Studi Perbandingan Efek Antimikroba Nanokomposit dan Komposit Berbasis Poli(butilena adipat-co-tereftalat) Menggunakan Cu dan Cu/Cu2O Nanopartikel dan CuSO4

Hasil dan Diskusi

Reometri digunakan untuk mendapatkan pengukuran dinamis dari sifat reologi nanokomposit dalam kondisi yang mendekati kondisi aktual di mana nanokomposit diproses. Untuk ini, pengukuran dilakukan untuk mengontrol perubahan viskositas selama pencampuran lelehan. Hasil pengukuran ini ditunjukkan dalam File tambahan 1:Gambar S5. Peningkatan torsi motor terkait dengan viskositas leleh polimer [21, 36], dan nilainya mulai konstan setelah 4 menit pencampuran. Ini menegaskan bahwa waktu pencampuran 7  menit yang ditetapkan dalam pekerjaan ini sudah cukup untuk mencapai pencampuran yang sempurna.

Nilai torsi untuk matriks PBAT dan NCs-PBAT/Cu 1% berkisar 19,86 N m. Kurva (File tambahan 1:Gambar S5) menunjukkan bahwa konsentrasi 1% Cu-NP memiliki sedikit efek pada sifat mekanik matriks, tetapi nilai torsi kesetimbangan yang lebih rendah sebesar 18,4 dan 17,4 N m diperoleh untuk NCs-PBAT/Cu 3 % dan NCs-PBAT/Cu masing-masing 5%. Hasil ini jelas menyiratkan bahwa kemampuan proses NCs-PBAT/Cu ditingkatkan sehubungan dengan matriks PBAT [37]. Hasil yang sama diperoleh dengan campuran NCs-PBAT/Cu|Cu₂ O, dimana nilai torsi keseimbangan menurun dengan peningkatan persentase beban menjadi 3%, tetapi beban 5% menghasilkan nilai yang sangat dekat dengan beban 1% Cu|Cu₂ O-NP. Nilai torsi kesetimbangan masing-masing adalah 19,39, 19,07, dan 19,37 Nm untuk 1, 3, dan 5%. Untuk MC-PBAT/CuSO₄ campuran, nilai torsi kesetimbangan meningkat seiring dengan beban CuSO₄ meningkat, yaitu 18,71 Nm untuk 1%, 19,16 Nm untuk 3%, dan 19,79 Nm untuk 5% beban. Perilaku ini dapat dikaitkan dengan ukuran CuSO₄ kristal. Secara bersamaan, File tambahan 1:Gambar S5 menunjukkan bahwa torsi kesetimbangan semua nanokomposit dan material komposit stabil dengan bertambahnya waktu pencampuran, menunjukkan bahwa dekomposisi termal tidak terjadi dalam mixer, mungkin karena nanopartikel menurunkan gaya kohesi antara rantai polimer dan kemungkinan besar melakukan pelumasan sendiri dalam proses pencampuran [37].

Properti Morfologi dan Struktural

Pertama, nanopartikel yang diperoleh dengan reduksi kimia dianalisis. Hasil Sintesis Cu|Cu₂ O-NP ditunjukkan pada Gambar. 1b. Mikrograf TEM menunjukkan campuran partikel bola dan partikel polihedral. Diameter rata-rata nanopartikel sferis adalah 26 nm (Gbr. 1c), sedangkan diameter nanopartikel polihedral berkisar antara 80 dan 160 nm. Komposisi nanopartikel ini ditentukan oleh difraksi elektron area terpilih (SAED) (Gbr. 1c), yang menemukan fase yang sesuai dengan logam Cu dan Cu₂ O. Temuan ini dikuatkan oleh difraktogram yang ditunjukkan pada Gambar 1a. Enam puncak difraksi teramati dengan jelas pada 2θ = 36,3°, 42,17°, 43,42°, 50,63°, 61,47°, dan 74,37°. Karena nanopartikel disintesis secara kimia mereduksi CuSO₄ untuk CuO, puncak difraksi diverifikasi oleh data untuk Cu dalam database X'Pert HighScore pola difraksi serbuk sinar-X. Kami mengamati bahwa puncak pada 2θ = 43,2°, 50,63°, dan 74,37° termasuk dalam bidang difraksi logam Cu (111), (200), dan (220). Tiga puncak lainnya menunjukkan bahwa nanopartikel yang disintesis mengandung lebih dari satu zat, sehingga pola difraksinya merupakan kombinasi keduanya. Wijesundera [38] menganalisis film tipis Cu₂ O menggunakan XRD dan menunjukkan bahwa bidang difraksi pada 2θ = 36,3°, 42,17°, dan 61,47° sesuai dengan indeks Miller (111), (200), dan (220). Indeks ini milik struktur kubik berpusat muka (FCC) yang sesuai dengan bagian dari area pusat struktur antifluorit, yang sesuai dengan struktur Cu₂ O, sesuai dengan temuan analisis SAED.

