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K. Ehrmann, C. Grasl, H. Bergmeister, H. Schima, B. Podesser, R. Liska, S. Baudis:
"Modular Design Principle for Personalized Artificial Vascular Grafts with Tunable Mechanical Properties and Degradation Speeds";
Vortrag: Termis Eu 2019, Rhodes, Greece; 27.05.2019 - 31.05.2019; in: "Termis EU 2019", (2019), S. 1112.

INTRODUCTION: Cardiovascular bypass surgery currently applies autologous grafts which brings along certain downsides: Blood vessel harvesting can lead to increased donor site morbidity and the approach might suffer from limited graft availability. Using small-diameter artificial grafts would eliminate these short-term side-effects, however, such substitutes tend to clog more easily in the long term. We argue that this disadvantage can be overcome: Natural tissue regeneration can be promoted by rendering the graft to be biodegradable on a similar time-scale as tissue regeneration takes place. By additionally utilizing a modular material-design principle, we are able to tailor the mechanical and degradation behavior of a graft substitute to specific needs.


METHODS: The polymer-class of thermoplastic polyurethanes (TPUs) was chosen as graft material due to their suitable properties: Linear polymer sections (soft blocks) make the material elastic. These are connected via small, hydrogen-bonding components (chain extenders). The aggregated areas of chain extenders (hard blocks) make the material resilient to mechanical stress (Figure 1). This modular architecture of TPUs enables fine tuning of mechanical and degradation properties through the specific exchange of polymer components.
Electrospinning allows for the manufacturing of highly porous grafts, aiding biodegradability. In this process, grafts are fabricated by injecting a polymer solution into a high-voltage electric field and collecting the emerging nano-fibers on a rotating rod.
RESULTS: We created a pool of low-toxic, degradable molecular compounds for their application as chain extenders in the polymer. A variety of polymers with altering components and component ratios was synthesized. The materials were fabricated into grafts via electrospinning and tested with respect to their mechanical, degradation, and in vivo and in vitro biocompati-bility properties. Obtained results show significant changes in material properties even upon minor component changes. This approach gave new TPU materials with improved mechanical properties, less inflammatory response, and faster degradation speeds. The modular design principle enabled the difficult optimization of the balance between mechanical properties and degradability.



Figure 1: Schematic representation of the polymer structure with the three modular components macromolecular diol (grey), diisocyanate (orange), and chain extender (green) and of the phase separation of hard and soft blocks.


DISCUSSION & CONCLUSIONS: The new materials derived from the modular design principle give rise to the possibility of customized artificial grafts for bypass surgery.

Cardiovascular bypass surgery, polymer-class of thermoplastic polyurethanes (TPUs), suitable properties, Linear polymer sections - material elastic