W Pickering Emulsion Templated Organo-hydrogels with Enhanced

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O/W Pickering Emulsion Templated Organo-hydrogels with Enhanced Mechanical Strength and Energy Storage Capacity Xingzhong Zhang, Yixiang Wang, Xiaogang Luo, Ang Lu, Yan Li, Bin Li, and Shilin Liu ACS Appl. Bio Mater., Just Accepted Manuscript • DOI: 10.1021/acsabm.8b00674 • Publication Date (Web): 29 Nov 2018 Downloaded from http://pubs.acs.org on November 30, 2018

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ACS Applied Bio Materials

O/W Pickering Emulsion Templated Organo-hydrogels with Enhanced Mechanical Strength and Energy Storage Capacity Xingzhong Zhanga,b, Yixiang Wangc*, Xiaogang Luod, Ang Lue*, Yan Lib, Bin Lib, Shilin Liua,b* a. Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology & Business University, Beijing, 100048, China; b. College of Food Science & Technology, Huazhong Agricultural University, Wuhan, Hubei, 430070, China; c. Department of Food Science and Agricultural Chemistry, McGill University, Ste Anne de Bellevue, Quebec, H9X 3V9, Canada; d. School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan, 430073, China; e. College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, Hubei, China.

ACS Paragon Plus Environment

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ABSTRACT The increased quantities of fat in plants could allow the cells to inhibit the growth of ice and thus prevent the damages of their tissue structure in winter. In view of the structural buildup of freezing tolerance mechanism, here we reported a facile way of employing O/W Pickering emulsion as a template to produce the freestanding organo-hydrogels with increased mechanical stability and energy storage capacity. The oil droplets stabilized by cellulose nanofibrils were dispersed in the alginate polymer network that cross-linked with Ca2+, resulting in homogeneous and closely packed microstructures. The prepared organo-hydrogels could maintain original gel structure under frozen conditions and had extraordinary mechanical performance. It could endure compressive stress up to 35 KPa (at 50% strain) and the elastic modulus was around 72 KPa, while the solid content of polysaccharides was only about 0.75%. By using our comprehensive strategy, organo-hydrogels with higher volumes of oil phase exhibited an enhanced cold storage capacity. For alginate hydrogel, it took 8 min when the temperature rose from 0 oC to 5 oC; while for the organo-hydrogel with oil volume of 30%, it took about 24 min. After 34 min, the inner temperature of alginate hydrogel was very close to 25 oC, while it needed about 70 min for the organo-hydrogel to reach 25 oC. This kind of gel materials with complementary hetero-networks will not only have potential applications in cold chain logistics, but also can be applied in other fields with unusual functions. KEYWORDS: organo-hydrogel, nanocellulose, Pickering emulsions, freezing tolerance


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1. INTRODUCTION Hydrogels with a large amount of water in their three-dimensional hydrophilic networks

have

attracted

considerable

interests

in

tissue-specific

organoid

engineering1-4, supercapacitor5-7, drug delivery8-10, biosensors11-14 and so on15,16. However, this kind of materials has poor mechanical strength and limited stiffness especially in the case of hydrogel with low solid content. It is because of the lack of effective energy dissipation pathway in the highly swollen matrix and the inhomogeneous intrinsic network17. Moreover, hydrogels will be frozen and lose the elasticity in subzero environment, which may impede their practical applications that require mechanical integrity18,19. Many attempts have been performed to improve the mechanical strength of hydrogels, including cross-linked polymer network20, double network structured hydrogels21, composite hydrogels22,23, interpenetrating polymer network24, and physical interaction hydrogels25. However, most of the strategies either suffered from the complex fabrication process or were limited by the raw materials. In nature, many plants living at high altitudes can survive in cold ambient conditions26. This exceptional freezing tolerance attributes to the increased quantity of fat, which inhibits the growth of ice to prevent the damage to cells27-29. In biological systems, it is important to provide materials with elasticity and freezing tolerance by the dynamic coexistence of opposite components (water and fatty)30,31. These phenomenon have encouraged researchers to design and fabricate high-performance materials by combining two components with entirely opposite physiochemical properties and introducing the cellular fibrous network32,33. Accordingly, the binary



