Supporting Information

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1 Supporting Information ph- and Amylase-Responsive Carboxymethyl Starch/Poly(2-Isobutyl-acrylic acid) Hybrid Microgels as Effective Enteric Carriers for Oral Insulin Delivery Liang Liu, a,b Ying Zhang, a,b Shuangjiang Yu, a Zhen Zhang, a,b Chaoliang He, a,b, * Xuesi Chen a,b, * a Key Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun , P. R. China b University of Chinese Academy of Sciences, Beijing , P. R. China * Corresponding authors. addresses: clhe@ciac.ac.cn (C. He); xschen@ciac.ac.cn (X. Chen). 1

2 S1. Supplementary experimental methods. S1.1. Synthesis of 2-isobutyl-acrylic acid (ibaa). Diethyl 2-isobutyl-malonate (2.163 g) and NaOH (0.88 g) were dissolved in deionized water (11 ml) and heated at reflux with stirring for 4 h. The reaction was stopped by diluting with deionized water (11 ml) and cooled to room temperature. Ethyl acetate was used to extract the reaction mixture to obtain the aqueous layer, which was then acidified to ph 1.0 with concentrated hydrochloric acid at 0 o C, followed by extracting the solution again with ethyl acetate for several times. The organic layer was dried with anhydrous sodium sulfate, and evaporated to obtain 2-isobutyl-malonic acids. The obtained 2-isobutyl-malonic acids (1.602 g) was then dissolved in deionized water (150 ml), followed by adding diethylamine hydrochloride (1.644 g) and paraformaldehyde (0.601 g). The mixture was stirred at room temperature for 10 min and then refluxed for 12 h. After that, the reaction was cooled to room temperature and extracted with diethyl ether for several times. The organic phase was dried with anhydrous sodium sulfate and the solvent was evaporated to give 2-isobutyl-acrylic acid (ibaa). S1.2. Synthesis of CMS-g-AA. Typically, carboxymethyl starch (CMS, 1.0 g) was firstly dissolved in 30 ml phosphate buffer (PB, ph 7.4). Acrylic acid (AA, 0.09 ml) was activated by EDC. HCl (0.27 g) and DMAP (0.04 g) in 2 ml solvent of DMSO. After activation of the carboxyl groups for 24 h, the AA solution was then added into the CMS solution in PB drop by drop. The reaction was allowed to proceed for an additional 48 h at room temperature. The product was purified by dialysis against deionized water for 3 days, and collected by freeze-drying. S1.3. Conductometric titration mg of dried microgel sample was dispersed in 50 ml of potassium chloride solution (KCl, 10-3 M) under uniform stirring (800 rpm) at 25 o C, and the ph was adjusted to 11.0 by adding NaOH. After bubbling with nitrogen for 30 min to remove CO 2 from the system, the sample solution was 2

3 titrated with 0.1 M HCl standard solution (freshly prepared and calibrated with NaOH standard solution). In the titration process, ph and conductivity were monitored simultaneously until the ph value approached 2.0. The concentration of carboxyl groups in the microgel sample was calculated according to the consumptions of HCl titrant at different transition points of the conductivity curve, and was converted into the PiBAA weight content. S1.4. Turbidity assay of CMS/PiBAA microgel suspension. The turbidity assay of the microgel suspension was performed by a UV-Vis spectrometer (Shimadzu UV-2401PC), equipped with the temperature controller (Shimadzu S-1700). The concentration of the microgel suspension was 1.0 mg/ml. The analyzing wavelength and temperature were set as 550 nm and 37 o C, respectively. The transmittance of each sample was detected for 2 hours at the given ph value from 1.0 to 8.0, with the dot-recording frequency of 25 points/hour. The ionic strength for each group was controlled to be 0.15 M by adding sodium chloride (NaCl). S1.5. Cytotoxicity evaluation. Lyophilized microgel samples were dispersed in phosphate-buffer saline (PBS) at the concentrations ranging from mg/ml. Caco-2 cells were seeded in 96-well plates at 6000 cells/well in 200 µl of MEM cell culture medium and incubated at 37 o C in 5% CO 2 for 24 h, representing the enterocytes in small intestine. After that, the microgel solutions were added into the wells and incubated for another 48 h, followed by removal of the materials. Then, 20 µl of MTT solution (5.0 mg/ml) in PBS was added. The plate was then incubated for 4 h, and the cells were washed thoroughly to ensure the unreacted MTT was removed. Finally, 200 µl of DMSO was added to each well to dissolve the formazan crystals. By using a microplate spectrophotometer (MultiskanMK3, Thermo Electron Corporation), the absorbance of each well was measured at the wavelength of 492 nm. Cells treated with PBS were taken as the negative control with 100% viability, while PEI25k solutions as the positive control. All the tests were carried out in sextuplicate. S1.6. Drug loading and release study of FITC-Ins in the microgels. 3

