Supporting Information

Antibacterial Anti-oxidant Electroactive Injectable Hydrogel as Self-healing

Wound Dressing with Hemostasis and Adhesiveness for Cutaneous Wound

Healing

Xin Zhao a,1, Hao Wu b,1, Baolin Guo a,, Ruonan Dong a, Yusheng Qiu b, Peter X. Ma a,

c,d,e,

a Frontier Institute of Science and Technology, and State Key Laboratory for

Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, 710049, China

b Department of Orthopaedics, the First Affiliated Hospital, College of Medicine,

Xi'an Jiaotong University, Xi'an, 710061, China

c Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI

48109, USA

d Department of Biologic and Materials Sciences, University of Michigan, 1011,

North University Ave., Room 2209, Ann Arbor, MI 48109, USA

e Macromolecular Science and Engineering Center, University of Michigan, Ann

Arbor, MI48109, USA

Materials and methods

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Synthesis of quaternized chitosan-g-polyaniline (QCSP). The quaternized

chitosan-g-polyaniline (QCSP) was synthesized as we previously reported [1]. Firstly,

quaternized chitosan (QCS) was synthesized. Briefly, 1 g of chitosan (J&K Chemical,

Mn =100,000-300,000 Da) was suspended in 36 mL of deionized water, and then 180

µL of glacial acetic acid (Sigma-Aldrich) was added to the suspension. After stirring

at 55 °C for 30 min, 1159 µL of glycidyltrimethylammonium chloride (GTMAC)

(Sigma-Aldrich) was added dropwise to the chitosan-glacial acetic acid mixture under

continuous stirring. The molar ratio of GTMAC to amino groups on chitosan

backbone was 1.5:1. The reaction mixture was stirred at 55 °C for 18 h. After the

reaction, the undissolved polymer was removed by centrifuging the mixture at 4500

rpm for 20 min at room temperature. The supernatant liquid was filtered through a

Buchner funnel under a reduced pressure, and the filtrate was precipitated in pre-

cooled acetone/ethyl alcohol mixture (1:1, v/v). The purification process was repeated

three times, and the purified QCS was dried in a vacuum oven at room temperature

for 3 days. The degree of substitution (DS) of the QCS was determined by titrating the

content of chlorine ion[2]. Then, the polyaniline (PANI) was grafted onto QCS

resulting in QCSP copolymer. In brief, 200 mg of QCS was added to 10 mL of 0.1 M

HCl aqueous solution in a round-bottom flask. Then 6.19 mg of aniline was

introduced into the QCS solution. After the dissolution of aniline, 15.15 mg of

ammonium persulfate (Sigma-Aldrich) was added to the mixture and the mixture was

stirred at room temperature for 24 h. Following the reaction, the mixture was

neutralized by 1 M NaOH aqueous solution and then dialyzed exhaustively (MWCO

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3500) against deionized water for 3 days. The pure product was obtained by

lyophilization.

Synthesis of benzaldehyde group functionalized poly(ethylene glycol)-co-poly

(glycerol sebacate). In brief, 3.63 g of sebacic acid (Sigma-Aldrich) and 9 g of PEG

(Mn=2000) (Sigma-Aldrich) were added into a 50 mL round-bottom flask (Figure S1).

After reacting at 125 oC for 12 h under nitrogen atmosphere, the pressure of the

round-bottom flask was reduced to 5 kPa and the mixture was allowed to react for

another 24 h. After that, 3.3 g of glycerol (Sigma-Aldrich) was introduced into the

above reactant under nitrogen environment. The mixture was allowed to react at 125

oC for 12 h under nitrogen environment and then react for another 48 h under a

pressure of 5 kPa. After the reaction, the mixture was dissolved in chloroform and

centrifuged under 4500 rpm for 5 min. Following that, the supernatant liquid

(unreacted glycerol) was removed and the residual solution was precipitated in excess

pre-cooled diethyl ether to obtain the glycerol capped poly(ethylene glycol)-co-

poly(glycerol sebacate) copolymer (PEGS). The above purification process was

repeated for another two times to remove the unreacted reagents and other copolymers

with low molecular weights. Then the purified PEGS copolymer was dried in vacuum

oven at room temperature for 48 h.

