Journal of Science: Advanced Materials and Devices (2018) 296e302 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Dried-state bacterial cellulose (Acetobacter xylinum) and polyvinylalcohol-based hydrogel: An approach to a personal care material N Chunshom a, P Chuysinuan b, S Techasakul b, S Ummartyotin a, * a b Materials and Textile Technology, Faculty of Science and Technology, Thammasat University, Patumtani, Thailand Laboratory of Organic Synthesis, Chulabhorn Research Institute, Bangkok, Thailand a r t i c l e i n f o a b s t r a c t Article history: Received May 2018 Received in revised form 15 June 2018 Accepted 23 June 2018 Available online 28 June 2018 Freeze-dried bacterial cellulose and polyvinyl alcohol were successfully prepared The weight ratios of polyvinyl alcohol to bacterial cellulose were set at 3:1, 5:1 and 10:1 With bacterial cellulose present in the polyvinyl alcohol matrix, H-bonds formed along the cross-linked hydrogel network The freeze-dried hydrogel presented good compatibility The hydrogel was thermally stable up to 200 C Scanning electron microscopy showed that the hydrogel presented an interconnected network containing various pore sizes Preliminary experiments on the swelling behavior of the hydrogel were done in DI water, an NaCl solution and a PBS solution The hydrogel showed good swelling characteristics within 30 Importantly, the freeze-dried hydrogel is an excellent candidate for pharmaceutical and cosmetic materials © 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Bacterial cellulose Freeze dried hydrogel Poly vinyl alcohol Introduction In recent years, hydrogel has been extremely developed for significant interest in biomedical fields Utilization of hydrogel based materials has gained much attraction because of their distinctive properties and benefit of exhibiting the characteristics similar to soft biological tissues [1] Due to the viscoelastic properties and high water content, the hydrogel was employed in various medical researches, such as bone and cartilage repair, drug delivery system, and cosmetics, as well as contact lens From the fundamental point of view, hydrogel can be divided into chemical gels and physical gels It can be defined that physical gel was formed by molecular self-assembly through ionic or hydrogen bond, while chemical gel was formed by covalent bond [2] Up to the present time, numerous polymers have been extensively investigated of the feasibility to become hydrogel One of the most interests was focused on poly(vinyl alcohol) It was considered as a well-known synthetic polymer ascribed to its desirable characteristics, such as water-soluble, nontoxic, transparent and biocompatible properties Our research group has successfully developed poly(vinyl alcohol) for the drug delivery system [3,4] It was found that poly(vinyl alcohol) presented the excellent properties such as its chemical * Corresponding author Fax: ỵ66 25644458 E-mail address: sarute.ummartyotin@gmail.com (S Ummartyotin) Peer review under responsibility of Vietnam National University, Hanoi stability and water-uptake capability Moreover, we have extended the scope of work for the gelatin based composite, and found that the utilization of the gelatin based hydrogel also provided good benefits such as cost effectiveness and degradability [5] However, the use of only neat poly(vinyl alcohol) was still problematic It affected on cell affinity and consequently caused the rejection due to weak adhesion To solve this issue, the design of poly(vinyl alcohol) based composite was considered as an alternative technique To design such a composite, bacterial cellulose was used as an effective reinforcement From the structural point of view, it was composed of nano-sized fibril network It was free from wax, lignin and hemicellulose Moreover, it possessed high tensile strength, low co-efficiency of thermal expansion, and high chemical stability The bacterial cellulose was therefore considered as a filler to design the polymer based composites [6e8] In an attempt to increase the properties of poly(vinyl alcohol) based composites for hydrogel, many scientists found that the bacterial cellulose can be used as a reinforcement material for poly(vinyl alcohol) based hydrogel Wang et al [9] investigated the preparation and the in vitro characteristics of a bacterial cellulose and poly(vinyl alcohol) hydrogel composite Gao et al [10] showed that the presence of bacterial cellulose in a hydrogel network had an effect on the mechanical and rheological properties of the material This effect was related to the numerical prediction [11] Furthermore, Wang et al [12] showed the effect of cellulose in the hydrogel network on the self-healing and antibacterial properties https://doi.org/10.1016/j.jsamd.2018.06.004 