and R. H. Goldsmith, “Optical microresonators as single-particle absorption spectrometers,” Nat. Photonics 10(12), 788–795 (2016).

Gong, Q.

L. Shao, X. F. Jiang, X. C. Yu, B. B. Li, W. R. Clements, F. Vollmer, W. Wang, Y. F. Xiao, and Q. Gong, “Detection of single nanoparticles and lentiviruses using microcavity resonance broadening,” Adv. Mater. 25(39), 5616–5620 (2013).
[PubMed]

B.-B. Li, Y.-F. Xiao, C.-L. Zou, Y.-C. Liu, X.-F. Jiang, Y.-L. Chen, Y. Li, and Q. Gong, “Experimental observation of Fano resonance in a single whispering-gallery microresonator,” Appl. Phys. Lett. 98(2), 021116 (2011).

B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96(25), 251109 (2010).

Gunn, J.

N. Bhattarai, J. Gunn, and M. Zhang, “Chitosan-based hydrogels for controlled, localized drug delivery,” Adv. Drug Deliv. Rev. 62(1), 83–99 (2010).
[PubMed]

Han, W.-T.

Hanna, M.

J. Acton, M. Hanna, and L. Satterlee, “Heat-induced gelation and protein-protein interaction of actomyosin,” J. Food Biochem. 5(2), 101–113 (1981).

Hao, P.

Hartwell, R. C.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
[PubMed]

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V. R. Machavaram, L. Wang, S. D. Pandita, S. Hellmann, F. N. Bogonez, and G. F. Fernando, “Multi-point monitoring of cross-linking reactions,” J. Appl. Polym. Sci. 131(22), 41088 (2014).

Henise, J.

G. W. Ashley, J. Henise, R. Reid, and D. V. Santi, “Hydrogel drug delivery system with predictable and tunable drug release and degradation rates,” Proc. Natl. Acad. Sci. U.S.A. 110(6), 2318–2323 (2013).
[PubMed]

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A. K. Higham, C. A. Bonino, S. R. Raghavan, and S. A. Khan, “Photo-activated ionic gelation of alginate hydrogel: real-time rheological monitoring of the two-step crosslinking mechanism,” Soft Matter 10(27), 4990–5002 (2014).
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Horak, E. H.

K. D. Heylman, N. Thakkar, E. H. Horak, S. C. Quillin, C. Cherqui, K. A. Knapper, D. J. Masiello, and R. H. Goldsmith, “Optical microresonators as single-particle absorption spectrometers,” Nat. Photonics 10(12), 788–795 (2016).

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J. H. Wen, L. G. Vincent, A. Fuhrmann, Y. S. Choi, K. C. Hribar, H. Taylor-Weiner, S. Chen, and A. J. Engler, “Interplay of matrix stiffness and protein tethering in stem cell differentiation,” Nat. Mater. 13(10), 979–987 (2014).
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M. Asano, Y. Takeuchi, W. Chen, Ş. K. Özdemir, R. Ikuta, N. Imoto, L. Yang, and T. Yamamoto, “Observation of optomechanical coupling in a microbottle resonator,” Laser Photonics Rev. 10(4), 603–611 (2016).

Imoto, N.

M. Asano, Y. Takeuchi, W. Chen, Ş. K. Özdemir, R. Ikuta, N. Imoto, L. Yang, and T. Yamamoto, “Observation of optomechanical coupling in a microbottle resonator,” Laser Photonics Rev. 10(4), 603–611 (2016).

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S. J. Buggy, E. Chehura, S. W. James, and R. P. Tatam, “Optical fibre grating refractometers for resin cure monitoring,” J. Opt. A, Pure Appl. Opt. 9(6), S60 (2007).

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J. Solon, I. Levental, K. Sengupta, P. C. Georges, and P. A. Janmey, “Fibroblast adaptation and stiffness matching to soft elastic substrates,” Biophys. J. 93(12), 4453–4461 (2007).
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Jiang, X. F.

L. Shao, X. F. Jiang, X. C. Yu, B. B. Li, W. R. Clements, F. Vollmer, W. Wang, Y. F. Xiao, and Q. Gong, “Detection of single nanoparticles and lentiviruses using microcavity resonance broadening,” Adv. Mater. 25(39), 5616–5620 (2013).
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B.-B. Li, Y.-F. Xiao, C.-L. Zou, Y.-C. Liu, X.-F. Jiang, Y.-L. Chen, Y. Li, and Q. Gong, “Experimental observation of Fano resonance in a single whispering-gallery microresonator,” Appl. Phys. Lett. 98(2), 021116 (2011).