a XRD nanopartikel Cu dan CuO2 disintesis. b , c Gambar TEM, distribusi ukuran, dan pola difraksi nanopartikel yang disintesis. d XRD nanopartikel Cu. e , f Citra TEM, distribusi ukuran, dan pola difraksi nanopartikel Cu

Wang dkk. [39] menemukan bahwa selama sintesis Cu-NPs dengan reduksi kimia, ukuran partikel berkisar antara 100 dan 150 nm. Mereka menggunakan C₆ H₈ O₆ sebagai zat pereduksi dan poli(vinilpirolidon) (PVP) sebagai surfaktan. Wajahnya tidak sesuai dengan wajah Cu₂ O karena PVP membantu menstabilkan benih yang sedang tumbuh, sehingga menghindari oksidasinya. Namun, tujuan dari penyelidikan kami adalah untuk mensintesis Cu₂ O NP, yang dapat dicapai dengan reduksi kimia tanpa menggunakan bahan penstabil seperti PVP.

Cu-NP yang digunakan dalam preparasi nanokomposit berbentuk bulat dengan diameter berkisar antara 100 dan 200 nm (Gbr. 1e, f). Dalam pola XRD untuk Cu-NP yang ditunjukkan pada Gambar 1d, tiga puncak jelas diamati pada 43,60 °, 50,72 °, dan 73,95 ° sesuai dengan bidang kristal (111), (200), dan (220), masing-masing. Struktur kristal kubik dengan grup ruang Fm3m (JCPDS No.85-1326) [55] sesuai dengan struktur yang ditemukan oleh analisis SAED (Gbr. 1d).

Partikel logam yang digunakan dalam penelitian kami diperoleh melalui sistem penggilingan mekanis, menurut pemasok. Kerugian dari metode ini adalah persentase partikel yang kecil (~ 10%) lebih besar dari 500 nm. Namun, ini tidak berdampak negatif terhadap tujuan penyelidikan kami. Di bawah ini, kami menunjukkan bagaimana dispersi ini memengaruhi sifat termomekanis matriks PBAT. Yang penting, metode penggilingan mekanis tidak menggunakan prekursor atau stabilisator, seperti halnya dengan metode sintesis basah, yang dikenal sebagai metode reduksi kimia. Oleh karena itu, permukaan Cu-NP yang diperoleh dengan penggilingan tidak dipasifkan oleh adsorpsi molekul baik dari penstabil atau produk samping reaksi. Dengan demikian, Cu-NP ini, meskipun tidak secara substansial meningkatkan sifat mekanik polimer, juga tidak menurunkannya. Namun, sifat antimikroba harus ditingkatkan karena migrasi Cu ²⁺ difasilitasi pada permukaan yang tidak dipasifkan.

Gambar 2 menyajikan spektrum XRD dari NCs-PBAT/Cu (Gbr. 2a), NCs-PBAT/Cu|Cu₂ O (Gbr. 2b), dan MCs-PBAT/CuSO₄ (Gbr. 2c). Gambar 2c disiapkan pada tiga konsentrasi (1, 2, dan 3% w /dengan ). Difraktogram ini dibandingkan dengan matriks polimer PBAT untuk menunjukkan pengaruh beban pada struktur polimer. Difraktogram PBAT menunjukkan pola difraksi dengan lima puncak difraksi pada 2θ = 16,1°, 17,3°, 20,2°, 23,1°, dan 25°, bersesuaian dengan bidang (011), (010), (101), (100), dan (111) masing-masing. Analisis ini mengungkapkan adanya kristalinitas dalam matriks polimer. Karakterisasi PBAT oleh Arruda et al. [40] menggunakan XRD juga menemukan lima puncak difraksi yang sama pada sudut yang sama seperti yang ditemukan dalam penyelidikan ini, sesuai dengan bidang yang sama.

