Agar-tragacanth/silk fibroin hydrogel containing Zn-based MOF as a novel nanobiocomposite with biological activity

In this study, a novel nanobiocomposite consisting of agar (Ag), tragacanth gum (TG), silk fibroin (SF), and MOF-5 was synthesized and extensively investigated by various analytical techniques and basic biological assays for potential biomedical applications. The performed Trypan blue dye exclusion assay indicated that the proliferation percentage of HEK293T cells was 71.19%, while the proliferation of cancer cells (K-562 and MCF-7) was significantly lower, at 10.74% and 3.33%. Furthermore, the Ag-TG hydrogel/SF/MOF-5 nanobiocomposite exhibited significant antimicrobial activity against both E. coli and S. aureus strains, with growth inhibition rates of 76.08% and 69.19% respectively. Additionally, the hemolytic index of fabricated nanobiocomposite was found approximately 19%. These findings suggest that the nanobiocomposite exhibits significant potential for application in cancer therapy and wound healing.

www.nature.com/scientificreports/different functional groups of the polymers.In this research, glutaraldehyde, an organic cross-linker, was used to form the Ag-TG hydrogel.Glutaraldehyde links two desired polymer chains through its two aldehyde functional groups 24 .This cross-linking process results in the development of a three-dimensional hydrogel structure with interconnected pores, enhancing its stability and porosity.Another advantage of these hydrogels is their ability to incorporate with other biological macromolecules, such as nucleic acids and proteins, which will improve their biomedical applications.In recent years, SF has gained significant attention among researchers as a natural protein with versatile properties.It can be combined with various components, making it an attractive material for a wide range of applications 25 .SF is derived from the Bombyx mori, commonly known as the silkworm.SF predominantly comprises two principal proteins, fibroin and sericin 26 .The adhesive sericin is a twisted protein around fibroin, and it can be isolated from the SF by different methods.Biocompatibility, non-cytotoxicity, antibacterial activities, high mechanical performance, and sufficient production provide the usage of SF in vast fields, such as drug delivery, gene therapy, wound healing, and bone and vascular tissue regeneration [27][28][29] .All natural biomacromolecules used in Ag-TG hydrogel/SF composite are biodegradable and can be broken down by enzymes or microorganisms 30 .Biodegradable hydrogels are designed to degrade over time, either through enzymatic or hydrolytic processes, allowing for the controlled release of drugs within the body 31 .One crucial biological characteristic that distinguishes composites from other materials is their ability to exhibit an antibacterial activity, which can be induced by utilizing various metal-organic frameworks (MOFs) 32 .MOFs are highly porous hybrid materials consisting of inorganic metal ions and organic ligands.These structures have garnered considerable attention due to their versatility and wide applications in the field of biotechnology 33 .Previous studies have displayed that MOFs operate as third-generation antibacterial agents through controlled ion release and interaction with bacteria cell walls 34 ; thus, combining MOF-5 with Ag-TG/SF hydrogel enhances its antibacterial properties.MOF-5, also known as IRMOF-1, is a three-dimensional cubic porous framework with the chemical formula [Zn 4 O(BDC) 3 ].Its exceptional surface area makes it highly suitable for various applications, including biosensing, gas storage, and drug release [35][36][37] .
In this study, a novel nanobiocomposite based on Ag, TG, glutaraldehyde, SF, and MOF-5 was prepared in a facial approach, then its proliferation, lytic effect on cells, and the antibacterial activity were investigated by trypan blue exclusion, hemolysis, and antibacterial assays.The proliferation percentage of HEK293T, MCF-7, and K-562 cells indicated that the Ag-TG hydrogel/SF/MOF-5 nanobiocomposite exhibited an anticancer effect against cancer cells.In addition, a significant decrease in bacterial growth was observed for both E. coli and S. aureus strains, with inhibition rates of 76.08% and 69.19% respectively.The results demonstrate that this novel nanobiocomposite is an appropriate candidate for wound healing and cancer therapy applications.

Preparation of Ag-TG hydrogel
Initially, the experimental procedure involved the dissolution of Ag (0.5g) and TG (0.5g) in 50 mL of distilled water individually.Subsequently, two drops of an HCl solution (37 wt.%) were added to the resultant mixture.Afterward, the entirety of the prepared solution was stirred for 30 min at 70 °C until effective homogenization of the respective polymers was achieved.In the experimental method shown in Fig. 1a, 2 mL of glutaraldehyde was added dropwise to the final solution with a time interval of 10 min.The solution was then kept under stirring conditions for 12 h at 70 °C.

