Sachin Shanbhag

Bio: Sachin Shanbhag is an academic researcher from Florida State University. The author has contributed to research in topics: Viscoelasticity & Physics. The author has an hindex of 22, co-authored 67 publications receiving 1572 citations. Previous affiliations of Sachin Shanbhag include University of Michigan & Florida A&M University – Florida State University College of Engineering.

Primitive Path Networks Generated by Annealing and Geometrical Methods: Insights into Differences

Abstract: Existing methods to obtain the primitive path network for monodisperse, linear polymers in the molten state are critically compared. A connection is established between the original “annealing” and newer geometrical approaches. A discrepancy of about 15% is observed in the mean primitive path length obtained by these methods for well-entangled polymers. This deviation is attributed to disentanglement that occurs during annealing. A number of well-equilibrated polymeric systems and some toy-configurations (rings) were studied to estimate the relative contributions of slip and constraint release by end-looping to the observed disentanglement. We found that about half (≈ 7.7%) of the discrepancy persists for ring polymers in which end-looping is not possible, and may be attributed to slip alone. It is argued that the characteristics of the network obtained by annealing become practically equivalent to those obtained by geometrical methods in the asymptotic limit of small chain diameter and rapid quenching.

A hierarchical algorithm for predicting the linear viscoelastic properties of polymer melts with long-chain branching

Abstract: The “hierarchical model” proposed earlier [Larson in Macromolecules 34:4556–4571, 2001] is herein modified by inclusion of early time fluctuations and other refinements drawn from the theories of Milner and McLeish for more quantitative prediction. The hierarchical model predictions are then compared with experimental linear viscoelastic data of well-defined long chain branched 1,4-polybutadienes and 1,4-polyisoprenes using a single set of parameter values for each polymer, which are obtained from experimental data for monodisperse linear and star polymers. For a wide range of monodisperse branched polymer melts, the predictions of the hierarchical model for monodisperse melts are very similar to those of the Milner–McLeish theories, and agree well with experimental data for many, but not all, of the branched polymer samples. Since the modified hierarchical model accounts for arbitrary polydispersity in molecular weight and branching distributions, which is not accounted for in the Milner–McLeish theories, the hierarchical algorithm is a promising one for predicting the relaxation of general mixtures of branched polymers.

Spontaneous transformation of CdTe nanoparticles into angled Te nanocrystals: from particles and rods to checkmarks, X-marks, and other unusual shapes.

Abstract: CdTe nanoparticles spontaneously transform into the branched Te nanocrystals with the unique, highly anisotropic shape of checkmarks after partial removal of the stabilizers of l-cysteine. The Te checkmarks are made in a relatively high yield and uniformity; the length of the arms is ca. 150 nm, whereas the angle between the arms is 74°. Subsequent growth of the particle yields mothlike nanocrystals retaining geometrical anisotropy. Unlike the previous synthesis methods of branched nanocrystals, they are formed via a merger of individual rod-shaped crystallites. High-energy crystal faces on their apexes act as the sticky points causing the particles to join in the ends. This is the first demonstration of spontaneous transformation of binary semiconductor particles into highly anisotropic nanocolloids in an angled conformation. The end reactivity of starting Te rods can be used both for bottom-up fabrication of nanoscale electronics and relatively safe and nontoxic method of synthesis of Te-based optical a...

Inverted colloidal crystals as three-dimensional microenvironments for cellular co-cultures

Abstract: Cellular scaffolds made on the basis of inverted colloidal crystals (ICC) provide a unique system for investigation of cell–cell interactions and their mathematical description due to highly controllable and ordered 3D geometry. Here, we describe three new steps in the development of ICC cell scaffolds. First, it was demonstrated that layer-by-layer (LBL) assembly with clay/PDDA multilayers can be used to modify the surface of ICC scaffolds and to enhance cell adhesion. Second, a complex cellular system made from adherent and non-adherent cells co-existing was created. Third, the movement of non-adherent cells inside the scaffold was simulated. It was found that floating cells are partially entrapped in spherical chambers and spend most of their time in the close vicinity of the matrix and cells adhering to the walls of the ICC. Using this approach one can efficiently simulate differentiation niches for different components of hematopoietic systems, such as T-, B- and stem cells.

On the origin of a permanent dipole moment in nanocrystals with a cubic crystal lattice: effects of truncation, stabilizers, and medium for CdS tetrahedral homologues.

Abstract: A large anomalous dipole moment has previously been reported for nanocrystals with a cubic crystal lattice. By considering truncations of a regular tetrahedral CdS nanocrystal, the hypothesis that shape asymmetry is responsible for the observed dipole moment was tested and verified. The location and degree of the truncations were systematically varied, and corresponding dipole moments were calculated by using a PM3 semiempirical quantum mechanical algorithm. The calculated dipole moment of 50−100 D is in good agreement with a variety of experimental data. This approach also affords simple evaluation of the potential effect of the media for aqueous dispersions of nanocrystals. The substitution of the truncated corner(s) by molecules of H2O typically results in a substantial increase of the dipole moment, and often, in the reversal of its direction. The molecular modeling approach presented here is suitable for detailed theoretical studies of the dipole moments of II−VI and other nanoparticles and interpart...

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Anisotropy of building blocks and their assembly into complex structures

Abstract: A revolution in novel nanoparticles and colloidal building blocks has been enabled by recent breakthroughs in particle synthesis These new particles are poised to become the ‘atoms’ and ‘molecules’ of tomorrow’s materials if they can be successfully assembled into useful structures Here, we discuss the recent progress made in the synthesis of nanocrystals and colloidal particles and draw analogies between these new particulate building blocks and better-studied molecules and supramolecular objects We argue for a conceptual framework for these new building blocks based on anisotropy attributes and discuss the prognosis for future progress in exploiting anisotropy for materials design and assembly

Biomedical Applications of Layer‐by‐Layer Assembly: From Biomimetics to Tissue Engineering

Abstract: The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer-by-layer assembly method introduced by Decher and co-workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials’ structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer-by-layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer-by-layer assembly are introduced. The applications of layer-bylayer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer-by-layer assembly are also discussed.

Three-dimensional cell culture matrices: state of the art.

Abstract: Traditional methods of cell growth and manipulation on 2-dimensional (2D) surfaces have been shown to be insufficient for new challenges of cell biology and biochemistry, as well as in pharmaceutical assays. Advances in materials chemistry, materials fabrication and processing technologies, and developmental biology have led to the design of 3D cell culture matrices that better represent the geometry, chemistry, and signaling environment of natural extracellular matrix. In this review, we present the status of state-of-the-art 3D cell-growth techniques and scaffolds and analyze them from the perspective of materials properties, manufacturing, and functionality. Particular emphasis was placed on tissue engineering and in vitro modeling of human organs, where we see exceptionally strong potential for 3D scaffolds and cell-growth methods. We also outline key challenges in this field and most likely directions for future development of 3D cell culture over the period of 5-10 years.