Controlling surface nano-structure using flow-limited field-injection electrostatic spraying (FFESS) of poly( , -lactide-co-glycolide)

Improved control of surface micro- and nano-structure may lead to enhanced performance of degradable biomedical devices such as surgical dressings, vascular grafts, tissue engineering scaffolds, sutures, and structures for guided tissue regeneration. An electrohydrodynamic method called flow-limited field-injection electrostatic spraying (FFESS) has been developed as an improved technique for the controlled deposition of polymeric material. Injecting charge using a nano-sharpened tungsten needle in a process called field ionization can efficiently induce an ionic state in a solution of poly( , -lactide-co-glycolide) increasing its capacity to carry charge. As a result, sprays have been produced that are finer and more precisely controlled than sprays produced by conventional electrospraying techniques, which employ hypodermic needles as the spray nozzle. Here, the effect of FFESS variables including applied voltage, polymer solution flow rate, and solvent properties (surface tension, viscosity, vapor pressure) on spray performance have been qualitatively evaluated. Under certain conditions, increasing the applied voltage produced an increasingly rough surface morphology. Similarly, by reducing solvent surface tension and increasing solvent vapor pressure, more distinct surface structures could be formed including uniform nanoparticles. Working ranges of the important parameters for the production of specific structure types such as smooth or porous surfaces, non-woven or melded fibers, and distinct or melded nanoparticles have been defined. FFESS technology provides a simple yet powerful technique for fabricating biomedical devices with a precisely defined nano-structure potentially capable of utilizing a broad range of biocompatible polymeric materials.