Carbon/gelatin/Ce (CGCe) composite was prepared with high antimicrobial activity. And the structure, thermal property, and antimicrobial activity of the composite were investigated. The research results showed that CGCe has a higher thermal property and antimicrobial activity against S. aureus and E. coli compared with CG. The influences of molecular weight of gelatin, pH, and concentration of Ce (III) on the antimicrobial activity were discussed, and the IC50, MIC, and MBC against S. aureus of CGCe are 185??m·mL-1, 525??m·mLl-1, and 700??m·mL-1, respectively, and the IC50, MIC, and MBC against E. coli of CGCe are 255??m·mL-1, 700??m·mL-1, and 1050??m·mL-1, respectively.

1. Introduction

Gelatin, which is mainly derived from land animals and fish-processing by-products, including skin, bone, tendon, and scale, has many excellent physical and chemical properties, such as good adhesion, dispersibility, and biocompatibility [1–4]. Thus, gelatin is widely used in food, health care, medicine, and other fields [5–7]. The applications of gelatin in the electrode and ink are hot research areas [3, 8–10]. However, due to the high nutrition of gelatin, it is easy to breed bacteria in the humid environment. So the application of CG has been restricted.

In recent years, rare earth cerium element and its complexes have attracted the worldwide attention because of their high medical value [11, 12]. Rare earth composite materials can play the role in antibacterial, anti-inflammatory, anticoagulant, prevention and treatment of cancer, and arterial hardening [13–15].

Besides, rare earth elements also have the characteristics of low toxicity, weak accumulation, no teratogenic changes, and no smell [16]. The related reports studied the preparation of complexes with gelatin and rare earth cerium, confirming that the antibacterial properties of gelatin solution were improved by using cerium, and the gelatin cerium complex had good antibacterial properties [17, 18]. However, the CG compounded with rare earth, which can improve the antibacterial property, is rarely reported. In this paper, we used gelatin and cerium nitrate as raw materials to prepare gelatin/cerium complex solution and then combined gelatin, cerium, and carbon materials to prepare CGCe. We discussed the antibacterial properties of CGCe and tested the properties of CGCe used as Chinese ink.

2. Materials and Methods2.1. Materials

Provided gelatin was purchased from Rousselot Co. (Guangdong, China). Cerium(III) nitrate hexahydrate was supplied by QinXi Chemical Co. (Shanghai, China). The carbon ink was supplied by Yidege Ink Industry Co. (Beijing, China); nutrient agar was supplied by Luqiao, Beijing; Staphylococcus aureus and Escherichia coli were supplied by Tianjin Centers for Disaster Control and Prevention. Other reagents were all used for purity analysis.

2.2. Preparation of CGCe

0.217?g Ce(NO3)3 was dissolved in 5?mL deionized water and the different pH was adjusted. Then, the Ce(NO3)3 solution was added to the gelatin solution (2?wt.%, 45?mL), and the mixed solution was placed in a water bath at 60°C for 4?h to achieve a homogeneous system. Then, 3.6?g of the gelatin cerium complex solution was added with 0.1?g carbon ink and a certain amount of Turkey red oil and glycerol and placed in a ball mill for several hours to prepare the CGCe composite solution. And the CGCe composite solution was further dried to prepare CGCe.

2.3. Structural Characterization of CGCe

The CGCe composite solution was dried to form a film. Then, the CGCe film was cut into strips as CGCe film samples. The infrared absorption spectrum of the CGCe film was tested by Fourier-transform infrared spectrometer (Nexus 670, Nicolet, USA), and the wave number range was 4000-400?cm-1. The CGCe composite solution was diluted to a fixed multiple and measured by UV-vis spectrophotometer (TU-1810, UNICO, USA) at a range of wavelength from 200 to 400?nm. The thermal property of CGCe was measured by a thermogravimetric analyser (HCT-1, China) from 25°C-800°C.

