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Scientific Reports volume 13, Article number: 7818 (2023 ) Cite this article Methylolacrylamide
In this study, we prepared a pH-responsive nanocomposite hydrogel based on chitosan grafted with acrylamide monomer and gold nanoparticles using gamma irradiation method (Cs-g-PAAm/AuNPs). The nanocomposite was enhanced with a layer coating of silver nanoparticles to improve the controlled release of the anticancer drug fluorouracil while increasing antimicrobial activity and decreasing the cytotoxicity of silver nanoparticles in nanocomposite hydrogel by combining with gold nanoparticles to enhance the ability to kill a high number of liver cancer cells. The structure of the nanocomposite materials was studied using FTIR spectroscopy and XRD patterns, which demonstrated the entrapment of gold and silver nanoparticles within the prepared polymer matrix. Dynamic light scattering data revealed the presence of gold and silver in the nanoscale with the polydispersity indexes in the mid-range values, indicating that distribution systems work best. Swelling experiments at various pH levels revealed that the prepared Cs-g-PAAm/Au–Ag-NPs nanocomposite hydrogels were highly responsive to pH changes. Bimetallic pH-responsive Cs-g-PAAm/Au–Ag-NPs nanocomposites exhibit strong antimicrobial activity. The presence of AuNPs reduced the cytotoxicity of AgNPs while increasing their ability to kill a high number of liver cancer cells.Cs-g-PAAm/Au–Ag-NPs has a high amount of fluorouracil drug loaded at pH 7.4 reaching 95 mg/g with a maximum drug release of 97% within 300 min. Cs-g-PAAm/Au–Ag-NPs have been recommended to use as oral delivery of anticancer drugs because they secure the encapsulated drug in the acidic medium of the stomach and release it in the intestinal pH.
Cancer is a difficult and stubborn disease to treat that claims many lives. More than ten million cases are discovered annually around the world1. There are numerous cancer treatments available, but their side effects on healthy organs are numerous and sometimes fatal2. Therefore, targeted treatment of cancerous and infected cells reduces side effects and dose used. Nanocomposites have attracted great interest as an unconventional and safe antimicrobial and antitumor, as well as a means of tracking treatment spread and measuring treatment progress3,4. Nanoparticles are highly chemically reactive and carry a large amount of the drug on their surface due to their small size. Because of their small size, they can also be deposited or oxidized greatly, losing their properties, so they must be protected by stabilizing agents such as polymers, surfactants, polysaccharides, etc. The effectiveness of nanoparticles as a catalyst, as well as their cytotoxicity, depends on several factors, including the type of polymer used, as well as the size and shape of the nanoparticles5,6. Ajitha et al., discovered that PVA-AgNPs have higher antibacterial activity than PEG-AgNPs7,8,9. Emphasis is placed on the production of nanocarriers that respond to stimuli and are more capable of targeted delivery and are more effective in eliminating cancer cells and microbes. Polymer composites provide excellent carriers for combining multiple treatments via the intelligent delivery of different functional nanomaterials. Researchers' efforts have focused on producing a new safe anti-cancer drug or strategy. Therefore, efforts focused on the production of biopolymer composites that can be extrinsically or internally induced and coupled (stimuli-response) with nanometer-sized materials and with an anti-cancer drug1,10,11. Polymers containing ionizable functional groups can be used in the production of pH stimuli-response polymers (SRP)12. Incorporating SRP with selected metal or metal oxide nanoparticles results in manufacturing stimuli response nanocomposites (SRNs), which can improve therapeutic response in particular disease regions to targeted tumor cells. Metal nanocomposite drug delivery is based on the concept of turning on/off bioactive compounds such as drugs, genes, and succession to specific tissues or organs through a stimulus such as heat, radiation, or pH change9. The pH-responsive nanocomposites or stimuli-responsive nanocomposites (SRNs) are one of the most successful and effective designs in the drug transport and delivery process, as the infected cells are acidic at a pH of 5 to 6.5 while healthy cells are at 7.4 neutral environments1,3. Loading the inorganic Nano materials onto the polymers enhances their stability, and efficiency facilitates drug release at the target site13,14, and prolongs blood circulation time in vivo. Gold nanoparticles are arising as promising agents for desease treatment, and nano-sized particles have been assessed against an assortment of human malignant gowth cells. Transition metals have antitumor activity, such as platinum, due to their ability to form complexes, and activate bonding and/or dissociation and oxidation–reduction chemistry. Platinum compounds have been used and tested for their ability to kill cancer cells and inhibit the growth of tumors, but they have severe side effects13,14,15. Silver and gold particles are also transition metals that have the advantage of killing microbes, as they impede the transfer of oxygen to bacteria2,16. Ag/Au NPs can also impede the transport of enzymes across the surface of the microbe or the surface of the cancer cell17. They can enter the microbial cell and change the cellular architecture of the microbe thus causing the death of the microbe or eliminating the infected cancer cells18. AgNPs and AuNPs are a type of broad-spectrum antibacterial agents and may serve as promising agents for treating cancer4. The results showed significant progress in dealing with Gram-negative and Gram-positive bacteria, such as Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, and Pediococcus acidilactici2. In precision medicine, gold and silver particles can also be used as drug delivery agents. Combining silver and gold particles can reduce cytotoxicity while increasing the efficiency of killing microbes and cancer cells2,16,19. Silver particles have a greater capacity as a cofactor, but their cytotoxicity to mammalian cells is high, whereas gold particles have very little cytotoxicity. Therefore, combining the two molecules reduces cytotoxicity while increasing activity. Combining the two molecules accelerates the reaction process16,17. To benefit from the shape and size of the Nano metals, they must be protected by a capping agent such as chitosan to support the stability and activity of the particles.
Chitosan is an ionic polysaccharide polymer that can be produced by partial deacetylation of chitin. Chitosan has wound-healing and antimicrobial properties, activates platelets, accelerates normal blood clotting, and reduces scar formation18,20. Chitosan is characterized as carrying ionizable functional groups that can be used to produce pH-responsive compounds for building nanomaterials-loaded supercarriers due to its high degree of confining efficacy, mechanical properties, and biocompatibility. By radiation induction, chitosan and acrylamide are combined to produce a strong and cohesive hydrogel that can withstand various acidic media19. The functional synthesis of combining gold and silver Nanoparticles with the chitosan/acrylamide hybrid polymer associated with studying their physical and chemical properties can play a vital role in many different applications, especially medical, whether by inhibiting microbial cells and fighting cancer cells or by carrying a drug targeted to specific tissues or organs.
The main hypothesis in this work is radiation-synthesized novel pH-responsive hybrid nanocomposites based on chitosan and bimetallic gold and silver nanoparticles to reduce cytotoxicity of silver nanoparticles by combining with gold nanoparticles. In general, silver nanoparticles are known to exhibit higher toxicity compared to gold nanoparticles. This is because silver is more reactive than gold and can easily release silver ions, which are known to have antimicrobial properties but can also be toxic to human cells. In addition, silver nanoparticles can easily penetrate cell membranes and accumulate in different organs, leading to various toxic effects such as oxidative stress, inflammation, and genotoxicity. Hybrid polymer chitosan/acrylamide AuNPs synthesized by in situ green method under the influence of gamma radiation followed by doping of chemically synthesized AgNPs. Synthesis of nanocomposite Cs-g-PAAm/Au–Ag-NPs using gamma radiation methods is highly appreciable due to the high efficacy, and safety. The prepared Cs-g-PAAm/Au–AgNPs nanocomposite hydrogel was investigated for structural and morphological. Swelling with different pH buffer solutions, and gelation percentage were studied. The drug loading and release were evaluated, as well as the cytotoxicity against liver cancer (HepG2) was also investigated. The antimicrobial property and cytotoxicity of Cs-g-PAAm/Au–AgNPs nanocomposite hydrogel were investigated. Synthesized Nanocomposites were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) studies, which were all used to determine the structural, and functional properties of the prepared nanocomposite hydrogels.
Chitosan (Cs) with a molecular weight of 100.000–300.000 and degree of deacetylation more than 85% (Acros, Belgium), Acrylamide (AAm) with a purity of 99.9% (Merck, Germany), Silver nitrate (AgNO3) and Sodium borohydride (NaBH4) (Qualikems Fine Chem., India), Gold (III) chloride (AuCl3) (Sigma-Aldrich, USA). Fluorouracil drug (Hikma Specialized Pharmaceuticals, Cairo, Egypt). Citric acid anhydrous (HOC(CH2CO2H)2), sodium citrate dihydrate (HOC(COONa)(CH2COONa)2·2H2O), sodium dihydrogen orthophosphate-1-hydrate (NaH2PO4·H2O), sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O), and dibasic sodium phosphate (NaH2PO4), trisodium citrate (Na3C6H5O7) were supplied from Merck Co., Ltd., Germany. Other chemicals, such as Hydrochloric acid, 36.5%, density: 1.18 g/cm3, and sodium hydroxide were purchased from El-Nasr Co. for Chemical Industries, Egypt, and utilized without further refining.
Different hydrogels and nanocomposite hydrogels were prepared utilizing the direct radiation technique. First, Cs-g-PAAm hydrogel was prepared by dissolving 3.3 wt% of Cs in 1% acetic acid solution at 75 °C with stirring for 2 h till complete dissolution was achieved. After that, Cs solution was cooled and 16.7 wt% of AAm was added and mixed well to prevent air bubbles from forming. Secondly, Cs-g-PAAm/AuNPs nanocomposite hydrogel was prepared by adding 5 mmol of AuCl3 to the previously prepared Cs/AAm solution where the total polymer/monomer concentration was (20 wt%), followed by 0.018 mL/mL of isopropyl alcohol as a hydroxyl radical scavenger. Then, all mixtures of Cs/PAAm and Cs/AAm-AuNPs solutions were put into glass test tubes, closed, then exposed to 20 kGy 60Co-gamma rays at a dose rate of 0.309 Gy/s. The vials were broken after graft copolymerization, and the produced hydrogels and nanocomposite hydrogels were sliced into almost equal discs. The non-crosslinked polymer was removed from the hydrogels and nanocomposite hydrogels by extracting them overnight in distilled water at 65 °C and thereafter air drying. The irradiation facility is located at the National Center for Radiation Research and Technology in Cairo, Egypt.
