3.1. SEM analysis
The morphology of NF samples was studied with the SEM technique. The SEM results of NFs with different blending ratios of EC, HPMC and selected NF with encapsulated Alv were illustrated in Fig 1. The average diameter of NF samples was assessed using Image J software. By changing the blended ratio of EC/HPMC, the morphology of NFs was improved. As shown in Fig. 1, the average NFs diameter was reduced by changing the combination ratio of EC/HPMC from 95:5 to 90:10 and 85:15. The fiber diameters of EC/HPMC with the blended ratios of 95:5, 90:10, and 85:15 were in the ranges of 601 ± 234, 556 ± 185, and 527 ± 136 nm, respectively. This reduction of fiber diameter with increasing the amount of HPMC in NFs could be associated with the increased conductivity, causing larger elongation forces and reduction of fibers diameter, which is in accordance with the results of previous studies [10]. The NF sample with a blending ratio of 85:15 of EC/HPMC illustrated the uniform, thin, and without bead fibers. Therefore, the EC/HPMC 85:15 NF sample was selected as the optimal NFs for encapsulation of Alv, since it has an appropriate morphology and thin fibers. After the addition of Alv, the average fiber diameter significantly reduced (319 ± 94.66 nm). The SEM analysis of EC/HPMC/Alv indicated a regular and beadless morphology. This result was in accordance with the results of previous study [7]. These results indicated the high compatibility among the NFs matrix and Alv which provided an appropriate choice for encapsulation of Alv into this NFs matrix without adverse effect on the morphological characteristics.
3.2. FTIR analysis
The FTIR spectra of Alv, EC, HPMC, EC/HPMC, and EC/HPMC/Alv NFs were presented in Fig. 2. The FTIR spectrum of Alv indicated specific absorptions at 1240 cm-1 (stretching of C-O groups of esters and phenols), 1560 cm-1 (C=O stretching), 1710 cm-1 (presence of carbonyl groups), 2910 cm-1 (symmetrical and asymmetrical C-H stretching), and 3311 cm-1 related to the hydrogen-bonded N-H stretching [7]. The EC spectrum showed the peaks at 1120 cm-1 (–C–O–C– stretching), and 2850-2962 cm-1 (–CH3 stretching) [9]. Furthermore, the peak at 1745 cm−1 was related to the stretching of C=O bonds [17]. FTIR spectrum of HPMC indicated the peaks at 1641 cm−1, 1458 cm-1 and 1375 cm−1 owing to the vibration of –OH group, asymmetric and symmetric vibrations of a methoxy group (–OCH3), respectively. Additionally, the peak at 1052 cm−1 was associated with the C–O–C stretching bond [18]. The FTIR spectrum of EC/HPMC exhibited the peaks at 1746 cm-1, 1638 cm−1, and 1123 cm-1, which indicates the suitable physical interactions between EC and HPMC. By comparing the FTIR spectrum of EC/HPMC, the characteristic peaks of EC/HPMC/Alv NF samples had blue shifts (1746→1753 cm-1, 1638→1644 cm-1, and 1123→1183 cm-1), showing the Alv was effectively encapsulated in the EC/HPMC NFs.
3.3. TGA analysis
Fig. 3, displayed the TGA thermograms of EC/HPMC NFs with various blending weight ratio of EC, HPMC, and optimal selected EC/HPMC NF samples containing 10% Alv. As can realize from this Fig, the first stage weight loss of NFs is between 50 and 150 ºC which is related to the loss of free and bound water in the structure of NFs [19]. The second stage of weight loss occurred at the range of 150-380 ºC which is associated to the thermal decomposition of the polymers [20]. Additionally, the next stage ranged between 380-600 °C can be related to the carbonization of polymeric materials [21]. There was not significantly difference in the thermal stability of NFs with different combination ratio of EC, and HPMC, indicating that the interactions between components were only physical rather than chemical interactions.
3.4. Mechanical properties
As shown in Table 1, the effect of different combination ratios of EC, HPMC (95:5, 90:10, and 85:15), and the encapsulation of Alv (10% w/v) into the EC/HPMC NFs was studied with the tensile stress (TS) analysis in the dry and wet conditions. The TS of NFs with various combination ratios of EC/HPMC in dry state was 4.96 MPa, 5.21 MPa, and 5.68 MPa for EC/HPMC 95:5, 90:10, and 85:15, respectively. These findings confirmed the TS improvement of EC-based NFs with the addition of HPMC. The encapsulation of Alv improved significantly (P < 0.05) the TS up to 6.70 MPa that was owing to the interaction between NFs and Alv. Also, a comparable trend was observed for the TS of NFs in the wet state: 2.32 MPa, 3.11 MPa, and 3.40 MPa for the EC/HPMC with ratios of 95:5, 90:10, and 85:15, respectively. Additionally, the encapsulation of Alv led to enhance in the TS up to 4.23 MPa in the produced NFs. The refined TS of EC/HPMC by increasing the HPMC content and encapsulation of Alv into the NF structure can be due to the increased intermolecular interactions between polymer chains and Alv [22–24]. The obtained results showed that EC/HPMC/Alv NFs had sufficient TS to withstand the force applied to them and can be used as a wound dressing [25–27].
Table 2. Tensile stress (TS) analysis of Ethyl cellulose/Hydroxypropyl methylcellulose (EC/HPMC) with different blending ratios of 95:5, 90:10, and 85:15, and optimal EC/HPMC NFs (85:15) containing 10% Aloe Vera (Alv) in dry and wet state.
