Highlighting the Compositional Changes of the Sm2O3/MgO-Containing Cellulose Acetate Films for Wound Dressings

The development of wound dressing materials with appropriate specifications is still a challenge to overcome the current limitations of conventional medical bandages. In this regard, simple and fast methods are highly recommended, such as film casting. In addition, deliverable nanoparticles that can act to accelerate wound integration, such as samarium oxide (Sm2O3) and magnesium oxide (MgO), might represent a potential design with a novel compositional combination. In the present research, the casted film of cellulose acetate (CA) was mixed with different ratios of metal oxides, such as samarium oxide (Sm2O3) and magnesium oxide (MgO). The tests used for the film examination were X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The SEM graphs of CA films represent the surface morphology of Sm2O3@CA, MgO@CA, and Sm2O3/MgO/GO@CA. It was found that the scaffolds’ surface contained a high porosity ratio with diameters of 1.5–5 µm. On the other hand, the measurement of contact angle exhibits a variable trend starting from 27° to 29° for pristine CA and Sm2O3/MgO/GO@CA. The cell viability test exhibits a noticeable increase in cell growth with a decrease in the concentration. In addition, the IC50 was determined at 6 mg/mL, while the concentration of scaffolds of 20 mg/mL caused cellular growth to be around 106%.


Introduction
Upon the environmental factors, wounds and injuries have become easy to occur in the body shield (skin) [1]. Skin is the first destination for protection against accidents [1]. Healing skin wounds in a short period is still a challenge for researchers [2]. The wounds were traditionally treated with antibiotics to prevent the wounds from being infected [3]. On the other hand, excessive use of antibiotics for a long time affects the healthcare system [4].
Wound healing is a major complex process that includes four stages: hemostasis, inflammatory reactions, cell proliferation, and tissue remodeling [5]. The traditional bandages could be enhanced with biomedical materials to cover all needs of the high-impact therapy [2,6]. Film casting is one of the ways of manufacturing bandages that may stimulate live cells. Wound dressings may be fabricated with thin polymeric films, which are suitable for wounds because of their biocompatibility, good adhesion, and flexibility [7].

Thin Film Fabrication
The nanoparticles like Sm 2 O 3 and MgO were used as supplied. Graphene oxide (GO) was prepared in the lab using the modified Hummer's method. A 3 g graphite powder was added to a 9:1 mixture of concentrated H 2 SO 4 /H 3 PO 4 with continuous stirring for 5 min. Then, 18 g of KMnO4 was added to the previous mixture with continuous stirring for 12 h. Then, 3 mL of H 2 O 2 was added and mixed for 1 h. The solution was washed with 30% HCl, then with distilled water, and with ethanol, and dried in the furnace-a solution of 7 wt.% CA was prepared. Five stock samples of CA were planned, each one containing 20 mL. The first one was kept pure as CA without any additives. The metal oxide nanoparticles were added to the other four CA solutions with a total weight of 0.25 g for each film. It could be noticed that the additives were dropped into each bottle, and the solutions in each bottle were stirred using a magnetic stirrer for 1 h to get well-dispersed solutions [2,9]. In addition, the contributions of CA and metal oxide nanoparticles are (1) pure CA, (2) 0.25 g of Sm 2 O 3 added to CA, (3) 0.25 g of MgO added to CA, (4) 0.125 g of Sm 2 O 3 and 0.125 g of MgO were added to CA, (5) 0.1 g of Sm 2 O 3 , 0.1 g of MgO and 0.05 g of GO were added to CA. Then, the samples were cast into a petri dish and left in the drier furnace till complete dryness.

XRD Measurements
X-ray diffraction (XRD) has been used to identify the formed phases. The specifications of the XRD apparatus were analytical-x' Pertpro with Cuk α1 , the Netherlands. All XRD curves were scanned in 5 • ≤ 2θ ≤ 70 • with a step size of 0.02 • and a step time of 0.5 s.

FT-IR Measurements
Fourier transforms infrared (FTIR) spectra were used for all samples by (Perkin-Elmer (FTIR). The analysis was scanned in the range of 400-4000 cm −1 via a transmittance mode. The films were scanned without additional KBr for dilution.

Morphology Investigation
The surface morphology was examined through a scanning electron microscope (SEM) (QUANTA-FEG250, Netherlands). The operating voltage was around 10 kV. Moreover, Energy dispersive X-ray (EDX) was performed using the same SEM instrument.

Contact Angle Test
The contact angle was evaluated by a custom system via water drops. A sample of 1.0 cm 2 of each cast film was fixed versus the camera. Moreover, the images were taken when the drop of water was released.

Swelling Degree Study
The swallow ability of the scaffolds has been done via soaking a constant weight of each sample (0.02 g) through 50 mL of deionized water for 12 h at 37 • C. During this time, the sample was taken out every period to be weighted. The total weights were compared with the dried weights to get the swelling degree for each scaffold.

In Vitro Cell Viability Tests
The cell viability was tested with normal lung cells (WI-38). The cell lines information is as follows: Database Name: ATCC, Accession Numbers: WI-38 (ATCC CCL-75). The WI-38 cell lines were isolated from the lung tissue of a 3-month-old female embryo, Organism: Homo sapiens, human, Cell Type: Fibroblast, Tissue: Lung, Age: 3 months' gestation, Gender: Female, Morphology: Fibroblast, Growth properties: Adherent, Disease: Normal.
The culture was in Gibco medium. The samples were weighed individually and then soaked in sterilized water for 24 h. The solution was serialized in 96 well-plate starting from the higher concentration to the lowest one of the scaffold. The scaffold was immersed in a tube containing sterilized water was a concentration of 4000 µg/mL. Then, the plates were incubated for 72 h at 37 • C. after that, the media was removed, and the (3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) was added to measure the cell viability using the optical density.

XRD
X-ray diffraction is used to determine the crystallinity and the compositions of the materials. As obvious in Figure 1, the XRD graph shows that CA exhibits several broad halos or hump peaks, which may refer to its low crystalline phase [26]. The reason behind these halos is the non-long-range order. Therefore, there are no well-defined scattering planes leading to the broadness of the peaks. However, the pattern indicates a hump peak at around 2-theta = 20 • . The Sm 2 O 3 display sharp peaks at 27.7 • , 28.9 • , 40.7 • , 49.3 • , 50.05 • , and 57.6 • . The miller indices of these peaks show that the Sm 2 O 3 was crystallized in a cubic structure (a = b = c) [13]. The diffraction peaks of MgO were maintained at 42.7 • and 62.2 • associated with diffraction planes of (002) and (022), respectively [19]. Likewise, the structure of MgO tends to be cubic [19]. Moreover, it can be noticed that the crystallinity of MgO is relatively low compared to Sm 2 O 3 . Therefore, the humps of the amorphous phase of CA are noticeable and clear. On the other hand, the low contribution of GO might limit its significant effects on the other structures. The sharp peaks performed at the curve of pure CA and the combination of CA with MgO. The curve of Sm 2 O 3 represents sharp peaks that define the major crystallinity. That means CA shows an amorphous phase, MgO has relatively low crystallinity, and Sm 2 O 3 shows a higher crystallinity, while GO cannot be detected due to its low quantity. The existence of low crystalline nanoparticles and amorphous CA can directly affect the roughness of the surface. Therefore, enhancing the attachment of cells leads to low cytotoxicity.

FTIR
The FT-IR spectra were examined for all compositions in the ran (Figure 2i,ii, Table 1). In the FTIR spectra for CA samples, the band at C-OH stretching [27]. The bands observed at 1025, 1159, and 1212 cm the C-O functional group in the absorption region, -CH groups of CA of the ester (C-O-C) [8,28]. In addition, the bands at 1369, 1426, 1662 ferred to methyl bending (C-CH3), -CH groups of CA, C=O stretch, an tions of carbonyl functional groups [8,[27][28][29]. In addition, the bands and hydroxyl stretching vibration were exhibited at 2943 and 3742 c other hand, the FTIR spectra for Sm2O3 have a band at 3454 cm −1 , w stretching vibration of the (-OH)group [13]. The determined bands fo at 476, 558, and 658 cm −1 , which corresponded to Mg-O-Mg bond stretching vibration mode and MgO vibrations [19,32]. The band at 3 hydroxyl groups (-OH) [33]. The spectrum of Sm2O3/MgO@CA exh 2972, 3393, and 3836 cm −1 , which referred to C-O, C-H stretching, (-O bonds [8,[33][34][35]. The addition of GO represents two bands at 1558 an are assigned to C=C bonds and C-H stretching [34,36]. The bands aro seem to be relatively very high compared with the OH bands. There might be covered, or their peaks look with low relative intensity. Her bands is magnified to be clearer, as obvious in Figure 2i.

FTIR
The FT-IR spectra were examined for all compositions in the range of 400-4000 cm −1 (Figure 2i,ii, Table 1). In the FTIR spectra for CA samples, the band at 906 cm −1 represents C-OH stretching [27]. The bands observed at 1025, 1159, and 1212 cm −1 corresponded to the C-O functional group in the absorption region, -CH groups of CA, an alkoxyl stretch of the ester (C-O-C) [8,28]. In addition, the bands at 1369, 1426, 1662, and 1742 cm −1 referred to methyl bending (C-CH 3 ), -CH groups of CA, C=O stretch, and stretching vibrations of carbonyl functional groups [8,[27][28][29]. In addition, the bands of -CH 2 stretching and hydroxyl stretching vibration were exhibited at 2943 and 3742 cm −1 [30,31]. On the other hand, the FTIR spectra for Sm 2 O 3 have a band at 3454 cm −1 , which indicates the stretching vibration of the (-OH)group [13]. The determined bands for MgO represented at 476, 558, and 658 cm −1 , which corresponded to Mg-O-Mg bonds indicated by the stretching vibration mode and MgO vibrations [19,32]. The band at 3439 referred to the hydroxyl groups (-OH) [33]. The spectrum of Sm 2 O 3 /MgO@CA exhibits bands at 1054, 2972, 3393, and 3836 cm −1 , which referred to C-O, C-H stretching, (-OH) group, and O-H bonds [8,[33][34][35]. The addition of GO represents two bands at 1558 and 2926 cm −1 , which are assigned to C=C bonds and C-H stretching [34,36]. The bands around 1000-1100 cm −1 seem to be relatively very high compared with the OH bands. Therefore, the OH bands might be covered, or their peaks look with low relative intensity. Here, the region of OH bands is magnified to be clearer, as obvious in Figure 2i.

Surface Morphology
The term (SEM) refers to a scanning electron microscope that is usually used to examine the surface morphology of the films. The topography of Sm2O3@CA film is shown in Figure 3 a,b. It illustrates that the surface tends to be smooth. However, some blocks containing pores and cracks tend to be slightly rough. As obvious in Figure 3c,d of Sm2O3/MgO@CA film, it is shown that with the addition of MgO, the surface became filled with pores, which have diameters in the range of 1.5-5 µm and lengths in the range of 0.5-9 µm. The borders of pores are illustrated with rough textures, which might represent strong adhesion [37]. Figure 3e,f shows the effect of adding GO exhibits a porosity ratio less than the previous one. The diameters of pores are between 0.5 and 5 µm. In addition, the surface roughness seems to be decreased according to the 2d surface of the GO nanosheet with low crystallographic defects, which might regulate the chemical interactions with good conductivity. Sivasankari et al. [38] prepared a membrane of CA loaded with hydroxyapatite (HAP). They found high porosity in the membrane of CA, which is important in biomedical applications. David et al. [39] prepared CA-collagen containing multi-wall carbon nanotubes (MWCNTs) decorated by Titanium dioxide (TiO2). The porous nature of CA film is also detected by SEM microscopy. Moreover, Liakos et al. [40]

Surface Morphology
The term (SEM) refers to a scanning electron microscope that is usually used to examine the surface morphology of the films. The topography of Sm 2 O 3 @CA film is shown in Figure 3a,b. It illustrates that the surface tends to be smooth. However, some blocks containing pores and cracks tend to be slightly rough. As obvious in Figure 3c,d of Sm 2 O 3 /MgO@CA film, it is shown that with the addition of MgO, the surface became filled with pores, which have diameters in the range of 1.5-5 µm and lengths in the range of 0.5-9 µm. The borders of pores are illustrated with rough textures, which might represent strong adhesion [37]. Figure 3e,f shows the effect of adding GO exhibits a porosity ratio less than the previous one. The diameters of pores are between 0.5 and 5 µm. In addition, the surface roughness seems to be decreased according to the 2d surface of the GO nanosheet with low crystallographic defects, which might regulate the chemical interactions with good conductivity. Sivasankari et al. [38] prepared a membrane of CA loaded with hydroxyapatite (HAP). They found high porosity in the membrane of CA, which is important in biomedical applications. David et al. [39] prepared CA-collagen containing multi-wall carbon nanotubes (MWCNTs) decorated by Titanium dioxide (TiO 2 ). The porous nature of CA film is also detected by SEM microscopy. Moreover, Liakos et al. [40] prepared CA-essential oil nanocapsules for antimicrobial biomedical applications. They reported that SEM micrographs captured the porosity in the CA film.

