Inuence of Bentonite Nanoparticles on Properties of PVP-CMC-Gums Biodegradable Hydrogel Films for Biomedical Applications

Using polymer daily becomes increasingly extensive; the many characteristics of hydrogel lead to a wide range of uses, particularly in biomedical applications. Hydrogel lms were made from a variety of materials in this investigation. Casting techniques and room temperature drying were used to make PVP-CMC- Gums lms based on hydrogels, however, the effects of adding bentonite clay were needed. SEM, FTIR, XRD, TGA, swelling, solubility, contact angle, and a variety of other studies were used to illustrate and analyze a variety of physical, mechanical, thermal, and many characteristics. The major ndings revealed new peaks, which indicate the creation of cross-linking bonds, which are the primary cause of capsulation and release characteristics, indicating that these lms might be utilized in drug delivery and a variety of other applications. The PCXB lm has the best color, surface hydrophobicity, solubility, and swelling properties, while the PCGB lm has the greatest biodegradability and permeability results, and both lms have strong thermal, mechanical, and releasing properties. As a result, adding bentonite clay to hydrogel lms improves all of their characteristics, making them suitable for a variety of biomedical applications such as dentistry root lling, tissue engineering, contact lenses, and bandages.


Introduction
Biomaterials have a massive effect on human health care. They are vastly used in biomedical applications because of their biocompatibility, biodegradability, non-toxicity, good structural properties, thermal abilities, and good broad characterizations. One of these biomaterials is hydrogel [1]. Hydrogel knows as a water-swollen polymer with a three-dimensional structure or crosslinking; it can absorb and retain aqueous solutions up to a hundred times its weight; it is also characterized by hydrophilicity and insolubility in water [2]- [4]. All the properties of hydrogels have been considered essential in many ways, where they can be used for various pharmaceutical and biomedical applications, such as drug delivery and tissue engineering, tooth root llings, contact lenses, bandages, and more [1].
Gums-based hydrogels have created extensive interest as biomaterials [1]. Hydrogel is considered a cheap, effective, convenient material for bio applications [5]. Also, it is used in other applications such as packaging materials [6], [7]. Polyvinylpyrrolidone (PVP) is a polymer that soluble in water, made from the monomer N-vinylpyrrolidone [8]. It has unique features which make it one of the best polymers that can be used with a human body, such as colloid protection, viscosity, hygroscopicity, hydrotropic, coagulation, high physiological adaptability, strong bonding ability [9]; PVP polymer can be used as one of the main components of the hydrogel preparation. PVP hydrogel itself does not display good swelling features, but when mingled with polysaccharides such as carboxymethylcellulose (CMC), their swelling properties upgrade [5]. CMC is involved in semisynthetic polymers, the most abundant organic material in nature [10]; CMC has many properties, especially biocompatibility, biodegradability, non-toxicity, costeffectiveness, good physicochemical properties [11]. Agar (AG) acts as a natural cross-linking agent, and its gelling characteristics provide mechanical reinforcement in hydrogels [5]. Agar has various properties; no need to add reagents to generate gelation; it is used among a wide range of pH, and is very stable, not caused a residue [12]. Polyethylene glycols (PEGs) are hydrophilic polymers; It has many properties such Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js as is non-toxic, colorless, inert, odorless, and non-volatile, soluble in water and organic solvents, it is retaining moisture, and has excellent absorbing and binding features. Also, its thermal stability is desired for various biomedical applications, PEG with crosslinking agents such as PVP, a strengthening agent, provides an impetus to the hydrogel's gelling behavior [13]. Guar gum (GG) is obtained from guar beans.
Its source is an annual pod-bearing called Guar. It has good additive properties; it emulsi es, binds water, inhibits ice crystals in frozen products, moisturizes, thickens, stabilizes, binding by hydrogen bond formation and gelling properties apart from easy solubility in cold water, wide pH tolerance, high thermal stability lm-forming ability and biodegradability and suspends many liquid-solid systems [14], [15].
Xanthan gum (XG) is an extracellular polysaccharide secreted by the microorganism Xanthomonas campestris. XG offers a potential utility as a drug carrier because of its inertness and biocompatibility. Also, Xanthan solutions are highly viscous even at low polymer concentrations [1], [16]. Geologists de ne Bentonite (BE) as a rock formed of highly colloidal and plastic clays composed mainly of montmorillonite. The unique characteristics of bentonite are the ability to form thixotropic gels with water and absorb vast quantities of water with an accompanying increase in the volume of 12-15 times its dry bulk and a high cation exchange capacity [17]. The clay application is usually in the form of a powder, suspension, emulsion, or gel [18].
Rare reports were available on the synthesis of hydrogels made from GG and XG, but no substantial work has been reported to grafting BE onto XG and GG hydrogels. The present article is based on the synthesis and characterization of crosslinking hydrogel by grafting BE onto XG and GG hydrogels and its abilities to be used in different biomedical applications. So the characterizations of the lms were studied based on the changes that happened based on the gums additions and gums with Be additions. The hydrogel lms were produced by casting method in laboratory Petri dishes; the composition of lms is mentioned in Table 1. Then all the components were mixed in a magnetic stirrer at 500 rpm for 30 min.
Then the mixtures were put in an ultrasonic device for 15 min. After that, the mixture was exposed to heat Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js for 45 min in an autoclave at 121°C. Finally, the mixtures were poured into the dishes using a transfer pipet. All the dishes were left at room temperature (23)(24)(25) °C to dry for two days. Later they were peeled off from the trays using the tweezers [6].

