Development of Amelogenin-chitosan Hydrogel for <em>In Vitro</em> Enamel Regrowth with a Dense Interface

Biomimetic enamel reconstruction is a significant topic in material science and dentistry as a novel approach for the treatment of dental caries or ...

University of Southern California

Bioactive monetite (anhydrous calcium hydrogen phosphate, CaHPO(4)) with orderly layered structure assembled by nanosheets has been successfully synthesized by a sonochemical-assisted method in the presence of cetyltrimethylammonium bromide (CTAB). The thicknesses of the nanosheets are 100-200 nm, and the lateral sizes are about 2 microm. Because of the strong affinity with the phosphate ions as well as the (200) faces of the crystals, CTAB molecules can make the formation and stabilization of monetite nanosheets with (200) exposed face. Ultrasonic irradiation makes the transition from disordered state to oriented state before the oriented assembly of monetite nanosheets. The ultrasonic irradiation provides enough external work to make the assemble process possible in thermodynamics. The drastic flow stirred by the supersonic jet in the solution accomplishes the transition and successive oriented assembly of nanosheets in dynamics. This study would offer a simple method to design and synthesize oriented-assembled materials.

Ultrasonic-irradiation-assisted oriented assembly of ordered monetite nanosheets stacking.

The layer-by-layer (LbL) assembly as a simple and effective method has been extensively used to prepare polyelectrolyte films but the buildup mechanism is expected to be further clarified. In this work, the structure and formation mechanism of LbL-assembled heparin/chitosan multilayer composite films were characterized by electrochemical system, scanning electron microscope and atom force microscope. The results revealed that the film grew linearly in the first 10 bilayers based on measured linear increase of film resistance with number of layers, while the film grew exponentially in the later 10 bilayers based on measured nonlinear increase of film resistance. The charge-transfer resistance increased in an oscillatory way or a linear way at different growing stages, which was discussed with their formation mechanism and the interfacial structure on electrode. A buildup mode of the LbL film was suggested based on the structural and electrochemical characters.

Investigation of layer-by-layer assembled heparin and chitosan multilayer films via electrochemical spectroscopy.

Here we report the design of a new external electric field-controlled release system using functional dipolar molecules as nanoimpellers. The dipolar molecule 4-(3-cyanophenyl)butylene, which can reorient in response to external electric fields with different frequencies because of its strong inherent dipole moment, was synthesized and grafted onto the inner surfaces of mesopores. Under an alternating electric field, the swinging flexible molecular chains consequently push guest molecules out of the pore voids. This innovative approach to controlled release may provide important application opportunities in tumor treatment with a number of advantages in terms of local release with targetability, external remote control, and the nonelectrochemical nature of the process.

Dipolar molecules as impellers achieving electric-field-stimulated release.

Using acetylene black as an assistant reagent in the ammonia atmosphere, one dimensional (1D) hexagonal single crystalline aluminum nitride (AIN) nanowires were successfully synthesized via carbothermal reduction and nitridation method. With smooth surface and uniform diameter, the wool-like product of AIN nanowires grow along [001] direction and are 80-120 nm in diameter and several tens micrometers in length. According to thermodynamic and kinetic analysis, AI2O3 initially was reduced to a volatile suboxide gas Al2O at 1800 degrees C. Then gaseous Al2O was transported by N2/NH3 mixtures to about 1200 degrees C, where 1D AIN nanowires formed by the reaction of Al2O gas, graphite and NH3. Due to high surface area, small particle size and amorphous structure, acetylene black maybe possess more active sites and more effective contact area, which benefits the first step reaction. The electrostatic polar charge model and crystallographic characteristics are employed to explain the growth mechanism of AIN nanowires. To our knowledge, acetylene black is the first time to be used for synthesizing 1D AIN nanostructures via carbothermal reduction and nitridation method, which would be an efficient, economical assistant reagent for fabricating nitride nanostructures.

Synthesis of h-AIN nanowires via carbothermal reduction and nitridation method using acetylene black.

A sensitive and effective amperometric glucose biosensor based on gold nanotubes electrode (GNTE) was investigated. Gold nanotubes (GNTs), which were prepared by electroless plating of the metal within the pores of nanoporous polycarbonate (PC) track-etched membranes, were filled into a hollow teflon cylinder to construct a GNTE. Glucose oxidase (GOD) was immobilized on the electrode via glutaraldehyde cross-linkage method. The electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The km value of the immobilized glucose oxidase on GNTE was 0.47 mM. The biosensor showed a linear range from 0.4 to 11 mM with excellent sensitivity of 8.77 microA cm(-2) mM(-1) and fast response time within 5 s.

An effective gold nanotubes electrode for amperometric biosensor.

Biomimetic reconstruction of tooth enamel is a significant topic of study in materials science and dentistry as a novel approach to the prevention, restoration, and treatment of defective enamel. We have developed a new amelogenin-containing chitosan hydrogel for enamel reconstruction that works through amelogenin supramolecular assembly, stabilizing Ca-P clusters and guiding their arrangement into linear chains. These amelogenin Ca-P composite chains further fuse with enamel crystals and eventually evolve into enamel-like co-aligned crystals, anchored to the natural enamel substrate through a cluster growth process. A dense interface between the newly grown layer and natural enamel was formed and the enamel-like layer improved the hardness and elastic modulus compared with etched enamel. We anticipate that this chitosan hydrogel will provide effective protection against secondary caries because of its pH-responsive and antimicrobial properties. Our studies introduce an amelogenin-containing chitosan hydrogel as a promising biomaterial for enamel repair and demonstrate the potential of applying protein-directed assembly to biomimetic reconstruction of complex biomaterials.

Qichao Ruan

Center for Craniofacial Molecular Biology,
Herman Ostrow School of Dentistry,
Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry

University of Southern California

Development of Amelogenin-chitosan Hydrogel for In Vitro Enamel Regrowth with a Dense Interface

Qichao Ruan

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Center for Craniofacial Molecular Biology,Herman Ostrow School of Dentistry,Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry

University of Southern California

Development of Amelogenin-chitosan Hydrogel for In Vitro Enamel Regrowth with a Dense Interface

Center for Craniofacial Molecular Biology,
Herman Ostrow School of Dentistry,
Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry