Facile encapsulation of cyanoacrylate-based bioadhesive by electrospray method and investigation of the process parameters

Abstract

Polymer microcapsules containing cyanoacrylates have represented a promising option to develop self-healing biomaterials. This study aims to develop an electrospray method for the preparation of capsules using poly(methyl methacrylate) (PMMA) as the encapsulant and ethyl 2-cyanoacrylate (EC) as the encapsulate. It also aims to study the effect of the electrospray process parameters on the size and morphology of the capsules. The capsules were characterized using Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and field-emission scanning electron microscopy (FE-SEM). Moreover, the effects of electrospray process parameters on the size were investigated by Taguchi experimental design. FTIR and TGA approved the presence of both PMMA and EC without further reaction. FE-SEM micrograph demonstrated that an appropriate choice of solvents, utilizing an appropriate PMMA:EC ratio and sufficient PMMA concentration are critical factors to produce capsules dominantly with an intact and spherical morphology. Utilizing various flow rates (0.3-0.5 ml/h) and applied voltage (18-26 kV), capsules were obtained with a 600-1000 nm size range. At constantly applied voltages, the increase in flow rate increased the capsule size up to 40% (ANOVA, p ≤ 0.05), while at constant flow rates, the increase in applied voltage reduced the average capsule size by 3.4-26% (ANOVA, p ≤ 0.05). The results from the Taguchi design represented the significance of solution flow rate, applied voltage, and solution concentration. It was shown that the most effective parameter on the size of capsules is flow rate. This research demonstrated that electrospray can be utilized as a convenient method for the preparation of sub-micron PMMA capsules containing EC. Furthermore, the morphology of the capsules is dominated by solvents, PMMA concentration, and PMMA:EC ratio, while the average size of the capsules can be altered by adjusting the flow rate and applied voltage of the electrospray process.

Keywords: Bioadhesive; Electrospray; Encapsulation; Microcapsules; Taguchi design.

Figure 1

Preparation, chemical composition, and thermogravimetry of PMMA/EC capsules: (a) schematic representation of the electrospray process utilized for the preparation of capsules and following characterizations. The components include a high voltage supply, syringe pump, syringe and nozzle assembly, aluminum foil substrate, and schematic magnification of prepared capsules. (b) FTIR spectra of neat PMMA, EC (n = 3), and (c) FTIR spectra of capsules prepared by electrospray of S₄, S₂, S₄, and S₅ solutions (n = 3) reveal the presence of EC in the PMMA capsules without any pre-mature reaction. (d) The TGA curves of neat EC, prepared capsule, and neat PMMA further represent the presence of the two components, EC and PMMA in the capsule structure (n = 3).

Figure 2

FE-SEM images of the capsules prepared by electrospray process using only a) DCM (S₅) or b) DMF (S₄) as solvent. The magnification of the FE-SEM images is $\times$ 2000.

Figure 3

FE-SEM images of capsules prepared by electrospray (a) S₂, (b) S₃, and (c) S₁ solutions. The magnification of the FE-SEM images is $\times$ 10,000.

Figure 4

FE-SEM images of the prepared capsules according to the number of experiments provided in Table 3: (a) experiment 1, (b) experiment 2, (c) experiment 3, (d) experiment 4, (e) experiment 5, (f) experiment 6, (g) experiment 7, (h) experiment 8, (i) experiment 9. The magnification of the FE-SEM images is $\times$ 10,000.

Figure 5

FE-SEM images of the prepared capsules according to the number of experiments provided in Table 3: (a) experiment 10, (b) experiment 11, (c) experiment 12, (d) experiment 13, (e) experiment 14, (f) experiment 15, (g) experiment 16, (h) experiment 17, (i) experiment 18. The magnification of the FE-SEM images is $\times$ 10,000.

Figure 6

The average size of prepared microcapsules from S1 and S2 solutions at constantly applied voltages of (a) 18 kV, (b) 22 kV, and (c) 26 kV. The average size of prepared microcapsules from S1 and S2 solutions at constant flow rates of (d) 0.3 ml/h, (e) 0.4 ml/h, and (f) 0.5 ml/h. The mean diameter of capsules and standard deviations were evaluated according to the FESEM micrograph using ImageJ software (n = 50).

Figure 7

(a) Main effects plot and (b) Interaction plot for means of the diameter of capsules prepared by electrospray.

Figure 8

Main effects plot for S/N ratios of the diameter of capsules prepared by electrospray.