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Kristi S. Anseth - One of the best experts on this subject based on the ideXlab platform.

  • three dimensional hmsc motility within peptide functionalized peg based hydrogels of varying adhesivity and Crosslinking Density
    Acta Biomaterialia, 2013
    Co-Authors: Kyle A Kyburz, Kristi S. Anseth
    Abstract:

    Abstract Human mesenchymal stem cell (hMSC) migration and recruitment play a critical role during bone fracture healing. Within the complex three-dimensional (3-D) in vivo microenvironment, hMSC migration is regulated through a myriad of extracellular cues. Here, we use a thiol–ene photopolymerized hydrogel to recapitulate structural and bioactive inputs in a tunable manner to understand their role in regulating 3-D hMSC migration. Specifically, peptide-functionalized poly(ethylene glycol) hydrogels were used to encapsulate hMSC while varying the Crosslinking Density, from 0.18 ± 0.02 to 1.60 ± 0.04 mM, and the adhesive ligand Density, from 0.001 to 1.0 mM. Using live-cell videomicroscopy, migratory cell paths were tracked and fitted to a Persistent Random Walk model. It was shown that hMSC migrating through the lowest Crosslinking Density and highest adhesivity had more sustained polarization, higher migrating speeds (17.6 ± 0.9 μm h −1 ) and higher cell spreading (elliptical form factor = 3.9 ± 0.2). However, manipulation of these material properties did not significantly affect migration persistence. Further, there was a monotonic increase in cell speed and spreading with increasing adhesivity that showed a lack of the biphasic trend seen in 2-D cell migration. Immunohistochemistry showed well-formed actin fibers and β1 integrin staining at the ends of stress fibers. This thiol–ene platform provides a highly tunable substrate to characterize 3-D hMSC migration that can be applied as an implantable cell carrier platform or for the recruitment of endogenous hMSC in vivo .

  • effects of peg hydrogel Crosslinking Density on protein diffusion and encapsulated islet survival and function
    Journal of Biomedical Materials Research Part A, 2009
    Co-Authors: Laney M Weber, Kristi S. Anseth, Christina G Lopez
    Abstract:

    The rational design of immunoprotective hydrogel barriers for transplanting insulin-producing cells requires an understanding of protein diffusion within the hydrogel network and how alterations to the network structure affect protein diffusion. Hydrogels of varying Crosslinking Density were formed via the chain polymerization of dimethacrylated PEG macromers of varying molecular weight, and the diffusion of six model proteins with molecular weights ranging from 5700 to 67,000 g/mol was observed in these hydrogel networks. Protein release profiles were used to estimate diffusion coefficients for each protein/gel system that exhibited Fickian diffusion. Diffusion coefficients were on the order of 10−6–10−7 cm2/s, such that protein diffusion time scales (td = L2/D) from 0.5-mm thick gels vary from 5 min to 24 h. Adult murine islets were encapsulated in PEG hydrogels of varying Crosslinking Density, and islet survival and insulin release was maintained after two weeks of culture in each gel condition. While the total insulin released during a 1 h glucose stimulation period was the same from islets in each sample, increasing hydrogel Crosslinking Density contributed to delays in insulin release from hydrogel samples within the 1 h stimulation period. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009

  • Crosslinking Density influences the morphology of chondrocytes photoencapsulated in peg hydrogels during the application of compressive strain
    Journal of Orthopaedic Research, 2004
    Co-Authors: Stephanie J. Bryant, David A. Lee, Kristi S. Anseth, Dan L. Bader
    Abstract:

