Safety and efficacy of an injectable extracellular matrix hydrogel for treating myocardial infarction.

New therapies are needed to prevent heart failure after myocardial infarction (MI). As experimental treatment strategies for MI approach translation, safety and efficacy must be established in relevant animal models that mimic the clinical situation. We have developed an injectable hydrogel derived from porcine myocardial extracellular matrix as a scaffold for cardiac repair after MI. We establish the safety and efficacy of this injectable biomaterial in large- and small-animal studies that simulate the clinical setting. Infarcted pigs were treated with percutaneous transendocardial injections of the myocardial matrix hydrogel 2 weeks after MI and evaluated after 3 months. Echocardiography indicated improvement in cardiac function, ventricular volumes, and global wall motion scores. Furthermore, a significantly larger zone of cardiac muscle was found at the endocardium in matrix-injected pigs compared to controls. In rats, we establish the safety of this biomaterial and explore the host response via direct injection into the left ventricular lumen and in an inflammation study, both of which support the biocompatibility of this material. Hemocompatibility studies with human blood indicate that exposure to the material at relevant concentrations does not affect clotting times or platelet activation. This work therefore provides a strong platform to move forward in clinical studies with this cardiac-specific biomaterial that can be delivered by catheter.

Catheter-deliverable hydrogel derived from decellularized ventricular extracellular matrix increases endogenous cardiomyocytes and preserves cardiac function post-myocardial infarction.

OBJECTIVES: This study evaluated the use of an injectable hydrogel derived from ventricular extracellular matrix (ECM) for treating myocardial infarction (MI) and its ability to be delivered percutaneously. BACKGROUND: Injectable materials offer promising alternatives to treat MI. Although most of the examined materials have shown preserved or improved cardiac function in small animal models, none have been specifically designed for the heart, and few have translated to catheter delivery in large animal models. METHODS: We have developed a myocardial-specific hydrogel, derived from decellularized ventricular ECM, which self-assembles when injected in vivo. Female Sprague-Dawley rats underwent ischemia reperfusion followed by injection of the hydrogel or saline 2 weeks later. The implantation response was assessed via histology and immunohistochemistry, and the potential for arrhythmogenesis was examined using programmed electrical stimulation 1 week post-injection. Cardiac function was analyzed with magnetic resonance imaging 1 week pre-injection and 4 weeks post-MI. In a porcine model, we delivered the hydrogel using the NOGA-guided MyoStar catheter (Biologics Delivery Systems, Irwindale, California), and utilized histology to assess retention of the material. RESULTS: We demonstrate that injection of the material in the rat MI model increases endogenous cardiomyocytes in the infarct area and maintains cardiac function without inducing arrhythmias. Furthermore, we demonstrate feasibility of transendocardial catheter injection in a porcine model. CONCLUSIONS: To our knowledge, this is the first in situ gelling material to be delivered via transendocardial injection in a large animal model, a critical step towards the translation of injectable materials for treating MI in humans. Our results warrant further study of this material in a large animal model of MI and suggest this may be a promising new therapy for treating MI.

Modulation of material properties of a decellularized myocardial matrix scaffold.

Injectable materials offer the potential for minimally invasive therapy for myocardial infarction (MI), either as an acellular scaffold or as a cell delivery vehicle. A recently developed myocardial matrix hydrogel, derived from decellularized porcine ventricular tissue, has the potential to aid in cardiac repair following an MI. Herein, we set out to study the effects of cross-linking on the cardiac hydrogel stiffness, degradation properties, cellular migration, and catheter injectability in vitro. Cross-linking increased stiffness, while slowing degradation and cellular migration through the gels. Additionally, the cross-linked material was pushed through a clinically relevant catheter. These results demonstrate that the material properties of myocardial matrix can be tuned via cross-linking, while maintaining appropriate viscosity for catheter injectability.

Injectable materials for the treatment of myocardial infarction and heart failure: the promise of decellularized matrices.

Cardiovascular disease continues to be the leading cause of death, suggesting that new therapies are needed to treat the progression of heart failure post-myocardial infarction. As cardiac tissue has a limited ability to regenerate itself, experimental biomaterial therapies have focused on the replacement of necrotic cardiomyocytes and repair of the damaged extracellular matrix. While acellular and cellular cardiac patches are applied surgically to the epicardial surface of the heart, injectable materials offer the prospective advantage of minimally invasive delivery directly into the myocardium to either replace the damaged extracellular matrix or to act as a scaffold for cell delivery. Cardiac-specific decellularized matrices offer the further advantage of being biomimetic of the native biochemical and structural matrix composition, as well as the potential to be autologous therapies. This review will focus on the requirements of an ideal scaffold for catheter-based delivery as well as highlight the promise of decellularized matrices as injectable materials for cardiac repair.

Fabrication of biologically derived injectable materials for myocardial tissue engineering.

