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Li X.,Clemson University | Murthy N.S.,New Jersey Center for Biomaterials | Latour R.A.,Clemson University
Macromolecules | Year: 2011

A new empirical sampling method termed "temperature intervals with global exchange of replicas and reduced radii" (TIGER3) is presented and demonstrated to efficiently equilibrate entangled long-chain molecular systems such as amorphous polymers. The TIGER3 algorithm is a replica exchange method in which simulations are run in parallel over a range of temperature levels at and above a designated baseline temperature. The replicas sampled at temperature levels above the baseline are run through a series of cycles with each cycle containing four stages: heating, sampling, quenching, and temperature level reassignment. The method allows chain segments to pass through one another at elevated temperature levels during the sampling stage by reducing the van der Waals radii of the atoms, thus eliminating chain entanglement problems. Atomic radii are then returned to their regular values and re-equilibrated at elevated temperature prior to quenching to the baseline temperature. Following quenching, replicas are compared using a Metropolis Monte Carlo exchange process for the construction of an approximate Boltzmann-weighted ensemble of states and then reassigned to the elevated temperature levels for additional sampling. Further system equilibration is performed by periodic implementation of the previously developed TIGER2 algorithm between cycles of TIGER3, which applies thermal cycling without radii reduction. When coupled with a coarse-grained modeling approach, the combined TIGER2/TIGER3 algorithm yields fast equilibration of bulk-phase models of amorphous polymer, even for polymers with complex, highly branched structures. The developed method was tested by modeling the polyethylene melt. The calculated properties of chain conformation and chain segment packing agreed well with published data. The method was also applied to generate equilibrated structural models of three increasingly complex amorphous polymer systems: poly(methyl methacrylate), poly(butyl methacrylate), and DTB-succinate copolymer. Calculated glass transition temperature (Tg) and structural parameter profile (S(q)) for each resulting polymer model were found to be in close agreement with experimental Tg values and structural measurements obtained by X-ray diffraction, thus validating that the developed methods provide realistic models of amorphous polymer structure. © 2011 American Chemical Society.

Murthy N.S.,New Jersey Center for Biomaterials | Wang W.,University of Vermont | Kohn J.,New Jersey Center for Biomaterials
Polymer | Year: 2010

Hydration- and temperature-induced microphase separations were investigated by simultaneous small- and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry (DSC) in a family of copolymers in which hydrophilic poly(ethylene glycol) (PEG) blocks are inserted randomly into a hydrophobic polymer made of either desaminotyrosyl-tyrosine ethyl ester (DTE) or iodinated I2DTE segments. Iodination of the tyrosine rings in I2DTE increased the X-ray contrast between the hydrophobic and hydrophilic segments in addition to facilitating the study of the effect of iodination on microphase separation. The formation of phase-separated, hydrated PEG domains is of considerable significance as it profoundly affects the polymer properties. The copolymers of DTE (or I2DTE) and PEG are a useful model system, and the findings presented here may be applicable to other PEG-containing random copolymers. In copolymers of PEG and DTE and I2DTE, the presence of PEG depressed the glass transition temperature (Tg) of the copolymer relative to the homopolymer, poly(DTE carbonate), and the DTE/I2DTE segments hindered the crystallization of the PEG segments. In the dry state, at large PEG fractions (>70 vol%), the PEG domains self-assembled into an ordered structure with 14-18 nm distance between the domains. These domains gave rise to a SAXS peak at all temperatures in the iodinated polymers, but only above the Tg in non-iodinated polymers, due to the unexpected contrast-match between the crystalline PEG domains and the glassy DTE segments. Irrespective of whether PEG was crystalline or not, immersion of these copolymers in water resulted in the formation of hydrated PEG domains that were 10-20 nm apart. Since both water and the polymer chains must be mobile for the phase separation to occur, the PEG domains disappeared when the water froze, and reappeared as the ice began to melt. This transformation was reversible, and showed hysteresis as did the melting of ice and freezing of the water incorporated into the polymer. PEG-water complexes and PEG-water eutectics were observed in WAXS and DSC scans, respectively. © 2010 Elsevier Ltd.

