Skin wound healing is an urgent problem in clinics and military activities. Although significant advances have been made in its treatment, there are several challenges associated with traditional methods, for example, limited donor skin tissue for transplantation and inflammation during long-term healing time. To address these challenges, in this study we present a method to fabricate Poly(ethylene-co-vinyl alcohol) (EVOH) nanofibres encapsulated with Ag nanoparticle using electrospinning technique. The fibres were fabricated with controlled diameters (59 nm–3
Skin wounds are a significant health problem, which negatively affect lives of millions of people worldwide inducing huge societal costs [
Existing methods in skin wound treatment have shown steady progress, with increasing survival rate in large-scale burn injuries. There are broadly two types of treatment methods for skin wounds. The first is the medication method, in which coating medicines are applied onto wounded area and covered with bandages. Frequent dressing changes are required to clear body discharges and replace medicines. However, such frequent changes cause severe pains and increase the rate of inflammation. The second method is skin transplantation, which is more effective in both improving healing and decreasing infections. However, this method is associated with several limitations such as the shortage of donor skin tissues and high cost [
In this study, we explored new nanofibres-based dressing materials with better clinical properties to address the problems associated with existing woven and nonwoven materials currently used in skin wound treatment. The advantages of nanofibres network over the traditional dressing materials come from its large surface/volume ratio [
Electrospinning phenomenon was firstly discovered in 1902 [
The fibre dries up or solidifies before being deposited onto the grounded collector. The setup used in this study is schematically shown in Figure
The electrospinning system. The electrospinning setup is composed of a syringe and blunt-end needle, a ground electrode as a collector, and a high-voltage supply with a low-current output (limited to a few mA) to generate a static electric field.
Poly(ethylene-co-vinyl alcohol) EVOH (Sigma-Aldrich, Batch number: 12822PE) was used to make nanofibres in this study for its good mechanical properties, the biocompatibility, and biodecomposability [
Six different concentrations of EVOH solutions (2.5, 5.0, 7.5, 10.0, 12.5, and 15.0 wt%) were prepared, which can be readily electrospun at the room temperature. To prepare an EVOH polymer solution, we diluted EVOH powders in solvent of propan-2-ol, and water. A variety of proportions of propan-2-ol and water were tried, and it is found that the combination of polymer EVOH, 80% propan-2-ol and 20% water heated at 80°C with a reflux setup for 2 to 3 hours produces the solvent for an optimal output of nanofibres. Although solutions of other solvent proportions can be electrospun into fibres, such as EVOH dissolved in 70% 2-propanol/30% water, they appear to be hindrance to the formation of Ag particles in fibres when AgNO3 was added, yielding in scattering Ag particle sizes and distributions.
The system used to carry out the “spinning” is composed of a high power supply (Spellman CZE1000R, 0–30 kV,) with very low-current output (
The suppressive effect of Ag to inflammation is well understood and utilized in clinical practice. To encapsulate Ag nanoparticles into fibres, AgNO3 of various concentrations was first added into 7.5 wt% EVOH solution which was then electrospun into nanofibres. AgNO3 in the fibres is deoxidized and forms into pure Ag nanoparticles when exposed to illumination. The speed of deoxidization can be accelerated by using UV lights. For fibres containing Ag, it was found that the collector is required to be changed from a plate shape to a stripe one without ground connection due to the increased conductivity of the fibre.
We fabricated nanofibres using different electrospinning parameters including the distance (15–35 cm) between the tip of the injecting needle and the collector, the voltage (8–20 kV) applied to generate the electric field, and the density (2.5–15.0 wt%) of the polymer solution. Scanning electron microscopy (JSM-6700 Cold FE SEM) was performed for fibre measurement. All fibre samples were mounted onto a copper stub and sputter coated with gold for energy spectrum analysis in SEM. Each sample was divided into 12 parts for diameter measurements. We used 12 uniform size conductive tapes (
Nanofibres and fabrication parameters. (a) An SEM picture of EVOH nanofibres produced with a solution in a stabilized temperature; (b) an SEM picture of EVOH nanofibres with a solution in decreasing temperature; (c) effect of the voltage on fibre diameters when the solution density is 7.5% (wt) and needle tip-to-collector distance is 30 cm; (d) effect of the density on fibre diameters when the voltage is 20 kV and the tip-to-collector distance is 30 cm; (e) effect of the distance on fibre diameters when the solution density is 7.5% (wt) and the voltage is 20 kV; (f) an example of SEM measurement of fibre diameters.
In addition, another important parameter which controls the fibre formation is the injection rate of the EVOH solution. This is normally done through the feeding speed control of the micropump. However, our study shows that there is only a very narrow window of the speed which can be utilized to produce fibres. In other words, there is no much room to play with the injection speed. One either gets it right for clear fibres, or wrong for no fibres or poor fibre formations. Thus, the injection speed is not really a “controllable” parameter. In this study, the speed we used was 1.5 ml/h which allows us to obtain fibres in the diameter range from 100 to 1000 nanometers.
Bacteria test was performed to test the ability of restraining pathogens using the fabricated Ag-encapsulating nanofibres.
EVOH is thermally sensitive which may affect the electrospinning process. To check the effect of temperature, we used SEM to assess the morphology of the nanofibres fabricated with/without temperature control during the fabrication. The temperature of the solution was controlled either at 80°C constantly or allowed to cool down from 80°C to room temperature naturally during the spinning process, respectively. Comparison of Figures
It is reported that the fibre diameter may influence the healing speed [
The suppressive effect of Ag on inflammation is related to the purity Ag (simple substance) encapsulated. To check the content of the Ag particles obtained, the energy spectrum function of the SEM was used. Figures
Fabrication Ag-encapsulated nanofibres and bacteria tests. (a) SEM image of nanofibre encapsulated with Ag nanoparticle (Tip-to-collector distance is 30 cm, voltage is 20 kV, and solution density is 7.5 wt%), (b) image of one set of culture test for bacteriostatic loop measurement, (c) averaged measurement of bacterial loop diameter versus Ag concentration (wt/10 mL), (d) a TEM image encapsulated with Ag nanoparticle (Tip-to-collector distance is 30 cm, voltage is 20 kV, and solution density is 7.5 wt %), (e) and (f) energy spectrum using SEM for encapsulated Ag particles, and (g) image of EVOH fibre without Ag particles in the bacteria test.
The main pathogens on the surface of skin burn is
In this study, no biodegradable tests were carried out on the nanofibres though this feature of the EVOH is well known [
Electrospinning is a straightforward approach to fabricate highly fibrous and porous EVOH materials for medical applications. In this study, we fabricated EVOH nanofibre encapsulated with Ag nanoparticles. The results of fibre characterization show that the nanofibre size can be controlled by regulating EVOH solution concentration, voltage, and distance of the electric field. Material characterization shows that 99% pure Ag particles can be formed in the fibre with AgNO3 added to the solution. Adding high concentration of Ag might change the fibre morphology; however, only low concentrations of Ag were used in our experiments. Compared under SEM and TEM observations, the morphology of Ag particles fibres is of no significant difference with pure EVOH fibres. Results of bacteria tests show that pathogen-restraining ability of the Ag-encapsulated nanofibres is effective and proportional over a range of Ag concentration, indicating its inflammation control capacity and the potential for applications in skin wound treatment. To further evaluate the suitability and effectiveness of Ag-encapsulating nanofibres on skin wound healing, animal tests have been planned in the next stage of study.
The work was partially supported by the National Natural Science Foundation of China (nos. 10825210, 10872157, and 31050110125) and the National 111 Project of China (no. B06024).