Difraktogram PBAT, NCs-PBAT/Cu, NCs-PBAT/Cu|Cu₂ O, dan MCs-PBAT/CuSO₄

Difraktogram nanokomposit dengan beban Cu-NP ditunjukkan pada Gambar 2a. Sinyal 2θ pada 43°, 50°, dan 74° adalah karakteristik bidang (111), (200), dan (220) struktur FCC Cu dengan grup ruang Fm3m (JCPDS No.85-1326) [ 41]. Tidak ada fase yang berhubungan dengan CuO atau Cu₂ O teramati pada difraktogram NCs-PBAT/Cu, sehingga kami menyimpulkan bahwa nanopartikel tidak teroksidasi selama sintesis nanokomposit. Selain itu, difraktogram menunjukkan bahwa nanopartikel tidak mempengaruhi atau memodifikasi struktur PBAT dan intensitas puncak berbanding lurus dengan persentase beban Cu-NP. Difraktogram dari NCs-PBAT/Cu|Cu₂ O memiliki enam puncak karakteristik pada 2θ = 36,4°, 43°, 42.4°, 50°, 61.5°, dan 74° (Gbr. 2b). Menurut literatur dan analisis nanopartikel, hanya tiga yang sesuai dengan logam Cu dan puncak pada 36,4°, 42,4°, dan 61,5° milik Cu₂ O, menurut spektrum jenis nanopartikel ini ditunjukkan pada Gambar. 1a [35].

Puncak difraksi sesuai dengan Cu|Cu₂ Penguatan O-NP menjadi lebih kuat seiring dengan peningkatan konsentrasi di dalam matriks, tetapi puncak yang termasuk dalam zona kristalin polimer sedikit menurun intensitasnya dengan penggabungan beban. Chivrac dkk. [42] melaporkan hasil yang sama dalam penelitian yang menggunakan banyak nanoclays di PBAT. Mereka menyarankan bahwa tidak ada transkristalinitas yang signifikan pada antarmuka polimer beban, dan oleh karena itu, tidak ada perubahan dalam struktur kristal polimer. Namun, penurunan intensitas puncak difraksi PBAT dengan peningkatan konsentrasi beban dalam matriks menunjukkan penurunan kristalinitas PBAT. Oleh karena itu, beban menghambat pertumbuhan kristal PBAT. Ini bisa menjelaskan sedikit penurunan puncak difraksi milik PBAT dengan peningkatan Cu|Cu₂ O-NP.

Gambar 2c menunjukkan spektrum XRD MC-PBAT/CuSO₄ untuk ketiga konsentrasi CuSO₄ dari 1, 3, dan 5%. Penambahan CuSO 1%₄ beban tidak menghasilkan perubahan pada polimer. CuSO 3 dan 5%₄ kurva beban hanya menunjukkan peningkatan minimum intensitas puncak pada 2θ = 36,4°, 40.25°, 43.94°, 57.9°, dan 75,7°, yang termasuk dalam Cu dan Cu₂ O hadir, menunjukkan bahwa sebagian kecil dari Cu₂ JADI₄ tereduksi dan teroksidasi selama proses pencampuran. Sedangkan untuk zona kristalin PBAT, terjadi peningkatan konsentrasi CuSO₄ penguatan menurunkan intensitas puncak difraksi di PBAT, seperti yang terjadi untuk NCs-PBAT/Cu dan NCs-PBAT/Cu|Cu₂ O. Dengan demikian, penggabungan CuSO₄ ke dalam matriks polimer menurunkan kapasitas kristalisasinya, mungkin karena CuSO₄ menghambat pertumbuhan kristal. Karena tidak ada informasi tambahan tentang spektrum XRD CuSO₄ dalam bahan komposit telah dilaporkan, kita harus menyelidiki perilakunya dalam polimer biodegradable. Derajat kristalinitas matriks dihitung sebagai:

dimana Aku _c adalah luas puncak fase kristal dan I _c + Aku _a adalah luas total di bawah difraktogram. Nilai derajat kristalinitas untuk masing-masing bahan disajikan pada Tabel 1. Hasil ini menunjukkan bahwa persentase kristalinitas meningkat seiring dengan konsentrasi Cu-NP dan Cu|Cu₂ O-NP meningkat dalam matriks PBAT, yang terbukti dengan meningkatnya intensitas puncak di masing-masing difraktogram.

