Fabrication of Gelatin Nanofibers by Electrospinning-Mixture of Gelatin and Polyvinyl Alcohol

Abstract

Gelatin, one of the most abundant, naturally derived biomacromolecules from collagen, is widely applicable in food additives, cosmetic ingredients, drug formulation, and wound dressing based on their non-toxicity and biodegradability. In parallel, polyvinyl alcohol (PVA), a synthetic polymer, has been commonly applied as a thickening agent for coating processes in aqueous systems and a major component in healthcare products for cartilage replacements, eye lubrication, and contact lenses. In this study, a new type of mixed hydrogel nanofiber was fabricated from gelatin and polyvinyl alcohol by electrospinning under a feasible range of polymer compositions. To determine the optimal composition of gelatin and polyvinyl alcohol in nanofiber fabrication, several key physicochemical properties of mixed polymer solutions such as viscosity, surface tension, pH, and electrical conductance were thoroughly characterized by a viscometer, surface tensiometer, water analyzer, and carbon electron probe. Moreover, the molecular structures of polymeric chains within mixed hydrogel nanofibers were investigated with Fourier-transform infrared spectroscopy. The morphologies and surface elemental compositions of the mixed hydrogel nanofibers were examined by the scanning electron microscope and energy-dispersive X-ray spectroscopy, respectively. The measurement of water contact angles was performed for measuring the hydrophilicity of nanofiber surfaces. Most importantly, the potential cytotoxicity of the electrospun nanofibers was evaluated by the in vitro culture of 3T3 fibroblasts. Through our extensive study, it was found that a PVA-rich solution (a volumetric ratio of gelatin/polyvinyl alcohol <1) would be superior for the efficient production of mixed hydrogel nanofibers by electrospinning techniques. This result is due to the appropriate balance between the higher viscosity (~420−~4300 10−2 poise) and slightly lower surface tension (~35.12−~32.68 mN/m2) of the mixed polymer solution. The regression on the viscosity data also found a good fit by the Lederer−Rougier’s model for a binary mixture. For the hydrophilicity of nanofibers, the numerical analysis estimates that the value of interfacial energy for the water contact on nanofibers is around ~−0.028 to ~−0.059 J/m2.

Keywords: Fourier-transform infrared spectrometer; electrospinning; gelatin; polyvinyl alcohol; spin coating; water contact angle.

Figure 1

Morphology of electrospun gelatin/PVA mixed nanofibers on top of a film made of identical material.

Figure 2

The averaged viscosity of gelatin/PVA mixed solution.

Figure 3

The average electrical conductance of gelatin/PVA mixed solutions.

Figure 4

The average pH values of gelatin/PVA mixed solutions.

Figure 5

The average surface tension of gelatin/PVA mixed solutions.

Figure 6

Morphology of electrospun gelatin/PVA mixed nanofibers on top of a film.

Figure 6

Morphology of electrospun gelatin/PVA mixed nanofibers on top of a film.

Figure 7

The averaged diameters for electrospun gelatin/PVA mixed nanofibers. (The symbols for amino acids are A: alanine, G: glycine, P: proline, R: arginine, E: glutamate, and O: hydroxyproline).

Figure 8

Variations of surface chemical elements from the EDS of electrospun gelatin/PVA mixed nanofibers.

Figure 9

FTIR spectra for electrospun gelatin/PVA nanofiber films with different volumetric mixing ratios.

Figure 10

Water contact angle as a function of time for electrospun gelatin/PVA nanofiber films with different volumetric mixing ratios.

Figure 11

The average optical density from MTT assay for 3T3 cultured in culture media and on gelatin/PVA nanofiber films. The optical density is ${\log }_{10}\left[\frac{\mathrm{incident} \mathrm{light} \mathrm{intensity}}{\mathrm{transmitted} \mathrm{light} \mathrm{intensity}}\right]$.

Figure 12

Selected optical images (50×) of cultured 3T3 in media from immersed gelatin/PVA = 8:2, 5:5, 2:8, and pure PVA.

Figure 13

A mixture model for fitting the viscosity of gelatin/PVA mixed solutions. The empirical coefficient α is obtained by minimizing errors in the L² norm (square root of the sum of error²) between experimental data and fitting numbers.

Figure 14

A schematic drawing of a drop of liquid on a partially wetted substrate.

Figure 15

Variations of the width r of water contact as functions of time.

Figure 16

The optimal estimate of interfacial energy ∆E from the width r of water contact and model proposed by Härth and Schubert.