EDX Analysis
Energy Dispersive X-ray (EDX) is an elemental test to determine the ratios of the contributed elements. According to Table 2 and Figure 4 the major ratios referred to oxygen and carbon by 48.84 and 43.17%, which were assigned to the high contribution of CA, besides the presence of GO. In addition, magnesium is determined by a ratio of about 2.74%. On the other hand, the minor concentration referred to Sm by 1.66%. The existence of the elements was approved by SEM test, and the nanoparticles were successfully fabricated on the surface of the films. Energy Dispersive X-ray (EDX) is an elemental test to determine the ratios of the contributed elements. According to Table 2 and Figure 4 the major ratios referred to oxygen and carbon by 48.84 and 43.17%, which were assigned to the high contribution of CA, besides the presence of GO. In addition, magnesium is determined by a ratio of about 2.74%. On the other hand, the minor concentration referred to Sm by 1.66%. The existence of the elements was approved by SEM test, and the nanoparticles were successfully fabricated on the surface of the films.

Contact Angle
The contact angle is an essential examination test to determine the ability of the casted film to interact with drops of distilled water on the film surface. As obvious in Figure 5a, the pure CA exhibits an average contact angle of 39.81°. The addition of Sm2O3 leads to reducing the angle to 24.8°, as in Figure 5b. On the other hand, the addition of MgO causes a slight increase to be at 24.9°. However, as shown in Figure 5d, the mixture of different contributions of the nanoparticles with CA exhibit a noticeable decrease till 23.9°. Then, the addition of GO to these composites led to a significant increase, and the contact angle was recorded at 29.4°.
The addition of Sm2O3 might promote the formation of crystal defects on the surface of CA. the effect of MgO on the surface of CA is approximated to the effect of Sm2O3. The combination of Sm2O3 and MgO might induce higher defects than the addition of each

Contact Angle
The contact angle is an essential examination test to determine the ability of the casted film to interact with drops of distilled water on the film surface. As obvious in Figure 5a, the pure CA exhibits an average contact angle of 39.81 • . The addition of Sm 2 O 3 leads to reducing the angle to 24.8 • , as in Figure 5b. On the other hand, the addition of MgO causes a slight increase to be at 24.9 • . However, as shown in Figure 5d, the mixture of different contributions of the nanoparticles with CA exhibit a noticeable decrease till 23.9 • . Then, the addition of GO to these composites led to a significant increase, and the contact angle was recorded at 29.4 • .
The addition of Sm 2 O 3 might promote the formation of crystal defects on the surface of CA. the effect of MgO on the surface of CA is approximated to the effect of Sm 2 O 3 . The combination of Sm 2 O 3 and MgO might induce higher defects than the addition of each one in a single phase due to the difference in crystallographic orientation. The additive of GO nanosheet might recover the addition of the other nanoparticles because of its low defects compared with Sm 2 O 3 and MgO. As a result, the degradation behavior might be promoted with the reduction of hydrophobicity that helps cells to attach, divide and promote wound healing. have reported the contact angle of CA fibrous materials at 123.10 ± 2.0°, which regulates the hydrophobic nature of this material. At the same time, the contact angles of the compositions CA/PVP and Curc/CA + PVP were evaluated at 36 ± 3.5° and 14.8 ± 1.7°, respectively, due to the hydrophilization characteristics of PVP. As a result, the hydrophilic behavior of PVP led to a reduction of the surface tension, which enhances the contact angle of CA. The literature refers that the contact angle can be affected by the quantity of CA and its solvent, in addition to the preparation method and the incorporated particles.

