[
    {
        "id": 1,
        "chunk": "# ADVANCED MATERIALS  \n\nSupporting Information  \n\nfor Adv. Mater., DOI: 10.1002/adma.202108889  \n\nA Universal Strategy for Growing a Tenacious Hydrogel Coating from a Sticky Initiation Layer  \n\nRongnian Xu, Yunlei Zhang, Shuanhong Ma,\\* Zhengfeng Ma, Bo Yu, Meirong Cai, and Feng Zhou\\*",
        "category": " References"
    },
    {
        "id": 2,
        "chunk": "# Supporting Information",
        "category": " References"
    },
    {
        "id": 3,
        "chunk": "# A Universal Strategy for Growing a Tenacious Hydrogel Coating from a Sticky Initiation Layer (SIL)  \n\nRongnian $X u^{\\#}$ , Yunlei Zhang#, Shuanhong Ma\\*, Zhengfeng Ma, Bo Yu, Meirong Cai, and Feng Zhou\\*  \n\nDr. R. Xu, Y. Zhang, Dr. S. Ma, Z. Ma, Prof. B. Yu, Prof. M. Cai, Prof. F. Zhou   \nState Key Laboratory of Solid Lubrication   \nLanzhou Institute of Chemical Physics   \nChinese Academy of Sciences   \nLanzhou 730000, China   \nE-mail: mashuanhong@licp.cas.cn; zhouf@licp.cas.cn   \nDr. R. Xu, Y. Zhang   \nCollege of Materials Science and Opto-Electronic Technology, University of Chinese   \nAcademy of Sciences,   \nBeijing 100049, China   \nDr. R. Xu   \nCollege of Chemistry and Chemical Engineering, Northwest Normal University,   \nLanzhou 730070, China   \nDr. S. Ma, Dr. Z. Ma   \nShandong Laboratory of Yantai Advanced Materials and Green Manufacture   \nYantai, 264006, China   \nDr. S. Ma, Dr. Z. Ma   \nYantai Zhongke Research Institute of Advanced Materials and Green Chemical Engineering   \nYantai, 264006, China",
        "category": " Abstract"
    },
    {
        "id": 4,
        "chunk": "#Dr. R. Xu and Y. Zhang contribute equally to this work. Keywords: surface modification, polymerization, hydrogel coatings, sticky initiation layer",
        "category": " Abstract"
    },
    {
        "id": 5,
        "chunk": "# Experimental Section  \n\nMaterials: Dopamine hydrochloride (DOPA, $98\\%$ , J&K Chemical Ltd.), trimethylaminomethane (Tris, $299.9\\%$ (titration), crystalline, ABCONE), citric acid monohydrate (AR, Chengdu Kelong Chemical Reagent Co. Ltd.), sodium hydroxide (NaOH, $296.0\\%$ , Tianjin li an Long Bohua Pharmaceutical Chemistry Reagent Co. Ltd.), Acrylamide (AM, $99\\%$ , J&K Chemicall Ltd.), Acrylic acid (AA, $599\\%$ , TCI Co. Ltd.), N, $\\mathbf{N^{\\prime}}$ - Methylenebis (acrylamide) (MBAA, $99\\%$ , Sigma–Aldrich), ammonium persulfate (APS, $298\\%$ , Chengdu Kelong Chemical Reagent Co. Ltd.), iron (III) chloride hexadydrate $\\mathrm{(FeCl_{3}.6H_{2}O}$ , AR, Tianjin Kemio Chemical Reagent Co. Ltd.), poly(vinyl alcohol) (PVA, $99.9\\%$ , Shanghai City Sinopharm Chemical Reagent Co. Ltd.), poly(ethylene glycol) methyl ether methacrylate (OEGMA, mean molecular weight: 475, 100 ppm MeHQ, 200 ppm BHT, MACKLIN), 2-hydroxyethyl methacrylate (HEMA, $99\\%$ , J&K Chemical Ltd), sodium alginate (SA, Xilong Chemical Co. Ltd.), calcium chloride $(\\mathbf{CaCl}_{2},\\mathbf{\\mu{\\geq}}96\\%$ , Tianjin Fengyue Chemical Co. Ltd.), rhodamine 6G ( $98.5\\%$ , J&K Chemical Ltd), and rhodamine B $(98.5\\%$ , Energy Chemical Ltd).  \n\nCharacterizations: An Olympus optical microscope was used to obtain cross-sectional images of the sample and the thickness of the hydrogel coating. The static contact angles were measured by a DSA-100 optical contact angle meter (Krüss Company, Germany) at ambient temperature $(25~^{\\circ}\\mathrm{C})$ with a droplet of ${5\\upmu\\mathrm{L}}$ of deionized water in air. The final contact angle value was averaged by measuring three different positions on the sample. The cross-sectional morphology was characterized by SEM (PhenomPro X, Netherlands). The $90^{\\circ}$ peeling test was performed on an electrical universal material testing machine with a $500\\mathrm{N}$ load cell (EZTest, SHIMADZU) under a tensile speed of $10\\ \\mathrm{mm/min}$ . The tensile measurement was also performed on an electrical universal material testing machine with a $500\\mathrm{N}$ load cell (EZ-Test, SHIMADZU) under a tensile speed of $100\\mathrm{mm/min}$ . The elastic modulus was calculated from the slope during $5\\%$ strain ratio of the stress-strain curve. The chemical composition of the samples was characterized by a PerkinElmer transform infrared spectrometer (PerkinElmer, USA) with attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR).  \n\nPDA deposition on versatile substrates: First, the versatile substrates were washed completely with alcohol and deionized water under ultrasound followed by drying under ${\\bf N}_{2}$ flow and activated with oxygen plasma for $2~\\mathrm{min}$ ; then, they were immersed in an aqueous solution of dopamine ( $2~\\mathrm{mg/mL}$ , in $10~\\mathrm{mM}$ Tris buffer, $\\mathrm{pH}~8.5\\$ under stirring for a certain time; finally, the samples were rinsed with deionized water and alcohol to remove unreacted chemicals and dried with ${\\bf N}_{2}$ .  \n\nThe production of the $F e^{2+}$ catalyst: First, 5.91 g CA and $5.09\\ \\mathrm{\\g\\FeCl_{3}{\\cdot}6H_{2}O}$ were dissolved in $150~\\mathrm{mL}$ deionized water, and 1 mol/L NaOH solution was added to the above solution until the $\\mathrm{pH}$ reached 4.0; then the substrate deposited with the PDA coating was immersed into the mixed solution for $3\\mathrm{~h~}$ ; finally, the substrates were exposed to UV light ( $365\\mathrm{nm}$ , $15\\mathrm{mW/cm}^{2}$ ) for 2 min to produce $\\mathrm{Fe}^{2+}$ in situ.  \n\nPreparation of HPAA-PAM coating on versatile substrates: The substrates after UV irradiation were immersed into the PAA-PAM monomer solution ( $4.26\\ \\mathrm{g}$ AM, $\\ensuremath{1.08\\mathrm{~g}}$ AA, $_{0.02\\mathrm{~g~}}$ APS and $0.05\\mathrm{~g~}$ MBAA, 30 mL $\\mathrm{H}_{2}\\mathrm{O}$ ) to perform SCIRP for a certain time to grow a uniform hydrogel coating. Furthermore, substrates/devices with growed hydrogel coatings after removal from the monomer solution will be allowed to naturally age for $5\\ \\mathrm{min}$ at room temperature. Meanwhile, the reserved $\\mathrm{Fe}^{2+}$ catalyst and $S_{2}{\\mathrm{O}}_{8}{}^{2-}$ initiator within the network of the formed hydrogel coating initiated further radical polymerization of monomers until most of them were completely consumed. In addition, the substrates with the HPAA-PAM coating after aging were rinsed with deionized water five times to further remove unreacted monomers.  \n\nPreparation of HPNIPAM-PAA coating on Ti substrate: The substrates after UV irradiation were immersed into the monomer solution $(6.78\\ \\mathrm{g}$ NIPAM, 0.864 g AA, $0.02{\\mathrm{~g~}}$ APS and 0.05 $\\mathbf{g}$ MBAA, 40 mL $\\mathrm{H}_{2}\\mathrm{O}$ ) to perform SCIRP for $25~\\mathrm{min}$ .  