Ultratough, Self-Healing, and Tissue-Adhesive Hydrogel for Wound

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Cite This: ACS Appl. Mater. Interfaces 2018, 10, 33523−33531

Ultratough, Self-Healing, and Tissue-Adhesive Hydrogel for Wound Dressing Tao Chen,†,§ Yujie Chen,*,†,§ Hafeez Ur Rehman,† Zhen Chen,† Zhi Yang,‡ Man Wang,† Hua Li,† and Hezhou Liu*,† †

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State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China ‡ Department of Oral & Cranio-Maxillofacial Science, Shanghai Ninth People’s Hospital, School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai Jiao Tong University, Shanghai 200240, P. R. China S Supporting Information *

ABSTRACT: A hydrogel for potential applications in wound dressing should possess several peculiar properties, such as efficient self-healing ability and mechanical toughness, so as to repair muscle and skin damage. Additionally, excellent cell affinity and tissue adhesiveness are also necessary for the hydrogel to integrate with the wound tissue in practical applications. Herein, an ultratough and self-healing hydrogel with superior cell affinity and tissue adhesiveness is prepared. The self-healing ability of the hydrogel is obtained through hydrogen bonds and dynamic Schiff cross-linking between dopamine-grafted oxidized sodium alginate (OSA-DA) and polyacrylamide (PAM) chains. The covalent cross-linking is responsible for its stable mechanical structure. The combination of physical and chemical cross-linking contributes to a novel hydrogel with efficient selfhealing ability (80% mechanical recovery in 6 h), high tensile strength (0.109 MPa), and ultrastretchability (2550%), which are highly desirable properties and are superior to previously reported tough and self-healing hydrogels for wound dressing applications. More remarkably, due to plenty of catechol groups on the OSA-DA chains, the hydrogel has unique cell affinity and tissue adhesiveness. Moreover, we demonstrate the practical utility of our fabricated hydrogel via both in vivo and in vitro experiments. KEYWORDS: self-healing hydrogel, mechanical toughness, tissue adhesiveness, mussel-inspired, wound dressing

1. INTRODUCTION Hydrogels are reported to be the best candidate compared with other materials for wound dressing, due to their unique properties, such as adequate flexibility, elasticity, biocompatibility, high water content, and great sensitivity to physiological environments.1−4 In recent years, considerable efforts have been devoted to developing hydrogels that facilitate wound healing. In particular, hydrogels with intrinsic self-healing ability have attracted much attention because they can self-heal after damage like a biological tissue does. Shi et al.5 designed a self-healing hydrogel based on bisphosphonate-modified hyaluronic acid through dynamic metal−ligand coordination bonds. The hydrogel showed an in vitro antibacterial property and could promote wound healing and tissue regeneration in a rat skin defect model. Xu et al.6 prepared a supramolecular self© 2018 American Chemical Society

healing hydrogel through cross-linkable supramonomers. With the benefit of the dynamic nature of the supramonomers, the hydrogel was easy to remove, which would alleviate pain and shorten wound-healing time for patients. However, these reported wound dressing hydrogels suffered from a poor mechanical property and could not withstand external damage. More importantly, they failed to be fixed with the wound tissues for their lack of tissue adhesiveness. These hydrogels behaved well in a rat skin defect model, while in some practical clinical situations where wound areas are large and need to be contracted, they do not work anymore. Received: June 16, 2018 Accepted: September 11, 2018 Published: September 11, 2018 33523

DOI: 10.1021/acsami.8b10064 ACS Appl. Mater. Interfaces 2018, 10, 33523−33531

Research Article

ACS Applied Materials & Interfaces Scheme 1. Synthesis Route of OSA-DA

hydrogel. In this hydrogel, dynamic covalent cross-linking was formed through Schiff base reaction between the aldehyde groups of the OSA-DA chains and the amino groups of the PAM chains. Reversible hydrogen bonds were formed between catechol groups in the OSA-DA chains. Hence, the doublenetwork hydrogel was physically and chemically cross-linked. As a result, the hydrogel could withstand large deformations as well as keep its elasticity. The reversible interactions, including hydrogen bonds and dynamic covalent cross-linking, can make the hydrogel self-heal efficiently without any external stimulus. More importantly, due to lots of catechol groups on the oxidized sodium alginate chains, the hydrogel had unique cell affinity and tissue adhesiveness, benefiting its further application in wound dressing.