B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96(25), 251109 (2010).

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S. Hvidt, E. B. Joergensen, W. Brown, and K. Schillen, “Micellization and gelation of aqueous solutions of a triblock copolymer studied by rheological techniques and scanning calorimetry,” J. Phys. Chem. 98(47), 12320–12328 (1994).

Ju, S.

Junge, C.

C. Junge, D. O’Shea, J. Volz, and A. Rauschenbeutel, “Strong coupling between single atoms and nontransversal photons,” Phys. Rev. Lett. 110(21), 213604 (2013).
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G. Nemova and R. Kashyap, “Silica bottle resonator sensor for refractive index and temperature measurements,” Sensors (Basel) 16(1), 87 (2016).
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N. A. Peppas, K. B. Keys, M. Torres-Lugo, and A. M. Lowman, “Poly(ethylene glycol)-containing hydrogels in drug delivery,” J. Control. Release 62(1-2), 81–87 (1999).
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A. K. Higham, C. A. Bonino, S. R. Raghavan, and S. A. Khan, “Photo-activated ionic gelation of alginate hydrogel: real-time rheological monitoring of the two-step crosslinking mechanism,” Soft Matter 10(27), 4990–5002 (2014).
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H. A. von Recum, S. W. Kim, A. Kikuchi, M. Okuhara, Y. Sakurai, and T. Okano, “Novel thermally reversible hydrogel as detachable cell culture substrate,” J. Biomed. Mater. Res. 40(4), 631–639 (1998).
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K. D. Heylman, N. Thakkar, E. H. Horak, S. C. Quillin, C. Cherqui, K. A. Knapper, D. J. Masiello, and R. H. Goldsmith, “Optical microresonators as single-particle absorption spectrometers,” Nat. Photonics 10(12), 788–795 (2016).

Kobayashi, K.

T. Koyano, N. Minoura, M. Nagura, and K. Kobayashi, “Attachment and growth of cultured fibroblast cells on PVA/chitosan-blended hydrogels,” J. Biomed. Mater. Res. 39(3), 486–490 (1998).
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T. Koyano, N. Minoura, M. Nagura, and K. Kobayashi, “Attachment and growth of cultured fibroblast cells on PVA/chitosan-blended hydrogels,” J. Biomed. Mater. Res. 39(3), 486–490 (1998).
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F.-L. Mi, C.-Y. Kuan, S.-S. Shyu, S.-T. Lee, and S.-F. Chang, “The study of gelation kinetics and chain-relaxation properties of glutaraldehyde-cross-linked chitosan gel and their effects on microspheres preparation and drug release,” Carbohydr. Polym. 41(4), 389–396 (2000).

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Lee, D. C.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
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F.-L. Mi, C.-Y. Kuan, S.-S. Shyu, S.-T. Lee, and S.-F. Chang, “The study of gelation kinetics and chain-relaxation properties of glutaraldehyde-cross-linked chitosan gel and their effects on microspheres preparation and drug release,” Carbohydr. Polym. 41(4), 389–396 (2000).

Levental, I.

J. Solon, I. Levental, K. Sengupta, P. C. Georges, and P. A. Janmey, “Fibroblast adaptation and stiffness matching to soft elastic substrates,” Biophys. J. 93(12), 4453–4461 (2007).
[PubMed]

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L. Shao, X. F. Jiang, X. C. Yu, B. B. Li, W. R. Clements, F. Vollmer, W. Wang, Y. F. Xiao, and Q. Gong, “Detection of single nanoparticles and lentiviruses using microcavity resonance broadening,” Adv. Mater. 25(39), 5616–5620 (2013).
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B.-B. Li, Y.-F. Xiao, C.-L. Zou, Y.-C. Liu, X.-F. Jiang, Y.-L. Chen, Y. Li, and Q. Gong, “Experimental observation of Fano resonance in a single whispering-gallery microresonator,” Appl. Phys. Lett. 98(2), 021116 (2011).

B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96(25), 251109 (2010).

Li, Y.