Lewitus D.Y.,New Jersey Center for Biomaterials | Landers J.,Rutgers University | Branch J.R.,New Jersey Center for Biomaterials | Smith K.L.,New York State Department of Health | And 3 more authors.
Advanced Functional Materials | Year: 2011

A novel approach for producing carbon nanotube fibers (CNF) composed with the polysaccharide agarose is reported. Current attempts to make CNFs require the use of a polymer or precipitating agent in the coagulating bath that may have negative effects in biomedical applications. It is shown that, by taking advantage of the gelation properties of agarose, one can substitute the bath with distilled water or ethanol and, hence, reduce the complexity associated with alternating the bath components or the use of organic solvents. It is also demonstrated that these CNF can be chemically functionalized to express biological moieties through available free hydroxyl groups in agarose. Agarose CNF are not only conductive and nontoxic; in addition, their functionalization is shown to facilitate cell attachment and response both in vitro and in vivo. Our findings suggest that agarose/CNT hybrid materials are excellent candidates for applications involving neural tissue engineering and biointerfacing with the nervous system. A novel approach for producing carbon nanotube fibers (CNF) composed with the polysaccharide agarose is reported. The TOC image shows representative immunohistochemical images of rat brain slices after insertion of CNT/agarose fiber-electrodes. Cell types shown are microglia (blue), astrocytes (orange), and neurons (green). A is a control electrode and B is an electrode functionalized with laminin, a neural extracellular matrix protein. Close inspection and quantification of the cell response reveals favorable tissue reaction to the laminin tethered electrode. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zhang Z.,New Jersey Center for Biomaterials | Tsai P.-C.,Rutgers University | Ramezanli T.,Rutgers University | Michniak-Kohn B.B.,New Jersey Center for Biomaterials | Michniak-Kohn B.B.,Rutgers University
Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology | Year: 2013

Human skin not only functions as a permeation barrier (mainly because of the stratum corneum layer) but also provides a unique delivery pathway for therapeutic and other active agents. These compounds penetrate via intercellular, intracellular, and transappendageal routes, resulting in topical delivery (into skin strata) and transdermal delivery (to subcutaneous tissues and into the systemic circulation). Passive and active permeation enhancement methods have been widely applied to increase the cutaneous penetration. The pathology, pathogenesis, and topical treatment approaches of dermatological diseases, such as psoriasis, contact dermatitis, and skin cancer, are then discussed. Recent literature has demonstrated that nanoparticles-based topical delivery systems can be successful in treating these skin conditions. The studies are reviewed starting with the nanoparticles based on natural polymers especially chitosan, followed by those made of synthetic, degradable (aliphatic polyesters), and nondegradable (polyacrylates) polymers; emphasis is given to nanospheres made of polymers derived from naturally occurring metabolites, the tyrosine-derived nanospheres (TyroSpheres™). In summary, the nanoparticles-based topical delivery systems combine the advantages of both the nanosized drug carriers and the topical approach, and are promising for the treatment of skin diseases. For the perspectives, the penetration of ultra-small nanoparticles (size smaller than 40 nm) into skin strata, the targeted delivery of the encapsulated drugs to hair follicle stem cells, and the combination of nanoparticles and microneedle array technologies for special applications such as vaccine delivery are discussed. © 2013 Wiley Periodicals, Inc.

Lewitus D.Y.,New Jersey Center for Biomaterials | Smith K.L.,New York State Department of Health | Shain W.,New York State Department of Health | Bolikal D.,New Jersey Center for Biomaterials | Kohn J.,New Jersey Center for Biomaterials
Biomaterials | Year: 2011

We have recently reported on an ultrafast degrading tyrosine-derived terpolymer that degrades and resorbs within hours, and is suitable for use in cortical neural prosthetic applications. Here we further characterize this polymer, and describe a new tyrosine-derived fast degrading terpolymer in which the poly(ethylene glycol) (PEG) is replaced by poly(trimethylene carbonate) (PTMC). This PTMC containing terpolymer showed similar degradation characteristics but its resorption was negligible in the same period. Thus, changes in the polymer chemistry allowed for the development of two ultrafast degrading polymers with distinct difference in resorption properties. The in vivo tissue response to both polymers used as intraparenchymal cortical devices was compared to poly(lactic-co-glycolic acid) (PLGA). Slow resorbing, indwelling implant resulted in continuous glial activation and loss of neural tissue. In contrast, the fast degrading tyrosine-derived terpolymer that is also fast resorbing, significantly reduced both the glial response in the implantation site and the neuronal exclusion zone. Such polymers allow for brain tissue recovery, thus render them suitable for neural interfacing applications. © 2011 Elsevier Ltd.