Swelling Degree
The ability of the scaffold to interact with the injury solutions is essential to keep the moisture of the wound and to avoid dehydration. As well, inhibition of inflammation might be achieved by controlling the solution path through the scaffolds that cover the wound area. In this regard, the swelling degree of the scaffolds has been carried out, as In a recent study by Elsherbiny et al. [41], the contact angle for pure CA was recorded at 81 • , which may pretend its hydrophobic nature. The composite of CA/lignin showed a noticeable decrease in the angle and was determined at 73 • . A variety of lignin concentrations represents contact angles at 45 • , 30 • , and 8 • for L29, L37, and L44. This significant decrease may be assigned to the hydrophilic nature of the lignin structure and the accelerated biodegradability of the scaffolds. Guezguez et al. [42] have prepared CA films, and they reported that the contact angle with water was around 54 • before the modifications. Mahdavi et al. prepared CA with different concentrations of different blends. They reported that the CA contact angle could be in the range of 25 • -70.4 • . Tsekova et al. [43] have reported the contact angle of CA fibrous materials at 123.10 ± 2.0 • , which regulates the hydrophobic nature of this material. At the same time, the contact angles of the compositions CA/PVP and Curc/CA + PVP were evaluated at 36 ± 3.5 • and 14.8 ± 1.7 • , respectively, due to the hydrophilization characteristics of PVP. As a result, the hydrophilic behavior of PVP led to a reduction of the surface tension, which enhances the contact angle of CA. The literature refers that the contact angle can be affected by the quantity of CA and its solvent, in addition to the preparation method and the incorporated particles.

Swelling Degree
The ability of the scaffold to interact with the injury solutions is essential to keep the moisture of the wound and to avoid dehydration. As well, inhibition of inflammation might be achieved by controlling the solution path through the scaffolds that cover the wound area. In this regard, the swelling degree of the scaffolds has been carried out, as illustrated in Figure 6. As may be seen, the ability to adsorb water increased with the additional nanoparticles of Sm 2 O 3 and MgO. The pure CA started its plateau after around 6 h of soaking with a degree of 150 ± 8%. Furthermore, the highest swelling degree was obtained with the scaffold containing Sm 2 O 3 /MgO/GO@CA with a degree of 340 ± 12% after 12 h of socking. The boosting in the swelling degree with the nanoparticle's modification might reflect the ability of these additives to manipulate the topographical features of the scaffold. Hence, controlling the additional nanoparticles through the scaffolds leads to a high adjustment of the surface roughness and, thus, good controlling of the wettability and swallowability. The biodegradation of these scaffolds through the biological environment also might be controlled via surface modification. Consequently, it is noticed that structural and morphological features are good tools to control the scaffold's response toward the biological milieu.
Polymers 2022, 14, x FOR PEER REVIEW 10 of 14 illustrated in Figure 6. As may be seen, the ability to adsorb water increased with the additional nanoparticles of Sm2O3 and MgO. The pure CA started its plateau after around 6 h of soaking with a degree of 150 ± 8%. Furthermore, the highest swelling degree was obtained with the scaffold containing Sm2O3/MgO/GO@CA with a degree of 340 ± 12% after 12 h of socking. The boosting in the swelling degree with the nanoparticle's modification might reflect the ability of these additives to manipulate the topographical features of the scaffold. Hence, controlling the additional nanoparticles through the scaffolds leads to a high adjustment of the surface roughness and, thus, good controlling of the wettability and swallowability. The biodegradation of these scaffolds through the biological environment also might be controlled via surface modification. Consequently, it is noticed that structural and morphological features are good tools to control the scaffold's response toward the biological milieu.

Cell Viability
The cell viability test is used to examine the viability of cells and indicates the biocompatibility of scaffolds within normal cells. As obvious in Figure 7a-c, the images of viable cells taken by the optical microscope depict a minority of spherical cells that represent the dead cells, while most of the oval cells represent the viable cells. On the other hand, the concentration of viable cells is shown in Figure 8 after culturing the scaffold for 72 h. The concentration of Sm2O3/MgO/GO@CA started from 7500 µg/ mL. In addition, the IC50 is obtained at 6 mg/mL, which has the ability to degenerate the viable cells with a concentration of 50%. After the addition of nanoparticles to CA, the concentration was determined at 20 mg/mL, and the cell growth reached around 106%. As a result, there is a reversible relation between cell growth and component concentration. The additional components of nanoparticles seem to exhibit significant effects in improving the safety of the scaffolds towards the normal cells [35][36][37].

