Current methodologies and approaches for the formation of core–sheath polymer fibers for biomedical applications

The application of polymer fibers has rocketed to unimaginable heights in recent years and occupies every corner of our day-to-day life, from knitted protective textile clothes to buzzing smartphone electronics. Polymer fibers could be obtained from natural and synthetic polymers at a length scale from the nanometer to micrometer range. These fibers could be formed into different configurations such as single, core–sheath, hollow, blended, or composite according to human needs. Of these several conformations of fibers, core–sheath polymer fibers are an interesting class of materials, which shows superior physical, chemical, and biological properties. In core–sheath fiber structures, one of the components called a core is fully surrounded by the second component known as a sheath. In this format, different polymers can be applied as a sheath over a solid core of another polymer, thus resulting in a variety of modified properties while maintaining the major fiber property. After a brief introduction to core–sheath fibers, this review paper focuses on the development of the electrospinning process to manufacture core–sheath fibers followed by illustrating the current methodology and approaches to form them on a larger scale, suitable for industrial manufacturing and exploitation. Finally, the paper reviews the applications of the core–sheath fibers, in particular, recent studies of core–sheath polymer fibers in tissue engineering (nerve, vascular grafts, cardiomyocytes, bone, tendons, sutures, and wound healing), growth factors and other bioactive component release, and drug delivery. Therefore, core–sheath structures are a revolutionary development in the field of science and technology, becoming a backbone to many emerging technologies and novel opportunities.