NF sample
|
TS (MPa) in dry state
|
TS (MPa) in wet state
|
EC/HPMC:95/5
|
4.96
|
2.32
|
EC/HPMC:90/10
|
5.21
|
3.11
|
EC/HPMC:85/15
|
5.68
|
3.40
|
EC/HPMC (85/15)/Alv (10 wt %)
|
6.70
|
4.23
|
3.5. Swelling degree
Swelling properties of produced NFs are very important to apply as a wound dressing [28]. The swelling degree of the EC/HPMC NF samples with various blending weight ratios (95:5, 90:10, and 85:15), and optimal EC/HPMC NF containing 10% Alv were calculated in PBS (pH 7.4) solution at 37 °C after 5, 10, 15, 20, and 25 h. Fig. 4, presented the swelling degree of NF samples. As can be seen from this Fig, the swelling ratio of NF samples increased over time particularly after 2 h with increasing the HPMC content and encapsulated Alv in NF samples. This result can be related to the formation of hydrogen bonds between the EC and HPMC, and also the ability to absorb and retain water by HPMC and Alv. Besides, increasing the HPMC content and encapsulation of Alv in NFs reduces the diameter of NFs and increases the porosity, which ultimately increases the ability to absorb and retain water [3, 15, 29, 30].
3.6. In vitro degradation studies
The degradation degree of EC/HPMC NFs with different blending ratios of 95:5, 90:10, and 85:15 were investigated as a function of incubation time at two different pH values (7.4, and 5.3). The produced NFs were degraded during 24 days. Depending on the combination ratios, the produced EC/HPMC NFs was illustrated the various degradation degree. As shown in Fig. 5, the order of the weight loss of EC/HPMC NFs with various blending ratio of EC, and HPMC was found as 85:15 > 90:10 > 95:5. These observations showed that with increasing HPMC content, the degradation degree also increases. This obtained result can be related to the reduction of the diameter of NFs with increasing HPMC content since it has been confirmed in previous studies that by the decreasing of the NF diameter and increasing the ratio of surface to volume, water penetration increases, thus the degradation degree also increases [3, 31, 32]. Furthermore, improving the degradation of NFs with increasing the content of HPMC may also be related to the hydrophilicity nature of HPMC. The produced NFs containing Alv indicated the highest degradation degree compared with other NFs, resulting in around 35% of its initial weight was dropped after 24 days. This result could be related to Alv’s ability to improve the hydrophilicity nature and water uptake of NFs, which could be the reason for the increased degradation degree [33]. Therefore, we can adjust the NFs degradation with the changing of the EC/HPMC combination ratio by the electrospinning method to be suitable for usage as a wound dressing. Additionally, the degradation degree could be affected by the change of pH value. As is clear in Fig. 5, the degradation degree of NFs in acidic pH (5.3) was more than that physiological pH (7.4). It should be noted that the degradation process of HPMC is based on a hydrolytic reaction. In the presence of water, the etheric bonds in the structure of HPMC are broken. Thus the length of the degradation chains becomes shorter and the shorter parts dissolve in water [34]. Thus, EC / HPMC NFs with higher HPMC content were more degraded. The weight loss of NFs with various combination ratios of EC/HPMC at acidic pH (5.3) was around 37%, 34%, and 29% for EC/HPMC 95:5, 90:10, and 85:15, respectively.
3.7. Cell proliferation and cell adhesion studies
The NIH-3T3 cell viability was assessed in the presence of EC/HPMC NFs with and without Alv content by the MTT assay after 1, 3, and 5 days. The results of this test were displayed in Fig. 6. The obtained results showed that there was no toxicity and these NFs enhanced cell proliferation. Also, the encapsulation of Alv into NFs due to the presence of glycoproteins in Alv structure has increased cell proliferation by up to 126%., which is in line with the reported previous literature [35–37]. The adhesion of NIH-3T3 cells on optimal EC/HPMC (85:15) NFs containing 10% Alv were shown with SEM technique after 1, 3, and 5 days. As shown in this Fig, the cell proliferation rate significantly depends on the hydrophilicity of the NFs [35].
The results of cell adhesion were presented in Fig. 7. As revealed in this Fig, NIH-3T3 cells were attached well on the surface of EC/HPMC/Alv NFs which illustrated good interaction between the NFs and the cells. Hydroxyl groups in HPMC polymer chains and Alv agent can increase the adhesion strength. These obtained results suggest that the encapsulation of Alv in the NFs provides an appropriate environment for cell viability and adhesion. This result could be related to the ability of Alv to improve the hydrophilicity nature and protein absorption of the NFs, which ultimately increase cell adhesion and proliferation [33, 38–40].
3.8. Antibacterial activity
To investigate the antibacterial ability of Alv (versus total polymer weight) loaded in NFs, the agar disc diffusion assay was used, which is founded on the amount of clear zone including a circular NF disk. The obtained results indicated that the control NFs did not inhibit the growth of the pathogenic bacteria. As shown in Fig. 8, E. coli (gram-negative bacteria), and S. aureus (gram- positive bacteria) were significantly (P < 0.05) sensitive to Alv. In accordance, the diameter of the clear zone was 10.21 ± 1.21 mm for S. aureus and 5.06 ± 1.3 mm for E. coli bacteria. The obtained results were consistent with the results of previous studies that investigating the antimicrobial activity of Alv [13, 40–44].