ABSTRACT
Engineered tissue constructs are inherently limited by their lack of microvascularization. Evidence suggests that combining a scaffold material with cells and their cell-secreted signals instigates tubule formation, and various strategies can be employed to tailor the vascular response. This review focuses on rationally designed materials capable of supporting functional neovessel formation and stabilization. Biomaterial scaffolds and their use as growth factor delivery systems are discussed, as well as other functional enhancement strategies to direct cellular responses for effective formation of a mature vascular network.
Subject(s)
Neovascularization, Physiologic , Tissue Engineering/methods , Tissue Scaffolds , Animals , Biocompatible Materials/metabolism , Humans , Intercellular Signaling Peptides and Proteins/administration & dosage , Microvessels/metabolismABSTRACT
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.
ABSTRACT
Mechanical conditioning represents a potential means to enhance the biochemical and biomechanical properties of tissue engineered vascular grafts (TEVGs). A pulsatile flow bioreactor was developed to allow shear and pulsatile stimulation of TEVGs. Physiological 120 mmHg/80 mmHg peak-to-trough pressure waveforms can be produced at both fetal and adult heart rates. Flow rates of 2 mL/sec, representative of flow through small diameter blood vessels, can be generated, resulting in a mean wall shear stress of approximately 6 dynes/cm(2) within the 3 mm ID constructs. When combined with non-thrombogenic poly(ethylene glycol) (PEG)-based hydrogels, which have tunable mechanical properties and tailorable biofunctionality, the bioreactor represents a flexible platform for exploring the impact of controlled biochemical and biomechanical stimuli on vascular graft cells. In the present study, the utility of this combined approach for improving TEVG outcome was investigated by encapsulating 10T-1/2 mouse smooth muscle progenitor cells within PEG-based hydrogels containing an adhesive ligand (RGDS) and a collagenase degradable sequence (LGPA). Constructs subjected to 7 weeks of biomechanical conditioning had significantly higher collagen levels and improved moduli relative to those grown under static conditions.
Subject(s)
Bioreactors , Blood Vessel Prosthesis , Blood Vessels/cytology , Blood Vessels/growth & development , Myocytes, Smooth Muscle/cytology , Myocytes, Smooth Muscle/physiology , Tissue Engineering/instrumentation , Animals , Bioprosthesis , Blood Flow Velocity/physiology , Cell Culture Techniques/instrumentation , Cell Culture Techniques/methods , Cell Line , Cell Proliferation , Equipment Design , Equipment Failure Analysis , Mechanotransduction, Cellular/physiology , Mice , Microfluidic Analytical Techniques/instrumentation , Microfluidic Analytical Techniques/methods , Polyethylene Glycols/chemistry , Pulsatile Flow/physiology , Tissue Engineering/methodsABSTRACT
Genetically engineered elastin-like polypeptide (ELP) hydrogels offer unique promise as scaffolds for cartilage tissue engineering because of the potential to promote chondrogenesis and to control mechanical properties. In this study, we designed and synthesized ELPs capable of undergoing enzyme-initiated gelation via tissue transglutaminase, with the ultimate goal of creating an injectable, in situ cross-linking scaffold to promote functional cartilage repair. Addition of the enzyme promoted ELP gel formation and chondrocyte encapsulation in a biocompatible process, which resulted in cartilage matrix synthesis in vitro and the potential to contribute to cartilage mechanical function in vivo. A significant increase in the accumulation of sulfated glycosaminoglycans was observed, and histological sections revealed the accumulation of a cartilaginous matrix rich in type II collagen and lacking in type I collagen, indicative of hyaline cartilage formation. These results provide evidence of chondrocytic phenotype maintenance for cells in the ELP hydrogels in vitro. In addition, the dynamic shear moduli of ELP hydrogels seeded with chondrocytes increased from 0.28 to 1.7 kPa during a 4-week culture period. This increase in the mechanical integrity of cross-linked ELP hydrogels suggests restructuring of the ELP matrix by deposition of functional cartilage extracellular matrix components.