For the synthesis of benzaldehyde group functionalized PEGS (PEGS-FA), 4-

formylbenzoic acid (FA) (Sigma-Aldrich) was grafted onto the PEGS by an

esterification reaction with EDC (Sigma-Aldrich) as the dehydrating agent and

DMAP (Sigma-Aldrich) as the catalyst (Figure S1). In brief, 1 g of PEGS and 0.206 g

3

of FA were dissolved in 10 mL anhydrous DMF, then 0.856 g of EDC and 0.169 g of

DMAP were dissolved in the above mixture. After that, the mixture was placed at

room temperature to react for 72 h under nitrogen atmosphere. After the reaction, the

mixture was precipitated in excess pre-cooled diethyl ether. The precipitation was

purified as following: the precipitation was dissolved in THF and centrifuged at 4500

rpm for 10 min, and then the supernatant was precipitated in excess pre-cooled diethyl

ether. The purification process was repeated for another two times. The PEGS-FA was

died in vacuum oven at room temperature for 48 h. The benzaldehyde content in

PEGS-FA were determined by UV-vis spectrophotometer at 267 nm in DMF with the

pure 4-formylbenzoic acid as standard.

Characterization

The molecular weight (Mn) of PEGS-FA was evaluated by gel permeation

chromatography (GPC). A Waters 1525 pump, a Waters 2414 refractive index detector

and a column heater equipped with two Waters Styragel columns (HT2 and HT4)

were used to perform the experiments. The mobile phase was THF and the flow rate

was 1 mL/min. The narrow polystyrene standards were used to calibrate the standard

curve of molecular weight.

1H NMR (400 MHz) spectra of PEGS and PEGS-FA were measured using a Bruker

Ascend 400 MHz NMR instrument and CDCl3 was used as the solvent and internal

standard (7.26 ppm).

FTIR spectra of QCSP, PEGS, PEGS-FA and hydrogel QCSP3/PEGS-FA2.0 (with 3

wt% of QCSP and 2 wt% of PEGS-FA in the hydrogel) were recorded in the range of

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4000-650 cm-1 by employing a Nicolet 6700 FT-IR spectrometer (Thermo Scientific

Instrument).

A field emission scanning electron microscope (FEI Quanta FEG 250) was used to

observe the morphologies of the freeze-dried hydrogels. Before observation, the

surface of the hydrogels was sprayed with a gold layer.

UV-vis spectra of hydrogel QCSP3/PEGS-FA1.5 dispersed in deionized water or 1 M

HCl were recorded from 900 nm to 250 nm using a UV-vis spectrophotometer

(PerkinElmer Lambda 35).

Cyclic voltammetry (CV) of hydrogel QCSP3/PEGS-FA1.5 was performed using an

Electrochemical Workstation (CHI 660D Instruments). The hydrogel was coated onto

the ITO conductive glass, and then the hydrogel film was dried at 55 oC before use. A

3-electrode system using a platinum-wire as the auxiliary electrode, an ITO

conductive glass coated hydrogel film as the working electrode, and an Ag/AgCl as

the reference electrode was employed. The test was conducted in DMSO/HCl

solution. After deoxygenating the solution by pouring nitrogen gas for 10 min, the

electrochemical test was performed with a scan rate of 50 mV s-1.

Conductivity of the hydrogels was determined by using a Pocket Conductivity Meter

(HANNA 8733). The hydrogels were prepared using deionized water and then

swelled in deionized water and the excess water on the hydrogel surface was removed

using filter paper. Before the test, the hydrogel was transferred into a cylinder after

exposed to air for 30 min, and the conductivity of hydrogels at 25 oC and 37 oC were

tested.

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The gelation time of the hydrogels was tested by tube inversion method. The polymer

mixture was added into a vial with a diameter of 2 cm and the vial was placed at 37

oC. The gelation time was determined as the time when the mixture stopped flowing

upon the tube inversion within 60 s.

