Horseradish peroxidase-catalyzed crosslinking of fibrin microthread scaffolds.

: Horseradish peroxidase (HRP) has been investigated as a catalyst to crosslink tissue engineered hydrogels because of its mild reaction conditions and ability to modulate the mechanical properties of the matrix. Here we report the results of the first study investigating the use of HRP to crosslink fibrin scaffolds. We examined the effect of varying HRP and hydrogen peroxide (H2O2) incorporation strategies on the resulting crosslink density and structural properties of fibrin in a microthread scaffold format. Primary (1o) and secondary (2o) scaffold modification techniques were evaluated to crosslink fibrin microthread scaffolds. A primary scaffold modification technique was defined as incorporating crosslinking agents into the microthread precursor solutions during extrusion. A secondary scaffold modification technique was defined as incubating the microthreads in a post-processing crosslinker bath. Fibrin microthreads were enzymatically crosslinked through primary, secondary, or a combination of both approaches. All fibrin microthread scaffolds crosslinked with HRP and H2O2 via primary and/or secondary methods exhibited an increase in dityrosine crosslink density compared to uncrosslinked control microthreads, demonstrated by scaffold fluorescence. Fourier transform infrared spectroscopy indicated the formation of isodityrosine bonds in 1o HRP crosslinked microthreads. Characterization of tensile mechanical properties revealed that all HRP crosslinked microthreads were significantly stronger than control microthreads. Primary (1o) HRP crosslinked microthreads also demonstrated significantly slower degradation than control microthreads, suggesting that incorporating HRP and H2O2 during extrusion yields scaffolds with increased resistance to proteolytic degradation. Finally, cells seeded on HRP crosslinked microthreads retained a high degree of viability, demonstrating that HRP crosslinking yields biocompatible scaffolds suitable for tissue engineering. The goal of this work was to facilitate the logical design of enzymatically crosslinked fibrin microthreads with tunable structural properties, enabling their application for engineered tissue constructs with varied mechanical and structural properties.