Scanning Electron Microscope:
The lms' cross-sectional and surfaces morphologies were studied under a eld emission scanning electron microscope (Nova NanoSEM™ by FEI™, USA); the lms were dried and sputter-coated with a thin layer of gold for better surface conductivity for 60 s at 30 mA. [14] The images were captured at a magni cation of 250 -5000x and 2 kV, 5 kV, and 10 kV.

Fourier-Transformed Infrared Spectroscopy:
The functional group analysis of the samples was done using Fourier transfer infrared (FTIR) spectroscopy in an attenuated total re ectance (ATR) mode (Nicolet iS5 by Thermo Scienti c, USA) [7].
The results are reported from a scanning range of 4000 to 500 cm −1 with an average of 16 scans and a resolution of 4 cm −1 .

X-Ray Diffraction:
XRD technique was applied to know the crystalline structure of the lms; the tests were done using an xray diffractometer (MiniFlex™600 x-ray diffractometer, Rigaku, Japan

Color Analysis:
The determination of color is essential for selecting the best lms for speci c biomedical applications based on color. The color was determined using NR100 Precision Colorimeter [6]. The L, a, and b values were obtained using the CIE lab scale. The total color difference (ΔE) and Chroma (C) were calculated with the following equations: The standard values for L, a, and b are 93.02, -0.46, and 3.58, respectively, and L 0 , a 0 , and b 0 are the color parameters of each lm.

Contact angle analysis:
The best explanation of contact angle is the "angle between a liquid and a solid within the body of the liquid formed at the gas-liquid-solid interface," the contact angle was determined through a static contact angle measuring System (Advex Instruments s.r.o, CZ) at RT 23°C and RH 57% [14]. The lms' dimension was 15 mm length and 40 mm width; images of both (lower and upper) surfaces of the lms were captured after 5µl of water was dropped on the lm surface using a micropipette. All the data represent an average of ve replications for every side.

Water vapor permeability:
By using (cup method) water vapor permeability (WVP) was measured. An easy explanation of WVP is the moisture that penetrates the lm. The cup has a circular radius of 20 mm, and the test area is 140.56 mm2. The lms are bigger than the cup radius, which covering an area of around 150 mm 2 . The lms were put and sealed to the cups with special silicone gel which is highly resistant to the passage of water vapor. Inside the cup, silica beads were put with a known amount. The empty cup, the cup with silica, and the cup with the lm and silica were weighted. All the cups were kept inside a climate desiccator at 20°C and 90 ± 2 % RH for 24 hr. The nal measurement was done after 24 hr of incubation in the climate chamber [14]. The WVP was calculated using the following equations: where WVTR is the measured water vapor transmission rate through the lm, ΔW is the change in weight of the cup, A is the test area, and t is the duration of the experiment, in our case 24 hr. δ is the lm thickness, and ΔP (=1.333×102 Pa) is the water vapor partial pressure difference across the two sides of the lm.