A swelling test was used to determine the swelling ratio (SR) and stability of the

hydrogels. The completely gelled wet hydrogels were put into 20 mL PBS (0.01 M pH

7.4) in sealed vials at 37 °C. When reaching the pre-set time interval, the hydrogels

were taken out from the solution and the superficial water was removed using a filter

paper. Following that, the hydrogels were weighed. The test was not finished until the

weight of hydrogel QCSP3/PEGS-FA2.0 kept constant. SR was calculated using the

following equation: SR= (Wt -Wi)/Wi, where Wi and Wt represented the initial weight

of the wet hydrogels and the weight after swelling equilibrium, respectively. The test

was repeated three times.

Rheological property of the hydrogels

The rheological measurements of the hydrogels were performed by employing a TA

rheometer (DHR-2) using four different methods. (1) A time sweep test with 1%

constant strain and a constant frequency of 10 rad/s at 37 oC was used to evaluate the

stiffness of the hydrogels. Before the collection of the data, 350 µL of the polymer

mixture was placed between 20 mm parallel plates with a gap of 1000 µm and the

periphery was sealed by silicone oil to prevent the evaporation of water. (2) After the

test of time sweep measurement, the completely gelled hydrogel between parallel

plates was directly used to perform the strain amplitude sweep test (γ=0.1%-600%)

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with constant frequency of 10 rad/s at 25 oC. (3) Completely gelled hydrogel disc with

a 20 mm diameter and a thickness of 1000 µm was placed between 20 mm parallel

plates with a gap of 1000 µm at 25 oC. Then, the alternate step strain sweep test was

performed at a fixed angular frequency (10 rad/s) at 25 oC. Amplitude oscillatory

strains were switched from small strain (γ=1.0%) to subsequent large strain (γ=500%)

with 100 s for every strain interval [3]. (4) As-prepared cylindrical hydrogel

QCSP3/PEGS-FA1.5 cut into disk (with a diameter of 20 mm and thickness of 1 mm)

was used to perform a time sweep test with 1% constant strain and a constant

frequency of 10 rad/s at 25 oC. Then, the hydrogel was cut into pieces, and added into

cylindrical mould (with an inner diameter of 20 mm) and placed at 37 oC for 12 h to

obtain completely self-healed hydrogel. The healed cylindrical hydrogel cut into disk

(with a thickness of 1 mm) was then used to perform time sweep test again.

Determination of hydrogel’s dynamic network

The dynamic hydrogel network was confirmed using two different methods. For the

first test, 1 mL of hydroxylamine solution was added to 1 mL of as-prepared hydrogel

QCSP3/PEGS-FA1.5 in a sealed bottle with a dimeter of 14 mm. After that, the bottle

was placed in a shaker at 37 oC until the hydrogel showed gel to sol transition to

demonstrate the dynamic crosslinking of the hydrogel via Schiff base reaction. Both

the situation of inverted bottle with hydrogel before adding hydroxylamine solution

and inverted bottle with hydrogel showing gel to sol transition was photographed. For

another test, the 1H NMR spectra of QCSP/PEGS-FA mixture (10 mg QCSP and 5 mg

PEGS-FA in 1000 µL deuteroxide) and QCSP/PEGS-FA mixture (10 mg QCSP and 5

7

mg PEGS-FA in 1000 µL deuteroxide) with 10 N hydroxylamine corresponding to

benzaldehyde groups from PEGS-FA were performed to determine the dynamic

reaction of QCSP and PEGS-FA.

Adhesive strength test of the hydrogel

As we previously described[4], the actual pigskin tissues surfaces were used. The skin

tissue surfaces were cut into 10 mm × 30 mm rectangle. Then, 40 µL of polymer

mixture was applied onto the surface of the fresh skin tissue and another skin was

placed on the top of the polymer mixture. The contact area of the two skin tissues was

kept 10 mm × 10 mm. After that, the samples were placed at room temperature for 3 h

for complete gelation before the lab shear test. The samples were lap shear-tested to

failure on an Instron Materials Test system (MTS Criterion 43, MTS Criterion)

equipped with a 50 N load cell by using a cross-head speed of 5 mm/min under

ambient conditions. All measurements were triplicate.

