Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

Abstract

In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping address fundamental questions about the mechanisms or the consequences of the self-assembly of molecules, including low molecular weight ones. Finally, we provide a perspective on supramolecular hydrogelators. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring supramolecular hydrogelators as molecular biomaterials for addressing the societal needs at various frontiers.

Figure 1

(A) Illustration of the process for creating polymeric hydrogels via cross-linking (left), or formation of supramolecular hydrogels via a chemical or physical perturbation initiated self-assembly (right). Adapted with permission from ref (6). Copyright 2006 Wiley-VCH Verlag GmbH & Co. KGaA. (B) Molecular structures of 1 and 2. (C) Molecular structure of Nap-FF (3). (D) Optical image and negatively stained TEM image of the hydrogel of 3. Adapted from ref (14). Copyright 2011 American Chemical Society.

Scheme 1. Representative Molecular Structures of Hydrogelators To Form Hydrogels after Receiving Different Stimuli

Scheme 2. Representative Molecular Structures of Precursors and Hydrogelators To Form Hydrogels after Chemical Reactions

Scheme 3. Representative Molecular Structures of Hydrogelators

Scheme 4. Molecular Structures of a Photochemical Precursor of a Hydrogelator

Scheme 5. Representative Molecular Structure of Hydrogelators

Scheme 6. Representative Molecular Structures of Precursors and Hydrogelators To Form Hydrogels on the Basis of Catalysis

Scheme 7. Representative Molecular Structures of Hydrogelators

Scheme 8. Representative Molecular Structures of Urea-Containing Hydrogelators

Scheme 9. Representative Molecular Structures of Pyridine-Containing Hydrogelators

Scheme 10. Alkyl-Chain-Containing Hydrogelators

Scheme 11. Representative Molecular Structures of Alkyl-Chain-Containing Hydrogelators

Scheme 12. Hydrogelators Containing Multi/Polyhydroxyl Groups

Scheme 13. Hydrogelators Having C₃ Symmetry

Figure 2

Cryo-TEM images of unilamellar dioleoylphosphocholine (DOPC) vesicles coexisting with a network of well-defined fibers of 67 with a high aspect ratio. Adapted with permission from ref (321). Copyright 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

Figure 3

Catalytic formation of trishydrazone hydrogelator 70 from soluble building blocks 68 and 69 leads to supersaturation followed by formation of fibers that eventually cross-link to form a network that traps the surrounding solvent, leading to gelation: blue, hydrophilic functional groups; red, hydrophobic functional groups. Adapted with permission from ref (142). Copyright 2014 Nature America.

Scheme 14. Bile Acid-Derived Hydrogelators

Scheme 15. Some Bile Acid- or Cholesterol-Derived Hydrogelators

Scheme 16. Bolaamphiphiles as Hydrogelators

Scheme 17. Some Hydrogelators Containing a Cavity

Scheme 18. Some Hydrogelators Containing a Polyaromatic Core

Scheme 19. Some Hydrogelators of Homotypic Hydrogels

Scheme 20. Some Hydrogelators Composed of Two Components

Scheme 21. Some Representative Hydrogelators Composed of Two Components

Figure 4

ORTEP diagrams of 150 and 151 with the atom numbering scheme for the asymmetric unit, and the molecular packing of 150 and 151 showing the columnar supramolecular architectures, characterized by a lipophilic exterior and a polar interior. Adapted with permission from ref (55). Copyright 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

Scheme 22. Ligands That Bind Metal Ions via Carboxylic Group To Form Supramolecular Hydrogels

Scheme 23. Some of the Ligands That Bind Metal Ions via Nitrogen in the Supramolecular Hydrogels and Some Representative Complexes

Scheme 24. Some of the Ligands That Bind Metal Ions via Nitrogen in the Supramolecular Hydrogels and Some Representative Complexes

Scheme 25. Some of the Ligands That Bind Metal Ions via Nitrogen in the Supramolecular Hydrogels and Some Representative Complexes

