Self-Healing and Injectable Shear Thinning Hydrogels Based on

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Self-healing and injectable shear thinning hydrogels based on dynamic oxaborole-diol covalent crosslinking Yinan Wang, Lin Li, Yohei Kotsuchibashi, Sergey Vshyvenko, Yang Liu, Dennis G Hall, Hongbo Zeng, and Ravin Narain ACS Biomater. Sci. Eng., Just Accepted Manuscript • DOI: 10.1021/acsbiomaterials.6b00527 • Publication Date (Web): 10 Oct 2016 Downloaded from http://pubs.acs.org on October 13, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Biomaterials Science & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Biomaterials Science & Engineering

Self-healing and injectable shear thinning hydrogels based on dynamic oxaborole-diol covalent crosslinking Yinan Wang,1,2 Lin Li, 1 Yohei Kotsuchibashi,3 Sergey Vshyvenko,4 Yang Liu,2 Dennis Hall,4 Hongbo Zeng,1 Ravin Narain1* 1

Department of Chemical and Materials Engineering, University of Alberta, 116 St and 85 Ave, Edmonton, AB T6G 2G6, Canada

2

Department of Civil and Environmental Engineering, University of Alberta, 116 St and 85 Ave, Edmonton, AB T6G 2G6, Canada 3

International Center for Young Scientists (ICYS) and International Center for Materials

Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan 4

Department of Chemistry, 4-010 Centennial Centre for Interdisciplinary Science, University of Alberta, 116 St and 85 Ave, Edmonton, AB T6G 2G6, Canada

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 34

ABSTRACT

Hydrogels containing sugar and oxaborole residues with remarkable self-healing properties were synthesized by free-radical polymerization in a facile and one pot process. The strong covalent interactions between the oxaborole residues and free adjacent hydroxyl groups of the pendent sugar residues of the glycopolymer allowed the in situ formation of hydrogels achievable under either neutral or alkaline conditions. These hydrogels showed excellent self-healing and injectability behaviors in aqueous conditions, and were found to be responsive to both pH and the presence of free sugars (such as glucose) in solution. Furthermore, these hydrogels can easily be re-constructed from their lyophilized powder into any desired three-dimensional scaffold. Additionally, the hydrogels can be designed to have very low cytotoxicity and hence can be used as a scaffold for cell encapsulation. With these unique properties, these biocompatible, biodegradable, re-buildable and self-healable hydrogels offer great potential in many biomedical applications.

Keywords: Self-Healing, Injectable Hydrogel, Oxaborole-Diol Dynamic Covalent Crosslinking, Stimulus Responsive Materials, Cell Delivery


2

Page 3 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Introduction Compared to metallic or ceramic implants, polymeric implants can be designed to have similar properties as biological tissues, and hence have been extensively investigated as synthetic equivalents for use in biological systems. However, their applications as effective biomaterials have been limited due to damage or fatigue during the normal operation. Therefore, self-healing materials that are capable of intrinsically self-repair at damage sites based on host-guest interaction,1 redox reaction,2 hydrogen bonding,3-8 electrostatic interaction,9,

10

metal

coordination,11-14 hydrophobic interactions,15 or by the delivery of encapsulated healing agents1618

have been extensively studied in the past decades. However, so far, most of the self-healing

materials were designed by exploiting relatively weak non-covalent interactions, while a handful of studies have mentioned the use of stronger dynamic covalent bonds (such as boronate-diol complex,19-21 urea bonds,22, 23 dimerization,24-28 and Diels-Alder reaction) to construct materials with self-repair properties. Inspired by nature that some mollusks, such as mussels, sandcastle worm and slugs, are able to attach strongly to a substrate surface underwater by secreting metal containing proteinaceous adhesives,29-32 in recent years, various polymers have been utilized to design and fabricate hydrogels by mimicking this process.7,11,13,33 These hydrogels showed great self-healing properties due to their reversible non-covalent (metal-ligand11 or hydrogen bonds5,7) nature. For biomedical applications, however, these hydrogels suffered from being potentially cytotoxic due to the presence of metal ions and their self-healing properties may be affected by the facile oxidation of the catechol residues.34 On the other hand, microorganisms, such as bacteria, can also firmly attach to a surface underwater by forming biofilms through the carbohydrate-lectin interactions.35 Using this


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 34

strategy, hydrogels formed by the interactions between glycopolymers and “synthetic lectins” (e.g. phenylboronic acid (PBA)) have also been reported as excellent candidates for some biological applications due to their enhanced stability and more biocompatible nature as compared to the catechols based materials.36-38 However, cytotoxic primary/secondary amines are usually introduced to the polymer backbones to adjust the PBA’s pKa values below the physiological pH ranges.36,39-41 Previously, our group had demonstrated the utilization of a 5methacrylamido-1,2-benzoxaborole (MAAmBo) containing copolymer to complex with a glycopolymer, namely (poly(3-gluconamidopropyl methacrylamide) (PGAPMA)) to generate hydrogels under physiological pH.42 However, this procedure required extensive efforts on polymer synthesis and purification, and the materials self-healing properties were not explored. Therefore, in this study, we propose a simple and straightforward approach towards the fabrication of self-healing hydrogels simply by exploiting the strong boronate-diol interactions (Scheme 1). The free hydroxyl groups of the pendent sugar moieties and the presence of close proximity oxaborole residues allowed covalent crosslinking of the polymer chains in the hydrogels. Due to the nature of the construct, the hydrogels are sensitive to both pH and the presence of free sugars. The presence of the oxaborole residues can also be exploited to interact with biological entities such as lectins or other glycoproteins on the mammalian tissue surface.4345

Materials and Methods Materials Acrylamide (AM) and 4,4'-azobis (4-cyanovaleric acid) (ACVA) were purchased from SigmaAldrich (Canada). Fluoresbrite® YG Microspheres (10.0 µm in diameter) were obtained from Polyscience, Inc. (Warminster, PA). 5-Amino-2-hydroxymethlphenylboronic acid HCl salt with


