Introduction

Polymer blending is considered the most interesting method employed in broad usages, such as; energy storage systems, fuel cells, and humidity sensors [1,2,3]. Due to its unique and sought-after properties, research on polymer blending has brought a significant shift in industrial practice and pharmaceuticals in recent years [4,5,6]. The presence of polymer in the form of films offers an opportunity to produce another variant of polymer with good mechanical, thermal, and inhibitory properties [7].

The importance of polyvinyl alcohol (PVA) as a polymer is highly rated because of its chemical and physical properties [8] over the years; research interest in this field has increased. PVA is semi-crystalline nature used widely in medical devices, because it possesses (among other things) adsorption, biocompatibility, and high solubility of water characteristics [9,10,11]. In addition, it is a nontoxic and low-cost polymer used in wound dressing, tissue engineering scaffolding, and as part of controlled drug delivery systems [12,13,14]. Polyvinyl Pyrrolidone (PVP) has a high polar group, low toxicity, biodegradable and amorphous nature with good film properties. It has two interactive sites N atom and C=O group. It acts as a protecting agent with other surfaces of inorganic compounds [15].

Over the past decade, metal nanoparticles were extensively studied because of their use in different usages [16,17,18,19,20,21,22]. Metal nanoparticles have a very important role in applied science and technology [23,24,25,26,27,28,29,30]. Numerous methods are used to prepare metal nanoparticles [31], such as laser ablation technique, method of chemical reduction, method of microorganism arc-discharge, photo-reduction, and bio-surfactant technique [32]. The attractive and innovative technique of laser ablation is currently and extensively employed to synthesize nanomaterials, which provide a clean, facile, and cost-effective method for preparation [33,34,35,36]. When an intense beam of laser hits the surface of the solid target, the nanoparticles are produced. It is a simple and non-contaminated technique [37].

Ionic metal oxides nanoparticles (NPs) such as CuO NPs are very interesting antimicrobial agents, because they have a high number of corners and edges, high surface areas, and many reactive sites [38]. It shows a variety of possible physical properties, and it can be easily combined with polymers to provide special physico-chemical properties to the composites. These nanoparticles, which have high surface areas and crystalline structures, can be used with a certain dose to have antimicrobial effects [39].

In this study, the structural, optical, and morphological characterization of PVA/PVP blend embedded by various ratios of CuO NPs by changing laser ablation time (3, 5, 10, and 15 min) were studied. The cell viability behavior and the antibacterial activity were performed for the prepared samples. This process provides an easy and low-cost method for preparing nanocomposite and uses it for biomedical application such as wound healing application.

Materials and method

Materials

PVA (M.W. ≈ 130 K) and PVP (M.W. ≈ 72 K) polymers brought from ACROS. Deionized water was used in the preparation of both PVA and PVP. The high pure copper plate was performed from Sigma-Aldrich.

Synthesis of PVA/PVP composite

0.7 gm of PVP and 0.7 gm of PVA have been dissolved in 70 ml of deionized water for 5 h at 50 °C to get a homogenous PVA/PVP composite.

Doping PVA/PVP with CuO NPs by laser ablation

CuONPs have been dispersed in PVA/PVP matrix by laser ablation. A pure copper plate with suitable dimensions has been placed in a beaker containing 10 ml of the produced PVA/PVP blend. Fundamental Nd:YAG laser beam having1064 nm wavelength, 10 Hz repetition rate, and 3.6 W power was streamlined and focused on a copperplate via the convex lens to be on its surface to support the ablation and formation of CuO NPs in the PVA/PVP matrix. This detailed experiment called the one-potential laser ablation process was obtained and employed [40]. Copper oxide nanoparticles have been doped with PVA/PVP blend with various ratios by changing the ablation times (0, 3, 5, 10, and 15 min) as obtained in Table 1. The nanocomposite blends are stirred well and sonicated using dip sonicator Hielscher Up 100 H to affirm the good dispersion of CuO NPs into blend solution. The resulting PVA/PVP blends have been casted in plastic Petri dishes then dried in an oven at 40 °C for 36 Hours. The thickness of the nanocomposites was found to be about 0.22 mm.