Scheme 26. Some of the Ligands Bearing Thiol Groups

Scheme 27. Chemical Structure of a Ligand Containing Phosphate Groups

Scheme 28. Metal Complexes As Hydrogelators

Scheme 29. Representative Molecular Structures of Amino Acid Derivative Hydrogelators Containing an Alkyl Chain

Scheme 30. Representative Hydrogelators of Ionic Amino Acid Derivatives

Scheme 31. Representative Molecular Structures of Hydrogelators Containing Aromatic Groups

Scheme 32. Representative Molecular Structure of a Hydrogelator Based on a Bolaamphiphile

Figure 5

Molecular model of 209 self-assembled structures. The model is based on the crystal X-ray structure of the diphenylalanine peptide. The dipeptide backbone and hydrophobic side chains are shown as stick representations. Adapted with permission from ref (564). Copyright 2007 Biophysical Society.

Scheme 33. Representative Molecular Structures of Cyclopeptide Hydrogelators

Scheme 34. Representative Molecular Structure of a Peptidic Hydrogelator with Capped N- and C-Terminals

Scheme 35. Representative Molecular Structures of Hydrogelators Containing Alkyl/Lipid Chains

Scheme 36. Representative Molecular Structures of Hydrogelators Containing Aromatic Groups

Figure 6

Molecular packing and hydrogen bonds in the crystal of 3 (recrystallized from ethanol): views from the (A) a, (B) b, and (C) c axes and (D) view from the c axis to show the hydrogen bonding (green dotted lines) of one molecule with four other molecules and some aromatic–aromatic interactions (yellow lines). Adapted from ref (14). Copyright 2011 American Chemical Society.

Scheme 37. Representative Molecular Structures of Hydrogelators Containing Naphthalenyl Groups

Scheme 38. Representative Molecular Structures of Hydrogelators Containing Pyrene Groups

Scheme 39. Representative Molecular Structures of Hydrogelators Containing Aromatic Groups

Scheme 40. Representative Molecular Structures of Hydrogelators Containing a Photoresponsive Group

Scheme 41. Representative Molecular Structures of Hydrogelators Based on Bolaamphiphiles

Scheme 42. Representative Molecular Structures of Hydrogelators Based on Dendrimers or Dendrons

Scheme 43. Representative Molecular Structures of Hydrogelators

Scheme 44. Hydrogelators Containing Nucleobases

Figure 7

TEM images of gel 340 (scale bar 50 nm). Adapted from ref (819). Copyright 2009 American Chemical Society.

Scheme 45. Nucleobase Derivatives for Multicomponent Hydrogels

Scheme 46. Some Monosaccharide-Based Hydrogelators

Scheme 47. Some Monosaccharide-Based Hydrogelators

Scheme 48. Monosaccharide-Based Hydrogelators

Scheme 49. Some Oligosaccharide-Based Hydrogelators

Scheme 50. Representative Molecular Structures of Hydrogelators for 3D Cell Culture

Figure 8

The viability of NIH/3T3 cells encapsulated in 30 mM 407 microgels was quantified with calcein/ethidium homodimer staining. The assay was conducted 2 h after the incubation of (a) 1 day, (b) 2 days, and (c) 3 days. The scale bar in (a) represents 100 mm. The magnification is the same in (a)–(c). Adapted with permission from ref (918). Copyright 2011 Royal Society of Chemistry.

Scheme 51. Representative Molecular Structures of Hydrogelators for 3D Cell Culture

Scheme 52. Representative Molecular Structures of Hydrogelators for 3D Cell Culture

Figure 9

Confocal microscopy of SHED cells 1, 3, or 11 days after 3D encapsulation in 422 hydrogels. Adapted from ref (934). Copyright 2014 American Chemical Society.

Scheme 53. Representative Molecular Structures of Hydrogelators for 3D Cell Culture

Scheme 54. Representative Molecular Structures of Hydrogelators for 3D Cell Culture

Scheme 55. Representative Molecular Structures of Cell-Compatible Hydrogelators

Scheme 56. Representative Molecular Structures of Cell-Compatible Hydrogelators

Figure 10

(A) Dephosphorylation process catalyzed by ALP with 454A to result in nanofibers and a hydrogel. (B) Cell viability test for 72 h of 454. (C) Optical images of HeLa cells on the surface 0 and 20 h after creation of scratchs in the presence of hydrogel 454T (by adding 27.7 mM 454T to the media). Adapted with permission from ref (965). Copyright 2011 Wiley-VCH Verlag GmbH & Co. KGaA.