4

Page 5 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


purity > 95% were purchased from Santa Cruz Biotechnology Inc. (Santa Cruz, CA). All other chemicals and solvents were used as received. Methods Synthesis of 5-methacrylamido-1,2-benzoxaborole (MAAmBO) 5-Methacrylamido-1,2-benzoxaborole (MAAmBO) was synthesized as previously reported.42 In brief, 5-amino-2-hydroxymethylphenylboronic acid HCl salt (1.0 g, 5.39 mmol) was added to an aqueous NaOH solution (1.7 M, 17 mL), and the reaction mixture was cooled to 0 ºC in an ice bath. After stirring for 15min, methacryloyl chloride (1.1 mL,11.3 mmol) was added to the reaction mixture through a syringe pump over a period of one hour, and the solution was kept stirring for another 3 h. The solution was then acidified slowly with concentrated HCl at 0 ºC, white precipitates were filtered and washed with cold water (2 × 5 mL). The precipitates were recrystallized using a mixture solvent of ethanol/water and a white solid (0.75 g, 65%) was obtained after the removal of solvent under high vacuum. 1

H NMR (500 MHz, DMSO-d6): δ[ppm] = 9.80 (s, 1H), 9.16 (s, 1H), 8.04 (d, 1H), 7.66 (dd, 1H),

7.32 (dd, 1H), 5.79 (t, 1H), 5.48 (dt, 1H), 4.93 (s, 2H), 1.94 (dd, 3H) (Figure S1). Synthesis of 3-gluconamidopropyl methacrylamide (GAPMA) Gluconolactone (16 g, 89.8 mmol) was first dissolved in 100 mL methanol with 20g of 3aminopropyl methacrylamide hydrochloride (APMA, 112.3 mmol). After the addition of trimethylamine (16 mL, 114.8 mmol), the reaction was conducted by stirring overnight at room temperature. The obtained solid was then precipitated from the reaction mixture at −10 °C, and the crude product was washed by 2-propanol three times and followed by acetone. The final yield after purification was ∼70%. The NMR data were in agreement with previous studies published from our group.47


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 34

Synthesis of the self-healing P(AM-st-GAPMA-st-MAAmBO) hydrogels The self-healing P(AM-st-GAPMA-st-MAAmBO) hydrogels were synthesized using one-pot free radical polymerization of a glucose containing GAPMA and a benzoboroxole containing MAAmBO. For a typical reaction, GAPMA (80 mg, 0.25 mmol) and AM (319.5 mg, 4.5 mmol) was dissolved in 1.4 mL of Tris buffer (pH 8.0) in a 10 mL Schlenk tube. The solution was then mixed with 1.1 mL of MAAmBo (52 mg, 0.25 mmol) and 4,4'-azobis (4-cyanovaleric acid) (ACVA) (14 mg, 0.05 mmol) DMF stock solution. The tube was then sealed and degassed by purging it with nitrogen for 30 minutes. Polymerization was carried out in an oil bath (70 °C) for 24 hours. After the polymerization, the as-prepared gel was immersed in a large amount of pH 7.4 phosphate buffered saline (PBS) for 2 days to reach equilibrium and to remove the residual chemicals and organic solvent. The high monomers concentration condition (2 M) is required to prevent phase separation during the polymerization. The hydrogels stabilities were evaluated in either NaOAc/HOAc buffer at pH 4.0 or 50 mM fructose Tris buffer at pH 8.0. Once the hydrogels were completely dissociated, the molecular weights (Mn) and molecular weight distributions (PDI) of the polymers in solutions were determined by an aqueous GPC (Viscotek GPC system) using Pullulan standards (Mw = 5900– 788 000 g mol–1) at room temperature with a flow rate of 1.0 mL/min. Synthesis of linear P(AM-st-GAPMA-st-MAAmBO) copolymer A P(AM-st-GAPMA-st-MAAmBO) copolymer was also synthesized using a method that similar to the synthesis of P(AM-st-GAPMA-st-MAAmBO) hydrogel. For a typical reaction, GAPMA (80 mg, 0.25 mmol) and AM (319.5 mg, 4.5 mmol) was dissolved in 7 mL of pH 4.0 NaOAc/HOAc buffer solution. The solution was then mixed with 5.5 mL of MAAmBO (52 mg, 0.25 mmol) and 4,4'-azobis (4-cyanovaleric acid) (ACVA) (14 mg, 0.05 mmol) DMF stock


6

Page 7 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


solution. The mixture solution was then sealed and degassed by purging it with nitrogen for 30 minutes. Polymerization was carried out in an oil bath (70 °C) for 24 hours. After the polymerization, the as-prepared gel was purified by dialysis and then freeze-drying to obtain a solid product. The low monomers concentration condition (0.5 M) and acidic condition are required to prevent the formation of hydrogel during the polymerization. The structure of the copolymer was characterized by 1H NMR (500 MHz) using D2O and DMSO-d6 mixture solvent. Synthesis of polyacrylamide and glycopolymers hydrogels As a control to investigate the presence of carbohydrates and oxaboroles on the formation and self-healing properties of the P(AM-st-GAPMA-st-MAAmBO) hydrogels, polyacrylamide and glycopolymers (glucose containing GAPMA or galactose containing 2-lactobionamidoethyl methacrylamide (LAEMA) (see structures in Scheme S1, supporting information)) hydrogels that crosslinked by 1 mol% of N,N'-methylenebisacrylamide (MBAm) were prepared by a similar procedure as we used to make the self-healing hydrogels. Typically, GAPMA (320 mg, 1 mmol), AM (284 mg, 4 mmol), ammonium persulfate (APS, 12 mg, 0.05 mmol), and 10 µL of tetramethylethylenediamine (TEMED) was mixed in 2.5 mL of Tris buffer (pH 8.0). The solution was then transferred to a 20 mL glass scintillation vial, sealed and degassed by purging it with nitrogen for 30 minutes. Polymerization was carried out at room temperature for 12 hours, and the as-prepared gel was immersed in a large amount of pH 7.4 PBS for 2 days to reach equilibrium and to remove the residual chemicals. Swelling measurements After reaching to their equilibrium state by incubation in PBS buffer at pH 7.4 for 2 days, the wet weight of P(AM-st-GAPMA-st-MAAmBO) hydrogels were determined by blotting with a filter