2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) N Chunshom et al / Journal of Science: Advanced Materials and Devices (2018) 296e302 297 Although the bacterial cellulose and poly(vinyl alcohol) based composites presented many advantages such as enhanced mechanical properties and thermal stability, they were still limited for the service lifetime of product Water in 3D network of hydrogel can cause a media for fungal and microbial specie As a consequence, the utilization of hydrogel was limited In order to use poly(vinyl alcohol) based hydrogel with higher efficiency, freezedried hydrogel was considered as one of the most effective routes for utilization In 2016, Butylina et al [13] investigated the properties of as-prepared and freeze-dried hydrogel made from poly(vinyl alcohol) and cellulose With pouring water to freeze-dried hydrogel, it was swelled and ready to use The utilization of the dried-state of hydrogel prepared from bacterial cellulose and poly vinyl alcohol can provide many benefits including lightweight, packaging design as well as storage One of the most important applications is focused on personal care cosmetics and treatment The use of the dried hydrogel has extensively been attractive for personal care materials, such as cleansing masks and moisturizer Future application may extend to skincare products, which are daily employed In this work, we investigated the physico-chemical properties of freeze-dried hydrogel prepared from poly(vinyl alcohol) and bacterial cellulose based composites Morphological, thermal, and structural properties of the freeze-dried hydrogel composites were presented The swelling behavior of the composite was also studied agent The reaction was performed at 70 C for h The chemical reaction that occurred between the bacterial cellulose and poly (vinyl alcohol), with 10 wt% of disodium tetraborate, is illustrated in Fig Subsequently, the hydrogel composite was washed with deionized water to remove any unreacted chemicals and stored at C In this experiment, neat poly (vinyl alcohol) was also studied for comparison The ratios of the poly (vinyl alcohol) and bacterial cellulose were set as 3:1, 5:1 and 10:1, respectively To prepare freeze-dried poly (vinyl alcohol) and bacterial cellulose composite, the as-prepared hydrogel composite was undergone a freeze-dry process Drying was performed for hours at a temperature of À80 C in vacuum of 0.12 mbar After the freeze-dry process, the sample was kept in a desiccator in order to prevent the moisture adsorption Experimental Wdry Q g=gị ẳ Wwet Wdry 2.1 Materials Bacterial cellulose was successfully extracted from Nata de coco product (Chaokoh coconut gel in syrup, Ampol Food Processing Ltd., Nakornpathom, Thailand) An indigenous dessert of which main component was reported as bacterial cellulose Characterizations of bacterial cellulose extracted from Nata de coco were carried out in our previous work; its characteristics matched those of bacterial cellulose extracted from the culture of Acetobacter Xylinum [6e8] On the other hand, poly(vinyl alcohol), sodium hydroxide were purchased from Ajax Fine-chem, Co LTD Thailand The average of the molecular weight was estimated to be 10,000 g/ mol Disodium tetraborate with a molecular weight of 381.37 g/ mole was also purchased from Ajax Fine-Chem Co LTD Thailand All chemical reagents were used as received without further purification 2.2 Methods 2.2.1 Bacterial cellulose extraction and purification Bacterial cellulose was extracted from nata de coco, which was rinsed with distilled water to remove excess sugar and blended in a laboratory blender to obtain nata de coco pellicles These pellicles were treated with 0.1 M NaOH at 80 C for h to remove any remaining microorganisms, medium components, and soluble polysaccharides The purified bacterial cellulose was then thoroughly washed with distilled water until a neutral pH was achieved 2.2.2 Preparation of freeze-dried bacterial cellulose and poly (vinyl alcohol) composite Bacterial cellulose and poly (vinyl alcohol) based composite was prepared as hydrogel form and freeze-dried powder To achieve this, poly (vinyl alcohol) was completely dissolved in water, and then a bacterial cellulose suspension was poured into the poly (vinyl alcohol) solution Borax was employed as a crosslinking 2.2.3 Investigation of swelling behavior of freeze-dried bacterial cellulose and poly vinyl alcohol based hydrogel composite The as freeze dried bacterial cellulose and poly vinyl alcohol hydrogel composite was investigated of swelling behavior and gel fraction In this study, the gravimetric technique was employed to determine the swelling and equilibrium data of the hydrogel It was immersed in DI water, 0.1 NaCl solution and PBS solution for h After an appropriate time interval, the specimens were removed from