Free-radical homopolymerizations of 2-hydroxyethyl methacrylate (HEMA) and diethylene glycol dimethacrylate (DEGDMA) photoinitiated by 2,2-dimethoxy-2-phenylacetophenone (DMPA) were studied. A novel analytical method for elucidating the free-volume dependencies of the propagation and termination kinetic constants from a single set of kinetic data is developed. The polymerization is divided into four regimes, nondiffusion limited, autoacceleration, reaction−diffusion without propagation limitations, and autodeceleration, in order to glean the parameters that describe the free-volume dependency. The parameters found via this method are used in a concurrently developed model to predict the polymerization rates and kinetic constant evolution throughout the polymerization. The rates and kinetic constants predicted by the model agree well with the experimentally determined rates and kinetic constants.

The polymerization behavior of a new class of dimethacrylated anhydride monomers that react to form highly cross-linked degradable networks was investigated using various photoinitiation schemes. Polymerizations occurred in seconds to minutes depending on the initiating conditions, and conversions in excess of 0.95 were achievable. A photobleaching visible light initiating system was used to improve the depth of cure for the production of polymers with appreciable dimensions. One potential application for the proposed multifunctional monomers is in vivo curing of high-strength, degradable polymers for fracture fixation or filling of trabecular bone defects.

No abstract

No abstract

No abstract

Because numerous drugs are administered through an oral route and primarily absorbed at the intestine, the prediction of drug permeability across an intestinal epithelial cell membrane has been a crucial issue in drug discovery. Thus, various in vitro permeability assays have been developed such as the Caco-2 assay, the parallel artificial membrane permeability assay (PAMPA), the phospholipid vesicle-based permeation assays (PVPA) and Permeapad. However, because of the time-consuming and quite expensive process for culturing cells in the Caco-2 assay and the unknown microscopic membrane structures of the other assays, a simpler yet more accurate and versatile technique is still required. Accordingly, we developed a new platform to measure the permeability of small molecules across a planar freestanding lipid bilayer with a well-defined area and structure. The lipid bilayer was constructed within a conventional UV spectrometer cell, and the transport of drug molecules across the bilayer was recorded by UV absorbance over time. We then computed the permeability from the time-dependent diffusion equation. We tested this assay for five exemplary hydrophilic drugs and compared their values with previously reported ones. We found that our assay has a much higher permeability compared to the other techniques, and this higher permeability is related to the thickness of the lipid bilayer. Also we were able to measure the dynamic permeability upon the addition of a membrane-disrupting surfactant demonstrating that our assay has the capability to detect real-time changes in permeability across the lipid bilayer.

No abstract

Micrometer-sized aqueous droplets serve as a unique reactor that drives various chemical reactions not seen in bulk solutions. However, their utilization has been limited to the synthesis of low molecular weight products at low reactant concentrations (nM to μM). Moreover, the nature of chemical reactions occurring outside the droplet remains unknown. This study demonstrated that oil-confined aqueous microdroplets continuously generated hydroxyl radicals near the interface and enabled the synthesis of polymers at high reactant concentrations (mM to M), thus successfully converting the interfacial energy into the synthesis of polymeric materials. The polymerized products maintained the properties of controlled radical polymerization, and a triblock copolymer with tapered interfaces was prepared by the sequential addition of different monomers into the aqueous microdroplets. Furthermore, a polymerization reaction in the continuous oil phase was effectively achieved by the transport of the hydroxyl radicals through the oil/water interface. This interfacial phenomenon is also successfully applied to the chain extension of a hydrophilic polymer with an oil-soluble monomer across the microdroplet interface. Our comprehensive study of radical polymerization using compartmentalization in microdroplets is expected to have important implications for the emerging field of microdroplet chemistry and polymerization in cellular biochemistry without any invasive chemical initiators.