Bon Kang Gu

Fabrication of sonicated chitosan nanofiber mat with enlarged porosity for use as hemostatic materials

Electrospinning of pure chitosan was employed to obtain a nanofibrous hemostatic material. Owing to the water-solubility of the resulting acidic chitosan nanofibers, the optimum neutralization conditions were identified by testing various alkaline solutions, so that an insoluble material could be achieved. The pore size and thickness of the neutralized chitosan nanofibers mat could be controlled using ultra-sonication. The porosity of the chitosan mat was increased from 79.9% to 97.2% with ultra-sonication treatment for 1 min, and the water absorption time decreased from 110s to 9s. The blood clotting efficiency measured for the sonicated chitosan nanofiber mat was 1.35- and 3.41-fold better than the efficiencies of the Surgicel(®) and chitosan sponge, respectively. In addition, the proliferation of normal human dermal fibroblasts on the sonicated nanofiber mat was found to be 1.4-fold higher than that on the non-sonicated material after 7 days of culture.

3-dimensional bioprinting for tissue engineering applications.

The 3-dimensional (3D) printing technologies, referred to as additive manufacturing (AM) or rapid prototyping (RP), have acquired reputation over the past few years for art, architectural modeling, lightweight machines, and tissue engineering applications. Among these applications, tissue engineering field using 3D printing has attracted the attention from many researchers. 3D bioprinting has an advantage in the manufacture of a scaffold for tissue engineering applications, because of rapid-fabrication, high-precision, and customized-production, etc. In this review, we will introduce the principles and the current state of the 3D bioprinting methods. Focusing on some of studies that are being current application for biomedical and tissue engineering fields using printed 3D scaffolds.

Direct fabrication of twisted nanofibers by electrospinning

The authors have fabricated artificial twisted nanofibers that resemble naturally twisted fiber structures, such as collagen fibril and double-strand DNA, using a modified conventional electrospinning system to directly develop the twisted nanofibers. The system modification allowed for the fabrication of twisted nanofibers by controlling the whipping jet using a modified electric field from an auxiliary electrode. Moreover, the authors calculated the magnitude of the electric field strength vectors using the Maxwell software program to identify the effect of the rotating electric field on the auxiliary electrode. Twisted nanofibers have a potential application in biomimetics, such as in artificial muscles, actuators, and nanoelectromechanical systems.

Gelatin blending and sonication of chitosan nanofiber mats produce synergistic effects on hemostatic functions.

To improve the hemostatic function of chitosan nanofiber mats, we studied the synergetic effects of gelatin blending and porosity control. Gelatin-blended-chitosan (Chi-Gel) nanofiber mats were evaluated with respect to surface morphology, mechanical properties and wettability, and functionally tested in a blood clotting study. The blood clotting efficiency of Chi-Gel nanofiber mats using rabbit whole blood in vitro was superior to that of chitosan nanofibers. Moreover, Chi-Gel nanofiber mats with enlarged porosity, produced by ultra-sonication, showed improved blood clotting efficiency, cell viability and cell infiltration compared with non-sonicated Chi-Gel nanofiber mats. Field-emission scanning electron microscopy revealed a richer density of platelets on sonicated nanofiber mats than on non-sonicated nanofiber mats after 3 min of blood clotting. The proliferation of human dermal fibroblast cells on sonicated Chi-Gel nanofiber mats using the DNA assay was higher than that on non-sonicated chitosan nanofiber mats after 7 days of culture. Confocal z-stack images showed that sonicated Chi-Gel nanofiber mats with high porosity supported active cell migration and infiltration into the 3-dimensional nanofiber mats. These results suggest that hydrophilic gelatin blending and sonication of chitosan nanofiber mats yields synergistic effects that not only improve hemostatic function but also promote wound repair.

Polycaprolactone-chitin nanofibrous mats as potential scaffolds for tissue engineering

We describe here the preparation of poly(caprolactone) (PCL)-chitin nanofibrous mats by electrospinning from a blended solution of PCL and chitin dissolved in a cosolvent, 1,1,1,3,3,3-hexafluoro-2-propanol and trifluoroacetic acid. Scanning electron microscopy showed that the neutralized PCL-chitin nanofibrous mats were morphologically stable, with a mean diameter of 340.5 ± 2.6 nm, compared with a diameter of 524.2 ± 12.1 nm for PCL mats. The nanofibrous mats showed decreased water contact angles as the proportion of chitin increased. However, the tensile properties of nanofibrous mats containing 30 ~ 50% (wt/wt) chitin were enhanced compared with PCL-only mats. In vitro studies showed that the viability of human dermal fibroblasts (HDFs) for up to 7 days in culture was higher on composite (OD value: 1.42 ± 0.09) than on PCL-only (0.51 ± 0.14) nanofibrous mats, with viability correlated with chitin concentration. Together, our results suggest that PCL-chitin nanofibrous mats can be used as an implantable substrate to modulate HDF viability in tissue engineering.