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 34

paper, blowing with a stream of air to remove the surface water and immediately weighting. The hydrogels were then freeze-dried, and the swelling ratio was calculated use the equation % =

× 100

(1)

where ms and md are the weights of the samples in the swollen and dry states respectively. Evaluation of the self-healing properties of the hydrogels The hydrogels’ self-healing properties were evaluated after they had been incubated in pH 7.4 PBS solutions for two days. The effects of the pH on the gel’s self-healing properties were also evaluated after the gels were incubated in Tris buffer at pH 8.0 for 2 days. The self-healing hydrogel was also cut and placed in pH 7.4 PBS buffer to evaluate the underwater self-healing properties. To evaluate the hydrogels’ mechanical and self-healing properties, a rheometer (TA instruments, AR-G2) equipped with a 20-mm parallel-plate configuration was used. Two types of rheological tests, including linear amplitude sweep followed by time-dependent modulus recovery test and cyclic strain step test, were conducted in this study. For the linear amplitude sweep tests, the values of G’ and G” were recorded with strain raising from 0.1 to 2500 %, at 25 °C and 1 Hz. The gel was allowed to heal for 5 min at 0 % strain prior to subject to a strain of 1% for 5 min to evaluate the modulus recovery performance. For the cyclic strain step tests, the sample was subjected to strain step cycled between 1 and 500 % for three times, at 25 °C and 1 Hz. A strain of 500% was applied to the sample for 4 min before it was allowed to heal for 5 min at 0% strain. The sample was then subjected to 1% strain for 4 min to evaluate its modulus recovery performance. Cell Culture and cell viability assay


8

Page 9 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Hela cells were maintained in DMEM supplemented with 10% FBS and 1% antibiotic at a humidified atmosphere at 37 °C containing 5% CO2. Upon 80% confluency the cells were harvested with 0.25% trypsin and seeded in 24 wells plates (50, 000 cells/well), in which the P(AM-st-GAPMA-st-MAAmBO) hydrogels were preloaded in a concentration range of 1 to 20 mg/mL. The cells were then incubated overnight and 200 µL of MTT dye was added per well. After 2 h, MTT lysis buffer (200 µL/well) was added and cells were allowed to lyse overnight. The absorbance was read at 570 nm using TECAN Genios pro microplate reader. The untreated cells and media alone were used as positive and negative controls, respectively. The percent cell viability was calculated as !!"#$%& '#'!

% = ('"%%&

'#'!#$%& '#'!

× 100

(2)

The IC50 values for different hydrogels were determined using Dose Response function provided from Origin Pro software.3 Cell encapsulation and release Hela cells were labeled with CellTracker Violet BMQC dye (Life Technologies), prior to use. 400 µL of cells suspension (106 cells/mL) in low glucose (1 g/L of glucose) DMEM media were then mixed with 40 mg of lyophilized hydrogel powders and incubated at 37 oC under 5% CO2 atmosphere for 30 min to allow rebuilding of the hydrogels. The hydrogels were then loaded to a 1 cc syringe and injected into 400 mL of low glucose DMEM media. The media was changed every two days, and the hydrogels were imaged on a confocal laser scanning microscope (fluoview fv10i, Olympus) at day 1, 2, 4, and 7. The hydrogels were then transferred to a new plate and incubated in 400 µL of high glucose (4 g/L of glucose) DMEM media for additional two days. Once the hydrogels were completely dissociated, the attached Hela cells were


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 34

trypsinized, labeled with CellTracker Violet BMQC dye again, and cultured for overnight. An image of attached cells were took on CLSM. Results and Discussions Hydrogel Synthesis. Hydrogels were synthesized by free-radical copolymerization of MAAmBO, GAPMA and acrylamide (AAm) in a sodium phosphate buffer at pH 8.0 (Scheme 1A and Figure 1A). The mole ratio of MAAmBO and GAPMA are kept the same. Hydrogels synthesized in this work were named as Gx, where x indicates mol% of MAAmBO presented in the gel network. As expected, monomer concentration, composition and solution pH were found to be important parameters in the formation of the hydrogels. As the hydrogels are formed in situ by the interaction of the oxaborole and sugar hydroxyl groups, a high monomer concentration (~ 2 M) were required during the polymerization. At low monomer concentration (1 M or lower), nanogels were instead formed, possibly due to phase separation during the polymerization.9,42 Interestingly, only linear copolymers, P(AM-st-GAPMA-st-MAAmBO), were obtained upon polymerization of the monomers in an acidic solution (pH - 4.0) due to the pH sensitive nature of the oxaborole-sugar covalent bonds (Figure S2). Additionally, for comparison purposes, P(AAm) homopolymer, P(AAm-co-GAPMA) and P(AAm-co-MAAmBO) were also synthesized under similar conditions (pH 8.0, 2 M monomer concentration) and, as expected, no hydrogel were formed in the absence of either or both of the oxaborole and sugar monomers (Figure 1B-D).46


10

Page 11 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. Hydrogel synthesis (A) and their self-healing behavior mediated by dynamic oxaborole-sugar hydroxyl groups interactions (B).

Figure 1. Formation of G5 under basic condition (A). Linear P(AAm) (B), P(AAm-co-GAPMA) (C) and P(AAm-co-MAAmBO) (D) polymers were obtained when polymerization was conducted in the absence of either or both of the GAPMA and MAAmBO monomers. Incubation of the hydrogels in sodium phosphate buffer at pH 7.4, pH 8.0, 4 g/L glucose at pH 7.4, and NaOAc/HOAc buffer at pH 4.0 (E, from left to right).