Cell Viability
The cell viability test is used to examine the viability of cells and indicates the biocompatibility of scaffolds within normal cells. As obvious in Figure 7a-c, the images of viable cells taken by the optical microscope depict a minority of spherical cells that represent the dead cells, while most of the oval cells represent the viable cells. On the other hand, the concentration of viable cells is shown in Figure 8 after culturing the scaffold for 72 h. The concentration of Sm 2 O 3 /MgO/GO@CA started from 7500 µg/ mL. In addition, the IC 50 is obtained at 6 mg/mL, which has the ability to degenerate the viable cells with a concentration of 50%. After the addition of nanoparticles to CA, the concentration was determined at 20 mg/mL, and the cell growth reached around 106%. As a result, there is a reversible relation between cell growth and component concentration. The additional components of nanoparticles seem to exhibit significant effects in improving the safety of the scaffolds towards the normal cells [35][36][37].

Conclusions
Nanoparticles with different ratios, including samarium oxide (Sm2O3) and magnesium oxide (MgO), were added to CA films and were fabricated by casting technique. Structural investigation via the X-ray diffraction technique (XRD) detected the cubic symmetry of MgO and Sm2O3. Further, the amorphous nature of CA was also detected. The result of the scanning electron microscope (SEM) represents the surface topography of CA with metal oxides, which have medium roughness and porosity with diameters in the range of 1.5-5 µm and 0.5-5 µm. The contact angle of the cast film indicated a noticeable change in the hydrophilic behavior with values from 27.9° to 29.4°. The cell viability test for Sm2O3/MgO/GO@CA films showed that the lowering in the concentration started from 7500 to 20 µg/mL, and the growth reached 106% after culturing the films for three days. The relatively high values of cell viability with good control of hydrophilicity might recommend these compositions for potential intensive applications, including dressing materials. The significant development of the physicochemical properties of CA scaffolds via the additional modifications indicates that Sm2O3 and MgO might provide a strategy to

Conclusions
Nanoparticles with different ratios, including samarium oxide (Sm2O3) and magnesium oxide (MgO), were added to CA films and were fabricated by casting technique. Structural investigation via the X-ray diffraction technique (XRD) detected the cubic symmetry of MgO and Sm2O3. Further, the amorphous nature of CA was also detected. The result of the scanning electron microscope (SEM) represents the surface topography of CA with metal oxides, which have medium roughness and porosity with diameters in the range of 1.5-5 µm and 0.5-5 µm. The contact angle of the cast film indicated a noticeable change in the hydrophilic behavior with values from 27.9° to 29.4°. The cell viability test for Sm2O3/MgO/GO@CA films showed that the lowering in the concentration started from 7500 to 20 µg/mL, and the growth reached 106% after culturing the films for three days. The relatively high values of cell viability with good control of hydrophilicity might recommend these compositions for potential intensive applications, including dressing materials. The significant development of the physicochemical properties of CA scaffolds via the additional modifications indicates that Sm2O3 and MgO might provide a strategy to

Conclusions
Nanoparticles with different ratios, including samarium oxide (Sm 2 O 3 ) and magnesium oxide (MgO), were added to CA films and were fabricated by casting technique. Structural investigation via the X-ray diffraction technique (XRD) detected the cubic symmetry of MgO and Sm 2 O 3 . Further, the amorphous nature of CA was also detected. The result of the scanning electron microscope (SEM) represents the surface topography of CA with metal oxides, which have medium roughness and porosity with diameters in the range of 1.5-5 µm and 0.5-5 µm. The contact angle of the cast film indicated a noticeable change in the hydrophilic behavior with values from 27.9 • to 29.4 • . The cell viability test for Sm 2 O 3 /MgO/GO@CA films showed that the lowering in the concentration started from 7500 to 20 µg/mL, and the growth reached 106% after culturing the films for three days. The relatively high values of cell viability with good control of hydrophilicity might recommend these compositions for potential intensive applications, including dressing materials. The significant development of the physicochemical properties of CA scaffolds via the additional modifications indicates that Sm 2 O 3 and MgO might provide a strategy to sup-