Materials for Functional and Structural Applications

By Philip Nash, PhD, Professor of Materials Engineering
Thermal Processing Technology Center, Mechanical, Materials, and Aerospace Engineering (MMAE) Department at IIT

Thermoelectrics, Shape Memory and Spintronics.

One Illinois Institute of Technology research project is focused on magnetic, thermoelectric and shape memory alloys based on specialty alloys[1].  These compounds are of interest because of a range of physical effects that occur in them that can be applied in mechanical or electronic devices, from mechanical actuators to refrigeration to conversion of waste heat into electrical power. These effects include ferromagnetism; magnetocaloric effect; thermoelectric effect; shape memory effect induced by temperature, stress or magnetic field; magnetostriction; magnetoresistance; half-metallic effect, where the material exhibits both conduction.

These effects are often a strong function of microstructural parameters, such as composition, degree of order and defect structure, consequently the defining parameters for these effects, e.g. Curie or martensite start temperature, magnetic moment or spin polarization, can be modified to be more appropriate for particular applications.

Indeed there are many studies on the effects of quaternary or quinary compositions based on these ternary compounds. Control of properties through control of microstructure is the realm of alloy development, which requires basic knowledge of crystal structures, phase equilibria and thermodynamic properties. Mechanical properties are also important for some applications, such as actuators based on shape memory effect.

The objectives of the research are to accurately determine heats of formation for functional ternary compounds, to make complementary measurements of heat capacity, phase equilibria, melting points and lattice parameters and to analyze these data to provide an understanding of the systematic alloying behavior in these systems.  Such data are of importance in providing benchmarks for first principles calculations and for optimization of thermodynamic descriptions of compounds.  Our collaborations will produce data on thermoelectric properties and generate thermodynamic descriptions and first principles calculations for select alloy systems of interest for functional applications.

[1] These are ternary Heusler alloys, composition type X₂YZ

Three-Dimensional Patterned Hydrogels for Tissue Engineering

By Eric Brey, PhD, Assistant Professor
Biomedical Engineering Department at IIT

The ability to control three-dimensional polymer structure is crucial for many research areas, including microfluidics, tissue engineering, and separation technologies. Photolithographic techniques allow precise control of topographical features and spatial presentation of desired materials in two dimensions. However, it is difficult to control these spatial features three-dimensionally.  If this challenge is overcome, patients with a variety of diseases might one day benefit from today's research.

Polyethylene glycol (PEG) is a hydrophilic and biocompatible polymer that has been investigated for a number of biomedical applications.  It has received significant attention for tissue engineering applications because of the ease with which biological molecules and cells can be incorporated into the network structure.

At the Illinois Institute of Technology, collaboration between Dr. Victor Perez-Luna (Associate Professor, Chemical and Biological Engineering) and Dr. Eric Brey (Assistant Professor, Biomedical Engineering) has been focused on the development of methods for creating three-dimensional channels within PEG hydrogels. The method depends on the use of two photopolymerizable macromers with different degradation kinetics: PEG-diacrylate (PEG-DA) and PEG-co(L-lactide) diacrylate (PEG-PLLA-DA).

PEG-PLLA (but not PEG-DA) gels degrade rapidly via hydrolysis.  Patterns of PEG-PLLA-DA structures were generated within multilayer PEG hydrogels by noncontact photolithography. The patterned PEG-PLLA-DA structures degraded rapidly, resulting in channels within the PEG-DA hydrogels. Multilayer patterned structures can be used to generate interconnected channels, and these channels can be modified to support cell adhesion and growth.  This technique could be used to generate three-dimensionally vascularized PEG hydrogels with precise control over the spatial orientation of the channels.

This project is one of two collaborations at IIT that are advancing bioartificial pancreas research. If successful, these programs could one day offer new hope to the millions of people who battle insulin-dependent diabetes and currently face a long list of life-altering and life-threatening complications.