This project creates materials that steer flowing particles over their surfaces, along different paths depending on particle type. The surfaces will be selectively adhesive and self cleaning, with the potential to generate particle-sensitive optical signals. The program employs models for a variety of particles (reactive capsules, drug delivery vehicles, cells, bacteria), 0.1 ¡V 25 Ãm (micron) in size. The surfaces, which contain patterns at a variety of length scales set the particle direction, path, and motion signature (rolling, slipping, skipping, arrest). The engineered surfaces will find use in microfluidic schemes for continuous on-line sorting and separation of cells and other particles based on size, shape, softness, and surface chemistry.
Intellectual merit: The program develops a mechanism that results from combined hydrodynamic and interfacial forces, where the latter uniquely result from chemical nanotextures and nano-topographical features that interact with the particles. These nanotextures impart selectivity (based on local particle curvature, softness, and chemical functionality) and control the motion signature of flowing particles that encounter the surface. An important regime for these surfaces is that where sustained rolling occurs over nanotextures. Here dynamic adhesion with selective and reversible binding allows particles to be continuously processed over the surface. Then the addition of micron-scale patterns of varied surface chemistry (including the nanotextures on some patterned regions) or topography, allows different particle populations, distinguished by their adhesive character and net contact area with the surface, to be steered in different directions over the surface. This program will develop patterns which direct different types of particles along different surfaces paths, as a means to separate particles based on subtle differences in their character: size, local shape / roughness, near-surface modulus, net charge, and distributions in surface charge. The program combines experiments and simulation to develop application-driven design rules and maximize separation efficiency.
The novelty of this program lies in the use of surface patterns and nanotextures to manipulate particles by combined hydrodynamic and surface interactions. The paradigm of continuous particle rolling over a surface for manipulation and separation of particles is a new and powerful idea which exploits a new interfacial mechanism. To date, the mechanism has been modeled in simple treatments but has not been confirmed experimentally. In addition to being scientifically complex, controlled particle rolling is technologically transformative because it facilitates continuous rather than batch-mode processing. Further, the state space approach to describe adhesive behavior in a complex multi-dimensional variable space is highly transformative as an engineering method. The surface force / flow problem is not generally amenable to simplification through dimensionless groups, and the state space approach provides the opportunity to develop simple scaling laws useful for application-driven designs.
Broader Impacts: In addition to the transformative methods to study complex dynamic problems at the interface between materials and transport-engineering, the program will transform technologies that demand precise separation and characterization of micron scale objects. Biomedical and pharmaceutical applications will benefit through the ultimate development of portable cell-sorting devices requiring minimal support instrumentation and technician time. The program also has the potential to overhaul strategies for the design of marine-anti fouling coatings through its incorporation of hydrodynamic considerations in materials design.
The program supports the continued development of multidisciplinary fundamental coursework at the intersection of materials and engineering. Efforts to maintain diversity and improve the participation by underrepresented and economically disadvantaged groups will be facilitated through participation with several existing organizations and groups at UMass (MRSEC, ICE, NEAGEP), that host recruiting trips and workshops.