Water Solubility:
The water solubility (WS) of the lms was measured, after cutting the lms for 25 mm long X 25 mm width, then weighted them after dried to constant weight at 60°C, the small pieces were immersed into in 50 ml of distilled water and kept in a Thermostatic Device Rotary Shaker (Changsha Yonglekang equipment, China) with low constant shaking (approx. 15 rpm) at RT 21°C and RH 57% for 24 hr. After 24 hr, the lms were taken from the water and dried to constant weight, to calculate the WS the following formula was used: where ΔM is weight loss in the water, M is the initial weight before immersing in water respectively [14].

Swelling ratio:
The water absorption of the hydrogel is the degree of swelling. The lms were dried at room temperature until they reach the constant weight; the lms were cut to 15 mm long X 15 mm wide and weighted, then all the pieces were immersed in distilled water for 330 min at room temperature, then the swollen lms were wiped off with tissues paper, then weighed again. By using the following equation [19], the degree of swelling corresponds to the water absorptivity of the lms was calculated: Ws and Wd are weights of swollen gel and dried gel, respectively [19].

Thermal analysis:
The thermal stability of lms has been tested using Thermogravimetric analysis (TGA Q500 by TA Instruments USA) based on thermal gravimetric (TG) and differential scanning calorimetry analysis (DSC The biodegradability investigation was performed using the soil burial method in the soil combination that facilitates quicker degradation over four weeks. The samples were made by cutting them in 30 mm X 50 mm rectangular pieces and letting them on Petri dishes between the two layers of compost soil. At temperatures of 30°C and RH 68-70 %, Petri plates were put in a humidity chamber. After wiping them using tissues that contain distilled water, the buried lms were removed from the compost soil and dried up to consistent weight each week and weighted [7], [14]. The degradation percentage was calculated using the formula of the lms in the compost: D is the degradation percentage, ΔW and W are the change in weight of the lms at different buried times, and the initial weight of the lms, respectively [7], [14].
2.2.14 Drug Loading: The cross-linked hydrogel lms releasing was studied by using antibiotic clindamycin 600 mg/4ml as a model drug; the drug was incorporated into the lms by using the diffusion method, where the lms were immersed into a solution contains 1.8 g clindamycin in 18 ml acetone for 5 hr; after that, the lms were cleaned form the residue on the surface by using distilled water, to prepare the lms for releasing study.
The buffers were made by preparing three solutions, 0.2 M of KCL, 0.2 N of HCL, and 0.2 N of NaOH. All solutions were put in a volumetric ask to make a volume of 100 ml with distilled water for each one. For pH 1.4 buffer, drops of HCL solution were added to 50 ml of KCL with continuous stirring until reaching the desired pH. Also, drops of NaOH solutions were added to 50 ml KCL solution for pH 6.4 buffer.
For the calibration curve, different clindamycin concentration solutions were prepared; 2, 2.5, 3, and 4 mg/ 50 ml distilled water clindamycin concentrations were used. The UV-Vis spectrophotometer was used for the analysis of these solutions (Spectronic 601, Milton Roy, Rochester, NY, USA) [23].

