In vitro and in vivo analysis of visible light crosslinkable gelatin methacryloyl (GelMA) hydrogels.

Photocrosslinkable materials have been frequently used for constructing soft and biomimetic hydrogels for tissue engineering. Although ultraviolet (UV) light is commonly used for photocrosslinking such materials, its use has been associated with several biosafety concerns such as DNA damage, accelerated aging of tissues, and cancer. Here we report an injectable visible light crosslinked gelatin-based hydrogel for myocardium regeneration. Mechanical characterization revealed that the compressive moduli of the engineered hydrogels could be tuned in the range of 5-56 kPa by changing the concentrations of the initiator, co-initiator and co-monomer in the precursor formulation. In addition, the average pore sizes (26-103 µm) and swelling ratios (7-13%) were also shown to be tunable by varying the hydrogel formulation. In vitro studies showed that visible light crosslinked GelMA hydrogels supported the growth and function of primary cardiomyocytes (CMs). In addition, the engineered materials were shown to be biocompatible in vivo, and could be successfully delivered to the heart after myocardial infarction in an animal model to promote tissue healing. The developed visible light crosslinked hydrogel could be used for the repair of various soft tissues such as the myocardium and for the treatment of cardiovascular diseases with enhanced therapeutic functionality.

Elastic, silk-cardiac extracellular matrix hydrogels exhibit time-dependent stiffening that modulates cardiac fibroblast response.

Heart failure is the leading cause of death in the United States and rapidly becoming the leading cause of death worldwide. While pharmacological treatments can reduce progression to heart failure following myocardial infarction, there still exists a need for new therapies that promote better healing postinjury for a more functional cardiac repair and methods to understand how the changes to tissue mechanical properties influence cell phenotype and function following injury. To address this need, we have optimized a silk-based hydrogel platform containing cardiac tissue-derived extracellular matrix (cECM). These silk-cECM hydrogels have tunable mechanical properties, as well as rate-controllable hydrogel stiffening over time. In vitro, silk-cECM scaffolds led to enhanced cardiac fibroblast (CF) cell growth and viability with culture time. cECM incorporation improved expression of integrin an focal adhesion proteins, suggesting that CFs were able to interact with the cECM in the hydrogel. Subcutaneous injection of silk hydrogels in rats demonstrated that addition of the cECM led to endogenous cell infiltration and promoted endothelial cell ingrowth after 4 weeks in vivo. This naturally derived silk fibroin platform is applicable to the development of more physiologically relevant constructs that replicate healthy and diseased tissue in vitro and has the potential to be used as an injectable therapeutic for cardiac repair. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3058-3072, 2016.

Lysyl oxidase expression in cardiac fibroblasts is regulated by α2ß1 integrin interactions with the cellular microenvironment.

Lysyl oxidase (LOX) catalyzes crosslink formation between fibrillar collagens and elastins and an increase in LOX activity has been associated with cardiac fibrosis following myocardial infarction (MI). It has been previously reported that LOX expression is regulated by growth factors and cytokines including transforming growth factor (TGF-ß1); however, it is unclear how the biophysical and biochemical properties of the cellular microenvironment affect LOX expression. In this study, we isolated rat cardiac fibroblasts (CF) and infarct cardiac fibroblasts (ICF), from healthy and 1-week post-MI left ventricular tissue respectively, and cultured them under varied substrate conditions in vitro to assess their influence on LOX expression. Culture of ICF on collagen I-coated plates increased LOX expression versus uncoated plates with an additional increase observed with the presence of TGF-ß1. To further investigate the effect of integrin interactions with collagen I on LOX expression, we inhibited the α2ß1 integrin from binding to collagen I and found gene and protein expression of LOX to be downregulated. Together, this demonstrates that the interaction of α2ß1 integrin to collagen I in the cellular microenvironment can regulate expression of LOX. Further studies investigating additional integrin interactions may identify therapeutic targets for treating cardiac fibrosis.