Table 1 Contents of copper oxide nanoparticles embedded in PVA/PVP blend by laser ablation
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Characterization techniques

XRD patterns of PVA/PVP composites embedded by different ratios of CuO NPs have been investigated by PANalytical X-Pert PRO by Cu target with Kα radiation of wavelength (λ = 1.540 Å)in Bragg angle (2θ) = (5–80°). FT-IR spectral data showed within the range 4000–400 cm−1 via Jasco spectrometer, 6100, Japan. UV–visible spectral data collected in the range of 180 to 1000 nm by a double beam spectrophotometer JASCO Corporation, V-570. Morphological features of films were obtained by FESEM type (Quanta FEG 250, USA). Differential scanning calorimetry (DSC-50, Shimadzu, Japan) has been used to conduct thermal analysis of the synthesized films, with a temperature range of ambient temperature to 375 °C with a heating rate of 10 °C/min.

The human osteoblast cell line HFB4 has been grown in Dulbecco's modified Eagle medium (DMEM, Gibpco) at 35 °C to evaluate the cell viability of PVA/PVP/CuONPs nanocomposites. Cells seeded at a density of 5 × 103 cells/cm2 have been grown on PVA/PVP/CuONPs nanocomposite in 12-well plates. The medium has been isolated after three days of incubation and MTT has been dispersed into each well, then the cell viability has been obtained using an optical analyzer as obtained in the following formula [41]:

The antimicrobial behavior of PVA/PVP blend embedded by various ratios of CuO NPs was performed against Gram-negative bacteria; E. coli and Gram-positive bacteria; S. aureus. PVA/PVP/CuO NPs were poured into Petri dishes containing Mueller-Hinton agar media and incubated at 38°Cfor 36 h. The antibacterial activity was calculated by measuring the diameter of the inhibition zone after incubation [42].

Results and discussion

X-ray Diffraction Analysis (XRD)

XRD scans offered a lot of valuable information about the compounds' scale, orientation, and crystal structure. XRD scans of PVA/PVP composite embedded by CuO NPs at various laser ablation times (0, 3, 5, 10, 15 min) at room temperature are presented in Fig. 1. Owing to the semi-crystalline structure of PVA supported by the hydrogen bonds, PVA has diffraction patterns at 2θ = 19.6° and 40.5°. There is another diffraction pattern at 2θ = 22.7° with low intensity [43,44,45]. Hence, PVP has two semicrystalline patterns at 2θ = 10.3° and 21.4° [46, 47].

Fig. 1
figure 1

XRD patterns of a PVA, b PVA/PVP, and PVA/PVP/CuO NPs at different laser ablation time c 3 min, d 5 min, e 10 min, f 15 min and g PVP

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The PVA/PVP blend film at laser ablation time (0 min) has two diffraction patterns at 2θ = 10.4° and 19.6°; this affirmed the interaction and miscibility between PVA and PVP because of the existence of O–H group in PVA and C=O group in PVP and the strong interaction between them [48].

For PVA/PVP blend films embedded by CuO NPs at various laser ablation times (3, 5, 10, 15 min), there is an additional diffraction peak at 2θ = 38.1º that is paralleled with CuO NPs [49]. There is a shift in the diffraction peak at 2θ = 10.4º towards a lower diffraction angle. As seen in Fig. 1 c-f, the intensity of peak at 2θ = 38.1º lowered with raising the time of ablation. This means that as more bonds were broken, new bonds were built in the polymer matrix between the blend groups and CuO NPs. Also, the peak broadening increases by raising the time of laser ablation, and this established the interaction between PVA/PVP polymer blend and CuO NPs.

The average crystal size (D) of CuO NPs is measured from XRD using Scherrer’s equation;

$$D = 0.915\lambda /F\cos \theta$$
(1)

The crystal size of CuO NPs was 32 nm.