2.4. Antibacterial Properties of CGCe

The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of CGCe were tested by the colony counting method. The bacterial solutions separately inoculated with S. aureus and E. coli were incubated at 37° C for 24?h and diluted to ?CFU/mL. The bacterial solutions were inoculated to the nutrient agar in the Petri dish, and CGCe solutions with different concentrations were added. After incubation at 37°C for 24?h, the growth of colonies in the culture dish was observed. The lowest concentration of the CGCe solution that completely inhibited the growth of colonies was determined as MIC. The highest concentration of the CGCe solution that exhibited no bacterial growth on agar plates after incubation at 37°C for another 18?h was identified as the MBC. Lasting antibacterial properties of CGCe were determined by the agar digging method, and the inhibition zone diameters were measured in a time range of 12-96?h. The half-maximal inhibitory concentration (IC50) of CGCe was evaluated by the serial dilution method, and the optical density measured at 600?nm using pan-wavelength microplate spectrophotometer (Molecular Devices, America).

2.5. Influence Factors of Antibacterial Properties of CGCe

We changed the molecular weight of gelatin, pH of system, and the concentration of Ce(III), then tested the antimicrobial activity of CGCe.

2.6. Application Test of CGCe Ink

CGCe was applied as an antibacterial ink, and its properties were tested as follows and compared with commercial ink (commercial 1 and 2): the blackness by reflection densitometer (MN-B2, China), the particle size by DLS (Omni, USA), the writing to observe carbon distribution by biologic photomicroscope (SG-1100, China), the water resistance activity by water bath method, the wettability by water contact angle method; the antimicrobial properties by the colony counting method and agar digging method, and the writing properties were tested.

3. Results and Discussion3.1. Characterization of CGCe

Previous researches demonstrated that there are three coordinate sides in gelatin which may react: oxygen in -COOH in side chains, nitrogen in -NH2, and nitrogen in -CONH2. When the pH is at about 4.6, the carboxyl group could react with Ce(III). It can be obviously seen that the FTIR spectra (Figure 1) of the CGCe are different from those of the CG: the amide I band shifted from 1454.34?cm-1 to 1450.16?cm-1; the amide II band shifted from 1639.28?cm-1 to 1673.46?cm-1. (difference of symmetric carboxyl and antisymmetric carboxyl) changed to 223.30?cm-1, which proved that Ce(III) reacted with the carboxyl group in side chains of gelatin.

Figure 1: FTIR spectra of CG and CGCe.

The UV-vis spectra (Figure 2) show that the gelatin/C composite displayed a distinct absorption peak at 230?nm and a weak absorption peak at 250?nm. In contrast, curve B shows that CGCe displayed a broad and sharper absorption peak at 230?nm and a sharper absorption peak at 250?nm, which might be attributed to the reaction between gelatin and Ce(III).

Figure 2: UV-vis spectra of CG and CGCe.

The TGA curves (Figure 3) revealed that the onset thermal-decomposed temperature between CG and CGCe has obviously improved by 69.4°C (from 272.1°C to 341.5°C), which demonstrated that the thermal stability had been improved due to the electrostatic crosslinking effect of Ce(III).

Figure 3: TGA test of CG and CGCe.3.2. Antibacterial Qualitative Analysis of CGCe

The result of antibacterial activity qualitative experiment against S. aureus and E. coli of gelatin, CG, and CGCe tested by the colony counting method (Figure 4) showed that the Petri dishes of gelatin and CG had obvious growth of bacteria, while the Petri dishes of CGCe had no bacteria, which can indicate that Ce(III) can improve the antibacterial activity of CGCe.

Figure 4: Antimicrobial qualitative test: ((1) gelatin; (2) CG; (3) CGCe; (a) S. aureus; (b) E. coli).3.3. Antibacterial Property of CGCe

The antibacterial properties of CGCe obtained from different gelatin molecular weights are shown in Figure 5. It displays that with the increase of gelatin molecular weight, the inhibition zones of CGCe decreased. It is because CGCe that is prepared with low-Mw gelatin has a low molecular weight, which can help the Ce-gelatin/C composite penetrate the lipid layer in cell membranes of bacteria more easily to retard bacterial growth.

Figure 5: Influence of Mw of gelatin on antimicrobial activity.

The effect of CGCe prepared by different pH systems on the antibacterial property is shown in Figure 6. With the increase of pH, the diameters of the inhibitory zone of CGCe against S. aureus and E. coli decreased first when the pH value is in the range of 2.6-4.6. The inhibition zone got lowest when . After that, the diameters of the inhibition zone on the two bacteria began to increase with the further increase of the pH value. The reason is that is the isoelectric point of gelatin and CGCe has the lowest solubility. So CGCe can hardly penetrate the glycerophospholipid bilayer in cell membranes of bacteria, which lead to a lower antibacterial property.