4 Insulin was labeled by FITC, and was loaded into the microgels with a swelling-diffusion method. Typically, FITC-Ins solution was prepared at the concentration of 0.2 mg/ml (ph = 7.4). Then, 40 mg of dried microgel sample was immersed into 100 ml of FITC-Ins solution and stirred for 24 hours to reach the swelling equilibrium at 37 o C. The FITC-Ins loaded microgels were collected by centrifugation at 15,000 rpm, and rinsed to remove the unloaded FITC-Ins with AGF, followed by freeze-drying. The combined supernatant was diluted to detect the concentration of remained dissociative FITC-Ins on a spectrofluorometer. The drug loading content (DLC) and drug loading efficiency (DLE) of FITC-Ins were calculated using the equations in Section 2.8. The release behaviors of FITC-Ins from the FITC-Ins loaded microgels were investigated in MEM cell culture medium at 37 o C with 5% CO 2 with the similar procedure according to Section 2.8. In the release medium, α-amylase was added with the concentration of 10 U/mL. All the tests were carried out in triplicate. S1.7. Cellular uptake of FITC-Ins mixed with CMS or D-glucose. Mixed with additional dissociative carboxymethyl starch (CMS) or D-glucose (0 µg/ml, 200 µg/ml, 400 µg/ml, 800 µg/ml and 1600 µg/ml) in the uptake medium, the cellular uptake assay for the free-form FITC-Ins was performed according to the same procedure in Section 2.9. The concentration of FITC-Ins in the uptake medium was 50 µg/ml for each well, and the incubation time with Caco-2 cells was set as 60 min. S1.8. Cellular uptake of RhoB-MG loaded with FITC-Ins. FITC-Ins was loaded into the rhodamine B labeled microgels (RhoB-MG), with the drug loading contents of 5.7% (RhoB-MG-1), 4.5% (RhoB-MG-2), 4.1% (RhoB-MG-3) and 2.2% (RhoB-MG-4), respectively. And the obtained samples were employed to conduct the cellular uptake assay with Caco-2 cells, by simultaneous detection of the fluorescent intensity from FITC and rhodamine B on a Guava EasyCyte flow cytometer (Guava Technologies). Briefly, Caco-2 cells were seeded on 12-well plates at cells/well and incubated for 24 h. Then, the culture medium was replaced by the 4

5 uptake medium, into which the RhoB-MG samples loaded with FITC-Ins were dispersed. The concentration of FITC-Ins in each well was set as 20 µg/ml, and Caco-2 cells were placed in the uptake medium for 60 min. Free-form FITC-Ins (20 µg/ml) and the empty RhoB-MG samples were used to act as the controls. The doses of empty RhoB-MG samples were equal to that for the FITC-Ins loaded RhoB-MG samples in this cellular uptake assay. S1.9. Bioactivity of insulin for the insulin-loaded microgels. The insulin-loaded microgel sample was redispersed into 10 ml of PBS containing α-amylase (10 U/mL), poured into a precise dialysis bag (MWCO 10 kda), and placed in a beaker containing 90 ml of fresh PBS, under a shaking rate of 100 rpm at 37 o C. After incubation for 12 h, the release of insulin was considered to reach the equilibrium. And the totally released insulin units (IU) from the microgel was determined by the porcine Insulin ELISA Kits, which were considered as the whole content of insulin encapsulated inside the microgel. Thus, the bioactivity (IU/mg) of insulin for the insulin-loaded microgel sample could be determined with the totally released insulin units (IU) divided by the feed sample weight (mg). Furthermore, the free-form insulin was treated in the same procedure as the experimental control, and the bioactivity of native insulin used in this work was confirmed to be ± 0.46 IU/mg. All tests for each sample were carried out in triplicate. S2. Supplementary results and discussion. S2.1. Characterization of ibaa. The 2-isobutyl-malonic acid was obtained as white solids in a yield of 83.5% via the deacetylation of diethyl 2-isobutyl-malonate in a strongly alkaline aqueous solution, which was examined by 1 H NMR (Fig. S1A). The 1 H NMR spectrum of 2-isobutyl-malonate displayed typical chemical shifts for -CH 3 (a, 0.95 ppm), -CH (b, 1.68 ppm), -CH 2 (c, 1.86 ppm), and -CH (d, 3.54 ppm). Secondly, the 2-isobutyl-acrylic acid (ibaa) was prepared as colorless oil, giving a yield of 73.6%, using the Mannich reaction of 2-isobutyl-malonate, diethylamine hydrochloride and paraformaldehyde. As shown in Fig. S1A, the proton resonance absorption peaks of the double bond from ibaa appear at 5