Furthermore, the Ti substrate with growed PNIPAM-PAA hydrogel coating after removing from the monomer solution was allowed for natural aging of $5\\mathrm{min}$ at room temperature. Finally, the substrates with the HPAAPAM coating after aging were rinsed with deionized water five times to further remove unreacted monomers.  \n\nPreparation of HPVA-PHEMA coating on Ti substrate: First, $6.5\\ \\mathrm{g}$ HEMA, 0.01 g MBAA, 0.02 g APS and $0.1\\ \\mathrm{g}$ AA were dissolved in 50 mL $\\mathrm{H}_{2}\\mathrm{O}$ (solution A), $20\\ \\mathrm{g}$ PVA was dissolved in 100 mL $\\mathrm{H}_{2}\\mathrm{O}$ and heated to $100~^{\\mathrm{{o}}}\\mathrm{{C}}$ until complete dissolution (solution B); then, solution A was mixed with solution B at a volume ratio of 1.5:1; finally, the substrates after UV irradiation were immersed in the above mixed monomer solution to perform SCIRP for 25 min and put into the freeze-dryer to experience freezing $\\left(-40~^{\\mathrm{{o}}}\\mathrm{{C})}$ and thawing $(20~^{\\circ}\\mathrm{C})$ for 3 cycles. After encountering the cyclic freezing-thawing process, the Ti substrate with the HPVAPHEMA coating was rinsed with deionized water five times to remove unreacted monomers.  \n\nPreparation of HPOEGMA-PAA coating on Ti substrate: The substrates after UV irradiation were immersed into the POEGMA-PAA monomer solution ( $\\ensuremath{\\mathrm{\\:6.5~g}}$ OEGMA, 1.08 g AA, 0.01 g MBAA, $_{0.02\\mathrm{~g~}}$ APS, 40 mL $\\mathrm{H}_{2}\\mathrm{O}$ ) to perform SCIRP for $25\\ \\mathrm{min}$ . Furthermore, the Ti substrate with growed POEGMA-PAA hydrogel coating after removing from the monomer solution was allowed to naturally age for 5 min at room temperature. Finally, the Ti substrate with the HPOEGMA-PAA coating after aging was rinsed with deionized water five times to further remove unreacted monomers.  \n\nPreparation of HPOEGMA-PAA-PHEMA coating on Ti substrate: The substrates after UV irradiation were immersed into the POEGMA-PAA monomer solution $3.75\\ \\mathrm{g}$ OEGMA, 3.25 g HEMA, $\\boldsymbol{1.08\\mathrm{g}}$ AA, $_{\\mathrm{0.01~g}}$ MBAA, $0.02{\\mathrm{~g~}}$ APS, 20 mL $\\mathrm{H}_{2}\\mathrm{O}$ ) to perform SCIRP for $25\\mathrm{min}$ . Furthermore, the Ti substrate with growed POEGMA-PAA-PHEMA hydrogel coating after removal from the monomer solution was allowed to naturally age for $5\\ \\mathrm{min}$ at room temperature. Finally, the Ti substrates with the HPOEGMA-PAA-PHEMA coating after aging were rinsed with deionized water five times to further remove unreacted monomers.",
        "category": " Materials and methods"
    },
    {
        "id": 6,
        "chunk": "# WILEY-VCH  \n\nPreparation of HPVA-PAA-PAM coating on Ti substrate: First, $4.26\\ \\mathrm{g}$ AM, $\\ensuremath{1.08\\mathrm{~g}}$ AA, $\\mathbf{0.02\\g}$ APS and $0.05\\mathrm{~g~}$ MBAA were dissolved in 30 mL $\\mathrm{H}_{2}\\mathrm{O}$ (solution C), $20\\ \\mathrm{g}$ PVA was dissolved in $100~\\mathrm{{mL}}$ $\\mathrm{H}_{2}\\mathrm{O}$ and heated to $100^{\\circ}\\mathrm{C}$ until complete dissolution (solution B); then, solution C was mixed with solution B at a volume ratio of 1:1; finally, the substrates after UV irradiation were immersed in the above mixed monomer solution to perform SCIRP for 2 min and put into the freeze-dryer to experience freezing $\\left(-40~^{\\mathrm{{o}}}\\mathrm{{C})}$ and thawing $(20~^{\\circ}\\mathrm{C})$ for 3 cycles. After encountering the cyclic freezing-thawing process, the Ti substrate with the HPVA-PAA-PAM coating was rinsed with deionized water five times to remove unreacted monomers.  \n\nPreparation of HPHEMA-SA-Ca coating on Ti substrate: First, $6.5\\mathrm{~g~}$ HEMA, 0.01 g MBAA, $0.02{\\mathrm{~g~}}$ APS and $_{\\textrm{1g}}$ SA were dissolved in 50 mL $_\\mathrm{H_{2}O}$ and stirred until complete dissolution; then, the substrates after UV irradiation were immersed into the above monomer solution to perform SCIRP for $2~\\mathrm{min}$ ; finally, the Ti substrate with HPHEMA-SA coating was immersed into CaCl2 solution $(2\\%)$ for $2\\mathrm{h}$ .  \n\nPreparation of patterned hydrogel coating on Ti substrate: First, $5.91\\ \\mathrm{g}$ CA and $5.09\\mathrm{~g~}$ FeCl3· $6\\mathrm{H}_{2}\\mathrm{O}$ were dissolved in $150~\\mathrm{mL}$ deionized water, and 1 mol/L NaOH solution was added to the above solution until the pH reached 4.0. Then, the substrate deposited with the PDA coating was immersed into the above mixed solution for $3\\mathrm{~h~}$ . Subsequently, the treated substrate was placed under the programmable UV light source of a 3D printer for $5~\\mathrm{min}$ to reduce $\\mathrm{Fe}^{3+}$ . Next, the substrate after irradiation with UV light was immersed in monomer solution A to grow a patterned hydrogel coating for a certain time. Correspondingly, the Ti substrate with a growed patterned PAA-PAM hydrogel coating after removal from the monomer solution was allowed to naturally age for $5~\\mathrm{min}$ at room temperature. Finally, the sample after aging was rinsed with deionized water five times to further remove unreacted monomers.  \n\nPreparation of hydrogel coating on the outer surface of various medical devices: First, the medical devices were washed with alcohol and deionized water under ultrasound conditions,",
        "category": " Materials and methods"
    },
    {
        "id": 7,
        "chunk": "# WILEY-VCH  \n\nwhich were followed by drying with ${\\bf N}_{2}$ flow and activating with oxygen plasma for $2~\\mathrm{min}$ . Subsequently, the treated medical devices were immersed in an aqueous solution of dopamine ( $2~\\mathrm{mg/mL}$ , in $10~\\mathrm{mM}$ Tris buffer, $\\mathrm{pH}8.5\\rangle$ ) under stirring for $24\\mathrm{~h~}$ to decorate the PDA layer. Next, the PDA-decorated medical devices were rinsed with deionized water and alcohol to remove unreacted chemicals. Then, $5.91\\ \\mathrm{g}\\ \\mathrm{CA}$ and $5.09\\ \\mathrm{g\\FeCl_{3}}{\\cdot}6\\mathrm{H}_{2}\\mathrm{O}$ were dissolved in 150 mL deionized water, and 1 mol/L NaOH solution was added to the above solution until the pH reached 4.0. The PDA-decorated medical devices were immersed in the above mixed solution for $3\\mathrm{{h}}$ . Hereafter, they were exposed to UV light ( $365\\mathrm{nm}$ , $15\\mathrm{mW}/\\mathrm{cm}^{2}$ ) for $2\\mathrm{min}$ to produce $\\mathrm{Fe}^{2+}$ in situ and then immersed in solution A to grow hydrogel coatings for a certain time. Correspondingly, the medical devices with growed PAA-PAM hydrogel coating after removal from the monomer solution were allowed to naturally age for $5~\\mathrm{{min}}$ at room temperature. Finally, the medical devices after aging were rinsed with deionized water five times to further remove unreacted monomers.  \n\nThe demonstrative experiment of alumina ball in PVC catheter: First, the PVC catheter within alumina ball inside was connected with the tube of peristaltic pump and fixed on the desk; then, the alumina ball was swept by the 50-rpm flow rate along the “S” track of PVC catheter.  \n\nFriction force test of alumina ball in PVC catheter: First, the alumina ball was glued to one end of wire, while the other end of wire was stuck into the upper clamp of universal material testing. Meanwhile, the alumina ball was inserted into the PVC catheter with deionized water as lubricant. The force curve was obtained with the dynamic movement of the upper clamp under a constant tensile speed of $5\\mathrm{{mm}/\\mathrm{{min}}}$ .  \n\nFriction force test of steel ball in cattle esophagus: First, the steel ball was glued to one end of the wire rod, while the other end of the wire rod was stuck into the upper clamp of universal material testing. Meanwhile, the steel ball was inserted into the cattle esophagus, while the cattle esophagus was fixed in the bottom tray. The force curve of the steel ball in the cattle esophagus was obtained with the movement of the upper clamp under a constant tensile speed of $50\\mathrm{{mm}/\\mathrm{{min}}}$ .  \n\nFriction Test: The friction test was performed on a conventional ball-on-disk reciprocating tribometer (CSM, Switzerland) under $0.2\\mathrm{~N~}$ and $1\\ \\mathrm{Hz}$ for 300 s in a water bath using elastomeric poly(dimethylsiloxane) (PDMS) hemispheres with a diameter of $6~\\mathrm{mm}$ as pins. The PDMS pins were made by putting the mixture of PDMS and curing agents (mass ratio $\\scriptstyle\\mathbf{\\alpha}=10:1$ ) into a polystyrene 96-well cell culture plate mode under incubation in a $60~^{\\mathrm{{o}}}\\mathrm{{C}}$ oven for $^{4\\mathrm{~h~}}$ . Each sample was measured three times at different positions to obtain the final average value.  \n\nWet mechanical modulus test of the HPAA-PAM coating: The modulus of the HPAA-PAM coating was measured by employing a micronanoindentation on a Bioindenter UNHT3 Bio (Anton Paar). The radius of the indenter (rubby ball) was $0.5\\mathrm{mm}$ , and the normal load was $200~\\upmu\\mathrm{N}$ in the test.  \n\n$$\n\\begin{array}{r l}&{\\mathsf{F e}^{2+}{+}\\mathsf{S}_{2}\\mathsf{O}_{8}{^{2-}}\\longrightarrow\\mathsf{F e}^{3+}{+}\\mathsf{S O}_{4}{^{2-}}\\le\\mathsf{S O}_{4}{^{-}}}\\\\ &{\\mathsf{S O}_{4}{^{-}}*\\mathsf{H}_{2}\\varpi\\longrightarrow\\mathsf{H O}\\bullet\\mathsf{H S O}_{4}}\\\\ &{\\mathsf{H O}\\bullet\\mathsf{H N H}\\longrightarrow\\mathsf{R N}\\bullet\\mathsf{H}_{2}\\mathsf{O}}\\\\ &{\\mathsf{R N}\\bullet\\mathsf{M}\\longrightarrow\\mathsf{R N M}\\bullet}\\end{array}\n$$  \n\n![](images/eb05cfcba48d5330c833b979c386ceadf56600c87c656de7486602645ca19435.jpg)  \nFigure S1. Mechanism for radical generation on the PDA backbone along with covalent coupling between PDA and the hydrogel network (RNH represents PDA, M represents monomer).   \nFigure S2. Component characterization after performing SIL $@$ UV-SCIRP. FT-IR spectra curves of titanium (Ti) and polyethylene (PE) substrates with HPAA-PAM coating.  \n\n![](images/b4c4ce5680b43035156dbaca79d3d5be9da3b7c982c5e56e7ada593edde5a479.jpg)  \nFigure S3. The reusable monomer solution for SIL $@$ UV-SCIRP. (a) Thickness of the HPAAPAM coating on the Ti substrate after growing in the same monomer solution for different times (deposition time: $24\\mathrm{~h~}$ , growth time: $2\\ \\mathrm{min}.$ ). (b) Optical images of fluorescent monomer solution after growing HPAA-PAM coating for different times.  \n\n![](images/5e775b57ec1b77a55ab06b7500a1f36efa00a24dd04ca68616d613338a464d3b.jpg)  \nFigure S4. Wettability characterization. The contact angles of various bare substrates before growing hydrogel coating.",
        "category": " Materials and methods"
    },
    {
        "id": 8,
        "chunk": "# WILEY-VCH  \n\n![](images/5636f38e6160729a94634c69f4a5afb21746550da8452034fc09b634e01646b0.jpg)  \nFigure S5. Fluorescence images of the PE substrate with hydrogel coating containing rhodamine B $\\mathrm{(1~mg/mL)}$ .  \n\n![](images/e7b563de450d0f1630674077006d7f6b6fe8cf533669d82d844ec64831a11749.jpg)  \nFigure S6. The Modulus of the HPAA-PAM coating measured by micro-nanoindentation.  \n\n![](images/d89ec408f52473a2dd6592aa1a4cf474f6f264f5b4eb30ac05d678a9c1693c7e.jpg)  \nFigure S7. Morphology characterization after performing SIL $@$ UV-SCIRP. (a) Crosssectional morphology of PE substrate convalently bonded with HPAA-PAM coating and (b) corresponding EDS mapping of carbon (C, red), oxygen (O, purple) and nitrogen (N, green).  \n\n![](images/e8c7c19fcb3345285a69a60cf3ad0403613d4d7a67bde65493d8089bf7664497.jpg)  \nFigure S8. The friction curve of the HPAA-PAM coating on PE substrate for 7200 sliding cycles.  \n\n![](images/0cbefa46201ce788f4ea975884bd76957084a094d13926aab0c5b75aacd1b72a.jpg)  \nFigure S9. Mechanical properties of the fiber-enhanced composite hydrogels prepared by the SIL $@$ UV-SCIRP method. (a) The stress-strain curves of pure fiber and fiber-hydrogel composite, and (b) the corresponding elastic modulus.  \n\n![](images/18d06c2584cec7793b80da847d993b8e22e8c03b817f85be99b1ce4deca09b47.jpg)  \nFigure S10. Surface lubrication modification of SIL $@$ UV-SCIRP. The cross-sectional fluorescence microscopic images of catheters modified with HPAA-PAM lubrication coating stained with rhodamine 6G. (a) PVC catheter and (b) Latex catheter.  \n\n![](images/3438540e9bf65a0509956f70a32d04c6c4f8734dc4a44dc8ba92c9a853429afb.jpg)  \nFigure S11. Demonstration of lubrication-assisted movement of hydrogel-decorated balls within confined channels. Schematic illustration of the movement of alumina ball and alumina ball modified with HPAA-PAM coating within the channel of an “S-shaped” PVC catheter under a $50\\mathrm{rpm}$ flow rate.  \n\n![](images/41360523ade5481aaac93af4c9bd8a189814f3fe24cc5707d4a7e4c43e5ea476.jpg)  \nFigure S12. The lift test method for capturing the friction force signal of steel ball in cattle esophagus.",
        "category": " Results and discussion"
    },
    {
        "id": 9,
        "chunk": "# Supporting Movies  \n\nSupplementary Movie 1: The moving process of a controlled alumina ball (left) and modified-alumina ball with HPAA-PAM coating (right) along the water flow within the “S” PVC catheter tube under a 50-rpm flow rate.",
        "category": " Results and discussion"
    }
]