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ABSTRACT: Hydrogels are used to create three-dimensional microenvironments with properties that direct cell function. The current study demonstrates the versatility of hyaluronic acid (HA) based hydrogels with independent control over hydrogel properties such as mechanics, architecture, and spatial distribution of biological factors. Hydrogels were prepared by reacting furan-modified HA with bis-maleimide-poly(ethylene glycol) in a Diels-Alder click reaction. Biomolecules were photopatterned into the hydrogel by 2-photon laser processing, resulting in spatially defined growth factor gradients. The Young's modulus was controlled by either changing the hydrogel concentration or the furan substitution on the HA backbone, thereby decoupling hydrogel concentration from mechanical properties. Porosity was controlled by cryogelation and pore size distribution by thaw temperature. The addition of galactose further influenced the porosity, pore size, and Young's modulus of the cryogels. These HA based hydrogels offer a tunable platform with a diversity of properties for directing cell function, with applications in tissue engineering and regenerative medicine.
Langmuir 01/2013; · 4.19 Impact Factor
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ABSTRACT: Polymeric nanoparticle micelles provide a possible platform for theranostic delivery, combining the role of therapeutics and diagnostics in one vehicle. To explore dual-functional micelles, the amphiphilic copolymer of poly(d,l-lactide-co-2-methyl-2-carboxytrimethylene carbonate)-graft-poly(ethylene glycol)-X (P(LA-co-TMCC)-g-PEG-X) was self-assembled to form micelles, with X representing either azide or furan. Micelles of P(LA-co-TMCC)-g-PEG-azide and P(LA-co-TMCC)-g-PEG-furan terminal functional groups were used to conjugate dibenzylcyclooctyne and maleimide-modified probes, respectively, taking advantage of orthogonal coupling chemistry. To verify the utility of the dual-functional micelles, trastuzumab-maleimide antibodies and FLAG-dibenzylcyclooctyne peptides were covalently bound by sequential click chemistry reactions. SKOV-3luc cells that were treated with the dual-functionalized micelles showed colocalization of the antibodies and peptides by confocal imaging, demonstrating the promise of this approach.
Bioconjugate Chemistry 01/2013; · 4.93 Impact Factor
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ABSTRACT: BACKGROUND: Human tumour xenografts in immune compromised mice are widely used as cancer models because they are easy to reproduce and simple to use in a variety of pre-clinical assessments. Developments in nanomedicine have led to the use of tumour xenografts in testing nanoscale delivery devices, such as nanoparticles and polymer-drug conjugates, for targeting and efficacy via the enhanced permeability and retention (EPR) effect. For these results to be meaningful, the hyperpermeable vasculature and reduced lymphatic drainage associated with tumour pathophysiology must be replicated in the model. In pre-clinical breast cancer xenograft models, cells are commonly introduced via injection either orthotopically (mammary fat pad, MFP) or ectopically (subcutaneous, SC), and the organ environment experienced by the tumour cells has been shown to influence their behaviour. METHODS: To evaluate xenograft models of breast cancer in the context of EPR, both orthotopic MFP and ectopic SC injections of MDA-MB-231-H2N cells were given to NOD scid gamma (NSG) mice. Animals with matched tumours in two size categories were tested by injection of a high molecular weight dextran as a model nanocarrier. Tumours were collected and sectioned to assess dextran accumulation compared to liver tissue as a positive control. To understand the cellular basis of these observations, tumour sections were also immunostained for endothelial cells, basement membranes, pericytes, and lymphatic vessels. RESULTS: SC tumours required longer development times to become size matched to MFP tumours, and also presented wide size variability and ulcerated skin lesions 6 weeks after cell injection. The 3 week MFP tumour model demonstrated greater dextran accumulation than the size matched 5 week SC tumour model (for P < 0.10). Immunostaining revealed greater vascular density and thinner basement membranes in the MFP tumour model 3 weeks after cell injection. Both the MFP and SC tumours showed evidence of insufficient lymphatic drainage, as many fluid-filled and collagen IV-lined spaces were observed, which likely contain excess interstitial fluid. CONCLUSIONS: Dextran accumulation and immunostaining results suggest that small MFP tumours best replicate the vascular permeability required to observe the EPR effect in vivo. A more predictable growth profile and the absence of ulcerated skin lesions further point to the MFP model as a strong choice for long term treatment studies that initiate after a target tumour size has been reached.