Figure 6: Influence of pH on antimicrobial activity.

Figure 7 shows the antibacterial activity of CGCe at different Ce(III) concentrations. It displays that with the increase of concentration of Ce(III), the inhibition zones against S. aureus and E. coli of CGCe were higher. It is indicated that with the addition of effective inhibitory substance Ce(III), the inhibitory effect of CGCe on bacteria is more obvious.

Figure 7: Influence of concentration of Ce(III) on antimicrobial activity.3.4. IC50, MIC, and MBC

Figure 8 and Table 1 show that the IC50, MIC, and MBC against S. aureus of CGCe are 185??g·mL-1, 525??g·mL-1, and 700??g·mL-1, respectively. And the IC50, MIC, and MBC against E. coli of CGCe are 255??g·mL-1,700??g·mL-1, and 1050??g·mL-1, respectively. These results suggest that the antimicrobial activity of CGCe can be improved with the added small quantity of Ce(III).

Figure 8: Inhibition rate of CGCe against S. aureus and E. coli.Table 1: IC50, MIC, and MBC of CGCe.3.5. Long-Lasting Antibacterial Property

The long-lasting antimicrobial properties of CGCe were tested. The result shows (see Figure 9) that 96 hours later, the inhibition zones against S. aureus and E. coli could still keep 89.3% and 89.5% of the 12-hour data, which indicated that CGCe had an excellent long-lasting antimicrobial activity.

Figure 9: Long-lasting antibacterial property of CGCe.

From the above antibacterial test results, it can be seen that CGCe has better antibacterial activity against S. aureus than E. coli. It may be because the cell wall of the Gram-positive bacteria consists of 90% peptidoglycan (a complex polysaccharide network) whereas that of the Gram-negative bacteria contains only 10% of this polysaccharide and S. aureus retains a greater amount of CGCe in the cell wall, helping to make the zone of inhibition wider.

3.6. Antibacterial Ink with CGCe

Tables 2 and 3 show that the blackness of commercial ink 1, commercial ink 2, and CGCe ink were 1.357, 1.510, and 1.452. The centrifugal blackness was 1.353, 1.459, and 1.358. The blackness of the CGCe ink was as good as that of the commercial ink and better than commercial 1. The standard for ink (QB/T 2860-2007) describes that the blackness of common ink, middling ink, and high-quality ink has to be equal or greater than 1.35, 1.40, and 1.45, respectively, and the centrifugal blackness of middling ink or high-quality ink has to be equal or greater than 90% of the original blackness. Therefore, the CGCe ink could satisfy the demand of standard for high-quality ink.

Table 2: Color test results of the ink.Table 3: Color test results of the ink after centrifugation.

The particle size and dispersity of different inks (Table 4) showed that the particle size of the CGCe ink was larger than that of the commercial ink, which means the fineness needs to be refined. The dispersity of the CGCe ink was smaller than that of the commercial ink, indicating that the CGCe ink dispersed better.

Table 4: Particle size and dispersity of different inks.

The distribution of carbon in the different ink writings was observed by an optical microscope at 400 times (Figure 10). It can be seen that carbon in the commercial 1 ink was less, and the blank area was obvious, indicating that the carbon distribution was not uniform enough; that of commercial 2 was more, but the blank regional was still obvious; the adhesion of carbon in the CGCe ink writing was sufficient and uniform; also, the blank area was inconspicuous.

Figure 10: OM image of different ink ((a) commercial 1; (b) commercial 2; (c) CGCe ink).

The standard for ink (QB/T 2860-2007) describes that after soaking in water (paper written with ink) for 6 hours, the solution can still keep clear at room temperature. The results show that the three inks can meet all the requirements (Figure 11). To compare the specific distinction among different inks in water-resistant activity, the temperature was improved from 40°C to 50°C. With the temperature increased, the rate of losing ink has increased (Figure 11 and Table 5). At the same temperature, the rate of losing ink of the CGCe ink was lower than that of the commercial ink, which explained that the modified antibacterial ink had a good water-resistant activity.

Figure 11: Water resistance test of different inks ((A) commercial 1; (B) commercial 2; (C) CGCe ink).Table 5: Rate of losing of different inks.

