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The process of melt electrospinning has received noteworthy attention due to its ability to fabricate micro scaled polymer fibers. Recently, a melt electrospinning process has been attracting attention for biomedical applications, in particular with scaffold fabrication for tissue engineering. In order to enhance cell attachment and proliferation on scaffolds, it is important to control fiber diameters to create an environment to which cells can attach, grow, and proliferate with ease. However, because electrospinning is a process with many parameters, it is particularly difficult to precisely control the diameter of the resulting fibers. Also, polymer powders or pellets melted in nozzles are typically used for melt electrospinning. However, a filament feeding melt electrospinning process has not been yet been implemented. In this study, we developed a melt electrospinning device which can feed PCL (Polycaprolactone, Mw: 80 000 g mol−1) filaments for advanced electrospun fiber diameter control. The PCL filaments were first fabricated by a small scale micro-compounder and then fed into the melting chamber of the electrospinning device. The system was then heated to a desired temperature, and the melt was extruded through a nozzle. The potential difference between the nozzle and counter electrode then drew down the PCL extrudate, creating fine microfibers. Temperature was controlled and monitored via a customized temperature control system. In order to control the dispensing of the PCL filaments, a customized control algorithm using NI (National Instruments) LabVIEW was used. In order to actively cool PCL filaments, a miniature computer fan was attached on the side of the melting chamber so that the filaments would not buckle. This paper reveals the investigation of significant process parameters that influence fiber diameters and their optimization. For instance, applied voltages, distances between the nozzle and a counter electrode, processing temperatures, and polymer resin flowrates were varied. We also studied and summarized the effect of duty cycle—a ratio of forward and backward motions of the filament within a cycle time—for advanced fiber diameter control. Moreover, the relationship between a flow rate and a duty cycle and their influences on a fiber diameter were studied.

Poly(vinyl alcohol) (PVA), a synthetic, nontoxic polymer, is widely studied for use as a biomedical hydrogel due to its structural and physicomechanical properties. Depending on the synthesis method, PVA hydrogels can exhibit a range of selected characteristics-strength, creep resistance, energy dissipation, degree of crystallinity, and porosity. While the structural integrity and behavior of the hydrogel can be finetuned, common processing techniques result in a brittle, linear elastic material. In addition, PVA lacks functionality to engage and participate in cell adhesion, which can be a limitation for integrating PVA materials with tissue in situ. Thus, there is a need to further engineer PVA hydrogels to optimize its physicomechanical properties while enhancing cell adhesion and bioactivity. While the inclusion of gelatin into PVA hydrogels has been shown to impart cell-adhesive properties, the optimization of the mechanical properties of PVA-gelatin blends has not been studied in the context of traditional PVA hydrogel processing techniques. The incorporation of poly(ethylene glycol) with PVA prior to solidification forms an organized, cell instructive hydrogel with improved stiffness. The effect of cryo-processing, i.e., freezethaw (FT) cycling was elucidated by comparing 1 FT and 8 FT theta-cryo-gels and cryo-gels. To confirm the viability of the gels, human mesenchymal stem cell (hMSC) protein and sulfated glycosaminoglycan assays were performed to verify the nontoxicity and influence on hMSC differentiation. We have devised an elastic PVA-gelatin hydrogel utilizing the theta-gel and cryo-gel processing techniques, resulting in a stronger, more elastic material with greater potential as a scaffold for complex tissues.

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