Blood clotting ability test of the hydrogel

The in vivo hemostatic property of the hydrogel was evaluated as the reference [5]

described. A hemorrhaging liver mouse model was employed (Sprague-Dawley rat,

200-240 g, male) and all animal studies were performed in compliance with

guidelines set by national regulations and were approved by the local animal

experiments ethical committee. In brief, the mouse was anesthetized by injecting 10

wt% chloral hydrate and fixed on a surgical corkboard. The liver of the mouse was

exposed by abdominal incision, and serous fluid around the liver was carefully

removed to prevent inaccuracies in the estimation of the blood weight obtained by the

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filter paper. A pre-weighted filter paper on a paraffin film was placed beneath the

liver. Bleeding from the liver was induced using a 20 G needle with the corkboard

tilted at about 30° and 50 μL of QCSP3/PEGS-FA1.5 mixture was immediately

applied to the bleeding site using the syringe. After 3 min, the weight of the filter

paper with absorbed blood was measured and compared with a control group (no

treatment after pricking the liver). All measurements were triplicate.

Biocompatibility evaluation of the hydrogels

The cytotoxicity of hydrogels was measured by employing a direct contact test

between hydrogels and L929 cells. As described before in the section of hydrogel

preparation, copolymer solution sterilized at 90 °C for 3 h was vortex mixed with

PEGS-FA solution sterilized by filtration (0.22 μm filter, Millipore) for 10 seconds

equivoluminally. The mixture was poured into a sterile Petri dish to form a hydrogel

film with about 1.5 mm thickness at 37 °C in CO2 incubator. Then hydrogel film was

cut into 5 mm diameter disks using a Harris Micro-Punch (Harris Uni-Core™, USA)

and the dulbecco’s modified eagle medium (DMEM) (Gibco) supplemented with 10%

fetal bovine serum (Gibco), 1.0 × 105 U/L penicillin (Hyclone) and 100 mg/L

streptomycin (Hyclone) was used as the complete growth medium. L929 cells were

seeded in 96-well plate at a density of 20000 cells/well. After cultured for 24 h, the

hydrogel disks were introduced into the wells. The cell proliferation and viability

under the hydrogel was evaluated by alamarBlue® assay and LIVE/DEAD®

Viability/Cytotoxicity Kit assay after 24 h. The hydrogel disks and medium were

removed and 10 μL of alamarBlue® reagent in 100 μL complete growth medium was

9

then added into each well. The plate was incubated for 4 h in a humidified incubator

containing 5% CO2 at 37 °C. After that, 100 μL of the medium in each well was

transferred into a 96-well black plate (Costar). Fluorescence was read using 560 nm as

the excitation wavelength and 600 nm as the emission wavelength using a microplate

reader (Molecular Devices) according to the manufacturer’s instructions. Cells seeded

on TCP without hydrogel disc served as the positive control group. Tests were

repeated four times for each group. Cell adhesion and viability were observed under

an inverted fluorescence microscope (IX53, Olympus). The cell viability was

evaluated by alamarBlue® assay after cultured for 24 h.

In vivo wound healing full-thickness skin defect model

Our animal experiments were approved by the institutional review board of Xi’an

Jiaotong University. Female Kunming mice weighting 30-40 g and 5-6-week age were

used for studies. All mice were randomly divided into 3 groups including control,

hydrogel QCS3/PEGS-FA1.5 and hydrogel QCSP3/PEGS-FA1.5. Each group

contained 15 mice. All mice were acclimatized for 1 week before surgery. For the

surgery part, all procedures were performed under aseptic condition. After standard

anesthesia procedure with intraperitoneal injection of chloral hydrate (0.3 mg/kg body

weight), the dorsal region of mice above the tail but below the back were shaved to

prepare for surgery. 7 mm diameter full thickness skin round wounds were created by

a needle biopsy. After the removal of wound skin, control wounds were added with 40

μL of PBS then dressed with Transparent Film Dressing Frame Style (3M Health

Care, USA), and hydrogel group wounds were added with 40 μL of hydrogel

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QCS3/PEGS-FA1.5 or hydrogel QCSP3/PEGS-FA1.5 without dressing with anything.

All tissues were collected on each 5 mice in 3 groups on 5th, 10th, 15th day. All

samples were stored at -80 °C before analysis. The regeneration process of wounds

was assessed by wound area monitoring, related genes expression and biochemical

and histomorphological determination. For wound area monitoring, on the 5th, 10th,

15th day, the mice in each group were performed standard anesthesia procedure with

intraperitoneal injection of chloral hydrate (0.3 mg/kg body weight), then wound area

were measured by tracing the wound boundaries on plotting papers.

