Comparative Properties of Ethyl, n-Butyl, and n-Octyl Cyanoacrylate Bioadhesives Intended for Wound Closure

Abstract

The properties of ethyl, n-butyl, and n-octyl cyanoacrylate (OCN) monomer and polymer intended as adhesives for wound closure have been studied and compared. The cyanoacrylate adhesives were characterized by IR and ¹H and ¹³C NMR spectroscopy, thermal gravimetric analysis, and scanning electron microscopy (SEM). By increasing the length of the alkyl chain in the cyanoacrylate monomer an increase in the relative intensity of the CH₂ and CH₃ bands and a decrease in the relative intensity of the C–O–C bands were produced. Similarly, the intensity of the signals corresponding to the protons of the C=C bond in the cyanoacrylate monomer decreased by increasing the length of the alkyl chain. On the other hand, the signals corresponding to the carbons of C=C, C=O, and C≡N groups displaced to higher values by increasing the length of the alkyl chain in the cyanoacrylate monomer. Polymerization of the monomers modified the chemical structure of the cyanoacrylate monomers. The polymerization produced the disappearance of the C=C bands and the intensity of the CH₃ groups decreased, the intensity of the cyanoacrylate group was strongly reduced, and two new intense bands at 856 and 1,246 cm⁻¹ due to C–O–C groups appeared.

The cyanoacrylate monomers show several thermal decompositions. The first one was found at about 120 °C and the weight loss associated to it decreased by increasing the length of the alkyl chain. Whereas the ethyl cyanoacrylate (ECN) was mainly composed of monomer, the n-butyl cyanoacrylate (BCN) contained monomer and some dimmers and the OCN had only a minor content of monomer. The thermal properties of the cyanoacrylate polymers also differed from those of the corresponding monomers. In general, the decomposition temperature increased by increasing the length of the alkyl chain of the cyanoacrylate. The SEM micrograph of the ECN polymer showed a homogeneous and smooth surface, whereas the SEM micrographs of the n-butyl and, more markedly, the OCN polymer showed a heterogeneous topography consisting in shredded polymer chains. Adhesion of the cyanoacrylate adhesives was obtained from single lap-shear tests of aluminum/cyanoacrylate monomer and pig skin/cyanoacrylate monomer joints. The single lap-shear strength values in the adhesive joints decreased by increasing the length of the alkyl cyanoacrylate chain. The adhesion in the joints produced with ethyl and n-butyl cyanoacrylate adhesives was high and sufficient for using in wound closure.