cooperative complementary principle could be applied in the fabrication of hetero-network gel materials to compensate for the weaknesses of traditional hydrogels and organogels. To study the effects of the liquid components in hydrogels and the hetero-network structure on performance, particularly the freezing tolerance and mechanical properties, will be highly desirable. Currently, the research of Pickering emulsion-based hydrogels has attracted considerable interests. Chen et al. reported that the macroporous composite hydrogel was obtained through the polymerization of the continuous phase utilizing graphene oxide/polyvinyl alcohol (GO/PVA) stabilized emulsion as a template, which can be further used for anticancer drug release to kill cancer cells34. Moreover, Zou et al. investigated Artemisia argyi oil (AAO)-loaded macroporous hydrogels with tunable pore structures fabricated by using Pickering high internal phase emulsions as templates. In their study, the hydrogel exhibited excellent and long-term antibacterial activity and thus provided promising applications in biomedical fields35. In this work, inspired by the freezing tolerance mechanisms of hetero-network gel materials and based on our previous works36-38, we reported a facile way of using O/W Pickering emulsion as template to produce freeze-tolerant and mechanically stable hetero-network organo-hydrogel. In this paper, the oil droplets stabilized by cellulose nanofibrils were dispersed in the alginate polymer network that cross-linked with Ca2+, resulting in homogeneous and closely packed microstructures. Since cellulose and sodium alginate are hydrophilic polysaccharides, they had good compatibility in the resultant composites. Meanwhile, it has been reported that cellulose nanofibrils were


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used as reinforcing components in alginate matrix to enhance mechanical strength39,40. The hetero-networks allowed the organo-hydrogel to have increased mechanical strength. In addition, the filled Pickering emulsions phase could prevent the formation of ice crystals, thus improved the mechanical stability of organo-hydrogel at cold temperature. This concept of complementary hetero-networks in organo-hydrogel would have potential applications in cold chain logistics and promote the development of multifunctional soft materials by the incorporation of water-soluble and liposoluble functional components. 2. EXPERIMENTAL SECTION 2.1. Materials Bacterial cellulose (BC) was obtained from the Yida Food Co.; Ltd (Hainan, China). Sodium alginate (SA, viscosity was 200 ± 20 mPa•s, USP grade) was purchased from Aladdin Reagent Co.; Ltd (Shanghai, China). Other reagents with analytical grade were purchased from the Sinopharm Chemical Reagent Co.; Ltd (China). Deionized water was used for all tests. 2.2. Methods 2.2.1. Preparation of Bacterial Cellulose Nanofibrils (BCNs) Bacterial cellulose hydrogels were treated with NaOH and then washed with deionized water to neutral. The sample was smashed with a disintegrator (IKA-T25, IKA Instruments Ltd, Germany), and after that, dispersed by a high-pressure



homogenizer at 800 bar. The obtained BCNs dispersions were concentrated to 1 wt% and stored in a refrigerator before being used. 2.2.2. Preparation of O/W Pickering emulsions and organo-hydrogel The oil-in-water (O/W) Pickering emulsion was prepared with controlled oil/water volume ratio of 10/90, and dodecane was used as oil phase. The BCNs or BCNs/SA aqueous dispersions were used as water phase. BCNs with contents of 0.1%, 0.2%, 0.3%, 0.4% and 0.5% were used for the emulsions preparation, and the ratio of BCNs: SA was controlled to 1:1.5 (w/w) for the BCNs/SA mixed dispersions. A high intensity ultrasonic processor (FS-600N, Shengxi Ltd, China) with a frequency of 20 kHz was used to prepare the emulsions. The Pickering emulsions filled hydrogel was obtained by adding calcium ions to the emulsion system to form the gels directly. Creaming Index (CI ) was calculated by using the following formula41: 𝐻𝑐

CI (%) = 𝐻𝑡 ∗ 100(%)

(1)

where Hc was the height of the cream layer and Ht was the total height of the emulsion. 2.3. Characterizations The morphology of the BCNs was characterized with Atomic force microscopy (AFM) (Cypher S, Asylum Research, USA). About 2 μL of BCNs dispersions were spread on the surface of freshly cleaned mica disk and dried at ambient conditions. AFM images were obtained with a tapping mode and analyzed with the Nanoscope


