Custom Engineered Tissue Culture Molds from Laser-etched Masters

Wet-Spun Polycaprolactone Scaffolds Provide Customizable Anisotropic Viscoelastic Mechanics for Engineered Cardiac Tissues

Myocardial infarction is a leading cause of death worldwide and has severe consequences including irreversible damage to the myocardium, which can lead to heart failure. Cardiac tissue engineering aims to re-engineer the infarcted myocardium using tissues made from human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to regenerate heart muscle and restore contractile function via an implantable epicardial patch. The current limitations of this technology include both biomanufacturing challenges in maintaining tissue integrity during implantation and biological challenges in inducing cell alignment, maturation, and coordinated electromechanical function, which, when overcome, may be able to prevent adverse cardiac remodeling through mechanical support in the injured heart to facilitate regeneration. Polymer scaffolds serve to mechanically reinforce both engineered and host tissues. Here, we introduce a novel biodegradable, customizable scaffold composed of wet-spun polycaprolactone (PCL) microfibers to strengthen engineered tissues and provide an anisotropic mechanical environment to promote engineered tissue formation. We developed a wet-spinning process to produce consistent fibers which are then collected on an automated mandrel that precisely controls the angle of intersection of fibers and their spacing to generate mechanically anisotropic scaffolds. Through optimization of the wet-spinning process, we tuned the fiber diameter to 339 ± 31 µm and 105 ± 9 µm and achieved a high degree of fidelity in the fiber structure within the scaffold (fiber angle within 1.8° of prediction). Through degradation and mechanical testing, we demonstrate the ability to maintain scaffold mechanical integrity as well as tune the mechanical environment of the scaffold through structure (Young’s modulus of 120.8 ± 1.90 MPa for 0° scaffolds, 60.34 ± 11.41 MPa for 30° scaffolds, 73.59 ± 3.167 MPa for 60° scaffolds, and 49.31 ± 6.90 MPa for 90° scaffolds), while observing decreased hysteresis in angled vs. parallel scaffolds. Further, we embedded the fibrous PCL scaffolds in a collagen hydrogel mixed with hiPSC-CMs to form engineered cardiac tissue with high cell survival, tissue compaction, and active contractility of the hiPSC-CMs. Through this work, we develop and optimize a versatile biomanufacturing process to generate customizable PCL fibrous scaffolds which can be readily utilized to guide engineered tissue formation and function.

Architected fibrous scaffolds for engineering anisotropic tissues

Mimicking the native three-dimensional microenvironment is of crucial importance when biofabricating a new healthcare material. One aspect of the native tissue that is often omitted when designing a suitable scaffold is its anisotropy. Not only is matching native mechanical properties important when designing implantable scaffolds or healthcare materials, but matching physiological structure is also important as many cell populations respond differently to fiber orientation. Therefore, novel aligned electrospun scaffolds with varying fiber angles and spacing of bundles were created and mechanically characterized. Through controlling the angle between the fibers in each layer of the scaffold, a range of different physiological anisotropic mechanical properties were achieved that encompasses values found in native tissues. Extrapolation of this mechanical data allowed for any native tissue's anisotropic Young's modulus to be mimicked by electrospinning fibers at a particular angle. These electrospun scaffolds were then incorporated with cell-laden hydrogels to create hybrid structures that contain the benefits of both scaffolding techniques with the ability to encapsulate cells in the hydrogel. To conclude, this study develops a novel bundled fiber scaffold that was architected to yield anisotropic properties matching native tissues.

A continuum model and simulations for large deformation of anisotropic fiber-matrix composites for cardiac tissue engineering

Cardiac patch therapies promise to restore heart function and lower the risk of heart failure after heart attack. Fiber-matrix engineered tissue scaffolds have gained significant attention due to their tunable micro-structures, providing nonlinear mechanical properties similar to native anisotropic heart tissues. Mechanical properties of engineered scaffolds directly affect the stress fields generated inside and around the tissue scaffolds and have significant impact on the tissue functionality. Currently, biomedical cardiac patches are designed through experimentation and there exists a need for an accurate model that will allow micro-structural design optimization and analysis of effectiveness of the implanted patches. We have developed a three-dimensional large strain continuum model that can predict nonlinear, anisotropic mechanical response of engineered tissue scaffolds that have two orientation families of fibers inside a bulk hydrogel matrix. We have validated the predictive capability of our continuum model for the fiber-matrix composite using selected experiments and a suite of detailed finite element analysis that incorporated the micro-structural details of the composites. Comparing the continuum model predictions (1 element) against the representative volume micro-structural geometry finite element simulations (with greater than 4,00,000 elements), we show that the proposed model can accurately predict nonlinear mechanical behavior of highly anisotropic tissue scaffolds in both the longitudinal and transverse directions, as a function of the critical design parameters inter-fiber angle and fiber spacing. We show that the model can also capture native heart tissue's anisotropic large strain mechanical response. We implemented our model in the finite element software Abaqus by writing a user material subroutine UANISOHYPER and demonstrated its predictive abilities by conducting a full three-dimensional analysis of engineered tissue patch application on an infarcted heart.

Optimizing Blended Collagen-Fibrin Hydrogels for Cardiac Tissue Engineering with Human iPSC-derived Cardiomyocytes

Natural polymer hydrogels are used ubiquitously as scaffold materials for cardiac tissue engineering as well as for soft tissue engineering more broadly because of FDA approval, minimal immunogenicity, and well-defined physiological clearance pathways. However, the relationships between natural polymer hydrogels and resident cell populations in directing the development of engineered tissues are poorly defined. This interaction is of particular concern for tissues prepared with iPSC-derived cell populations, in which population purity and batch-to-batch variability become additional critical factors to consider. Herein, the design space for a blended fibrin and collagen scaffold is characterized for applications in creating engineered myocardium with human iPSC-derived cardiomyocytes. Stiffness values of the acellular hydrogel formulations approach those of native myocardium in compression, but deviate significantly in tension when compared to rat myocardium in both transverse and longitudinal fiber orientations. A response surface methodology approach to understanding the relationship between collagen concentration, fibrin concentration, seeding density, and cardiac purity found a statistically significant predictive model across three repeated studies that confirms that all of these factors contribute to tissue compaction. In these constructs, increased fibrin concentration and seeding density were each associated with increased compaction, while increased collagen concentration was associated with decreased compaction. Both the lowest (24.4% cTnT⁺) and highest (60.2% cTnT⁺) cardiomyocyte purities evaluated were associated with decreased compaction, whereas the greatest compaction was predicted to occur in constructs prepared with a 40–50% cTnT⁺ population. Constructs prepared with purified cardiomyocytes (≥75.5% cTnT⁺) compacted and formed syncytia well, although increased fibrin concentration in these groups was associated with decreased compaction, a reversal of the trend observed in unpurified cardiomyocytes. This study demonstrates an analytical approach to understanding cell–scaffold interactions in engineered tissues and provides a foundation for the development of more sophisticated and customized scaffold platforms for human cardiac tissue engineering.