Drug Release Study:
The release of entrapped drugs, clindamycin, was examined by putting the lms loaded with the drug into 10 ml buffer solutions with pH 1.4 and 6.4 at 37°C. 3 ml from the samples were periodically withdrawn every 30 min using a pipette. The sample volume was replaced with water that had been distilled. Using a UV-Vis Spectrophotometer, withdrawn quantities were examined. The maximum absorption wavelength was determined at 150 nm. The amount of released amoxicillin was calculated using an appropriate calibration curve, curves of the released drug in pH 1.4, 6.4 solutions were showed in Fig. 7 [23], [24] 3. Result And Discussion:

Surface, Structural and Morphological Investigations:
The surface microscope images of the lms are shown in Fig. 1 Fig. 2 where (a) the surface images and (b) cross-sectional images, the pictures show both the surface and the side parts of the lm; the surface nature of the lms differ, some of which directly depict the pores, [7,21] and some of which have a rough surface and even the smooth surface of the lms. Some pictures show some clumps or bulges [21]. It seems that the Bentonite covers the pores on the surface as it appears in PCGB and PCXB. For cross-sectional, the images demonstrate porous presence in structure in the hydrogel [7], [14] despite its different sizes and shape, the pores are the gate for the exchange of gases and water vapor through the membranes, these pores appear in the form of laments, and in some lms, they appear as cracks or smaller pores accompanied with hole-shaped wrinkles. For some lms, it is not easy to estimate the exact dimensions within the lm and the porosity, but the general morphological information is a crucial indicator of their behavior in water absorption and water retention capabilities [20].

FTIR Analysis:
In Fig. 3a, FTIR is shown for the lms, there are new peaks appears compared with the pure components, these peaks may refer to the presence of cross-linking bonds. In the lm PCG, we can see aromatic rings,

XRD Analysis:
The XRD in Fig. 3b, a clear beak refers to the polymer blend showing the characteristic peaks for PVP-CMC-based polymer at 20.02°. It can be attributed to the amorphous nature of PVP for all the lms, maybe it crystalline peak, and there is another peak at 16.16° for PCG lm [6, 7, 23], so we can notice the presence of GG in the hydrogel lms may change the crystalline nature slightly and make some new peaks, and the BE can inhibit this ability.

Mechanical Properties:
The mechanical properties are important factors in biomedical elds; here, the mechanical properties are the young's modulus, elongation at break, and tensile strength [6], [7], [14], and all are listed in Table 2; in this table, we can see the tensile strength of all the four lms. We can see that young's modules or elasticity are described by the degree of deformation after the stress is removed, increase with tensile properties, and decrease elongation at break. We can refer that to the meshes of the networks [25], or in other words, the differences in the polymer's arrangement and Hydrogen binding [7]. The best lms were PCXB and PCGB, and we can refer that adding nanoparticle BE led to increasing the elasticity [26]; also, Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js the presence of CMC may have attributed to the better mechanical properties, which biopolymer is expected to improve the mechanical properties of a lm due to the increased a nity in the lm [6]. Other reasons for good elasticity, may be the addition of XG enhanced the mechanical properties and incorporated with other components [27]. Thus, PCXB and then PCGB have the best mechanical properties among the other lms, so BE enhanced the mechanical properties, and the impact of the gums is clear especially XG, which makes the mechanical properties more strength.

Color Qualities:
The color tests are essential to determine the appearance when this lm is used in biomedical soft contact lenses. In Table 3, the color test was based on standers values; we can notice that the color difference between all the lms [7]. Thus, all the lms have a slight color difference but are still visible to the human eye [6], [14]. The chroma signi es the color purity of a material or is entangled with the brightness and emitting or re ecting surface of an object [6]. PCXB has the highest color difference and chroma, which means that it is darker (more yellowish) and has the minor color purity of the four lms; the lightness (L), a, and b values also changed for the lms with the addition of additives to the PVP-CMC base material. Here again, XG has an impact on the colors, both PCXB is darker than PCGB and PCX is darker than PCG, and the addition of BE enhanced this ability to make the lms XG is the more visible lm among the others with almost ≈ 7 in ΔE and ≈10 in C. The contact angle evaluates the surface or the material hydrophobicity, which indicates the wettability of the bio lms. In Table 4, we can observe the differences between the lower and the upper sides [7]; in this case, we found in the lower and upper side of the PCGB lm, has lost its hydrophobicity or has low hydrophobicity comparing with the other lms, and for PCX, it close to be hydrophobic in the upper side, where the lower side through the experiment the water's drop did not make any contact angle, and the drop was absorbed directly. On the contrary, the contact angle of the upper and lower sides for the PCXB lm was increased; It has a high hydrophobicity; it is evident that all the lm's upper surface has better hydrophobicity than the lower surface [14]. The hydrophilic components (CMC, PEG, etc) may be compressed as they go down their tracks, in hydrogel composition [7], So, the best hydrogel lm is PCXB, it is evidence that BE enhanced the hydrophobicity of and XG hydrogel lms, more than the other lms and that's mean GG and XG lms have no good surface hydrophobicity themselves, but with BE, XG's ability increased.

