Molecularly Imprinted Polymers for the isolation of bioactive naphthoquinones from plant extracts

Molecularly Imprinted Polymers (MIPs) targeting shikonin, a potent antioxidant and wound healing agent, have been prepared using methacrylic acid (MAA) and 2-diethylaminoethyl methacrylate (DEAEMA) as functional monomers. An investigation of solution association between shikonin and both acidic and basic functional monomers by UV-Vis titrations, suggested stronger affinity towards the basic functionality. Strong inhibition of the co-polymerisation reaction of such basic monomers was observed, but was overcome by reduction of the amount of template used during polymer synthesis. Polymer morphology was severely impacted by the template’s radical scavenging behaviour as demonstrated by solid state NMR spectroscopy measurements. HPLC evaluation of the final materials in polar conditions revealed limited imprinting effects and selectivity, with the MAA polymers exhibiting marginally better performance. During application of the polymers as MI-SPE sorbents in non-polar solvents it was found that the DEAEMA based polymer was more selective towards shikonin compared to the MAA counterpart, while shikonin recoveries of up to 72% were achieved from hexane solutions of a commercial sample of shikonin, hexane extract of Alkanna tinctoria roots and a commercial pharmaceutical ointment.

Endodontic 'Solutions'. Part 2:An audit comparing current practice in Belfast with UK and Republic of Ireland Dental Schools

Endodontic lubricants, irrigating solutions and medicaments help reduce the microbial load within root canals. Primary and secondary cases involve different microbes. Each'solution'or combinations thereof could play a significant role but no detailed guidelines exist on their use. An audit was undertaken to compare current practice in Belfast Dental School to the others across the UK and Republic of Ireland (ROI). This audit highlighted three main differences between Belfast and other dental schools. Many other institutions utilized other irrigants besides sodium hypochlorite (NaOCl), different intracanal medicaments, including calcium hydroxide, and higher concentrations of NaOCl. Having gathered this information, we ask, 'Is there sufficient evidence to change the endodontic regime currently used at Belfast Dental School?'. Using the findings from the literature review (Part 1), we introduce new evidence-based protocols for primary and secondary cases for use in Belfast Dental School. Clinical Relevance: In the absence of detailed clinical guidelines on the use of endodontic lubricants, irrigants and medicaments in primary and secondary cases, it is important to be aware of current practice in UK and ROI dental schools where dentists and specialists are trained.

Dental erosion among 12-14 year old school children in Khartoum:A pilot study

Objectives: To investigate dental erosion among 12-14 year old Sudanese school children and evaluate the associated risk factors. Basic Research Design: Cross sectional survey in secondary schools in Khartoum city, Sudan. Method and Participants: A sample of 157 school children was obtained from both private and public schools. Erosion on the labial and palatal surfaces of maxillary incisors was measured by criterion based on the Smith and Knight Tooth Wear Index. Dietary intake and other related factors were assessed using a questionnaire. Results: The overall erosion prevalence in this group was 66.9%, of which 45.2% was mild and 21.7% was moderate erosion. A strong association was found between erosion and private schooling (higher socioeconomic groups), carbonated drinks, herbal hibiscus drink and traditional acidic food consumption. Conclusion: There was a high prevalence of dental erosion among Sudanese school children which was mild to moderate in severity and was strongly associated with acidic dietary intake © BASCD 2007.

Degradable Polymer Networks and Star Polymers Based on Mixtures of Two Cleavable Dimethacrylate Crosslinkers: Synthesis, Characterization, and Degradation

Mixtures of two cleavable dimethacrylate crosslinkers, the hydrolyzable di(methacryloyloxy-1-ethoxy)methane (DMOEM) and the thermolyzable 1,1-ethylene-diol dimethacrylate (EDDMA), were used for the preparation of neat crosslinker polymer networks, randomly crosslinked polymer networks of methyl methacrylate (MMA), and star polymers of MMA, using group transfer polymerization in tetrahydrofuran (THF). All star polymers and randomly crosslinked polymer networks containing mixtures of the hydrolyzable DMOEM and the thermolyzable EDDMA crosslinkers gave THF-soluble final products when subjected to sequential thermolysis and hydrolysis, in this order. When applying sequential hydrolysis and thermolysis, only the star polymers with an EDDMA crosslinker content equal to or higher than 50% gave THF-soluble final products.

A cleavable network based on crosslinked star polymers containing acid-labile diacetal crosslinks: Synthesis, characterization and hydrolysis

A hydrolyzable model network comprising interconnected star polymers was prepared by the sequential group transfer polymerization of methyl methacrylate and the acid-labile diacetal-based dimethacrylate crosslinker bis[(2-methacryloyloxy)ethoxymethyl] ether. in contrast to other polymer networks previously synthesized by our group, all the branching points of this polymer network were found to hydrolyze under mildly acidic conditions, giving a linear copolymer with the theoretically expected molecular weight and composition. The ease of hydrolysis of this polymer network renders it a good candidate for use in the biomedical field. The characterization of the synthesized network, its linear and star polymer precursors and the hydrolysis products of the network and its precursors, by a variety of techniques, established the successful synthesis and hydrolysis of this well-defined polymer nanostructure.