the solution, dried with a filter paper to remove excess solvent, and were measured Five samples were investigated, and the data were reported as the statistical average and standard deviation The swelling ratio was determined as follows (Eq (1)): (1) where Wwet is the weight of a swollen hydrogel at a submersion time, and Wdry is the initial weight of the dry hydrogel 2.3 Instruments 2.3.1 Thermogravimetric analysis The thermal degradation behavior of the freeze-dried hydrogel composite was characterized using TGA (TGA Q500, TA Instruments) In total, 20 mg of the sample was heated from room temperature to 700 C in N2 at a heating rate and a flow rate of C/ and 70 ml/min, respectively 2.3.2 Scanning electron microscopy The freeze dried hydrogel composite was investigated using SEM (SEM, Quanta 250 microscope, Japan) The specimens were gold-coated using a sputtering device (Jeol, JFC-1200) prior to the SEM observation A magnification of 1000Â was used 2.3.3 Fourier transform infrared spectroscopy FTIR spectra were recorded using a Fourier transform infrared spectrometer (PerkinElmer, USA) Spectra were measured at room temperature in the spectral range from 4000 to 400 cmÀ1 with a resolution of ±4 cmÀ1 and a scan frequency of 32 times 2.3.4 X-ray diffraction The crystal structure of the freeze dried hydrogel composite was investigated by X-ray diffraction (XRD, Phillips P.W 1830 diffractometer), which was employed using nickel-filtered CuKa radiation The diffraction patterns were recorded over a range of 10 e80 2.3.5 Differential scanning calorimetry DSC of the freeze dried hydrogel composite was performed from room temperature to 400 C at a heating rate of 10 C/min with a TA-10000 DSC (TA Instruments, DE, USA) The aluminum pan was 298 N Chunshom et al / Journal of Science: Advanced Materials and Devices (2018) 296e302 Fig Schematic diagram of as freeze dried poly(vinyl alcohol) and bacterial cellulose hydrogel composite preparation used for the sample holder The glass transition temperature, melting temperature, and specific heat capacity were determined from the heat flow curve Results and discussion 3.1 Physico-chemical properties of the freeze-dried hydrogel composites Fig presents FTIR spectra of the freeze-dried hydrogel composite The characteristic absorption bands at 1100 cmÀ1 and 1750 cmÀ1 were attributed to CeO stretching and C]O stretching, respectively It was referred to poly vinyl alcohol With the existence of bacterial cellulose, the characteristic cellulose signals of CeOeC pyranose ring skeletal vibration at 1050 cmÀ1 was observed This was similar to that reported by Lin et al [14] It can be implied that the characteristic peak of poly vinyl alcohol was slightly shifted toward that of cellulose in the composite samples The characteristic peak at 2900 cmÀ1 was attributed to CeH stretching of both bacterial cellulose and poly vinyl alcohol The OeH stretching was due to the hydrophilic surface Fig shows the crystal structure of the freeze-dried hydrogel composites Without the water, it was important to note that XRD patterns exhibited a crystalline peak at 2q ¼ 23 corresponding to the (200) crystal plane, which was coincided with the result reported by Yan et al [15] When bacterial cellulose has been inserted into the freeze-dried poly vinyl alcohol based composite, the intensity of the bacterial cellulose peak became stronger It can be suggested that the relative degree of crystallinity of the freezedried hydrogel composite was significantly increased The role of Fig FTIR patterns of the freeze-dried hydrogel composites with various PVA to BC ratios N Chunshom et al / Journal of Science: Advanced Materials and Devices (2018) 296e302 Fig XRD patterns of the freeze-dried hydrogel composites with various PVA to BC ratios bacterial cellulose in the freeze-dried hydrogel composite was to provide the good mechanical and thermal properties The amorphous region of polyvinyl alcohol was reduced due to the addition of bacterial cellulose It can be implied that there is an occurrence reaction between polyvinyl alcohol and bacterial cellulose Fig exhibits the thermal decomposition of the freeze-dried hydrogel composite Neat polyvinyl alcohol was provided for comparison Thermal decomposition of the freeze-dried hydrogel can be categorized into three different regions From room temperature to 250 C, the thermal decomposition was involved in water evaporation approximately 10 %wt of weight loss was observed, suggesting that the weight loss was ascribed to the loss of free and bound water It was important to note that freeze-dried hydrogel was easy to adsorb moisture This is consistent with what was discussed by Qi et al [16] After that, with the increment on temperature to 250e500 C, the weight loss was attributed to decomposition of polyvinyl