Consequently, both an excellent mechanical property and tissue adhesiveness must be considered when designing wound dressing hydrogels. Usually, hydrogels with a single component have a poor mechanical property; therefore, recent trends have selected hybrid or composite hydrogels to meet the typical requirements of wound dressing hydrogels.1 Recently, because of nontoxicity, biodegradability, biocompatibility, stability and gelling ability, sodium alginate has been widely employed for preparing tough and self-healing hydrogels.7−10 These hydrogels often possess an excellent adhesive property and biological affinity, but their adhesive strength decreases dramatically in physiological conditions, which greatly limits their clinical applications. Balakrishnan et al.11 endowed sodium alginate with aldehyde groups through an oxidation reaction and then made a hydrogel by cross-linking this with gelatin. Though the adhesive strength has been improved, the result is still not satisfied especially in physiological conditions. Currently, mussel materials have given researchers great inspiration for the development of hydrogels with exceptional tissue adhesiveness.12−16 Dopamine is a kind of derivative from tyrosine in mussel proteins. It has been used to improve the adhesive property of hydrogel, especially in wetting conditions.17,18 Most research found that catechols in dopamine are easy to oxidize and transform into semiquinones or quinones which would further react with amine or thiol containing substrates via aryl−aryl coupling or possibly via Michael-type addition reactions.19−22 Han et al.23 developed a polydopamine−polyacrylamide single network hydrogel with remarkable tissue adhesiveness. However, this single network design also suffered from poor mechanical properties. Low tensile strength (∼0.027 MPa) limited its use for damageresistant wound dressing material. Generally, an ideal hydrogel for wound dressing should have several typical properties, such as efficient self-healing ability, high toughness, outstanding cell affinity, and tissue adhesiveness.24,25 However, it is quite difficult to integrate so many functions into one hydrogel. Herein, we prepared a mechanically tough self-healing hydrogel with exceptional adhesive strength and cell affinity, showing great potential for wound dressing applications. The hydrogel was synthesized by physically and chemically crosslinking through a two-step process. First, dopamine (DA) was grafted to the oxidized sodium alginate (OSA) to form dopamine-grafted oxidized sodium alginate (OSA-DA). Second, acrylamide (AM) monomers were conjugated with OSA-DA via Schiff base reaction, then chemically polymerized with the presence of ammonium persulfate (APS) and N,N′methylenebis-acrylamide (BIS), to form the OSA-DA-PAM

2. EXPERIMENTAL SECTION 2.1. Materials. Sodium alginate (SA, 200−500 mPa s), dopamine hydrochloride (DA), sodium periodate, acrylamide (AM), ammonium persulfate (APS), N,N′-methylenebis-acrylamide (BIS), and N,N,N′,N′-tetramethylethylenediamine (TEMED) were purchased from Sinopharm Chemical Reagent. 1-(3-(Dimethylamino)propyl)-3ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were purchased from Shanghai Macklin Biochemical Co., Ltd. Epidermal growth factor (EGF) was purchased from Absin Bioscience Inc. (Shanghai, China). 2.2. Oxidation of Sodium Alginate. A 20 g portion of sodium alginate was dispersed in 100 mL of ethanol, and then 100 mL of distilled water containing 20 g sodium periodate was added in the above solution. The mixture was magnetically stirred in the dark environment at 25 °C for 6 h. Then, 10 mL of ethylene glycol was added to stop the reaction. After this stirred for another 2 h, 1.0 L of ethanol was poured into the reaction mixture. The precipitate was collected by suction filtration. Then, the crude OSA was dialyzed with deionized water for 3 days followed by freeze-drying. 2.3. Grafting of Dopamine to Oxidized Sodium Alginate. The grafting of dopamine was carried out according to a reported method.26−28 Oxidized sodium alginate (2 g) was dissolved in 200 mL of PBS buffer (50 mmol, pH 5.7). EDC (1.936 g) and NHS (1.164 g) were added in the above solution for 30 min stirring, followed by the addition of 3.84 g of dopamine. The whole mixture was stirred for 12 h under N2 protection to suppress uncontrolled oxidation and subsequent self-polymerization. A 1.0 L portion of ethanol was poured into the reaction mixture. The precipitate was collected by suction filtration. Then, the product was dialyzed with deionized water for 3 days followed by freeze-drying. The synthesis route of OSA-DA is presented in Scheme 1. 2.4. Preparation of Hydrogels. OSA-DA and AM were added to 2 mL of deionized water. After 20 min of stirring, APS, BIS, and TEMED were added. The mixture was degassed with N2 for 30 min and reacted at 60 °C for 4 h to obtain the hydrogel. Hydrogels with different OSA-DA contents were also fabricated (Table S1, Supporting Information). 33524


