Electrospinning Equipment: The Versatility of Electrospun Janus Wound Dressings

Electrospun nanofibers prepared by the single-fluid blending process have successfully demonstrated their potential as highly effective wound dressings. However, electrospun Janus nanofibers, which can be designed with multiple chambers in different polymer matrices to load different active pharmaceutical ingredients, further exhibit their versatility in promoting wound healing. This review points out that wound dressings generally require multiple functional properties to promote wound healing. Janus nanofibers have unique advantages, as their different parts can interact with the environment, thus providing a versatile platform for the development of novel wound dressings. This review discusses two recent examples, each with a different preparation strategy for developing novel wound dressings, and emphasizes the promising future of Janus nanofibers in wound dressing applications.

1. Multifunctional Properties of Ideal Wound Dressings

As the largest organ of the human body, the skin is always prone to injury due to surgery, burns, mechanical forces, or chronic diseases. Therefore, new types of wound dressings that can shorten the treatment time and promote skin repair have received much attention.

An ideal wound dressing should have the following functions: promoting angiogenesis and tissue regeneration through the sustained release of drug molecules, providing analgesic and anti-inflammatory effects, while preventing microbial infection, absorbing excess exudate, and allowing gas exchange.

Currently, wound dressings come in various forms, including sponges, films, foams, hydrogels, powders, and nanofiber membranes. Among them, drug-loaded nanofibers prepared by electrospinning have attracted much attention due to their high porosity, large surface area, and strong drug-loading capacity. The structure of nanofiber membranes is similar to that of the natural extracellular matrix (ECM), which helps to create a microenvironment conducive to cell adhesion, proliferation, and differentiation. With the development of nanoscience and nanoengineering, nanomedicine is penetrating various types of wound dressings. The multi-chamber Janus nanostructure of drugs is one of the most promising methods for developing high-performance wound dressings.

2. Side-by-Side Electrospinning and Janus Nanostructures

Electrospinning machines can directly produce polymer nanofibers. Initially, the nanoscale diameters of these nanofibers were explored to ensure a variety of functional applications. Later, coaxial electrospinning became one of the most significant breakthroughs because it can create core-shell nanostructures simply and robustly.

Although dual-fluid coaxial, triple-fluid coaxial, and quadruple-fluid coaxial electrospinning have been successively reported for generating dual-chamber core-shell nanofibers, triple-chamber, and quadruple-chamber nanofibers, respectively, dual-fluid side-by-side electrospinning and its related dual-chamber Janus nanofibers have received little attention. Figures 1(a,b) show the schematic diagrams of a traditional single-fluid blending electrospinning device and a dual-fluid side-by-side eccentric electrospinning device, respectively. Apparently, the four basic components of these devices are similar, and the coaxial electrospinning system and the side-by-side electrospinning system also do not have significant differences.

The reasons for the huge gap between dual-fluid side-by-side electrospinning and dual-chamber structures are revealed in the rightmost part of Figure 2(b). When two parallel metal capillaries are used for side-by-side electrospinning, the same charges on the two working fluids and the small contact point (shown as "A" in Figure 2(b)) may cause the working fluids to separate, making it impossible to create integrated Janus nanofibers. Real digital photos of this situation are provided in the two upper-left insets of Figure 2(c), with one side marked with methylene blue. In contrast, when an eccentric spinneret is used for side-by-side electrospinning, a complete compound Taylor cone and the uniform light blue color of the collector can be seen in the two upper-right insets of Figure 2(c), indicating a successful process and the formation of an integrated Janus nanostructure. From left to right at the bottom of Figure 2(c), the schematic diagrams of the spinneret and Taylor cone, the charge distribution on the nozzle, a real digital image, and possible Janus nanofiber structures are shown.