Kashyap H.K.,University of Iowa | Santos C.S.,Rutgers University | Annapureddy H.V.R.,University of Iowa | Murthy N.S.,New Jersey Center for Biomaterials | And 2 more authors.
Faraday Discussions | Year: 2012

In this article we determine the temperature-dependent structure of the tetradecyltrihexylphosphonium bis(trifluoromethylsulfonyl)amide ionic liquid using a combination of X-ray scattering and molecular dynamics simulations. As in many other room-temperature ionic liquids three characteristic intermolecular peaks can be detected in the structure function S(q). A prepeak or first sharp diffraction peak is observed at about q = 0.42 Å -1. Long range anion-anion correlations are the most important contributors to this peak. In all systems we have studied to date, this prepeak is a signature of solvation asymmetry. The peak in S(q) near q = 0.75 Å -1 is the signature of ionic alternation and arises from the charge ordered separation of ions of the same charge. The most intense diffraction peak near q = 1.37 Å -1 arises from short-range separation between ions of opposite charge combined with a significant contribution from cationic carbon-carbon interactions, indicating that cationic hydrophobic tails have significant contacts. © 2012 The Royal Society of Chemistry.

Lewis D.R.,Rutgers University | Kamisoglu K.,Rutgers University | York A.W.,New Jersey Center for Biomaterials | Moghe P.V.,Rutgers University
Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology | Year: 2011

Coronary arterial disease, one of the leading causes of adult mortality, is triggered by atherosclerosis. A disease with complex etiology, atherosclerosis results from the progressive long-term combination of atherogenesis, the accumulation of modified lipoproteins within blood vessel walls, along with vascular and systemic inflammatory processes. The management of atherosclerosis is challenged by the localized flare-up of several multipronged signaling interactions between activated monocytes, atherogenic macrophages and inflamed or dysfunctional endothelial cells. A new generation of approaches is now emerging founded on multifocal, targeted therapies that seek to reverse or ameliorate the atheroinflammatory cascade within the vascular intima. This article reviews the various classes and primary examples of bioactive configurations of nanoscale assemblies. Of specific interest are polymer-based or polymer-lipid micellar assemblies designed as multimodal receptor-targeted blockers or drug carriers whose activity can be tuned by variations in polymer hydrophobicity, charge, and architecture. Also reviewed are emerging reports on multifunctional nanoassemblies and nanoparticles for improved circulation and enhanced targeting to atheroinflammatory lesions and atherosclerotic plaques. © 2011 John Wiley and Sons, Inc.

Treiser M.D.,Rutgers University | Yang E.H.,Rutgers University | Gordonov S.,Rutgers University | Cohen D.M.,University of Pennsylvania | And 4 more authors.
Proceedings of the National Academy of Sciences of the United States of America | Year: 2010

Stem cells that adopt distinct lineages cannot be distinguished based on traditional cell shape. This study reports that higher-order variations in cell shape and cytoskeletal organization that occur within hours of stimulation forecast the lineage commitment fates of human mesenchymal stem cells (hMSCs). The unique approach captures numerous early (24 h), quantitative features of actin fluororeporter shapes, intensities, textures, and spatial distributions (collectively termed morphometric descriptors). The large number of descriptors are reduced into "combinations" through which distinct subpopulations of cells featuring unique combinations are identified. We demonstrate that hMSCs cultured on fibronectin-treated glass substrates under environments permissive to bone lineage induction could be readily discerned within the first 24 h from those cultured in basal- or fat-inductive conditions by such cytoskeletal feature groupings. We extend the utility of this approach to forecast osteogenic stem cell lineage fates across a series of synthetic polymeric materials of diverse physico-chemical properties. Within the first 24 h following stem cell seeding, we could successfully "profile" the substrate responsiveness prospectively in terms of the degree of bone versus nonbone predisposition. The morphometric methodology also provided insights into how substrates may modulate the pace of osteogenic lineage specification. Cells on glass substrates deficient in fibronectin showed a similar divergence of lineage fates, but delayed beyond 48 h. In summary, this high-content imaging and single cell modeling approach offers a framework to elucidate and manipulate determinants of stem cell behaviors, as well as to screen stem cell lineage modulating materials and environments.

