Bioprinting and In Vitro Characterization of an Egg White-Based Cardiac Patch for Myocardial Infarction

Myocardial infarction (MI) or heart attack occurs when the bloodstream to the heart is blocked, which may destroy a part of the heart muscle (or myocardium) and form perdurable scarred tissue. The infarcted myocardial muscle nowadays has no revival treatments, and also transplantation is limited as an option. Tissue engineering has the potential to restore myocardial function after an MI by fabricating tailored tissues for treatment. For tissue engineering, three-dimensional (3D) bioprinting is a fabrication method to create 3D constructs with living cells, which would be impossible by other traditional methods. Although various biomaterials, biologically-derived or synthetic, are available, only a few can be used in 3D bioprinting of cardiovascular tissues due to their mechanical weakness of natural biomaterials and/or limited bioactivity (in terms of promoting cell functions) of synthetic ones. The present study aims to develop a novel biomaterial solution for bioprinting (referred to as bioink) and on this basis, to bioprint cell-laden patches and characterize the patches in vitro for potential use in MI treatment. For this, a new bioink was formulated based on chicken egg white (EW) and sodium alginate (Alg). EW, as a rich source of albumin and well-known for its drug delivery applications, has been strategically combined with Alg, a common printable polysaccharide with a non-thrombogenic nature. EW was utilized to improve bioactivity and cell adhesion sites and sodium alginate was considered as an extrudability enhancer to provide good printability. The following research objectives were pursued: I) develop and rheologically characterize the albumin-based bioink by adding minimal amounts of alginate as a printability enhancer biomaterial; II) characterize the mechanical properties of the 3D printed albumin-based patches by compression testing and monitoring the swelling and degradation behavior; and III) characterize the biological properties of the 3D bioprinted cell-laden albumin-based patch by examining the in vitro cell viability. EW-Alg blends with different alginate concentrations were synthesized by mixing the pasteurized egg white with sodium alginate powder. Then the blends were tested in terms of their rheological behavior and showed a non-Newtonian shear-thinning functioning, i.e. the increase of shear strain led to a decline in viscosity. Moreover, the addition of each 0.5 gram alginate in 100 milliliter egg white significantly consolidated the blend’s texture and notably changed its viscosity and handling. Hence, the more alginate was used in the solution. Hence, the more alginate was used in the solution, the higher the blend’s viscosity and the required extrusion pressure. Compression elastic moduli of the 3D printed patches from the printable EW-Alg blends (2.0, 2.5, and 3.0% Alg in EW) with the range 20-27 kPa showed the similarity of these constructs mostly to human cadaver limb specimens with 10-38 kPa compressive elastic modulus. Furthermore, swelling measurements performed in phosphate-buffered saline (PBS) showed swelling ratios of more than 1800% for all three concentrations of the EW-Alg blend, representing these 3D printed patches’ ability to uptaking ionic fluids from a body-like environment. Also, all of the constructs showed signs of biodegradation within a month. The EW-2.0%Alg blend, which had the highest egg white ratio to alginate and the lowest viscosity, was 3D bioprinted as a cell-laden bioink. The loaded human umbilical vein endothelial cells (HUVECs) survival rate was more than 90% in all of the time points within a week, showing high biocompatibility of the EW-Alg bioink. The present study developed an egg white-based bioink for 3D cardiac patch bioprinting. Fabricated patches exhibited suitable mechanical properties and biocompatibility in vitro, to be potentially used for MI treatment.