Injectable and Spatially Patterned Microporous Annealed Particle (MAP) Hydrogels for Tissue Repair Applications.

Spatially patterned hydrogels are becoming increasingly popular in the field of regenerative medicine and tissue repair because of their ability to guide cell infiltration and migration. However, postfabrication technologies are usually required to spatially pattern a hydrogel, making these hydrogels difficult to translate into the clinic. Here, an injectable spatially patterned hydrogel is reported using hyaluronic acid (HA)-based particle hydrogels. These particle hydrogels are sequentially loaded into a syringe to form a pattern and, once injected, they maintain the pattern. The applicability of this hydrogel in a wound healing skin model, a subcutaneous implant model, as well as a stroke brain model is examined and distinct patterning in all models tested is shown. This injectable and spatially patterned hydrogel can be used to create physical or biochemical gradients. Further, this design can better match the scaffold properties within the physical location of the tissue (e.g., wound border vs wound center). This allows for better design features within the material that promote repair and regeneration

Stress echocardiography in elderly patients with coronary artery disease Applicability, safety and prognostic value of dobutamine and adenosine echocardiography in elderly patients

AbstractObjectives. Our aim was to determine the applicability, safety and prognostic value of adenosine and dobutamine stress echocardiography in patients ≥70 years old.Background. These tests are sometimes mandatory because of difficulties and inaccuracies in interpreting traditional electrocardiographic stress tests. Furthermore, if these tests could be used to avoid coronary arteriography and cardiac catheterization, they would become essential in the care of the elderly, whose numbers are increasing.Methods. We performed coronary arteriography and dobutamine and adenosine stress echocardiographic tests in 120 patients (72 men) ≥70 years old who entered the hospital because of chest pain and had known or suspected coronary artery disease. The stress tests were performed on separate days, within 2 weeks of coronary arteriography. Both the arteriograms and the echocardiograms were analyzed by two experts who had no knowledge of the patients' other data or the other interpreter's report. Tests were judged to have positive or negative results, and the patients were followed up for the development of cardiac events. Univariate and multivariate analyses and other statistical modalities were applied for comparisons.Results. Documented coronary artery disease was found in 89 patients. During the 14 ± 7 months of follow-up, cardiac events developed in 50 patients, including 3 (7.9%) of 38 patients with negative dobutamine and 12 (20.7%) of 58 patients with negative adenosine test results. Demonstration of any abnormality on stress echocardiography was an independent factor for cardiac events, both for dobutamine (relative risk 7.3) and for adenosine (relative risk 3.0). Both cessation of dobutamine or adenosine tests and diagnosis of disease in two or more coronary vessels were also independent predictors. ST segment depression ≥1 mm was related to future events only with the dobutamine test.Conclusions. These echocardiographic stress tests proved safe and well tolerated. They successfully stratified this cohort of elderly patients with coronary artery disease to low or high risk subgroups for subsequent cardiac events

Integrating light-sheet imaging with virtual reality to recapitulate developmental cardiac mechanics

Currently, there is a limited ability to interactively study developmental cardiac mechanics and physiology. We therefore combined light-sheet fluorescence microscopy (LSFM) with virtual reality (VR) to provide a hybrid platform for 3D architecture and time-dependent cardiac contractile function characterization. By taking advantage of the rapid acquisition, high axial resolution, low phototoxicity, and high fidelity in 3D and 4D (3D spatial + 1D time or spectra), this VR-LSFM hybrid methodology enables interactive visualization and quantification otherwise not available by conventional methods, such as routine optical microscopes. We hereby demonstrate multiscale applicability of VR-LSFM to (a) interrogate skin fibroblasts interacting with a hyaluronic acid–based hydrogel, (b) navigate through the endocardial trabecular network during zebrafish development, and (c) localize gene therapy-mediated potassium channel expression in adult murine hearts. We further combined our batch intensity normalized segmentation algorithm with deformable image registration to interface a VR environment with imaging computation for the analysis of cardiac contraction. Thus, the VR-LSFM hybrid platform demonstrates an efficient and robust framework for creating a user-directed microenvironment in which we uncovered developmental cardiac mechanics and physiology with high spatiotemporal resolution