B.-B. Li, Y.-F. Xiao, C.-L. Zou, Y.-C. Liu, X.-F. Jiang, Y.-L. Chen, Y. Li, and Q. Gong, “Experimental observation of Fano resonance in a single whispering-gallery microresonator,” Appl. Phys. Lett. 98(2), 021116 (2011).

B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96(25), 251109 (2010).

Liu, Y.-C.

B.-B. Li, Y.-F. Xiao, C.-L. Zou, Y.-C. Liu, X.-F. Jiang, Y.-L. Chen, Y. Li, and Q. Gong, “Experimental observation of Fano resonance in a single whispering-gallery microresonator,” Appl. Phys. Lett. 98(2), 021116 (2011).

Lowman, A. M.

N. A. Peppas, K. B. Keys, M. Torres-Lugo, and A. M. Lowman, “Poly(ethylene glycol)-containing hydrogels in drug delivery,” J. Control. Release 62(1-2), 81–87 (1999).
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V. R. Machavaram, L. Wang, S. D. Pandita, S. Hellmann, F. N. Bogonez, and G. F. Fernando, “Multi-point monitoring of cross-linking reactions,” J. Appl. Polym. Sci. 131(22), 41088 (2014).

Marg, B.

T. Yeung, P. C. Georges, L. A. Flanagan, B. Marg, M. Ortiz, M. Funaki, N. Zahir, W. Ming, V. Weaver, and P. A. Janmey, “Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesion,” Cell Motil. Cytoskeleton 60(1), 24–34 (2005).
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K. D. Heylman, N. Thakkar, E. H. Horak, S. C. Quillin, C. Cherqui, K. A. Knapper, D. J. Masiello, and R. H. Goldsmith, “Optical microresonators as single-particle absorption spectrometers,” Nat. Photonics 10(12), 788–795 (2016).

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F.-L. Mi, C.-Y. Kuan, S.-S. Shyu, S.-T. Lee, and S.-F. Chang, “The study of gelation kinetics and chain-relaxation properties of glutaraldehyde-cross-linked chitosan gel and their effects on microspheres preparation and drug release,” Carbohydr. Polym. 41(4), 389–396 (2000).

Miller, J. L.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
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Ming, W.

T. Yeung, P. C. Georges, L. A. Flanagan, B. Marg, M. Ortiz, M. Funaki, N. Zahir, W. Ming, V. Weaver, and P. A. Janmey, “Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesion,” Cell Motil. Cytoskeleton 60(1), 24–34 (2005).
[PubMed]

Minoura, N.

T. Koyano, N. Minoura, M. Nagura, and K. Kobayashi, “Attachment and growth of cultured fibroblast cells on PVA/chitosan-blended hydrogels,” J. Biomed. Mater. Res. 39(3), 486–490 (1998).
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P. B. Sutar, R. K. Mishra, K. Pal, and A. K. Banthia, “Development of pH sensitive polyacrylamide grafted pectin hydrogel for controlled drug delivery system,” J. Mater. Sci. Mater. Med. 19(6), 2247–2253 (2008).
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J. M. Ward, D. G. O’Shea, B. J. Shortt, M. J. Morrissey, K. Deasy, and S. G. Nic Chormaic, “Heat-and-pull rig for fiber taper fabrication,” Rev. Sci. Instrum. 77(8), 083105 (2006).

Mosbach, K.

P.-O. Larsson and K. Mosbach, “Immobilization and steroid-transforming microorganisms in polyacrylamide,” Methods Enzymol. 44, 183–190 (1976).
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H. J. Naghash and O. Okay, “Formation and structure of polyacrylamide gels,” J. Appl. Polym. Sci. 60(7), 971–979 (1996).

Nagura, M.

T. Koyano, N. Minoura, M. Nagura, and K. Kobayashi, “Attachment and growth of cultured fibroblast cells on PVA/chitosan-blended hydrogels,” J. Biomed. Mater. Res. 39(3), 486–490 (1998).
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G. Nemova and R. Kashyap, “Silica bottle resonator sensor for refractive index and temperature measurements,” Sensors (Basel) 16(1), 87 (2016).
[PubMed]

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B. W. Garner, T. Cai, S. Ghosh, Z. Hu, and A. Neogi, “Refractive index change due to volume-phase transition in polyacrylamide gel nanospheres for optoelectronics and bio-photonics,” Appl. Phys. Express 2(5), 057001 (2009).