Cs-g-PAAm hydrogel and Cs-g-PAAm/AuNPs nanocomposite hydrogels were equilibrated for one day in distilled water. After that, the swelled hydrogels and nanocomposite hydrogels were subsequently equilibrated in silver nitrate solution (1, 10, 20 mM) for additional 24 h. The silver salt-loaded nanocomposite hydrogels were transferred to a beaker containing cold aqueous NaBH4 solution (2, 20, 40 mM). To reduce silver ions into silver nanoparticles, the beaker was maintained at 4 °C for 2 h. To eliminate unreacted silver ions and NaBH4, Cs-g-PAAm/AgNPs and Cs-g-PAAm/Au–Ag-NPs nanocomposites were washed three times with distilled water and thereafter air drying.
Solution A: 0.1 M citric acid anhydrous, 192.1 g mol−1 (19.21 g dissolved in 1000 mL distilled water).
Solution B: 0.1 M sodium citrate dihydrate, 294.10 g mol−1 (29.4 g dissolved in 1000 mL distilled water.
Solution C: 0.1 M monobasic sodium dihydrogen phosphate dihydrate,156.05 g mol−1 (31.2 g dissolved in 1000 mL dist. water).
Solution D: 0.2 M dibasic sodium phosphate, 141.96 g mol−1 (28.4 g dissolved in 1000 mL distilled water).
Solutions of different pH values (3–8) were prepared by combining the proportions listed in Table 1 noticing that the final volumes of pH solutions must be diluted with distilled water to a volume of 100 mL. Also, Solutions of different pH (1–2) were adjusted by 1 M hydrochloric acid, 36.46 g mol−1, (84.8 mL miscible in 1000 mL distilled water).
Estimating the insoluble fraction after extraction was used to evaluate the gelation percentages of Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposite hydrogels. The dried samples were weighed and then steeped in double distilled water for 24 h at 65 °C to remove the soluble components. The residual gel was then dried at 25 °C to a set weight. The gelation percentage was calculated using the following equation:
where Wo is the initial weight of the dried samples and Wd is the weight of the dried samples after extraction.
Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites of known weights were immersed in buffer solutions with varying pH values from 1.5 to 7.4 at definite intervals of time until equilibrium was reached. The swelled samples were re-weighed after the excess surface water was immediately removed with filter paper. The following equation was used to calculate the degree of swelling21:
where Wd and Ws are the weights of the dried and swelled samples, respectively.
The weighted dry disk of Cs-g-PAAm/Au–Ag-NPs nanocomposite was soaked in a buffer solution of pH 7.4 for 1 h and weighed every 15 min. Then, removed, soaked in a buffer solution of pH 1.5 for another 1 h, and also weighed every 15 min. This process was repeated at definite intervals of time. Then, the degree of swelling was calculated utilizing Eq. (2)22.
DLS (Nicomp 380 ZLS, USA Submicron particle size analyzer) was used to examine the size of the Au-NPs and Ag-NPs.
ATR-FT-IR (Bruker, Unicom infra-red spectrophotometer, Germany) was used to investigate the crosslinking between Cs and AAm. The fingerprints of infrared radiation were reported to be between 4000 and 400 cm−1.
SEM (ZEISS EVO-15, UK) with a low vacuum pump was used to examine the surface morphology of hydrogels and nanocomposites attached to the EDX unit with an accelerating voltage of 30 K.V.
The XRD was performed on a Shimadzu 6000 (Japan) X-ray diffractometer with Ni-filtered and Cu–K targets, a scan speed of 8°/min, and a voltage of 40 kV. The crystallinity of the Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposite samples under investigation were estimated utilizing Eq. (3); where the total area below all amorphous peaks is denoted by the symbol ƩAa, and the total area below all crystalline peaks is denoted by the symbol ƩAC23,24. Also, the average sizes for gold and silver nanoparticles were estimated utilizing Scherrer's Eq. (4); Where K denotes the Scherrer's constant (≈ 0.94), θ denotes the diffraction angle that corresponds to the peak in the XRD pattern with the highest intensity, FWHM is the full width of the peak at half its highest intensity (rad), λ denotes the X-ray wavelength (1.5406 Å)23,25.
The swelling equilibrium method was used to load fluorouracil drug onto Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposite hydrogel. All samples were soaked for 24 h in a known concentration of fluorouracil drug at various pHs 1.5, 5.2, and 7.4 after that dried at room temperature (25 ± 3 °C). The concentration of the rejected solution was calculated to determine the percentage entrapment of the fluorouracil drug in the polymer matrix using a UV/VIS Spectrometer (UV-Analytic Jena AG, German, the scan range of 190–1100 nm at 25 °C, at the wavelength of 300 nm. The amount of fluorouracil drug loaded per g was estimated from Eq. (5); where V denotes the fluorouracil drug solution's volume in mL, and W is the dried hydrogel's weight in g. Ci and Ce are the initial and equilibrium concentrations of the fluorouracil drug solution in mg/mL, respectively.
Fluorouracil drug’s in vitro release experiment was studied by immersing pre-weighed samples loaded with the drug in a definite volume of the buffer-releasing medium which is simulated intestinal fluid (SIF) at 37 °C. The amount of drug released was measured spectrophotometrically at 300 nm. A simulated intestinal fluid medium was prepared by adding 250 mL of 0.2 M sodium dihydrogen phosphate and 118 mL of 0.2 M NaOH26.
Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites were studied for their releasing kinetic parameters. To determine the fluorouracil drug rate coefficient (ks) at time (t), Eq. (6) was used. In addition, it was possible to determine how fluorouracil drug moves through the prepared nanocomposite hydrogel by applying Eq. (7); where F denotes the fractional of drug release at timet; Mt and M∞ are the drug intakes by the releasing system at time t and after it has reached equilibrium, respectively; k denotes a constant incorporating a feature of the polymeric network system, and n denotes the diffusion exponent indicating the transport mechanism with noting that, n = 0.5 for Fickian diffusion, n = 1 for case II diffusion, and 0.5 < n < 1 for sigmoidal or anomalous of non- Fickian diffusion, where both diffusion and polymer relaxation controlled occurred. Finally, 0.5 > n > 1 for super case II diffusion27,28,29. Then, both diffusion coefficient (D) and sorption rate constant (K) were estimated utilizing Eqs. (8, 9); where h denotes the thickness of samples.
Antimicrobial activities testing of Cs-g-PAAm/Ag, Cs-g-PAAm/AuNPs, and Cs-g-PAAm/Au–Ag-NPs were measured at Ultra Biotechnology Research Laboratory by using the diffusion method in agar. The volume of the microbial inoculum is spread over the entire agar surface. Then, a volume (20–100 ml) of the antimicrobial agent is introduced by making a hole with a diameter of 6 to 8 mm in a sterile manner using a borer or extraction solution of the desired concentration into the hole. Then, depending on the test microorganisms, the agar plates are incubated under appropriate conditions. plates should be incubated within 15 min. The antimicrobial agent diffuses into the agar medium which inhibits the growth of the tested microbial strain30. Test results appear after 16–18 h of incubation. The areas to prevent the spread of microbes are observed and measured in millimeters (inhibition zone) surrounding the wells, and to study whether they are resistant or sensitive to microbes31,32.
Cytotoxicity assay was done at Science Way Laboratory for Scientific Researches using the MTT protocol. The effect of Cs-g-PAAm, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs on the cell viability of HepG-2 (human hepatoma) cancer cells was evaluated. The method is described as following steps:
The 96-well tissue culture plate was inoculated with 1 × 105 cells/mL (100 μl/well) and incubated at 37 °C for 24 h to develop a complete monolayer sheet.
The growth medium was decanted from 96 well microtiter plates after a confluent sheet of cells was formed, and the cell monolayer was washed twice with wash media.
Two-fold dilutions of the tested sample were made in RPMI medium with 2% serum (maintenance medium).
0.1 ml of each dilution was tested in different wells leaving 3 wells as control, receiving only maintenance medium.
The plate was incubated at 37 °C and examined. Cells were checked for any physical signs of toxicity, e.g. partial or complete loss of the monolayer, rounding, shrinkage, or cell granulation.
MTT solution was prepared (5 mg/ml in PBS) (BIO BASIC CANADA INC).
20 ul MTT solution was added to each well. Place on a shaking table, 150 rpm for 5 min, to thoroughly mix the MTT into the media.
Incubate (37 °C, 5% CO2) for 4 h to allow the MTT to be metabolized.
9 Dump off the media. (dry the plate on paper towels to remove residue if necessary.
Resuspend formazan (MTT metabolic product) in 200 ul DMSO. Place on a shaking table, 150 rpm for 5 min, to thoroughly mix the formazan into the solvent.
Read optical density at 560 nm and subtract background at 620 nm. Optical density should be directly correlated with cell quantity.
The half-maximal inhibitory concentration (IC50) values were calculated.
The one-way ANOVA was utilized to statistically analyze all of the results at P < 0.05. Duncan’s multiple range tests were utilized to examine mean differences using IBM SPSS software version 24 as a statistical tool. The average of each experiment's three runs was calculated. The mean standard deviation (± SD) is shown in bars. https://www.ibm.com/support/pages/downloading-ibm-spss-statistics-24.
Modifying polymers with ionizing radiation is incredibly effective. The polymer, irradiation parameters, and state of the material during irradiation all affect the modifications that radiation causes in polysaccharide materials. Two reactions—main chain scission, degradation, and crosslinking are what ultimately determine the properties of irradiated polymers. Ionizing gamma radiation was used to start a radiation graft copolymerization reaction between acrylamide and chitosan in an aqueous medium33.
