1 Supporting Information pH-programmable sequential dissolution of ...
Supporting Information pH-programmable sequential dissolution of multilayer stacks of hydrogen-bonded polymers Hyomin Leea, Caitlin Sampleb, Robert E. Cohena* and Michael F. Rubnerb* a
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge 02139
b
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge 02139 Corresponding Authors: [email protected] (R.E.C); [email protected] (M.F.R).
Materials. Partially hydrolyzed poly(vinyl alcohol)(PVAP, Mw = 131 000 g/mol, PDI = 1.50, 87-89% hydrolyzed, Sigma-Aldrich), fully hydrolyzed poly(vinyl alcohol) (PVAF, Mw = 144 000 g/mol, PDI = 1.34, 98-99% hydrolyzed, Sigma-Aldrich), poly(acrylic acid) (PAA, Mw = 225 000 g/mol, 20% aqueous solution, Sigma-Aldrich), poly(allylamine hydrochloride) (PAH, 56 000 g/mol, Sigma-Aldrich), poly(diallyldimethylammonium chloride)(PDAC, Mw = 200 – 350 000 g/mol, 20% aqueous solution, Sigma-Aldrich), poly(fluorescein isothiocyante allylamine hydrochloride) (PAH-FITC, Mw = 56 000 g/mol, Sigma-Aldrich), poly(sodium 4-styrene-sulfonate)(SPS, Mw = 70 000 g/mol, Sigma-Aldrich), 2butanone (MEK, 99+% A.C.S. reagent, Sigma-Aldrich), poly(glycidyl methacrylate) (PGMA, Mw = 25 000 g/mol, 10% solution in MEK, Polysciences), poly(methacrylic acid) (PMAA, Mw = 100 000 g/mol, Polysciences), poly(ethylene oxide) (PEO, Mw = 100 000 g/mol, Sigma-Aldrich), Iron oxide magnetic nanoparticle (Fe3O4 NP or MNP, average diameter = 10 nm, anionic, 3.9 % vol. aqueous suspension stabilized with anionic surfactant, Ferrotec EMG 705) were used as received. Standard soda lime glass microscope slides and phosphate buffer saline (PBS) were obtained from VWR. Deionized water (DI, 18.2 MΩ·cm, MilliQ) was used in all aqueous polymer solutions and rinsing procedures.
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Methods. Thin film assembly. The glass substrates were degreased and oxygen plasma treated using previously published protocols.1 PGMA was used as the binder to covalently bond the first layer of PVA to the glass substrate prior to multilayer film assembly in the cases where other adhesion layers were not used. Films were constructed using a Stratosequence VI spin dipper (Nanostrata Inc.) and StratoSmart v6.2 software. The LbL assembly process included dipping times of 10 min for the polymer solutions, followed by three rinses of 2, 1, and 1 min. The concentration of the polymer solutions used was 1 mg/mL and the pH of these solutions and the rinse water were adjusted with 0.1 M HCl or 0.1 M NaOH with no extra salt. For the polymers used in adhesion layers, 100 mM sodium chloride was added before adjusting pH. The nomenclature for LbL films follows conventions depending on the primary driving force: (polycation/polyanion)Z for electrostatic interactions, and (hydrogen bonding acceptor/donor)Z for hydrogen-bonding interactions, where Z is the total number of bilayers deposited. Most of the LbL films were assembled at pH 2.0 conditions, and therefore the pH conditions are not specified unless other conditions were used. In cases where (PEO/PAA) multilayer films were assembled as sacrificial layers to generate freestanding films, adhesion layers consisting of (PDAC/SPS)10.5 were used prior to deposition of sacrificial layer instead of starting with covalent attachment of PVA. Functional modification with fluorescent dye and magnetic nanoparticles. (PDAC/SPS)10.5(PAA/PEO)30.5(PVAP/PAA)30 multilayer film was assembled on glass substrate at low pH conditions (pH 2.0) and crosslinked at 140°C for 5 min. Then, a 10 bilayer film of (PAHFITC3.0/MNP4.0) was LbL assembled subsequently on this multilayer film using a previously published protocol.2 Briefly, Fe3O4 superparamagnetic nanoparticle (MNP) solution was prepared by adding 0.5 mL of a 3.9 % w/v stock solution in 400 mL DI water and adjusting the pH to 4.0. The concentration of PAH-FITC was 1 mg/mL and adjusted to pH 3.0.