Li X.,Clemson University | Murthy N.S.,New Jersey Center for Biomaterials | Latour R.A.,Clemson University
Macromolecules | Year: 2012

The effect of hydration on the molecular structure of amorphous poly(d,l-lactic acid) (PDLLA) with 50:50 L-to-D ratio has been studied by combining experiments with molecular simulations. X-ray diffraction measurements revealed significant changes upon hydration in the structure functions of the copolymer. Large changes in the structure functions at ∼10 days of incubation coincided with the large increase in the water uptake from ∼1 to ∼40% and the formation of voids in the film. Computer modeling based on the recently developed TIGER2/TIGER3 mixed sampling scheme was used to interpret these changes by efficiently equilibrating both dry and hydrated models of PDLLA. Realistic models of bulk amorphous PDLLA structure were generated as demonstrated by close agreement between the calculated and the experimental structure functions. These molecular simulations were used to identify the interactions between water and the polymer at the atomic level including the change of positional order between atoms in the polymer due to hydration. Changes in the partial O-O structure functions, about 95% of which were due to water-polymer interactions, were apparent in the radial distribution functions. These changes, and somewhat smaller changes in the C-C and C-O partial structure functions, clearly demonstrated the ability of the model to capture the hydrogen-bonding interactions between water and the polymer, with the probability of water forming hydrogen bonds with the carbonyl oxygen of the ester group being about 4 times higher than with its ether oxygen. © 2012 American Chemical Society.

Hsia H.C.,New Jersey Center for Biomaterials | Nair M.R.,New Jersey Center for Biomaterials | Mintz R.C.,New Jersey Center for Biomaterials | Corbett S.A.,New Jersey Center for Biomaterials
Plastic and Reconstructive Surgery | Year: 2011

Background: The ideal scaffold material should provide immediate capacity to bear mechanical loads and also permit eventual resorption and replacement with native tissue of similar mechanical integrity. Scaffold characteristics such as fiber diameter provide environmental cues that can influence cell function and differentiation. In this study, the impact of fiber diameter of scaffolds constructed from a tyrosine-based bioresorbable polymer on cellular response was investigated. Methods: Electrospun bioresorbable poly(desamino tyrosyl-tyrosine ethyl ester carbonate) scaffolds composed of microfibers or nanofibers were constructed and seeded with human dermal fibroblasts. The impact of fiber diameter on actin cytoskeletal morphology, focal adhesion size, fibronectin matrix assembly, and cell proliferation was evaluated using immunofluorescent microscopy and computer-assisted image analysis. Results: Actin stress fibers were more easily observed in cells on microfiber scaffolds compared with those on nanofiber scaffolds. Cells on nanofiber scaffolds developed smaller focal adhesion complexes compared with those on microfiber scaffolds (p < 0.0001). The temporal patterns of fibronectin matrix assembly were affected by scaffold fiber diameter, with cells on microfiber scaffolds showing a delayed response in dense fibril formation compared with nanofiber scaffolds. Cells on nanofiber scaffolds showed higher proliferation compared with microfiber scaffolds at time points under 1 week (p < 0.01), but by 2 weeks significantly higher cell proliferation was observed on microfiber scaffolds (p < 0.01). Conclusions: The fiber diameter of bioresorbable scaffolds can significantly influence cell response and suggests that the ability of scaffolds to elicit consistent biological responses depends on factors beyond scaffold composition. Such findings have important implications for the design of clinically useful engineered constructs. Copyright © 2011 by the American Society of Plastic Surgeons.

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