Headen D.M.,Georgia Institute of Technology |
Headen D.M.,Petit Institute for Bioengineering and Bioscience |
Lu H.,Petit Institute for Bioengineering and Bioscience |
Garcia A.J.,Georgia Institute of Technology |
Garcia A.J.,Petit Institute for Bioengineering and Bioscience
Advanced Materials | Year: 2014
Cell and islet microencapsulation in synthetic hydrogels provides an immunoprotective and cell-supportive microenvironment. A microfluidic strategy for the genaration of biofunctionalized, synthetic microgel particles with precise control over particle size and molecular permeability for cell and protein delivery is presented. These engineered capsules support high cell viability and function of encapsulated human stem cells and islets. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Milam V.T.,Petit Institute for Bioengineering and Bioscience
Langmuir | Year: 2010
Akey advantage of DNA-mediated colloidal assembly is the ability to tune the strength of adhesion between particles based on sequence characteristics. In the current study, we have investigated DNA-mediated assembly of polystyrene colloidal particles as a function of sequence length, sequence fidelity, and probe density for DNA sequences patterned from the Salmonella genome. The results of our work indicate that the density of DNA probe strands heavily influences the ability of immobilized sequences to hybridize between surfaces of bidisperse colloidal particles. Incubating suspensions at higher temperatures (to minimize secondary structures that might otherwise compromise duplex formation) was also found to have less effect than duplex density on DNA-mediated particle assembly. We believe these results may add to the understanding and design considerations of directed particle assembly using DNA hybridization, especially in the submicrometer and micrometer size regime. © 2010 American Chemical Society.
Pendergrass K.D.,Georgia Institute of Technology |
Pendergrass K.D.,Emory University |
Varghese S.T.,Georgia Institute of Technology |
Varghese S.T.,Emory University |
And 11 more authors.
Circulation: Heart Failure | Year: 2011
Background-Reactive oxygen species, such as hydrogen peroxide (H 2O2), contribute to progression of dysfunction after myocardial infarction (MI). However, chronic overexpression studies do not agree with acute protein delivery studies. The purpose of the present study was to assess the temporal role of cardiomyocyte-derived H2O2 scavenging on cardiac function after infarction using an inducible system. Methods and Results-We developed a tamoxifen-inducible, cardiomyocyte-specific, catalase-overexpressing mouse. Catalase overexpression was induced either 5 days before or after MI. Mice exhibited a 3-fold increase in cardiac catalase activity that was associated with a significant decrease in H2O 2 levels at both 7 and 21 days. However, cardiac function improved only at the later time point. Proinflammatory and fibrotic genes were acutely upregulated after MI, but catalase overexpression abolished the increase despite no acute change in function. This led to reduced overall scar formation, with lower levels of Collagen 1A and increased contractile Collagen 3A expression at 21 days. Conclusions-In contrast to prior studies, there were no acute functional improvements with physiological catalase overexpression before MI. Scavenging of H2O2, however, reduced proinflammatory cytokines and altered cardiac collagen isoforms, associated with an improvement in cardiac function after 21 days. Our results suggest that sustained H 2O2 levels rather than acute levels immediately after MI may be critical in directing remodeling and cardiac function at later time points. (Circ Heart Fail. 2011;4:98-106.) © 2011 American Heart Association, Inc.
Reed A.L.,Georgia Institute of Technology |
Reed A.L.,Petit Institute for Bioengineering and Bioscience |
Rowson S.A.,Georgia Institute of Technology |
Dixon J.B.,Parker H Petit Institute For Bioengineering And Bioscience
Pharmaceutical Research | Year: 2013
Purpose: The lymphatic system plays crucial roles in tissue fluid balance, trafficking of immune cells, and the uptake of dietary lipid from the intestine. Given these roles there has been an interest in targeting lymphatics through oral lipid-based formulations or intradermal delivery of drug carrier systems. However the mechanisms regulating lipid uptake by lymphatics remain unknown. Thus we sought to modify a previously developed in vitro model to investigate the role of ATP in lipid uptake into the lymphatics. Methods: Lymphatic endothelial cells were cultured on a transwell membrane and the effective permeability to free fatty acid and Caco-2 cell-secreted lipid was calculated in the presence or absence of the ATP inhibitor sodium azide. Results: ATP inhibition reduced Caco-2 cell-secreted lipid transport, but not dextran transport. FFA transport was ATP-dependent primarily during early periods of ATP inhibition, while Caco-2 cell-secreted lipid transport was lowered at all time points studied. Furthermore, the transcellular component of transport was highly ATP-dependent, a mechanism not observed in fibroblasts, suggesting these mechanisms are unique to lymphatics. Total transport of Caco-2 cell-secreted lipid was dose-dependently reduced by ATP inhibition, and transcellular lipoprotein transport was completely attenuated. Conclusion: The transport of lipid across the lymphatic endothelium as demonstrated with this in vitro model occurs in part by an ATP-dependent, transcellular route independent of passive permeability. It remains to be determined the extent that this mechanism exists in vivo and future work should be directed in this area. © 2013 Springer Science+Business Media New York.
