Jigeng Xu

Encapsulation of enzymes in mesoporous host materials via the nonsurfactant-templated sol–gel process

Abstract A new, simple, one-step method for enzyme immobilization is demonstrated with encapsulating alkaline phosphatase in mesoporous sol–gel silica. Since the pore size (e.g., ∼30 A) of the mesoporous silica is much greater than that (e.g., ∼15 A) in traditional microporous sol–gel silica, enzymatic activity is increased by a factor of 2 to 10 because of easy diffusion of the substrate molecules. Compared to macroporous materials, the channel is narrow enough to prevent the enzyme from leaking out of its cage.

Novel organic–inorganic chemical hybrid fillers for dental composite materials

A series of new polymethacrylate–silica chemical hybrid dental fillers has been prepared by the sol–gel reactions of poly[methyl methacrylate-co-3-(trimethoxysilyl) propyl methacrylate] or poly[3-(trimethoxysilyl)propyl methacrylate] with tetraethyl orthosilicate at various compositions. In these hybrid fillers, the polymethacrylate chains are uniformly distributed in and covalently bonded to the silica networks at molecular level without macroscopic organic–inorganic phase separation. The contact angle and surface tension parameters indicate that the hybrid fillers have better wetting properties with the 2,2-bis(p-2-hydroxy-3-methacryloxypropoxyphenyl)propane/triethyleneglycol dimethacrylate resin and stronger interfacial bonding with the polymer matrix than pure silica fillers. The compressive testing results demonstrate that the dental composites prepared with the hybrid fillers tend to have enhanced mechanical properties in comparison to those with the silane-treated fused silica and the pure sol-gel silica fillers at the same silica content. Scanning electron micrographic study reveals that upon compressive tests the dental composites with the hybrid fillers have fewer failures at the filler–matrix interface than those with pure silica fillers.

Synthesis of Mesoporous Silica Materials via Nonsurfactant Urea-Templated Sol-Gel Reactions

Mesoporous silica materials with pore diameters of 2 to 6 nm have been prepared using urea as a nonsurfactant template or pore-forming agent in HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate, followed by removing the urea molecules by extraction with methanol or water. Characterization results from nitrogen sorption isotherm, powder X-ray diffraction, and transmission electron microscopy indicate that the materials have large specific surface areas (e.g., 600 m2/g) and pore volumes (e.g., 0.8 cm3/g) as well as narrow pore size distributions. The mesoporosity is arisen from interconnecting wormlike channels and pores of regular diameters. As the urea concentration is increased, the nitrogen sorption isotherms of the silica matrices transform from the reversible type I to the type IV form with type H2 hysteresis, along with increases in the diameter and volume of the pores.

Compression and Aging Properties of Experimental Dental Composites Containing Mesoporous Silica as Fillers

ABSTRACT Porous fillers can be used to obtain micromechanical interlocking between the filler particles and polymer matrix. Micromechanical interlocking in dental composites can overcome the traditional problem of hydrolysis associated with silane coupling. Such an interlocking could also enhance the overall performance of dental composites. In the current study, mesoporous silica was used as fillers to obtain experimental composites. Light curable dental resin (BisGMA/TEGDMA) was used as polymer matrix. The mechanical (compressive) and aging properties of these experimental composites were investigated. The results demonstrated that mesoporous fillers improved the mechanical and aging properties of experimental dental composites.

Sol-Gel Synthesis of Mesoporous Titania using Nonsurfactant Organic Compounds as Templates

Abstract Organic-inorganic composite materials were prepared via HCl-catalyzed sol-gel reactions of tetrabutyl titanate at room temperature in the presence of nonsurfactant compounds, such as 2,2-bis(hydroxymethyl)propionic acid, glycerin and pentaerythritol, as templates or pore-forming agents. Removal of the nonsurfactant molecules from the composites by extraction with water resulted in mesoporous titania materials. Characterized with nitrogen adsorption-desorption isotherms, X-ray diffraction and transmission electron microscopy, these materials were found to have large surface areas (∼300 m2/g) and pore volumes (∼0.25 cm3/g) as well as narrowly distributed pore diameters of around 3.2 nm. Similar results were also obtained when a neutral surfactant poly(ethylene glycol) was used as the templates. In the presence of templates, the titania materials obtained may contain crystalline anatase phase.