The water contact angle of the commercial 1 ink, commercial 2 ink, and CGCe ink was 44.5°, 44.0°, and 44.5°(Figure 12) and showed that the wetting properties of the CGCe ink is as good as that of the commercial ink because glycerol and Turkey red oil are both surface-active agents and can improve the wetting property of the CGCe ink.

Figure 12: Water contact angle of different inks ((a) commercial 1; (b) commercial 2; (c) CGCe ink).

According to Figures 13 and 14, the Petri dishes of the commercial ink had obvious growth of bacteria and had no obvious inhibition zones, while the Petri dishes of the CGCe ink had no growth of bacteria and obvious inhibition zones, which indicated that the CGCe ink had a better antibacterial activity than the commercial ink against S. aureus and E. coli. Meanwhile, the CGCe ink used Ce(III) instead of phenol; therefore, it had higher biosecurity.

Figure 13: Antimicrobial qualitative test ((1) commercial 1; (2) commercial 2; (3) CGCe ink; (a) S. aureus; (b) E. coli).Figure 14: Inhibition zone test ((1) commercial 1; (2) commercial 2; (3) CGCe ink; (a) S. aureus; (b) E. coli).

According to Table 6, the writing image of different inks showed that the CGCe ink was as good as the commercial ink. The CGCe ink had a good sense of depth and a good blackness and can be used to write smoothly; meanwhile, it can dry rapidly and the wring had no granular sensation and better than the commercial 2 ink. It can be concluded that CGCe ink can be used in practical application.

Table 6: Writing activity test of different inks.4. Conclusions

The antibacterial activity of CG has been improved using Ce(III) as an additive. The results of the FTIR spectra and UV-vis spectra tests showed that the O of -COOH on the side chains of gelatin reacted with Ce(III) to form a coordination structure.

CGCe has a relatively high thermal stability and antibacterial activity and a good antimicrobial durability against S. aureus and E. coli.

The results showed that the IC50, MIC, and MBC against S. aureus of CGCe are 185??g·mL?1,525??g·mL?1, and 700??g·mL?1, respectively, and the IC50, MIC, and MBC against E. coli of CGCe are 255??g·mL?1,700??g·mL?1, and 1050??g·mL?1, respectively.

The CGCe ink was as good as the commercial ink and shows better antibacterial activity and biosecurity than the commercial ink.

Data Availability

The data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

Acknowledgments

This work was supported by the China Postdoctoral Science Foundation (no. 2018M631527).

