Kemin Wang

Photopolymerization of methacrylated chitosan/PNIPAAm hybrid dual-sensitive hydrogels as carrier for drug delivery

A series of hybrid hydrogels based on glycidyl methacrylated chitosan (CS-GMA) and N-isopropylacrylamide (NIPAAm) were designed and prepared via photopolymerization technology. The hydrogels were characterized by Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC) and optical transmittance. The interior morphology of hydrogels was investigated by scanning electron microscopy (SEM). The swelling experiment results revealed that hybrid hydrogel exhibited combined pH and temperature sensitivities. Acid orange 8 (AO8) and 5-flurouracil (5-Fu) were selected as model drugs for examining their release from hydrogels. The results suggested that hydrogel composition and pH value of buffer solution had great influences on release profiles.

Design of genipin-crosslinked microgels from concanavalin A and glucosyloxyethyl acrylated chitosan for glucose-responsive insulin delivery

Glucose-responsive systems are significant for self-regulated insulin delivery. The aim of this study was to assess the potential of genipin-crosslinked concanavalin A/GEA-chitosan microgels as a glucose-responsive insulin delivery system. A chitosan derivative (GEA-chitosan) was designed in this study as the polymer ligand of concanavalin A (Con A), which not only exhibits a strong affinity to Con A, but also could be directly crosslinked with Con A by genipin, thus avoiding the modification of Con A during an immobilization process. Glucose responsive microgels were fabricated by the reversed-phase emulsion crosslinking method. The in vitro release of insulin indicated that the insulin release was influenced by glucose concentrations, and a desired pulsatile release behavior was detected in response to stepwise glucose challenges for more than eight cycles. The release data were fitted well to an exponential model, without any significant influence of the surface effect. The released insulin was proved to remain active without destruction of the tertiary structure. The analysis of L929 cells viability suggested that these microgels possessed no in vitro cytotoxicity. The obtained genipin crosslinked Con A/GEA-chitosan microgels might be a potential candidate for self-regulated insulin delivery.

Sesamin as a co-initiator for unfilled dental restorations.

A natural component, sesamin (SA), was used to replace conventional amine as co-initiator for dental composite. A combination of camphorquinone (CQ) and SA was employed to initiate the photopolymerization of 2-2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl] propane/triethylene glycol dimethacrylate (70/30wt.%). The kinetics was recorded by real-time Fourier transform infrared spectroscopy. The mechanical properties were measured by dynamic mechanical analysis, the cell toxicity was investigated by MTT assay and a mixture of CQ and ethyl 4-N,N-dimethylaminobenzoate (EDMAB) was used as control in the same photocuring condition. The results indicated that the addition of SA as co-initiator greatly improved the rate of polymerization and final double-bond conversion (DC) when compared with the system initiated by CQ alone. Compared with EDMAB, the final DC of the CQ/SA system (71%) was slightly lower than that of CQ/EDMAB (76%); SA resulted in approximately the same storage modulus at around 37 degrees C, but a slightly higher glass transition temperature. SA produced lower yellowing effect and good in vitro biocompatibility. The water sorption and solubility for two mixtures were very close and within the range of the ISO 4049 specification. These results suggest that SA is an effective alternative co-initiator to conventional amine. The natural compound characteristics of SA make it more promising than amine in dental resin formulations.

Preparation and characterization of water-soluble chitosan derivative by Michael addition reaction.

The efficient procedure to prepare novel water-soluble chitosan derivative was established by Michael addition reaction to introduce sodium allylsulfonate into the chitosan at mild condition. The chemical structure of the chitosan derivative was characterized by FT-IR, (1)H NMR and Elemental analysis. The degree of substitution (DS) was calculated by Elemental analysis. The chitosan derivative exhibited an excellent solubility in the distilled water. The physical properties were analyzed by XRD and TG. The XRD study indicated that the crystallinity of chitosan derivative decreased. The thermal analysis showed that chitosan derivative had lower thermal stability than chitosan.

Influence of chemical structures of benzodioxole-based coinitiators on the properties of the unfilled dental resin

To investigate the influence of chemical structures of benzodioxole-based coinitiator on the initiating reactivity and the mechanical properties of cured samples for the unfilled dental resin, a mixture of 2,2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl]propane (bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) (70/30 wt.%) was photoinduced by combinations of camphorquinone (CQ) and benzodioxole derivatives. 2-(N,N-Dimethylamino)ethyl methacrylate (DMEM) was used as control. The kinetics was monitored by a real-time Fourier transformation infrared spectroscopy (FTIR) and the dynamic mechanical analysis was performed on a dynamic mechanical analyzer (DMA). The cytotoxicity property of the cured samples was evaluated by MTT assay in vitro using VERO as reference cell lines. The results indicated that the 4-position phenyl ring substituents of the benzodioxole-based coinitiator had great influence on the initiating reactivity. Incorporating substituents with pi electron acceptors in the 4-position of phenyl ring led to the decrease of the rate of polymerization (R(p)) of the CQ/benzodioxole derivatives. However, the electron-donating substituents were useful to increase the reactivity. When compared with CQ/amine initiating systems, the combination of CQ and benzodioxole compounds caused lower R(p) but the comparable final double bond conversion. All the cured films initiated by CQ/benzodioxole derivatives had almost the same glass transition temperature (T(g)) and storage modulus. Indirect cytotoxicity assessment indicated low cytotoxicity of benzodioxole derivatives. These results were very useful for the design of benzodioxole derivatives with satisfactory reactivity and biocompatibility, and are very important for clinical applications.