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software. Zeta potential of the SA solutions, BCNs and BCNs/SA dispersions was determined in triplicate by electrophoretic light scattering with a laser diffraction device (Zetasizer Nano ZS, Malvern, UK). Rheological behaviors of the prepared emulsions were investigated by using rotational rheometer (Discovery DHR-2, TA Instruments, USA) with a 40 mm parallel plate geometry, and the measurement gap was set to 1,000 μm. The steady shearing test was carried out at shear rates in the range of 0.1-100 s-1. Frequency sweeps were carried out at a strain of 0.5% and the frequency was 0.1-100 Hz. All rheological tests were repeated three times with the same sample and performed at 25 °C. The dynamic interfacial tension as a function of time was performed through a drop shape analyzer rheometer (Tracker-H, Teclis, France). The water phase (BCNs or BCNs/SA mixtures) and oil phase (dodecane) were placed in the cuvette and syringe, respectively. The test was carried out at 25 °C and continued for 7,200 s by using an oil drop with volume of 15 μL. The water phase was BCNs or BCNs/SA dispersions with BCNs concentration of 0.01%, 0.05% and 0.1%, respectively, and the ratio of BCNs/SA was 1:1.5 (w/w). Particle size distribution of the prepared emulsions was monitored by using a Mastersizer (APA2000, Malvern, UK). The mean particle diameter of the emulsions was taken to be the volume-weighted diameter D(4,3), which was calculated as equation42: 4 𝐷 (4.3) = ∑𝑁𝑖 × 𝐷𝑖 ∑𝑁𝑖 × 𝐷3𝑖

(2)

Where, Ni was the number of the particles with the diameter Di. The microstructure of the emulsions and emulsion templated organo-hydrogels was



characterized by using scanning electron microscopy (SEM, S4800, Hitachi, Japan). The samples were freeze-dried, and then sputter-coated with Pt. The compressive property of organo-hydrogels was investigated by using material testing system (Instron 5967, MTS Systems Ltd, USA). The cylindrical shaped samples were placed with a mold (10 mm diameter, 10 mm height) and compressed (50%) between two parallel plates with a 200 N load cell at a speed of 2 mm∙min-1. The simulated freeze-thaw experiment was carried out by using the following method: before the test, the alginate hydrogel and organo-hydrogels with 10%, 20%, and 30% of oil were kept at -15oC for 12 h. Then all the samples were placed in the same thermostat box at 30 oC. Thermometers were inserted in the middle of the hydrogels and organo-hydrogels, respectively, and the temperature during the thawing process was recorded every 2 min. Each sample was tested for three times, and water with the same volume was used as control. 3. RESULTS AND DISCUSSION Bacterial cellulose nanofibrils (BCNs) were synthesized by Acetobacter xylinum during the fermentation to form a highly swollen hydrogel. After being treated with high-pressure homogenization, the hydrogel network was destroyed, and the uniform BCNs aqueous dispersions were obtained. As shown in Figure 1, BCNs had a mean width of 57.6 ± 2.6 nm and a height of 7.2 ± 0.4 nm, and a length in micron scale. The BCNs aqueous dispersions exhibited a shear thinning behavior (Figure S-1), and a zeta potential of about -9.3 mv (Figure 2). With the addition of alginate, the BCNs/SA


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dispersions exhibited the increased negative zeta potential, which indicated that the stability and dispersibility of BCNs were improved. Since the hydroxyl groups of BCNs and the carboxyl and hydroxyl groups of alginate had an influence on their colloidal properties, the pH and ionic strength of dispersions should be considered seriously when a stable Pickering emulsion was preferred. The zeta potential of BCNs under different pH or ionic strength was presented in Figure S-2. The zeta potential of BCNs was only slightly affected by changing the pH and ion strength. However, the zeta potential of BCNs/SA gradually decreased when pH value varied from 9 to 3 and ionic strength rose from 0 to 400 mM. This variation of zeta potential was largely due to the electrostatic shielding effect and the subsequent aggregation of alginate, and would affect the emulsion stability. The O/W Pickering emulsion stabilized by pure BCNs was shown in Figure S-3. The droplet size decreased and the stability of emulsion increased when the BCNs contents went up. However, the emulsions had a wider particle size distribution when comparing with that of the emulsions stabilized by BCNs/SA (Figure S-4). In Figure 3, the microscopy images of O/W Pickering emulsions stabilized by different concentrations of BCNs/SA were presented. All the droplets exhibited the spherical shape. With the increase of the concentration of BCNs/SA, the size of the emulsion droplets gradually decreased and became uniform. The CI of the emulsions had a negative relationship with the BCNs/SA concentration. In other words, the increase of BCNs/SA concentration could promote the stability of the emulsion. The change of emulsion droplet size at different BCNs/SA concentrations was attributed to the