Di sisi lain, difraktogram menunjukkan bahwa nanopartikel tidak mempengaruhi atau memodifikasi struktur PBAT dan intensitas puncak berbanding lurus dengan persentase beban Cu-NP dan Cu|Cu₂ O-NP. Selain itu, penambahan CuSO₄ garam prekursor menurunkan kristalinitas polimer dibandingkan dengan polimer dalam keadaan murni. Kondisi ini terjadi karena penambahan konsentrasi beban pada nanokomposit meningkatkan persentase relatif kristalinitas tetapi menurunkan kristalinitas PBAT, sehingga secara umum dilaporkan sedikit peningkatan persentase total kristalinitas. MC-PBAT/CuSO₄ beban tidak menyajikan puncak kristal dalam spektrum XRD mereka. Oleh karena itu, mereka tidak berkontribusi pada peningkatan kristalinitas tetapi menyebabkan penurunan kristalinitas dalam rantai polimer, yang menjelaskan penurunan persentase total kristalinitas dalam material komposit. Beberapa penelitian telah menunjukkan bahwa nanopartikel logam bertindak sebagai pusat nukleasi dalam orientasi rantai polimer, yang pada gilirannya meningkatkan kristalinitas polimer [43].

The FTIR (Additional file 1:Figure S6) spectra show that the characteristic peaks at different load concentrations are at the same frequency but have different intensities. The spectra show that as the concentration of nanoparticles in the polymer matrix increased, the intensity of the peaks corresponding to NCs-PBAT/Cu and NCs-PBAT/Cu|Cu₂ O increased with respect to the PBAT. Therefore, there was no effective interaction between the chains of the PBAT and the nanoparticles. Had there been interaction, some of the signals in the FTIR spectrum would have been displaced as a result of the interaction of the functional groups of the polymer with the surface of the PBAT [40].

Mechanical Properties (Tensile Test)

To give multifunctionality to biopolymers, nanomaterials that provide special properties to a nanocomposite are usually incorporated. Their inclusion will change the mechanical properties of the material and the intensity of the changes is directly related to the union of the nanostructure with the polymer network [44]. We conducted tensile tests on the nanocomposites and the composite material. The tensile strength and maximum deformation values are summarized in Table 2.

Figure 3 shows the average curves of the tensile tests on the nanocomposites and composite material. As the permanent deformation of the material began, the effect of the concentration of the nanoparticles in the polymer could be distinguished. Figure 3a shows the results for NCs-PBAT/Cu. The results show that the inclusion of nanostructures did not considerably affect the elastic range but there were noticeable changes in the yield strength. As the concentration of the Cu-NPs increased, maximum resistance increased and maximum elongation decreased. These changes clearly indicate that the nanostructures harden the PBAT. At 3% concentration of Cu-NPs, the tensile strength slightly increased but the elongation percentage in the fracture decreased between 30 and 35%.

Stress and strain of PBAT, NCs-PBAT/Cu, NCs-PBAT/Cu|Cu₂ O, and MCs-PBAT/CuSO₄

Figure 3b shows the results of the tensile tests on the NCs-PBAT/Cu|Cu₂ O. The 1% load nanocomposite clearly showed an increase in tensile strength and elongation with respect to the PBAT. There was no appreciable effect on the elastic range, but it did appear to be above the yield stress. In addition, the curve for the 3% load NCs-PBAT/Cu|Cu₂ O shows there was no significant difference with respect to the PBAT. The same behavior is seen with curve for the 5% load NCs-PBAT/Cu|Cu₂ O. The curves for MCs-PBAT/CuSO₄ (Fig. 3c) show that the yield stress decreased for the three concentrations of CuSO₄ with respect to the PBAT.

From the results, we can conclude that the reinforcements did not significantly change the mechanical properties of the PBAT. Venkatesan and Rajeswari [45] showed a significant increase in mechanical properties by incorporating ZnO nanoparticles in a PBAT matrix with respect to that of the PBAT. Similar results with some improvements were obtained by Chen and Yang [46]. They elaborated a PBAT nanocomposite with montmorillonite nanoparticles using melt blending.

