Role of molecular interactions on the mechanics of nanocomposites

Nanocomposite materials are well characterized using a variety of advanced microscopy and spectroscopy techniques. In particular, the interfaces in the nanocomposites are often tailored (in engineered composites) and evolved (in biological nanocomposites) to unique molecular characteristics that provide optimized and superior properties to the nanocomposites. In this presentation, we will describe a multiscale mechanics perspective on role of molecular interactions as well as the nano and microstructures on the mechanics of nanocomposites. Specific examples including biological and synthetic nanocomposites will be presented. We have demonstrated a quantitative correlation of energies of molecular interactions albeit nonbonded in the nanocomposites to the overall mechanics and deformation behavior of the nanocomposites. Modeling strategies spanning from ab initio, molecular dynamics to discrete element and finite element methods will be presented in the context of four nanocomposite systems: (1) seashell (nacre), (2) bone, (3) polymer clay nanocomposites and (4) scaffolds for bone tissue engineering. In addition we will illustrate the importance of molecular interactions in behaviors of swelling clays used in polymer clay nanocomposites (Figure 1). The modeling and experimental techniques presented here bridge a significant range of length scales from nano/micro to macroscale using ab-initio, molecular dynamics, discrete element and finite element for modeling; and FTIR and photoacoustic spectroscopy, electron microscopy and nanomechanical testing for experimental investigation. The robust multiscale models presented can be used for a simulation based design of these nanocomposite systems. We report in each of these examples the significant role of proximity of mineral and organic phases on mechanics. The weak nonbonded interactions between organics and minerals; collagen and hydroxyapatite in bone, proteins and aragonite in nacre, nanoclay and polymers in polymer clay nanocomposites, and interactions in various constituents of nanocomposites that make tissue engineering scaffolds are shown to largely impact the overall mechanical behavior of the nanocomposite. These weak interactions, a hallmark of biology, but also useful in synthetic nanocomposites control mechanical behavior of nanocomposites. In the biological examples we evaluate the differences in role of weak non bonded interactions on structural stability vs. mechanics of the structure. For instance, the hydrogen bonding in collagen is important for structural stability of the molecule in bone microstructures but contributes marginally to mechanics. We will provide a summary of results for each of the material systems elucidating the impact of a large number of low energy molecular interactions on the elastic response of the nanocomposite

Remedial Measures to Seepage and Instability Aspect of a Dam Near Bombay

The paper describes the distress caused to a minor earth dam constructed at a high elevation in a mountainous area to conserve water. The distress related to instability of the dam and also due to high percolation underneath the dam coupled with formation of piping. The remedial measures taken to rectify instability and reduce percolation are described in this paper

Nanoclay based composite scaffolds for development of novel humanoid environment

Cancer cells are adept at invading, migrating to and colonizing on an organ away from its origin resulting in metastatic cancer. The process through which cancer cells colonize on a distant organ is known as metastasis. It is estimated that about 90% of the deaths associated with cancer are attributed to metastasis, yet the fundamental mechanisms of cancer metastasis are unknown. Several cancers are known to metastasize to bone. Of these, the most prolific are prostate, breast and colon cancers. Molecular, microstructural and physiological interactions between the metastatic cancer cells and bone microenvironment have been shown to be suggestive of causing tumor formation on bone as a result of a variety of cancers. The natural bone environment is three dimensional, and hierarchical, factors that further control cancer formation. Thus, it is of interest to build 3D models of bone environment that mimic natural bone microenvironment to evaluate the mechanisms and microstructures of the origins of metastasis. Further, the 3D models bridge the gap between 2D substrates and animal experiments that do not capture the human-like behavior accurately. Here we report new bone mimetic nanocomposite scaffolds that are synthesized using a biomineralization process enabled through mineralization of hydroxyapatite inside amino acid modified nanoclay galleries. These nanoclays are built into scaffolds with synthetic and biopolymers to yield scaffolds that mimic mechanics, and biological behavior (such as enabling human mesenchymal stem cells to differentiate) of human bone. These nanocomposite scaffolds also enable the vesicular delivery of minerals to the extra cellular matrix triggering bone mineralization, much like that observed in biological systems. We also developed a sequential cell culture methodology in 3D to provide prostate cancer cells a bone mimicking microenvironment. Human mesenchymal stem cells (MSCs) were first seeded on polycaprolactone (PCL) nanoclay-hydroxyapatite scaffolds. These stem cells differentiated into osteoblastic lineages and this new-bone microenvironment was then seeded with prostate cancer cells. The cellular morphology of cancer growth on this bone environment showed development of tight 3D spheroids or tumoroids. We also report the cytotoxic efficacy of anticancer drug encapsulated polymersome on the 3D cancer models. Results of several assays on cancer growth, cellular differentiations etc. are reported. Overall, the biomimetic scaffold system presented here represents an excellent bone-mimetic environment for a humanoid level study of tumor formation and cancer metastasis to bone. In addition these humanoid models can be effectively used to evaluate drug efficacies and drug delivery agent efficacies

Nature and Properties of Earthquake Energy and Waves and their Contribution to Liquefaction Aspects at Adani Port During 2001 Bhuj Earth Quake

During Bhuj earthquake of 2001, certain distinct phenomenon in coastal saturated granular deposits were observed causing extensive distress to Adani Port facilities. An attempt is made to analyse the root cause by examining nature and properties of earthquake energy, geometry of earth and the origin of energy and propagation of waves, including excess pore water pressure contributed by Pwave. Although pile raft system were less damaged due to liquefaction, the tests showed extensive loss of load capacity. These aspects are presented in this paper

In-silico design of nanocomposite scaffolds for bone regeneration

The accurate prediction of the evolution of mechanical properties of tissue engineering scaffolds to bridge nonunion bone defects is critical for the bone regenerative technologies to become viable in clinical applications. In addition to the scaffold geometry, the scaffold mechanics needs to be tailored to the patient for an effective outcome. In in vivo conditions, the cell seeded scaffolds degrade as the cells seeded on the scaffolds grow, differentiate and regenerate tissue. A fine balance of degradation and “healing” of the living-non-living construct needs to be achieved to fill the defect. In our research group, clay based nanocomposite materials have been used to regenerate bone that has structure and properties identical to human bone. The scaffolds are made of unnatural-aminoacid intercalated clay, in-situ mineralized hydroxyapatite (HAP) in the clay galleries and a degradable polymer polycaprolactone. These scaffolds are shown to mediate mesenchymal stem cell differentiation to osteoblastic lineages. We have developed a novel computational multiscale approach that spans molecular scale to the macroscale. The model incorporates degradation of nanocomposite bone tissue engineering scaffold system and “healing” as the tissue is regenerated. Realistic molecular models of the nanocomposite material system are created using molecular dynamics. Steered molecular dynamics simulations provide the stress-strain response of the material. The response is introduced into microCT image based 3D finite element models of the scaffolds. Damage mechanics based analytical degradation and healing models capture the evolving scaffold mechanics with time. This in silico approach provides the ability to predict the response of implanted scaffolds over time and also tailor the design of nanocomposite biomaterials and scaffolds with targeted properties for bridging nonunion bone defects for personalized medicine. Please click Additional Files below to see the full abstract