Effect of Porous Substrate Topographies on Cell Dynamics: A Computational Study

Controlling cell-substrate interactions via the microstructural characteristics of biomaterials offers an advantageous path for modulating cell dynamics, mechanosensing, and migration, as well as for designing immune-modulating implants, all without the drawbacks of chemical-based triggers. Specifically, recent in vivo studies have suggested that a porous implant's microscale curvature landscape can significantly impact cell behavior and ultimately the immune response. To investigate such cell-substrate interactions, we utilized a 3D computational model incorporating the minimum necessary physics of cell migration and cell-substrate interactions needed to replicate known in vitro behaviors. This model specifically incorporates the effect of membrane tension, which was found to be necessary to replicate in vitro cell behavior on curved surfaces. Our simulated substrates represent two classes of porous materials recently used in implant studies, which have markedly different microscale curvature distributions and pore geometries. We found distinct differences between the overall migration behaviors, shapes, and actin polymerization dynamics of cells interacting with the two substrates. These differences were correlated to the shape energy of the cells as they interacted with the porous substrates, in effect interpreting substrate topography as an energetic landscape interrogated by cells. Our results demonstrate that microscale curvature directly influences cell shape and migration and, therefore, is likely to influence cell behavior. This supports further investigation of the relationship between the surface topography of implanted materials and the characteristic immune response, a complete understanding of which would broadly advance principles of biomaterial design.

Mitigating Bubble Traffic in Gas-Evolving Electrodes via Spinodally Derived Architectures

Porous electrodes are widely used in the industry because of their high surface area to volume ratio. However, the stochastic morphology of most commercially available porous electrodes results in poor electrical connections in the solid phase and inefficient mass transport through the pore phase. This can be especially detrimental for gas-evolving processes such as water electrolysis for hydrogen and oxygen generation. Bicontinuous interfacially jammed emulsion gels (bijels) offer templates from which to create porous electrodes with robust solid-state interconnectivity and a uniform pore structure that facilitate improved electron and mass transport. In this study, gas release rates and electrochemical experiments are utilized to study the effects of powder- and bijel-derived microstructures on hydrogen generation by water electrolysis. The bijel-derived electrodes are shown to expel product gas faster and require up to 25% less overpotential to drive water electrolysis over the range of current densities tested (-5 to -40 mA/cm²) than their powder-derived analogs. Our findings suggest that the uniform and bicontinuous domains of bijel-derived porous electrodes can mitigate the limited current distribution and deleterious bubble effect found in stochastic electrodes, in turn improving the overall performance of electrolytic processes requiring transport of gaseous species.

Composite bijel-templated hydrogels for cell delivery

Numerous processing techniques aim to impart interconnected, porous structures within regenerative medicine materials to support cell delivery and direct tissue growth. Many of these techniques lack predictable control of scaffold architecture, and rapid prototyping methods are often limited by time-consuming, layer-by-layer fabrication of micro-features. Bicontinuous interfacially jammed emulsion gels (bijels) offer a robust, self-assembly-based platform for synthesizing a new class of morphologically unique cell delivery biomaterials. Bijels form via kinetic arrest of temperature-driven spinodal decomposition in partially miscible binary liquid systems. These non-equilibrium soft materials are comprised of co-continuous, fully percolating, non-constricting liquid domains separated by a nanoparticle monolayer. Through the selective introduction of biocompatible precursors, hydrogel scaffolds displaying the morphological characteristics of the parent bijel can be formed. We report using bijel templating to generate structurally unique, fibrin-loaded polyethylene glycol hydrogel composites. Demonstration of composite bijel-templated hydrogels (CBiTHs) as a new cell delivery system was carried out in vitro using fluorescence-based tracking of cells delivered to previously acellular fibrin gels. Imaging analysis confirmed repeatable delivery of normal human dermal fibroblasts to acellular fibrin gels.