Fourier transform infrared (FTIR)

Figure 2 illustrates FT-IR spectra of PVA, PVP, and PVA/PVP blend films embedded by CuO NPs at various times of laser ablation (0, 3, 5, 10, 15 min). For PVA, the O–H stretching vibration has been cleared at 3305 cm−1. The symmetric stretching vibrations of C-H group have been seen at 2923 cm−1. The asymmetric stretching vibrations of C–H group were seen at 2852 cm−1. The vibrational band at 1725 cm−1was attributed to C=C stretching vibration, while O–H bending vibration was cleared at 1651 cm−1. The bending vibration of C-H group was seen at 1431 cm−1. The wagging vibration of C-H group was seen at 1375 cm−1, respectively. At 1242 cm−1, the C-H wagging of acetate residue was obtained and C-O stretching vibrations were located at 1087 cm−1 and 1023 cm−1. At 845 cm−1, the rocking vibration of CH2 was seen [50,51,52]. For PVP, the stretching vibration of O–H group was obtained at 3405 cm−1. The C-H bending vibrations have two bands at 1427 cm−1 and 1373 cm−1. The C-N bending vibration was observed at 1278 cm−1. CH2 twisting and rocking vibrational bands were seen at 1220 cm−1 and 1012 cm−1. The band at 564 cm−1 is assigned to N–C=O bending vibrations [53,54,55,56].

Fig. 2
figure 2

FTIR-ATR of a PVA, b PVP, c PVA/PVP, and PVA/PVP/CuO NPs at different laser ablation time d 3 min, e 5 min, f 10 min and g 15 min

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For PVA/PVP blend film at laser ablation time (0 min), there was a shift in O–H stretching vibration, in addition to the appearance of new bands at 1740 cm−1, 1490 cm−1, and 1250 cm−1 that corresponded to C=O stretching vibration, C-H bending vibration and C–O–C stretching. There was also a shift in the bands at 1644 cm−1 with a decrease in intensity of all bands. These results agreed with XRD analysis and confirmed the complexation between PVA and PVP [57].

For PVA/PVP blend films embedded by CuO NPs at various times of laser ablation (3, 5, 10, 15 min), there was a slight shift in O–H stretching vibration that became broader compared to PVA/PVP polymer blend film at laser ablation time (0 min). In addition, the intensities of all bands changed irregularly with the addition of CuO NPs and ablation time. This indicates that there was an interaction between PVA/PVP and CuO NPs.

Optical properties

Figure 3 obtains UV–Vis spectra of PVA/PVP composite embedded by CuO NPs at several times of laser ablation (0, 3, 5, 10, 15 min). There was a maximum absorption peak at 225 nm in PVA/PVP composite film at laser ablation time (0 min) spectrum that corresponded to π-π* transition of unsaturated bonds in polymer blend [58].

Fig. 3
figure 3

UV–Vis of a PVA/PVP and PVA/PVP/CuO NPs at different laser ablation time b 3 min, c 5 min, d 10 min and e 15 min

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For PVA/PVP blend films embedded by CuO NPs at various times of laser ablation (3, 5, 10, 15 min), there was a small shift toward high wavelength. This shift correlated with the intermolecular bonding of hydrogen between the adjacent hydrogen groups in the chain of polymer and Cu ions or due to the bonding of hydrogen between C=O of PVP and Cu ions [49]. In addition, there was an additional peak at 336 nm and their intensity was raised by raising the time of laser ablation that approved the complexation between PVA/PVP and CuO NPs polymer.

It is known that Beer–Lambert law demonstrates the transfer of light through the materials according to that relation [59].

$$\mathrm{I}={\mathrm{I}}_{0}{\mathrm{e}}^{-\mathrm{\alpha d}}$$
(2)

where I is the intensity of the transmitted light and I0is the intensity of the incident light, d is the thickness of the film and α is the absorption coefficient that must be analyzed in order to examine the existence of any changes in the band structure. The above relation can be written as following [60]:

$$\mathrm{\alpha }*\mathrm{d}=\mathrm{ln}\frac{{\mathrm{I}}_{0}}{\mathrm{I}}=\mathrm{ln}10*\mathrm{log}\frac{{\mathrm{I}}_{0}}{\mathrm{I}}=2.303*\mathrm{A }\to \mathrm{ \alpha }=\frac{2.303}{\mathrm{d}}\mathrm{ A}$$
(3)

where A is the absorbance.