Cellular and soft tissue compatibility to high interconnectivity between pores of chitosan scaffold

AbstractIn the field of tissue engineering and regenerative medicine, porosity, pore size, and pore interconnectivity of three-dimensional scaffolds affect cellular attachment, proliferation and, migration, and degree of tissue infiltration. In this study, porous chitosan scaffolds with macropores interconnected by micropores were prepared using a thermally induced phase-separation process. Water adsorption properties of scaffolds were investigated by soaking in phosphate-buffered saline (PBS) at room temperature. The chitosan scaffold with macropores interconnected by micropores (CS-10B) adsorbed PBS more rapidly than a chitosan scaffold containing only macropores (CS). An investigation of cell attachment and distribution showed that human dermal fibroblasts (HDFs) culture on chitosan scaffolds in vitro were present on both the surface and cross-sections of the CS-10B scaffold, but only on the surface of the CS scaffold. Studies of tissue responses to the prepared scaffolds, evaluated by subcutaneous implantation in rats, showed that the organization of tissues in the CS-10B scaffold was superior to that in the CS scaffold, and the CS-10B implant degraded faster than the CS implant in vivo. The high interconnectivity of porous scaffolds with macropores interconnected by micropores enhanced biocompatibility and biodegradability, suggesting the excellent potential applications of such chitosan scaffolds in the field of tissue engineering and regenerative medicine.

Fabrications of nanofibers as crossed arrays by electrospinning.

We have developed a new method for obtaining nanofiber crossed arrays by exploiting an auxiliary electrode subjected to electrical frequencies, between the capillary tip and the grounded target in an electrospinning machine. The frequencies generated crossed arrays on a flat collector, used instead of a rotating wheel because of intersecting jets. We observed many straight and crossed structures. We determined the variation in morphology with changes in frequency, and characterized the samples using optical microscopy and a field emission scanning electron microscope. This paper reports on a simple, easy method for generating crossed array nanofibers on a flat substrate using electrical frequency in an auxiliary electrode.

Neuropeptide Substance-P-Conjugated Chitosan Nanofibers as an Active Modulator of Stem Cell Recruiting

The goal to successful wound healing is essentially to immobilize and recruit appropriate numbers of host stem or progenitor cells to the wound area. In this study, we developed a chitosan nanofiber-immobilized neuropeptide substance-P (SP), which mediates stem cell mobilization and migration, onto the surfaces of nanofibers using a peptide-coupling agent, and evaluated its biological effects on stem cells. The amount of immobilized SP on chitosan nanofibers was modulated over the range of 5.89 ± 3.27 to 75.29 ± 24.31 ng when reacted with 10 to 500 ng SP. In vitro migration assays showed that SP-incorporated nanofibers induced more rapid migration of human mesenchymal stem cells on nanofibers compared to pristine samples. Finally, the conjugated SP evoked a minimal foreign body reaction and recruited a larger number of CD29- and CD44-positive stem cells into nanofibers in a mouse subcutaneous pocket model.

Anomalous pH Actuation of a Chitosan/SWNT Microfiber Hydrogel with Improved Mechanical Property

Composite fibers composed of chitosan and single-wall carbon nanotubes (CNTs) have been fabricated using a wet spinning method. The dispersion was improved by the sonic agitation of the CNTs in a chitosan solution followed by centrifugation to remove tube aggregates and any residual catalyst. The mechanical behavior was investigated using a dynamic mechanical analyzer (DMA). The mechanical tests showed a dramatic increase in Youngs modulus for the chitosan/CNT composite fibers fabricated using the improved dispersion method. The strain on the microfibers was determined from tensile load measurements during pH switching in acidic or basic electrolyte solutions. The microfibers showed a general actuation behavior of expanding at pH = 2 and contracting at pH = 7 under low tensile loads. However, a reverse of this actuation behavior was exhibited under high tensile loads. This anomalous pH actuation is both new and surprising. It was explained from an analysis of the differences in sample stiffness and Poisson’s ratio under tensile load in electrolyte solutions with different pH values.

Substance-P Immobilized Chitosan Nanofibers

The surface of biodegradable chitosan nanofibers was functionalized with pristine amine groups and used for immobilization of substance-P, which mediates pain perception and regulates wound healing, inflammation, and angiogenesis. The objectives of this study were to develop substance-P immobilized chitosan nanofibers and to evaluate the biological effects of the immobilized substance-P. Under the same conditions, the amount of substance-P covalently immobilized on chitosan nanofibers was 72.5 ± 16.9 ng compared to 7.3 ± 2.2 ng in passively absorbed samples. Substance-P on chitosan nanofibers released slowly and promoted greater proliferation (∼1.4-fold) of human mesenchymal stem cells than pristine samples after 7 days in culture.