In situ crosslinking of electrospun gelatin for improved fiber morphology retention and tunable degradation

Electrospinning is a popular technique to fabricate tissue engineering scaffolds due to the exceptional tunability of the fiber morphology, which can be used to control the scaffold mechanical properties, degradation rate, and cell behavior. Recent work has focused on electrospinning natural polymers such as gelatin to improve the regeneration potential of these grafts. Gelatin scaffolds must be crosslinked to avoid rapid dissolution upon implantation with current crosslinking strategies requiring additional post-processing steps. Despite the strong dependence of scaffold properties on fiber morphology, there has been minimal emphasis on retaining the original fiber morphology of electrospun gelatin scaffolds after implantation. This work describes a method for in situ crosslinking of gelatin to produce electrospun fibers with improved fiber morphology retention after implantation. A double barrel syringe with an attached mixing head and a diisocyanate crosslinker were utilized to generate electrospun scaffolds that crosslink during the electrospinning process. These in situ crosslinked fiber meshes retained morphology after 1 week incubation in water at 37 °C; whereas, uncrosslinked meshes lost the fibrous morphology within 24 hours. Degree of crosslinking was quantified and relationships between the crosslinker ratio and enzymatic degradation rate were evaluated. The degradation rate decreased with increased crosslinker ratio, resulting in a highly tunable system. Additionally, tensile testing under simulated physiological conditions indicated that increased crosslinker ratios resulted in increases in initial modulus and tensile strength. Overall, this in situ crosslinking technique provides a method to crosslink gelatin during electrospinning and can be used to tune the degradation rate of resulting scaffolds while enabling improved fiber morphology retention after implantation.