Abstract:

Objective Collagen peptide (COP) is a small molecular weight polypeptide with excellent solubility, but is difficult in filament formation compared with collagen. In this study, polyethylene glycol (PEG) was incorporated with COP, aiming to improve the poor spinnability of COP.

Method COP was blended with PEG to form the spinning solution with 60% formic acid as solvent. The surface tension and conductivity properties of the solution were measured by a tensiometer and conductivity meter. Scanning electron microscope was utilized to observe the surface morphology of the electrospun nanofibers. The interaction between COP and PEG was analyzed by Fourier transform infrared spectroscope, and the positions and strength distributions of different types of hydrogen bonds were fitted by the Gaussian method in the range of 3 000-3 600 cm^-1. The fibrous membranes' thermal characteristics and crystalline structure were also examined using differential scanning calorimeter and X-ray diffractometer(XRD), respectively.

Results By testing the solution properties of different COP mass fraction blended spinning solutions, it was found that the electrical conductivity and surface tension increased with the increase of COP mass fraction (Tab. 1). The incorporation of PEG improved the spinnability of COP obviously (Fig.1). The average diameter of fibers increased with COP mass fraction increasing and became most uniform when the COP content reached 20%. Moreover, when the mass fraction of COP is 12%, 16%, 20% and 24%, the average diameter of the fiber is 173, 205, 308, 319 nm respectively (Fig.2). FT-IR spectrum Gaussian fitting results showed that COP and PEG formed hydrogen bond, and the intramolecular hydrogen bond decreased while intermolecular hydrogen bond increased. It was discovered that the intramolecular hydrogen bond contact was primarily of OH … OH interaction, with some occurring as cyclic polymers, while the intermolecular hydrogen bond had a variety of OH … O, OH … N and OH … π interactions (Fig.3 and Tab.2). During electrospinning, the endothermic peak of the nanofiber membrane occured at 88 ℃, but the endothermic peaks for COP and PEG were at 100 ℃ and 72 ℃, respectively (Fig.4). From the XRD curves and statistical results of relative crystallinity of COP, PEG and nanofibrous membranes, it was found that COP at 2θ of 21.6° with a broad peak, PEG at 2θ of 19.2° and 23.4°, respectively, had one crystal diffraction peak, and 2θ exhibited a smaller peak in the 26°-28° range (Fig. 5). The nanofiber membrane, there were broad peaks representing COP and crystal diffraction peaks of PEG, respectively, with the addition of COP, the strength increases, and the crystallinity of the fiber membrane after electrospinning also increased (Tab.3).

Conclusion It was difficult to obtain well formed nanofibers by electrospinning using pure COP, but the addition of PEG was shown to have improved the poor spinnability of COP. The effect of the size of its mass fraction on the surface tension of the spinning fluid fluctuated in a small range due to the low COP molecular weight, while the conductivity increased with increasing COP mass fraction. When the COP mass fraction was 20%, the electrospun fibers exhibit uniform morphology, the relative strength of intermolecular hydrogen bonding was 52.42%, and the crystallinity also reached a maximum (62.53%) with a melting enthalpy of 55.81 J/g. PEG and COP formed hydrogen bond when the solutions were mixed. It is found that after electrospinning the intramolecular hydrogen bond of the fiber membrane decreases, while the intermolecular hydrogen bond increases.

Key words: electrospinning, collagen peptide, polyethylene glycol, nanofiber, spinnability