The radiolysis of water by gamma rays in an aqueous solution produces a large number of hydrated electrons (e aq-), hydrogen gas (H2), hydroxyl radicals (OH·), hydrogen peroxide (H2O2), and hydrogen radicals (H·), (Eq. 10). Strong reducing agents such as (H·) and (e aq-) can easily reduce metallic ions (Au3+) to zero valence metal particles (Au0). In contrast, a powerful oxidizing species (OH·) that can raise ions or atoms to a higher oxidation state. Therefore, before irradiation, a scavenger for the (OH·) radical such as isopropanol should be added to the precursor solutions. Multivalent ions (Au3+) are converted to Au0 via a series of steps, some of which may involve valence state disproportion as described in Fig. 1 (Eqs. 11–15)34. The isopropanol radical reduces more slowly than an electron in water, allowing for a narrower size distribution35. The benefit of this technique is that the main reducing agent in the absence of oxygen is the hydrated electron, which has a high negative redox potential. This allows any metal ion to be reduced to zero valent metal atoms without the use of chemical reducing agents. Therefore, primary atoms are generated independently at the origin, and they are separated and evenly distributed, just like ionic precursors. In addition, when Cs/AAm, and Cs/AAm/AuCl3 solutions (both yellowish colors) were subjected to gamma irradiation, Cs-g-PAAm hydrogel was formed with no change in color, and also Cs-g-PAAm/AuNPs nanocomposite hydrogel was formed but with change in color (reddish color). Moreover, when AgNO3 loaded onto the prepared Cs-g-PAAm, and Cs-g-PAAm/AuNPs, the color changed again from yellow and reddish to black as shown in Fig. 2. This color change revealed that multivalent Au3+ ions had been reduced to Au0 via gamma irradiation as well as monovalent Ag+ ions had been reduced to Ag0 using sodium borohydride as reducing agent proving the production of AuNPs and AgNPs successfully. The gelation percentages for Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–AgNPs estimated utilizing Eq. (1) and data were summarized in Table 2. Gamma radiation breaks the O–H and N–H bonds of chitosan and acrylamide, creating free radical sites that crosslink with each other to form a cohesive, crosslinked hydrogel with unique properties and a gelation ratio of 94% for Cs-g-PAAm hydrogel. The rate of gelation decreases when gold chloride is added (Cs-g-PAAm/AuNPs), which with exposure to radiation turns into nano-gold. Converting gold ions to gold nanoparticles consumes a significant portion of the ionizing radiation required for the crosslinking process between chitosan and acrylamide molecules, where gold ions act as a scavenger for the free radicals formed. The nanoparticles also disrupt the regular arrangement of the polymer network formed, resulting in a slight decrease in the gel fraction4. The gelation percent increases again on the prepared nanocomposite by adding silver ions (Cs-g-PAAm/Au–Ag-NPs). These results suggest that the presence of Ag0 in the hydrogel matrix led to a more solid-like response36.
Mechanism for preparation of Cs-g-PAAm/Au–Ag-NPs using gamma irradiation techniques.
Images for preparation of Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs and Cs-g-PAAm/Au–Ag-NPs nanocomposite hydrogels.
Figure 3 shows the effect of time on the degree of swelling of Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs and Cs-g-PAAm/Au–Ag-NPs nanocomposites at three different pH values (1.5, 5.4, and 7.4). The degree of swelling incremented with raising time reaching an equilibrium state at 6 h for all samples as shown in Fig. 3A–C. Also, the degree of swelling is incremented with raising pH levels. Chitosan behaves as a weak polybase in a pH-sensitive manner due to the abundance of amino groups along its chain. At low pH levels (pH 1.5), chitosan dissolves easily due to the protonation of amino groups (NH2 to NH3+) leading to electrostatic chain repulsion by the positive charge NH3+–NH3+, diffusion of proton and counter ions together with water inside the gel, and dissociation of secondary interactions37. Although swelling of PAAm is not pH-dependent due to its non-ionic character, but also it is a hydrophilic polymer. At higher pH levels, the protonation decreased but the degree of swelling remained high due to intermolecular hydrogen bond formation being weak and the hydrophilicity of PAAm. Thus, the crosslink density is reduced, allowing the network structure to relax more and allow more water molecules to enter. In addition, the existence of AuNPs in the nanocomposites improved the degree of swelling due to the availability of more free spaces that allow the rapid diffusion of water molecules into the nanocomposite. From the results, it is also clear that by adding silver ions to the polymer mixture, the degree of swelling of the C-g-PAAm/Au–Ag-NPs nanocomposite decreases, which is due to the presence of AgNPs increases the crosslink density strengthening the network and reducing the swelling capacity. This is because Ag nanoparticles can interact with the functional groups of the hydrogel matrix through electrostatic interactions, thus reducing the area required for the high level of swelling38. So, the maximum degree of swelling for Cs-g-PAAm/Au–Ag-NPs was choosen at pH 7.4, which makes it suitable for application in intestines drug release.
(A–C) Degree of swelling (%) as a function of time (h) at different pHs, of (I) Cs-g-PAAm hydrogel, (II) Cs-g-PAAm/AuNPs, (III) Cs-g-PAAm/AgNPs, (V) Cs-g-PAAm/Au–Ag-NPs, respectively, and (D) reversible on–off degree of swelling at pH 1.5 and 7.4 values for Cs-g-PAAm/Au–AgNPs, (E, F, G, H, I, J, K, and L) Digital camera for dried and swelled hydrogel and nanocomposites in phosphate buffer at pH 7.4.
Figure 3D confirms that Cs-g-PAAm/Au–Ag-NPs nanocomposite is responsive to pH by testing it in a reversible on–off degree of swelling in two buffer solutions at pH 1.5 and 7.4 values. The nanocomposite appeared to expand at pH 7.4, whereas appeared to shrink at pH 1.5, demonstrating good reversible swelling behavior. It can be noted that repeating of expand- shrink operation in the third-period relaxation of the chains may occur, which is responsible for increasing the swelling in the third cycle. The obtained result proved that Cs-g-PAAm/Au–Ag-NPs is a good pH-responsive nanocomposite and was chosen to be utilized in drug delivery systems that can release drugs such as fluorouracil when the pH is altered.