Scheme 57. Representative Molecular Structures of Cell-Compatible Hydrogelators

Figure 11

Formation mechanism of hydrogel 465: (A) hydrogen-bond-driven self-assembly, (B) self-assembled fibrils, (C) fibrils with a hydrogelator concentration lower than the minimum gelation concentration (MGC), (D) entangled fibrils with a hydrogelator concentration higher than the MGC, (D) well-organized 3D hierarchical nanoarchitectures with ultrasound treatment, (F) cells seeded in hydrogels, (G) optical image of the hydrogel (the transition from solution to hydrogel was reversible). Adapted with permission from ref (85). Copyright 2013 Royal Society of Chemistry.

Scheme 58. Representative Molecular Structures of Cytotoxic Hydrogelators

Figure 12

Histological section of rabbit eyes which underwent filtration surgery (a) alone at 14 days postsurgery, received the Fmoc-FF (6) hydrogel at (b) 7 and (c) 14 days postsurgery, and received the glycopeptide hydrogel (476) at (d) 7, (e) 14, and (f) 21 days postsurgery. Hematoxylin–eosin; magnification 100×. Adapted with permission from ref (92). Copyright 2012 Royal Society of Chemistry.

Scheme 59. Representative Molecular Structures of Hydrogelators for Cell Adhesion

Figure 13

(A) Percentages of strongly attached 3T3-L1 cells. 3T3-L1 cells were incubated on the flat hydrogels composed of 482 containing 0%, 10%, or 20% 483, fibronectin (FN), tissue-culture-treated plates (TCTPs), or nonadhesive plate surfaces in Dulbecco’s modified Eagle’s medium containing 5 mM Ca²⁺. (B) Fluorescence microscopic images of cell-adhered peptide gel strings. PC12 cells were cultured in Dulbecco’s modified Eagle’s medium containing 5 mM Ca²⁺ for 6 days. The scale bar represents 100 μm. Adapted with permission from ref (993). Copyright 2012 The Society of Polymer Science, Japan (SPSJ).

Scheme 60. Representative Molecular Structures of Hydrogelators for Cell Adhesion

Scheme 61. Representative Molecular Structures of Hydrogelators

Scheme 62. Representative Molecular Structures of Hydrogelators

Figure 14

Temperature-dependent UV/vis spectra of aqueous solutions (∼10^–5 M) of (A) 494 and (B) 495 containing 1 equiv of disperse orange 3. Arrows indicate the spectroscopic changes with increasing temperature. The insets depict the changes in the absorbance at 400 nm as a function of temperature. Adapted with permission from ref (1021). Copyright 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Scheme 63. Representative Molecular Structures of Hydrogelators for Chemosensing

Scheme 64. Representative Molecular Structures of Hydrogelators for Chemosensors

Figure 15

Schematic illustration of the sensing strategy of diffraction grating for human thrombin detection. (A) The hydrogel 508 contains an aptamer and its complementary sequence as the supermolecular cross-linking points and swells when exposed to the human thrombin. (B) Response of the hydrogel grating to human thrombin in the solution. Adapted with permission from ref (1036). Copyright 2013 Royal Society of Chemistry.

Scheme 65. Representative Molecular Structures of Hydrogelators for Biosensors

Scheme 66. Representative Molecular Structures of Fluorescent Hydrogelators

Figure 16

(A) Optical images of the oxidation-induced gel–sol transition and the TEM images corresponding to the samples at different states of transition. The hydrogel (reduced state) is formed by 0.8% (w/v) 10 in water at pH 1. The scale bar represents 10 nm. (B) Fluorescent images of a HeLa cell incubated with 3 (200 μM, 24 h). Adapted from ref (117). Copyright 2013 American Chemical Society.