3. Advantages of Electrospun Janus Nanofibers as Wound Dressings

Compared with traditional homogeneous nanofibers produced by single-fluid blending electrospinning and core-shell nanostructures produced by coaxial electrospinning, Janus nanostructures produced by side-by-side electrospinning have unique characteristics and a series of advantages that support their diverse applications in promoting effective wound healing. These advantages can be summarized as follows:

Advantages and characteristics similar to electrospun monolithic nanofiber mats:

i) Unique physical properties (small diameter, large porosity, 3D network structure, large surface area, and structural characteristics similar to the extracellular matrix);

ii) Adjustable functional properties through the polymer matrix (such as pH sensitivity, mechanical properties, and hydrophilicity);

iii) High drug encapsulation efficiency;

iv) A robust and simple process, that is, a direct one-step "top-down" nanofabrication process.

Special advantages compared with nanomaterials prepared by traditional blending electrospinning:

i) The powerful ability of the multi-chamber structure allows different types of active ingredients to be co-loaded into their respective chambers, each with its own controlled release profile to achieve a synergistic wound healing effect;

ii) The integration of different polymer matrices in different chambers can be a powerful tool for tailoring the apparent properties of the fiber mat, such as mechanical properties, bioadhesion properties, and hydrophilicity;

iii) Only one of the multiple fluids needs to be electrospinnable, which endows the ability to convert various non-spinnable fluids into structural nanofibers.

Special advantages compared with core-shell nanomaterials prepared by coaxial electrospinning:

i) All chambers can contact the surrounding environment, making them more effective in creating a suitable microenvironment for the wound site;

ii) More triple-chamber subcategory variations to support the development of novel functional materials with specific structure-property relationships;

iii) The separated sides provide a powerful tool for developing additional functional properties beyond drug loading and controlled release, such as nanofiber alignment, bioadhesion, and mechanical properties.

Zhang et al. recently reported a type of triple-chamber eccentric Janus nanofibers (TEJNs) prepared by a triple-fluid side-by-side electrospinning process (Figure 3(a)). TEJNs exhibit antibacterial and antioxidant properties, indicating their potential in various biomedical applications, including wound dressings. The multi-fluid side-by-side electrospinning process was robustly and continuously implemented using a homemade electrospinning device. In vitro dissolution tests showed that TEJNs could provide a sustained release of 90% of the loaded Cur and VE for 34.30 h and 24.86 h, respectively. Antibacterial and antioxidant experiments indicated that TEJNs offered enhanced effects compared to traditional homogeneous electrospun nanofibers.

4. Using Janus Nanofibers to Fabricate More Complex Janus Structures

There are many literature reports on Janus membranes and particles for wound dressing applications. However, almost all so-called Janus membranes are essentially a type of bilayer membrane. Most of them are two-layer membranes, each layer composed of electrospun monolithic nanofibers with different components and compositions, and some membranes consist of one layer of electrospun monolithic drug-loaded nanofibers and another layer of a casting film or just electrosprayed micro/nano-particles. Although these Janus membranes have been proven useful for treating targeted wound areas, they are essentially "Janus" in a macroscopic sense and usually require multiple steps, various working fluids, and operating conditions. 

The layer-by-layer collection strategy can also be combined with side-by-side electrospinning to enhance the ability of electrospinning to generate novel nanofiber membranes. Nanostructures always play an important role in the development of various functional nanomaterials. Among them, side-by-side electrospinning and its various multi-chamber Janus nanostructures are expected to provide more hope for new wound dressings with higher therapeutic effects.

Figure 4 shows several typical multi-chamber Janus nanostructures.

5. Conclusion

The popularity of electrospun drug - loaded nanofibers implies great potential for electrospun Janus nanofibers in wound dressings. Using an eccentric spinneret, triple - fluid side - by - side electrospinning can create triple - chamber nanostructures. Janus nanostructures' multiple chambers can encapsulate components and contact the environment, meeting wound dressing needs. Blending and side - by - side processes can form Janus or triple - layer membranes, enriching development methods.

Article source: https://doi.org/10.1080/17435889.2024.2446139