alcohol and bacterial cellulose The decomposition curve of the neat polyvinyl alcohol was shifted toward a slightly higher 299 temperature This also indicated that with the existence of bacterial cellulose, the composite presented higher thermal stability as also suggested by Saba et al [17] Bacterial cellulose has high melting temperature and it consequently provided high thermal stability for the composite It was notable that both the polyvinyl alcohol and composite exhibited two steps of degradation In the temperature region of 300e400 C, the weight loss was due to the elimination of the residual water trapped in the polyvinyl alcohol and bacterial cellulose Within the temperature region of 400e500 C, it was involved in the decomposition of both polyvinyl alcohol and bacterial cellulose They changed to CO2 The evaporation of water and CO2 has been observed as pathway of the evaporation It presented as a porous structure With the temperature above 500 C, the decomposition was terminated 10e20 %wt of yield was observed as a residual It can be also implied that with the existence of bacterial cellulose, higher percent yield of residual was observed, suggesting that bacterial cellulose provided higher thermal stability to the composite From the TGA curves, it can be concluded that there is no change in thermal stability on the utilization of the freeze-dried hydrogel at room temperature Fig exhibits the DSC curves of the freeze-dried hydrogel composites It was important to note that the glass transition temperature of neat polyvinyl alcohol was estimated to be 70 C, which was very much close to the reported value (about 68 C) [18] With the existence of bacterial cellulose, the glass transition temperature of the polyvinyl alcohol based composite was slightly shifted to a higher value It can be implied that strong interaction between bacterial cellulose and polyvinyl alcohol occurred as suggested by Jipa et al [19] In addition, the melting temperature of the freeze-dried hydrogel composite was investigated The endothermic peak was estimated to be 320 C This temperature can be used to explain conformational changes within the polymer network It may involve the size of the crystallites and the degree of crystallinity as suggested by Hassan et al [20] It was remarkable to note that as compared with neat poly vinyl alcohol; the melting point of the composite was slightly higher It could be attributed to the dissociation process of inter- and intra-hydrogen bonding Fig Thermal stability of the freeze-dried hydrogel composites 300 N Chunshom et al / Journal of Science: Advanced Materials and Devices (2018) 296e302 Fig DSC thermograms of the freeze-dried hydrogel composites between bacterial cellulose and polyvinyl alcohol The increment on the melting temperature of the composite indicated that the incorporation of bacterial cellulose weakened the interaction between poly vinyl alcohol chain and hindered the crystallization of poly vinyl alcohol This discussion was fully supported by the XRD data and analysis Fig depicts the SEM images revealing the morphological properties of the freeze-dried bacterial cellulose and poly vinyl alcohol based hydrogel composites It was important to note that the hydrogel based composite exhibited an interconnected porous structure with a regular pore distribution The average pore size declined with increment on poly vinyl alcohol content The pore Fig SEM micrographs of the freeze-dried hydrogel composites: (A) neat poly vinyl alcohol, (B) 3:1 ratio of poly vinyl alcohol and bacterial cellulose, (C) 5:1 ratio of poly vinyl alcohol and bacterial cellulose, (D) 10:1 ratio of poly vinyl alcohol and bacterial cellulose N Chunshom et al / Journal of Science: Advanced Materials and Devices (2018) 296e302 size was therefore ranging from 10 mm to 100 nm Various pore sizes provided a better explanation for the swelling capacity and water evaporation characteristics of the freeze-dried hydrogel composites With the existence of bacterial cellulose, the physical crosslinking density of the hydrogel composite increased, causing the water content in the hydrogel composite to decrease However, from the fundamental point of view, in a freeze dry process, free water was frozen into larger ice crystals which were eventually represented by larger pores This discussion was in agreement with that of Dinu et al [21] These results are considered an important relationship in tuning of the size distribution, which can facilitate permeation of cellular growth factors when the freeze-dried hydrogel composite is employed as a medical material 301 3.2 Swelling properties of the freeze-dried hydrogel composites Fig presents the swelling behavior of the as freeze-dried bacterial cellulose and poly vinyl alcohol based hydrogel composites The experiment was