coverage of BCNs/SA at the O/W interface, which protected the emulsion droplets against coalescence by forming a mechanically robust layer. The BCNs/SA would insufficiently cover on the oil-water interface at low concentration, which easily led to the coalescence and creaming of emulsions during the storage, resulting in the non-uniform distribution of the droplets. With the increase of the concentration of BCNs/SA, more and more particles were absorbed at the O/W interface, which could decrease the droplets size and prevent their coalescence or flocculation. Consequently, the emulsion had the small droplet size and a homogeneous distribution (Figure 4). Moreover, the emulsions stabilized by BCNs/SA revealed a narrower particle size distribution and smaller droplet size in comparison with that stabilized by BCNs at the same concentration, indicating that BCNs/SA possessed increased emulsifying performance than BCNs. The rheological behavior of the emulsions stabilized by BCNs/SA dispersions was shown in Figure 5. The emulsions expressed a gel-like three-region (shear thinning, shear plateau, shear thinning) rheological behavior with increasing the shear rate. Similar to emulsion stabilized by pure BCNs (Figure S-5), the shear viscosity of emulsions stabilized by BCNs/SA dispersions was also increased with the increase of the concentration of BCNs/SA, and the viscosity was higher than that of BCNs stabilized emulsions with the same concentration due to the thickening properties of alginate. All the emulsions showed gel-like behaviors where storage modulus (G') dominated over loss modulus (G"), and both dynamic moduli were significantly increased with the increase of the concentration of BCNs and BCNs/SA. It indicated


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that a gel-like viscoelastic network had formed in emulsions and the network structure became more cohesive and compact with higher contents of BCNs and BCNs/SA. Besides, the G' of emulsions stabilized by BCNs/SA was higher than that of emulsions stabilized by BCNs with the same concentration. It indicated that the network structure of the emulsions stabilized by BCNs/SA exhibited more solid-like properties (as shown in Figure 6). The influence of time, ion strength and pH in the stability of the emulsions stabilized by BCNs and BCNs/SA is shown in Figures S-6, S-7 and S-8. With the addition of alginate in BCNs dispersions, the prepared emulsions had higher apparent viscosity, which was helpful to further formation of organo-hydrogels structure after cross-linking with Ca2+. Interfacial tension as a function of time was used to assess the adsorption of BCNs and BCNs/SA at the oil-water interface. As shown in Figure 7, BCNs could reduce the oil-water interfacial tension, and the interfacial tension was decreased from 46.7 to 37.6 mN/m with the increase of the content of BCNs from 0.01 to 0.1 wt%. For BCNs/SA, the interfacial tension was decreased from 41.7 to 34.2 mN/m with the increase of the content of BCNs/SA from 0.01 to 0.1 wt%. It indicated that the BCNs/SA was preferentially adsorbed onto the oil-water interface. The minimum interfacial tension value was obtained when alginate was added. It suggested that polysaccharides could cover the oil-water interface sufficiently and a three dimensional network could form by entangled fibrils, which resulted in the smaller droplets, narrower size distribution and efficiently restrained phase separation of emulsion.