Scheme 67. Representative Molecular Structures of Hydrogelators

Figure 17

(A) The nanofibers of 520 could specifically bind to Cu²⁺, leading to the formation of fluorescence-quenched elongated nanofibers. Confocal images (bright field + fluorescence) of (B) HeLa cells treated with 520 (0.05 wt %) at a 2 h time point and (C) HeLa cells pretreated with 100 μM Cu²⁺ and then treated with 520 (0.05 wt %) at a 6 h time point. Adapted from ref (1065). Copyright 2014 American Chemical Society.

Figure 18

LSCM xy projections taken of 2.5 × 10³ CFUs/dm²E. coli incubated on (A) a borosilicate control surface and (B) the hydrogel of 2 wt % 251 after 24 h. The gel is viewed parallel to the z-axis. Green fluorescence denotes live cells, and red fluorescence denotes dead cells with compromised membranes. (C) LSCM xy projections taken of 2.5 × 10⁹ CFUs/dm²E. coli incubated on the surface of the hydrogel of 2 wt % 251 viewed perpendicular to the z-axis. Arrows denote the gel–bacterial interface. Adapted from ref (1068). Copyright 2007 American Chemical Society.

Scheme 68. Representative Molecular Structures of Antibacterial Hydrogelators

Scheme 69. Representative Molecular Structures of Antibacterial Hydrogelators

Figure 19

(A) Representative SEM images and (B) overlapping fluorescence images for the LIVE/DEAD bacterial staining assay of S. aureus before and after contact with the coassembled (200 + 533) hydrogel for 2 h. Two fluorescent dyes were used in LIVE/DEAD staining in which SYTO 9 with green color labeled both live and dead bacteria while propidium iodide with red color stained only dead bacteria. Adapted with permission from ref (1082). Copyright 2015 Wiley-VCH Verlag GmbH & Co. KGaA.

Scheme 70. Representative Molecular Structures of Hydrogelators for Tissue Engineering

Figure 20

Nanofibrous hydrogels are reported to be compatible with NIH/3T3 fibroblasts. In the presence of serum, fibroblasts spread by 28 h. At 72 h, spreading appeared to be spindle-like, resembling the natural morphology of the cell type. The fibroblasts proliferated for a minimum of 96 h. These images are from a single hydrogel of 544. Adapted with permission from ref (1117). Copyright 2012 Royal Society of Chemistry.

Figure 21

(A–L) Analysis of transplanted mucosal epithelial cells in recipient tissues at postoperative days 14 and 28. Serial frozen sections of middle-ear bullae after transplantation (0.5 × 10⁶ cells/mL) at (A–F) postoperative day 14 and (G–L) postoperative day 28. (A, B, G, H) Fluorescence images at several time points. Enhanced green fluorescent protein (EGFP)-expressing cells were detected on the internal surface of recipient middle-ear bullae (green, EGFP; blue, 4′,6-diamidino-2-phenylindole) (A, G). Results of immunostaining with (C, I) antipancytokeratin, (D, J) antivimentin, (E, K) anticollagen III, and (F, L) anticollagen IV antibody. EGFP-expressing cells were positive for pancytokeratin (C, I, arrows), but not for vimentin (D, J). Collagen III-positive regions were detected mainly in the subepithelium (E, K). Collagen IV-positive regions were detected under the monolayer structure of donor cells at 14 and 28 days after transplantation (F, L, arrowheads). The scale bars represent 50 μm. Adapted with permission from ref (1121). Copyright 2013 Dove Medical Press Ltd.

Scheme 71. Representative Molecular Structures of Hydrogelators Encapsulating Drugs

Figure 22

(a) Profiles of the mean blood concentration of ¹²⁵I-NaI vs time after subcutaneous (sc) administration to rats (160 μCi/kg) (■, control, ¹²⁵I-NaI solution, AUC (area under the curve) = 1213.3 μCi·h/L; ●, experimental, ¹²⁵I-NaI in gel II, AUC = 1453.5 μCi·h/L). (b) Dynamic (upper two lines) and static (lower line) single-photon emission computed tomography (SPECT) images of rats with ¹³¹I-NaI (500 μCi/rat; left, in solution; right, in gel II) administered sc. (c) Profiles of the mean blood concentration of ¹²⁵I-epidepride vs time after sc administration to rats (160 μCi/kg) (■, control, ¹²⁵I-epidepride solution, AUC = 645.5 μCi·h/L; ●, experimental, ¹²⁵I-epidepride in gel II, AUC = 693.6 μCi·h/L). (d) Dynamic SPECT images of rats with ¹³¹I-epidepride (500 μCi/rat; left, in gel II; right, in solution) administered sc. Adapted from ref (1176). Copyright 2009 American Chemical Society.

