The addition of small amounts of clay platelet filler to a polymer matrix greatly enhances many chemical and mechanical material properties of the matrix polymer. This well-developed area of materials science and engineering is producing new materials in diverse areas such as engineering thermoplastics and robust polymer-based batteries. Our interest in nanocomposites is to produce strong, robust materials using biopolymers as the matrix material and using assembled, fibrillar peptide nanostructures as the reinforcement phase.. Strong materials can then be produced with inherent bioproperties (biocompatibility, biodegradability, antimicrobial) due to the completely biomolecular nature of the material.

STAFF
Grad Students
Rohan Hule
Post Docs and Graduates
Dr. Vahik Krikorian
Dr. Hasna Ramay

PUBLICATIONS

1. Hule, R. A.; Pochan, D. J. "Polymer Nanocomposites for Biomedical Applications", MRS Bulletin, 2007, 32, 354-358

2. Rohan Hule and Darrin Pochan"Polypeptide-Based Layered Silicate Nanocomposite: Effect of Poly-l-lysine Secondary Structure on the Physical Properties of the Hybrid" , Journal of Polymer Science, Polymer Physics, 2007, 45, 239-252.

3. Krikorian, V.; Pochan, D.J. "Crystallization Behavior of Poly(l-lactic acid) Nanocomposites: Nucleation and Growth Probed by Infrared Spectroscopy", Macromolecules, 2005, 38, 6520 -6527.

4. Krikorian, V.; Pochan, D.J.* "Unusual Crystallization Behavior of Organoclay Reinforced Poly (L-lactic acid) Nanocomposites", Macromolecules, 2004,37, 6480-6491

5. Krikorian, V.; Pochan, D.J.* "Poly(L-lactic acid)/Layered Silicate Nanocomposite: Fabrication, Characterization and Properties" Chemistry of Materials, 2003, 15, 4317-4324

6. Krikorian, V.; Nowak, A.P.; Deming, T.J.; Kurian, M.; Galvin, M.E.; Pochan, D.J. "Polypeptide-based Nanocomposite: Structure and Properties of Poly(L-lysine)/Na+-Montmorillonite" J. Polym. Sci., Polym. Phys.,2002, 40, 2579-2586.

In order to directly observe the effects of complicated environments on polymer crystallization, we solution grow and characterize single crystals of the polymer used in nanocomposites and responsive hydrogel formation and the oligopeptides used in responsive hydrogel formation. Only by characterizing the single crystal structure of the different molecules can one begin to elucidate the effects of more complicated phases (bulk state, thin films) and mixtures (nanocomposite formation) on the crystallization of the biomolecules. The crystallinity, both extent and morphology of, plays a significant role in the ultimate material properties of the systems studied.

STAFF

Students
Honggang Cui
Kelly Hales
Vahik Krikorian
Matthew Lamm
Bulent Ozbas
Lisa Pakstis
Tuna Yucel
Rohan Hule

Post Docs
Zhibin Li

COLLABORATORS

Prof. Tim Deming, Department of Bioengineering, UCLA

Prof. Joel Schneider, Chemistry and Biochemistry, University of Delaware

Exploratory Project - Silk-like biopolymers are being studied as directed self-assembly agents for mixtures with magnetic materials. The self-assembly behavior of the polypepetides causes the directly assembly of the magnetic materials to produce nanocomposites with desired superlattice structure and consequent magnetic properties. The synthetic proteins are silk-like in sequence and the magnetic nanoparticles are currently based on gadolinium and dysprosium.

COLLABORATORS

Prof. Regina Valluzzi

Prof. Dave Kaplan, Tufts University

Amphiphilic block copolypeptides are designed with desired charge character and secondary structure in order to self-assemble in aqueous solution. The final material formed is a dilute but rigid hydrogel (rigid gels are formed down to ~0.5 wt% polypeptide) with several important innate properties such as both nanoscale and microscale porosity (important for potential tissue engineering applications), shear thinning rheological behavior (easily processed into a desired geometry) with a quickly recovering modulus on cessation of shear, and mechanical properties (shear moduli) that are dependent on molecular secondary structure. New designs take advantage of the peptidic chemistry of the assemblers to build in specific biofunctionality (cell binding sites, growth factors) in the hydrogels.

