Cellular Response
To evaluate the response of neural cell populations to these biomaterials, the adhesion density and process extension of PC-12 cells were measured. Briefly, 150 μL of each sample type was evenly spread on the bottoms of standard 24-well flat bottom culture plates (Becton Dickinson Labware). Culture medium consisted of 84% high glucose DMEM, 12.5% platelet poor horse serum, 2.5% fetal bovine serum, and 1% PenStrep. Cells were plated atop chitosan, chitosan-genipin, and control surfaces of a tissue culture polystyrene (TCPS) at a density of 5.0 x104 cells/well with n=4 wells/sample. Culture plates were maintained in an incubator at 37oC and 5% CO2 for 96 hours. Cells were then fixed with 4% paraformaldehyde, permeabilized with 0.1% Triton X-100, and stained with propidium iodide (0.05 mg/mL). A Nikon Diaphot 300 microscope, Nikon mercury lamp, and a CCD (Diagnostic Instruments) were used for imaging. Adhesion density and process length were quantified with Image-J.
F. Statistical Analysis
Results are reported as mean values±standard error of the mean. One-tailed ANOVA was used to compare means: between groups. Post-hoc comparisons were performed using Tukey’s and Dunnet’s test. Significance was ascribed to p-values less than 0.05.
III. RESULTS
Rheometrical characterization of each chitosan-genipin revealed a trend of increasing storage modulus for every increase in genipin concentration (Figure 1). Concentrations of 0.05% genipin possessed a storage modulus of 13.53 Pa in the LVR, while 0.20% genipin yielded 239.92 Pa. Natural nerve tissue was significantly more deformable (p < 0.01) than all genipin-chitosan hydrogels at a LVR storage modulus of 1.15 Pa (Figure 2).
PC-12 cells plated atop genipin-chitosan gels adhered at a significantly greater density (p < 0.01) when compared to adhesion on TCPS and un-crosslinked chitosan substrates (Figure 3). Likewise, PC-12 process extension was measured on each surface. Chitosan did not have any identifiable process extension. In comparing process extension in all genipin-chitosan surfaces against TCPS, no significant differences were found (p > 0.05).