Improved hemodynamics with a novel miniaturized intra-aortic axial flow pump in a porcine model of acute left ventricular dysfunction.

Currently, long-term mechanical circulatory support (MCS) is limited to large, complex devices that require invasive, high-risk surgical implantation. These devices are mainly used in patients with late stage heart failure (HF). We are developing a novel percutaneous intra-aortic micro-axial fluid entrainment pump intended for long-term MCS in patients with earlier stage HF. This study examined the pump's hemodynamic effects in a porcine model of acute HF. In three porcine experiments, the pump was deployed in the thoracic aorta by standard cardiac catheterization techniques and was anchored with self-expanding struts. Acute cardiac dysfunction was induced by infusing esmolol continuously. Pump support increased cardiac output (+10.4%), stroke volume (+8.9%), and ejection fraction (+10.8%) while decreasing cardiac stroke work (-10.8%) and afterload (-22.7%). Furthermore, pump support significantly enhanced renal perfusion through sustained increases in both renal artery flow (+36.4%) and pressure (+73.6%). In a porcine model of acute HF, the catheter-based intra-aortic fluid entrainment pump improved hemodynamics and renal perfusion. These results suggest that the pump could improve HF outcomes and patients' quality of life by resting the heart, promoting reverse remodeling, and augmenting end-organ perfusion. Furthermore, the enhanced renal perfusion may help disrupt the cardiorenal syndrome cycle and improve HF treatment.

Multilayer microfluidic poly(ethylene glycol) diacrylate hydrogels.

Development of robust, in vivo like tissues in vitro holds the potential to create regenerative medicine-based therapeutics, provide more physiologically significant preclinical models and supply a pharmacological and toxicological screening platform that reflects in vivo systems in both complexity and function. This protocol describes a simple, robust, multilayer replica molding technique in which poly(dimethylsiloxane) (PDMS) and poly(ethylene glycol) diacrylate (PEGDA) are serially replica molded to develop microfluidic PEGDA hydrogel networks embedded within independently fabricated PDMS housings, using a combination of soft and photo-lithography. This work has direct applications toward the development of robust, complex, cell-laden hydrogels for in vitro diagnostics and regenerative medicine applications.

Fabrication and mechanical evaluation of anatomically-inspired quasilaminate hydrogel structures with layer-specific formulations.

A major tissue engineering challenge is the creation of multilaminate scaffolds with layer-specific mechanical properties representative of native tissues, such as heart valve leaflets, blood vessels, and cartilage. For this purpose, poly(ethylene glycol) diacrylate (PEGDA) hydrogels are attractive materials due to their tunable mechanical and biological properties. This study explored the fabrication of trilayer hydrogel quasilaminates. A novel sandwich method was devised to create quasilaminates with layers of varying stiffnesses. The trilayer structure was comprised of two "stiff" outer layers and one "soft" inner layer. Tensile testing of bilayer quasilaminates demonstrated that these scaffolds do not fail at the interface. Flexural testing showed that the bending modulus of acellular quasilaminates fell between the bending moduli of the "stiff" and "soft" hydrogel layers. The bending modulus and swelling of trilayer scaffolds with the same formulations were not significantly different than single layer gels of the same formulation. The encapsulation of cells and the addition of phenol red within the hydrogel layers decreased bending modulus of the trilayer scaffolds. The data presented demonstrates that this fabrication method can make quasilaminates with robust interfaces, integrating layers of different mechanical properties and biofunctionalization, and thus forming the foundation for a multilaminate scaffold that more accurately represents native tissue.

Integration of Self-Assembled Microvascular Networks with Microfabricated PEG-Based Hydrogels.

Despite tremendous efforts, tissue engineered constructs are restricted to thin, simple tissues sustained only by diffusion. The most significant barrier in tissue engineering is insufficient vascularization to deliver nutrients and metabolites during development in vitro and to facilitate rapid vascular integration in vivo. Tissue engineered constructs can be greatly improved by developing perfusable microvascular networks in vitro in order to provide transport that mimics native vascular organization and function. Here a microfluidic hydrogel is integrated with a self-assembling pro-vasculogenic co-culture in a strategy to perfuse microvascular networks in vitro. This approach allows for control over microvascular network self-assembly and employs an anastomotic interface for integration of self-assembled micro-vascular networks with fabricated microchannels. As a result, transport within the system shifts from simple diffusion to vessel supported convective transport and extra-vessel diffusion, thus improving overall mass transport properties. This work impacts the development of perfusable prevascularized tissues in vitro and ultimately tissue engineering applications in vivo.

Flexural characterization of cell encapsulated PEGDA hydrogels with applications for tissue engineered heart valves.

The limitations of the current clinical options for valve replacements have inspired the development of enabling technologies to create a tissue engineered heart valve (TEHV). Poly(ethylene glycol) diacrylate (PEGDA) hydrogel scaffolds permit greater biological and biomechanical customization than do non-woven mesh scaffold technologies. However, the material characterization of PEGDA hydrogels has been predominantly limited to compression and tension, as opposed to bending. Since large flexural deformations result in points of maximum stress in native valves as well as TEHVs, it is crucial to evaluate any potential scaffold material in this mode. The effect of formulation parameters on the bending mechanics of cell-seeded PEGDA hydrogels were investigated with a custom designed bending tester. Three molecular weights (3.4, 6, and 8 kDa) and three weight fractions (5%, 10%, and 15%, w/v) were subjected to three-point bending tests and the flexural stiffness was calculated. Manipulating the composition of the hydrogels resulted in flexural stiffnesses comparable with native tissues (15-220 kPa) with varied mesh sizes and swelling ratios. Hydrogels containing encapsulated valve cells, methacrylated heparin (Hep-MA), or both were substantially less stiff than acellular hydrogels. In conclusion, PEGDA hydrogels are an attractive potential scaffold system for TEHVs because they are not only cytocompatible and modifiable but can also withstand bending deformations. These studies are the first to explore the encapsulation of valvular interstitial cells in pure PEGDA hydrogels as well as to investigate the bending properties of PEGDA gels.

Multilayer microfluidic PEGDA hydrogels.

Development of robust 3D tissue analogs in vitro is limited by passive, diffusional mass transport. Perfused microfluidic tissue engineering scaffolds hold the promise to improve mass transport limitations and promote the development of complex, metabolically dense, and clinically relevant tissues. We report a simple and robust multilayer replica molding technique in which poly(dimethylsiloxane) (PDMS) and poly(ethylene glycol) diacrylate (PEGDA) are serially replica molded to develop microfluidic PEGDA hydrogel networks embedded within independently fabricated PDMS housings. We demonstrate the ability to control solute-scaffold effective diffusivity as a function of solute molecular weight and hydrogel concentration. Within cell laden microfluidic hydrogels, we demonstrate increased cellular viability in perfused hydrogel systems compared to static controls. We observed a significant increase in cell viability at all time points greater than zero at distances up to 1 mm from the perfused channel. Knowledge of spatiotemporal mass transport and cell viability gradients provides useful engineering design parameters necessary to maximize overall scaffold viability and metabolic density. This work has applications in the development of hydrogels as in vitro diagnostics and ultimately as regenerative medicine based therapeutics.