STAFF

Students
Honggang Cui
Kelly Hales
Vahik Krikorian
Matthew Lamm
Bulent Ozbas
Lisa Pakstis
Tuna Yucel
Rohan Hule

Post Docs
Zhibin Li

COLLABORATORS

Prof. Tim Deming, Department of Bioengineering, UCLA

PUBLICATIONS

Pakstis, L.; Nowak, A.P.; Deming, T.J.; Pochan, D.J.* "The Effect of Chemistry and Morphology on the Biofunctionality of Self-Assembling Diblock Copolypeptide Hydrogels" Biomacromolecules, 2004, 5, 312-318.

Nowak, A.P.; Breedveld, V.; Pakstis, L.; Pine, D.J.; Pochan, D.J.; Deming, T.J. "Rapid Recovering Hydrogel Scaffolds From Self-Assembling Diblock Copolypeptide Amphiphiles" Nature, 2002, 417, 424 - 428

Pochan, D.J.; Pakstis, L.; Ozbas, B.; Nowak, A.K.; Deming, T.J. "SANS and cryoTEM Study of Self-Assembled Diblock Copolypeptide Hydrogels with Rich Nano- Through Microscale Morphology." Macromolecules, 2002, 35, 5358-5360.

This interdisciplinary project involves polymer chemistry, surface science, inorganic/organic cocrystallization, rheology, and material morphology characterization. The research approach involves the systematic ordering, in solution and on substrates, of crosslinked assemblies of copolymers, as robust, nanoscale building blocks having complex structure and composition. These assemblies are being studied as potentially leading to a diverse set of technologies such as read-write memory arrays and well-defined substrates for controlled nucleation and growth of inorganic and biomolecular crystals. The morphology of individual polymer nanoparticles and final hybrid assemblies and the assembly process are the primary focus at UD.

COLLABORATORS

Washington University at St. Louis

CMU

Michigan State

IBM

PUBLICATIONS

Pochan, D.J.*; Chen, Z.; Cui, H.; Hales, K.; Qi, K.; Wooley, K.L. "Toroidal Triblock Copolymer Assemblies: Advancing the complexity of bioinspired materials," submitted to Science, under review

Oligopeptides are designed to intramolecularly fold in response to a desired environmental cue. After folding, self-assembly into a desired structure/material occurs. Importantly, by linking peptide folding with self-assembly , material formation is completely reversible providing for materials with properties responsive to the environment surrounding them. This interdisciplinary work involves peptide design through materials characterization. The first examples of responsive materials are extremely dilute but rigid hydrogels completely reversible with pH and temperature.

STAFF

Students
Honggang Cui
Kelly Hales
Vahik Krikorian
Matthew Lamm
Bulent Ozbas
Lisa Pakstis
Tuna Yucel
Rohan Hule

Post Docs
Zhibin Li

COLLABORATORS

Prof. Joel Schneider, Chemistry and Biochemistry, University of Delaware

PUBLICATIONS

Ozbas, B.; Kretsinger, J.; Rajagopal, K.; Schneider, J.P.*; Pochan, D.J.* "Salt-Triggered Peptide Folding and Consequent Self-Assembly into Hydrogels with Tunable Modulus," Macromolecules, 2004, in press.

Schneider, J.P.*; Pochan, D.J.*; Ozbas, B.; Rajagopal, K.; Pakstis, L.M. ; Gill, J. "Responsive Hydrogels From the Intramolecular Folding and Self-Assembly of a Designed Peptide" JACS, 2002, 124, 15030-15037

Pochan, D.J.*; Schneider, J.S.*; Kretsinger, J.; Ozbas, B.; Rajagopal, K.; Haines, L. " Thermally Reversible Hydrogels via Intramolecular Folding and Consequent Self-Assembly of a de Novo Designed Peptide" JACS, 2003, 125, 11802-11803.

Amphiphilic block copolypeptides are designed with PEGylated, nonionic hydrophilic blocks and hydrophobic blocks with varying secondary structure. These molecules are robust membrane and micelle formers in aqueous solution. Molecular parameters (e.g. relative block length, block secondary structure) are chosen in an effort to design a priori a desired assembly shape and size. These designed assemblies hold promise in the areas of drug and cell delivery.

STAFF

Students
Honggang Cui
Kelly Hales
Vahik Krikorian
Matthew Lamm
Bulent Ozbas
Lisa Pakstis
Tuna Yucel
Rohan Hule

Post Docs
Zhibin Li

COLLABORATORS
Prof. Tim Deming, Department of Bioengineering, UCLA

PUBLICATIONS

Bellomo, E.G.; Wyrsta, M.D.; Pakstis, L.; Pochan, D.J.; Deming, T.J.*, "Stimuli Responsive Polypeptide Vesicles via Conformation Specific Assembly", Nature Materials, 2004, 3, 244-248.