Investigation of an electrospun, degradable polar hydrophobic ionic polyurethane patch for cardiac tissue regeneration

Chan, Jennifer 1, 2; Santerre, J Paul 1, 2, 3

1. Institute of Biomaterials and Biomedical Engineering, University of Toronto; 
2. Translational Biology and Engineering Program, Ted Rogers Centre for Heart Research, University of Toronto; 
3. Faculty of Dentistry, University of Toronto

Introduction
Coronary artery disease can lead to myocardial infarction, cardiomyocyte death, myocardium damage, and ultimately heart failure, due to the limited regenerative potential of cardiomyocytes (CMs). Cardiac tissue engineering can be used to repair and replace damaged myocardium. Engineered cardiac tissue scaffolds need to be biocompatible, be biodegradable, be functional, readily accommodate various cell types, and have mechanical properties that resemble native heart tissue. The objective of this project is to electrospin a degradable polar hydrophobic ionic polyurethane (D-PHI), a novel biomaterial developed in our lab, to generate a functional cardiac patch that can support CM function.

Methods
D-PHI was synthesized, integrated with a degradable linear polycarbonate polyurethane (PCNU), and incorporated into an appropriate solvent to generate a solution. The solution was electrospun with in situ UV cross-linking to generate aligned nanofibre scaffolds. The fibre morphology was determined using scanning electron microscopy; cross-linking efficiency was determined by Fourier transform infrared spectroscopy; water contact angle studies were used for surface analysis; scaffold stiffness was measured using tensile testing; in vivo degradation was determined by performing subcutaneous implants in rats; and in vitro biocompatibility was performed using human embryonic stem cell derived CMs.

Results
50:50 D-PHI:PCNU scaffolds yielded an average fibre diameter of 410±349nm and an alignment of 0.60 (aligned=1, random=0). The cross-linking efficiency of D-PHI/PCNU scaffolds was 93±1%, which is comparable to pure D-PHI films that were light cured without electrospinning. Water contact angle of D-PHI/PCNU scaffolds decreased when compared to pure PCNU scaffolds (44±6° vs 88±7° respectively) indicating greater polarity in the blend. The elastic moduli of D-PHI/PCNU wet and dry scaffolds were 55±12MPa and 142±59MPa, respectively. Preliminary histology results showed some cellular infiltration into the scaffold and the formation of some blood vessels around the scaffold after 30 days, but minimal fibre degradation of the scaffold. CMs cultured on Matrigel coated D-PHI/PCNU scaffolds showed good adhesion and viability that was comparable to Matrigel coated tissue culture polystyrene (TCPS) (94±2% vs 93±4% respectively after 7 days). The majority of CMs continued to express cardiac troponin-T and myosin light chain 2 after a 7 day culture period on the D-PHI/PCNU scaffold and expression was similar to that on TCPS. CM orientation was greater on D-PHI/PCNU scaffolds.

Conclusion
The D-PHI/PCNU scaffold is not toxic to CMs and enabled CM growth and maintenance of key CM functional markers after 7 days. It is anticipated that a degradable D-PHI/PCNU cardiac patch could be used to overcome limitations on biocompatibility, biodegradability, and mechanical properties faced by current engineered cardiac tissue scaffolds used to support cardiac tissue regeneration.