    Abstract Chondrocyte deformation, which occurs during mechanical loading, is thought to play an important role in the mechanotransduction pathway. In designing a scaffold that can be gelled in situ for cartilage tissue engineering, an important consideration is the influence of mechanical loading. This study tested the hypothesis that changes in the Crosslinking Density of a hydrogel scaffold influence the morphology of encapsulated chondrocytes in response to an applied load. Chondrocytes were entrapped in photocrosslinkable hydrogel scaffolds based on poly(ethylene glycol) (PEG) with two Crosslinking densities, 0.119 and 0.376 mol/l, with the higher Density having a 11-fold higher compressive modulus. The cell-embedded hydrogels were subjected to static compressive strains between 0% and 20% after 1 and 6 days of culture. Using confocal laser scanning microscopy, chondrocytes in the highly crosslinked gel at day 1 deformed more than gels in the more loosely crosslinked gel. By day 6, this finding was reversed. When single cells within a region were followed, heterogeneities in cell deformation were observed on both a macroscopic and microscopic scale. These heterogeneities were greater in the highly crosslinked gel. These findings demonstrate that different levels of cell deformation and heterogeneity may be obtained by varying the Crosslinking Density in PEG hydrogels.

  • Crosslinking Density influences chondrocyte metabolism in dynamically loaded photocrosslinked poly(ethylene glycol) hydrogels.
    Annals of Biomedical Engineering, 2004
    Co-Authors: Stephanie J. Bryant, Tina T. Chowdhury, David A. Lee, Dan L. Bader, Kristi S. Anseth
    Abstract:

    In approaches to tissue engineer articular cartilage, an important consideration for in situ forming cell carriers is the impact of mechanical loading on the cell composite structure and function. Photopolymerized hydrogel scaffolds based on poly(ethylene glycol) (PEG) may be synthesized with a range of Crosslinking densities and corresponding macroscopic properties. This study tests the hypothesis that changes in the hydrogel Crosslinking Density influences the metabolic response of encapsulated chondrocytes to an applied load. PEG hydrogels were formulated with two Crosslinking densities that resulted in gel compressive moduli ranging from 60 to 670 kPa. When chondrocytes were encapsulated in these PEG gels, an increase in Crosslinking Density resulted in an inhibition in cell proliferation and proteoglycan synthesis. Moreover, when the gels were dynamically loaded for 48 h in unconfined compression with compressive strains oscillating from 0 to 15% at a frequency of 1 Hz, cell proliferation and proteoglycan synthesis were affected in a Crosslinking-Density-dependent manner. Cell proliferation was inhibited in both crosslinked gels, but was greater in the highly crosslinked gel. In contrast, dynamic loading did not influence proteoglycan synthesis in the loosely crosslinked gel, but a marked decrease in proteoglycan production was observed in the highly crosslinked gel. In summary, changes in PEG hydrogel properties greatly affect how chondrocytes respond to an applied dynamic load.

  • the effects of Crosslinking Density on cartilage formation in photocrosslinkable hydrogels
    Biomedical sciences instrumentation, 1999
    Co-Authors: Stephanie J. Bryant, Charles R Nuttelman, Kristi S. Anseth
    Abstract:

    Photoencapsulation of chondrocytes to produce tissue engineered cartilage provides many benefits including rapid polymerization times, the ability to fabricate complex architectures in vivo, and spatial and temporal control during polymerization. Recently, we have examined the cytocompatibility of several photoinitiation schemes and found that low photoinitiator concentrations and light intensities in the ultraviolet and visible range are cytocompatible. In this work, we are currently investigating photocrosslinkable hydrogels based on poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO) as scaffolds for tissue engineering cartilage. In particular, the influence of the network Crosslinking Density, swelling ratio, and chemical composition on the ability of encapsulated chondrocytes to form extracellular matrix is examined. The cartilage produced in these hydrogels will be quantified using biochemical assays that measure DNA content and the amount of sulfated glycosaminoglycans and total collagen in the extracellular matrix. We have demonstrated that chondrocytes encapsulated in a polymer scaffold made from a 20 wt% solution of PEODM/PEO (40 wt% dimethacrylated PEO (MW 3400)/60 wt% PEO (MW 100 K)) form cartilage, and after four weeks the results based on the wet weight of cartilage were approximately 0.03 million cells/mg cartilage, approximately 1.5% glycosaminoglycans and approximately 4.5% total collagen.