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 34

The synthesized hydrogels are stable and do not degrade under neutral and alkaline pH. However, under acidic conditions (pH ~ 4.0), the hydrogels start to dissociate into linear polymers with molecular weight ranged from 10 to 20 kDa (Figure 1E, Figure 2A and Table S1). Similarly, when the hydrogels are incubated in a 4 g/L glucose solution at pH 7.4, the hydrogels dissociate due to the competitive displacement of pendant sugar residues with the free glucose in the solution (Figure 1E, Figure 2B and Table S1).39,47,48 Hydrogels incubated in high glucose solution was found to dissociate faster and release more linear polymers as compared to those undergoing acid treatment (Figure 2B v.s Figure 2A). In either treatment, the rate of dissociation of the hydrogels was found to be dependent on the amount of oxaborole-sugar pairs in the gel network. Since the molecular weight cut-off for glomerular filtration is reported in a range of 30– 50 kDa,49 this “degradable” hydrogels may show great potential applications as biomaterials for drug delivery or tissue engineering.

Figure 2. GPC results obtained after the incubation of hydrogels in pH 4.0 (A) and 4 g/L glucose solution at pH 7.4 (B) for 48 hr.


12

Page 13 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Self-healing Properties. The self-healing properties of the hydrogels obtained after dialysis against sodium phosphate buffer at pH 7.4 (Figure 3) and 8.0 (Figure S3) have been studied using a rheometer. Figure 3A shows the instantaneous self-healing behavior of a hydrogel that was initially cut into two pieces. After the hydrogel were brought into contact, the contact interface disappeared within 5 min (See Supporting Information, Video 1). Figure 3B shows the changes of shear storage (G’) and loss (G”) moduli from strain sweep experiment at a frequency of 1.0 Hz at 25 °C. The G5 hydrogel was swept from 1 to 2500% strain and then back to 1% strain after 5 min of healing. The G’ values, which are comparable to the hydrogels formed by catechol-boronate interactions,19,21 are found to be larger than the G” values and remained constant until the strain reached 80%, suggesting that the hydrogel formed by the boronate-diol covalent bonds could withstand relatively large deformations. The gel disintegrated into a sol state when sheared with a strain over 100% due to the dissociation of the polymer chains. Once the strain was reduced to 1%, both G’ and G” could be restored to 100% of their original values. This recovery process could be achieved almost instantaneously and was totally reversible during the cyclic tests. This result is in good agreement to the self-healing test as shown in Figure 3A and also reveals that the G5 hydrogel has an excellent self-healing behavior due to the dynamic deformation/re-construction of the boronate-diol complex. When the hydrogel was subjected to a continuous step strain measurement (strain switched between 1 and 500%) at a constant frequency of 1.0 Hz at 25 °C, G’ and G” values immediately dropped to 50 and 200 Pa, respectively and recovered to initial values when the strain was restored to 1% (Figure 3C). These values were consistent with the results in Figure 3B, indicating a reversible and reproducible self-healing process during the cyclic tests. To further demonstrate our idea that this self-healing hydrogel could be used as a biomaterial under the physiological conditions, the G5


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 34

hydrogel was cut and brought into contact in a pH 7.4 buffer solution. As expected, the two hydrogel fragments could bond strongly and heal to form a single piece after being in contact for a few seconds (See Supporting Information, Video 2).


14

Page 15 of 34


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment

15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 34

Figure 3. Rapid self-healing of G5 hydrogel in air (within 5 min) (A). Strain sweep measurements of the G5 hydrogel at 25 °C with a frequency of 1.0 Hz. The storage (G’) and loss (G”) moduli were recorded as a function of strain (γ). The gel was swept from 1 to 2500% strain, and then back to 1% strain (B). G’ and G” recorded during the cyclic strain changes between 1 and 500% of strain at 25 °C with a frequency of 1.0 Hz (C). To further illustrate the hydrogel’s self-healing mechanism as well as to explore its possibility to be used as a tissue glue, the interaction between G5 hydrogel and chemically cross-linked P(AM-st-GAPMA) (with glucose-derived pendant residues), P(AM-st-LAEMA) (with galactose pendent residues) and PAM hydrogels were also studied. Figure S4 shows the interaction between G5 hydrogel and chemically crosslinked P(AM-st-GAPMA) and P(AM-st-LAEMA) gels in air (Figure S4A and S4B, and Supporting Information, Video 3) and pH 7.4 buffer solution (Figures S4C and S4D, and Supporting Information, video 4). The results revealed that both glycopolymer hydrogels were able to interact with the G5 hydrogel under similar conditions mentioned above. As expected, no interactions between G5 and PAM hydrogels (See Supporting Information, Video 5) were observed and therefore the G5 hydrogel’s self-healing properties were found to be exclusively due to the dynamic covalent interaction of the boronate and hydroxyl groups of the sugar residues.50 Interestingly, when we increase oxaborole and sugar content in the hydrogels to 10 and 20 mol%, although hydrogels were formed after polymerization, and the materials showed good self-healing properties in air (Figure 4, Figure S5A and Supporting Information, video 6) and sodium phosphate buffer at pH 7.4 (Figure S5B), a sol-like behavior (G’ < G”) was recorded after hydrogels were dialyzed against buffer at pH 7.4 (Figure 4) or 8.0 (Figure S6 and S7). These observations are possibly due to shorter relaxation time of the gel as compared to the


16

Page 17 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


angular frequency (6.28 rad/s) of the dangling polymers,13,51,52 which is supported by the relaxation of G10 and G20 hydrogels at 500% strain (Figure 4C and 4D).