Grafting of AAm onto chitosan was confirmed by FTIR as shown in Fig. 4A. Figure 4A shows the FTIR spectra of Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites. For Cs-g-PAAm hydrogel, showed a strong broad band centered at 3400 cm−1 due to the axial asymmetric stretching vibration of O–H and N–H of Cs and PAAm. The band observed at 2894 cm−1 corresponded to the symmetric stretching vibration C-H. The band appears at 1655 cm−1 corresponding to the (amide I) stretching of C=O bonds of the acetamide groups of Cs and PAAm. The band at 1590 cm−1 corresponds to the N–H deformation of the amino group of Cs. These results confirm that PAAm grafted onto Cs polymer successfully. On the other hand, an increase in the intensity of the stretching vibration band of O–H and N–H between 3200 and 3400 cm−1 was reported for the Cs-g-PAAm/AuNPs nanocomposite hydrogel39. This explained how Au0 and nitrogen atoms interacted by wrapping around Au0 and allowing them to stay stable in the solution. The sharpness and intensity of the band at 1030 cm−1 that was incremented and ascribed to C-O corroborated this interaction40. The fact that the band at 1320 cm−1 increased in intensity while the band at 1408 cm−1 decreased suggested that the Au0 nanoparticles were coated with Cs-g-PAAm hydrogel. For Cs-g-PAAm/Au–Ag-NPs from the chart, it can be seen that no new peaks were observed but a slight decrease in the intensity of the peaks was noted.
(A) FTIR spectra, and (B) XRD diffraction patterns for Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposite hydrogels.
Figure 4B depicts the XRD patterns of the studied polymer samples, which demonstrate that the Cs-g-PAAm (black line) sample is amorphous in nature41. New diffraction peaks appeared for Cs-g-PAAm/AuNPs (blue line) at 2 theta values 38.2°, 44.8°, 64.4°, and 77° assigned to the (111), (200), (220) and (311) features of gold with face-centered cubic crystal structure, respectively. The presence of these peaks confirms that Au0 was incorporated into Cs-g-PAAm successfully. Another diffraction peak appeared for Cs-g-PAAm/AgNPs (pink line) at 2 theta values 32.6°, 38.7°, 45.3°, 50.12°, 60.6°, 64.1°, and 77.1° assigned to the (311), (101), (103), (104), (105), (110), and (201) features of silver with face-centered cubic crystal structure, respectively. The presence of these peaks confirms that Ag0 was incorporated into Cs-g-PAAm successfully. The peak at 38.2° and 44.8° in Cs-g-PAAm/AuNPs incremented in broadening and shifted to a higher 2 theta values of 39.4°and 46.5° with introducing other new peaks in Cs-g-PAAm/Au–Ag-NPs (red line) at 2 theta values 20°, 28.4°, 33.4°, 34.8°, 49.6°, 53.1°, and 61.6° assigned to the (200), (220), (311), (222), (422), (511) and (531) features of silver with also face-centered cubic crystal structure confirming that Ag0 was prepared successfully. These results are in accordance with good agreement with the Inorganic Crystal Structure Database (ICSD) record No. 7440-57-5 for gold and record No. 01-1167 for silver. The percentage of crystallinity was calculated from the area under the peak in the XRD pattern utilizing Eq. (3) and data were summarized in Table 3. It is obvious that the crystallinity percentage incremented by introducing metal nanoparticles conforming the bonding between metal ions and functional groups in the polymer, which leads to an increase in the intensity of crystallization4,42. Furthermore, the average sizes of gold and silver nanoparticles were estimated from the broadening in the XRD pattern utilizing Eq. (4) at three different 2 theta values corresponding to the highest three I/I1 values, and data were summarized in Table 4. It is clear that the average particle size of Au0, and Ag0 nanoparticles were found to be 41.7 nm, and 66.7 nm respectively.
Figure 5A–C confirms the incorporation of Au and Ag nanoparticles into the Cs-g-PAAm hydrogel. This is evident from spot EDX on the presence of Ag and Au nanoparticles in the hydrogel samples. The weight percentages of Au0 and Ag0 nanoparticles in all nanocomposites were 0.86 and 0.52 wt%, respectively.
EDX graphs of (A) Cs-g-PAAm/AuNPs, (B) Cs-g-PAAm/AgNPs, and (C) Cs-g-PAAm/Au–Ag-NPs.
The surface morphologies of the investigated Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs samples were examined by SEM as shown in Fig. 6. The SEM image of Cs-g-PAAm/AuNPs nanocomposite (Fig. 6A) appeared as a net-like structure with pores due to the hydrophilicity of AAm, that has a great affinity to swell in water. White spots were scattered across the pore surface, which proved the existence of Au0 nanoparticles in the nanocomposite hydrogels. After immersion of Cs-g-PAAm, and Cs-g-PAAm/AuNPs nanocomposites in silver nitrate and sodium borohydride solutions to reduce Ag to Ag0, many spherical Ag0 nanoparticles were deposited on the pores and surface as shown in Fig. 6B,C.
SEM images of (A) Cs-g-PAAm/AuNPs, (B) Cs-g-PAAm/AgNPs, and (C) Cs-g-PAAm/Au–Ag-NPs.