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Characterization. Dry film thicknesses were measured using a Tencor P16 surface profilometer with a 2 μm stylus tip, 2 mg stylus force, and a scanning rate of 50 μm/s. The extent of pH-triggered dissolution was determined by measuring the dry film thickness before and after 2 hr incubation in pH-adjusted DI water. For the pH 7.4 case, PBS buffer was used instead of pH adjusted DI water for the reference purposes. Exposure time for fluorescence microscopy images was 958 ms.
Figure S1. (A) Schematic representation of (PAH/SPS)y blocking layers sandwiched between (PVAP/PMAA: pHcrit = 6.5)x and (PVAP/PAA: pHcrit = 2.5)30 layers. Dry film thickness before (black) and after (red) exposure to pH 5.0 DI water for 2 hr is shown with variation in x and y. (B) y = 0, x = 0, 3.5, 5.5, 10.5, 30.5., (C) y = 1.5, x = 0, 3.5, 5.5, 10.5, 30.5., (D) y = 10.5, x = 0, 3.5, 5.5, 10.5, 30.5.
The mode of disassembly of the PVA-based system is dependent on the number of high pH stability pairs in the surface stack, with an increase in the number of bilayers of more stable polymer pairs 3
(PVAP/PMAA) resulting in an increase in the portion of the film remaining on the glass substrate after exposure to intermediate pH conditions as shown in Figure S1B. Moreover, it was found that conventional methodology3 of using a blocking layer to inhibit the diffusion of subsequently assembled more stable polymer pairs into the underlying layer fails for PVA-based systems. As shown in Figure S1C, and 1D, blocking layers (PAH/SPS) are somewhat effective in suppressing interlayer diffusion up to certain extent but starts to fail as the number of bilayers of more stable polymer pairs increases. Also, the presence of blocking layer facilitates uncontrollable deposition of subsequent polymer layers and irregular disassembly behavior which may introduce multiple complication if intend to design two distinctive regions of layers with desired thickness and functionality.
Figure S2. pH-triggered dissolution of (PVAP/PMAA: pHcrit = 6.5)10(PVAF/PMAA: pHcrit = 4.5)10(PVAP/PAA: pHcrit = 2.5)10 assembled at pH 2.0 and subsequently exposed to pH conditions of 4.0, 6.0 and 8.0, respectively. The dotted line in Figure S2 represents the dry film thicknesses measured between the assemblies of each 10 bilayers of polymer pair. Sample 1 (■) was exposed to multiple wetto-dry cycles at pH 4.0 and starts to dissolve away after exposure to pH 6.0 for 1.5 hr. Sample 2 (●) was conditioned at pH 4.0 for 4 hr (one wet-to-dry cycle) and starts to dissolve away after exposure to pH 6.0 for 2 hr and completely dissolves at 3 hr. Sample 3 (▲) was conditioned at pH 4.0 and pH 6.0 for 4 hr each (two wet-to-dry cycle in total) and dissolved immediately after exposure to pH 8.0.
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While conducting multiple thickness measurements on a single sample at shorter intervals, it was observed that multiple wet-to-dry cycles in pH conditions just below pHcrit may facilitate dissolution of that film as shown in Figure S2. Comparison between samples in Figure S2 shows that the pH-triggered dissolution of multilayer film is dependent not on the total amount of time exposed but rather on how many wet-to-dry cycles the sample went through in pH conditions close to the pHcrit.
Figure S3. (A) A photograph of PVA-based freestanding film suspended in PBS buffer solution (pH 7.4)., (B) A photograph of PVA-based freestanding film stained with methylene blue for better image contrast., (C) A photograph of PVA-based freestanding film removed from solution and dried at ambient lab conditions.
Figure S4. (A) (PDAC/SPS)15.5(PEO/PAA)30.5(PVAP/PAA)30(PAH-FITC/MNP)10 multilayer film on glass substrate before exposure to PBS buffer solution. (B) Residual on glass substrate after immersion in PBS buffer for 2 hr. (C) Freestanding multilayer film ((PVAP/PAA)30(PAH-FITC/MNP)10) mounted on a glass substrate after exposure to PBS buffer solution for 2 hr. Scale bar is 100 μm and exposure time is 958 ms. 5
References (1) Lee, H.; Mensire, R.; Cohen, R. E.; Rubner, M. F. Macromolecules 2012, 45, 347-355. (2) Swiston, A. J.; Cheng, C.; Um, S. H.; Irvine, D. J.; Cohen, R. E.; Rubner, M. F. Nano. Lett. 2008, 8, 4446-4453. (3) Gilbert, J. B.; Rubner, M. F.; Cohen, R. E. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 6651-6656.
