Abstract
In the past ten years, an increasing number of thermo-sensitive hydrogels have been widely reported in the literature for various biomedical applications, including drug delivery, cell encapsulation, and tissue repair. These thermo-sensitive hydrogels are injectable fluids that can be introduced into the body in a minimally invasive manner prior to solidifying or gelling with the desired tissue or organ. Additionally, the thermo-sensitive hydrogels own many advantages, such as it does not require organic solvents and can be an in-situ forming gel. Because of the simplicity of pharmaceutical and biomedical uses of the water-based sol–gel transition that can be used as drug delivery-control systems, bioactive compounds delivery, and tissue engineering. When the formed gel is proven to be biocompatible and biodegradable, producing non-toxic degradation products, it will provide further benefits for in vivo applications where degradation is desired. In this study, a series of the biodegradable thermo-sensitive hydrogels were synthesised by the ring open polymerization of the methoxy polyethylene glycol with various kinds of the ester monomers, such as the D,L-lactide, glycolide, b-propiolactone, d-valerolactone and e-caprolactone. Results of those products defined by 1H n.m.r. spectras indicated that these materials were indeed the compounds expected. The critical micelle concentrations of those copolymers were measured by the UV-VIS Spectrophotometer and the particle sizes of those polymeric micelles were measured by the dynamic light scattering (DLS). The thermo-sensitive properties of those copolymeric hydrogels were measured by the UV-VIS Spectrophotometer. The viscoelastic properties of those copolymers were measured by Rheostress(Haake rheostress 600). The sol-gel transition behavior of diblock copolymers was confirmed by the nano micelle spontaneous aggregating to physical gel with increasing temperature. The biocompatability of those novel thermo-sensitive hydrogels were tested by the agar diffusion. The biomedical applications were tested by the drug delivery of cyclosporine A and teicoplanin, the bioglue for skin in vitro and the bone tissue repair in vivo, the therapy of osteomyelitis in vivo, and the induced tolerance of the composite tissue allotransplanation (CTA). The sustained release of cyclosporine A and teicoplanin was about 70% for 31 and 13 days, respectively. The mPEG-PLGA hydrogel containing teicoplanin was effective for treating osteomyelitis in rabbits as detected by the histological staining and immunoblotting analyses. The results of the osteomyocutaneous flap transfer indicated that the CTA with the immunosuppression drug, CsA, was an excellent allograft with the mPEG-PVLA sol-gel delivery system.