References

1. H. Li, Y. Xia, J. Wu et al., “Surface modification of smooth poly (l-lactic acid) films for gelatin immobilization,” ACS Applied Materials & Interfaces, vol. 4, no. 2, pp. 687–693, 2012. View at Publisher · View at Google Scholar · View at Scopus
2. L. Ge, M. Zhu, X. Li et al., “Development of active rosmarinic acid-gelatin biodegradable films with antioxidant and long-term antibacterial activities,” Food Hydrocolloids, vol. 83, pp. 308–316, 2018. View at Publisher · View at Google Scholar · View at Scopus
3. Y. Wang, Y. Guan, Y. Yang, P. Yu, and Y. Huang, “Enhancing the stability of immobilized catalase on activated carbon with gelatin encapsulation,” Journal of Applied Polymer Science, vol. 130, no. 3, pp. 1498–1502, 2013. View at Publisher · View at Google Scholar · View at Scopus
4. S. A. Jang, Y. J. Shin, and K. B. Song, “Effect of rapeseed protein-gelatin film containing grapefruit seed extract on ‘Maehyang’ strawberry quality,” International Journal of Food Science & Technology, vol. 46, no. 3, pp. 620–625, 2011. View at Publisher · View at Google Scholar · View at Scopus
5. Q. Lu, S. Zhang, M. Xiong et al., “One-pot construction of cellulose-gelatin supramolecular hydrogels with high strength and pH-responsive properties,” Carbohydrate Polymers, vol. 196, pp. 225–232, 2018. View at Publisher · View at Google Scholar · View at Scopus
6. A. Meimandi-Parizi, A. Oryan, and H. Gholipour, “Healing potential of nanohydroxyapatite, gelatin and fibrin-platelet glue combination as tissue engineered scaffolds in radial bone defects of rats,” Connective Tissue Research, vol. 59, no. 4, pp. 332–344, 2018. View at Publisher · View at Google Scholar · View at Scopus
7. S. M. Noorbakhsh-Soltani, M. M. Zerafat, and S. Sabbaghi, “A comparative study of gelatin and starch-based nano-composite films modified by nano-cellulose and chitosan for food packaging applications,” Carbohydrate Polymers, vol. 189, pp. 48–55, 2018. View at Publisher · View at Google Scholar · View at Scopus
8. H. Onishi, “Ink set and ink cartridge and recording method, recording material and recording apparatus,” 2001. View at Google Scholar
9. H. A. Rather, R. Thakore, R. Singh, D. Jhala, S. Singh, and R. Vasita, “Antioxidative study of cerium oxide nanoparticle functionalised PCL-gelatin electrospun fibers for wound healing application,” Bioactive Materials, vol. 3, no. 2, pp. 201–211, 2018. View at Publisher · View at Google Scholar · View at Scopus
10. M. Naseri-Nosar, S. Farzamfar, H. Sahrapeyma et al., “Cerium oxide nanoparticle-containing poly (?-caprolactone)/gelatin electrospun film as a potential wound dressing material: in vitro and in vivo evaluation,” Materials Science and Engineering: C, vol. 81, pp. 366–372, 2017. View at Publisher · View at Google Scholar · View at Scopus
11. A. A. A. Mohamed, M. F. Bakr, and K. A. Abd el-Fattah, “Thermodynamic studies on the interaction between some amino acids with some rare earth metal ions in aqueous solutions,” Thermochimica Acta, vol. 405, no. 2, pp. 235–253, 2003. View at Publisher · View at Google Scholar · View at Scopus
12. L. Paciello, F. C. Falco, C. Landi, and P. Parascandola, “Strengths and weaknesses in the determination of Saccharomyces cerevisiae, cell viability by ATP-based bioluminescence assay,” Enzyme and Microbial Technology, vol. 52, no. 3, pp. 157–162, 2013. View at Publisher · View at Google Scholar · View at Scopus
13. Y. Huang, T. Wei, and Y. Ge, “Preparation and characterization of novel Ce(III)-gelatin complex,” Journal of Applied Polymer Science, vol. 108, no. 6, pp. 3804–3807, 2008. View at Publisher · View at Google Scholar · View at Scopus
14. A. Karimi, S. W. Husain, M. Hosseini, P. A. Azar, and M. R. Ganjali, “Rapid and sensitive detection of hydrogen peroxide in milk by enzyme-free electrochemiluminescence sensor based on a polypyrrole-cerium oxide nanocomposite,” Sensors and Actuators B Chemical, vol. 271, pp. 90–96, 2018. View at Publisher · View at Google Scholar · View at Scopus
15. D. A. Agarkov, M. A. Borik, S. I. Bredikhin et al., “Structure and transport properties of zirconia-based solid solution crystals co-doped with scandium and cerium oxides,” Russian Journal of Electrochemistry, vol. 54, no. 6, pp. 459–463, 2018. View at Publisher · View at Google Scholar · View at Scopus
16. X. Gan, Z. Yu, K. Yuan et al., “Effects of cerium addition on the microstructure, mechanical properties and thermal conductivity of YSZ fibers,” Ceramics International, vol. 44, no. 6, pp. 7077–7083, 2018. View at Publisher · View at Google Scholar · View at Scopus
17. C. Huang, Y. Huang, N. Tian, Y. Tong, and R. Yin, “Preparation and characterization of gelatin/cerium(III) film,” Journal of Rare Earths, vol. 28, no. 5, pp. 756–759, 2010. View at Publisher · View at Google Scholar · View at Scopus
18. F. M. Ali, R. M. Kershi, M. A. Sayed, and Y. M. AbouDeif, “Evaluation of structural and optical properties of Ce 3+, ions doped (PVA/PVP) composite films for new organic semiconductors,” Physica B: Condensed Matter, vol. 538, pp. 160–166, 2018. View at Publisher · View at Google Scholar · View at Scopus

» Author: Tengfei Yu,1 Yang Guo,2 Bin Ning,1 Peiyi Gao,1 and Yaqin Huang2

» Reference: International Journal of Polymer ScienceVolume 2019, Article ID 3901572, 8 pageshttps://doi.org/10.1155/2019/3901572

» Publication Date: 12/02/2019

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