Extraction of SF
According to the previous studies 38 , at first, three pieces of silkworm cocoons were boiled in 500 mL of aqueous Na 2 CO 3 solution (0.025 M) for 2 h until the yellow sericin protein was separated; then, the degummed white cocoons were cleanly washed three times with distilled water and were dried in ambient conditions.After completely drying fibroin protein fibers, they were weighed (0.583 g) and then dissolved in LiBr aqueous solution with a concentration of 9.3 M.This dissolution process was carried out for 2 h at 60 °C.The solution was dialyzed by an appropriate dialysis cellulose membrane for three days with frequent exchange of distilled water.This dialysis process effectively removed LiBr from the solution during the rehydration process.After the mentioned time, the extracted SF was provided for the next steps (Fig. 1b).

Nanobiocomposite extraction for biological assays
The extraction process involved dissolving 50 mg of the Ag-TG/SF/MOF-5 nanobiocomposite in 1 ml of PBS.The dissolution was carried out in a shaker incubator at 37 °C for 48 h 40,41 .

Trypan blue exclusion test
To investigate the biocompatibility and anticancer activity of the Ag-TG/SF/MOF-5 nanobiocomposite, three cell lines were used: HEK293T (human embryonic kidney cell line), MCF-7 (human breast cancer cell line), and K-562 (human erythroleukemia cancer cell line).These cell lines were obtained from the Pasteur Institute of Iran.
The HEK293T and MCF-7 cell lines were cultured in DMEM/F12 medium supplemented with 10% fetal bovine serum.On the other hand, the K-562 cell line was cultured in RPMIv1640 medium also supplemented with 10% fetal bovine serum.After culturing, the cells were seeded at a density of 104 cells per well in a 24-well plate and incubated for 48 h.Next, 40 µl of the nanobiocomposite extract was added to the cells, and they were treated for 48 h.Each sample was tested in triplicate.The PBS-treated cell lines were considered as the negative control.Finally, the treated cells were collected and diluted tenfold with Trypan blue dye.The cell count was performed using a Neubauer chamber hemocytometer.The proliferation percentage of the treated cells was calculated using the following formula: 25,27,42 .

Hemolysis assay
To investigate the blood compatibility of the Ag-TG/SF/MOF-5 nanobiocomposite, the percentage of human red blood cell (RBC) lysis was measured.Firstly, a fresh O-negative blood group sample was obtained from a volunteer and diluted in PBS at a ratio of 1:20.Then, 100 µl of the diluted blood sample were mixed with 100 µl of the nanobiocomposite extract in a 96-well plate.The plate was then incubated at 37 °C for 1 h.After incubation, the samples were collected and centrifuged at 3000 rpm for 15 min.In this assay, 1% Triton X-100 was used as the positive control, while 0.9% NaCl solution was used as the negative control.Supernatant photometric analysis was performed to quantify the absorbance values at a wavelength of 405 nm using an ELISA Reader.The hemolysis percentage of the samples was determined utilizing the following formula 43 :

Antibacterial assay
To assess the antibacterial properties of the Ag-TG/SF/MOF-5 nanobiocomposite, the inhibition rate of E. coli and S. aureus bacteria was measured 44,45 .For this purpose, E. coli and S. aureus bacteria were cultured overnight in an MHA culture medium.Afterward, the bacteria were inoculated into an MHB culture medium and incubated until they reached a final McFarland concentration 0.5.Next, 50 μL of each inoculated bacteria and 0.01 g of the Ag-TG/SF/MOF-5 nanobiocomposite were added to two test tubes containing 5 ml of sterile MHB culture medium.These test tubes were then placed in a shaker incubator set at 37 °C to provide optimal growth conditions for the bacteria.Agitation was achieved by setting the shaker incubator at 150 rpm for 24 h.All experiments were repeated three times.Finally, the absorbance of each tube was measured at a wavelength of 600 nm; then, the growth inhibitory percentage was calculated using the following mathematical expression:

Statistical analysis
The statistical software SPSS Statistics 22.0 was used to perform data analyses using the t-test, an inferential technique.In statistical analysis, P-values of P ≥ 0.05 (*), P ≤ 0.05 (**), and P ≤ 0.001 (***) corresponded to statistical insignificance, significance, and high significance, respectively.The error bar used in this study was of the standard deviation type.

Ethical issues
The present investigation complied with the ethical principles stipulated in the Declaration of Helsinki.Furthermore, it should be noted that the Ethics Research Committee of the Pasteur Institute of Iran sanctioned the investigative techniques employed and the protocol for obtaining informed consent.

Result and discussion
In this study, a novel nanobiocomposite with biocompatible, non-toxic, anti-cancer and antibacterial properties was developed through a three-step process.The first step involved synthesizing a cross-linked multi-polymeric Ag-TG hydrogel using glutaraldehyde as a cross-linker.In the second step, SF and MOF-5 were incorporated into the hydrogel to enhance its biological and antibacterial properties.Various analytical techniques, such as FT-IR, EDX, FE-SEM, XRD, and TGA, were performed to determine the functional group characterization, elemental composition, morphology, crystallinity, and thermal stability of the nanobiocomposite.