Scheme 72. Representative Molecular Structures of Hydrogelators Encapsulating Drugs

Figure 23

(A) Illustration of the injectable nature of the hydrogel and its vitamin release phenomenon with vitamin B₁₂. (B) Percentage release plot of some important biomolecules from hydrogel 564 at physiological pH (7.46) and temperature (37 °C), where the concentration of the drugs loaded into the hydrogel was 1.14 mg/mL for cyanocobalamin (vitamin B₁₂) and 0.24 mg/mL for vancomycin. Adapted from ref (1179). Copyright 2014 American Chemical Society.

Scheme 73. Representative Molecular Structures of Hydrogelators Encapsulating Drugs

Scheme 74. Representative Molecular Structures of Hydrogelators Conjugated with Drugs

Figure 24

Supramolecular nanofibers sequester the potential targets (e.g., 16S rRNA (in red)) in the gel phase. Adapted with permission from ref (1202). Copyright 2012 Royal Society of Chemistry.

Scheme 75. Representative Molecular Structures of Hydrogelators Conjugated with Drugs

Scheme 76. Representative Molecular Structures of Hydrogelators Conjugated with Drugs

Scheme 77. Representative Molecular Structures of Hydrogelators Conjugated with Drugs

Figure 25

(A) Percentage of wound area left in different groups at day 7 compared to the original wound area (mean ± SEM) at day 0. (B) Photographs of wounds in animals treated with PBS buffer, 3 (hydrogel containing 1.0 wt % 3), free NO + GAL (solution containing 0.2 wt % NO donor with daily addition of 1.5 × 10^–4 U of β-galactosidase), NO gel (hydrogel containing 1.0 wt % 3 and 0.6 wt % 595 without the addition of β-galactosidase), and NO gel + GAL (hydrogel containing 1.0 wt % 3 and 0.6 wt % 595 with the addition of 1.5 × 10^–4 U of β-galactosidase each day). Adapted with permission from ref (1211). Copyright 2013 Royal Society of Chemistry.

Scheme 78. Representative Molecular Structures of Hydrogelators for Immunological Modulation

Figure 26

Process of a peptide-based nanofibrous hydrogel enhancing the immune responses of HIV DNA vaccines. Adapted from ref (943). Copyright 2014 American Chemical Society.

Scheme 79. Representative Molecular Structures of Hydrogelators for Immunological Modulation

Figure 27

(A) Molecule 623 self-assembles to form a hydrogel. Gross appearance of the wound site treated without (B) or with (C) the gel on day 6. Adapted with permission from ref (1235). Copyright 2007 Royal Society of Chemisty.

Scheme 80. Some Supramolecular Hydrogelators for Wound Healing

Figure 28

Interplay between supramolecular assemblies and proteins. (I) Enzyme-instructed self-assembly (EISA): the enzyme transforms a precursor to the self-assembling small molecules (i.e., hydrogelator) to form the supramolecular assemblies (in the form of nanofibers/hydrogel). (II) Molecular hydrogel protein binding (MHPB) assay: the hydrogels formed by the supramolecular assemblies bind proteins for proteomic analysis and identification of the protein targets of the assemblies.

Figure 29

Illustration of EISA to form supramolecular nanofibers via bond formation or bond cleavage and the macroscopic outcomes (i.e., viscosity change or hydrogelation).

