Objectives This study demonstrates the effects of nano-scale prepolymer particles as additives to model dental monomer and composite formulations. Methods Discrete nanogel particles were prepared by solution photopolymerization of isobornyl methacrylate and urethane dimethacrylate in the presence of a chain transfer agent, which also provided a means to attach reactive groups to the prepolymer. Nanogel was added to triethylene glycol dimethacrylate (TEGDMA) in increments between 5 and 40 wt% with resin viscosity, reaction kinetics, shrinkage, mechanical properties, stress and optical properties evaluated. Maximum loading of barium glass filler was determined as a function of nanogel content and composites with varied nanogel content but uniform filler loading were compared in terms of consistency, conversion, shrinkage and mechanical properties. Results High conversion, high molecular weight internally crosslinked and cyclized nanogel prepolymer was efficiently prepared and redispersed into TEGDMA with an exponential rise in viscosity accompanying nanogel content. Nanogel addition at any level produced no deleterious effects on reaction kinetics, conversion or mechanical properties, as long as reactive nanogels were used. A reduction in polymerization shrinkage and stress was achieved in proportion to nanogel content. Even at high nanogel concentrations, the maximum loading of glass filler was only marginally reduced relative to the control and high strength composite materials with low shrinkage were obtained. Significance The use of reactive nanogels offers a versatile platform from which resin and composite handling properties can be adjusted while the polymerization shrinkage and stress development that challenge the adhesive bonding of dental restoratives are controllably reduced.
Purpose-To develop a light activated polycaprolactone dimethacrylate and hydroxyethyl methacrylate based gel network that sustains the release of stable, active bevacizumab (an anti-VEGF antibody used to treat choroidal neovascularization) and to assess sustained ex vivo delivery in rabbit eyes and in vivo delivery in rat eyes following in situ gel formation in the suprachoroidal space.Methods-Polycaprolactone dimethacrylate (PCM) was synthesized from polycaprolactone diol (PCD) and evaluated using NMR spectroscopy. PCM was used to cross-link hydroxyethyl methacrylate (HEMA) in the presence of 365 nm UV light and 2, 2-dimethoxy-2-phenylacetophenone (DMPA) as a photoinitiator. Bevacizumab was entrapped in the gel using 3 different cross-linking durations of 3, 7, and 10 minutes. In vitro release of bevacizumab in PBS pH 7.4 at 37°C during a 4 months study was quantified using a VEGF-binding based ELISA. Stability of released bevacizumab was monitored by size exclusion chromatography (SEC) and circular dichroism. Alexa Fluor ® 488 dye conjugated bevacizumab mixed with polymers was injected suprachoroidally in rabbit eyes to study the effect of different cross-linking durations on the spread of the dye conjugated bevacizumab. In vivo delivery was assessed in Sprague Dawley (SD) rats by injecting Alexa Fluor ® 488 dye conjugated bevacizumab mixed with polymers followed by cross-linking for 10 minutes. Spread in the rabbit eyes and in vivo delivery in rat eyes was monitored noninvasively using a fundus camera and Fluorotron Master™.Results-Formation of PCM was confirmed by the disappearance of hydroxyl peak in NMR spectra. Cross-linking duration of 10 minutes resulted in a burst release of 21 % of bevacizumab. Other cross-linking durations had ≥ 62 % burst release. Bevacizumab release from 10 minute cross-linked gel was sustained for ∼ 4 months. Release samples contained ≥ 96. bevacizumab in the monomeric form as observed in SEC chromatograms. Circular dichroism confirmed that secondary β-sheet structure of bevacizumab was maintained after release from the gel. As the cross-linking duration was increased to 10 minutes, the gel/antibody was better confined at the injection site in excised rabbit eye suprachoroidal space. Delivery of Alexa Fluor ® 488 dye conjugated bevacizumab was sustained for at least 60 days in the suprachoroidal space of SD rats.Conclusion-PCM and HEMA gel sustained bevacizumab release for 4 months and maintained the stability and VEGF-binding activity of bevacizumab. Light activated PCM and HEMA gel is suitable for in situ gel formation and sustained protein delivery in the suprachoroidal space.