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ACS Applied Materials & Interfaces Scheme 2. Synthetic Process and Schematic Structure of OSA-DA-PAM Hydrogel

Figure 1. Scanning electron microscopy (SEM) images of (a) the PAM hydrogel and (b) the OSA-DA-PAM hydrogel. 2.5. Characterization. Nuclear magnetic resonance (NMR) spectra were obtained from AVANCE III 400 MHz. FTIR spectra were obtained from a Nicolet 6700 FTIR instrument. Ultraviolet− visible spectroscopy was adopted to reveal catechol units on OSA-DA by UV/EV300 spectrophotometer. The morphology of hydrogels was characterized by a scanning electron microscope (NOVA Nano SEM 230). Before SEM characterization, hydrogels were freeze-dried. 2.6. Mechanical Test. Tensile tests were carried out on a universal testing machine (WDW-05, TIME Group Inc., China). 2.7. Dynamic Rheological Test. Dynamic rheological tests were carried out on a strain-controlled rheometer (MCR302, Anton Paar, Austria). 2.8. Tensile/Adhere Test. To measure the adhesive strength of the hydrogel, metal, porcine skin, glass, and plastic were applied for the tensile/adhere test on the universal testing machine. 2.9. Epidermal Growth Factor (EGF) Release Experiment. The release behavior of EGF from the hydrogel was evaluated by the half-change method using ELISA kits. EGF-loaded hydrogel was

prepared by immersing hydrogel (30 mg) in EGF containing PBS buffer (30 μg/mL). The hydrogel was soaked in PBS buffer solution (pH 7.4) at 37 °C. At five intervals (1, 3, 5, 10, and 15 days), 50% of the buffer was collected and replaced by fresh PBS buffer. 2.10. Cytotoxicity Evaluation. NIH-3T3 fibroblasts were used to measure the cytotoxicity of the hydrogel by CCK-8. Hydrogels purified by deionized water were placed in Dulbecco’s modified Eagle’s medium for 48 h in CO2 humidified atmosphere at 37 °C. The morphology of the fibroblasts on the hydrogel was observed using a scanning electron microscope. 2.11. In Vivo Experiments. Five male Sprague−Dawley rats were used to investigate the effect of an OSA-DA-PAM hydrogel on wound healing. After being injected with chloral hydrate (10 wt %), the back areas of five rats were depilated, and three circular wounds were created by a special scalpel (5 mm in diameter). The wounds were treated with EGF loaded OSA-DA-PAM hydrogel and OSA-DA-PAM hydrogel only. An untreated one was chosen as a blank group. The optical images of the wound site were recorded by a digital camera at 33525


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ACS Applied Materials & Interfaces

Figure 2. Optical images of OSA-DA-PAM-2 hydrogel sample without stretch (a1) and stretched under a strain of 2500% (a2). (b) Tensile stress− strain curves of hydrogels with different OSA-DA contents. (c) Loading−unloading tensile test of the OSA-DA-PAM-1 hydrogel under 850% strain.

Figure 3. (a) Cut−heal test. (a1, a2) The OSA-DA-PAM-3 hydrogel was cut in half. (a3) The two halves were contacted and self-healed for 1 h. (a4) The self-healed hydrogel was stretched. (b) Tensile stress−strain curves of the original and self-healed OSA-DA-PAM-3 hydrogels. (c) Dynamic rheological behavior of the OSA-DA-PAM-3 hydrogel. predetermined intervals (0, 5, and 15 days) after surgery. Then, the wound areas were accurately measured using professional software (ImageJ). All the rats were sacrificed on day 15, and then the newly regenerated tissue and surrounding tissue were harvested immediately. The method using hematoxylin-eosin and Masson’s trichrome staining was adopted to observe histological changes.