Figure 4 obtains the relation between α and photon energy (hʋ). It is shown that the value of absorption edge of PVA/PVP blend was decreased irregularly by the addition of CuO NPs at various times of laser ablation (see Table 2). The shift to lower photon energy means that the bandgap lowered.

Fig. 4
figure 4

Relation between α and hʋ for PVA/PVP and PVA/PVP/CuO NPs at different laser ablation time (3, 5, 10 and 15 min)

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Table 2 Optical parameters values of PVA/PVP blend embedded by various ratios of CuO NPs at various laser ablation time
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In amorphous and disordered materials, the Urbach tail has been observed and is one of the tools that is used for describing the characteristics of the electronic transition of these materials. Urbach tail width is a measure of the defect levels between the conduction and valence bands in the forbidden bandgap. Previous research showed that the absorption coefficient was represented by the Urbach relationship in the exponential-edge region [61, 62].

$$\alpha = \alpha_{{0{ }}} \exp \left( {\frac{{{\text{h}}\upsilon }}{{{\text{E}}_{{{\text{ur}}}} }}} \right)$$
(4)

where α0 is a constant and Eur is the width of the band tails. The relationship between lnα and hʋ in Fig. 5 was depicted by a straight line. Values of Eur are listed in Table 2, as seen with the addition of CuO NPs and increasing the times of ablation, Eur increased. The raising in Eur indicates a raise in the amorphous regions in the materials. There are no sharp cutoffs for both conduction and valence bands, in amorphous materials, but in the lower energy region, they have tails of localized states.

Fig. 5
figure 5

Relation between ln α and hʋ for PVA/PVP and PVA/PVP/CuO NPs at different laser ablation time (3, 5, 10 and 15 min)

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The increase in tail width could be due to the fact that raising the CuO NPs content and ablation time in the PVA/PVP blend can contribute to the production of ionic complexes, disorders, and imperfections. This leads to a rise in localized states within the forbidden bandgap of energy [63].

Davis and Shalliday obtained the indirect and direct transitions that could be occurred near the edge of the basic band, and via plotting (αhʋ)1/2 versus hʋ used to perform the optical bandgap by using this relation [64, 65].

$$\left( {\alpha {\text{h}}\upsilon } \right)^{{{1}/{2}}} = {\text{B }}({\text{h}}\upsilon - {\text{E}}_{{\text{g}}} )$$
(5)

The plot of (αhʋ)1/2 versus hʋ is obtained in Fig. 6. As seen in Table 2 the values of indirect bandgap energy decreased compared to PVA/PVP polymer blend at laser ablation time (0 min). This means that as the amorphous region in PVA/PVP blend increases, by addition of CuO NPs, the disordering increases.

Fig. 6
figure 6

Relation between (αhʋ)0.5 and hʋ for PVA/PVP and PVA/PVP/CuO NPs at different laser ablation time (3, 5, 10 and 15 min)

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Scanning Electron Microscopy (SEM)

SEM images of PVA/PVP embedded by CuO NPs are obtained in Fig. 7. SEM micrographs show the homogenous nature of pure PVA/PVP blend in Fig. 7a. Figure 7b obtains SEM photographs that show a homogenous distribution of CuO NPs through the prepared blend on its surface. CuO NPs appear on the surface as spherical white points. These white points in the high laser ablation time (15 min) were observed as big points because of the aggregations of copper oxide nanoparticles. In other words, the white points are raising as the ratio of CuO NPs raised in the PVA/PVP composite when the laser ablation time is raised. These photographs approved the distribution of CuO NPs on the surface of the PVA/PVP blend sample in semi-uniform manner.

Fig. 7
figure 7

FESEM photographs for PVA/PVP and PVA/PVP/CuO NPs at laser ablation time (15. min)

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Differential scanning calorimetry (DSC)

Figure 8 represents the DSC thermogram of PVA, PVP, PVA/PVP and PVA/PVP incorporated with CuO NPs at various laser ablation time. As seen PVA has melting temperature at 191 °C and decomposition temperature at 316 °C [66], while PVP has melting temperature at 98 °C [67]. For PVA/PVP and PVA/PVP/CuO NPs, there is a noticeable shift to higher temperature either with blending or by additive of nano-fillers. These affirm the thermal stability of polymer nanocomposite increases with addition of CuO NPs and confirmed the intermolecular interaction between PVA/PVP polymer chains and nano-filler.