Majumder A.,University of Georgia |
Dhara S.K.,Indian Veterinary Research Institute |
Swetenburg R.,University of Georgia |
Mithani M.,University of Georgia |
And 7 more authors.
Stem Cell Research | Year: 2013
Understanding how to specify rapid differentiation of human neural progenitor towards enriched non-transformed human astrocyte progenitors will provide a critical cell source to further our understanding of how astrocytes play a pivotal role in neural function and development. Human neural progenitors derived from pluripotent embryonic stem cells and propagated in adherent serum-free cultures provide a fate restricted renewable source for quick production of neural cells; however, such cells are highly refractive to astrocytogenesis and show a strong neurogenic bias, similar to neural progenitors from the early embryonic central nervous system (CNS). We found that several astrocytic genes are hypermethylated in such progenitors potentially preventing generation of astrocytes and leading to the proneuronal fate of these progenitors. However, epigenetic modification by Azacytidine (Aza-C) and Trichostatin A (TSA), with concomitant signaling from BMP2 and LIF in neural progenitor cultures shifts this bias, leading to expression of astrocytic markers as early as 5. days of differentiation, with near complete suppression of neuronal differentiation. The resultant cells express major astrocytic markers, are amenable to co-culture with neurons, can be propagated as astrocyte progenitors and are cryopreservable. Although previous reports have generated astrocytes from pluripotent cells, the differentiation required extensive culture or selection based on cell surface antigens. The development of a label free and rapid differentiation process will expedite future derivation of astrocytes from various sources pluripotent cells including, but not limited to, human astrocytes associated with various neurological diseases. © 2013 Elsevier B.V.
Selvam S.,Petit Institute for Bioengineering and Bioscience |
Selvam S.,Georgia Institute of Technology |
Kundu K.,Georgia Institute of Technology |
Templeman K.L.,Petit Institute for Bioengineering and Bioscience |
And 3 more authors.
Biomaterials | Year: 2011
Implant-associated inflammation is a major cause for the reduced performance/lifetime and failure of numerous medical devices. Therefore, the ability to non-invasively and quantitatively monitor implant-associated inflammation is critically important. Here we show that implant-associated inflammation can be imaged via fluorescence imaging using near-infrared hydrocyanine dyes delivered either locally or intravenously in living mice. This imaging strategy allowed quantitative longitudinal monitoring of inflammation by detecting reactive oxygen species (ROS) released by inflammatory cells in response to implanted poly(ethylene terephthalate) (PET) disks or injected poly (lactic-co-glycolic acid) (PLGA) microparticles, and exhibited a strong correlation to conventional analysis of inflammation. Furthermore, modulation of inflammatory responses via controlled release of the anti-inflammatory agent dexamethasone was detected using this sensitive imaging approach. Thus, hydrocyanine-based fluorescence imaging of ROS could serve as a surrogate measure for monitoring implant-associated inflammation as well as evaluating the efficacy of therapeutic approaches to modulate host responses to implanted medical devices. © 2011 Elsevier Ltd.
Gaulding J.C.,Petit Institute for Bioengineering and Bioscience |
Saxena S.,Georgia Institute of Technology |
Montanari D.E.,Petit Institute for Bioengineering and Bioscience |
Lyon L.A.,Petit Institute for Bioengineering and Bioscience
ACS Macro Letters | Year: 2013
Hybrid nanoparticles with complex architectures combine the properties of two distinct materials and integrate them to synergistically provide new characteristics to the assembly. In this work we demonstrate the ability to decorate the surface of a variety of micrometer-sized "core" particles with responsive microgels, forming raspberry-like particles. We use a templating technique wherein the microgel coating is applied from a high-volume-fraction colloidal phase, leading to high surface coverage and enhanced colloidal stability of the resultant particles. Concentrated colloidal dispersions enable microgel/core combinations driven by both specific and nonspecific interactions and offer improved coverage relative to dilute heteroaggregation. This approach is versatile and allows both the core material and microgel phase to be altered while still remaining effective. Though the recovered particles are highly diluted, recycling the unincorporated microgels following raspberry-like particle isolation and reforming the packed colloidal assembly allow multiple cycles of particle synthesis, which improves overall yield. © 2013 American Chemical Society.