The mechanical properties of the organo-hydrogels were measured by using compression test at room temperature. Figure 8a showed the typical compressive strain-stress curves of organo-hydrogels cross-linked by different concentrations of Ca2+. The Ca2+ crosslinked BCNs/SA hydrogel with same solid content was too soft to determine the mechanical strength (Figure S-9). However, the organo-hydrogels prepared from Pickering emulsion templated method were able to sustain the stress of 11 KPa at 50% strain. The compressive stress increased when higher concentrations of Ca2+ were added. It was worth noting that the compressive stress reached to 22 KPa when the content of BCNs/SA was 0.5 %. The oil droplets embedded in the organo-hydrogel network could effectively transfer energy across the interface and reduce the stress concentration. It also indicated that the strength of the organo-hydrogels could be easily tuned. Figures 8a’-c’ demonstrated the elastic modulus of the organo-hydrogels prepared from different conditions. The organo-hydrogels filled with Pickering emulsions had a much higher elastic modulus. This result offered powerful evidence for the validity of our organo-hydrogel fabrication strategy to obtain organo-hydrogels with high mechanical performance. Alginate hydrogel cross-linked by Ca2+ was brittle, and it had low fracture energy and elastic modulus. Here, we demonstrated that Pickering emulsion filled hydrogels could achieve both toughness and stiffness. In the organo-hydrogels, the inserted Pickering emulsions increased the stiffness, while the polymer matrix dissipated energy to achieve high strength. Figure 9 showed the SEM images of the emulsions and organo-hydrogels prepared


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from different contents of BCNs/SA and cross-linked with Ca2+. Figures 9a-c showed the microstructures of the formed Pickering emulsions that did not cross-linked with Ca2+, and the dried samples had loose structures. While for the organo-hydrogels prepared from Pickering emulsions templated method and cross-linked with Ca2+, they had closely packed structures. The skeleton of the network became tougher with the increase of BCNs/SA concentration, and the structure of the organo-hydrogels was sponge-like. With the increase of the content of BCNs/SA, the obtained organo-hydrogel had closer microstructures, which was the key factor for the contribution to the high mechanical strength. It was significant measure to design the organo-hydrogels with high mechanical strength by the incorporation of Pickering emulsion, which could provide a new fabrication strategy for the soft materials. In

order

to

demonstrate

the

thermal

management

application

of

the

organo-hydrogels, the temperature variations of the organo-hydrogels with time after freezing were recorded. As shown in Figure 10, the temperature of the alginate hydrogel was close to 25 oC after 34 min, while for the organo-hydrogels, the temperature was in the range of 0.8 oC - 2 oC. After about 70 min, the temperature of the organo-hydrogels reached 25 oC. Obviously, the temperature of the pure water and hydrogel increased much faster in comparison with that of organo-hydrogels. The thermal regulation performance of the organo-hydrogel could be improved by increasing its volume and thickness. For the purpose of temperature regulation, an advantage of the organo-hydrogel was the high water absorption/retention. It was a promising lightweight, structural and functional candidate for energy storage



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technology. 4. CONCLUSIONS In summary, we have presented a method to prepare organo-hydrogels with hetero-network by using O/W Pickering emulsion as templates to incorporate oil in the hydrogels. The preparation procedure had the advantages that capsule-like emulsions formed during the process, and emulsion stabilization and dispersions were integrated in the biomaterial matrix. The weaknesses of traditional hydrogels and organogels could be overcome through this integration of oil and hydrogels. More importantly,

the

amphiphilic

nature

of

the

hetero-network

allowed

the

organo-hydrogels to simultaneously contain water and oil in the three-dimensional network structures, so many water-soluble and liposoluble functional compounds could be incorporated. These organo-hydrogels bridged the hydrogels and organogels, and would have promising applications. 

ASSOCIATED CONTENT

Supporting Information The viscosity versus shear rate for BCNs aqueous dispersions with solid content of 0.25%; the influence of ionic strength and pH on the zeta-potential of BCNs and BCNs/SA dispersions; optical microscopy images of emulsions containing 10 v% oil phase stabilized by BCNs with different concentration; particle size distributions of the emulsions containing 10 v% oil phase stabilized by BCNs with different concentration; the viscosity versus shear rate and viscoelastic modulus versus angular


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frequency for the emulsion containing 10 v% oil phase stabilized by BCNs with different concentration; digital photos of emulsions stabilized by BCNs and BCNs/SA with different concentration and storage time; the influence of concentration of NaCl and pH on the particle size of the Pickering emulsions stabilized by 0.3% BCNs; the influence of concentration of NaCl and pH on the particle size of the Pickering emulsions stabilized by BCNs/SA with BCNs content of 0.3%; the digital photo of SA hydrogel and emulsion hydrogel prepared with the same content of SA. 

