ABSTRACT
Fully integrated hydrogel channels were fabricated via interfacial bioorthogonal cross-linking, a diffusion-controlled method for the creation and patterning of synthetic matrices based on the rapid bioorthogonal reaction between s-tetrazines (Tz) and trans-cyclooctene (TCO) dienophiles. Injecting an aqueous solution of a bisTCO cross-linker into a reservoir of tetrazine-modified hyaluronic acid (HA-Tz), while simultaneously drawing the syringe needle through the reservoir, yielded a cross-linked hydrogel channel that was mechanically robust. Fluorescent tags and biochemical signals were spatially patterned into the channel wall through time-dependent perfusion of TCO-conjugated molecules into the lumen of the channel. Different cell populations were spatially encapsulated in the channel wall via temporal alteration of cells in the HA-Tz reservoir. The interfacial approach enabled the spatial patterning of vascular cells, including human abdominal aorta endothelial cells, aortic vascular smooth muscle cells, and aortic adventitial fibroblasts, into the hydrogel channels with high viability and proper morphology in the anatomical order found in human arteries. The bioorthogonal platform does not rely on external triggers and represents the first step toward the engineering of functional and implantable arteries.
Subject(s)
Aorta, Abdominal/growth & development , Endothelial Cells/drug effects , Hydrogels/pharmacology , Muscle, Smooth, Vascular/growth & development , Aorta/drug effects , Aorta/growth & development , Aorta, Abdominal/drug effects , Cell Survival/drug effects , Cross-Linking Reagents/chemistry , Cyclooctanes/chemistry , Endothelial Cells/pathology , Fibroblasts/drug effects , Humans , Hydrogels/chemical synthesis , Hydrogels/chemistry , Muscle, Smooth, Vascular/drug effects , Tetrazoles/chemistry , Tissue Engineering/trendsABSTRACT
We employed a systematic processing approach to control phase separation in polymer blend thin films and significantly reduce dynamic friction coefficients (µ)s. We leveraged this modulation of phase separation to generate composite surfaces with dynamic friction coefficients that were substantially lower than expected on the basis of simple mixing rules, and in several cases, these friction coefficients were lower than those of both pure components. Using a model polyisoprene [PI]/polystyrene [PS] composite system, a minimum µ was found in films with PS mass fractions between 0.60 and 0.80 (µblend = 0.11 ± 0.03); that value was significantly lower than the friction coefficient of PS (µPS = 0.52 ± 0.01) or PI (µPI = 1.3 ± 0.09) homopolymers and was comparable to the friction coefficient of poly(tetrafluoroethylene) [PTFE] (µPTFE = 0.09 ± 0.01) measured under similar conditions. Additionally, through experiments in which the domain size was systematically varied at constant composition (through an annealing process), we demonstrated that µ decreased with decreasing characteristic domain size. Thus, the tribological synergy between PS and PI domains (discrete size, physical domain isolation, and overall film composition) was shown to play an integral role in the friction and wear of these PS/PI composites. Overall, our results suggest that even high friction polymers can be used to create low friction polymer blends by following appropriate design rules and demonstrate that engineering microstructure is critical for controlling the friction and adhesion properties of composite films for tribologically relevant coatings.