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Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge 02139
b
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge 02139 Corresponding Authors: [email protected] (R.E.C); [email protected] (M.F.R).
Materials. Partially hydrolyzed poly(vinyl alcohol)(PVAP, Mw = 131 000 g/mol, PDI = 1.50, 87-89% hydrolyzed, Sigma-Aldrich), fully hydrolyzed poly(vinyl alcohol) (PVAF, Mw = 144 000 g/mol, PDI = 1.34, 98-99% hydrolyzed, Sigma-Aldrich), poly(acrylic acid) (PAA, Mw = 225 000 g/mol, 20% aqueous solution, Sigma-Aldrich), poly(allylamine hydrochloride) (PAH, 56 000 g/mol, Sigma-Aldrich), poly(diallyldimethylammonium chloride)(PDAC, Mw = 200 – 350 000 g/mol, 20% aqueous solution, Sigma-Aldrich), poly(fluorescein isothiocyante allylamine hydrochloride) (PAH-FITC, Mw = 56 000 g/mol, Sigma-Aldrich), poly(sodium 4-styrene-sulfonate)(SPS, Mw = 70 000 g/mol, Sigma-Aldrich), 2butanone (MEK, 99+% A.C.S. reagent, Sigma-Aldrich), poly(glycidyl methacrylate) (PGMA, Mw = 25 000 g/mol, 10% solution in MEK, Polysciences), poly(methacrylic acid) (PMAA, Mw = 100 000 g/mol, Polysciences), poly(ethylene oxide) (PEO, Mw = 100 000 g/mol, Sigma-Aldrich), Iron oxide magnetic nanoparticle (Fe3O4 NP or MNP, average diameter = 10 nm, anionic, 3.9 % vol. aqueous suspension stabilized with anionic surfactant, Ferrotec EMG 705) were used as received. Standard soda lime glass microscope slides and phosphate buffer saline (PBS) were obtained from VWR. Deionized water (DI, 18.2 MΩ·cm, MilliQ) was used in all aqueous polymer solutions and rinsing procedures.
1
Methods. Thin film assembly. The glass substrates were degreased and oxygen plasma treated using previously published protocols.1 PGMA was used as the binder to covalently bond the first layer of PVA to the glass substrate prior to multilayer film assembly in the cases where other adhesion layers were not used. Films were constructed using a Stratosequence VI spin dipper (Nanostrata Inc.) and StratoSmart v6.2 software. The LbL assembly process included dipping times of 10 min for the polymer solutions, followed by three rinses of 2, 1, and 1 min. The concentration of the polymer solutions used was 1 mg/mL and the pH of these solutions and the rinse water were adjusted with 0.1 M HCl or 0.1 M NaOH with no extra salt. For the polymers used in adhesion layers, 100 mM sodium chloride was added before adjusting pH. The nomenclature for LbL films follows conventions depending on the primary driving force: (polycation/polyanion)Z for electrostatic interactions, and (hydrogen bonding acceptor/donor)Z for hydrogen-bonding interactions, where Z is the total number of bilayers deposited. Most of the LbL films were assembled at pH 2.0 conditions, and therefore the pH conditions are not specified unless other conditions were used. In cases where (PEO/PAA) multilayer films were assembled as sacrificial layers to generate freestanding films, adhesion layers consisting of (PDAC/SPS)10.5 were used prior to deposition of sacrificial layer instead of starting with covalent attachment of PVA. Functional modification with fluorescent dye and magnetic nanoparticles. (PDAC/SPS)10.5(PAA/PEO)30.5(PVAP/PAA)30 multilayer film was assembled on glass substrate at low pH conditions (pH 2.0) and crosslinked at 140°C for 5 min. Then, a 10 bilayer film of (PAHFITC3.0/MNP4.0) was LbL assembled subsequently on this multilayer film using a previously published protocol.2 Briefly, Fe3O4 superparamagnetic nanoparticle (MNP) solution was prepared by adding 0.5 mL of a 3.9 % w/v stock solution in 400 mL DI water and adjusting the pH to 4.0. The concentration of PAH-FITC was 1 mg/mL and adjusted to pH 3.0.
