Preparation And Characterization Of PH And Temperature Sensitive Nanogels

Owning some preferred properties, such as biodegradable, biocompatible, and gentle physical and chemical profiles, hydrogels are extensively used as carriers in drug delivery and drugs are expected to get sustained release from these gels. Multiple functional gels were developed to carry drug for different objects. When the body get inflamed, The pH value would decline in these region. At the same time, there would be more pyrogen, causing temperature higher than normal tissue. Especially, certain malignancies can cause two stimulis around tumor site at the same time. One is a slight local temperature increase and the other is a minor decrease in extracellular pH. Thus, properly designed nanocarriers that are dual-responsive to both temperature and pH may be able to intelligently distinguish between normal and pathological tissues, achieving better targeting and treatment efficacy. In this paper, we present a facile method to prepare stabilized nanogels with dual temperature- and pH-sensitivity composed of maleilated dextran (Dex-MA) and NIPAAm. HCPT as model drug was entrapped into nanoparticle and the drug release characteristics of nanogels in vitro were investigated.1. Preparation of the maleilated dextran (Dex–MA)Dextran and maleic anhydride were dissolved in a LiCl/DMF solvent system, triethylamine was used to be catalyst. Maleilated dextran was prepared in some conditions. The degree of substitution (DS) of maleilated dextran (Dex–MA) was determined by 1H-nuclear magnetic resonance (1H-NMR).2. Preparation of Dex-MA-graft-PNIPAAm nanogelsIn these process, firstly an optimal procedure was chosen to prepare Dex-MA-graft-PNIPAAm nanogels after comparing soap-free emulsion polymerization with precipitation polymerization. Secondly, an optimal surfacant was chosen from three surfactants, which were cetriminium, tween-80, sodium dodecyl sulfate(SDS), respectively. Precipitation polymerization using SDS as surfactant was the final adopted procedure. Last, we studied the effects of the amounts of surfactant on the size distribution properties, and characterized pH and temperature sensitive of nanogels.3. Characteristics of obtained nanogelsThe physicochemical characteristics of the nanogels were studied by FT-IR, 1H-NMR, TEM and zeta-potential measurements. The resultant nanogels showed spherical with diameter smaller than 300 nm by adjusting the composition ratio or the amounts of surfactant. The lower critical solution temperatures (LCST) decreased at pH 3.0, but increased at pH 6.0 with increase in Dex-MA content, which suggested that the LCST may change by adjusting the composition ratio or the pH value of nanopaticle solutions. HCPT as model drug, in vitro pH and temperature sensitive drug release profiles were obtained by a dynamic dialysis method. The release experiments were conducted at 37℃and pH 7.4, respectively. It was observed that after 12h the release of HCPT was about 11% at pH 2.0, 19.65% at pH 5.0, whereas at pH 7.4, the release was about 33%. It was worth noting that the release profiles showed a pH dependence. The higher the medium pH, the faster the release of HCPT from the nanogels. All the release profiles obtained here exhibited a very steady sustained-release pattern with negligible initial burst release. In temperature-sensitive aspect, as the temperature increased from 37℃to 40℃, the cumulative release rate increased from 15% to 25% after 4h. Since the reaction was heated above the LCST of NP8 at 40℃, which was 38.1℃in this condition, the PNIPAAm became hydrophobic during the polymerization. The cumulative release rate of HCPT increased because the hydrophobic degree of nanoparticle increased along with the temperature increasing.4. Application of nanogels in ocular drug delivery systemCytotoxicity assay exhibited no significant toxicity of the copolymer. Using FITC-loaded NPs, the influence of several parameters on the extent of NPs internalization by RPE cells were studied:(1): Concentration of NPs: Cells were incubated for 6 h with 0.01 mg/mL, 0.1 mg/mL, 1 mg/mL of NPs in 0.5 ml of medium. Remaining NPs were removed by three washing and new medium was added and the cultures were examined 48 h later. Result shows that the relative number of ingesting cells within the culture increases in parallel with the initial added NP concentration from 0.01 mg/mL to 1 mg/mL. (2): Duration of NP contact with RPE cells: After 48h of culture, cells were incubated with 1 mg/ml of NPs for 1h, 3h, 6h, 24h. The remaining NPs were washed out. The cultures were examined 48h later. Kinetics of NPs internalization shows that the process is rapid. The number of internalized NPs per cell increases rapidly when the contact time between cultured RPE cells and NPs is increased to 24h. In conclusion, the Dex-MA-g-PNIPAAm nanogel is non-toxic, non-stimulate and biocompatible biomedical material.