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Cardiac tissue engineering in magnetically actuated scaffolds.

ABSTRACT: Cardiac tissue engineering offers new possibilities for the functional and structural restoration of damaged or lost heart tissue by applying cardiac patches created in vitro. Engineering such functional cardiac patches is a complex mission, involving material design on the nano- and microscale as well as the application of biological cues and stimulation patterns to promote cell survival and organization into a functional cardiac tissue. Herein, we present a novel strategy for creating a functional cardiac patch by combining the use of a macroporous alginate scaffold impregnated with magnetically responsive nanoparticles (MNPs) and the application of external magnetic stimulation. Neonatal rat cardiac cells seeded within the magnetically responsive scaffolds and stimulated by an alternating magnetic field of 5 Hz developed into matured myocardial tissue characterized by anisotropically organized striated cardiac fibers, which preserved its features for longer times than non-stimulated constructs. A greater activation of AKT phosphorylation in cardiac cell constructs after applying a short-term (20 min) external magnetic field indicated the efficacy of magnetic stimulation to actuate at a distance and provided a possible mechanism for its action. Our results point to a synergistic effect of magnetic field stimulation together with nanoparticulate features of the scaffold surface as providing the regenerating environment for cardiac cells driving their organization into functionally mature tissue.

SUBMITTER: Sapir Y

PROVIDER: S-EPMC5562154 | biostudies-other | 2014 Jan

REPOSITORIES: biostudies-other

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Project description:Myocardial infarction (MI) causes significant cell loss and damage to myocardium. Cell-based therapies for treatment of MI aim to remuscularize the resultant scar tissue, but the majority of transplanted cells do not survive or integrate with the host tissue. Scaffolds can improve cell retention following construct implantation, but often do little to enhance host-graft integration and/or show limited biodegradation. Fibrin is an ideal biomaterial for cardiac tissue engineering as it is a natural, biodegradable polymer that can induce neovascularization, promote cell attachment, and has tunable mechanical properties. Here we describe a novel, high-density microtemplated fibrin scaffold seeded with a tri-cell mixture of cardiomyocytes, endothelial cells (ECs), and fibroblasts to mimic native cardiac tissue in structure and cellular composition to improve cell retention and promote integration with the host tissue. Scaffolds were designed with uniform architecture of parallel 60 ?m microchannels surrounded by an interconnected microporous network of 27-?m-diameter pores and mechanical stiffness comparable to native cardiac tissues (70-90kPa). Scaffold degradation was controlled with the addition of Factor XIII (FXIII) and/or protease inhibitor (aprotinin). Unmodified scaffolds had a fast degradation profile both in vitro (19.9%±3.9% stiffness retention after 10 days) and in vivo. Scaffolds treated with FXIII showed an intermediate degradation profile in vitro (45.8%±5.9%), while scaffolds treated with aprotinin or both FXIII and aprotinin showed significantly slowed degradation in vitro (60.9%±5.2% and 76.4%±7.6%, respectively, p<0.05). Acellular aprotinin scaffold myocardial implants showed decreased collagen deposition after 7 days. Unmodified and aprotinin implants could not be located by 14 days, while 2 of 8 FXIII implants were found, but were significantly degraded. Constructs supported seeded cell survival and organization in vitro, promoting EC-lined lumen structure formation in construct channels and colocalization of viable ECs and cardiomyocytes. In addition, constructs promoted extracellular matrix deposition by seeded cells, as shown by collagen staining within construct channels and by significant increases in construct stiffness over 10 days in vitro (209%±32%, p<0.05). The data suggest our fibrin scaffolds are ideally designed to promote graft cell survival and organization, thus improving chances of promoting construct integration with the host tissue upon implantation.

Project description:Providing the right stimulatory conditions resulting in efficient tissue promoting microenvironment in vitro and in vivo is one of the ultimate goals in tissue development for regenerative medicine. It has been shown that in addition to molecular signals (e.g. growth factors) physical cues are also required for generation of functional cell constructs. These cues are particularly relevant to engineering of biological tissues, within which mechanical stress activates mechano-sensitive receptors, initiating biochemical pathways which lead to the production of functionally mature tissue. Uniform magnetic fields coupled with magnetizable nanoparticles embedded within three dimensional (3D) scaffold structures remotely create transient physical forces that can be transferrable to cells present in close proximity to the nanoparticles. This study investigated the hypothesis that magnetically responsive alginate scaffold can undergo reversible shape deformation due to alignment of scaffold's walls in a uniform magnetic field. Using custom made Helmholtz coil setup adapted to an Atomic Force Microscope we monitored changes in matrix dimensions in situ as a function of applied magnetic field, concentration of magnetic particles within the scaffold wall structure and rigidity of the matrix. Our results show that magnetically responsive scaffolds exposed to an externally applied time-varying uniform magnetic field undergo a reversible shape deformation. This indicates on possibility of generating bending/stretching forces that may exert a mechanical effect on cells due to alternating pattern of scaffold wall alignment and relaxation. We suggest that the matrix structure deformation is produced by immobilized magnetic nanoparticles within the matrix walls resulting in a collective alignment of scaffold walls upon magnetization. The estimated mechanical force that can be imparted on cells grown on the scaffold wall at experimental conditions is in the order of 1 pN, which correlates well with reported threshold to induce mechanotransduction effects on cellular level. This work is our next step in understanding of how to accurately create proper stimulatory microenvironment for promotion of cellular organization to form mature tissue engineered constructs.

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Cardiac tissue engineering in magnetically actuated scaffolds.

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