Pagba C.V.,Petit Institute for Bioengineering and Bioscience |
Chi S.-H.,Georgia Institute of Technology |
Perry J.,Georgia Institute of Technology |
Barry B.A.,Petit Institute for Bioengineering and Bioscience
Journal of Physical Chemistry B | Year: 2015
In proteins, proton-coupled electron transfer (PCET) can involve the transient oxidation and reduction of the aromatic amino acid tyrosine. Due to the short life time of tyrosyl radical intermediates, transient absorption spectroscopy provides an important tool in deciphering electron-transfer mechanisms. In this report, the photoionization of solution tyrosine and tyrosinate was investigated using transient, picosecond absorption spectroscopy. The results were compared to data acquired from a tyrosine-containing β-hairpin peptide. This maquette, peptide A, is an 18-mer that exhibits π-π interaction between tyrosine (Y5) and histidine (H14). Y5 and H14 carry out an orthogonal PCET reaction when Y5 is oxidized in the mid-pH range. Photolysis of all samples (280 nm, instrument response: 360 fs) generated a solvated electron signal within 3 ps. A signal from the S1 state and a 410 nm signal from the neutral tyrosyl radical were also formed in 3 ps. Fits to S1 and tyrosyl radical decay profiles revealed biphasic kinetics with time constants of 10-50 and 400-1300 ps. The PCET reaction at pH 9 was associated with a significant decrease in the rate of tyrosyl radical and S1 decay compared to electron transfer (ET) alone (pH 11). This pH dependence was observed both in solution and peptide samples. The pH 9 reaction may occur with a sequential electron-transfer, proton-transfer (ETPT) mechanism. Alternatively, the pH 9 reaction may occur by coupled proton and electron transfer (CPET). CPET would be associated with a reorganization energy larger than that of the pH 11 reaction. Significantly, the decay kinetics of S1 and the tyrosyl radical were accelerated in peptide A compared to solution samples at both pH values. These data suggest either an increase in electronic coupling or a specific, sequence-dependent interaction, which facilitates ET and PCET in the β hairpin. © 2014 American Chemical Society.
Garcia J.R.,Georgia Institute of Technology |
Garcia J.R.,Petit Institute for Bioengineering and Bioscience |
Singh A.,Georgia Institute of Technology |
Singh A.,Petit Institute for Bioengineering and Bioscience |
And 2 more authors.
Methods in Cell Biology | Year: 2014
In the pursuit to develop enhanced technologies for cellular bioassays as well as understand single cell interactions with its underlying substrate, the field of biotechnology has extensively utilized lithographic techniques to spatially pattern proteins onto surfaces in user-defined geometries. Microcontact printing (μCP) remains an incredibly useful patterning method due to its inexpensive nature, scalability, and the lack of considerable use of specialized clean room equipment. However, as new technologies emerge that necessitate various nano-sized areas of deposited proteins, traditional μCP methods may not be able to supply users with the needed resolution size. Recently, our group developed a modified "subtractive μCP" method which still retains many of the benefits offered by conventional μCP. Using this technique, we have been able to reach resolution sizes of fibronectin as small as 250. nm in largely spaced arrays for cell culture. In this communication, we present a detailed description of our subtractive μCP procedure that expands on many of the little tips and tricks that together make this procedure an easy and effective method for controlling protein patterning. © 2014 Elsevier Inc.
PubMed | Petit Institute for Bioengineering and Bioscience
Type: Journal Article | Journal: Biomaterials | Year: 2011
Implant-associated inflammation is a major cause for the reduced performance/lifetime and failure of numerous medical devices. Therefore, the ability to non-invasively and quantitatively monitor implant-associated inflammation is critically important. Here we show that implant-associated inflammation can be imaged via fluorescence imaging using near-infrared hydrocyanine dyes delivered either locally or intravenously in living mice. This imaging strategy allowed quantitative longitudinal monitoring of inflammation by detecting reactive oxygen species (ROS) released by inflammatory cells in response to implanted poly(ethylene terephthalate) (PET) disks or injected poly (lactic-co-glycolic acid) (PLGA) microparticles, and exhibited a strong correlation to conventional analysis of inflammation. Furthermore, modulation of inflammatory responses via controlled release of the anti-inflammatory agent dexamethasone was detected using this sensitive imaging approach. Thus, hydrocyanine-based fluorescence imaging of ROS could serve as a surrogate measure for monitoring implant-associated inflammation as well as evaluating the efficacy of therapeutic approaches to modulate host responses to implanted medical devices.