AUTHOR INFORMATION

Corresponding Author Dr. Shilin Liu

ORCID: 0000-0002-5077-5539

*E-mail: [email protected]. Dr. Yixiang Wang

ORCID: 0000-0001-8386-7491

E-mail: [email protected]. Dr. Ang Lu

ORCID : 0000-0001-6457-8264

E-mail: [email protected]. Notes The authors declare no competing financial interest. 

ACKNOWLEDGEMENTS



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This work was supported by the project of the Fundamental Research Funds for the Central Universities (2662018PY060). 

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Gong, J. P. Structure Optimization and Mechanical Model for Microgel-Reinforced Hydrogels with High Strength and Toughness. Macromolecules 2012, 45, 5218-5228. (18) Nonoyama, T.; Wada, S.; Kiyama, R.; Kitamura, N.; Mredha, M. T.; Zhang, X.; Kurokawa, T.; Nakajima, T.; Takagi, Y.; Yasuda, K.; Gong, J. P. Double-Network Hydrogels Strongly Bondable to Bones by Spontaneous Osteogenesis Penetration. Adv. Mater. 2016, 28, 6740-6745. (19) Ismail, Y. A.; Shin, S. R.; Shin, K. M.; Yoon, S. G.; Shon, K.; Kim, S. I.; Kim, S. J. Electrochemical Actuation in Chitosan/Polyaniline Microfibers for Artificial Muscles Fabricated Using An in Situ Polymerization. Sensor. Actuat. B-Chem. 2008, 129, 834-840. (20) Pacelli, S.; Rampetsreiter, K.; Modaresi, S.; Subham, S.; Chakravarti, A. R.; Lohfeld, S.; Detamore, M. S.; Paul, A. Fabrication of a Double-Cross-Linked Interpenetrating Polymeric Network (IPN) Hydrogel Surface Modified with Polydopamine to Modulate the Osteogenic Differentiation of Adipose-Derived Stem Cells. ACS Appl. Mater. Interfaces 2018, 10, 24955-24962. (21) Tamesue, S.; Noguchi, S.; Kimura, Y.; Endo, T. Reversing Redox Responsiveness of Hydrogels due to Supramolecular Interactions by Utilizing Double-Network Structures. ACS Appl. Mater. Interfaces 2018, 10, 27381-27390. (22) Bonifacio, M. A.; Cometa, S.; Cochis, A.; Gentile, P.; Ferreira, A. M.; Azzimonti, B.; Procino, G.; Ceci, E.; Rimondini, L.; Giglio, E. Antibacterial Effectiveness Meets Improved Mechanical Properties: Manuka Honey/Gellan Gum Composite Hydrogels



for Cartilage Repair. Carbohyd. Polym. 2018, 198, 462-472. (23) Han, J. W.; Wang, K.; Liu, W. H.; Li, C.; Sun, X. Z.; Zhang, X.; An, Y. B.; Yi, S.; Ma, Y. W. Rational Design of Nano-Architecture Composite Hydrogel Electrode towards High Performance Zn-Ion Hybrid Cell. Nanoscale 2018, 10, 13083-13091. (24) Abandansari, H. S.; Ghanian, M. H.; Varzideh, F.; Mahmoudi, E.; Rajabi, S.; Taheri, P.; Nabid, M. R.; Baharvand, H. In Situ Formation of Interpenetrating Polymer Network Using Sequential Thermal and Click Crosslinking for Enhanced Retention of Transplanted Cells. Biomaterials 2018, 170, 12-25. (25) Wang, X. H.; Song, F.; Qian, D.; He, Y. D.; Nie, W. C.; Wang, X. L.; Wang, Y. Z. Strong and Tough Fully Physically Crosslinked Double Network Hydrogels with Tunable Mechanics and High Self-Healing Performance. Chem. Eng. J. 2018, 349, 588-594. (26) Thomashow, M. F. Plant Cold Acclimation: Freezing Tolerance Genes and Regulatory Mechanisms. Annu. Rev. Plant Physiol. Plant. Mol. Biol. 1999, 50, 571-599. (27) Moellering, E. R.; Muthan, B.; Benning, C. Freezing Tolerance in Plants Requires Lipid Remodeling at the Outer Chloroplast Membrane. Science 2010, 330, 226-228. (28) Takahashi, D.; Imai, H.; Kawamura, Y.; Uemura, M. Lipid Profiles of Detergent Resistant Fractions of the Plasma Membrane in Oat And Rye in Association with