Figure 4. Rheology test results for G10 (A) and G 20 (B) hydrogels: Strain sweep measurements of G10 and G20 hydrogels, respectively, at 25 °C and 1.0 Hz. The storage (G’) and loss (G”) moduli were recorded as a function of strain (γ). The gel was swept from 1 to 2500% strain, and


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 34

then back to 1% strain. (C) and (D): G’ and G” recorded when G10 and G20 hydrogels subjected to the cyclic strain changes between 1 and 500% of strain at 25 °C with a frequency of 1.0 Hz, respectively. We were then performing dynamic frequency sweep measurements on G10 and G20 hydrogels to determine the crossover frequency (ωc) and quantify the gel strength (Figure 5). For hydrogels with lower ωc, the mechanical properties are dominated by the storage modulus (G’) over a broader frequency range, resulting in more elastic behavior and higher strength.53 As predicted, both G10 and G20 hydrogels demonstrated frequency-dependent viscoelastic behavior (Figure 5). The ωc values, which are higher than 7 rad s-1 at pH 7.4 condition, showed a good agreement to the results from the Figure 4 () *+ , - = 2/ × 0 12 ). On the other hand, the ωc values also correlated with the materials pH responsiveness, in which the ωc decreasing as pH is increased. For example, ωc of the G10 hydrogel was 14 rad s−1 at pH 7.4, and decreased to 0.6 rad s−1 at pH 8.0 (Figure 5A). Comparatively, at pH 7.4 the ωc for G20 hydrogel was 7 rad s−1 (Figure 5B), indicating stronger gel formation as compared to the ωc of G10 at the same pH (Figure 5A). Interestingly, at pH 8.0, the G10 hydrogel has shown stronger mechanical strength than that of G20 hydrogel, despite that the latter possesses higher amount of oxaborole/sugar pairs in the gel network. This is possibly due to imperfections in the gel network due to the free chains or the formation of primary loops.


18

Page 19 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. Dynamic oscillatory frequency sweeps performed at 25 °C of G10 (A) and G20 (B) hydrogels at pH 7.4 (red dots) and 8.0 (blue dots). Arrows denote representative crossover frequencies (ωc). Injectable shear-thinning hydrogels. The hydrogels showed a frequency-dependent viscoelastic behavior (Figure 5), which is a typical behavior of dynamic gel networks.54 Next, we studied the shear-thinning properties of these hydrogels. We first measured the effect of shear rates on gel viscosity, which is a critical parameter for the hydrogels injectability. As expected, the viscosity of G5 and G10 hydrogels at room temperature decreased with the increasing of shear rates (Figure 6A), indicating a shear-thinning behavior due to the disruption of dynamic cross-links in the gel network. Compared to G10 hydrogel, the G5 hydrogel showed a lower viscosity value at high shearing rate (17 Pa s-1), which makes the latter much easier to be injected through a 23 G needle in air or in a pH 7.4 solution (Figure 6B and 6C). As for G20 hydrogel, it was found to be more cytotoxic as compared to G5 and G10 (Figure 6D) and hence is less likely to be used as an injectable hydrogels for biomedical applications. We also incorporated 10 µm FITC labeled polystyrene microsphere into the G5 hydrogel and injected in air and aqueous solution to test the materials potential application for cell delivery.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 34

The distributions of the microspheres could be visualized by a fluorescent microscope or a UV lamp. The results showed all microspheres are well retained in the gel matrix during the injection.

Figure 6. Viscosity and shear-thinning behavior of G5 and G10 hydrogels (A). Injection of G5 (encapsulated with 10 µm FITC-PS microsphere) hydrogels in air (B) and a buffer solution at pH 7.4 (C) through a 23 G needle. The distribution of the encapsulated PS microsphere can be visualized by a fluorescent microscope (B), or a UV lamp (C). Scale bar = 100 µm. MTT assay of cell viability to determine hydrogels cytotoxicity (D). Rebuildable hydrogel. Due to the self-healing properties of the hydrogels, we also demonstrate that hydrogels can be re-constructed into the desired 3D structures simply from their lyophilized powders. To do this, the G5 hydrogel was freeze-dried and ground into a fine powder. The hydrogel dried powder was filled into a mold of a desired shape as shown in Figure 7A and then incubated in a phosphate buffer at pH 7.4. After 30 min of incubation, the desired 3D hydrogel was formed as shown in Figure 7B. The self re-constructed bulk hydrogel, containing about 90


20

Page 21 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


wt% water, showed excellent self-healing properties (Figure 7C) and hence can potentially be used for 3/4D printing.

Figure 7. Rebuild of a G5 hydrogel from its lyophilized powders in pH 7.4 buffer solution at room temperature. (A) lyophilized and ground G5 hydrogel powder in a maple leaf mold. (B) self-glued hydrogel was formed after incubated the G5 hydrogel powder in pH 7.4 buffer solution for 30 min. (C) Strain sweep measurements of the rebuilt G5 hydrogel at 25 °C with a frequency of 1.0 Hz. The storage (G’) and loss (G”) moduli were recorded as a function of strain (γ). The gel was swept from 1 to 1500% strain, and then back to 1% strain. 3D Cell encapsulation in the Self-Healing Hydrogels: Given the excellent injectability, rebuildability and cell viability of G5 hydrogel, we decided to evaluate G5 hydrogel as a cell delivery vehicle. For this, we used Hela cells as a model and, after incubation of the cells (106


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 34

cells/mL suspended in low glucose DMEM media) with G5 gel powder, the cells were found to be encapsulated into the re-constructed G5 hydrogel after 30 min of incubation in the cell/hydrogel suspension mixture (Figure 8A). The gel containing the encapsulated cells was subsequently injected to a low glucose DMEM cell culture media. The re-built G5 hydrogel with HeLa cells was found to be stable for at least 7 days in the culture media without any deleterious effect on the cell viability, and a marked increase in cell numbers were noted from day 2 of cell culture (Figure 8A). Interestingly, the G5 hydrogel was found to dissociate and release of the encapsulated cells when incubated in a high glucose condition (4 g/L of glucose) from day 4. The higher glucose concentration in the media competitively disrupt the sugar-oxaborole linkage in the gel network. It should be noted that the released cells were found viable and were able to be re-stained and attached on a solid surface (Figure 8B).