FT-IR analysis
FT-IR analysis is a widely used technique for determining the functional groups and chemical bonds of synthesized composites.In this research, FT-IR analysis was applied to investigate the structure of the nanobiocomposite components at each step of preparation.All FT-IR spectra of Ag-TG hydrogel, Ag-TG hydrogel/SF, and Ag-TG hydrogel/SF/MOF-5 have been exhibited in Fig. 1.In Fig. 2a, the strong, broad peak (3200-3600 cm −1 ) is related to the abundant O-H stretching vibration bands of Ag and TG polymers presented in the hydrogel structure 46 .The C-H stretching vibration was determined by absorption bands at 2919 cm −1 .The assigned peaks at 1661 cm −1 and 1382 cm −1 are related to C=O and C-OH deformation vibrations respectively, as well as the O-C-O symmetric stretching vibration of carboxylate groups in TG 16 .The broad absorption peak at the range of (1000-1200 cm −1 ) has been identified as C-O (ether) and C-O-C (acetal ring) bands.This peak signifies the formation of cross-linking bonds within the hydrogel structure 47,48 .In Fig. 2b, additional peaks related explicitly to SF bonds were observed alongside the peaks corresponding to the Ag-TG hydrogel.The peak at 3304 cm −1 is attributed to the N-H stretching vibrations band, and the absorption peak at 1636 cm −1 is related to C=O bands of amide I in SF fibers.It is worth noting that the wavelength of this peak is lower than the carboxylic functional groups.Moreover, the assigned band at 1528 cm −1 is related to the N-H bending vibration mode of amide II.This particular band is ascribed explicitly to β-sheets in the structure of SF 49 .In Fig. 2c www.nature.com/scientificreports/ the Ag-TG hydrogel/SF, several peaks were observed in the FT-IR spectrum specifically in the region under 1000 cm −1 .The absorption band at 552 cm −1 is attributed to the Zn-O stretching band.The two close peaks at 728 cm −1 and 785 cm −1 are related to the in-plane bending of C-H bonds in the benzene ring in the MOF-5 50 .Also, the symmetric and asymmetric stretching of the carboxyl group in BDC (benzene-1,4-dicarboxylate), which is bonded to Zn, are obtained at two wavelengths: 1624 cm −1 and 1422 cm −151 .

FE-SEM imaging
For determination of the morphology of the nanobiocomposite components, FE-SEM images were taken after the preparation of all three samples: Ag-TG hydrogel, Ag-TG hydrogel/SF, and Ag-TG hydrogel/SF/MOF-5 (Fig. 3). Figure 3a, which is related to Ag-TG hydrogel, it can be observed that the hydrogel has a highly porous structure.This porous structure makes it a suitable substrate for cell growth and proliferation in wound healing applications.In Fig. 3b, the porosity of the hydrogel is maintained, but with the difference that the SF biopolymer strands cover the surface of the hydrogel.In Fig. 2c, with higher magnification, the MOF-5 was observed definitely in the final structure of the composite loaded in Ag-TG hydrogel/SF (Fig. 3c, d).

EDX analysis
The EDX analysis was performed to specify the elemental structure of the synthesized Ag-TG hydrogel/SF/ MOF-5 nanobiocomposite.The spectrum obtained from the EDX analysis exhibits that the C and O peaks corresponded to the used biopolymers, including Ag, TG, and SF, as well as the glutaraldehyde cross-linking agent.
The N peak confirms the existence of SF which contains amide functional groups in its amino acid units.Also, the Zn peak is correlated with MOF-5, which is loaded in the final nanobiocomposite (Fig. 4).

TGA
The TGA analysis was carried out over a temperature range of 25 °C to 600 °C, with a heating rate of 10 °C/ min, using a sample weighing precisely 4.1637 mg.The obtained thermogram exhibited two significant weight loss in two distinct temperature ranges.The first weight loss, observed in the temperature range of 25-110 °C, can be attributed to the evaporation of volatile molecules and dehydration of the polymers.The second weight loss, occurring in the temperature range of 200-600 °C, can be attributed to the degradation of TG, Ag, and SF.These polymers were degraded into lower-weight molecules, including CO, CO 2 , CH 4 , NO 2 , and other volatile compounds.It is worth noting that the degradation of TG took place at a lower temperature (240 °C) compared to the degradation temperature of Ag and SF (280 °C) (Fig. 6) [57][58][59] .

