Zong-Chun Wang

Synthesis and properties of pH and temperature sensitive P(NIPAAm-co-DMAEMA) hydrogels

In order to investigate the influence of the continuous alkylamide sequence having pH sensitive unit on the temperature sensitivity of poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel, a monomer, N-(2-(dimethylamino) ethyl)-methacrylamide (DMAEMA), having an ethylamide group as well as an aliphatic tertiary amino group, was designed and synthesized. Hydrogels based on NIPAAm and DMAEMA were prepared via free radical polymerization. The resulted P(NIPAAm-co-DMAEMA) hydrogels were characterized in terms of maximum swelling ratio, swelling kinetics, temperature response kinetics, and effect of pH. The data obtained show that the novel hydrogels have the strong desire to respond to external temperature and pH stimuli. Importantly, because the P(NIPAAm-co-DMAEMA) hydrogels have the continuous alkylamide sequence containing isopropylamide pendant groups from PNIPAAm and ethylamide pendant groups from PDMAEMA, the incorporation of DMAEMA moiety not only provides the pH sensitivity, but also maintains the thermal properties of P(NIPAAm-co-DMAEMA) hydrogels, even as the molar percentage of DMAEMA moiety reaches 14 mol%.

Modular Synthesis of Thermosensitive P(NIPAAm-co-HEMA)/β-CD Based Hydrogels via Click Chemistry

Two kinds of representative polymers, poly(N-isopropylacrylamide) (PNIPAAm) and β-cyclodextrin (β-CD) were selected and modified with azide and alkyne fucntional groups, respectively. When the solutions of these two modified polymers were mixed together, a cross-linking reaction, a type of Huisgens 1,3-dipolar azide-alkyne cycloaddition, occurred in the presence of Cu(I) catalyst. The strategy described here provides several advantages for the hydrogel formation including mild reaction conditions and controllable gelation rate. The resulted hydrogels were studied in terms of scanning electric microscopy (SEM), equilibrium swelling ratio and swelling/shrinking kinetics. The data obtained demonstrated the hydrogels had a porous structure as well as favorable thermosensitivity.

In situ formation of thermosensitive PNIPAAm-based hydrogels by Michael-type addition reaction.

To investigate the possibility of in situ thermosensitive hydrogel formation via Michael-type addition reaction, we designed and prepared thiol- and vinyl-modified poly(N-isopropylacrylamide) (PNIPAAm)-based copolymers. When the solutions of these two kinds of PNIPAAm-based copolymers were mixed at physiological temperature (37 degrees C), a physical gelation resulting from the hydrophobic aggregation of PNIPAAm based copolymers and chemical cross-linking between thiol and vinyl functional groups or so-called chemical gelation occurred, resulting in the formation of a three-dimensional hydrogel. Because all the gelations were performed at a high temperature (above LCSTs of the PNIPAAm based copolymers), these in situ formed hydrogels presented heterogeneous network structures, resulting in an improved thermosensitivity in comparison with the conventional one.

Study on novel hydrogels based on thermosensitive PNIPAAm with pH sensitive PDMAEMA grafts

A series of novel hydrogels based on poly(N-isopropylacrylamide) (PNIPAAm) with pendant poly(N-(2-(dimethylamino) ethyl)-methacrylamide) (PDMAEMA) grafts were designed and synthesized. The influence of the pendant PDMAEMA grafts on the properties of the resulted hydrogels was examined in terms of morphology observed by scanning electron microscopy (SEM), thermal property characterized by differential scanning calorimetry (DSC) and shrinking/swelling kinetics upon external temperature changes. In comparison with the conventional PNIPAAm hydrogels, resulting hydrogels presented favorable pH sensitivity as well as improved thermosensitive properties, including enlarged water containing capability at room temperature and faster shrinking/swelling rate upon heating. In addition, fish DNA, used as a model drug, was loaded into the hydrogels, and the controlled release behavior of the drug-loaded hydrogels at different temperatures (22 and 37 degrees C) was further studied.

Fabrication of a novel pH-sensitive glutaraldehyde cross-linked pectin nanogel for drug delivery

A novel pH-sensitive nanogel based on pectin cross-linked with glutaraldehyde (PT-GA) was designed and synthesized for drug delivery. Transmission electron microscope observation shows that the nano-sized gel particles exhibit a spherical morphology. The optical absorbance study of nanogel suspension reveals its pH sensitivity. Cytotoxicity study shows that the nanogel has no apparent inhibitory effect on cells. The in vitro drug-release behavior of the drug-loaded nanogel particles in three kinds of media, i.e., simulated gastric fluid, simulated intestine fluid and simulated colon fluid, was studied. PT-GA nanogel exhibits a faster release at a high pH, and the release could be further accelerated in the presence of pectinolytic enzyme, indicating that the nanogel may be used for colon-specific drug delivery.

Efficient Capture and High Activity Release of Circulating Tumor Cells by Using TiO2 Nanorod Arrays Coated with Soluble MnO2 Nanoparticles

Effective capture and release of circulating tumor cells (CTCs) with high viability is still a challenge in medical research. We design a novel approach with efficient yield and high cell activity for the capture and release of CTCs. Our platform is based on TiO2 nanorod arrays coated with transparent MnO2 nanoparticles. We use hydrothermal synthesis to prepare TiO2 nanorod arrays, the MnO2 nanoparticles are fabricated through in situ self-assembly on the substrate to form a monolayer and etched by oxalic acid with low concentration at room temperature. Up to 92.9% of target cells are isolated from the samples using our capture system and the captured cells can be released from the platform, the saturated release efficiency is 89.9%. Employing lower than 2 × 10-3 M concentration of oxalic acid to dissolve MnO2, the viability of MCF-7 cancer cells exceed 90%. Such a combination of the two-dimensional and three-dimensional platforms provides a new approach isolate CTCs from patient blood samples.