BMC Cancer 12/2012; 12(1):579. · 3.01 Impact Factor
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ABSTRACT: Many small molecules, including bioactive molecules and approved drugs, spontaneously form colloidal aggregates in aqueous solution at micromolar concentrations. Though it is widely accepted that aggregation leads to artifacts in screens for ligands of soluble proteins, the effects of colloid formation in cell-based assays have not been studied. Here, seven anticancer drugs and one diagnostic reagent were found to form colloids in both biochemical buffer and in cell culture media. In cell-based assays, the antiproliferative activities of three of the drugs were substantially reduced when in colloidal form as compared to monomeric form; a new formulation method ensured the presence of drug colloids versus drug monomers in solution. We also found that Evans Blue, a dye classically used to measure vascular permeability and to demonstrate the "enhanced permeability and retention (EPR) effect" in solid tumors, forms colloids that adsorb albumin, as opposed to older literature that suggested the reverse.
ACS Chemical Biology 05/2012; 7(8):1429-35. · 6.45 Impact Factor
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Christi M Terry,
Li Li,
Huan Li,
Ilya Zhuplatov,
Donald K Blumenthal,
Seong-Eun Kim, Shawn C Owen,
Eugene G Kholmovski,
Kirk D Fowers,
Ramesh Rathi,
Alfred K Cheung
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ABSTRACT: Synthetic arteriovenous (AV) hemodialysis grafts are plagued by hyperplasia resulting in occlusion and graft failure yet there are no clinically available preventative treatments. Here the delivery and degradation of a sirolimus-laden polymer gel were monitored in vivo by magnetic resonance imaging (MRI) and its efficacy for inhibiting hyperplasia was evaluated in a porcine model of AV graft stenosis. Synthetic grafts were placed between the carotid artery and ipsilateral jugular vein of swine. A biodegradable polymer gel loaded with sirolimus (2.5mg/mL) was immediately applied perivascularly to the venous anastomosis, and reapplied by ultrasound-guided injections at one, two and three weeks. Control grafts received neither sirolimus nor polymer. The lumen cross-sectional area at the graft-vein anastomosis was assessed in vivo by non-invasive MRI. The explanted tissues also underwent histological analysis. A specifically developed MRI pulse sequence provided a high contrast-to-noise ratio (CNR) between the polymer and surrounding tissue that allowed confirmation of gel location after injection. Polymer signal decreased up to 80% at three to four weeks after injection, slightly faster than its degradation kinetics in vitro. The MR image of the polymer was confirmed by visual assessment at necropsy. On histological assessment, the mean hyperplasia surface area of the treated graft was 52% lower than that of the control grafts (0.43mm(2) vs. 0.89mm(2); p<0.003), while the minimum cross-sectional lumen area, as measured on MRI, was doubled (5.3mm(2) vs 2.5mm(2); p<0.05). In conclusion, customized MRI allowed non-invasive monitoring of the location and degradation of drug delivery polymer gels in vivo. Perivascular application of sirolimus-laden polymer yielded a significant decrease in hyperplasia development and an increase in lumen area at the venous anastomosis of AV grafts.
Journal of Controlled Release 03/2012; 160(3):459-67. · 5.73 Impact Factor
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ABSTRACT: The stability of polymeric nanoparticles in serum is critical to their use in drug delivery where dilution after intravenous injection often results in nanoparticle disassembly and drug unloading; however, few investigate this in biologically relevant media. To gain greater insight into nanoparticle stability in blood, the stability of self-assembled polymeric micelles of poly(d,l-lactide-co-2-methyl-2-carboxytrimethylene carbonate)-g-poly(ethylene glycol), P(LA-co-TMCC)-g-PEG, were tested in both serum and individual serum protein solutions. By encapsulating Förster resonance energy transfer pairs and following their release by fluorescence, these micelles demonstrated excellent thermodynamic and kinetic stability in the presence of serum. Further analyses by fast protein liquid chromatography and dynamic light scattering confirmed these data. Moreover, these micelles are compatible with red blood cells, as shown by a hemolysis assay. The stability and compatibility demonstrated in blood suggest that these micelles may be stable in vivo, which is critical for intravenous drug delivery applications. This comprehensive approach to understanding micelle stability and compatibility is broadly applicable.