Nanometer-sized particles are commonly present in many different types of materials and DLS is used to measure the hydrodynamic diameter of the particles, which is the distance from the center of the particle to the shear plane at the surface. Figure 7 illustrates the size distribution (number-based) of the prepared AuNPs and AgNPs in the Cs-g-PAAm/AuNPs and Cs-g-PAAm/AgNPs nanocomposite hydrogels with mean diameters of 40 and 69 nm, respectively. These particle sizes are coincident with that calculated from XRD data. The polydispersity index is a measure of the width of the size distribution43. The polydispersity index less than 0.08 denotes a nearly monodisperse sample, and the mid-range value is between 0.08 and 0.70, where the distribution algorithms perform best over this range. In addition, when the polydispersity index is more than 0.7 and close to 1.0 denotes a very wide broaddistribution of droplet sizes44. In the present work and from DLS data presented in Fig. 7, the polydispersity indexes are 0.250 for Cs-g-PAAm/AuNPs and 0.343 for Cs-g-PAAm/AgNPs nanocomposite hydrogels which are in the mid-range values indicating distribution systems work best.
The size distribution by the number of (A) Cs-g-PAAm/AuNPs, and (B) Cs-g-PAAm/AgNPs nanocomposite hydrogels, respectively.
The smaller the size of the particles, the higher their efficiency45. Metallic nanoparticles Au/Ag-NPs can penetrate the surface of microbial cells and bind to proteins and enzymes within microbial cells, causing a stop function and microbial death. Moreover, metal nanoparticles can greatly absorb oxygen on the surface of the cells, causing hypoxia within microbial cells and, as a result, microbe death46. Therefore, Au–Ag NPs have good antimicrobial properties. In this work, gold and silver particles were combined to increase the microbial growth inhibition property and increase the effectiveness. The antimicrobial activity of the prepared hydrogel based on bimetallic gold and silver nanoparticles was studied. Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and bimetallic Cs-g-PAAm/Au–Ag-NPs Nanocomposites against various bacteria (two strains gram-positive bacteria, and two strains gram-negative bacteria), as well as fungal cells (two strains), were investigated as shown in Fig. 8. It is clear from results represented in Table 5, that Cs-g-PAAm/Au–Ag-NPs has a higher inhibiting zone of the growth for the Gram-positive bacteria such as Bacillus Subtilis and Staphylococcus aureus (40 ± 9.8 mm) and (28 ± 2.7 mm) respectively, and for Gram-negative bacteria such as Escherichia coli and Klebsiella pneumonia (26 ± 1.8 mm) and (20 ± 1.2 mm), respectively, as well as the highest inhibition of the growth of fungi such as Candida albicans (36 ± 2.99 mm). It is noticeable that the Au–Ag NPs were more active against Gram-positive bacteria than the Gram-negative isolates. This result can be attributed to the fact that the cell wall of Gram-negative pathogens contains double layers of peptidoglycan and lipopolysaccharide, which impede the action of silver and gold nanoparticles due to the positive charges of Au–Ag NPs that cross-link with the polysaccharide layer while Gram-positive isolates contain single structural layer of peptidoglycan12. Combining anti-cancer and anti-microbial platforms in cancer drug carriers aims to create therapeutic agents that can target both cancer cells and microbial infections simultaneously. This approach has the potential to improve the efficacy and safety of cancer treatments, particularly in patients with weakened immune systems who are more susceptible to infection.
Antimicrobial images of (I) Cs-g-PAAm/AgNPs hydrogel, (II) Cs-g-PAAm/AuNPs, and (III) Cs-g-PAAm/Au–Ag-NPs nanocomposites against various bacteria and fungi.
The half-maximal inhibitory concentration (IC50) quantifies a substance’s ability to inhibit a certain biological or metabolic function. The IC50 was used to describe the toxicity of prepared Cs-g-PAAm/AgNPs, Cs-g-PAAm/AuNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites. The cytotoxicity of different concentrations (31.25, 62.5, 125, 250, 500, and 1000 µg/mL) of Cs-g-PAAm/AgNPs, Cs-g-PAAm/AuNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites in HepG2 cancer cell was assessed utilizing MTT protocol as shown in Fig. 9. Table 6 illustrates surviving, inhibiting fraction percentages at 1000 µg/mL and IC50 values of prepared nanocomposites. It is clear that for prepared Cs-g-PAAm/AgNPs, Cs-g-PAAm/AuNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites killed 95.8, 78.6, and 91.7% of the cells, respectively. This means that C-g-PAAm/AgNPs nanocomposite hydrogel inhibits cell proliferation the most effectively with IC50 value of 8.6 ± 1.34 which is considered a very strong cytotoxic biomaterial47. In addition, the greatest of IC50 values were observed with Cs-g-PAAm/AuNPs nanocomposite hydrogel reaching 39.6 µg/mL. The combination of bimetallic gold and silver nanoparticles reduces the cytotoxic effect of prepared nanocomposite with IC50 value 24.3 ± 1.39 µg/mL that is considered as a moderate cytotoxic nanocomposite and at the same time killed a high number of cancer cells (91.7%) (Fig. 7). These results proved that the pH-responsive Cs-g-PAAm/Au–Ag-NPs nanocomposite has lower cytotoxicity and can inhibit cell proliferation which makes it a good carrier for anticancer drugs.
Effect of prepared nanocomposites on HepG2 cells at different concentrations.