Wound contraction (%) were calculated using the formula below:

Wound contraction= (area (0 day)-area (n day))/ (area (0 day)) ×100%,

where “n” represents the day, such as 5th, 10th, 15th day. All results were analyzed by

one-way ANOVA test.

For the biochemical analysis, samples collected on 5th, 10th and 15th day for

biochemical analysis were made into 1 cm2 square shape, and collagen amount was

evaluated by estimating hydroxylproline content using a commercial kit (Jiancheng

Bioengineering, China). All operations were strictly followed manufacture’s

instruction.

Related genes expression

All samples collected on 5th, 10th and 15th day for real time PCR with healthy skin,

extra fat and other tissue were pruned for RNA extraction. The total RNA were

extracted using Trizol (Invitrogen, USA) according to the manufacturer’s instructions.

1 µg of RNA was used to synthesize cDNA using a reverse transcription reagents kit

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(Roche, Germany). The quantitative real-time PCR was carried out following the

protocol and conducted with an Applied Biosystems 7500 Fast Real-time PCR system

(Applied Biosystems, USA) with the following temperature profile: at 95 °C for 2

minutes, then 40 cycles at 95 °C for 3 seconds and at 60 °C for 30 seconds. Epidermal

growth factor (EGF), tissue growth factor-β (TGF-β) and vascular endothelial growth

factor (VEGF) were aimed to assess the wound healing process. All primer sequences

were as following: EGF, forward 5’-TCTGAACCCGGACGGATTTG-3’, reverse 5’-

GACATCGCTCGCCAACGTAG-3’. TGF-β, forward 5’-

ATGACATGAACCGACCCTTC-3’, reverse 5’-TGTGTTGGTTGTAGAGGGCA-3’.

VEGF forward 5’- TCACTATGCAGATCATGCGGA-3’, reverse 5’-

GTCACTATGCAGATCATGCGGA-3’.

Histomorphological determination

For evaluation of epidermal regeneration and inflammation in wound area, samples

collected on 5th, 10th, 15th day were fixed with 4% paraformaldehyde for 1 h then

embedded in paraffin and cross sectioned to 4 μm thickness slices, and then stained

with Haematoxylin-Eosin (Beyotime, China). All slices were analyzed and photo-

captured by microscope ((IX53, Olympus, Japan).

Antioxidant efficiency of hydrogels

The antioxidant efficiency of hydrogels was tested by measuring their capacity to

scavenge the stable 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical, using the

method reported by Serpen with minor modification [6]. The hydrogels in HCl doped

state were made into homogenate by using tissue grinder. DPPH (3.0 ml, 100 µM) and

12

dispersion of samples (containing 4 mg conductive polymer) in methanol was stirred

and incubated in a dark place for 30 min. Then, wavelength scanning was performed

using a UV–vis spectrophotometer. The DPPH degradation was calculated using the

following equation:

DPPH scavenging %=AB−AH

AB×100

where AB being the absorption of the blank (DPPH + methanol) and AH the absorption

of the hydrogel (DPPH +methanol +hydrogel). To determine the effect of HCl on the

radical scavenging efficiency, the same mole of HCl which doped hydrogel

QCSP3/PEGS-FA1.5, and camphorsulfonic acid (another common dopant for

polyaniline in biomedical applications) doped hydrogel QCSP3/PEGS-FA1.5 were

also tested with the same method.

Results and discussions

Synthesis of benzaldehyde group functionalized poly(ethylene glycol)-co-

poly(glycerol sebacate)

The 1H NMR spectrum of PEGS was shown in Figure S3a. The peaks at 1.31, 1.62,

and 2.35 ppm corresponding to methylene protons of sebacic acid, the peaks from

4.05–4.35 ppm and 5.05–5.30 ppm assigned to protons in the glycerol and the peak at

3.64 ppm corresponding to methylene protons of PEG segments were observed in the

spectrum of PEGS copolymer, suggesting the successful synthesis of PEGS

copolymer. Compared with 1H NMR spectrum of PEGS, new peaks at 10.10 ppm

corresponding to aldehyde, at 8.22 and 7.96 ppm assigned to benzene ring and at 4.51

