Todd D. Johnson

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.

Injectable hydrogel therapies and their delivery strategies for treating myocardial infarction

Introduction: Heart failure following myocardial infarction (MI) impacts millions of people each year in the US. The field of tissue engineering has developed several potential therapies for treating MI including injectable acellular hydrogels. These injectable biomaterials can either be synthetic or naturally derived, and have the potential to be delivered minimally invasively. Areas covered: This review covers the different methods of delivery and presents the initial work on the use of injectable biomaterial scaffolds alone to improve cardiac function post-MI. Several naturally derived materials including alginate, collagen, chitosan, decellularized tissues, fibrin, hyaluronic acid, keratin, and Matrigel, as well as a few synthetic materials have shown promise on their own without the addition of therapeutics such as cells or growth factors. These biomaterials can be potentially delivered via endocardial, epicardial, or intracoronary injections and some can even utilize current catheter technology, indicating a potential for avoiding invasive surgical procedures. Once injected into the wall of the heart, these hydrogels create a scaffold that provides biochemical and structural cues, and the ability for cellular infiltration and remodeling of the local environment. Expert opinion: Injectable biomaterials have several crucial challenges that should be over come to design optimal therapies for MI and heart failure, including optimizing material properties, methods of injection and understanding the mechanisms of action. But, studies in both small and large animals have shown significant improvement in important parameters including wall thickness, vascularization of the ischemic region, left ventricular volumes, and cardiac function. Thus, the application of injectable biomaterials shows promise for developing into new therapies to treat MI, potentially improving millions of lives.

Tailoring material properties of a nanofibrous extracellular matrix derived hydrogel.

In the native tissue, the interaction between cells and the extracellular matrix (ECM) is essential for cell migration, proliferation, differentiation, mechanical stability, and signaling. It has been shown that decellularized ECMs can be processed into injectable formulations, thereby allowing for minimally invasive delivery. Upon injection and increase in temperature, these materials self-assemble into porous gels forming a complex network of fibers with nanoscale structure. In this study we aimed to examine and tailor the material properties of a self-assembling ECM hydrogel derived from porcine myocardial tissue, which was developed as a tissue specific injectable scaffold for cardiac tissue engineering. The impact of gelation parameters on ECM hydrogels has not previously been explored. We examined how modulating pH, temperature, ionic strength, and concentration affected the nanoscale architecture, mechanical properties, and gelation kinetics. These material characteristics were assessed using scanning electron microscopy, rheometry, and spectrophotometry, respectively. Since the main component of the myocardial matrix is collagen, many similarities between the ECM hydrogel and collagen gels were observed in terms of the nanofibrous structure and modulation of properties by altering ionic strength. However, variation from collagen gels was noted for the gelation temperature along with varied times and rates of gelation. These discrepancies when compared to collagen are likely due to the presence of other ECM components in the decellularized ECM based hydrogel. These results demonstrate how the material properties of ECM hydrogels could be tailored for future in vitro and in vivo applications.

Quantification of decellularized human myocardial matrix: A comparison of six patients

The purpose of this study was to characterize and quantitatively analyze human cardiac extracellular matrix (ECM) isolated from six different cadaveric donor hearts.

Human versus porcine tissue sourcing for an injectable myocardial matrix hydrogel

Heart failure (HF) after myocardial infarction (MI) is a leading cause of death in the western world with a critical need for new therapies. A previously developed injectable hydrogel derived from porcine myocardial matrix (PMM) has had successful results in both small and large animal MI models. In this study, we sought to evaluate the impact of tissue source on this biomaterial, specifically comparing porcine and human myocardium sources. We first developed an analogous hydrogel derived from human myocardial matrix (HMM). The biochemical and physical properties of the PMM and HMM hydrogels were then characterized, including residual dsDNA, protein content, sulfated glycosaminoglycan (sGAG) content, complex viscosity, storage and loss moduli, and nano-scale topography. Biochemical activity was investigated with in vitro studies for the proliferation of vascular cells and differentiation of human cardiomyocyte progenitor cells (hCMPCs). Next, in vivo gelation and material spread were confirmed for both PMM and HMM after intramyocardial injection. After extensive comparison, the matrices were found to be similar, yet did show some differences. Because of the rarity of collecting healthy human hearts, the increased difficulty in processing the human tissue, shifts in ECM composition due to aging, and significant patient-to-patient variability, these studies suggest that the HMM is not a viable option as a scalable product for the clinic; however, the HMM has potential as a tool for in vitro cell culture.

