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ABSTRACT: The feasibility of using a star-shaped crosslinker to produce a hydrogel with controlled mechanical properties and degradation rates was investigated. The aqueous blends of functional polymers and crosslinkers formed a solution at low temperature and a hydrogel with desired mechanical properties at body temperature. The introduction of star-shaped crosslinkers affected the microscopic and macroscopic properties of the hydrogel. The fabricated hydrogels could be suitable for many potential biomedical applications because of their injectability, tunable mechanical properties, controlled degradation rate and gel formation under physiological conditions.
Macromolecular Bioscience 03/2011; 11(5):689-99. · 3.89 Impact Factor
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ABSTRACT: Rapidly photocrosslinkable and thermosensitive polyphosphazene polymers have been prepared to overcome the limitations associated with long UV exposure. Short UV exposure on the thermosensitive gels under mild conditions leads to quick photocrosslinking of the acrylate groups in the polymer network, and results in a dual crosslinked network with enhanced mechanical strength. The accelerated photocrosslinking can be attributed to the high reactivity of the acrylate double bond and hydrophobic interactions in the polymer network. The effects on the degree of photocrosslinking of the UV light intensity and the concentration of the photoinitiator were studied. In vitro and in vivo photocrosslinkings were accomplished within 120 and 180 s of exposure times, respectively. The degradation rate of the polymers depended on the degree of acrylate substitution in the polymer network. These results demonstrate that the injectable hydrogels with desired mechanical properties and degradation rates can be created in situ under mild photocrosslinkable conditions, and the dual crosslinkable acrylated poly(organophosphazenes) may hold great promise for biomedical delivery applications of biological molecules, cells, and drugs.
Macromolecular Rapid Communications 12/2010; 31(24):2133-9. · 4.60 Impact Factor
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ABSTRACT: A new class of injectable, self cross-linkable, and thermosensitive polyphosphazene-based blending systems of functional thiolated and acrylated polymers was designed and synthesized to develop an ideal injectable carrier, and to overcome many barriers associated with developing the injectable carriers, such as the uses of monomeric crosslinkers, catalysts, oxidants, pH adjustments, initiators, UV light, heat production and organic solvent. The aqueous solutions of the polymer blends were exhibited a solution state at low temperature, and transformed into a hydrogel state with desired mechanical strength at body temperature via thermosensitive hydrophobic interactions. The mechanical strength was further improved by the cross-linking of thiol groups with acrylate groups in the polymer network under physiological conditions. The thermoresponsive hydrophobic interactions in the polymer network accelerated the chemical cross-linking to improve the mechanical property. The mechanical strength, inner three-dimensional network, and degradation rate can be tuned through the degree of cross-linking between the thermosensitive and functional blended polymers. The results suggest that the self cross-linkable thermosensitive polyphosphazene blend systems have great potentials to play a crucial role as an injectable carrier because of their improved suitable mechanical properties for application potentials, in addition to their inherent advantages such as injectable, biodegradable and thermosensitive properties.
Biomaterials 11/2010; 31(32):8107-20. · 7.40 Impact Factor
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ABSTRACT: Photo-cross-linkable, functionalized, and thermosensitive polyphosphazenes were synthesized to develop a dual cross-linking system with properties of mechanically suitable strength and controllable biodegradation for injectable biomedical applications. The aqueous solutions of the polymers exhibited sol-gel transition behaviors against temperature. The incorporated methacrylate groups were photo-cross-linked upon UV light under mild conditions, which resulted in the formation of compact three-dimensional networks. The thermoresponsive hydrophobic interactions at body temperature facilitated the rapid dual cross-linking accomplishment of the photo-cross-linking even under mild conditions. The characteristics of the polymers such as pore size and density showed that the inner three-dimensional networks depended on the degree of cross-linking of methacrylate units. Mechanical properties of the gel were also improved several folds after developing the photo-cross-linking in the network from the in vivo degradation studies. The results demonstrate that the photo-cross-linkable and thermoresponsive polyphosphazenes have great potential as injectable, biodegradable, and controllable carriers for various biomedical applications by tuning the mechanical gel property and the degradation rate.
Biomacromolecules 07/2010; 11(7):1741-53. · 5.48 Impact Factor
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ABSTRACT: Chemically crosslinkable and thermosensitive poly(organophosphazenes) containing multiple thiol (-SH) groups along with hydrophobic isoleucine ethyl ester and hydrophilic alpha-amino-omega-methoxy-poly(ethylene glycol) of the molecular weight 550 have been synthesized and characterized as an injectable biomaterial. The aqueous solutions of these polymers were transformed into hydrogel with desired gel strength at body temperature via hydrophobic interactions, and the gel strength was further improved by the cross-linking of thiol groups with crosslinkers, divinyl sulfone (VS) and PEG divinyl sulfone (PEGVS) under physiological conditions. The kinetics of cross-linking behavior of polymer thiol groups with crosslinkers was studied in both in vitro and in vivo conditions. Field Emission-Scanning Electron Microscopy (FE-SEM), swelling experiments, and rheology study of present polymers revealed that the inner three-dimensional hydrogel networks depended on the degree of thiol units in the polymer network. From the in vivo (in mice) degradation studies, the dual cross-linked gels showed to have a controlled degradation. These results demonstrate that the inner network of the hydrogels can be tuned, gel strength and degradation rate can be controlled, and the chemically crosslinkable and thermosensitive poly(organophosphazenes) hold promises for uses as injectable systems for biomedical applications including tissue engineering and protein delivery.
Biomaterials 09/2009; 30(31):6178-92. · 7.40 Impact Factor