Integrating light-sheet imaging with virtual reality to recapitulate developmental cardiac mechanics

Currently, there is a limited ability to interactively study developmental cardiac mechanics and physiology. We therefore combined light-sheet fluorescence microscopy (LSFM) with virtual reality (VR) to provide a hybrid platform for 3D architecture and time-dependent cardiac contractile function characterization. By taking advantage of the rapid acquisition, high axial resolution, low phototoxicity, and high fidelity in 3D and 4D (3D spatial + 1D time or spectra), this VR-LSFM hybrid methodology enables interactive visualization and quantification otherwise not available by conventional methods, such as routine optical microscopes. We hereby demonstrate multiscale applicability of VR-LSFM to (a) interrogate skin fibroblasts interacting with a hyaluronic acid–based hydrogel, (b) navigate through the endocardial trabecular network during zebrafish development, and (c) localize gene therapy-mediated potassium channel expression in adult murine hearts. We further combined our batch intensity normalized segmentation algorithm with deformable image registration to interface a VR environment with imaging computation for the analysis of cardiac contraction. Thus, the VR-LSFM hybrid platform demonstrates an efficient and robust framework for creating a user-directed microenvironment in which we uncovered developmental cardiac mechanics and physiology with high spatiotemporal resolution

Manipulating Hydrogel Microstructure for the Purpose of Brain Repair After Stroke

Stroke is the leading cause of adult disability in the United States. The severe and highly reactive inflammation immediately following stroke onset leads to a series of destructive events including neuronal death and a clearance of cellular debris. The brain’s defense mechanism is to compartmentalize the injured tissue via a highly reactive and neurotoxic astrocytic scar that acts as a physical and chemical barrier to recovery. There has been much debate whether reactive astrocytes are beneficial in the recovery process. Highly reactive astrocytes are neurotoxic while pro-recovery astrocytes are crucial in synaptogenesis and coordinating neural circuits. Thus, one therapeutic strategy emerges whereby limiting highly reactive astrocytes and promoting pro-recovery astrocytes could prove beneficial. The brain’s liquefactive necrosis and compartmentalization leads to a stroke cavity that can accept a large volume transplant without causing further damage. This cavity provides an opportunity for biomaterial tissue regeneration strategies. Biomaterials, specifically polymeric hydrogels can act as extra cellular matrix (ECM) mimics by providing neighboring cells with mechanical structure and biochemical cues. Most hydrogel studies conducted in the brain utilize the hydrogel solely as a delivery vehicle for small molecule, growth factor, or stem cell transplantation. This dissertation focuses on engineering the biomaterial itself to unlock its inherit therapeutic potential, focusing on manipulation of astrocyte reactivity. A novel class of injectable microporous annealing particle (MAP) hydrogels is used and optimized for direct injection into the stroke cavity for brain repair. This material’s backbone is first transitioned to hyaluronic acid (HA), a glycosaminoglycan commonly found in the native brain ECM. The mechanical properties such as void space and pore size are fully characterized and the material is engineered to match the mechanical stiffness of rodent brain. The HA MAP gel is tested in vitro and proven to be cell friendly. This hydrogel is used in two different rodent stroke models and shown to have anti-inflammatory effects. Deeper investigation into astrocyte reactivity in response to the hydrogel injection shows the MAP gel is capable of decreasing highly reactive astrocytes and promoting infiltration of pro-recovery astrocytes into the stroke. This pro-recovery astrocyte infiltration is also correlated with neuronal axon penetration into the lesion. Finally, long-term studies show the MAP gel is capable of better preserving brain shape and function. The unlocking of the inherit hydrogel therapeutic potential will hopefully allow for more focus placed on the optimization of biomaterials in the field of stroke regeneration, rather than simply being used as delivery vehicles