Fabrication and Characterization of Injectable Hydrogels Derived from Decellularized Skeletal and Cardiac Muscle

Biomaterials, which can contain appropriate biomechanical and/or biochemical cues, are increasingly being investigated as potential scaffolds for tissue regeneration and/or repair for treating myocardial infarction, heart failure, and peripheral artery disease. Specifically, injectable hydrogels are touted for their minimally invasive delivery, ability to self-assemble in situ, and capacity to encourage host tissue regeneration. Here we present detailed methods for fabricating and characterizing decellularized injectable cardiac and skeletal muscle extracellular matrix (ECM) hydrogels. The ECM derived hydrogels have low cellular and DNA content, retain sulfated glycosaminoglycans and other extracellular matrix proteins such as collagen, gel at physiologic temperature and pH, and assume a nanofibrous architecture. These injectable hydrogels are amenable to minimally invasive, tissue specific biomaterial therapies for treating myocardial infarction and peripheral artery disease.

Extracellular Matrix Hydrogel Promotes Tissue Remodeling, Arteriogenesis, and Perfusion in a Rat Hindlimb Ischemia Model

Summary Although surgical and endovascular revascularization can be performed in peripheral arterial disease (PAD), 40% of patients with critical limb ischemia do not have a revascularization option. This study examines the efficacy and mechanisms of action of acellular extracellular matrix-based hydrogels as a potential novel therapy for treating PAD. We tested the efficacy of using a tissue-specific injectable hydrogel derived from decellularized porcine skeletal muscle (SKM) and compared this to a new human umbilical cord-derived matrix (hUC) hydrogel, which could have greater potential for tissue regeneration because of the younger age of the tissue source. In a rodent hindlimb ischemia model, both hydrogels were injected 1-week post-surgery and perfusion was regularly monitored with laser speckle contrast analysis to 35 days post-injection. There were significant improvements in hindlimb tissue perfusion and perfusion kinetics with both biomaterials. Histologic analysis indicated that the injected hydrogels were biocompatible, and resulted in arteriogenesis, rather than angiogenesis, as well as improved recruitment of skeletal muscle progenitors. Skeletal muscle fiber morphology analysis indicated that the muscle treated with the tissue-specific SKM hydrogel more closely matched healthy tissue morphology. Whole transcriptome analysis indicated that the SKM hydrogel caused a shift in the inflammatory response, decreased cell death, and increased blood vessel and muscle development. These results show the efficacy of an injectable ECM hydrogel alone as a potential therapy for treating patients with PAD. Our results indicate that the SKM hydrogel improved functional outcomes through stimulation of arteriogenesis and muscle progenitor cell recruitment.

Injectable ECM scaffolds for cardiac repair.

Injectable biomaterials have been developed as potential minimally invasive therapies for treating myocardial infarction (MI) and heart failure. Christman et al. first showed that the injection of a biomaterial alone into rat myocardium can improve cardiac function after MI (Christman et al. Tissue Eng 10:403-409, 2004). More recently, hydrogel forms of decellularized extracellular matrix (ECM) materials have shown substantial promise. Here we present the methods for fabricating an injectable cardiac specific ECM biomaterial shown to already have positive outcomes in small and large animal models for cardiac repair (Singelyn et al. Biomaterials 30:5409-5416, 2009; Singelyn et al. J Am Coll Cardiol 59:751-763, 2012; Seif-Naraghi et al. Sci Transl Med 5:173ra25, 2013). Also covered are the methods for the injection of a biomaterial into rat myocardium using a surgical approach through the diaphragm. Although the methods shown here are for injection of an acellular biomaterial, cells or other therapeutics could also be added to the injection for testing other regenerative medicine strategies.

Fibronectin and Cyclic Strain Improve Cardiac Progenitor Cell Regenerative Potential In Vitro.

Cardiac progenitor cells (CPCs) have rapidly advanced to clinical trials, yet little is known regarding their interaction with the microenvironment. Signaling cues present in the microenvironment change with development and disease. This work aims to assess the influence of two distinct signaling moieties on CPCs: cyclic biaxial strain and extracellular matrix. We evaluate four endpoints for improving CPC therapy: paracrine signaling, proliferation, connexin43 expression, and alignment. Vascular endothelial growth factor A (about 900 pg/mL) was secreted by CPCs cultured on fibronectin and collagen I. The application of mechanical strain increased vascular endothelial growth factor A secretion 2–4-fold for CPCs cultured on poly-L-lysine, laminin, or a naturally derived cardiac extracellular matrix. CPC proliferation was at least 25% higher on fibronectin than that on other matrices, especially for lower strain magnitudes. At 5% strain, connexin43 expression was highest on fibronectin. With increasing strain magnitude, connexin43 expression decreased by as much as 60% in CPCs cultured on collagen I and a naturally derived cardiac extracellular matrix. Cyclic mechanical strain induced the strongest CPC alignment when cultured on fibronectin or collagen I. This study demonstrates that culturing CPCs on fibronectin with 5% strain magnitude is optimal for their vascular endothelial growth factor A secretion, proliferation, connexin43 expression, and alignment.