The Degradation and Performance of Electrospun Supramolecular Vascular Scaffolds Examined Upon <i>In Vitro</i> Enzymatic Exposure

Abstract

To maintain functionality during in situ regeneration of load-bearing tissues, a balance between the rates of implant degradation and neo-tissue formation is required. Strictly segmented thermoplastic elastomers with supramolecularly interacting bis-urea (BU) hard blocks are attractive biomaterials for vascular tissue engineering, as these polymers are soft, tough, and biodegradable. Moreover, these materials possess a sequence-controlled macromolecular structure, so their susceptibility to degradation is tunable by controlling the nature of the polymer backbone. It is unknown, however, how the implant’s functionality is affected by the degradation of the polymers it is composed of. We therefore examined the macro- and microscopic features as well as the mechanical performance of vascular scaffolds upon in vitro enzymatic degradation. Three candidate biomaterials (‘slow-degrading’ polycarbonate-BU (PC-BU), ‘intermediate-degrading’ polycarbonate-ester-BU (PC(e)-BU), and ‘fast-degrading’ polycaprolactone-ester-BU (PCL-BU)) were synthesized and electrospun into microporous scaffolds. The scaffolds were incubated in lipase and monitored for changes in physical, chemical, and mechanical properties. Remarkably, comparing PC-BU to PC(e)-BU, we observed that small changes in macromolecular structure led to significant differences in degradation kinetics. All three scaffold types degraded via surface erosion, which was accompanied by fiber swelling for PC-BU scaffolds, and some bulk degradation and a collapsing network for PCL-BU scaffolds. For the PC-BU and PC(e)-BU scaffolds this resulted in retention of mechanical properties, whereas for the PCL-BU scaffolds this resulted in stiffening. Our in vitro study demonstrates that vascular scaffolds, electrospun from sequence-controlled supramolecular materials with varying ester contents, not only display different susceptibilities to degradation, but also degrade via different mechanisms.