One of the leading causes of death in the world, and México, is myocardial infarction (MI). During MI cardiac muscle suffers hypoxia which leads to cardiomyocyte death, consequently a fibrous collagen scar substitute’s muscle tissue and compromises heart function. Since this only affects the infarcted area, many patients would benefit from small pieces of muscle for transplant. Cardiac tissue engineering promises to bring significant treatment advances for these patients. One of the basis for this field is the development of materials that can sustain cell growth and mechanically assist the heart wall. Thus, studying cellular response to a material can help determine if it will produce cytotoxic effects, and, if it has appropriate physicochemical properties to promote cell adhesion and growth (4). Previous work has demonstrated that polyurethanes have favorable properties to support cells for cardiac tissue engineering. Parrag et al, for example, cultured murine embryonic stem cell derived cardiomyocytes on polyurethane films with good cell survival rates. It has been demonstrated that sca-1+/CD45- cardiac progenitor cells (CPCs) are responsible for cardiac homeostasis and represent a suitable cell source for cardiac tissue engineering (8, 9), which makes them ideal as a target cell line since they could repopulate the material in vitro and then differentiate in vivo.
We performed cell-based studies on elastomeric biodegradable putrescine-based polyurethane ureas to measure sca-1+/CD45- cell proliferation and the materials cytotoxicity. These studies are the preliminary work needed to move forward in using these materials to create tissue engineered cardiac patches.
Materials and Methods
We synthesized four polyurethane ureas via a two-step polycondensation reaction using polycaprolactone diol (PCL, MW 2000 g/mol, Polysciences, Warrington, PA, USA) end-capped with Methylene bis-(4-cyclohexylisocyanate) (HMDI, Sigma-Aldrich, St. Louis, MO, USA) and chain extended with butanediamine (BDA, Sigma-Aldrich, St. Louis, MO, USA). Briefly, in the first step a 10% w/v solution of PCL diol in dimethylformamide was mixed with stannous octoate (SO, Sigma-Aldrich, St. Louis, MO, USA), at about 0.01 weight percentage, for an hour in a magnetically stirred reactor at 70°C. The reaction was performed under a nitrogen atmosphere and excess diisocyanate was used to obtain an isocyanate-terminated prepolymer at four different NCO:OH ratios (1.2, 2, 3, and 4) while maintaining the NCO:OH to NH ratio at 1:1. After cooling the reactor to 25°C, we performed the extension step by slowly adding butanediamine and then the reaction continued for one hour at 80°C. Afterwards, we precipitated and washed the polymers in deionized water for three days (21). Table 1 shows the sample nomenclature and some of the polymer properties.
PUU films were prepared on 12 well corning costar® plates (Corning Life Sciences, Union City, California, USA)...