Permeability:
WVP test is essential for determining the barrier properties of any lm; we can see from Table 5, PCGB has the best permeability while PCXB has the lowest permeability, and the reason may be for the lms' permeability have decreased with the introduction of various polysaccharides to the base PVP-CMC polymeric lms, The reason for the reduction in permeability may be due to the physical attractions among phases, which made the network denser and less prone to be penetrated by the permeant. The available volume for the gaseous interchange most likely has decreased because of the reactions among different ingredients in the nal polymeric network [14]. From this experiment, the permeability of all the lms is close to each other, but the impact of adding BE on GG increased its ability while on XG decreases its ability.
Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js 3.8 Solubility Assay: The ability to be dissolved, especially in water, is known by solubility, in Fig. 4a; the results of the solubility test are shown, The PCG lm is less solubility, and that may be because of the strong hydrogen bond that produced [14], compared with all the lms, PCXB lm has more solubility than the rest. Both bentonite lms were signi cantly soluble in water, compared with the PCXB lm which was soluble more than the other lms. However, despite GG and XG have high solubility in general [28], the effect of BE was remarkable for both. Both BE lms were signi cantly soluble in water. Furthermore, PCXB underwent structural deformation. In contrast, the other lms kept their shapes during the solubility assay. We can notice that GG solubility is less than XG in both cases, and no changes in the order with BE, which means XG is good soluble itself, and with BE this ability increased.

Swelling Assay:
Hydrogel swelling is typically de ned as an accumulation of uid, in Fig. 4b, the lms show good swelling properties, add to that GG and XG are soluble themselves [28]. The best lm is PCXB, although PCXB is highly soluble, it has a high swelling behavior also; To understand this, we should know the thermodynamic and kinetics factors determined by the time, so changes in the cross-linking make the polymer soluble and swollen, and layer thickness decreases with time due to the desorption of polymer chains [29], [30]. Thus, the best-swollen lm is PCXB. Furthermore, PCGB with PCXB, both contain BE. It was mentioned in [21] that BE increases the swelling abilities, especially with XG.