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(35) Zou, S. W.; Wei, Z. J.; Hu, Y.; Deng, Y. H.; Tong, Z.; Wang, C. Y. Macroporous Antibacterial Hydrogels with Tunable Pore Structures Fabricated by Using Pickering High Internal Phase Emulsions as Templates. Polym. Chem. 2014, 5, 4227-4234. (36) Li, W.; Wu, Y. H.; Liang, W.; Li, B.; Liu, S. Reduction of the Water Wettability of Cellulose Film Through Controlled Heterogeneous Modification. ACS. Appl. Mater. Interfaces 2014, 6, 5726-5734. (37) Liu, S. L.; Tao, D. D.; Yu, T. F.; Shu, H.; Liu, R.; Liu, X. Y. Highly Flexible, Transparent Cellulose Composite Films Used in UV Imprint Lithography. Cellulose 2013, 20, 907-918. (38) Wu, Y. H.; Qian, Z. J.; Lei, Y. J.; Li, W.; Wu, X.; Luo, X. G.; Li, Y.; Li, B.; Liu, S. L. Superhydrophobic Modification of Cellulose Film Through Light Curing Polyfluoro Resin in Situ. Cellulose 2018, 25, 1617-1623. (39) Sirviö, J. A.; Kolehmainen, A.; Liimatainen, H.; Niinimäki, J.; Hormi, O. E. Biocomposite Cellulose-Alginate Films: Promising Packaging Materials. Food Chem. 2014, 151, 343-351. (40) Naseri, N.; Deepa, B.; Mathew, A. P.; Oksman, K.; Girandon, L. Nanocellulose-Based Interpenetrating Polymer Network (IPN) Hydrogels for Cartilage Applications. Biomacromolecules 2016, 17, 3714-3723. (41) Chen, L.; Chen, J. S.; Ren, J. Y.; Zhao, M. M. Effects of Ultrasound Pretreatment on the Enzymatic Hydrolysis of Soy Protein Isolates and on the Emulsifying


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Figure 1. Digital photo (left) and AFM image (right) of BCNs aqueous dispersion with concentration of 0.1 wt%.


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-70 -60

Zeta-potential (mv)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-50 -40 -30 -20 -10 0 0.1%BCNs 1:0.5

1:1

1:1.5

1:2

1:2.5

0.1%SA

Ratio BCNs:SA

Figure 2. Effect of BCNs/SA ration on the zeta-potential of the dispersions. The concentration of BCNs was controlled to 0.1 wt%. Inset: digital photos of corresponding dispersions.



Figure 3. Optical microscopy images of emulsions containing 10 v% oil phase stabilized by BCNs/SA dispersions with BCNs concentration of 0.1% (a), 0.2% (b), 0.3% (c), 0.4% (d), and 0.5% (e), respectively. The ratio of BCNs/SA was controlled to 1:1.5 (w/w). (f) Digital photos of BCNs/SA emulsions.


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10

0.1% 0.2% 0.3% 0.4% 0.5%

8

Volume (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6

4

2

0 0.1

1

10

100

Size (m)

1000

10000

Figure 4. Particle size distributions of the emulsions containing 10 v% oil phase stabilized by BCNs/SA dispersions with BCNs concentration of 0.1%, 0.2%, 0.3%, 0.4% and 0.5%. The ratio of BCNs/SA was controlled to 1:1.5 (w/w).



3

10

a

0.1% 0.2% 0.3% 0.4% 0.5%

2

Viscosity (Pa.s)

10

1

10

0

10

-1

10

-2

10

0.1

1

4

10

b

Shear rate (1/s)

10

100

3

10

2

10

G'/G'' (Pa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1

10

0

10

0.1% 0.2% 0.3% 0.4% 0.5%

-1

10

0.1% 0.2% 0.3% 0.4% 0.5%

-2

10

0.1

1

Frequency (Hz)

10

100

Figure 5. The viscosity versus shear rate for the emulsion stabilized by BCNs/SA dispersions with BCNs concentration of 0.1%, 0.2%, 0.3%, 0.4% and 0.5% (a).The ratio of BCNs/SA was controlled to 1:1.5 (w/w). The storage modulus G' (solid


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symbols) and loss modulus G" (open symbols) versus angular frequency of emulsions (b).



