Education

• B.S. University of Puerto Rico at Mayaguez, 2001.
• M.S. Carnegie Mellon University, 2006.
• Ph.D. Carnegie Mellon University, 2006.
• Postdoctoral Fellow, U. Maryland NIST-NCNR, 2007

Research Interests

• Nanomaterials, biomaterials, colloids and polymers
• Rheology of self-assembled materials
• Neutron and x-ray scattering

My research interests focus primarily on improving our understanding of the structure-function relationships in colloidal and nanostructured materials. Currently, a major thrust in my research has centered on polymer networks and self-assembled nano-materials. These materials, natural or synthetic, have a number of applications in sectors including biotechnology, medicine and nanotechnology as well as in everyday consumer products.

To probe these systems, we use a variety of experimental techniques from polymer and colloidal science. Among these techniques, rheology allows us to correlate the mechanical properties of a material to the internal structure of its components. We also utilize light, x-rays and neutrons to probe the nanoscale structure and the dynamics of bulk materials at equilibrium or under externally applied mechanical and electric fields.

Small angle neutron scattering (SANS) is used to probe the nanometer structure of complex materials under a variety of conditions that emulate real world processes.

Mechanical Properties of Blood Clots

One of our recent projects focuses on identifying the relationship between the structure and the mechanical properties of fibrin networks and blood clots. Fibrin, a highly organized filamentous protein, is the major structural component of a blood clot. The shear modulus of a fibrin network can easily exceed 1000 Pa despite the fact that the material contains more than 99% water. They also show a high degree of reversible strain-hardening, a property that is common in biological networks but unusual in synthetic materials. Despite its importance and relevance to trauma and to numerous diseases (Ex. hemophilia and stroke), the relationship between the properties and the structure of blood clots under mechanical deformation remains unknown. We use rheology with in-situ structural probes (neutron scattering, light scattering and birefringence) to directly examine these materials as they are being deformed. Deciphering the origin of these properties will also allow us to emulate them in synthetic analogs such as biomaterials and scaffolds for tissue engineering.

Strain hardening response of a fibrin clot compared to the linear behavior of the synthetic network polyacrylamide. Also shown are the SANS profiles of a fibrin clot at rest and when it is deformed by simple shear.

Novel Matrices for Electrophoretic Separations

We are also using a novel approach to intelligently design efficient matrices for electrophoretic separations of charged particles. Electrophoresis, the motion of charged particles due to an externally applied electric field, is commonly used to separate biomolecules from complex mixtures (Ex. plasma). The efficiency of this separation is essential to the development of new techniques for the early diagnosis of diseases like cancer as well as possible genetic disorders. In order to have an efficient separation, an uncharged polymeric sieving matrix is typically placed in the electrolyte. A variety of ordered and disordered polymer networks have been used to perform these separations with various levels of success. In this project we use a combination of neutron, x-ray and light scattering to probe the structure of the polyelectrolytes (Ex. proteins or DNA) during electrophoretic transport. This characterization allows us to correlate the conformation of the migrating molecules to the properties of the sieving matrix and ultimately to the efficiency of the separation (speed and resolution). More importantly, this knowledge will improve the design of novel separation matrices.

Selected Recent Publications

• Newbloom, G.M., Weigandt, K.M., Pozzo, D.C. Electrical, Mechanical, and Structural Characterization of Self-Assembly in Poly(3-hexylthiophene) Organogel Networks. Marcromolecules 2012: 45(8): pp. 3452-3462.
• Larson-Smith, K., Jackson, A., Pozzo, D.C. SANS and SAXS Analysis of Charged Nanoparticle Adsorption at Oil-Water Interfaces. Langmuir 2012, 28(5): pp. 2493-2501.
• Richards, J.J., Weigandt, K.M., Pozzo, D.C. Aqueous dispersions of colloidal poly(3-hexylthiophene) gel particles with high internal porosity. Journal of Colloid and Interface Science 2011, 364(2): pp. 341-350.
• Pai, S.S., Hammouda, B., Hong, K.L., Pozzo, D.C., Przybycien, T.M., Tilton, R.D. The Conformation of the Poly(ethylene glycol) Chain in Mono-PEGylated Lysozyme and Mono-PEGylated Human Growth Hormone. Bioconjugate Chemistry 2011, 22(11): pp. 2317-2323.
• Porcar, L., Pozzo, D., Langenbucher, G., Moyer, J., Butler, P.D. Rheo-small-angle neutron scattering at the National Institute of Standards and Technology Center for Neutron Research. Review of Scientific Instruments 2011, 82(8).
• Newsbloom, G.M., Kim, F.S., Jenekhe, S.A., Pozzo, D.C. Mesoscale Morphology and Charge Transport in Colloidal Networks of Poly(3-hexylthiophene). Macromolecules 2011, 44(10): pp. 3801-3809.
• Ospinal-Jimenez, M., Pozzo, D.C. Structural Analysis of Protein Complexes with Sodium Alkyl Sulfates by Small-Angel Scattering and Polyacrylamide Gel Electrophoresis. Langmuir 2011, 27(3): pp. 928-935.
• Larson-Smith, K., Pozzo, D.C. Scalable synthesis of self-assembling nanoparticle clusters based on controlled steric interactions. Soft Matter 2011, 7(11): pp. 5339-5347.
• Weigandt, K.M., Porcar, L., Pozzo, D.C. In situ neutron scattering study of structural transitions in fibrin networks under shear deformation. Soft Matter 2011, 7(21): pp. 9992-10000.
• Larson-Smith, K., Jackson, A., Pozzo, D.C. Small angle scattering model for Pickering emulsions and raspberry particles. Journal of Colloid and Interface Science 2010, 343(1): pp. 36-41