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Recently, a research team published a paper titled "Synergistic improvements of properties of cellulose acetate based curcumin@TiO₂ nanofibers via triaxial electrospinning". Currently, the forefront of nanoscience focuses on the creation of complex nano - structures and nano - devices, and the core - sheath structure is crucial for the research and development of new functional nanomaterials. Against this background, this study aims to solve many problems in the preparation of electrospun medicated polymeric nanofibers and their drug delivery applications, such as the easy clogging of the spinneret by working fluids, the initial burst release and insufficient late - stage release of drugs, the uneven distribution of functional nanoparticles affecting their functions, and the controversial drug encapsulation efficiency.
One of the frontiers of nanoscience is the fabrication of complex nanostructures and devices, which requires advanced technologies and materials with good processability. Multi - chamber structures are important because they can generate a variety of complex structural features. The core - shell structure, as a type of bi - chamber structure, has provided a rich research basis for the development of new functional nanomaterials.
In the past two decades, research on electrospun core - shell nanofibers has advanced. Multilayer structures have emerged, and new materials are often developed by designing the components of the shell and core layers. Researchers speculate that distributing TiO₂ in the shell layer and drugs in the core layer can enhance the performance of nanofibers.
However, there are some problems in the preparation of electrospun medicated polymeric nanofibers. Highly volatile solvents easily clog the spinneret; drug/polymer blended nanofibers have issues of initial burst release and insufficient late - stage release; functional nanoparticles are evenly dispersed in the matrix and difficult to fully function; and the drug encapsulation efficiency (EE%) is controversial. To solve these problems, the research team proposed an improved triaxial electrospinning device electrospinning method, using a pure organic solvent mixture to prevent spinneret clogging and constructing a core - shell structure with TiO₂ in the shell layer and drugs in the core layer.
Figure 1. A diagram about the modified triaxial electrospinning with an outer solvent as the working fluid to ensure a continuous and robust preparation, and the resultant core-sheath nanostructure with TiO2 and Cur separately distributed only at the sheath and core CA matrices for a joint antibacterial effect, respectively.
(1) The Process of Preparing Nanofibers by Triaxial Electrospinning
The research team used a homemade tri - layer concentric spinneret in the electrospinning machine to inject an outer organic solvent mixture, a middle CA - TiO₂ solution, and an inner CA - curcumin solution. Under the action of a high - voltage electric field, the three - layer fluid formed a compound Taylor cone and was stretched into fibers, which were finally deposited on the collector. Thus, core - shell structured nanofibers with TiO₂ nanoparticles distributed in the shell layer and curcumin (Cur) loaded in the core part, based on cellulose acetate (CA), were successfully prepared.
Figure 2: The organization of the detachable tri-layer concentric spinneret for implementing the modified triaxial electrospinning: (a) a diagram showing the arrangements of the all the parts of the spinneret and its inner routes of the three working microfluids; (b) the traditional concentric spinneret and a tapering PP tubing; (c) the outer PP was fixed on the metal spinneret; (d) a digital image of the tri-layer concentric outlets; (e) an elastic silica tubing with a sharp metal needle (outer diameter/wall thickness: 0.3/0.05 mm) for leading the outer solvent to lubricate the middle CA solution for a smooth preparation; (5) a digital image of the spinneret connected with three syringes
(2) Improving the Drug Encapsulation Efficiency of Nanofibers
The paper prepared nanofibers with a special core - shell structure through the improved triaxial electrospinning technology, effectively improving the drug encapsulation efficiency. In the traditional electrospinning process, the drug encapsulation efficiency (EE%) is highly controversial. Some studies report that it can reach 100%, while others report as low as 22.7%. In this study, it was accurately determined through experiments that the drug encapsulation rate of homogeneous nanofibers (F1) is 91.7 ± 5.7%, and that of core - shell nanofibers (F3) is 97.3 ± 4.8%. The core - shell nanofiber F3 in this study inhibits the diffusion of drug molecules through the middle CA - TiO₂ layer, thus achieving a higher drug encapsulation efficiency than traditional blended nanofibers.