Figure 8. Hela cells are stained with Celltracker BMQC dye, encapsulated in G5 hydrogel and incubated in low glucose (1 g/L) DMEM media for different time length (a). After 4 days of incubation, the gel was transferred to a high glucose (4 g/L) DMEM for 2 days to release the encapsulated cells. The cells were re-stained with the same dye and allowed to grow on a glass slide for overnight (b). Red arrow: x axis, scale 636.40 μm, green arrow: y axis, scale 636.40 μm, blue arrow: z axis, scale 200 μm.


22

Page 23 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Conclusions Self-healing hydrogels, that are responsive to pH and free sugars, were synthesized by a simple and one pot free radical polymerization process. The formation of the hydrogels is shown to be mediated by the strong and dynamic interactions of the oxaborole and adjacent hydroxyl groups of the sugar residues. The mechanical properties of gels are dependent on the oxaborole and sugar contents in the hydrogel as well as the pH of the solution. These hydrogels are injectable due to their shear thinning properties and are self-healable in air and under physiological conditions. More interestingly, due to their rapid self-healing property in aqueous system, the hydrogels can also be rebuilt from their lyophilized powders to a designated shape, which may allow them being potentially used for 3/4D bio-printing. In addition, hydrogels compositions can be controlled to have low cytotoxicity and hence suitable for cell encapsulation and delivery.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 34

ASSOCIATED CONTENT Supporting Information Characterization of the hydrogels and their corresponding linear polymers. Videos for the hydrogels self-healing tests and macroscopic interaction with carbohydrate surfaces. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author Email: [email protected]

Notes The authors declare no competing financial interests. ACKNOWLEDGMENT This research was supported by research grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation (CFI). REFERENCES (1) Chen, H.; Ma, X.; Wu, S.; Tian, H., A Rapidly Self-Healing Supramolecular Polymer Hydrogel with Photostimulated Room-Temperature Phosphorescence Responsiveness. Angew. Chem. Int. Ed. 2014, 53, 14149-14152. (2) Nakahata, M.; Takashima, Y.; Yamaguchi, H.; Harada, A., Redox-responsive self-healing materials formed from host–guest polymers. Nat Commun 2011, 2, 511.


24

Page 25 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(3) Phadke, A.; Zhang, C.; Arman, B.; Hsu, C.-C.; Mashelkar, R. A.; Lele, A. K.; Tauber, M. J.; Arya, G.; Varghese, S., Rapid self-healing hydrogels. Proc. Natl. Acad. Sci. 2012, 109, 43834388. (4) Cordier, P.; Tournilhac, F.; Soulie-Ziakovic, C.; Leibler, L., Self-healing and thermoreversible rubber from supramolecular assembly. Nature 2008, 451, 977-80. (5) Ahn, B. K.; Lee, D. W.; Israelachvili, J. N.; Waite, J. H., Surface-initiated self-healing of polymers in aqueous media. Nat. Mater. 2014, 13, 867-872. (6) Faghihnejad, A.; Feldman, K. E.; Yu, J.; Tirrell, M. V.; Israelachvili, J. N.; Hawker, C. J.; Kramer, E. J.; Zeng, H., Adhesion and Surface Interactions of a Self-Healing Polymer with Multiple Hydrogen-Bonding Groups. Adv. Funct. Mater. 2014, 24, 2322-2333. (7) Li, L.; Yan, B.; Yang, J.; Chen, L.; Zeng, H., Novel Mussel-Inspired Injectable SelfHealing Hydrogel with Anti-Biofouling Property. Adv. Mater. 2015, 27, 1294-1299. (8) Zhang, H.; Xia, H.; Zhao, Y., Poly(vinyl alcohol) Hydrogel Can Autonomously Self-Heal. ACS Macro Letters 2012, 1, 1233-1236. (9) Sun, T. L.; Kurokawa, T.; Kuroda, S.; Ihsan, A. B.; Akasaki, T.; Sato, K.; Haque, M. A.; Nakajima, T.; Gong, J. P., Physical hydrogels composed of polyampholytes demonstrate high toughness and viscoelasticity. Nat. Mater. 2013, 12, 932-937. (10) Luo, F.; Sun, T. L.; Nakajima, T.; Kurokawa, T.; Zhao, Y.; Ihsan, A. B.; Guo, H. L.; Li, X. F.; Gong, J. P., Crack Blunting and Advancing Behaviors of Tough and Self-healing Polyampholyte Hydrogel. Macromolecules 2014, 47, 6037-6046.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 34

(11) Holten-Andersen, N.; Harrington, M. J.; Birkedal, H.; Lee, B. P.; Messersmith, P. B.; Lee, K. Y. C.; Waite, J. H., pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli. Proc. Natl. Acad. Sci. 2011, 108, 26512655. (12) Sun, J. Y.; Zhao, X.; Illeperuma, W. R.; Chaudhuri, O.; Oh, K. H.; Mooney, D. J.; Vlassak, J. J.; Suo, Z., Highly stretchable and tough hydrogels. Nature 2012, 489, 133-6. (13) Sato, T.; Ebara, M.; Tanaka, S.; Asoh, T.-A.; Kikuchi, A.; Aoyagi, T., Rapid self-healable poly(ethylene glycol) hydrogelsformed by selective metal–phosphate interactions. PCCP 2013, 15, 10628-10635. (14) Mozhdehi, D.; Ayala, S.; Cromwell, O. R.; Guan, Z., Self-Healing Multiphase Polymers via Dynamic Metal–Ligand Interactions. J. Am. Chem. Soc. 2014, 136, 16128-16131. (15) Tuncaboylu, D. C.; Sari, M.; Oppermann, W.; Okay, O., Tough and Self-Healing Hydrogels Formed via Hydrophobic Interactions. Macromolecules 2011, 44, 4997-5005. (16) Toohey, K. S.; Sottos, N. R.; Lewis, J. A.; Moore, J. S.; White, S. R., Self-healing materials with microvascular networks. Nat. Mater. 2007, 6, 581-5. (17) White, S. R.; Sottos, N. R.; Geubelle, P. H.; Moore, J. S.; Kessler, M. R.; Sriram, S. R.; Brown, E. N.; Viswanathan, S., Autonomic healing of polymer composites. Nature 2001, 409, 794-7. (18) Lv, L.-P.; Zhao, Y.; Vilbrandt, N.; Gallei, M.; Vimalanandan, A.; Rohwerder, M.; Landfester, K.; Crespy, D., Redox Responsive Release of Hydrophobic Self-Healing Agents from Polyaniline Capsules. J. Am. Chem. Soc. 2013, 135, 14198-14205.


