•The challenges and solutions of alginate electrospinning were reviewed for the first time.•High density of intra- and intermolecular hydrogen bonding restricts alginate electrospinnability.•Alginate ...electrospinnability can be improved by blending with carrier polymers.•Electrospinning of alginate can be dramatically facilitated through chemical modifications.•Alginate nanofibers can be used in tissue engineering and drug delivery systems.
Alginate as a naturally-derived biomaterial with marine algae sources has gained much attention in both laboratorial and industrial applications due to its structural and chemical resemblance to extracellular matrix (ECM) as well as desirable properties like biocompatibility, biodegradability, processability and low cost. Electrospun alginate nanofibrous scaffolds have found wide applications in biomedical field such as tissue engineering, biomedicine and drug delivery systems. However, electrospinning of alginate is challenging due to the low solubility and high viscosity of high molecular weight alginate, high density of intra- and intermolecular hydrogen bonding, polyelectrolyte nature of aqueous solution and lack of appropriate organic solvent. The aim of this review is to summarize the challenges and obstacles in alginate electrospinning reported in the literature as well as the introduced solutions for them, in order to open new opportunities for more intended and successful investigations in the field.
Hypothesis: Due to the presence of intra- and inter molecular hydrogen bonding in alginate chemical structure, its electrospinning capability is weak. However, this weakness can be improved through ...substitution of hydroxyl groups by sulfate groups. This article focuses on the role of degree of substitution of sulfate groups on the physicochemical properties of electrospinning solutions, such as viscosity, electrical conductivity and electrospinning conditions. Methods: Sodium sulfated alginate (SSA) was synthesized through the reaction of sodium alginate and chlorosulfonic acid in formamide as the solvent. The amount of chlorosulfonic acid was varied in order to obtain the SSA samples with different degrees of substitution. The chemical structures of neat alginate and SSA were studied by FTIR and 1H NMR spectroscopy. Degree of sulfation of samples was measured using CHNS elemental analysis, and the electrical conductivity and viscosity of SSA solutions were measured. The SSA nanofibers were fabricated using electrospinning and further crosslinked by a solution of calcium chloride to improve its hydrolytic stability. Finally, the fiber diameter and mechanical properties of the nanofibrous mat were studied by SEM and a tensile mechanical machine. Findings: Both FTIR and 1H NMR analyses have confirmed the formation of sulfate groups in SSA structure. Based on elemental analysis, the degree of substitution (DS) of SSA samples has been measured as 0.9 and 0.5 for SSA1 and SSA0.5, respectively. The electrical conductivity and viscosity of the SSA solutions also increased and decreased by increasing DS, respectively. The SSA1 sample showed better electrospinning capability and higher SSA content in dry electrospun mat compared to those in SSA0.5 sample. Finally, the crosslinked SSA1 mat revealed a lower mechanical strength compared to SSA0.5 mat due to lower crosslink density and higher chain scission of polymeric chains resulted from sulfation reaction.
Despite numerous applications of nanofibrous alginate (Alg) mat, its facile fabrication via electrospinning is still challenging. The low alginate content compared to the carrier polymer and ...existence of impurities are the main drawbacks of existing approaches. The purpose of this research is both to study and improve alginate electrospinnability by focusing on the effect of inter- and intramolecular hydrogen bonding. Based on hard and soft acids and bases (HSAB) theory, the Na+ cations (carboxylate counter-cation) were substituted with a harder acid, Li+ cation, to increase the strength of ionic interaction and decrease the density of hydrogen bonding. Viscosity and electrical conductivity measurements as well as FTIR and 1H NMR revealed a lower intramolecular hydrogen bonding density in Li-Alg. SEM images showed improvement of alginate electrospinnability for Li-Alg compared to the salts of Na-Alg and K-Alg. This study sheds more light on underlying reasons hindering alginate electrospinning and introduces a simple method for fabrication of nanofibers with high alginate content.
