Fabrication of high performance silk fibroin fibers via stable jet electrospinning for potential use in anisotropic tissue regeneration.

Regenerated silk fibroin (SF) from Bombyx mori silkworm cocoons is a highly regarded natural protein-biomaterial suitable for engineering a variety of biological tissues. Electrospinning offers a unique approach to fiber formation that can readily produce micro- and nano-scale fibers recapitulating the ultrastructure of a native extracellular matrix. However, SF fibers from conventional electrospinning suffer from the problem of poor mechanical properties for load-bearing relevant tissue regeneration applications. In this study, highly aligned high-strength SF fibers were fabricated by a recently emerged stable jet electrospinning (SJES) approach, with the aid of high molecular weight poly(ethylene oxide) (PEO) acting as a fiber-forming ingredient to increase control over the jetting instability during electrospinning. The results showed that 90% of the collected SF/PEO (mass ratio 88 : 12) fiber assembly via SJES oriented unidirectionally with an angle variation of <1° and displayed obvious anisotropic wettability. Mechanically, the as-electrospun highly aligned SF/PEO fibers exhibited a 22.0-fold increase in ultimate tensile strength (50.85 ± 1.13 MPa) and a 49.3-fold increase in Young's modulus (1185.99 ± 164.56 MPa) compared with the randomly oriented SF fibers. A subsequent methanol treatment further remarkably boosted the tensile strength to 73.91 ± 5.15 MPa and Young's modulus to 2426.13 ± 86.67 MPa. The mechanical performance of the SF fibers via SJES was also impressive, even when tested in the wet state. The substantial improvement in the mechanical properties of the electrospun SF fibers is attributed to the SJES-enabled higher molecular orientation and contents of the secondary structure (α-helix and ß-pleated sheet), as well as the high degree of fiber alignment. Moreover, biological tests verified that these SF-based fibrous scaffolds supported the induced pluripotent stem cell derived mesenchymal stem cells to adhere, migrate and grow in a manner of orienting along the fiber axis. We speculate that these high-performance biomimicking SF fibers might give rise to improved efficacy while being utilized to architecturally regenerate anisotropic load-bearing tissues (e.g., tendon, ligament, and blood vessel).

Alkali-Mediated Miscibility of Gelatin/Polycaprolactone for Electrospinning Homogeneous Composite Nanofibers for Tissue Scaffolding.

Electrospun natural-synthetic composite nanofibers, which possess favorable biological and mechanical properties, have gained widespread attention in tissue engineering. However, the development of biomimetic nanofibers of hybrids remains a huge challenge due to phase separation of the polymer blends. Here, aqueous sodium hydroxide (NaOH) solution is proposed to modulate the miscibility of a representative natural-synthetic hybrid of gelatin (GT) and polycaprolactone (PCL) for electrospinning homogeneous composite nanofibers. Alkali-doped GT/PCL solutions and nanofibers examined at macroscopic, microscopic, and internal molecular levels demonstrate appropriate miscibility of GT and PCL after introducing the alkali dopant. Particularly, homogeneous GT/PCL nanofibers with smooth surface and uniform diameter are obtained when aqueous NaOH solution with a concentration of 10 m is used. The fibers become more hydrophilic and possess improved mechanical properties both in dry and wet conditions. Moreover, biocompatibility experiments show that stem cells adhere to and proliferate better on the alkali-modified nanofibers than the untreated one. This study provides a facile and effective approach to solve the phase separation issue of the synthetic-natural hybrid GT/PCL and establishes a correlation of compositionally and morphologically homogeneous composite nanofibers with respect to cell responses.

Highly aligned core-shell structured nanofibers for promoting phenotypic expression of vSMCs for vascular regeneration.

This study was designed to assess the efficacy of hyaluronan (HA) functionalized well-aligned nanofibers of poly-l-lactic acid (PLLA) in modulating the phenotypic expression of vascular smooth muscle cells (vSMCs) for blood vessel regeneration. Highly aligned HA/PLLA nanofibers in core-shell structure were prepared using a novel stable jet electrospinning approach. Formation of a thin HA-coating layer atop each PLLA nanofiber surface endowed the uni-directionally oriented fibrous mats with increased anisotropic wettability and mechanical compliance. The HA/PLLA nanofibers significantly promoted vSMC to elongation, orientation, and proliferation, and also up-regulated the expression of contractile genes/proteins (e.g., α-SMA, SM-MHC) as well as the synthesis of elastin. Six weeks of in vivo scaffold replacement of rabbit carotid arteries showed that vascular conduits made of circumferentially aligned HA/PLLA nanofibers could maintain patency and promoted oriented vSMC regeneration, lumen endothelialization, and capillary formation. This study demonstrated the synergistic effects of nanotopographical and biochemical cues in one biomimetic scaffold design for efficacious vascular regeneration.