Our investigation found that the NCs-PBAT/Cu|Cu2O 3 and 5% and MCs-PBAT/CuSO4 1 and 5% had slightly decreased tensile strength, that is, there were no significant variations in the mechanical properties. However, the NCs-PBAT/Cu|Cu₂ O 1% and MCs-PBAT/CuSO₄ 3% had slightly increased tensile strength. Therefore, no reinforcement at any concentration in the matrix caused remarkable variations in the mechanical properties of the PBAT. In addition, as the concentration of Cu-NPs increased, their mechanical properties increased the resistance of the PBAT but elongation could not be maintained. The results of the tensile tests showed that the commercial Cu nanoparticles improved the tensile strength of the PBAT slightly more than did the Cu|Cu₂ O nanoparticles and the CuSO₄ partikel. The difference between the tensile properties found in our investigation and those in the literature could be attributed to load dispersion because the agglomerated particles act as stress concentrators [47]. Finally, the variations in the test values were explained by the preparation conditions of the test samples, the degree of crystallinity of the PBAT, the molecular mass, the degree of interaction at the polymer-reinforcement interface, and the load dispersion because the agglomerates in the matrix could act as stress concentrators.

Thermal Properties

One of the disadvantages of the PBAT is its low thermal stability because the fusion process can degrade its polymer chains [48]. Therefore, the effect of nanometric and micrometric loads on the decomposition of this biopolymer must be investigated. TGA of NCs-PBAT/Cu, NCs-PBAT/Cu|Cu₂ O, and MCs-PBAT/CuSO₄ was carried out to observe the changes in the thermal stability of the PBAT caused by the presence of Cu nanoparticles in the matrix. The TGA results are shown in Fig. 4, and the initial (T _di ) and final (T _df ) decomposition temperatures of the analyzed samples are summarized in Table 3. The thermograms show that the polymer without any load had a weight loss of 1% at 420.77 °C, while the nanocomposites NCs-PBAT/Cu 1, 3, and 5% presented a weight loss of around 3% (Fig. 4a). This suggests that the presence of Cu-NPs at concentrations of 3 and 5% slightly increases the thermal stability of the nanocomposites compared to that of the unloaded polymer. After the final thermal decomposition, the degradation percentages, at around 420–427 °C, of the PBAT matrix and nanocomposites NCs-PBAT/Cu 1, 3, and 5% were 98.9, 97.5, 95.4, and 96.8%, respectively. The residues were higher for Cu-NPs-incorporated nanocomposite samples. Similar results have been reported for PBAT nanocomposites with different loads of Ag-NPs [49].

TGA of a PBAT and NCs-PBAT/Cu, b NCs-PBAT/Cu|Cu₂ O, and c MCs-PBAT/CuSO₄ , DTG of d PBAT and NCs-PBAT/Cu, e NCs-PBAT/Cu|Cu₂ O, f MCs-PBAT/CuSO₄

Although no significant change is seen among the curves in Fig. 4b for the NCs-PBAT/Cu|Cu₂ O, the results show that as the Cu|Cu₂ O-NPs increased in the polymer structure, T _di increased and T _df decreased with respect to the initial and final degradation temperatures of PBAT; in addition, the total mass loss decreased. By calculating the derivative of the mass with respect to the temperature, we obtained the curves in Fig. 4d–f for the indicated peaks of the nanocomposite with Cu|Cu₂ O-NPs and found that T _df , at which the maximum decomposition occurs, was between 402 and 403 °C (Table 3).

The CuSO₄ loads incorporated into the polymer matrix, i.e., MCs-PBAT/CuSO₄ , yielded the same behavior as that of the NCs-PBAT/Cu|Cu₂ O, with an increase in T _di and a decrease in T _df with respect to the PBAT polymer. T _di values of the NCs-PBAT/Cu|Cu₂ O and the MCs-PBAT/CuSO₄ were greater than that of the NCs-PBAT/Cu, but the T _df and degradation percentage values were less than those of the nanocomposites with Cu-NPs loads.