Fluorouracil drug was loaded onto the prepared hydrogel and nanocomposites via hydrogen bonding and van der Waals interactions48 as illustrated in Fig. 10. The amount of drug loaded at various fluorouracil concentrations at pH 7.4 was displayed in Fig. 11A. It is obvious that, the loaded amount of fluorouracil drug incremented by increasing drug concentration for all Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites. This increase was ascribed to Cs-g-PAAm/Au–Ag-NPs nanocomposite having higher swelling values due to free volume accessible sites on the polymer matrix which makes the chains more flexible and allows for the diffusion of more drug molecules into the polymer matrix. It was found that the best concentration was 1.0 mg/mL, which yielded approximately a fluorouracil drug-loaded amount of 44.3, 95, 20, and 89, mg/g for Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites, respectively, and was employed in the in vitro drug release investigation.
Fluorouracil drug loaded mechanism of the prepared hydrogel and nanocomposites.
(A) Fluorouracil drug loaded, (B) released as a function of time in SIF at pH 7.4 of (I) Cs-g-PAAm, (II) Cs-g-PAAm/AuNPs, (III) Cs-g-PAAm/AgNPs, (V) Cs-g-PAAm/Au–AgNPs.
Figure 11B displays the effect of time on the fluorouracil drug release percentage (in vitro) incorporated into all Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites at pH 7.4, respectively. It is found that the release of fluorouracil drug in SIF is dependent on pH and fluorouracil drug release incremented by raising the time until reaches the optimum releasing percentage through 315, 450, 375, and 300 min with a maximum drug release of 33, 87, 22, and 97% for Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposites, respectively. The existence of AuNPs in nanocomposites not only enhanced the releasing percentage in Cs-g-PAAm hydrogel and Cs-g-PAAm/Au–Ag-NPs nanocomposites but also rapid the releasing time from 450 min in Cs-g-PAAm/AuNPs to 300 min in Cs-g-PAAm/Au–Ag-NPs. According to the data obtained from the in vitro release, the pH-sensitive Cs-g-PAAm/Au–Ag-NPs nanocomposite is an ideal localized drug delivery system for fluorouracil in the neutral environment of the intestine.
The mechanism and releasing kinetics parameters of Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposite hydrogels were investigated utilizing Eqs. (6–9). Figure 12A–D depict the releasing kinetic curves of various applied expressions, and Table 7 displays the analyzed data. It is found that the release in this work was shown to follow the super case II diffusion mechanism for all Cs-g-PAAm hydrogel, Cs-g-PAAm/AuNPs, Cs-g-PAAm/AgNPs, and Cs-g-PAAm/Au–Ag-NPs nanocomposite hydrogels, with n values of 1.39, 1.27, 1.11, and 1.31, respectively. These results proved that the pH-responsive Cs-g-PAAm/Au–Ag-NPs nanocomposite has a higher release for fluorouracil drug and can be used as a drug delivery system in the neutral environment of the intestine.
Releasing kinetic curves for (I) Cs-g-PAAm, (II) Cs-g-PAAm/AuNPs, (III) Cs-g-PAAm/AgNPs, (V) Cs-g-PAAm/Au–AgNPs.
In this study pH-responsive, Cs-g-PAAm/Au–Ag-NPs were prepared via gamma irradiation technique as a clean and accurate method. The prepared nanocomposite was prepared as a targeted drug carrier for cancer cells with the ability to move through a change in pH changes. AuNPs were prepared in situ during the polymerization process. Silver nanoparticles were loaded via chemical reduction as a support for gold nanoparticles. According to the main hypothesis of our work, bimetallic Au–Ag NPs enhanced the coherent structure of the prepared hydrogel by increasing the swelling and conversion yield properties of the prepared nanocomposites. Also, Au–Ag NPs increased the releasing efficiency when Cs-g-PAAm/Au–Ag-NPs loaded with Fluorouracil anticancer drug. In addition, bimetallic Cs-g-PAAm/Au–Ag-NPs nanocomposites have high antimicrobial activity against some types of pathogenic bacteria and fungi and higher cytotoxicity of AgNPs was reduced by the existence of AuNPs with an increase in the ability to kill a high number of liver cancer cells. In addition to improving treatment outcomes, combining anti-cancer and anti-microbial platforms in drug delivery systems can also help address the issue of drug resistance, as some microbial infections are becoming increasingly resistant to existing antibiotics. By targeting both cancer cells and microbial infections, this approach may provide a more effective and sustainable treatment option for patients. As a result, our main hypothesis was successfully tested, and the prepared pH-responsive Cs-g-PAAm/Au–Ag-NPs nanocomposite hydrogel candidate for future use as a carrier for anticancer drug delivery.
All data generated or analyzed during this study available from the corresponding author on request.
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The working authors are all individuals who made major contributions to the work stated in the paper (e.g., technical assistance, writing and editing assistance, general support), and we thank the Egyptian Atomic Energy Authority for the support required to accomplish this work.
Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).
Radiation Research of Polymer Chemistry Department, National Center for Radiation Research and Technology, Egyptian Atomic Energy Authority, Cairo, Egypt
Shaimaa M. Nasef, Ehab E. Khozemy & Ghada A. Mahmoud
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Nasef, S.M., Khozemy, E.E. & Mahmoud, G.A. pH-responsive chitosan/acrylamide/gold/nanocomposite supported with silver nanoparticles for controlled release of anticancer drug. Sci Rep 13, 7818 (2023). https://doi.org/10.1038/s41598-023-34870-w
DOI: https://doi.org/10.1038/s41598-023-34870-w
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