This protocol provides methods for the preparation of an injectable extracellular matrix (ECM) gel for myocardial tissue engineering applications. Briefly, decellularized tissue is lyophilized, milled, enzymatically digested, and then brought to physiological pH. The lyophilization removes all water content from the tissue, resulting in dry ECM that can be ground into a fine powder with a small mill. After milling, the ECM powder is digested with pepsin to form an injectable matrix. After adjustment to pH 7.4, the liquid matrix material can be injected into the myocardium. Results of previous characterization assays have shown that matrix gels produced from decellularized pericardial and myocardial tissue retain native ECM components, including diverse proteins, peptides and glycosaminoglycans. Given the use of this material for tissue engineering, in vivo characterization is especially useful; here, a method for performing an intramural injection into the left ventricular (LV) free wall is presented as a means of analyzing the host response to the matrix gel in a small animal model. Access to the chest cavity is gained through the diaphragm and the injection is made slightly above the apex in the LV free wall. The biologically derived scaffold can be visualized by biotin-labeling before injection and then staining tissue sections with a horse radish peroxidase-conjugated neutravidin and visualizing via diaminobenzidine (DAB) staining. Analysis of the injection region can also be done with histological and immunohistochemical staining. In this way, the previously examined pericardial and myocardial matrix gels were shown to form fibrous, porous networks and promote vessel formation within the injection region.

Preparation and characterization of a pH- and thermally responsive poly(N-isopropylacrylamide-co-acrylic acid)/porous SiO(2) hybrid.

A multifunctional nanohybrid composed of a pH- and thermoresponsive hydrogel, poly(N-isopropylacrylamide-co-acrylic acid), poly(NIPAM-co-AAc) is synthesized in-situ within the mesopores of an oxidized porous Si template. The hybrid is characterized by electron microscopy and by thin film optical interference spectroscopy. The optical reflectivity spectrum of the hybrid displays Fabry-Pérot fringes characteristic of thin film optical interference, enabling direct, real-time observation of the pH- induced swelling and volume phase transitions associated with the confined poly(NIPAM-co-AAc) hydrogel. The optical response correlates to the percentage of AAc contained within the hydrogel, with a maximum change observed for samples containing 20% AAc. The swelling kinetics of the hydrogel are significantly altered due to the nanoscale confinement; displaying a more rapid response to pH or heating stimuli relative to bulk polymer films. The inclusion of AAc dramatically alters the thermoresponsiveness of the hybrid at pH 7, effectively eliminating the lower critical solution temperature (LCST). The observed changes in the optical reflectivity spectrum are interpreted in terms of changes in the dielectric composition and morphology of the hybrids.

Injectable myocardial matrix as a scaffold for myocardial tissue engineering.

Current injectable materials utilized in myocardial tissue engineering have been borrowed from other tissue engineering applications and have not been specifically designed for the myocardium. We have recently tested the feasibility of using an injectable form of myocardial extracellular matrix that would provide cardiac specific matrix cues as well as be amenable to minimally invasive delivery. We have demonstrated that this material self-assembles in vivo to form a nanofibrous scaffold, which supports the infiltration of neovasculature. We have also demonstrated that this material may be delivered minimally invasively through a catheter.

Naturally derived myocardial matrix as an injectable scaffold for cardiac tissue engineering.

Myocardial tissue lacks the ability to significantly regenerate itself following a myocardial infarction, thus tissue engineering strategies are required for repair. Several injectable materials have been examined for cardiac tissue engineering; however, none have been designed specifically to mimic the myocardium. The goal of this study was to investigate the in vitro properties and in vivo potential of an injectable myocardial matrix designed to mimic the natural myocardial extracellular environment. Porcine myocardial tissue was decellularized and processed to form a myocardial matrix with the ability to gel in vitro at 37 degrees C and in vivo upon injection into rat myocardium. The resulting myocardial matrix maintained a complex composition, including glycosaminoglycan content, and was able to self-assemble to form a nanofibrous structure. Endothelial cells and smooth muscle cells were shown to migrate towards the myocardial matrix both in vitro and in vivo, with a significant increase in arteriole formation at 11 days post-injection. The matrix was also successfully pushed through a clinically used catheter, demonstrating its potential for minimally invasive therapy. Thus, we have demonstrated the initial feasibility and potential of a naturally derived myocardial matrix as an injectable scaffold for cardiac tissue engineering.

A surface-charge study on cellular-uptake behavior of F3-peptide-conjugated iron oxide nanoparticles.

Surface-charge measurements of mammalian cells in terms of Zeta potential are demonstrated as a useful biological characteristic in identifying cellular interactions with specific nanomaterials. A theoretical model of the changes in Zeta potential of cells after incubation with nanoparticles is established to predict the possible patterns of Zeta-potential change to reveal the binding and internalization effects. The experimental results show a distinct pattern of Zeta-potential change that allows the discrimination of human normal breast epithelial cells (MCF-10A) from human cancer breast epithelial cells (MCF-7) when the cells are incubated with dextran coated iron oxide nanoparticles that contain tumor-homing F3 peptides, where the tumor-homing F3 peptide specifically bound to nucleolin receptors that are overexpressed in cancer breast cells.