This enhancement of the thermal stability of the PBAT is attributed to the barrier effect of the loads. The loads were also supposed to have a shielding effect on the matrix to slow the rate of mass loss of the decomposition product [50]. The data obtained by our analysis were compared with published results to verify that the indicated behavior is usual for this type of polymer. Sinha Ray et al. [51] found by thermal analysis of PBAT reinforced with nanoclays that the degradation temperatures of the nanocomposites were greater than or at least equal to that of the PBAT. In general, the reinforcements improve the thermal stability of the polymer matrix because they act as a heat barrier, which improves the total thermal stability of the system. However, the studies of Sinha Ray et al. and this investigation showed that the thermal stability of the nanocomposite and PBAT compounds only slightly improved. To explain the relatively low improvement in the thermal stability of some nanocomposites, Sinha Ray et al. assumed that in the early stages of thermal decomposition, the reinforcements displace the decomposition to higher temperatures, but in a second stage, the clay layers accumulate heat and then act as a source of heat. This heat source, along with the heat flow supplied by the external heat source, promotes the acceleration of decomposition. This could explain the behavior of the reinforcements in the NCs-PBAT/Cu|Cu₂ O and MCs-PBAT/CuSO₄ . Thus, we conclude that the thermal properties of the nanocomposites and the composite material slightly improve but not significantly. On the other hand, the results of DSC (Additional file 1:Figure S7 and Table S1) indicated that the addition of reinforcements to the matrix slightly hindered the kinetics and degree of crystallization of the PBAT. The addition of clays increased the crystallization temperature from 1 to 10 °C and the melting temperature from 1 to 5 °C. These phenomena were probably due to an increase in the viscosity of the polymer with the addition of clays, which reduced the mobility of the macromolecular chains against the growth of crystals.

Comparative Evaluation of the Antimicrobial Activity of NCs-PBAT/Cu, NCs-PBAT/Cu|Cu₂ O, and MCs-PBAT/CuSO₄

Qualitative Test

After the experimental procedure was performed, we wanted to observe whether bacterial colonies were inhibited by each PBAT sample, i.e., NCs-PBAT/Cu 1, 3, and 5%; NCs-PBAT/Cu|Cu₂ O 1, 3, and 5%; and MCs-PBAT/CuSO₄ 1, 3, and 5%. We decided to use the 3% concentrations because the 1% concentrations did not produce enough bacterial inhibition and the 5% concentration produced behavior similar to that of the 3% concentration, the minimum percentage with activity that avoided toxicity in the polymer.

Quantitative Test

The study was carried out at different contact times using four bacterial strains and the PBAT samples NCs-PBAT/Cu 3%, NCs-PBAT/Cu|Cu₂ O 3%, and MCs-PBAT/CuSO₄ 3%. The times and colony-forming unit counts (CFU/mL) are presented in Table 4, and the bacterial activity and colony count for each Petri dish are shown in Fig. 5. In addition, a graphical analysis is shown in Fig. 6, where images of bacterial growth are also presented. The statistical analysis of the data is summarized in Table 5.

Bacterial activity and colonization count PBAT, NCs-PBAT/Cu-3%, NCs-PBAT/Cu|Cu₂ O 3%, and MCs-PBAT/CuSO₄ 3% for each strain of bacteria. Staphylococcus aureus , Acinetobacter baumanni , Enterococcus faecalis , Streptococcus mutans

Graphical analysis of colony count (CFU/mL) vs time (h) of PBAT, NCs-PBAT/Cu-3% NCs-PBAT/Cu|Cu₂ O 3%, and MCs-PBAT/CuSO₄ 3% for each strain of bacteria. Enterococcus faecalis , Acinetobacter baumanni , Streptococcus mutans , Staphylococcus au reus

The study of A. baumannii found that the colonies grew in all periods (2, 4, 6, and 8 h) in the samples containing Cu-NPs, Cu|Cu₂ O-NPs, and PBAT. High bactericidal activity occurred with the sample containing CuSO₄ during exposure times of 4, 6, and 8 h, decreasing from 7 × 10 ⁵ to 0 CFU/mL. The sample containing Cu-NPs showed a significant increase in the growth of bacterial colonies from 1 × 10 ⁵ to 6 × 10 ⁶  CFU/mL, with an average of 2 × 10 ⁶  CFU/mL. The bacterial colonies in the sample containing Cu|Cu₂ O-NPs grew from 7 × 10 ⁵ in time I to 6 × 10 ⁶ in time IV, with an average growth of 3.19 × 10 ⁶  CFU/mL. Bacterial growth in the PBAT reached an average of 1.75 × 10 ⁶  CFU/mL.