William P King - One of the best experts on this subject based on the ideXlab platform.

  • nanoindentation of shape memory polymer networks
    Polymer, 2007
    Co-Authors: Edem Wornyo, Ken Gall, Fuzheng Yang, William P King
    Abstract:

    Abstract This work examines the small-scale deformation and thermally induced recovery behavior of shape memory polymer networks as a function of Crosslinking structure. Copolymer shape memory materials based on diethylene glycol dimethacrylate and polyethylene glycol dimethacrylate with a molecular weight of 550 crosslinkers and a tert-butyl acrylate linear chain monomer were synthesized with varying weight percentages of crosslinker from 0 to 100%. Dynamic mechanical analysis is used to acquire the bulk thermomechanical properties of the polymers, including the glass transition temperature and the elastic modulus over a wide temperature range. Instrumented nanoindentation is used to examine ambient temperature deformation of the polymer networks below their glass transition temperature. The glassy modulus of the networks measured using nanoindentation is relatively constant as a function of Crosslinking Density, and consistent with values extracted from monotonic tensile tests. The ambient temperature hardness of the networks increases with increasing Crosslinking Density, while the dissipated energy during indentation decreases with increasing Crosslinking Density. The changes in hardness correlated with the changes in glass transition but not changes in the rubbery modulus, both of which can scale with a change in crosslink Density. Temperature induced shape recovery of the indentations is studied using atomic force microscopy. For impressions placed at ambient temperature, the indent shape recovery profile shifts to higher temperatures as crosslink Density and glass transition temperature increase.

Xiao Dong Chen - One of the best experts on this subject based on the ideXlab platform.

  • physical properties and loading capacity of starch based microparticles crosslinked with trisodium trimetaphosphate
    Journal of Food Engineering, 2009
    Co-Authors: Bingzheng Li, Lijun Wang, Dong Li, Yu Lung Chiu, Zhongjie Zhang, Xiao Dong Chen
    Abstract:

    Starch-based microparticles were prepared by emulsion Crosslinking method, using trisodium trimetaphosphate (TSTP) as Crosslinking agent. The prepared TSTP-crosslinked starch microparticles (TSMs) were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) technique. SEM pictures showed smooth face and spherical shape for the TSMs. XRD patterns revealed that TSMs were of amorphous structure mostly. This result was confirmed by FTIR spectra. Influence of Crosslinking Density on particle size, swelling degree and loading capacity of TSMs was studied by varying TSTP concentration. It was found that with increasing TSTP concentration from 0.1 to 0.4 g/g, the particle size and loading capacity increased, but swelling degrees showed a bell-shaped dependence on TSTP concentration with maximum values at the concentration of 0.2 g/g in different media. However, the changes of these three aspects became inconspicuous when TSTP concentration increased to 0.4 g/g. It is estimated that the Crosslinking Density had nearly reached its full extent at such concentration. The present investigated TSMs could potentially be applied in dry powder form for food ingredients delivery.

Edem Wornyo - One of the best experts on this subject based on the ideXlab platform.

  • nanoindentation of shape memory polymer networks
    Polymer, 2007
    Co-Authors: Edem Wornyo, Ken Gall, Fuzheng Yang, William P King
    Abstract:

