Poster BB7 - Ultrasound-Enhaced Electrospinning Generates Gradient-Structures from Gelatin Methacryloyl for Advanced Tissue Engineering

Introduction: Electrospinning (ES) is an electrohydrodynamic process that produces polymeric fibers with thicknesses in the nano- and micrometer scale. These electrospun fiber constructs have been widely used in tissue engineering, since they can mimic the natural anisotropic, fibrous nature of the extracellular matrix (ECM). However, wider use of these constructs is limited due to low production rates and lack of control over the fiber diameter during the ES process to generate suitable mechanical and physical gradient structures that are present in native ECM. We present ultrasound-enhanced electrospinning (USES) (Fig. 1) as the means of addressing the aforementioned issues and limitations. USES is a needle-free, open-surface electrospinning method where focused ultrasound (US) is used to produce nanofibers of which diameter can be controlled on-the-fly by changing the US actuation parameters. USES can create multi-layered structures by varying fiber diameter in a graduated manner to mimic the anisotropic architecture of the native ECM. In the present work, we investigated the ability of USES to generate gradient-structures from gelatin methacryloyl (GelMA), which has been widely used in tissue engineering due its biological and rheological properties.

Materials and

Methods: The ES solutions were prepared by dissolving the GelMA aerogels in 90% acetic acid at a concentration of 18 wt.%. An in-house built USES device was used to generate the GelMA nanofibers. In USES, a pulsed sinusoidal US is used to generate an acoustic protrusion on the polymer solution – air interphase to produce an acoustic protrusion that acts as the Taylor cone in the ES process. The US parameters; i.e., amplitude, pulse repetition frequency (PRF), and cycles per burst; can be varied, which affects the thickness of the spun fibers. To the aim of generating a physical gradient structure from GelMA, we studied the effect of six different acoustic parameters on fiber thickness. Traditional needle-based ES (TES) was used as generate reference structures from the same GelMA solution. The size and morphology of the fiber structures was analyzed with scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-Ray diffraction analysis (XRD) will be used to study the physicochemical properties and crystallinity of the produced fiber structures.

Results, Conclusions, and Discussions: Figure 2, shows SEM images of USES-spun GelMA nanofibers with two different magnifications. The fibers appear smooth and round with diameters in the submicron (100 – 700 nm) range, mimicking the ECM and being ideal for tissue engineering. Little to no defects, such as beads or other discontinuities, were seen in obtained nanofibers. Instead, there are bright, white areas on the fibers' surface, showing possibly crystalline GelMA. In comparison, the GelMA fibers obtained via TES show fibers in the same size range with more defects (Fig. 3). Overall, GelMA presented stable electrospinnability with the novel USES method. Following, the effect of the ultrasound parameters on the fiber thickness will be evaluated.

FTIR analysis of the GelMA aerogels revealed its characteristic peaks (Fig. 4), while XRD was used to elucidate its crystalline nature (Fig. 5). These results will be compared against the GelMA nanofibers, obtained via USES and TES. Further comparison between USES and TES is of interest, since USES has been shown to produce fibers that are more amorphous than the ones obtained via TES.

Acknowledgements (Optional): This work was supported by the Estonian Research Council Grant (PRG1903).