The study of E. faecalis found good bactericidal activity by the samples containing Cu-NPs, Cu|Cu₂ O-NPs, and CuSO₄ , with average colony growth of 5 × 10 ² , 1 × 10 ⁴ , and 2.2 × 10 ³  CFU/mL, respectively, while the PBAT did not show bactericidal activity and the colonies grew at all times. Colony growth in the sample containing Cu-NPs was 2 × 10 ³  CFU/mL at 2 h then dropped to zero at 4, 6, and 8 h, whereas the samples containing Cu|Cu₂ O-NPs had 0 CFU/mL at times I, II, and III, but 4 × 10 ⁴  CFU/mL at time IV. Samples containing CuSO₄ prevented the growth of bacteria in times I and II with growth activity of 0 CFU/mL, but colonies grew to 4 × 10 ³ and 5 × 10 ³  CFU/mL for times III and IV, respectively. PBAT did not show bactericidal activity against E. faecalis .

The study of S. mutans found no colony growth in the samples containing Cu|Cu₂ O-NPs and CuSO₄ . The sample containing Cu-NPs showed very good bactericidal activity except at time I, at which colony growth was 4 × 10 ³  CFU/mL, making the average growth for the four times 8 × 10 ²  CFU/mL. PBAT without reinforcement showed no bactericidal activity against S. mutans . The samples containing Cu-NPs, Cu|Cu₂ O-NPs, and CuSO₄ in contact with S. aureus showed an excellent bactericidal response. They completely inhibited the growth of colonies, while PBAT did not show any bactericidal activity against S. aureus , which grew an average of 6 × 10 ³  CFU/mL.

In general, the antibacterial effectiveness of polymer-and-metal nanocomposites improves with a high surface/volume ratio, which increases the number of ions released from the nanoparticles into the polymer. The mechanism of the corrosion of Cu in aqueous solutions and the resulting Cu species vary with pH. In general, the species Cu₂ O and CuO are formed and can be dissolved in Cu ions. Elemental metal particles require the presence of water and oxygen molecules to release a small amount of ions. Therefore, retention of water and oxygen within the polymer is crucial for the release of Cu ions. Some properties of polymer-and-metal nanocomposites such as the crystallinity and polarity of the matrix, which constitute a barrier for the diffusion of water molecules and ions during their propagation, can affect the rate of release. Shankar and Rhim [49] prepared films composed of PBAT and Ag nanoparticles (PBAT/Ag-NPs) that showed strong antibacterial activity against E. koli and Listeria monocytogenes compared with that of PBAT films without Ag-NPs. Similar results were obtained by Venkatesan and Rajeswari [45] when they evaluated the antimicrobial activity of ZnO-NPs incorporated in a PBAT matrix. The PBAT compound, which was used as a control matrix, showed no antimicrobial activity compared to the PBAT/ZnO-NPs nanocomposite films. The results showed that the films had high bactericidal activity against the pathogens tested (E. coli dan S. aureus ), with increased inhibition of bacterial growth as the ZnO load concentration increased from 1 to 10% by weight. This ability of Cu, Zn, and Ag nanoparticles to inhibit bacterial growth is mainly due to the irreparable damage to the membrane of the bacterial cells caused by the interaction between the surface of the bacteria and these oxides and metals [52, 53]. Compared with the works discussed above, our investigation found significant antimicrobial activity against inpatient and oral-resistant strains.

To complement this investigation, we performed water absorption tests using three different media and following point 7.4, “Long-Term Immersion”, in ASTM D570-98. The results of these tests are reported in the supplementary material, Additional file 1:Table S2–S4 and Figure S8, with their respective analysis. Analysis showed that sulfate-based composite materials absorb large amounts of water, even in acidic and basic environments. This phenomenon greatly affects the mechanical properties of these materials; however, resistant bacteria, such as A. baumannii , require an immediate Cu ⁺ distribution to control them. This explains the antimicrobial power of CuSO₄ within the PBAT matrix.