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The Research on the pH-sensitive Photocrosslinked Hydrogels and Hollow Nano-hydrogels

Author: XuSha
Tutor: YinYiHua
School: Wuhan University of Technology
Course: Pharmacy
Keywords: photocrosslinking pH-sensitive hydrogel slow-release pH-sensitive hollow nanogel
CLC: O648.17
Type: Master's thesis
Year: 2010
Downloads: 136
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Abstract

The main advantage of using UV irradiation to initiate the chain reaction lies in the very high polymerization rates that can be reached within a fraction of a second, and the reaction is readily controlled by adjusting the irradiation conditions. In this paper, two typies of carboxymethyl chitosan derivatives were synthesized through the reaction of carboxymethyl chitosan (CMCS) with 4-azidobenzaldehyde (4-AZIDE) and 4-azidobenzoic acid (4-AZIID). And the biopolymeric hydrogels and the hollow nanogels by photocrosslinking were prepared. The main studies of this dissertation are shown as follows:(1) The pH sensitivety and the swelling kinetics of the photocrosslinked hydrogels based on 4-AZIID-CMCS (Ad-CMCS) were investigated.The Ad-CMCS could be cross-linked to form transparent hydrogels by UV irradiation. These hydrogels have good pH sensitivity. The manner of UV-induced cross-linking can achieve in situ loading the drugs and avoid some shortcomings of chemical cross-linking.The swelling kinetics of the hydrogels in pH<5.0 buffer solutions displayed an overshooting effect. The overshooting effect may be attributed to the cooperative physical cross-linking caused by the hydrogen bond formation between the carboxy groups of the hydrogels during the swelling processes. The overshoot processes follow a quantitative model proposed by Diez-Pena.E et al. While in pH≥5.0 buffer solutions, the overshoot effect didn’t appear and the swelling processes followed Schott’s second-order rate equation.(2) The feasibility of the photocrosslinked hydrogel as a slow-release pesticide formulation was studied.The slow-release hydrogel membrane formulation can be obtained by exposure the mixture of Ad-CMCS and diuron as a model drug to UV (simulated sunlight) to induce in situ cross-linking. The diuron releases in the buffer solution at pH6.0 (the pH of dew or rain is about 6.0) show that the hydrogel formulations have good slow-release properties, it had been taken 450 hours (19 days) at least to release 80% of the diuron from the hydrogel formulations. The drug release processes of the hydrogels loading diuron followed Ritger-Peppa model and the release mechanism was Fick diffusion.The forming membrane manner and slow-release property in respond to the pH6.0 buffer of the photocrosslinked hydrogel have the important values for developing new slow-release pesticide formulations.(3) The photocross-linked hollow nanogels based on 4-AZIDE-CMCS (Az-CMCS) were prepared by one-pot synthesis method. And their pH sensitivety and stability were studied.Az-CMCS can self-assemble into monodisperse hollow nanocapsules for its amphipathicity, and subsequently the nanocapsule solution was exposed to UV light for 15 min using an ultraviolet lamp (20 W,253.7 nm) to induce in situ cross-linking of the hydrophobic photoreactive functional groups (phenyl azide groups) in the shells, and forming shell cross-linked hollow nanogels. The TEM images showed the nanogels have void configuration and regular shape.Results obtained by light scattering research show that the photocrosslinked nanogels exhibit a higher stability and a narrower size distribution than the nanocapsules before photocross-linking.The photocrosslinked nanogels have good pH sensitivities. The dimensions of the hollow nanogels increase with increasing pH. The pH-sensitivity is related to the photocross-linking degree, the result indicated an increase in the photocross-linking degree leads to a low pH-sensitivity. In addition, these nanogels would precipitate at pH<4.0This method is an attractive new one-pot route to shell cross-linked nanospheres, as it not only avoids chemical degradation of the core-forming blocks, but also don’t require any surfactants, toxic organic solvents, emulsion phases, or template cores. Furthermore, the carboxylic acid group located at the surface of the nanoparticles could be available as a conjugation site of various ligands. These features indicate the potential utility of nanocages in the diverse fields of functional nanometer

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