Nic Chormaic, S. G.

J. M. Ward, D. G. O’Shea, B. J. Shortt, M. J. Morrissey, K. Deasy, and S. G. Nic Chormaic, “Heat-and-pull rig for fiber taper fabrication,” Rev. Sci. Instrum. 77(8), 083105 (2006).

Nicolais, L.

M. Giordano, L. Nicolais, A. M. Calabrò, S. Cantoni, A. Cusano, G. Breglio, and A. Cutolo, “A fiber optic thermoset cure monitoring sensor,” Polym. Compos. 21(4), 523–530 (2000).

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T. Norisuye, A. Strybulevych, M. Scanlon, and J. Page, “Ultrasonic investigation of the gelation process of poly (acrylamide) gels,” in Macromol Symp. (2006), pp. 208–215.

Nossal, R.

S. Zustiak, R. Nossal, and D. L. Sackett, “Multiwell stiffness assay for the study of cell responsiveness to cytotoxic drugs,” Biotechnol. Bioeng. 111(2), 396–403 (2014).
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Nyström, B.

A.-L. Kjøniksen and B. Nyström, “Effects of polymer concentration and cross-linking density on rheology of chemically cross-linked poly (vinyl alcohol) near the gelation threshold,” Macromolecules 29(15), 5215–5222 (1996).

O’Shea, D.

C. Junge, D. O’Shea, J. Volz, and A. Rauschenbeutel, “Strong coupling between single atoms and nontransversal photons,” Phys. Rev. Lett. 110(21), 213604 (2013).
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M. Pöllinger, D. O’Shea, F. Warken, and A. Rauschenbeutel, “Ultrahigh-Q tunable whispering-gallery-mode microresonator,” Phys. Rev. Lett. 103(5), 053901 (2009).
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J. M. Ward, D. G. O’Shea, B. J. Shortt, M. J. Morrissey, K. Deasy, and S. G. Nic Chormaic, “Heat-and-pull rig for fiber taper fabrication,” Rev. Sci. Instrum. 77(8), 083105 (2006).

Okano, T.

H. A. von Recum, S. W. Kim, A. Kikuchi, M. Okuhara, Y. Sakurai, and T. Okano, “Novel thermally reversible hydrogel as detachable cell culture substrate,” J. Biomed. Mater. Res. 40(4), 631–639 (1998).
[PubMed]

Okay, O.

H. J. Naghash and O. Okay, “Formation and structure of polyacrylamide gels,” J. Appl. Polym. Sci. 60(7), 971–979 (1996).

Okuhara, M.

H. A. von Recum, S. W. Kim, A. Kikuchi, M. Okuhara, Y. Sakurai, and T. Okano, “Novel thermally reversible hydrogel as detachable cell culture substrate,” J. Biomed. Mater. Res. 40(4), 631–639 (1998).
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F. Ordikhani, S. P. Zustiak, and A. Simchi, “Surface Modifications of Titanium Implants by Multilayer Bioactive Coatings with Drug Delivery Potential: Antimicrobial, Biological, and Drug Release Studies,” JOM 68(4), 1100–1108 (2016).

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T. Yeung, P. C. Georges, L. A. Flanagan, B. Marg, M. Ortiz, M. Funaki, N. Zahir, W. Ming, V. Weaver, and P. A. Janmey, “Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesion,” Cell Motil. Cytoskeleton 60(1), 24–34 (2005).
[PubMed]

Özdemir, S. K.

M. Asano, Y. Takeuchi, W. Chen, Ş. K. Özdemir, R. Ikuta, N. Imoto, L. Yang, and T. Yamamoto, “Observation of optomechanical coupling in a microbottle resonator,” Laser Photonics Rev. 10(4), 603–611 (2016).

Page, J.

T. Norisuye, A. Strybulevych, M. Scanlon, and J. Page, “Ultrasonic investigation of the gelation process of poly (acrylamide) gels,” in Macromol Symp. (2006), pp. 208–215.

Pal, K.

P. B. Sutar, R. K. Mishra, K. Pal, and A. K. Banthia, “Development of pH sensitive polyacrylamide grafted pectin hydrogel for controlled drug delivery system,” J. Mater. Sci. Mater. Med. 19(6), 2247–2253 (2008).
[PubMed]

Pandita, S. D.