Figure 6. Digital photos of emulsions stabilized by BCNs dispersions with concentrations of 0.3% (a) and 0.5% (b); and BCNs/SA dispersions with BCNs concentrations of 0.3% (c) and 0.5% (d). The ratio of BCNs/SA was controlled to 1:1.5 (w/w).


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60

Interfacial tension (mN/m)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.01% BCNs 0.10% BCNs 0.05% BCNs/SA

55

0.05% BCNs 0.01% BCNs/SA 0.10% BCNs/SA

50 45 Sample

40 35

Interfacial tension (mN/m)

BCNs-0.01%

46.77

BCNs-0.05%

40.05

BCNs-0.10%

37.58

BCNs/SA-0.01%

41.72

BCNs/SA-0.05%

40.21

BCNs/SA-0.10%

34.17

30 10

100

1000

5000 6000 7000

Time (s)

Figure 7. Time dependence of interfacial tension at the dodecane-water interface. The water phase contained BCNs or BCNs/SA dispersions with BCNs concentrations of 0.01%, 0.05% and 0.1%, respectively, and the ratio of BCNs/SA was controlled to 1:1.5 (w/w).



35

35

a 2+

20 15 10 5

0

10

20

40

10

10

50

20 15 10 5

35

10

30

40

20 15 10 5

0

10

20

30

Strian (%)

40

50

0.4

0.5

b'

20

10

80

10% oil 20% oil 30% oil

100

30

70

25

50

CaCl 2 concentration (mM)

40

0

50

Strain (%)

c

30

20

Young's modulus (kPa)

0

5 0

50

0.3% BCNs/SA 0.4% BCNs/SA 0.5% BCNs/SA

25

0

15

b

30

0

20

Strain (%)

35

Stress (kPa)

30

25


Stress (kPa)


10 mM Ca 2+ 50 mM Ca 2+ 100 mM Ca

25

0

a'

30

30

Stress (kPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.3

BCNs/SA concentration (wt%)

c'

60 50 40 30 20 10 0

10

20

30

Oil fraction (%)

Figure 8. Compressive stress-strain curves of (a) 10 v% oil in water emulsion hydrogels stabilized by BCNs/SA with BCNs concentration of 0.3 wt%, and treated with Ca2+ concentrations of 10 mM, 50 mM, 100 mM); (b) 10 v% oil in water emulsion hydrogels stabilized by BCNs/SA with BCNs concentration of 0.3 wt%, 0.4 wt%, 0.5 wt%, and treated with 50 mM Ca2+; (c) emulsion hydrogels stabilized by BCNs/SA with BCNs concentration of 0.3 wt% and treated with 50 mM Ca2+, the oil fraction was 10%, 20% and 30%, respectively. (a'), (b') and (c') were for the corresponding compressive modulus at a strain of 50%. The ratio of BCNs/SA was controlled to 1:1.5 (w/w).


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Figure 9. SEM images of emulsions and emulsion hydrogels: (a-c) emulsions stabilized by BCNs/SA with BCNs concentration of 0.1%, 0.3% and 0.5%, respectively; (d-f) emulsion hydrogels stabilized by BCNs/SA with BCNs concentration of 0.1%, 0.3% and 0.5% and crosslinked with 50 mM Ca2+. The ratio of BCNs/SA was 1:1.5 (w/w).



30 25 H2O

20

Temperature (°C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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SA BCNs/SA-10% BCNs/SA-20% BCNs/SA-30%

15 10 5 0 0

10

20

30

40

50

-5

60

70

Time (min)

80

90

100 110 120

-10 -15

Figure 10. Time dependence of temperature of different gels in the continuous thawing

process

at

30

oC.

Ice

(or

water)

was


used

for

comparison.

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Graphical Abstract


W Pickering Emulsion Templated Organo-hydrogels with Enhanced

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