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Characterization. Dry film thicknesses were measured using a Tencor P16 surface profilometer with a 2 μm stylus tip, 2 mg stylus force, and a scanning rate of 50 μm/s. The extent of pH-triggered dissolution was determined by measuring the dry film thickness before and after 2 hr incubation in pH-adjusted DI water. For the pH 7.4 case, PBS buffer was used instead of pH adjusted DI water for the reference purposes. Exposure time for fluorescence microscopy images was 958 ms.
Figure S1. (A) Schematic representation of (PAH/SPS)y blocking layers sandwiched between (PVAP/PMAA: pHcrit = 6.5)x and (PVAP/PAA: pHcrit = 2.5)30 layers. Dry film thickness before (black) and after (red) exposure to pH 5.0 DI water for 2 hr is shown with variation in x and y. (B) y = 0, x = 0, 3.5, 5.5, 10.5, 30.5., (C) y = 1.5, x = 0, 3.5, 5.5, 10.5, 30.5., (D) y = 10.5, x = 0, 3.5, 5.5, 10.5, 30.5.
The mode of disassembly of the PVA-based system is dependent on the number of high pH stability pairs in the surface stack, with an increase in the number of bilayers of more stable polymer pairs 3
(PVAP/PMAA) resulting in an increase in the portion of the film remaining on the glass substrate after exposure to intermediate pH conditions as shown in Figure S1B. Moreover, it was found that conventional methodology3 of using a blocking layer to inhibit the diffusion of subsequently assembled more stable polymer pairs into the underlying layer fails for PVA-based systems. As shown in Figure S1C, and 1D, blocking layers (PAH/SPS) are somewhat effective in suppressing interlayer diffusion up to certain extent but starts to fail as the number of bilayers of more stable polymer pairs increases. Also, the presence of blocking layer facilitates uncontrollable deposition of subsequent polymer layers and irregular disassembly behavior which may introduce multiple complication if intend to design two distinctive regions of layers with desired thickness and functionality.
Figure S2. pH-triggered dissolution of (PVAP/PMAA: pHcrit = 6.5)10(PVAF/PMAA: pHcrit = 4.5)10(PVAP/PAA: pHcrit = 2.5)10 assembled at pH 2.0 and subsequently exposed to pH conditions of 4.0, 6.0 and 8.0, respectively. The dotted line in Figure S2 represents the dry film thicknesses measured between the assemblies of each 10 bilayers of polymer pair. Sample 1 (■) was exposed to multiple wetto-dry cycles at pH 4.0 and starts to dissolve away after exposure to pH 6.0 for 1.5 hr. Sample 2 (●) was conditioned at pH 4.0 for 4 hr (one wet-to-dry cycle) and starts to dissolve away after exposure to pH 6.0 for 2 hr and completely dissolves at 3 hr. Sample 3 (▲) was conditioned at pH 4.0 and pH 6.0 for 4 hr each (two wet-to-dry cycle in total) and dissolved immediately after exposure to pH 8.0.
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While conducting multiple thickness measurements on a single sample at shorter intervals, it was observed that multiple wet-to-dry cycles in pH conditions just below pHcrit may facilitate dissolution of that film as shown in Figure S2. Comparison between samples in Figure S2 shows that the pH-triggered dissolution of multilayer film is dependent not on the total amount of time exposed but rather on how many wet-to-dry cycles the sample went through in pH conditions close to the pHcrit.
Figure S3. (A) A photograph of PVA-based freestanding film suspended in PBS buffer solution (pH 7.4)., (B) A photograph of PVA-based freestanding film stained with methylene blue for better image contrast., (C) A photograph of PVA-based freestanding film removed from solution and dried at ambient lab conditions.
Figure S4. (A) (PDAC/SPS)15.5(PEO/PAA)30.5(PVAP/PAA)30(PAH-FITC/MNP)10 multilayer film on glass substrate before exposure to PBS buffer solution. (B) Residual on glass substrate after immersion in PBS buffer for 2 hr. (C) Freestanding multilayer film ((PVAP/PAA)30(PAH-FITC/MNP)10) mounted on a glass substrate after exposure to PBS buffer solution for 2 hr. Scale bar is 100 μm and exposure time is 958 ms. 5
References (1) Lee, H.; Mensire, R.; Cohen, R. E.; Rubner, M. F. Macromolecules 2012, 45, 347-355. (2) Swiston, A. J.; Cheng, C.; Um, S. H.; Irvine, D. J.; Cohen, R. E.; Rubner, M. F. Nano. Lett. 2008, 8, 4446-4453. (3) Gilbert, J. B.; Rubner, M. F.; Cohen, R. E. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 6651-6656.
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