microfibrils was mostly attributed to the intermolecular interactions between OSA-DA and PAM chains. To further examine the chemical structure of the hydrogel, 1H NMR spectra, FTIR spectra, and UV−vis spectrum were presented in Figures S1−S3 (Supporting Information). 3.2. Mechanical Property of OSA-DA-PAM Hydrogel. Figure 2a presents the optical images of the OSA-DA-PAM-2 hydrogel sample with an initial length of 10 mm and a stretched length of 254 mm. According to the typical stress− strain curves (Figure 2b), OSA-DA chains played a vital role in the high tensile strength and superstretchability of OSA-DAPAM hydrogels. The OSA-DA-PAM hydrogel consisted of two networks. One was a tightly cross-linked PAM network, and the other was a loosely cross-linked OSA-DA network. The synergistic effect of these two networks contributed to the high tensile strength (0.109 MPa) and fracture strain (1500%) for the OSA-DA-PAM-1 hydrogel. When the OSA-DA content was increased to 40 mg, the proportion of the soft and tough OSA-DA network was enhanced and the entanglement between OSA-DA and PAM chains was improved by lots of

3. RESULTS AND DISCUSSION 3.1. Synthesis of OSA-DA-PAM Hydrogel. The synthetic procedure to prepare OSA-DA-PAM hydrogel is presented in Scheme 2. In the first step, AM was attached to OSA-DA chains through the Schiff base reaction. In the second step, the attached AM along with free AM monomers were polymerized with the presence of initiator (APS). SEM images of cross-sectional PAM and OSA-DA-PAM hydrogel samples were shown in Figure 1. The three-dimensional network structure that existed in the OSA-DA-PAM hydrogel was revealed. Interwoven microfibrils were clearly observed in the OSA-DA-PAM hydrogel (Figure 1b), while they were not found in the PAM hydrogel. The existence of interwoven 33526


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Figure 4. OSA-DA-PAM-3 hydrogel tightly adhered to various substrates: (a) human skin, (b) metal, (c) glass, and (d) plastic. (e) The adhesive strength of the hydrogel to different substrates. (f) The adhesive strength of the hydrogel to different substrates over three adhere/peel-off cycles.

immediately. However, the following cycles showed small hysteresis loops, reflecting finite energy dissipation. 3.3. Self-Healing Ability of OSA-DA-PAM Hydrogel. Figure 3 studied the self-healing behavior of the OSA-DAPAM hydrogel. As presented in Figure 3a, the hydrogel was cut into two halves and then brought into physical contact for 1 h. Consequently, the cut trace could not be seen even after the self-healed hydrogel was stretched by the author. When two halves were brought into contact, dynamic Schiff bonds between OSA-DA and PAM functional groups re-formed, leading to the recovery of hydrogel. Furthermore, hydrogen bonds between catechol groups in the OSA-DA chains can also contribute a lot to this healing process. In order to quantitatively evaluate the self-healing ability of the OSADA-PAM hydrogel, we measured the tensile strength of a selfhealed sample after being cut off. Figure 3b showed the typical tensile stress−strain curves of the original and self-healed OSADA-PAM-3 hydrogels. After 6 h, the tensile strength and fracture strain of the self-healed OSA-DA-PAM-3 hydrogel can be recovered significantly. The self-healing efficiency, defined as the tensile strength ratio of the self-healed sample to the original sample, was 80% for the OSA-DA-PAM-3 hydrogel. A dynamic rheological test was also carried out to confirm the self-healing ability of OSA-DA-PAM hydrogel. First, a 1000% strain was subjected to damage the hydrogel. Second, the high strain was taken off and replaced by a low strain (γ = 0.01%; frequency = 1 Hz) so as to let the hydrogel network restore. As demonstrated in Figure 3c, the storage modulus G′ of the OSA-DA-PAM-3 hydrogel decreased dramatically under the high strain, while it nearly came back to its original value in 15 min after stopping the high strain. This quickly recoverable behavior after disruption also occurred in the cyclic rheological test of switching from low strain to high strain (details are presented in Supporting Information). These results thereby