26

Page 27 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19) Vatankhah-Varnoosfaderani, M.; Hashmi, S.; Ghavaminejad, A.; Stadler, F. J., Rapid selfhealing and triple stimuli responsiveness of a supramolecular polymer gel based on boron– catechol interactions in a novel water-soluble mussel-inspired copolymer. Polym. Chem. 2014, 5, 512-523. (20) Deng, C. C.; Brooks, W. L. A.; Abboud, K. A.; Sumerlin, B. S., Boronic Acid-Based Hydrogels Undergo Self-Healing at Neutral and Acidic pH. ACS Macro Letters 2015, 220-224. (21) He, L.; Fullenkamp, D. E.; Rivera, J. G.; Messersmith, P. B., pH responsive self-healing hydrogels formed by boronate–catechol complexation. Chem. Commun. 2011, 47, 7497-7499. (22) Ying, H.; Zhang, Y.; Cheng, J., Dynamic urea bond for the design of reversible and selfhealing polymers. Nat Commun 2014, 5, 3218. (23) Yang, Y.; Urban, M. W., Self-Repairable Polyurethane Networks by Atmospheric Carbon Dioxide and Water. Angew. Chem. Int. Ed. 2014, 53, 12142-12147. (24) Imato, K.; Nishihara, M.; Kanehara, T.; Amamoto, Y.; Takahara, A.; Otsuka, H., SelfHealing of Chemical Gels Cross-Linked by Diarylbibenzofuranone-Based Trigger-Free Dynamic Covalent Bonds at Room Temperature. Angew. Chem. Int. Ed. 2012, 51, 1138-1142. (25) Amamoto, Y.; Otsuka, H.; Takahara, A.; Matyjaszewski, K., Self-Healing of Covalently Cross-Linked Polymers by Reshuffling Thiuram Disulfide Moieties in Air under Visible Light. Adv. Mater. 2012, 24, 3975-3980. (26) Zheng, P.; McCarthy, T. J., A Surprise from 1954: Siloxane Equilibration Is a Simple, Robust, and Obvious Polymer Self-Healing Mechanism. J. Am. Chem. Soc. 2012, 134, 20242027.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 34

(27) Lu, Y.-X.; Guan, Z., Olefin Metathesis for Effective Polymer Healing via Dynamic Exchange of Strong Carbon–Carbon Double Bonds. J. Am. Chem. Soc. 2012, 134, 14226-14231. (28) Imato, K.; Ohishi, T.; Nishihara, M.; Takahara, A.; Otsuka, H., Network Reorganization of Dynamic Covalent Polymer Gels with Exchangeable Diarylbibenzofuranone at Ambient Temperature. J. Am. Chem. Soc. 2014, 136, 11839-11845. (29) Bradshaw, A.; Salt, M.; Bell, A.; Zeitler, M.; Litra, N.; Smith, A. M., Cross-linking by protein oxidation in the rapidly setting gel-based glues of slugs. The Journal of Experimental Biology 2011, 214, 1699-1706. (30) Moeser, G. M.; Carrington, E., Seasonal variation in mussel byssal thread mechanics. J. Exp. Biol. 2006, 209, 1996-2003. (31) Baier, R. E.; Shafrin, E. G.; Zisman, W. A., Adhesion: Mechanisms That Assist or Impede It. Science 1968, 162, 1360-1368. (32) Zeng, H.; Hwang, D. S.; Israelachvili, J. N.; Waite, J. H., Strong reversible Fe3+-mediated bridging between dopa-containing protein films in water. Proc. Natl. Acad. Sci. 2010, 107, 12850-12853. (33) Sedó, J.; Saiz-Poseu, J.; Busqué, F.; Ruiz-Molina, D., Catechol-Based Biomimetic Functional Materials. Adv. Mater. 2013, 25, 653-701. (34) Yu, J.; Wei, W.; Danner, E.; Ashley, R. K.; Israelachvili, J. N.; Waite, J. H., Mussel protein adhesion depends on interprotein thiol-mediated redox modulation. Nat. Chem. Biol. 2011, 7, 588-90.


28

Page 29 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Diggle, S. P.; Stacey, R. E.; Dodd, C.; Cámara, M.; Williams, P.; Winzer, K., The galactophilic lectin, LecA, contributes to biofilm development in Pseudomonas aeruginosa. Environ. Microbiol. 2006, 8, 1095-1104. (36) Ma, R.; Yang, H.; Li, Z.; Liu, G.; Sun, X.; Liu, X.; An, Y.; Shi, L., Phenylboronic AcidBased Complex Micelles with Enhanced Glucose-Responsiveness at Physiological pH by Complexation with Glycopolymer. Biomacromolecules 2012, 13, 3409-3417. (37) Kataoka, K.; Miyazaki, H.; Bunya, M.; Okano, T.; Sakurai, Y., Totally Synthetic Polymer Gels Responding to External Glucose Concentration: Their Preparation and Application to On−Off Regulation of Insulin Release. J. Am. Chem. Soc. 1998, 120, 12694-12695. (38) Qin, Y.; Cheng, G.; Sundararaman, A.; Jäkle, F., Well-Defined Boron-Containing Polymeric Lewis Acids. J. Am. Chem. Soc. 2002, 124, 12672-12673. (39) Bull, S. D.; Davidson, M. G.; van den Elsen, J. M. H.; Fossey, J. S.; Jenkins, A. T. A.; Jiang, Y.-B.; Kubo, Y.; Marken, F.; Sakurai, K.; Zhao, J.; James, T. D., Exploiting the Reversible Covalent Bonding of Boronic Acids: Recognition, Sensing, and Assembly. Acc. Chem. Res. 2012, 46, 312-326. (40) Guo, Q.; Wu, Z.; Zhang, X.; Sun, L.; Li, C., Phenylboronate-diol crosslinked glycopolymeric nanocarriers for insulin delivery at physiological pH. Soft Matter 2014, 10, 911920. (41) Wiskur, S. L.; Lavigne, J. J.; Ait-Haddou, H.; Lynch, V.; Chiu, Y. H.; Canary, J. W.; Anslyn, E. V., pKa Values and Geometries of Secondary and Tertiary Amines Complexed to Boronic AcidsImplications for Sensor Design. Org. Lett. 2001, 3, 1311-1314.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 34

