Pure starch was electrospun after dissolving in 95 % aqueous dimethylsulfoxide solution. The starch solution was extruded into an “electro-wetspinning” setup consisting of an ethanol bath. After electrospinning, the fibers were heat treated to increase crystallinity and later cross-linked using glutaraldehyde vapors to improve water stability [14Kon]. In another study, researchers have suggested that the forma­tion of electrospun starch fibers in DMSO solutions was dependent on entanglement concentration and that an entanglement concentration of 1.2-2.7 times was necessary to obtain fibers. Similarly, starch with amylose content higher than 35 % was required for fiber formation. Extent of molecular entanglements, molecular conformations, and shear viscosity were other parameters that also had an influence on fiber formation [12Kon]. Fibers obtained had average diameters of 2.6 pm and the cross — linked fibers were stable and did not disperse after immersion in water. Electrospun starch fibers were proposed to be useful for food, textile, and biomedical applications. Hierarchical starch-based fibrous scaffolds for bone tissue applications were devel­oped by rapid prototyping and electrospinning approaches [09Mar].

Fig. 58.16 SEM and p-CT images depicting the morphology and hierarchical structure of the starch-based scaffolds. a and c are rapid prototyped samples and b and d are scaffolds that contain rapid prototyped and randomly distributed nanofibers. [09Mar]. Reproduced with permission from John Wiley and Sons

Starch-polycaprolactone (30/70) blends were made into hierarchical nanofiber meshes and 3D scaffold structures shown in Fig. 58.16 and used as substrates to grow human osteoblast cells. It was found that the nanofiber meshes had topology similar to that of the extracellular matrix and the 3D fibrous structure provided mechanical stability.

Starch-polycaprolactone (30/70) blend was dissolved in acetic acid or chloro­form and electrospun into fibers with diameters between 130 and 180 nm when the solution concentration was between 5 and 15 %. Particles, supposed to be starch and with diameters between 4 and 66 nm, were found embedded in the fibers. The fibers developed were considered to be useful for bone, skin, and cartilage tissue engi­neering [08Juk].

Potato starch and PVA were blended and made into nanofibers through electrospinning after the addition of about 5 % of ethanol. However, the properties or the stability of the fibers in water was not reported [10Suk]. In another research, oxidized starch was blended with PVA in various ratios and the solution was extruded into fibers. Oxidized starch performed as a polyelectrolyte and improved electrospinnability. Increasing the ratio of starch decreased fiber diameter with average fiber diameters decreasing from 460 to 147 nm [11Wan].

Hydroxypropyl starch was blended with poly(ethylene oxide) to develop fibrous scaffolds for tissue engineering [13Sil]. Various ratios of starch and PEO (from 30 to 90 %) were used with electrospinning voltage varying from 11 to 14 kV.

Average fiber diameters obtained varied from 143 to 334 nm. However, an experi­mental study on the relationship between electrospinning conditions and fiber diameters found that starch concentration had higher impact than electrospinning voltage and distance to determine fiber diameter [13Kon]. To improve stability, fibers were coated with polymethyl methacrylate, leading to increase in fiber diameters. In vitro degradation studies showed that fibers containing higher amounts of PEO degraded faster and the weight loss after 700 h in PBS at 37 °C varied from 30 to 50 % [13Sil].

Electrospun fibers from starch acetate were prepared for potential use as drug carriers. Starch acetate with a degree of acetylation of 1.1 and 2.3 was electrospun using formic acid/water or formic acid/ethanol to assist fiber formation [09Xu3]. Effects of degree of acetylation and concentration of the polymer in the solution on properties of the electrospun structures were studied. Fiber matrices with strength ranging from 5 to 18 MPa in the dry state and 5-6 MPa in the wet state were obtained. It was also found that increasing the concentration of starch acetate from 12 to 20 % increased the tenacity from 5.9 to 16 MPa. However, the tenacity of the matrices decreased marginally from 18 to 16 MPa when the degree of substitution (DS) of starch was increased from 1.1 to 2.3 due to decreasing solubil­ity. The fiber matrices retained about 60 % of their strength after being in 90 % humidity for 32 days. Fibers made from higher DS starch acetate had low initial burst and a more sustained release of diclofenac used a model drug [09Xu3].

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