Cell lines proliferation assay
Figure 7 shows the difference between the proliferation of the treated cell lines and the control groups.The results are the average values obtained from three independent experiments.As observed in Fig. 7, the proliferation percentage of MCF-7 and K-562 cells treated with the Ag-TG/SF/ MOF-5 nanobiocomposite decreased by more than 90%, with values of 10.8% and 3.38%, respectively.These findings indicate the potential anticancer effects of the nanobiocomposite on the MCF-7 and K-562 cancer cell lines.The results demonstrated significant statistical differences between the negative control and experimental groups, where the former exhibited notably higher values (P ≤ 0.001, very significant compared to the negative control group).In contrast, the proliferation rate of HEK293T cells, a healthy cell line, was not significantly affected by the nanobiocomposite extract (P ≥ 0.05, indicating insignificance compared to the negative control group).The proliferation rate of HEK293T cells decreased by less than 30%, with a value of 71.22%.These results suggest that the Ag-TG/SF/MOF-5 nanobiocomposite is not toxic to this healthy cell line.www.nature.com/scientificreports/ Figure 8 shows the morphologic differences of cells using an inverted microscope.As observed, the treated MCF-7 and K-562 cells exhibited significant morphological changes, altering their original structure.Additionally, a considerable number of these cells were lost in the medium.These cells appeared as stuck-together pieces in certain areas, indicating cell death.At the same time, no significant changes were observed in HEK293T cells after treatment.These cells did not adhere to each other and maintained their original structure.They were kept in large numbers and separately.

Blood compatibility
The measured hemolysis of the negative control group was 1.27%, while the Ag-TG/SF/MOF-5 nanobiocomposite extract-treated RBCs exhibited a hemolysis rate of 19.88%.These results indicate a significant lytic effect of the nanobiocomposite extract (P ≤ 0.05).In comparison, the positive control, Triton X-100, demonstrated considerable hemolysis.Figure 9 displays the hemolysis percentage and the appearance of the treated 96-well plate.It is important to note that the results presented in this report are the average outcomes from three distinct and separate trials.

Bacteria growth inhibition
The Ag-TG/SF/MOF-5 nanobiocomposite exhibited an antibacterial efficacy of 76.17% against E. coli and 69.14% against S. aureus bacteria strains (Fig. 10).These results highlight the potent antibacterial activity of the nanobiocomposite.It is important to note that the reported results represent the mean of three independent experiments.
The proposed mechanism for annihilation of the bacteria involves using of Ag-TG hydrogel/SF, which can disrupt the bacterial cell membrane and cause depolarization, resulting in bacterial cell death.Furthermore, the MOFs in the nanobiocomposite can release metal ions that interfere with the bacteria's DNA, disrupt their enzyme activity, and induce oxidative stress.

Conclusions
In this study, a novel Ag-TG hydrogel/SF/MOF-5 nanobiocomposite was synthesized using a facial approach.To check this nanobiocomposite's effect on the living cells, the proliferation of the HEK293T, MCF-7, and K-562 cells was investigated using Trypan blue exclusion method.The results show that the nanobiocomposite is biocompatible against normal cells; however, it exhibits anticancer activity against cancer cells.Moreover, the lytic effect of the nanobiocomposite was assessed by evaluating the percentage of RBC hemolysis.The antibacterial property  was examined with photometric antibacterial tests against E. coli and S. aureus strains.This nanobiocomposite prevented the growth of E. coli and S. aureus (76.08% and 69.19%) with high efficiency.According to biological assays, the natural-based Ag-TG hydrogel/SF/MOF-5 nanobiocomposite offers several advantages in biological applications.It is biocompatible, reducing the risk of adverse reactions or inflammation.It is also less toxic than synthetic materials, making them safer for medical use.Additionally, the natural biomacromolecules in the nanobiocomposite are renewable, sustainable, and exhibit enhanced biodegradability without leaving harmful residues.The porosity of the nanobiocomposite is crucial in biomedical applications like wound healing.Its porous structure allows for better oxygen and nutrient exchange, supports cell attachment and proliferation, facilitates fluid absorption and retention, and enables controlled release of bioactive agents.The incorporation of MOF-5 into the Ag-TG hydrogel/SF biocomposite, enhances the antibacterial activity of the nanobiocomposite to provide additional therapeutic functionalities, such as preventing infections, and promoting wound healing.Henceforth, future research should focus on conducting more studies to explore the potential of the Ag-TG hydrogel/SF/MOF-5 nanobiocomposite in biomedical applications, particularly in wound healing and cancer therapy.

Figure 10 .
Figure 10.Percentage inhibition of bacterial growth (n = 3).These graphs show the ability of Ag-TG/SF/MOF-5 nanobiocomposite to prevent the growth of E. coli and S. aureus and confirm its antibacterial effects.