Abstract
Electrospun nanofibrous membranes of natural polymers, such as gelatin, are fundamental in the design of regenerative devices. Crosslinking of electrospun fibres from gelatin is required to prevent dissolution in water, to retain the original nanofibre morphology after immersion in water, and to improve the thermal and mechanical properties, although this is still challenging to accomplish in a controlled fashion. In this study, we have investigated the scalable manufacture and structural stability in aqueous environment of a UV-cured nanofibrous membrane fabricated by free surface electrospinning (FSES) of aqueous solutions containing vinylbenzylated gelatin and poly(ɛ-caprolactone) dimethacrylate (PCL-DMA). Vinylbenzylated gelatin was obtained via chemical functionalisation with photopolymerisable 4-vinylbenzyl chloride (4VBC) groups, so that the gelatin and PCL phase in electrospun fibres were integrated in a covalent UV-cured co-network at the molecular scale, rather than being simply physically mixed. Aqueous solutions of acetic acid (90 vol%) were employed at room temperature to dissolve gelatin-4VBC (G-4VBC) and PCL-DMA with two molar ratios between 4VBC and DMA functions, whilst viscosity, surface tension and electrical conductivity of resulting electrospinning solutions were characterised. Following successful FSES, electrospun nanofibrous samples were UV-cured using Irgacure I2959 as radical photo-initiator and 1-Heptanol as water-immiscible photo-initiator carrier, resulting in the formation of a water-insoluble, gelatin/PCL covalent co-network. Scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, differential scanning calorimetry (DSC), tensile test, as well as liquid contact angle and swelling measurements were carried out to explore the surface morphology, chemical composition, thermal and mechanical properties, wettability and water holding capacity of the nanofibrous membranes, respectively. UV-cured nanofibrous membranes did not dissolve in water and showed enhanced thermal and mechanical properties, with respect to as-spun samples, indicating the effectiveness of the photo-crosslinking reaction. In addition, UV-cured gelatin/PCL membranes displayed increased structural stability in water with respect to PCL-free samples and were highly tolerated by G292 osteosarcoma cells. These results therefore support the use of PCL-DMA as hydrophobic, biodegradable crosslinker and provide new insight on the scalable design of water-insoluble, mechanical-competent gelatin membranes for healthcare applications.
Highlights
In the past decades, electrospun nanofibrous membranes have attracted great attention due to the small size fibres with fine interconnected pores, extremely large surface area to volume ratio and the versatility of polymers, polymer blends and organic-inorganic composite materials that can be smoothly electrospun [1,2,3,4,5,6]
UV-cured membranes are indicated as ‘F-GXW’ or ‘F-GYPZW’, where ‘W’ identifies the concentration of I2959 photoinitiator used during UVcuring, whereby low (0.1% w/v I2959) and high (0.5% w/v) photoinitiator concentrations were coded as either ‘L’ or ‘H’, respectively
Free surface electrospinning was employed to investigate the scalable manufacture and respective wet-state structural stability of gelatin-based fibrous membranes. 4-vinylbenzyl chloride (4VBC)-functionalised gelatin was used as suitable biomimetic backbone with photopolymerisable groups and dissolved with poly(ɛ-caprolactone) dimethacrylate (PCL-DMA), which was applied as hydrophobic, degradable crosslinker
Summary
Electrospun nanofibrous membranes have attracted great attention due to the small size fibres with fine interconnected pores, extremely large surface area to volume ratio and the versatility of polymers, polymer blends and organic-inorganic composite materials that can be smoothly electrospun [1,2,3,4,5,6]. Electrospinning can hardly meet the needs of industrial scale nanofibre manufacture compared with currently available microfibre spinning technologies, enabling the collection of nanofibre nonwoven fabric area of up to 25 cm2 [11, 12]. To overcome this limitation and increase the yield of fibre formation, a great deal of attention has been put towards the development of needle-free electrospinning apparatus, e.g. by Formhals et al [13] and Jirsak et al [14, 15]. With nanofibrous nonwoven membranes obtained with 50 - 500 nm nanofibre diameter at a production rate of 1.5 g.min-1 per meter of roller length [16], this mechanism enables high scalability, low cost, as well as easy operation in comparison with nonwoven membranes electrospun from single spinneret
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