Bio-Inspired Composite Single Crystals: From Structural Evolution to Mechanical Characterization (Funded by Materials World Network DMR/NSF)
In collaboration with Meldrum Group (University of Leeds, U.K.), Armes Group (University of Sheffield, U.K.), Baker Group (Cornell)
This research aims to develop a unified understanding of the formation, structure, and mechanical properties of synthetic and biologic single crystal composites. The Materials World Network team with members from Cornell University (supported by the Division for Materials Research), Lawrence Berkeley National Labs, and the UK (Universities of Leeds and Sheffield, supported by the EPSRC) offers a rare synergy of expertise in crystal growth, biomineralization, materials synthesis, polymer and colloid synthesis, mechanical properties, and materials characterization. Many natural systems produce elaborate composites in which fragile mineral single crystals and soft polymers are combined to create materials with superior mechanical properties. Such composites are typically understood and modeled in terms of homogeneous ideal mineral crystals embedded in a host organic matrix. However, the mineral single crystals are themselves composites in which a variety of organic and inorganic materials are occluded. Very little is known about how these single crystal composites form or their extraordinary properties. The research goals of this international collaboration are to: (1) Characterize single crystal biominerals and determine how their design leads to superior mechanical properties; (2) Translate these design strategies to the synthesis of calcite crystals occluding small molecules, structurally and chemically well-defined polymers and particles, and compliant and stiff frameworks, and evaluate the growth mechanisms involved; (3) Characterize and model the structural and mechanical properties of the composite crystals to elucidate synthesis-structure-function relationships; and (4) Begin to apply the understanding gained to generate novel composite materials. Just as the inspiration for this work comes from biological systems, the insights gained can be applied to better understanding the biological systems themselves.
The agarose gel network visualized inside of a single crystal of calcite using annular dark field scanning transmission electron microscopy (ADF-STEM) tomography.
Controlling Structure Formation Pathways in Functional Bio-Hybrid Nanomaterials (Funded by DOE/BES)
Collaboration with U. Wiesner
This project aims to understand the structure formation pathways in organic-inorganic hybrid materials in which information transfer from the organic into the inorganic phase is critical to directing the assembly of the composites. Self-assembly of silica nanomaterials directed by small molar mass surfactants is the simplest system of study, both in terms of the organic, as well as the amorphous, inorganic phase. The second system uses synthetic block copolymers to direct the assembly of amorphous calcium phosphate hybrids. The structural complexity of the organic structure-directing agents, as well as the inorganic phase is enhanced over the first system, resulting in an increase in the complexity of the expected chemical pathways. Finally, we are using synthetic/peptide block copolymers to direct the formation of crystalline calcium phosphate bio-hybrids. In this system, we are looking at the effect of peptide sequence, i.e. a significantly increased information transfer from the organic phase, on the crystallization of the calcium phosphate phase. In all three cases, controlling interactions at the interfaces of organic and inorganic materials and elucidating assembly pathways is a central focus. Efforts include synthesis of all organic/inorganic precursors and their composites, as well as in-depth characterization of local, global, and where possible interface structure, of assembly intermediates and final products to elucidate governing principles for structure/shape control in the materials synthesis. When successful, results will provide general guidelines and methodologies for the controlled synthesis of hybrid nanomaterials with increasing complexity offering enormous scientific and technological promise, in areas ranging from energy conversion and storage to drug delivery and bone repair.
Crystalline and Amorphous Nanomaterials in Breast Cancer Bone Metastasis (Funded by NCI/NIH)
Collaboration with Claudia Fischbach-Teschl (BME)
Metastatic bone disease is a frequent cause of morbidity in patients with advanced breast cancer, and the physicochemical characteristics of bone may be critical to this condition. At bone metastatic sites, breast cancer cells interact closely with the biomineralized bone matrix, a composite structure of collagen fibers reinforced with nano-scale crystals of hydroxyapatite (Ca10(PO4)6(OH)2). The nanostructure of the biogenic hydroxyapatite (HA) crystals (i.e., crystallinity, chemical composition, size, and aspect ratio) play an important role in determining the biological and physicochemical characteristics of the particles, and may vary as a function of bone age, location, and disease state. It may be possible that these intrinsic differences impact malignant progression and bone degradation (osteolysis) in breast cancer patients, however, it remains unclear which factors are most important. This lack of understanding is partly due to a paucity of pathologically relevant culture systems to study changes in tumor cell behavior as a function of varying HA nanoscale properties. Therefore, we sought to utilize synthetically prepared HA nanoparticles to determine the impact of particle size and crystallinity on mammary cancer cell activity. The long-term goal of this SEED project is to elucidate the functional relationships between the nano-scale characteristics of HA, mammary tumor cell behavior, and osteolytic bone metastasis, potentially establishing a new paradigm for the induction and progression of tumor-bone interactions during metastatic breast cancer.
Understanding and Controlling the Formation of Hybrid Organic/Inorganic Materials (Funded by CCMR Seed)
In collaboration with Kourkoutis Group (AEP, Cornell) and Wiesner Group (MSE, Cornell)
Hybrid organic/inorganic materials, nano-composites with organic and inorganic components intimately mixed, have attracted great interest due to their potential in a range of applications including catalysis, energy storage and conversion, sensing, smart membranes and nanomedicine. Understanding and controlling the formation pathways of these hybrid materials is the central goal of this Seed, which will ultimately allow us to engineer new hybrids with tailored properties. Combining the expertise of hybrid organic/inorganic materials’ synthesis (Estroff, Wiesner) with that of cryo-electron microscopy (Kourkoutis), we will capture the initial stages of formation of hybrid nanostructures such as functional mesoporous silica nanoparticles that can be tuned from single pore nanometer-scale rings to silica solids exhibiting exceptionally large specific surface areas due to their ordered sub-10 nm pores (Fig. 1). Revealing the materials' formation pathways is a critical step in controlling their synthesis and in creating new structures by design. Similarly, understanding the early stages of biomineralization, the process by which biological organisms form organic/mineral composites, will help design strategies and synthetic methods that mimic nature’s ability to form materials with tailored properties, such as the exceptional mechanical properties of sea urchin skeletal parts and mollusk shells. Cryo-scanning transmission electron microscopy will allow us to simultaneously image the inorganic and the organic components in hybrid materials, stabilized by snap-freezing, and will give us the resolution to gain insights into the interactions between these two components at the initial stages of formation which is key to understanding and ultimately controlling these processes in synthetic systems. For hybrid structures at latter stages of development where the sample thickness limits the imaging resolution, the Seed will combine cryo-focused ion beam milling with cryo-scanning transmission electron microscopy to peer inside these hybrid materials, producing 3D images of their structure and chemistry. Understanding the stages of formation of these nanostructures will allow us to create materials analogous to many of the complex structures that exist in nature and entirely new materials for a wide range of applications from energy storage to therapeutics.