Preparation and properties of cyclic acetal based biodegradable gel by thiol-ene photopolymerization.

Synthetic, hydrolytically degradable biomaterials have been widely developed for biomedical use; however, most of them will form acidic products upon degradation of polymer backbone. In order to address this concern, we proposed to fabricate a biodegradable gel based on the crosslinking of a cyclic acetal monomer with reactable diallyl group and multifunctional thiols by thiol-ene photopolymerization. This gel produces diols and carbonyl end groups upon hydrolytic degradation and could be entirely devoid of acidic by-products. Real time infrared spectroscopy was employed to investigate the effect of different light intensities and concentrations of photoinitiator on the polymerization kinetics. With the increase of the concentration of photoinitiator and light intensity, both the rate of polymerization and final double bond conversion increased. Degradation of cyclic acetal based networks was investigated in PBS medium so as to simulate physiological conditions. The remaining mass of the materials after 25 days incubation was 84%. TGA analysis showed that the gels exhibited a typical weight loss (97.2%) at around 378 °C. In vitro cytotoxicity showed that the cyclic acetal based gels had non-toxicity to cell L-929 and had good biocompatibility.

Synthesis and characterization of water-soluble glucosyloxyethyl acrylate modified chitosan

A novel water-soluble chitosan derivative, glucosyloxyethyl acrylated chitosan was successfully synthesized by Michael addition reaction of chitosan with glucosyloxyethyl acrylate (GEA), and the obtained glyco-chitosan derivative was characterized by FT-IR, (1)H NMR, elemental analysis, XRD, TG, DSC and SEM. The FT-IR and (1)H NMR results showed that GEA residues were grafted onto the amino group of chitosan. The degree of substitution (DS) was calculated by elemental analysis. XRD data revealed that the introduced saccharide moieties decreased the crystalline structure of chitosan. TG and DSC results demonstrated that the glucosyloxyethyl acrylated chitosan was less thermal stable than chitosan. This efficient synthetic method provided an approach of preparing water-soluble glyco-chitosan derivatives. The obtained derivatives would show stronger specific affinity of lectin than chitosan thus would have potential applications in biomaterials.

Material design and photo-regulated hydrolytic degradation behavior of tissue engineering scaffolds fabricated via 3D fiber deposition

An ideal behavior of a tissue engineering scaffold is that it degrades and reshapes at a rate that matches the formation of new tissues. However, this ideal situation may not occur as the scaffold often undergoes too slow or too fast degradation. To test the promise of the active control of scaffold degradation, in this work, a photo/water dual-degradable porous scaffold was designed and fabricated using a 3D fiber deposition (3DF) system from a linear biopolymer (named PLANB) that combined the o-nitrobenzyl linkages and hydrolysable ester bone in the polymer chains. The chemical structure, molecular weight and polydispersity of PLANB were characterized by IR, NMR, GPC and MALDI-TOF-MS. The thermal properties of PLANB evaluated by DSC and TGA assays enabled a 3DF printing at the temperature around its melting point without chemical changes. The introduction of a real-time IR (RTIR) technique not only facilitated the determination of photolysis kinetics and quantum yield, but also enabled the capture of intermediate products during the photo-cleavage process of PLANB scaffolds. A minute-scale daily photolysis combined with a continuous hydrolysis process was implemented to test the photo-regulated hydrolytic degradation behavior of PLANB scaffolds in vitro, and the results obtained from both the SEM image and the mass loss profile demonstrated a porous-void microstructure along the strands of scaffolds and an apparent increase of the mass loss amount compared with the control group without photo-irradiation. Furthermore, PLANB scaffolds showed low cytotoxicity to L929 cells and performed well in promoting cell adhesion. It can therefore be concluded that such scaffolds have great potential in offering a diverse range of control over degradation kinetics of tissue engineering scaffolds to be tailored to individual tissue regeneration situations.

In-situ dispersed photopolymerization of cyclic acetals/hydroxyapatite composites: effects of the content of hydroxyapatite.

In this work, hydroxyapatite (HA) was first dispersed into cyclic acetal unit based monomers (EHD), and then EHD/HA composites were obtained by in-situ photopolymerization. FTIR and XRD analyses were used to successfully confirm the chemical composition of this composite. Real-time FTIR revealed that there was no significant effect on the photopolymerization process until the HA content was up to 30%. Several samples of such a composite with different loading amounts of HA were prepared to study effects of HA concentrations on the EHD/HA composite in particular in terms of SEM, TG, DMA, water contact angel and in-vitro biocompatibility. The results appeared that the loading of HA could significantly improve the thermal stability, mechanical properties and in vitro biocompatibility of the EHD/HA composite compared with EHD networks.

Synthesis and photopolymerization kinetics of a single-molecular hydrogen-abstract free radical photoinitiator 1,3-Benzodioxole-5-yl-Methyl-Maleimide

1,3-benzodioxole-5-yl-methyl-maleimide (BDOMM), a type of hydrogen-abstraction photoinitiator with both hydrogen donor and acceptor in one molecule for free radical photopolymerization, was synthesized through the reaction of piperonyl amine and maleic anhydride and characterized by IR, UV and 1H NMR spectroscopy. The results obtained indicated that the introduction of BDOMM could avoid the use of additional amine coinitiator, decrease the leachablity of photoinitiator and maintain high photo-initiation efficiency.