V. R. Machavaram, L. Wang, S. D. Pandita, S. Hellmann, F. N. Bogonez, and G. F. Fernando, “Multi-point monitoring of cross-linking reactions,” J. Appl. Polym. Sci. 131(22), 41088 (2014).

Papon, P.

M. Djabourov, J. Leblond, and P. Papon, “Gelation of aqueous gelatin solutions. I. Structural investigation,” J. Phys. 49(2), 319–332 (1988).

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Park, S. J.

Parker, N.

N. Parker and M. Povey, “Ultrasonic study of the gelation of gelatin: phase diagram, hysteresis and kinetics,” Food Hydrocoll. 26(1), 99–107 (2012).

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N. A. Peppas, K. B. Keys, M. Torres-Lugo, and A. M. Lowman, “Poly(ethylene glycol)-containing hydrogels in drug delivery,” J. Control. Release 62(1-2), 81–87 (1999).
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Petteway, S. R.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
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M. Pöllinger, D. O’Shea, F. Warken, and A. Rauschenbeutel, “Ultrahigh-Q tunable whispering-gallery-mode microresonator,” Phys. Rev. Lett. 103(5), 053901 (2009).
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N. Parker and M. Povey, “Ultrasonic study of the gelation of gelatin: phase diagram, hysteresis and kinetics,” Food Hydrocoll. 26(1), 99–107 (2012).

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J. P. Baker, L. H. Hong, H. W. Blanch, and J. M. Prausnitz, “Effect of initial total monomer concentration on the swelling behavior of cationic acrylamide-based hydrogels,” Macromolecules 27(6), 1446 (1994).

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A. K. Denisin and B. L. Pruitt, “Tuning the range of polyacrylamide gel stiffness for mechanobiology applications,” ACS Appl. Mater. Interfaces 8(34), 21893–21902 (2016).
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Quillin, S. C.

K. D. Heylman, N. Thakkar, E. H. Horak, S. C. Quillin, C. Cherqui, K. A. Knapper, D. J. Masiello, and R. H. Goldsmith, “Optical microresonators as single-particle absorption spectrometers,” Nat. Photonics 10(12), 788–795 (2016).

Raghavan, S. R.

A. K. Higham, C. A. Bonino, S. R. Raghavan, and S. A. Khan, “Photo-activated ionic gelation of alginate hydrogel: real-time rheological monitoring of the two-step crosslinking mechanism,” Soft Matter 10(27), 4990–5002 (2014).
[PubMed]

Rauschenbeutel, A.

C. Junge, D. O’Shea, J. Volz, and A. Rauschenbeutel, “Strong coupling between single atoms and nontransversal photons,” Phys. Rev. Lett. 110(21), 213604 (2013).
[PubMed]

M. Pöllinger, D. O’Shea, F. Warken, and A. Rauschenbeutel, “Ultrahigh-Q tunable whispering-gallery-mode microresonator,” Phys. Rev. Lett. 103(5), 053901 (2009).
[PubMed]

Reid, R.

G. W. Ashley, J. Henise, R. Reid, and D. V. Santi, “Hydrogel drug delivery system with predictable and tunable drug release and degradation rates,” Proc. Natl. Acad. Sci. U.S.A. 110(6), 2318–2323 (2013).
[PubMed]

Ross, P. D.

W. A. Eaton, J. Hofrichter, P. D. Ross, R. G. Tschudin, and E. D. Becker, “Comparison of sickle cell hemoglobin gelation kinetics measured by NMR and optical methods,” Biochem. Biophys. Res. Commun. 69(2), 538–547 (1976).
[PubMed]

Rubenstein, R.

D. C. Lee, C. J. Stenland, R. C. Hartwell, E. K. Ford, K. Cai, J. L. Miller, K. J. Gilligan, R. Rubenstein, M. Fournel, and S. R. Petteway., “Monitoring plasma processing steps with a sensitive Western blot assay for the detection of the prion protein,” J. Virol. Methods 84(1), 77–89 (2000).
[PubMed]

Sackett, D. L.

S. Zustiak, R. Nossal, and D. L. Sackett, “Multiwell stiffness assay for the study of cell responsiveness to cytotoxic drugs,” Biotechnol. Bioeng. 111(2), 396–403 (2014).
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Zhu, H.