(42) Kotsuchibashi, Y.; Agustin, R. V. C.; Lu, J.-Y.; Hall, D. G.; Narain, R., Temperature, pH, and Glucose Responsive Gels via Simple Mixing of Boroxole- and Glyco-Based Polymers. ACS Macro Letters 2013, 2, 260-264. (43) Xu, X. D.; Cheng, H.; Chen, W. H.; Cheng, S. X.; Zhuo, R. X.; Zhang, X. Z., In situ recognition of cell-surface glycans and targeted imaging of cancer cells. Scientific reports 2013, 3, 2679. (44) Liu, H.; Li, Y.; Sun, K.; Fan, J.; Zhang, P.; Meng, J.; Wang, S.; Jiang, L., DualResponsive Surfaces Modified with Phenylboronic Acid-Containing Polymer Brush To Reversibly Capture and Release Cancer Cells. J. Am. Chem. Soc. 2013, 135, 7603-7609. (45) Lee, Y. C.; Lee, R. T., Carbohydrate-Protein Interactions: Basis of Glycobiology. Acc. Chem. Res. 1995, 28, 321-327. (46) Song, G.; Zhang, L.; He, C.; Fang, D.-C.; Whitten, P. G.; Wang, H., Facile Fabrication of Tough Hydrogels Physically Cross-Linked by Strong Cooperative Hydrogen Bonding. Macromolecules 2013, 46, 7423-7435. (47) Wang, Y.; Kotsuchibashi, Y.; Uto, K.; Ebara, M.; Aoyagi, T.; Liu, Y.; Narain, R., pH and glucose responsive nanofibers for the reversible capture and release of lectins. Biomater. Sci. 2015, 3, 152-162. (48) Hall, D. G., Structure, Properties, and Preparation of Boronic Acid Derivatives. Overview of Their Reactions and Applications. In Boronic Acids, Wiley-VCH Verlag GmbH & Co. KGaA: 2006; pp 1-99.


30

Page 31 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(49) Ruggiero, A.; Villa, C. H.; Bander, E.; Rey, D. A.; Bergkvist, M.; Batt, C. A.; ManovaTodorova, K.; Deen, W. M.; Scheinberg, D. A.; McDevitt, M. R., Paradoxical glomerular filtration of carbon nanotubes. Proc. Natl. Acad. Sci. 2010, 107, 12369-12374. (50) Nakahata, M.; Mori, S.; Takashima, Y.; Hashidzume, A.; Yamaguchi, H.; Harada, A., pHand Sugar-Responsive Gel Assemblies Based on Boronate–Catechol Interactions. ACS Macro Letters 2014, 3, 337-340. (51) Piest, M.; Zhang, X.; Trinidad, J.; Engbersen, J. F. J., pH-responsive, dynamically restructuring hydrogels formed by reversible crosslinking of PVA with phenylboronic acid functionalised PPO–PEO–PPO spacers (Jeffamines®). Soft Matter 2011, 7, 11111-11118. (52) Patel, S. K.; Malone, S.; Cohen, C.; Gillmor, J. R.; Colby, R. H., Elastic modulus and equilibrium swelling of poly(dimethylsiloxane) networks. Macromolecules 1992, 25, 5241-5251. (53) Appel, E. A.; Biedermann, F.; Rauwald, U.; Jones, S. T.; Zayed, J. M.; Scherman, O. A., Supramolecular Cross-Linked Networks via Host−Guest Complexation with Cucurbit[8]uril. J. Am. Chem. Soc. 2010, 132, 14251-14260. (54) McKinnon, D. D.; Domaille, D. W.; Cha, J. N.; Anseth, K. S., Biophysically Defined and Cytocompatible Covalently Adaptable Networks as Viscoelastic 3D Cell Culture Systems. Adv. Mater. 2014, 26, 865-872.

Table of Contents


31


Page 32 of 34


32

Page 33 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Graphical Abstract

Self-healing and injectable shear thinning hydrogels based on dynamic oxaborole-diol covalent crosslinking Yinan Wang,1,2 Lin Li, 1 Yohei Kotsuchibashi,3 Sergey Vshyvenko,4 Yang Liu,2 Dennis Hall,4 Hongbo Zeng,1 Ravin Narain1* 1

Department of Chemical and Materials Engineering, University of Alberta, 116 St and 85 Ave, Edmonton, AB T6G 2G6, Canada 2 Department of Civil and Environmental Engineering, University of Alberta, 116 St and 85 Ave, Edmonton, AB T6G 2G6, Canada 3 International Center for Young Scientists (ICYS) and International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan 4 Department of Chemistry, 4-010 Centennial Centre for Interdisciplinary Science, University of Alberta, 116 St and 85 Ave, Edmonton, AB T6G 2G6, Canada




Page 34 of 34

Self-Healing and Injectable Shear Thinning Hydrogels Based on

Recommend Documents