6 5.59 ppm (d ) and 6.31 ppm (d ). The -CH 3 (a, 0.89 ppm), -CH (b, 1.83 ppm), and -CH 2 (c, 2.16 ppm) were attributed to the chemical shifts of protons in the isobutyl group. The 13 C NMR spectra of 2-isobutyl-malonate and 2-isobutyl-acrylic acid were provided as the Supporting Information (Fig. S1B) for further confirmation of the molecular structure. S2.2. Characterization of CMS-g-AA. After purification and lyophilization, CMS-g-AA was obtained in a yield of 67.9%. The FT-IR spectra of CMS and CMS-g-AA were shown in Fig. S2. Compared with CMS, IR spectrum of CMS-g-AA showed a new absorption peak at 1653 cm -1 (ν C=O ), which was assigned to the carbonyl group of AA, indicating the successful coupling between AA and CMS, and the formation of ester bond. The absorption peaks at 1603 cm -1 (ν C=O ) and 3402 cm -1 (ν O-H ) appeared for both of CMS and CMS-g-AA, which could be attributed to the sodium carboxymethyl and hydroxyl from CMS. The substitution degree of AA was evaluated by elemental analysis. By calculation according to the elemental composition (wt%) of carbon in CMS, acryl group and CMS-g-AA, the weight fraction (wt%) of acryl group in CMS-g-AA was 4.74%. S2.3. Cytotoxicity of the microgels. Since the CMS/PiBAA hybrid microgels were designed for oral administration, the cytotoxicity was studied by MTT assay, using Caco-2 cells as the model of enterocytes in small intestine. As shown in Fig. S8, at the low concentration (less than 2.5 mg/ml), the microgel suspensions presented good biocompatibility with the relative cell viabilities all above 85%. While raising the concentration to a rather high value of 10 mg/ml, the relative cell viabilities of the microgels exhibited considerable reductions. It might be attributed to the eukaryotic membrane disruptive property of the PiBAA segments, which possessed abundant isobutyl side groups and a physiological pk a value, thus led to the cytolysis via the colloid osmotic mechanism. 6

7 Table S1. The amount of rhodamine B labeled on the microgels Sample codes [a] RhoB-MG-1 RhoB-MG-2 RhoB-MG-3 RhoB-MG-4 RhoB labeled on microgels (wt%) [b] a) Rhodamine B (RhoB) labeled Microgel-1, Microgel-2, Microgel-3, and Microgel-4 were tagged as RhoB-MG-1, RhoB-MG-2, RhoB-MG-3, and RhoB-MG-4, respectively. b) Calculated from the following equation: RhoB (wt%) = (W R /W RM ) 100, where W R was the weight of rhodamine B labeled on the microgels, while W RM was the weight of dried RhoB-MG samples. Table S2. Characterization of the insulin-loaded microgels Sample codes Microgel-1 Microgel-2 Microgel-3 Microgel-4 DLC 1 of insulin (%) [a] 6.8 ± ± ± ± 0.8 DLE 1 of insulin (%) [b] 15.0 ± ± ± ± 1.4 DLC 2 of FITC-Ins (%) [c] 6.4 ± ± ± ± 0.8 DLE 2 of FITC-Ins (%) [d] 13.5 ± ± ± ± 1.3 Bioactivity of insulin (IU/mg) [e] 1.96 ± ± ± ± 0.15 a) Drug loading contents (DLC 1 ) and b) drug loading efficiencies (DLE 1 ) of insulin for the microgels, determined on a UV/Vis spectrophotometer according to the procedure in Section 2.8. c) Drug loading contents (DLC 2 ) and d) drug loading efficiencies (DLE 2 ) of FITC Labeled insulin (FITC-Ins) for the microgels, determined on a spectrofluorometer according to the procedure in Section S1.6. e) Bioactivities of insulin (IU/mg) for the insulin-loaded microgels, determined by the porcine Insulin ELISA Kits according to the procedure in Section S1.9. The bioactivity for the native porcine insulin used in this work was confirmed to be ± 0.46 IU/mg. 7