X. Fan, I. M. White, S. I. Shopova, H. Zhu, J. D. Suter, and Y. Sun, “Sensitive optical biosensors for unlabeled targets: A review,” Anal. Chim. Acta 620(1-2), 8–26 (2008).
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F. Ordikhani, S. P. Zustiak, and A. Simchi, “Surface Modifications of Titanium Implants by Multilayer Bioactive Coatings with Drug Delivery Potential: Antimicrobial, Biological, and Drug Release Studies,” JOM 68(4), 1100–1108 (2016).

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Adv. Drug Deliv. Rev. (1)

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Adv. Mater. (1)

L. Shao, X. F. Jiang, X. C. Yu, B. B. Li, W. R. Clements, F. Vollmer, W. Wang, Y. F. Xiao, and Q. Gong, “Detection of single nanoparticles and lentiviruses using microcavity resonance broadening,” Adv. Mater. 25(39), 5616–5620 (2013).
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Anal. Biochem. (1)

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Appl. Phys. Lett. (3)

B.-B. Li, Q.-Y. Wang, Y.-F. Xiao, X.-F. Jiang, Y. Li, L. Xiao, and Q. Gong, “On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator,” Appl. Phys. Lett. 96(25), 251109 (2010).

B.-B. Li, Y.-F. Xiao, C.-L. Zou, Y.-C. Liu, X.-F. Jiang, Y.-L. Chen, Y. Li, and Q. Gong, “Experimental observation of Fano resonance in a single whispering-gallery microresonator,” Appl. Phys. Lett. 98(2), 021116 (2011).

A. Armani, D. Armani, B. Min, K. Vahala, and S. Spillane, “Ultra-high-Q microcavity operation in H2O and D2O,” Appl. Phys. Lett. 87(15), 151118 (2005).

Biochem. Biophys. Res. Commun. (1)

W. A. Eaton, J. Hofrichter, P. D. Ross, R. G. Tschudin, and E. D. Becker, “Comparison of sickle cell hemoglobin gelation kinetics measured by NMR and optical methods,” Biochem. Biophys. Res. Commun. 69(2), 538–547 (1976).
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J. Topolancik and F. Vollmer, “Photoinduced transformations in bacteriorhodopsin membrane monitored with optical microcavities,” Biophys. J. 92(6), 2223–2229 (2007).
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Biotechnol. Bioeng. (3)

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Figures (4)

Fig. 1
Fig. 1 Gelation mechanism of polyacrylamide hydrogels. Ammonium persulfate (APS) acts as a free-radical initiator, while Tetramethylethylenediamine (TEMED) catalyzes the polymerization. The bis-acrylamide crosslinks the polyacrylamide chains to form a hydrogel network.
Fig. 2
Fig. 2 Schematic drawing of the optical characterization setup. Inset: micrograph of a typical bottle WGM resonator.
Fig. 3
Fig. 3 (a) Transmission spectrum of a bottle resonator embedded in a PA-08-37 gel. (b) Wavelength shift of five different WGMs, which are indicated in (a), compared with the wavelength shift obtained from a cross-correlation method. (c) Temperature change within the gel measured by a thermistor. (d) Wavelength shift during gelation (blue, solid curve) measured by a WGM resonator, and storage modulus change during gelation (red, dotted curve) measured by rheology. The gelation times (tgelation), for both the WGM curve and the rheology curve, are indicated in the figure.
Fig. 4
Fig. 4 Gelation kinetics of PA hydrogels prepared with varying amounts of acrylamide and bis-acrylamide. (a) Increase in %T led to a decrease in gelation time measured by WGM and rheology. (b) Increase in %T caused an increase in both the final steady-state resonance wavelength shift and storage modulus. (c) Increase in %C led to a decrease in gelation time measured by WGM and rheology. (d) Increase in %C caused an increase in final steady-state storage modulus, but did not lead to a change in resonance wavelength shift.

Tables (2)

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Table 1 Gel composition of PA precursor solution with increasing %T

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Table 2 Gel composition of PA precursor solutions with increasing %C

Equations (5)

Equations on this page are rendered with MathJax. Learn more.

%T= M A c r + M B i s V S o l ×100
%C= M B i s M A c r + M B i s ×100
Δ λ shift = argma λ x(( f t * f t+Δt )(λ)).
G'(t)= G ' 1 1+ ( t g e l a t i o n t ) m
Δλ(t)=Δ λ 1 1+ ( t g e l a t i o n t ) m

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