Figure 30

(A) Molecular structures of the precursor 14 and its corresponding hydrogelator 15 and the enzymatic transformation. (B) Transmission electron microscopy (TEM) image of the nanofibers made by the self-assembly of 15. Optical images of (C) the solution of 14 in alkali buffer (pH 9.8) and (D) the hydrogel formed by adding the phosphatase to the solution of 14 to produce the nanofibers of 15. Adapted with permission from ref (153). Copyright 2004 Wiley-VCH Verlag GmbH & Co. KGaA.

Figure 31

(A) Structures of the precursors 200 and 208 and the hydrogelator 447 and the enzymatic transformation. (B) SEM image of the corresponding nanofibers (scale bar 500 nm). Inset: optical image of the hydrogel. Adapted from ref (162). Copyright 2006 American Chemical Society.

Figure 32

(A) Structures of the precursor 630 and the hydrogelator 631 and the corresponding transformations catalyzed by phosphatase and kinase. (B) TEM images showing (I, left) the nanofibers of 630 formed by adjusting the pH, (II, middle) the absence of nanofibers due to enzymatic phosphorylation of 630, and (III, right) the restored nanofibers of 630 by enzymatic dephosphorylation of 631. (C) Optical images of (I) the hydrogel of 630 formed by changing the pH, (II) the solution obtained by treating the hydrogel with a kinase and ATP (at 50% conversion), and (III) the hydrogel of 630 restored by adding phosphatase. Adapted from ref (1254). Copyright 2006 American Chemical Society.

Figure 33

(A) Optical image of the hydrogel formed 1 h after subcutaneously injecting the solution of the precursor 631 into the mice. (B) Weight gain of the mice (n = 6, initial body weight 20 ± 2 g) after subcutaneously injecting 0.5 mL of 631 at 0.8 wt % concentration. A saline solution (0.5 mL) served as the control. Adapted from ref (1254). Copyright 2006 American Chemical Society.

Figure 34

(A) Structures of the precursor 632 and the hydrogelator 633 and the enzyme-catalyzed transformation. (B) TEM image of the nanofibers of 633. (C) Hydrogel formed by mixing blood, PBS buffer, and alkaline phosphatase. (D) Gel formed by mixing the solution of 632 (1.0 wt % in PBS buffer, pH 7.4), alkaline phosphatase, and the cytoplasm collected from 1.0 × 10⁶ broken HeLa cells. Adapted with permission from ref (1255). Copyright 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

Figure 35

(A) Structures of the precursor 634 and the hydrogelator 635 and the β-lactamase-catalyzed transformation. (B) TEM images showing the enzymatic formation of nanofibers of 635: top, the solution, bottom, the gel. (C–F) Images showing formation of nanofibers of 635 in the lysates of E. coli that express different β-lactamases (C, CTX-M13; D, CTX-M14; E, SHV-1; F, TEM-1). Adapted from ref (159). Copyright 2007 American Chemical Society.

Scheme 81. Molecular Structures of Representative Hydrogelators Formed via Enzymatic Transformation

Scheme 82. Molecular Structures of Small Representative Hydrogelators Formed via Enzymatic Transformation

Figure 36

(A) An esterase to convert the precursor 653 to the hydrogelator 654. (B) TEM image of the nanofiber formed by 654 (inset: optical image of the hydrogel). MTT assays of (C) NIH/3T3 cells and (D) HeLa cells treated with 653 at concentrations of 0.08, 0.04, and 0.02 wt %. Adapted with permission from ref (1289). Copyright 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

Figure 37

(A) A schematic representation of intracellular nanofiber formation and the inhibition of bacterial growth. (B, C) Structures and graphic representations of the precursor 656 and the corresponding hydrogelator 657. (D) TEM image of the nanofibers of 657 (indicated by arrows) formed inside the bacteria after culturing with 656. (E) Concentration of 656 needed to inhibit BL21(P+) and BL21 by forming nanofibers of 657 inside the bacteria. Adapted with permission from ref (1259). Copyright 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

Scheme 83. Some Precursors and Hydrogelators for Intracellular Self-Assembly

Figure 38

(A) Principle of imaging enzyme-instructed self-assembly inside cells. (B) Chemical structures of 658a. (C) TEM image of the hydrogel made of 658b. (D) Fluorescent confocal microscopy images showing the time course of fluorescence emission inside the HeLa cells incubated with 500 or 50 μM 658a in PBS buffer. Adapted with permission from ref (156). Copyright 2012 Nature Publish Group.

