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 (1 degrees) and secondary (2 degrees) 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 postprocessing crosslinker bath. Fibrin microthreads were enzymatically crosslinked through primary, secondary, or a combination of both approaches. All fibrin microthread scaffolds crosslinked with HRP and H(2)O(2)via primary and/or secondary methods exhibited an increase in dityrosine crosslink density compared with uncrosslinked control microthreads, demonstrated by scaffold fluorescence. Fourier transform infrared spectroscopy indicated the formation of isodityrosine bonds in 1 degrees HRP crosslinked microthreads. Characterization of tensile mechanical properties revealed that all HRP crosslinked microthreads were significantly stronger than control microthreads. Primary (1 degrees) HRP crosslinked microthreads also demonstrated significantly slower degradation than control microthreads, suggesting that incorporating HRP and H(2)O(2)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 that are 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. Impact statement This study is the first to report the use of horseradish peroxidase to dityrosine crosslink a fibrin scaffold. We demonstrate the strategic engineering of fibrin microthread scaffolds with tunable biophysical properties by a facile method of varying crosslinker incorporation. The incorporation of crosslinking agents into precursor solutions during microthread extrusion was considered a primary method, whereas soaking microthreads in a postprocessing crosslinker bath was considered a secondary method. The ability to generate tunable scaffold mechanics and degradation rates will enable the application of fibrin microthreads toward the design of engineered tissues with varying architectures, mechanical properties, and functional requirements.