8 Figure S1. A) 1 H NMR spectra of 2-isobutyl-malonate (red) and 2-isobutyl-acrylic acid (blue) in CDCl 3. B) 13 C NMR spectra of 2-(isobutyl)-malonate (red) and 2-(isobutyl)-acrylic acid (blue) in CDCl 3. 8

9 Figure S2. FT-IR spectra of carboxymethyl starch (CMS, red) and acrylate-grafted-carboxymethyl starch (CMS-g-AA, blue). 9

10 Figure S3. UV-vis transmittance vs. time profiles of Microgel-1 (red), Microgel-2 (blue), Microgel-3 (green), and Microgel-4 (pink) suspensions at different ph, respectively (I = 0.15 M). Each time interval for detection at given ph value was set as 2 hours. 10

11 Figure S4. Visualization of the various microgel suspensions (1.0 mg/ml) after incubation for 2 h at different ph and at 37 o C (I = 0.15 M). The ph value was set as 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0 and 8.0, respectively, from left to right. 11

12 Figure S5. Particle size measurements for insulin-loaded microgels (0.2 mg/ml) after redispersion for 8 h in AGF (ph = 1.2, red), AIF (ph = 6.8, green), and MEM cell culture medium (ph = 7.4, pink), respectively. 12

13 Figure S6. Particle size measurements for the degradation behaviors of the microgels in AIF with α-amylase (1.0 U/mL). The concentration of the microgel suspensions was set as 0.2 mg/ml. 13

14 Figure S7. Drug loading content (DLC %) and drug loading efficiency (DLE %) of the microgels. 14

15 Figure S8. Relative cell viabilities of the microgel suspensions in various concentrations after incubation with Caco-2 cells for 48 h (n = 6). PEI25k served as the positive control in this assay. 15

16 Figure S9. (A) Intracellular fluorescent intensity of FITC after incubation of Caco-2 cells with free-form FITC-Ins in the presence of dissociative CMS or (B) D-glucose as endocytic adjuvants at the concentrations of 200 µg/ml, 400 µg/ml, 800 µg/ml, and 1600 µg/ml, respectively. 16

17 Figure S10. Cumulative release profiles of the FITC-Ins loaded microgels in MEM cell culture medium with α-amylase (10 U/mL) (5% of CO 2, 37 o C) (n = 3). 17

18 Figure S11. Percentages (%) of fluorescigenic cells (red for RhoB-MG and green for FITC-Ins). 18

19 Figure S12. Visualization of endocytosis of FITC-Ins in Caco-2 cells by CLSM after incubation with free-form FITC-Ins or FITC-Ins loaded microgels. From left to right, the groups of PBS, free-form FITC-Ins, FITC-Ins loaded Microgel-1, FITC-Ins loaded Microgel-2, FITC-Ins loaded Microgel-3, and FITC-Ins loaded Microgel-4 were arrayed in turn (scale bar: 50 µm). 19

20 Figure S13. Visualization of the lower compartments in the transmembrane transport assay for the microgels labeled by rhodamine B (RhoB-MG) after incubation for 60 min. The cumulative amount of the microgel carriers across Caco-2 cell monolayers from the upper compartments could be reflected by the red color of rhodamine B dye (n = 4). 20