Thermal Analysis:
The thermal behavior of lms was studied in Fig. 5, based on the carves on gures, we investigate the degradation of the hydrogel lms almost divided into three stages [1], [21], the rst stages are below 110 C for PCGB, and below 100 ̊ C for PCXB, PCG, and PCX, which small weight is lost from all the lms, but guar gums lms lost it more. They may be due to the water evaporation from the lms. The second stage in all the lms was the signi cant weight loss from 150 to 320 ̊ C for PCG, 150 to 340 ̊ C for PCX, and PCGB, for PCXB 90 to 380 ̊ C. The nal further weight loss beyond 350 to 480 ̊ C for PCG, 360 to 460 ̊ C for PCX, for PCGB 370 to 500 ̊ C, and PCXB 410 ̊ C to 490 ̊ C have corresponded to the decomposition of oxygen-containing groups like hydroxyl, carboxyl, and/or epoxide groups, The decomposition process Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js nish at around 500 ̊ C with almost80% weight loss for all the lms [7]. We can notice PCGB and PCXB were the last degraded lms, so based on the results, the addition of BE could enhance the thermal stability of hydrogel lms [21]. Thus, PCGB and PCXB lms both have excellent thermal stability, and if the lms contain no BE, still GG lm better than XG. The signi cance of hydrogel is strongly in uenced by biodegradation study. It is one of the most important aspects that explain the impact of these lms on the environment, as well as the potential of their being converted into harmless material, particularly in soil. The ndings of this experiment are given in Table 6, which depicts the deterioration of the lms over four weeks and their initial weight. All of the hydrogel lms demonstrated their remarkable ability to biodegrade even in the absence of earthworms and only by the action of compost-rich soil during the trial period, as the lms disintegrated and lost more than three-quarters of their weight (30 days). BE has little in uence on decomposition rates, as evidenced by the fact that lms containing BE and those without it disintegrate at nearly the same rates, while the addition of GG has an impact.
One of the other ndings of this study is that most of the lms turned brown and did not return to their original color even after being washed with distilled water, indicating that soil content penetration and spread of soil moisture through the lms continue and that the degradation continues. Film thickness has also decreased dramatically every week. What evidence do you have that the lm has lost weight? This research backs up previous ndings on the degradation of hydrogel lms, which showed that breaking glycosidic bonds in the polymer chains leaves behind other free-moving components like PEG, which degrade slowly, and PVP, which may remain in the soil without causing any negative environmental effects.
These lms might decay to 90-95 percent of their original weight if the burry time is extended for another three weeks. So, PCG and PCGB are the most degraded lms, which means GG itself is the factor of increasing biodegradation. The amount of drug release from hydrogel lms was evaluated in this study. The release of water-soluble medicines trapped in hydrogels occurs when water enters the polymer network to expand and dissolve the drug. This medication diffuses to the lm surface via the waterways. As illustrated in Fig. 6, a clindamycin release pro le for drug-loaded hydrogel lms was provided in various liberation media or buffers, pH 1.4 and pH 6.4.
All of the lms have demonstrated a high level of drug release. It can also be seen that all lms release the drug in the same manner. In a lm PCGB, the maximum drug release rate was reported at 33% after 30 minutes When the medium was pH 1.4, the lowest rate of release was 31% in a lm PCX. Following that, the lms returned to release in a bigger number, surpassing 43 % of the lm PCX and around 40 % of the lm PCG after 90 minutes, before gradually decreasing.
When the medium was pH 6.4, the lms reacted similarly, with the maximum release reported at around 33% for a lm PCX and 31% for a lm PCXB at the 30th minute. After that, during the 90th minute, the lm's release a signi cant quantity of over 45 % for a PCGB lm and above 40 % for PCG, and then the release rate drops somewhat.
According to this method, around 95-99 % of the medication will be released from the lms after about 5 hours, ensuring the lms' e ciency in loading and discharging medicines. We may infer that the lm PCGB containing BE had the best release when tested at a medium pH of 6.4, whereas the PCXB lm had the highest release when tested at a medium pH of 1.4. Even though the percentages are almost similar, the drug release at medium pH 6.4 was signi cantly higher. So, we can understand the impact of adding BE in the releasing properties of the drug in the hydrogel lms, and that is clear in PCGB and PCXB lms, and that could be noticed separately in GG lms which have low releasing abilities.

Conclusion
In this study, four PVP-CMC-gums based on hydrogel lms were produced, and the impact of adding Gums, and Bentonite clay were studied; all the results show that Bentonite enhanced most of the properties of hydrogel lms, and we can refer that sometimes to the addition of the gum which means these lms can be used in various biomedical applications based on the main desired feature of the application.
From the results, we can see the new peaks of the lm, which are different from the pure materials, and that means, in these lms, some reactions and bindings happened and played a role in creating new cross-linking, that ensures the high success of these hydrogel lms in speci c biomedical applications such as drug delivery. SEM and Microscope showed the possibility of founding porous structure inside the lms, we can conclude from color, surface hydrophobicity, solubility, and swelling, properties PCXB lm is the best. In contrast, PCGB lm has the best results in biodegradation and permeability results, and         Loading [MathJax]/jax/output/CommonHTML/fonts/TeX/fontdata.js