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Abraham Stroock: Give the Material Life PDF Print E-mail
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Tuesday, 05 October 2010 16:06

When Abraham Stroock, associate professor at Cornell University, looks at a tree, he sees a complex feat of engineering. Inside the trunk, the branches, and the leaves, an intricate network of capillaries draws water dozens of meters into the air, with nary a pump in sight. This incredible system inspires Stroock's approach to microfluidics.

Microfluidics involves moving tiny volumes of liquid through channels that are usually etched into a rigid material such as glass or silicon. Stroock, however, works with hydrogels, soft polymers that absorb water. Recently, he molded a capillary system that mimics a tree's into a slab of hydrogel. This "synthetic tree" uses evaporation to pull water through its capillaries. The force it achieves is equivalent to that required to move liquid up a vertical column 85 meters high--the height of a redwood.


Liquid diffuses out of the hydrogel capillaries and into the surrounding material, just as it would in living tissue. Hydrogels are also biologically compatible, so such systems could serve as wound dressings that remove fluid and deliver drugs to promote healing. They could also act as three-dimensional scaffolds for engineered tissues; oxygen and nutrients could travel to cells inside the scaffolds. To mimic real tissues, the materials will ultimately have to provide conduits for proteins and cells--another step in Stroock's plan to "give the material life."

Research Focus

In our research effort, we couple deterministic micro and nano-scale structure with physical principles to create interesting phenomena and to develop new technology. As an integral part of this effort, we build theoretical models in order to direct our experimentation and establish engineering principles for future applications. With this spirit, we are pursuing several themes of research that allow us to address both timely technological challenges in microchemical technology, medicine, and materials development, and timeless questions in transport phenomena, biology, and chemical thermodynamics.

Current Projects

Transport phenomena in microfluidics

Inspired by the success of integrated electronics, scientists and engineers have initiated an effort in the past decade to miniaturize chemical processes such as analysis, synthesis, and biochemical manipulations. Technologically, these microfluidic systems offer increased integration of function, increased portability, increased rates of process, and decreased volumes of reagents and wastes relative to conventional instruments. Scientifically, these systems can act as a new type of laboratory that allows for deterministic control of chemical and transport processes on a scale (< 1 mm) that was previously inaccessible. This field is a great opportunity for Chemical Engineers to take the lead in the invention, characterization, and implementation of new concepts. Our current research is focused on theoretical and experimental studies of two of the most fundamental aspects of chemical process: mixing and mass transfer to boundaries. We are particularly interested in the role of chaotic dynamics in controlling heat and mass transfer processes in low Reynolds number flows. We are using our insights into these processes to design microfluidic fuel cells for portable power applications and for the optimization of surface-based bioassays. We collaborate on this topic with Prof. Hector Abruña (Chemistry, Cornell University), Prof. Donald Koch (Chemical Engineering, Cornell University), and Prof. Kelvin Lee (Chemical Engineering, University of Delaware).

 

 

Microfluidic biomaterials

In an effort that complements our work on basic transport phenomena, we are developing new technologies to exploit microfluidic structure as a vascular system with which to mediate efficient mass transfer and control (spatially and temporally) the chemical environment inside biomaterials. This approach represents a significant departure from those pursued either in the field of microfluidics (focused on the use of materials to simply define plumbing) or the field of biomaterials (focused on the passive, chemical and mechanical character of the material). In Microfluidic Biomaterials, the microfluidic infrastructure allows for the chemical state of the material to be programmed externally. The applications we are targeting for these active materials are Tissue Engineering and Wound Healing. We are developing all aspects of this new field, from the fabrication, through the characterization of mass transfer, to the application in biological and clinical contexts. We collaborate on this topic with Prof. Lawrence Bonassar (Biomedical Engineering, Cornell University), Prof. Suzanne Schwartz (Department of Surgery, Weill Medical College), and Prof. Thomas Sato (Department of Cell and Developmental Biology, Weill Medical College).

 

 

A Chemistry of Colloids

In a third theme of research, we address a distinct challenge in the development of micro- and nano-technologies: the control of structure and dynamics of collections of micro or nano-scale particles or colloids. This control can complement conventional, lithographic methods of defining microstructure by, for example, allowing for the growth of 3D structure in a parallel manner (e.g., for photonics) or by generating structure in a reversible manner (e.g., to control mechanical properties). To achieve this control, we are pursuing a chemical approach by which we tailor thermodynamics to drive the desired interactions among particles. The development of this Chemistry of Colloids requires the creation of building blocks (the elements) that can be made to interact selectively and directionally (the bonds) with control over the thermodynamics and kinetics (the reaction mechanisms). As a first approach to this challenge, we are using the geometry-dependence of the depletion interaction. Our effort is distinct from others in the colloid community in that we are tailoring the structure of individual particles in rational way to dictate the desired collective behavior. We collaborate on this topic with Prof. Fernando Escobedo (Chemical Engineering, Cornell University).

 

 

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