Fig. 8
figure 8

DSC curves for PVA, PVP, PVA/PVP, and PVA/PVP/CuO NPs at different laser ablation time (3, 5, 10 and 15 min)

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Cell viability

The responses of the cell line of fibroblasts toward PVA/PVP/CuO NPs nanocomposite predict the propensity of these films to be recommended for wound healing usages applications. The cell viability of these nanocomposites has been investigated as obtained in Fig. 9. It is evident that the cell viability of PVA/PVP matrix was 78.1 ± 3.4% and has been increased to 81.2 ± 4.2% after PVA/PVP matrix is embedded by CuO NPs via laser ablation time (3 min). The values of cell viability were increased by raising the ratios of CuO NPs inside PVA/PVP blend to 96.7 ± 3.5% for PVA/PVP blend film at laser ablation time (15 min). This is a strong indication that there is a presence of high biocompatibility of copper oxide in the PVA/PVP composite. The low ratios of CuO NPs inside PVA/PVP blend potentiate its degradation without causing fatal adverse effects. This behavior of cell viability could affect the antibacterial activity that could decrease the possible invasion and enable the development and distribution of normal cells instead of death.

Fig. 9
figure 9

Cell viability for PVA/PVP and PVA/PVP/CuO NPs at different laser ablation time (3, 5, 10 and 15 min) through HFB4 cell line in vitro

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Antibacterial assessment

The potential to facilitate wound healing and other biomedical applications relies heavily on bacterial invasion inhibition, as the latter can deteriorate the cohesion of the wound. The antibacterial activity of PVA/PVP blend doped with various ratios of CuO NPs by laser ablation has been investigated against E. coli and S. aureus. As shown in Fig. 10 and Table 3, pure PVA/PVP blend (at laser time ablation (0 min)) obtain the low inhibition zone; 8.2 ± 0.5 and 9.5 ± 0.4 against E. coli and S. aureus, respectively. Moreover, the inhibition zone of PVA/PVP blend embedded in CuO NPs via laser ablation time (3 min) was 13.2 ± 0.4 and 15.4 ± 0.6 against E. coli and S. aureus, respectively. The values of inhibition zones were raised by increasing the ratios of CuO NPs inside PVA/PVP composite to 18.5 ± 0.5 and 20.4 ± 6.0 against E. coli and S. aureus, respectively, for PVA/PVP blend at laser ablation time (15 min). The antibacterial activity has been attributed to an increase in the copper oxide nanoparticles inside PVA/PVP blend and it depends on the capability of the released ionic CuO to degenerate bacterial cells [68]. The high antibacterial activity of the polymeric nanocomposite requires further investigation before it can be used in clinical applications.

Fig. 10
figure 10

Antibacterial behavior for PVA/PVP and PVA/PVP/CuO NPs at different laser ablation time (3, 5, 10 and 15 min) against E. coli and S. aureus

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Table 3 Antibacterial activity of PVA/PVP blend embedded by various ratios of CuO NPs against E. coli and S. aureus
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Conclusion

PVA/PVP doped with different ratios of CuO NPs prepared via laser ablation (0, 3, 5, 10, 15 min) using casting technique method is characterized using XRD, FTIR-ATR, and UV–Vis techniques. Confirmation of the interaction and compatibility between PVA, PVP, and CuO NPs are affirmed by XRD and FTIR-ATR. UV–Vis and optical parameters showed that embedding by CuO NPs into PVA/PVP composite decreased the crystallinity of the nanocomposite system. It seems from DSC analysis that thermal stability increased by increasing CuO NPs. Antibacterial activity and cell viability have been increased with increasing CuO NPs at laser ablation time 15 min. These results could lead to the suggestion of PVA/PVP/CuO NPs for wound healing utilization.