set up based on swelling behavior on DI water, 0.1 NaCl solution and PBS solution, respectively From the fundamental point of view, lesser cross-linked hydrogel exhibited higher water uptake ability, due to the highly crosslinked structure that could not sustain much water within a hydrogel structure In our experiment, the neat poly vinyl alcohol was provided for comparison It was remarkable that poly vinyl alcohol was easy to dissolve in three different media With the existence of bacterial cellulose, the swelling behavior of the as freeze dried hydrogel was determined This phenomenon was attributed to the hydrophilic nature of bacterial cellulose and poly vinyl alcohol [22] However, with the increment on the fraction of bacterial cellulose, the decrease on the swelling behavior of the as freeze dried hydrogel probably occurred due to the reinforcing effect of the bacterial cellulose It was considered as a nanoreinforcing element in the poly vinyl alcohol matrix, restraining the swelling mechanically, resulting in a decrease of water and solvent adsorption at higher bacterial cellulose addition levels This discussion was fully consistent with that of Naizi et al [23] Compared to different solutions, the swelling behaviors of the as freeze dried bacterial cellulose and poly vinyl alcohol hydrogel were lesser This was due to less amount of free ion in the solutions The hypothesis of swelling behavior in different solutions was set up based on ionic strength of the medium that had a vital influence on the swelling capabilities of the as freeze dried bacterial cellulose and poly vinyl alcohol hydrogel It may involve in interaction either through surface adsorption or hydrogen bonding between bacterial cellulose and poly vinyl alcohol as suggested by Mandal et al [24] It was important to note that only in DI water, the swelling behavior was significantly less DI water is in neutral pH and there is no ion to adhere on the functional group of bacterial cellulose and poly vinyl alcohol based hydrogel Compared to 0.1 NaCl and PBS solution, there were positive and negative free ions in the solutions, they were consequently dissolved and adhered on the functional group of bacterial cellulose and poly vinyl alcohol based hydrogel Higher swelling ratios were therefore observed Conclusion Fig Swelling behaviors of (A) DI water, (B) 0.1 M NaCl solution, (C) PBS solution of the freeze-dried hydrogel composites The physico-chemical properties of the as-freeze dried bacterial cellulose and poly vinyl alcohol composites were investigated It was found that the properties of the as-freeze dried hydrogel could be modified by adding bacterial cellulose into the poly vinyl alcohol network The 3:1 ratio of the poly vinyl alcohol and bacterial cellulose presented the outstanding swelling behavior The freeze dry technique was used to remove water from hydrogel network It resulted in shrinkage of the hydrogel composite The presence of bacterial cellulose had an important effect on pore size as observed by scanning electron microscope The high amount of bacterial cellulose in the hydrogel composite could form the interaction between poly vinyl alcohol networks, suggesting that the high gel fraction could be obtained No obvious change in the crystallinity of hydrogel was found after the addition of bacterial cellulose For potential biomedical applications of hydrogel, it presented the excellent characteristic in high water absorption The utilization of the freeze-dried hydrogel can be beneficial for the design and point of care product for patients It should be further employed and developed for pharmaceutical technology and cosmetic products 302 N Chunshom et al / Journal of Science: Advanced Materials and Devices (2018) 296e302 Acknowledgments The authors would like to acknowledge the financial support provided by Thammasat University (2018) We are grateful for the space and research facilities supported by the Chulabhorn Research Institute Special thank was extended to Plastic Institute of Thailand References [1] K Varaprasad, et al., A mini review on hydrogels classification and recent developments in miscellaneous applications, Mater Sci 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Thanyacharoen, et al., Development of a gallic acid-loaded chitosan and polyvinyl alcohol hydrogel composite: release characteristics and antioxidant activity, Int J Biol Macromol 107 (Part A) ... (2016) 554e559 [3] T Thanyacharoen, et al., The chemical composition and antioxidant and release properties of a black rice (Oryza sativa L.)-loaded chitosan and polyvinyl alcohol composite, J... et al / Journal of Science: Advanced Materials and Devices (2018) 296e302 297 Although the bacterial cellulose and poly(vinyl alcohol) based composites presented many advantages such as enhanced