[Show abstract][Hide abstract] ABSTRACT: Photopolymerized hydrogels are extensively investigated for various tissue engineering applications, primarily due to their ability to form hydrogels in a minimally invasive manner. Although photocrosslinkable hydrogels provide necessary biological and chemical characteristics to mimic cellular microenvironments, they often lack sufficient mechanical properties. Recently, nanocomposite approaches have demonstrated potential to overcome these deficits by reinforcing the hydrogel network with. In this study, we investigate some physical, chemical, and biological properties of photocrosslinked poly(ethylene glycol) (PEG)-silica hydrogels. The addition of silica nanospheres significantly suppresses the hydration degree of the PEG hydrogels, indicating surface interactions between the silica nanospheres and the polymer chains. No significant change in hydrogel microstructure or average pore size due to the addition of silica nanospheres was observed. However, addition of silica nanospheres significantly increases both the mechanical strength and the toughness of the hydrogel networks. The biological properties of these nanocomposite hydrogels were evaluated by seeding fibroblast cells on the hydrogel surface. While the PEG hydrogels showed minimum cell adhesion, spreading and proliferation, the addition of silica nanospheres enhanced initial cell adhesion, promoted cell spreading and increased the metabolic activity of the cells. Overall, results indicate that the addition of silica nanospheres improves the mechanical stiffness and cell adhesion properties of PEG hydrogels and can be used for biomedical applications that required controlled cell adhesion.
Materials Science and Engineering C 01/2013; 33(3):1800 -1807. · 2.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we present an injectable PEG/collagen hydrogel system with robust networks for use as elastomeric tissue scaffolds. Covalently crosslinked PEG and physically crosslinked collagen form semi-interpenetrating networks. The mechanical strength of the hydrogels depends predominantely on the PEG concentration but the incorporation of collagen into the PEG network enhances hydrogel viscoelasticity, elongation, and also cell adhesion properties. Experimental data show that this hydrogel system exhibits tunable mechanical properties that can be further developed. The hydrogels allow cell adhesion and proliferation in vitro. The results support the prospect of a robust and semi-interpenetrating biomaterial for elastomeric tissue scaffolds applications.
[Show abstract][Hide abstract] ABSTRACT: Mechanical properties of polymer hydrogels are critical to their performance as tissue engineering scaffolds especially in load bearing tissues and wound sealants. In this study, we aim to synthesize mechanically tough nanocomposite hydrogels by photo-cross-linking PEO–PPO–PEO triblock copolymer diacrylates (Pluronic F127 diacrylate) in the presence of silicate nanoparticles, Laponite. The resulting hydrogels have high elongations and improved toughness when compared to their polymer hydrogel counterparts. Oscillatory shear and creep experiments suggest that the silicate nanoparticles physically interact with the covalently cross-linked polymer networks and impart viscoelasticity to the hydrogels. Imaging the structures of deformed nanocomposite hydrogels with cryo-scanning electron microscopy (cryo-SEM) leads us to believe that stretched hydrogels have finer network structures with smaller pore sizes when compared to the unstretched ones. The structural transitions observed in cryo-SEM and the viscoelastic properties measured suggest that noncovalent, physical interactions between Pluronic F127 and Laponite may contribute to rearrangements of network structures at high deformations. Overall, we expect the relationships between mechanical properties and network structures to provide valuable knowledge for the future design of high-performance hydrogels with use in a variety of biotechnological, biomedical, and pharmaceutical applications.
[Show abstract][Hide abstract] ABSTRACT: Cell-penetrating peptides have been used as a method of delivering biologically active peptide for over two decades. In this paper, we covalently attached four different cell-penetrating peptides to a peptide that inhibits a kinase important in inflammation, mitogen-activated protein kinase activated protein kinase 2 (MAPKAP2 or MK2). We evaluated the specificity, toxicity, and functionality of these therapeutics in an in vitro model of inflammation using THP-1 monocytes. When treated with the MK2 peptide inhibitors, activated THP-1 human monocytes challenged with lipopolysaccharide (LPS) showed a decrease in TNF-α and IL-6 excretion without apparent toxicity. In addition, western blot analysis revealed decreases in the phosphorylation of heat shock protein 27 (HSP27), a downstream substrate of MK2. These results suggested that our peptides inhibited MK2 activity in vitro and should be investigated further as a potential therapeutic for applications involving inflammation. Furthermore, our results suggested that cell-penetrating peptides can be bioactive.
Journal of Controlled Release 05/2011; 155(2):128-33. · 7.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The properties of GaN have made it not only an ideal material for high power and high frequency electronic devices, but also a semiconductor suitable for application in biosensing devices. The utilization of GaN in electronic biosensors has increased the importance of characterizing robust and easily implemented organic functionalization methods for GaN surfaces. This work demonstrates and characterizes a route to functionalize the GaN (0001) surface with two organic molecules, hexylamine and a peptide, through olefin cross-metathesis with Grubbs first generation catalyst. The GaN (0001) surface was chlorinated, functionalized with a terminal alkene group using a Grignard reaction, and then terminated with a carboxyl group using an olefin cross-metathesis reaction. With a condensation reaction, the final step in the reaction scheme bound hexylamine or a peptide to the carboxyl terminated GaN surface. Qualitative and quantitative X-ray photoelectron spectroscopy (XPS) data verified the success of each step in the reaction scheme. Surface element composition, adlayer coverages, and adlayer thicknesses were calculated based on the XPS data. At least a monolayer of surface molecules covered the GaN surface.