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Gary E. Wnek, LaShanda Korley, Suresh Shenoy, David Stone; Electrospun Polymer Micro- and Nanofibers as Biomaterials: Modulation of Optical Properties. Invest. Ophthalmol. Vis. Sci. 2011;52(14):471.
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Significant opportunities exist in regenerative medicine and drug delivery for stuctural materials exhibiting multi-functionality (e.g., delivery of therapeutic compounds) that are easily fabricated and utilized. Electrospinning has the versatility to meet these characteristics. Here, we summarize work on two important approaches for improved optical transparency in electrospun fibers, namely highly-oriented fibers and infiltration of isotropic mats with polymer matrices.
Highly aligned fibers of polystyrene, PMMA, poly(HEMA) and PLGA, are readily obtained by judicious control of electrospinning parameters such as voltage and needle-to-drum distance. The key is to allow electrical forces to not dominate viscous forces. An alternative approach involves filling void spaces with a material having a greater refractive index than air and close to that of random electrospun fibers. Toward that end, electrospun poly(vinyl alcohol) (PVA) fibers were impregnated with rubbery 1:1 ethyleneoxide/epichlorohydrin copolymer (EO-EPI) as the matrix.
Figure 1a shows an SEM photo of aligned PLGA fibers (ca. 5 µm diameter), and Figure 1b illustrates the rather high optical transparency of the mat when placed close to a substrate. A random fiber mat of a similar thickness is highly opaque. The optical transparency of the aligned mat is partially the result of rather thick fibers but more importantly due to the great reduction in void spaces between the fibers. Cross-sectional SEM revealed a sandwich-type structure in the composite film with regions of neat polymer on both sides of the electrospun mat. Preliminary results on PVA/EO-EPI composites demonstrate that the this material is considerably more transparent than the neat PVA electrospun mat.
Two approaches have been outlined for the achievement of reasonable optical properties using electrospun polymer fibers. Additional work with these materials systems that combines the ability to release therapeutic small molecules and/or macromolecules will be presented at the meeting.
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