Manipulating Hydrogel Microstructure for the Purpose of Brain Repair After Stroke

Stroke is the leading cause of adult disability in the United States. The severe and highly reactive inflammation immediately following stroke onset leads to a series of destructive events including neuronal death and a clearance of cellular debris. The brain’s defense mechanism is to compartmentalize the injured tissue via a highly reactive and neurotoxic astrocytic scar that acts as a physical and chemical barrier to recovery. There has been much debate whether reactive astrocytes are beneficial in the recovery process. Highly reactive astrocytes are neurotoxic while pro-recovery astrocytes are crucial in synaptogenesis and coordinating neural circuits. Thus, one therapeutic strategy emerges whereby limiting highly reactive astrocytes and promoting pro-recovery astrocytes could prove beneficial. The brain’s liquefactive necrosis and compartmentalization leads to a stroke cavity that can accept a large volume transplant without causing further damage. This cavity provides an opportunity for biomaterial tissue regeneration strategies. Biomaterials, specifically polymeric hydrogels can act as extra cellular matrix (ECM) mimics by providing neighboring cells with mechanical structure and biochemical cues. Most hydrogel studies conducted in the brain utilize the hydrogel solely as a delivery vehicle for small molecule, growth factor, or stem cell transplantation. This dissertation focuses on engineering the biomaterial itself to unlock its inherit therapeutic potential, focusing on manipulation of astrocyte reactivity. A novel class of injectable microporous annealing particle (MAP) hydrogels is used and optimized for direct injection into the stroke cavity for brain repair. This material’s backbone is first transitioned to hyaluronic acid (HA), a glycosaminoglycan commonly found in the native brain ECM. The mechanical properties such as void space and pore size are fully characterized and the material is engineered to match the mechanical stiffness of rodent brain. The HA MAP gel is tested in vitro and proven to be cell friendly. This hydrogel is used in two different rodent stroke models and shown to have anti-inflammatory effects. Deeper investigation into astrocyte reactivity in response to the hydrogel injection shows the MAP gel is capable of decreasing highly reactive astrocytes and promoting infiltration of pro-recovery astrocytes into the stroke. This pro-recovery astrocyte infiltration is also correlated with neuronal axon penetration into the lesion. Finally, long-term studies show the MAP gel is capable of better preserving brain shape and function. The unlocking of the inherit hydrogel therapeutic potential will hopefully allow for more focus placed on the optimization of biomaterials in the field of stroke regeneration, rather than simply being used as delivery vehicles

Injection of Microporous Annealing Particle (MAP) Hydrogels in the Stroke Cavity Reduces Gliosis and Inflammation and Promotes NPC Migration to the Lesion

With the number of deaths due to stroke decreasing, more individuals are forced to live with crippling disability resulting from the stroke. To date, no therapeutics exist after the first 4.5 h after the stroke onset, aside from rest and physical therapy. Following stroke, a large influx of astrocytes and microglia releasing proinflammatory cytokines leads to dramatic inflammation and glial scar formation, affecting brain tissue's ability to repair itself. Pathological conditions, such as a stroke, trigger neural progenitor cells (NPCs) proliferation and migration toward the damaged site. However, these progenitors are often found far from the cavity or the peri-infarct tissue. Poststroke tissue remodeling results in a compartmentalized cavity that can directly accept a therapeutic material injection. Here, this paper shows that the injection of a porous hyaluronic acid hydrogel into the stroke cavity significantly reduces the inflammatory response following stroke while increasing peri-infarct vascularization compared to nonporous hydrogel controls and stroke only controls. In addition, it is shown that the injection of this material impacts NPCs proliferation and migration at the subventricular zone niche and results, for the first time, in NPC migration into the stroke site