13

ppm assigned to ester methylene were observed in the 1H NMR spectrum of PEGS-FA

copolymer (Figure S3b), which indicated the FA was successfully grafted onto PEGS

chain. The FTIR spectra results of PEGS and PEGS-FA shown in Figure S4 were

consistent with the 1H NMR results. The PEGS copolymer spectrum showed a strong

absorption peak around 1732 cm-1 corresponding to carbonyl groups (C O stretch)

from the ester groups and a broad band at 3459 cm-1 assigned to the free hydroxyl

groups (-OH stretch), confirming the successful synthesis of PEGS copolymer.

Moreover, compared with FTIR spectrum of PEGS, PEGS-FA copolymer spectrum

presented reduced free hydroxyl groups (-OH stretch) absorption, and new peak at

about 1702 cm-1 attributed to aldehyde groups and new peak around 1575 cm-1

corresponding to stretching vibration of C=C bond in the aromatic ring, suggesting

that FA was successfully grafted onto PEGS chain via an esterification reaction. The

benzaldehyde groups in one PEGS-FA molecular was about 11 calculated by using

UV-vis spectrophotometer at 267 nm.

14

Figure S1. Synthesis of PEGS-FA copolymer and QCSP copolymer in detail.

Figure S2. Self-healing ability evaluation of the hydrogels with different crosslinker

concentrations. (1): QCSP3/PEGS-FA0.5; (2): QCSP3/PEGS-FA1.0; (3):

QCSP3/PEGS-FA1.5; (4): QCSP3/PEGS-FA2.0; (5): QCSP3/PEGS-FA2.5; (6):

QCSP3/PEGS-FA3.0. Hydrogel were cut into pieces (0 h); Self-healed hydrogel

pieces for 12 h; Self-healed hydrogel pieces for 24 h. Scar bar: 1.2 cm.

15

Figure S3. 1H NMR spectra of PEGS (a) and PEGS-FA (b).

Figure S4. FTIR spectra of PEGS and PEGS-FA.

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Table S1 Conductivity of hydrogels at 25 oC and 37 oC.

Hydrogel Conductivity at 25 oC

(mS/cm)

Conductivity at 37 oC

(mS/cm)

QCS3/PEGS-FA1.5 1.55 1.87

QCSP3/PEGS-FA0.5 3.50 4.24

QCSP3/PEGS-FA1.0 3.13 3.81

QCSP3/PEGS-FA1.5 2.37 2.86

QCSP3/PEGS-FA2.0 2.25 2.77

Figure S5. UV-vis spectra of DPPH and DPPH after scavenged by hydrogels for 30

min.

17

Figure S6. The time sweep test of original hydrogel QCSP3/PEGS-FA1.5 (a) and

hydrogel QCSP3/PEGS-FA1.5 after experiencing cutting-healing process.

Figure S7. (a) Photographs of an inverted bottle containing hydrogel QCSP3/PEGS-

FA1.5 and an inverted bottle containing hydrogel QCSP3/PEGS-FA1.5 in sol state

after adding hydroxylamine. (b) 1H NMR spectra of QCSP/PEGS-FA mixture (10 mg

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QCSP and 5 mg PEGS-FA in 1000 µL deuteroxide), and QCSP/PEGS-FA mixture (10

mg QCSP and 5 mg PEGS-FA in 1000 µL deuteroxide) with hydroxylamine. Scar bar:

5 mm.

Figure S8. Photographs of supernatants from the blood suspensions after contacting

with hydrogel surfaces, TCP and Triton-X100. (1): QCSP3/PEGS-FA0.5; (2):

QCSP3/PEGS-FA1.0; (3) QCSP3/PEGS-FA1.5; (4) QCSP3/PEGS-FA2.0; (5) TCP;

(6) Triton-X100.

Figure S9. LIVE/DEAD staining of L929 cells when contacting with the hydrogel

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surfaces and TCP for 24 h. (A): QCSP3/PEGS-FA0.5; (B): QCSP3/PEGS-FA1.0; (C):

QCSP3/PEGS-FA1.5; (D): QCSP3/PEGS-FA2.0; (E): TCP. Scar bar: 1 mm.

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