(3) Increasing the Distribution of TiO₂ on the Surface of CA Nanofibers
The core - shell nanofibers prepared by the improved triaxial electrospinning technology achieve an increase in the distribution of TiO₂ on the surface of CA nanofibers. Both Figure 3c and 3d show images of core - shell nanofibers (F3). In the complete nanofiber image shown in Figure 5c, the nanofiber has a distinct bi - chamber core - shell nanostructure. In addition, the periphery of nanofiber F3 contains a large number of TiO₂ NPs, exceeding that in the central region. This heterogeneous distribution indicates that TiO₂ nanoparticles are concentrated in the shell layer of nanofiber F3. This special distribution enriches the TiO₂ on the surface of the nanofiber.
Thanks to this, on the one hand, the photocatalytic activity of TiO₂ nanoparticles and the antibacterial properties of Cur act synergistically to enhance the antibacterial performance of the nanofibers. On the other hand, the rich distribution of TiO₂ greatly increases the ultraviolet protection factor (UPF) value of the nanofibers. The UPF value of nanofiber F0 is 8.75 ± 0.78, that of CA - TiO₂ nanofiber F2 is increased to 87.64 ± 4.39, and due to the large amount of TiO₂ distributed in the shell layer of core - shell nanofiber F3, the UPF value is further increased to 357.34 ± 7.56.
Figure 3: TEM images of the three types of medicated nanofibers: (a) nanofibers F1; (b) nanofibers F2; (c) and (d) core-sheath nanofibers F3 with different magnifications.
(4) Prolonging the Release Curve of Curcumin
By preparing core - shell structured nanofibers, the release curve of curcumin (Cur) is effectively prolonged, and the drug release performance is improved. This is because in the core - shell nanofiber F3, Cur is located in the inner core part, and CA itself is insoluble, which makes the release of Cur slower and more durable. This structure effectively delays the drug release rate, reduces the initial burst release, and realizes the long - term release of the drug.
Figure 4: The modifications of drug sustained release profiles by the electrospun nanofibers: (a) The whole-time period drug sustained release profiles; (b) the release profiles of raw drug particles and electrospun nanofibers at the first day; (c) the drug sustained release profiles expressed through the times needed for reaching a certain percentage release, i.e. 30%, 50%, and 90%; (d) drug release mechanisms regressed according to the Peppas equation.
(5) Enhancing the Hydrophobicity and Antibacterial Properties of Nanofibers
Cellulose acetate (CA) itself has a certain degree of hydrophobicity, with a water contact angle of 91.3 ± 3.4°. When curcumin (Cur) and TiO₂ nanoparticles are added respectively, the contact angles of nanofibers F1 and F2 increase to 93.5 ± 2.8° and 105.8 ± 4.7° respectively. The core - shell nanofiber F3 has the largest water contact angle of 114.2 ± 3.9° due to the high surface concentration of TiO₂ nanoparticles in its shell layer. This indicates that the special core - shell structure and the distribution of TiO₂ nanoparticles in the shell layer significantly improve the hydrophobicity of the nanofibers. (See Figure 5)
In terms of antibacterial properties, Gram - negative Escherichia coli (E. coli) and Gram - positive Staphylococcus aureus (S. aureus) were selected as test bacteria. As blended nanofibers, nanofibers F1 and F2 have a certain inhibitory effect on S. aureus and E. coli. The inhibition rates of F1 are 43.64% and 58.91% respectively, and those of F2 are 72.18% and 81.28% respectively. In the core - shell nanofiber F3, Cur and TiO₂ nanoparticles are distributed in a special core - shell structure, and the inhibition rates against S. aureus and E. coli increase significantly, reaching 87.29% and 93.63% respectively, showing excellent synergistic antibacterial effects.
Figure 5: The properties and antibacterial performances of the prepared nanofibers: (a) hydrophobic property; (b) UPF; (c) and (d) OD600 values and inhibition rates against E. coli and S. aureus after 24 h, respectively.
III. Research Conclusions
This paper mainly discussed the core - shell nanofibers based on cellulose acetate (CA) prepared by improved triaxial electrospinning device electrospinning technology. Through the improved triaxial electrospinning technology, CA - based core - shell nanofibers with TiO₂ nanoparticles in the shell layer and curcumin (Cur) in the core layer were successfully prepared. This study opens up a new way for the functional transformation of polymeric excipients and lays a foundation for a deeper understanding of the structure - performance relationship of advanced functional nanomaterials with core - shell structures.
Electrospinning Nanofibers Article Source: https://doi.org/10.1016/j.cej.2025.160117
