(323b) Acetalated Dextran Nanofibrous Scaffolds for Temporal Release of Proteins

Tunable temporal release of molecules from a microstructured scaffold can be advantageous for the regeneration of healthy functional tissues.  To this end, we have taken the novel biopolymer Acetalated Dextran (Ac-DEX) and created eletrospun scaffolds.  Ac-DEX is unique from other biodegradable polymers because it has tunable degradation rates that can vary from hours to months and has benign degradation products that are pH neutral.  The degradation rate of the polymer varies with Ac-DEX reaction time due to the cyclic acetal coverage of the pendent hydroxyl group present on the parent dextran molecule.  Both fast (reaction time 5 minutes, cyclic coverage ~60%) and slow (reaction time 6 hours, cyclic coverage ~90%) degrading Ac-DEX was fabricated from 71K molecular weight dextran.  To fabricate scaffolds, the concentration of Ac-DEX was varied while the flow rate kept constant (4 mL/hr).  At a concentration of 0.2 g Ac-DEX/mL in ethanol, a complex structure of particles and fibers was formed, as the concentration increased from 0.3 g/mL, discrete ribbons formed.  The increase in concentration resulted generally in an increase in fiber width, with sizes of approximately 3 microns at low flowrates (0.3 g/mL) and 8 microns at higher flowrates (0.4 and 0.5 g/mL).  With respect to increasing flowrate at a fixed concentration (0.4 g/mL), fiber width increased with flowrate (from approximately 6 to 10 microns) and fiber thickness stayed relatively constant around 1.5 microns.  Fiber width and thickness did not vary significantly between the fast and slow degrading polymer scaffolds.  SEM micrographs of the scaffolds displayed a fairly uniform ribbon structure with some beading observed at the edge of the ribbons.  The scaffolds displayed tunable degradation characteristics with the fast degrading scaffolds reporting a half-live of approximately 1.5 days, and the slow degrading scaffolds displaying a degradation of approximately 20% after 7 days, at pH 7.4.  A model protein, bovine serum albumin (BSA), was loaded into the scaffolds.  Both BSA (1% wt/wt) and Ac-DEX were dissolved in ethanol and spun at a rate of 4 mL/hr and concentration of 0.4 g Ac-DEX/mL.  For the fast degrading scaffolds, an encapsulation efficiency (EE) of 87.5 ± 7.3 was achieved, with an EE of 80.6 ± 1.5 for the slow degrading polymer.  At pH 7.4, the release of BSA was approximately 95% after 2 days with the fast degrading polymer, and approximately 40% after two days for the slow degrading polymer, illustrating the temporal release potential of these scaffolds.  The biocompatibility of the scaffolds was illustrated by culturing 3T3 fibroblasts on the surface and performing a fluorescent live/dead assay as well as noting cell area and circularity.  The survival of the fibroblast was upwards of 92% on either scaffold surface, with the cells significantly more circular and smaller on the fast degrading scaffold over the slow degrading scaffold.  To increase the number of cells attached to the scaffold surface, the scaffolds were plasma treated at varying times.  The plasma treatment resulted in visually more rough ribbon surfaces, as imaged with SEM.  For both the fast and slow degrading scaffold, maximum cell attachment, near that of the glass control, was achieved after 60 seconds of plasma treatment, with over double the number of cells on the surface, compared to the untreated control.  Cells seeded on surfaces treated for longer than 60 seconds, were progressively decreasing in number up to 300 second of plasma treatment, indicating that plasma treatment offered diminishing returns after 60 seconds of treatment.  These studies were performed with unaligned scaffolds, but future work will involve aligning the scaffolds as well as culturing PC12 cells on the surfaces.  Overall, we have demonstrated the first report of electrospun Ac-DEX scaffolds for the tunable temporal release of biologics.