    Abstract This work examines the small-scale deformation and thermally induced recovery behavior of shape memory polymer networks as a function of Crosslinking structure. Copolymer shape memory materials based on diethylene glycol dimethacrylate and polyethylene glycol dimethacrylate with a molecular weight of 550 crosslinkers and a tert-butyl acrylate linear chain monomer were synthesized with varying weight percentages of crosslinker from 0 to 100%. Dynamic mechanical analysis is used to acquire the bulk thermomechanical properties of the polymers, including the glass transition temperature and the elastic modulus over a wide temperature range. Instrumented nanoindentation is used to examine ambient temperature deformation of the polymer networks below their glass transition temperature. The glassy modulus of the networks measured using nanoindentation is relatively constant as a function of Crosslinking Density, and consistent with values extracted from monotonic tensile tests. The ambient temperature hardness of the networks increases with increasing Crosslinking Density, while the dissipated energy during indentation decreases with increasing Crosslinking Density. The changes in hardness correlated with the changes in glass transition but not changes in the rubbery modulus, both of which can scale with a change in crosslink Density. Temperature induced shape recovery of the indentations is studied using atomic force microscopy. For impressions placed at ambient temperature, the indent shape recovery profile shifts to higher temperatures as crosslink Density and glass transition temperature increase.

Chao Zeng - One of the best experts on this subject based on the ideXlab platform.

  • Multifunctional poly(lactic acid) copolymers with room temperature self-healing and rewritable shape memory properties via Diels-Alder reaction
    Materials Research Express, 2019
    Co-Authors: Zhe Qiang, Chao Zeng
    Abstract:

    Here, we present a series of novel block copolymers (BCP) from bio-derived monomers, poly(lactic acid)-block- poly(2, 5-furandimethylene succinate) (PLA-b-PFS), in which the furan groups from PFS block can be crosslinked with bis(maleimido) triethylene glycol (M2) through a Diels-Alder reaction. This dynamic Crosslinking reaction leads to a network structure for enhancing the mechanical properties compared to their linear BCP analogous. Decreasing the Crosslinking Density leads to a decrease of glass transition temperature of BCPs and a transition from glassy to rubbery-like behavior at room temperature. This allows a wide tunablity of both elastic moduli and yields of the materials. For the lowest Crosslinking Density. the material exhibits an over 50% self-healing efficiency at room temperature after five days, attributed to the low Tg (15.2 °C) from the introduction of PFS block, allowing sufficient chain mobility for structure re-organization. Moreover, with the appropriate selection of Crosslinking Density (PLA-b-PFS/M2 (6/1)), it also shows an excellent shape memory property with a high recovery rate of 96.3% and a fixity rate of 97.3%. The permanent shape can be rewriteable due to the reversibility of Diels-Alder reaction. With these advanced functionalities and ease in large-scale fabrication, the PLA-b-PFS/M2 shows great promises for self-healing coatings or films with shape memory properties in a wide variety of applications such as packaging materials.

  • Multifunctional Biodegradable Polymers with Room Temperature Self-Healing and Rewritable Shape Memory Properties via Diels-Alder Reaction
    2018
    Co-Authors: Zhe Qiang, Chao Zeng
    Abstract:

    Here, we present a series of novel block copolymers (BCP) from bio-derived monomers, poly(lactic acid)-block-poly(2,5-furandimethylene succinate) (PLA-b-PFS), in which the furan groups from PFS block can be crosslinked with bis(maleimido) triethylene glycol (M2) through a Diels-Alder reaction. This dynamic Crosslinking reaction leads to a network structure for enhancing the mechanical properties compared to their linear BCP analogous. Decreasing the Crosslinking Density leads to a decrease of glass transition temperature of BCPs and a transition from glassy to rubbery-like behavior at room temperature. This allows a wide tunablity of both elastic moduli and yields of the materials. For the lowest Crosslinking Density. the material exhibits an over 50% self-healing efficiency at room temperature after five days, attributed to the low Tg (15.2 C) from the introduction of PFS block, allowing sufficient chain mobility for structure re-organization. Moreover, with the appropriate selection of Crosslinking Density (PLA-b-PFS/M2 (6/1)), it also shows an excellent shape memory property with a high recovery rate of 96.3% and a fixity rate of 97.3%. The permanent shape can be rewriteable due to the reversibility of Diels-Alder reaction. With these advanced functionalities and ease in large-scale fabrication, the PLA-b-PFS/M2 shows great promises for self-healing coatings or films with shape memory properties in a wide variety of applications such as packaging materials