Figure 39

(A) Precursor 659a self-assembles to form nanofibers/hydrogels upon the addition of ALP. (B–I) Correlative light and electron microscopy (CLEM) images of HeLa cells incubated for 48 h with 500 μM 659a and 200 nM 660a. (B–E) Differential interference contrast (DIC) and fluorescence light microscopy images of treated HeLa cells growing on an Aclar plastic film. (F–I) TEM images of the cell of interest shown in (B)–(E). Adapted from ref (212). Copyright 2013 American Chemical Society.

Scheme 84. Structures of Precursors That Are the Substrates of Ectophosphatases and the Corresponding Hydrogelators

Figure 40

(A) Overlaid images and (B) 3D stacked z-scan image of Congo red- and DAPI-stained HeLa cells after the incubation of the HeLa cell with 661a for 12 h. (C) TEM image of the pericellular hydrogels on the HeLa cells treated by 661a (280 μM). (D) Change of the relative amount of apoptosis signal molecules over time in HeLa cells treated by 661a (280 μM). (E) Cell viability of HeLa cells incubated with 661a (280 μM), 661b (280 μM), and 661a (280 μM) plus l-Phe (1.0 mM). (F) Illustration of enzyme-instructed self-assembly to form pericellular nanofibers/hydrogel and selectively induce cell death. Adapted with permission from ref (288). Copyright 2014 John Wiley and Sons. Adapted from ref (1256). Copyright 2014 American Chemical Society.

Figure 41

IC₅₀ values of precursors and their hydrogelators on HeLa cells. F and Y indicate phenylalanine and tyrosine. Adapted from ref (1256). Copyright 2014 American Chemical Society.

Figure 42

(A) Chemical structures of precursors and hydrogelators made of a carbohydrate amphiphile. (B) Enzyme-instructed self-assembly for pericellular nanofiber formation/hydrogelation on Saos-2 cells. Adapted from ref (1285). Copyright 2015 American Chemical Society.

Figure 43

(A) Molecular structures of the precursors and the hydrogelators containing different fluorophores. (B) Illustration of the distinct spatial distribution of the small molecules in a cellular environment. Fluorescent confocal images of the HeLa cells incubated with 500 μM (C) 658a, (D) 664a, (E) 665a, and (F) 666a for 30 min. Adapted from ref (1063). Copyright 2013 American Chemical Society.

Figure 44

(a) Illustration of how enzyme-instructed molecular self-assembly induces cancer cell death. (b) Chemical structures of precursor ER-C16 (667) and hydrogelators G-C16 (668). Adapted from ref (894). Copyright 2015 American Chemical Society.

Figure 45

Illustration of the MHPB assay and hydrogel protein pull-down coupled with electrophoresis and tandem mass spectrometry for identifying cytosolic proteins that bind to supramolecular nanofibers. (A) Photoreaction of the hydrogelator and supramolecular nanofibers that bind with proteins. (B) Silver staining of the SDS–PAGE gel shows that different conditions alter the protein binding on the supramolecular hydrogel. Adapted with permission from ref (883). Copyright 2012 Royal Society of Chemistry.

Figure 46

(a) Molecular hydrogel protein binding (MHPB) assay: upper panel, silver staining of SDS–PAGE reveals a major protein band at ∼55 kDa in lane B; lower panel, Western blot confirms the cytoskeletal proteins as the primary protein targets. (b) Tubulin polymerization assays with 3. (c–e) Confocal images showing the assemblies of 3 impede the dynamics of cytoskeletal proteins. (f) Cellular uptake of 3 in HeLa cells treated by endocytosis inhibitors. (g) Time-dependent activation of the apoptotic proteins of HeLa cells treated with 3. (h) Mechanism of the selective cytotoxicity of 3 toward cancer cells. Adapted with permission from ref (1248). Copyright 2014 American Society for Biochemistry and Molecular Biology. Adapted with permission from ref (1290). Copyright 2013 John Wiley and Sons.