Macromolecules 08/2011; 44(15):6002-6008. · 5.17 Impact Factor
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ABSTRACT: Hyaluronic acid (HA) is a naturally occurring polymer that holds considerable promise for tissue engineering applications. Current cross-linking chemistries often require a coupling agent, catalyst, or photoinitiator, which may be cytotoxic, or involve a multistep synthesis of functionalized-HA, increasing the complexity of the system. With the goal of designing a simpler one-step, aqueous-based cross-linking system, we synthesized HA hydrogels via Diels-Alder "click" chemistry. Furan-modified HA derivatives were synthesized and cross-linked via dimaleimide poly(ethylene glycol). By controlling the furan to maleimide molar ratio, both the mechanical and degradation properties of the resulting Diels-Alder cross-linked hydrogels can be tuned. Rheological and degradation studies demonstrate that the Diels-Alder click reaction is a suitable cross-linking method for HA. These HA cross-linked hydrogels were shown to be cytocompatible and may represent a promising material for soft tissue engineering.
Biomacromolecules 02/2011; 12(3):824-30. · 5.48 Impact Factor
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ABSTRACT: A detailed understanding of the biophysical features that affect cell growth and development is important in guiding the design of biomimetic scaffolds. The cellular microenvironment is a network of structural and functional components that provide mechanical and chemical stimuli, which influence cell function and fate. Important developmental signals are conveyed to cells through interactions with neighboring cells, the extracellular matrix (ECM), and growth factors. Currently, there are number of approaches to create 3D tissue models in vitro that allow for control over cell adhesion, the physical properties of the surrogate matrix, and the spatial distribution of growth factors. This review describes some of the most significant biological features of the ECM, and several engineering methods currently being implemented to design and tune synthetic scaffolds to mimic these features.
Journal of Biomedical Materials Research Part A 09/2010; 94(4):1321-31. · 2.63 Impact Factor
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ABSTRACT: Sustained delivery of anti-proliferative drugs to the perivascular area using an injectable polymeric platform is a strategy to inhibit vascular hyperplasia and stenosis. In this study, the concentrations of sirolimus in vascular tissues were evaluated after delivery using an injectable platform made of poly(lactic-co-glycolic acid)-polyethylene glycol-poly(lactic-co-glycolic acid) (PLGA-PEG-PLGA). In order to optimize the drug release profile, the effect of two solvents or solid loading of the sirolimus into the polymer gel was first examined in vitro. The early release was slower with loading of dry drug into the polymer, compared to drug dissolution in solvents. Dry sirolimus was therefore used to load the polymer and applied to the perivascular surface of the graft-venous anastomosis at the time of surgical placement of a carotid-jugular synthetic hemodialysis graft in a porcine model. This was replenished by ultrasound-guided injection of additional drug-laden polymer at one, two and three weeks post-operatively. Magnetic resonance imaging (MRI) using pulse sequences specifically designed for optimal detection of the polymeric gel showed that the polymer injected post-operatively remained at the juxta-anastomotic perivascular site at two weeks. Sirolimus was extracted from various segments of the juxta-anastomotic tissues and the drug concentrations were determined using HPLC MS/MS. Tissue sirolimus concentrations at one and two weeks were highest near the venous anastomosis, which were approximately 100- to 500-fold greater than the concentrations necessary to inhibit vascular smooth muscle cell proliferation in vitro. Drug concentrations remained above the inhibitory concentrations for at least six weeks post-operatively. Thus, serial injections of sustained-delivery polymer gel loaded with sirolimus can provide high localized concentrations at target vascular tissues and thus may be useful for the prevention and treatment of vascular proliferative disorders such as hemodialysis graft stenosis. In addition, MRI is useful for the monitoring of the location of the drug depot.
Journal of Controlled Release 05/2010; 146(1):23-30. · 5.73 Impact Factor