A series of nanogel compositions were prepared from urethane dimethacrylate (UDMA) and isobornyl methacrylate (IBMA) in the presence of a thiol chain transfer agent. The linear oligomer of IBMA was synthesized by a similar solution polymerization technique. The nanogels were prepared with different crosslinker concentrations to achieve varied branching densities and molecular weights. The prepolymers were dispersed in triethylene glycol dimethacrylate at loading levels ranging from 10 wt% to 50 wt%. Photopolymerization reaction kinetics of all prepolymer modified systems were enhanced relative to the nanogel-free control during early stage polymerization while limiting conversion was similar for most samples. Volumetric polymerization shrinkage was reduced proportionally with the prepolymer content while the corresponding decrease in polymerization stress was potentially greater than an additive linear behavior. Flexural strength for inert linear polymer-modified systems decreased significantly with the increase in the prepolymer content; however, with an increase in the crosslinker concentration within the nanogel additives, and an increase in the concentration of residual pendant reactive sites, flexural strength was maintained or improved regardless of the nanogel loading level. This demonstrates that covalent attachment rather than just physical entanglement with the polymer matrix is important for effective polymer mechanical reinforcement by nanogel additives. Reactive nanogel additives can be considered as a practical, generic means to achieve substantial reductions in polymerization shrinkage and shrinkage stress in common polymers.
A total of 32 mutations were generated within the TATA-proximal site 1 (-72 to -47) of soybean heat shock gene Gmhsp17.5E in order to functionally define the optimal configuration of sequences within the heat shock element (HSE). Mutants were tested in vivo utilizing sunflower tumors transformed by a T-DNA based vector. Promoter activity was determined by S1 nuclease hybrid protection analysis of tumor transcripts. A total of five repeats (5'-nGAAn-3' or 5'-nTTCn-3') which comprise the HSE at site 1 were required for full transcription induction by heat stress. Analysis of non-conserved bases flanking the central trinucleotide block indicated that 5'-aGAAg'-3' is the optimum sequence for the 5 bp repeat.
Brain-targeted delivery of various drugs can be successfully achieved by chemical delivery systems (CDS) that contain a 1,4-dihydropyridine-based redox targetor moiety and undergo a sequential metabolism. However, the susceptibility of this moiety toward hydration in acidic media may limit the shelf-life of such compounds in aqueous formulation. Here, a systematic investigation of the chemical stability toward oxidation and hydration of ester and amide derivatives of 3-substituted 1,4-dihydropyridine, 1,4-dihydroquinoline, and 4-substituted 1,2-dihydroisoquinoline is reported, together with the in vitro stability and in vivo (rat) distribution of isoquinoline-based testosterone and hydrocortisone chemical delivery systems, which were selected as having the most suitable acid-resistant targetor moieties.
Current challenges in adhesive dentistry include over-hydrophilic bonding formulations, which facilitate water percolation through the hybrid layer and result in unreliable bonded interfaces. This study introduces nanogel-modified adhesives as a way to control the material's hydrophobic character without changing the basic monomer formulation (keeping water-chasing capacity and operatory techniques unaltered). Nanogel additives of varied hydrophobicity were synthesized in solution, rendering 10-to 100-nm-sized particles. A model BisGMA/HEMA solvated adhesive was prepared (control), to which reactive nanogels were added. The increase in adhesive viscosity did not impair solvent removal by air-thinning. The degree of conversion in the adhesive was similar between control and nanogel-modified materials, while the bulk dry and, particularly, the wet mechanical properties were significantly improved through nanogel-based network reinforcement and reduced water solubility. As preliminary validation of this approach, short-term micro-tensile bond strengths to acid-etched and primed dentin were significantly enhanced by nanogel inclusion in the adhesive resins.
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