reversible covalent bonds and hydrogen bonds. As a result, the fracture strain of the OSA-DA-PAM-2 hydrogel was further increased to a maximum of 2550%. However, the tensile strength of the hydrogel decreased unexpectedly. This phenomena could be ascribed to the DA strong inhibiting effect on AM polymerization.23 With the increase in OSA-DA content, the polymerization of AM was gradually inhibited, resulting in a low degree of polymerization and a weak PAM network. When further increasing OSA-DA content to 50 mg, due to retardation of polymerization, the synergistic effect of the two networks was dramatically weakened, leading to a drop both in tensile strength and fracture strain. In addition, when the OSA-DA content reached 60 mg, the hydrogel cannot form because of the strong polymerization retardation. In addition, toughness of the hydrogel often contributes a lot to energy dissipation,29 which is vital to practical application in wound dressing. Hence, cyclic loading−unloading test at strain of 850% was preformed to evaluate energy dissipation of the OSA-DA-PAM hydrogel. As demonstrated in Figure 2c, an obvious hysteresis loop was observed in the first testing cycle, indicating that the hydrogel could dissipate energy effectively. Cross-linked by reversible covalent bonds and hydrogen bonds, OSA-DA-PAM can generate energy dissipation through chain dissociations when the hydrogel suffers tensile deformation, leading to a big hysteresis loop. When the hydrogel is being stretched, the OSA-DA and PAM chains transfer from an entangled state to a disentangled state and the breakup of the hydrogen bonds and dynamic Schiff bonds between OSA-DA and PAM chains takes place at the same time. Once the loading is removed, the disentangled chains begin to curl again with the re-forming of hydrogen bonds and dynamic Schiff bonds. After the first testing cycle, the following cycles were subjected to the same hydrogel sample 33527


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of EGF as they could react with amine or thiol containing biomolecules via aryl−aryl coupling or possibly via Michaeltype addition reactions and physically immobilize growth factors through a noncovalent interaction.17,37,38 Yoshihiro et al.39 found that DA modified titanium and stainless steel surfaces effectively immobilized EGF and enhanced cell growth efficiently. In summary, catechol groups in the hydrogel contribute to growth factor immobilization, which facilitates the practical application of the hydrogel in wound dressing. 3.6. In Vitro Cell Culture and In Vivo Rat Experiment. Biocompatibility is vital to the hydrogel for its application in wound dressing.40 Therefore, we employed NIH-3T3 fibroblasts to evaluate cell cytotoxicity of the hydrogels by CCK-8. As indicated with black arrows in Figure 6a, the fibroblasts attached to the OSA-DA-PAM hydrogel and spread well. Remarkably, compared with pure PAM hydrogel, OSA-DAPAM hydrogel promoted the propagation of fibroblasts (Figure 6b), showing higher affinity to fibroblasts. This result can be attributed to catechol groups in the hydrogel which can form a strong contact with fibroblasts through interactions with thiols or imidazoles in the cell membrane.41 The in vivo rat experiment showed that the OSA-DA-PAM hydrogel could promote tissue regeneration and accelerate the process of wound healing. As presented in Figure 6c, the optical images of the wound at predetermined intervals (0, 5, and 15 days) were recorded. The remaining wound ratio was defined as the ratio of the wound area after treatment to the original wound area. From day 0 to day 5, the remaining wound ratios of hydrogel treated groups decreased from 100% to 83.8% and 81.2%, respectively, while the blank group showed a little decrease. Although the wound areas of the three groups were gradually being closed over 15 days, the remaining wound ratios of the hydrogel treated groups were still lower than that of the blank group (Figure 6d). As shown in Figure 6e, obvious cell interstitial edema and inordinate fibroblast in the blank group were observed, while in hydrogel treated groups there were a lot of mature and compact collagen fibers. On the basis of the above results, hydrogel treated groups showed a faster healing process than the blank group, especially when treated by EGF containing hydrogel. The good performance of the OSA-DA-PAM hydrogel in promoting tissue regeneration and accelerating the woundhealing process can be attributed to three reasons. First, due to the exceptional tissue adhesiveness of the OSA-DA-PAM hydrogel, the wound site can be protected from microorganisms, infections, or contaminations and maintained in a wet environment which is vital to skin healing and renewing without formation of eschars or inflammation.3 Second, the good cell affinity of the hydrogel is also helpful for cell adhesion and migration. Finally, the hydrogel can stably release EGF, which can also enhance the migration and recombination of the endothelial cells and promote their proliferation, resulting in faster tissue regeneration.42 These properties make the hydrogel a promising material in wound dressing.

confirm the excellent self-healing ability of OSA-DA-PAM, and it can be attributed to catechol-mediated hydrogen bonds30 and dynamic covalent cross-linking through Schiff base reaction. 3.4. Adhesive Property of OSA-DA-PAM Hydrogel. The pure PAM hydrogel showed little adhesive property, while the OSA-DA-PAM hydrogel can adhere to various organic and inorganic substrates. The catechol groups of OSA-DA chains endowed the OSA-DA-PAM hydrogel with an exceptional adhesive property. As shown in Figure 4a, the OSA-DA-PAM hydrogel can help a water-filled tube stick to the author’s skin without any skin tissue irritation or inflammatory response, benefiting its further application in wound dressing. In addition, the OSA-DA-PAM hydrogel also showed a unique adhesive property to other various substrates, which was similar to the adhesive behavior of mussels in the sea.12,31−33 As shown in Figure 4b, a metal ring (90 g) was glued under a metal clamp firmly by the OSA-DA-PAM hydrogel. Figure 4c,d showed strong adhesive ability of OSA-DA-PAM hydrogel to glass and plastic. Glass bottles or plastic bottles full of water can be cohered firmly through the OSA-DA-PAM hydrogel. The adhesive strength of the hydrogel to the above substrates was measured using a universal testing machine. The porcine skin was used to replace human skin to complete the test. As demonstrated in Figure 4e, the adhesive strength was 8.7 kPa for metal, 6.5 kPa for porcine skin, 5.9 kPa for glass, and 3.4 kPa for plastic, which was strongly related to the substrates. The hydrogel showed the highest adhesive strength to metal, possibly resulting from the interactions between lots of active groups on the metal surface and the free catechol groups in the hydrogel. Furthermore, the OSA-DA-PAM hydrogel showed reversible adhesive behavior. As demonstrated in Figure 4f, the adhesive strength for different substrates was kept at the same level after three adhere/peel-off cycles. The free catechol groups dispersed in OSA-DA-PAM hydrogel could react with amine or thiol containing substrates via aryl−aryl coupling or possibly via Michael-type addition reactions,34 which was responsible for its exceptional adhesive property. In addition, a lot of aldehyde groups in OSA-DA chains can also contribute to the exceptional adhesiveness through Schiff base reaction with an amino group. 3.5. EGF Releasing Behavior from OSA-DA-PAM Hydrogel. Due to its ability to promote tissue regeneration and accelerating wound healing,35,36 EGF was loaded in the OSA-DA-PAM hydrogel for further application in wound dressing. As shown in Figure 5, EGF was released continuously during the whole experiment. This result indicated that EGF was stably immobilized in the hydrogel. Free catechol groups in the hydrogel were responsible for the stable immobilization

4. CONCLUSION In conclusion, we have developed a novel double-network hydrogel based on dopamine-grafted oxidized sodium alginate (OSA-DA) and polyacrylamide (PAM). The combination of physical and chemical cross-linking was applied to solve the urgent problem that wound dressing hydrogel as reported cannot provide the wound site with firm mechanical protection. Moreover, efficient self-healing ability and excep-

Figure 5. Releasing behavior of EGF from the hydrogel. 33528


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Figure 6. (a) SEM image of fibroblasts adhered to the OSA-DA-PAM hydrogel. (b) Optical density of fibroblasts on the hydrogels. (c) Optical images of wound sites were taken on days 0, 5, and 15 after surgery. (d) Remaining wound ratios for each group. (e) Histological evaluation of wounds after 15 days.

tional tissue adhesiveness made this novel hydrogel extremely suitable for repairing wound tissue. Last but not least, an in vivo rat experiment showed that the OSA-DA-PAM hydrogel could promote tissue regeneration and accelerate the process of wound healing. These results suggest the OSA-DA-PAM hydrogel is a very suitable and promising biomaterial for wound dressing.

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Additional characterization information including composition information; NMR, FTIR, and UV−vis spectra; swelling and rheological information; and GC (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

ASSOCIATED CONTENT

Yujie Chen: 0000-0003-2513-7559 Hua Li: 0000-0003-2852-4722

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b10064.

Author Contributions §

T.C. and Y.C. contributed equally to this work.

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ACS Applied Materials & Interfaces Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by funding from the Natural Science Foundation of China (NSFC) (Grants U1733130 and 11704244), Shanghai Sailing Plan Project (Grant 16YF1406100), Shanghai Natural Science Funding (Grant 17ZR1441000), Medical-Engineering Cross Research Funding of SJTU (YG2017MS01), Basic Research Field of Shanghai Science and Technology Innovation Program (Grant 16JC1401500), and Shanghai Science and Technology Innovation Action Plan (Grant 18511109000).

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Ultratough, Self-Healing, and Tissue-Adhesive Hydrogel for Wound

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