Thermolyzable polymer networks and star polymers containing a novel, compact, degradable acylal-based dimethacrylate cross-linker: Synthesis, characterization, and thermolysis

A compact, cleavable acylal dimethacrylate cross-linker, 1,1-ethylenediol dimethacrylate (EDDMA), was synthesized from the anhydrous iron(III) chloride-catalyzed reaction between methacrylic anhydride and acetaldehyde. The ability of EDDMA to act as cross-linker was demonstrated by using it for the preparation of one neat cross-linker network, four star polymers of methyl methacrylate (MMA), and four randomly cross-linked MMA polymer networks using group transfer polymerization (GTP). For comparison, the corresponding polymer structures based on the commercially available ethylene glycol dimethacrylate (EGDMA) cross-linker (isomer of EDDMA) were also prepared via GTR The number of arms of the EDDMA-based star polymers was lower than that of the corresponding EGDMA polymers, whereas the degrees of swelling in tetrahydrofuran of the EDDMA-based MMA networks were higher than those of their EGDMA-based counterparts. Although none of the EDDMA-containing polymers could be cleanly hydrolyzed under basic or acidic conditions, they could be thermolyzed at 200 degrees C within 1 day giving lower molecular weight products.

Synthesis and characterization of star polymers and cross-linked star polymer model networks with cores based on an asymmetric, hydrolyzable dimethacrylate cross-linker

A hydrolyzable dimethacrylate cross-linker, 2-methyl-2,4-pentanediol dimethacrylate (MPDMA), was synhesized by the reaction of 2-methyl-2,4-pentanediol and methacryloyl chloride in the presence of triethylamine. This cross-linker was used to prepare a neat cross-linker network and three cross-linked star polymer model networks (CSPMNs) of methyl methacrylate (MMA), as well as star-shaped polymers of MMA, by group transfer polymerization (GTP). Gel permeation chromatography (GPC) in tetrahydrofuran (THF) confirmed the narrow molecular weight distributions (MWDs) of the linear polymer precursors, and demonstrated the increase in molecular weight (MW) on each successive addition of cross-linker or monomer. Characterization of the star polymers by static light scattering (SLS) in THF showed that star polymers with MPDMA cores bear a relatively small number of arms, between 7 and 35. All star polymers and polymer networks containing the MPDMA cross-linker were hydrolyzed at room temperature in neat trifluoroacetic acid to yield lower-MW products.

Synthesis and characterization of polymer networks and star polymers containing a novel, hydrolyzable acetal-based dimethacrylate cross-linker

An acid-labile dimethaerylate acetal cross-linker,di(methacryloyloxy-l-ethoxy)methane(DMOEM), was synthesized by the reaction of 2-hydroxyethyl methacrylate and paraformaldehyde using p-toluenesulfonic acid and toluene as catalyst and solvent, respectively. Group transfer polymerization was employed to use this cross-linker in the preparation of nine hydrolyzable polymer structures: one neat cross-linker network, one randomly cross-linked network of methyl methacrylate (MMA), and seven star-shaped polymers of MMA. Gel permeation chromatography (GPC) in tetrahydrofuran (THF) confirmed the narrow molecular weight distributions of the linear polymer precursors to the stars and demonstrated the increase in molecular weight upon the addition of cross-linker for the formation of star-shaped polymers. Characterization of the star polymers in THF using static light scattering and GPC showed that the molecular weights and the number of arms of each star polymer increased with an increase in the molar ratio of cross-linker to initiator and with a decrease in the molar ratio of monomer to initiator. The star polymers with DMOEM cores bore a smaller number of arms than those cross-linked with the non-hydrolyzable commercial cross-linker ethylene glycol dimethacrylate due to the bulkier structure of DMOEM. All DMOEM-containing polymer networks and star polymers were completely hydrolyzed within 48 h using hydrochloric acid in THF.

Synthesis and characterization of star polymers and cross-linked star polymer model networks containing a novel, silicon-based, hydrolyzable cross-linker

An acid-labile dimethacrylate cross-linker, dimethyldi(methacryloyloxy-l-ethoxy)silane (DMDMAES), was synthesized by the reaction of 2-hydroxyethyl methacrylate (HEMA) and dichlorodimethylsilane in the presence of triethylamine. Group transfer polymerization (GTP) was employed to use this cross-linker in the preparation of six hydrolyzable polymer structures: one neat cross-linker network, one randomly cross-linked network of methyl methacrylate (MMA), two star-shaped polymers of MMA, and two cross-linked star polymer model networks (CSPMNs) of MMA. A nonhydrolyzable CSPMN of MMA, based on a stable cross-linker, was also synthesized. Gel permeation chromatography (GPC) in tetrahydrofuran (THF) confirmed the narrow molecular weight distributions (MWDs) of the linear polymer precursors and demonstrated the increase in molecular weight (MW) upon each successive addition of cross-linker or monomer. Characterization by static light scattering (SLS) and GPC showed that star polymers with DMDMAES cores bear a relatively small number of arms, around 7. All star polymers and polymer networks were hydrolyzed using hydrochloric acid in THF. While the MWs of the products from the hydrolysis of the star polymers, the neat cross-linker network, and the randomly cross-linked network were as expected, those from the CSPMNs were of a much higher than expected MW, indicating extensive star-star coupling.

Human dental pulp fibroblasts express the "cold-sensing" transient receptor potential channels TRPA1 and TRPM8.

Abstract
INTRODUCTION:
Transient receptor potential (TRP) channels comprise a group of nonselective calcium-permeable cationic channels, which are polymodal sensors of environmental stimuli such as thermal changes and chemicals. TRPM8 and TRPA1 are cold-sensing TRP channels activated by moderate cooling and noxious cold temperatures, respectively. Both receptors have been identified in trigeminal ganglion neurones, and their expression in nonneuronal cells is now the focus of much interest. The aim of this study was to investigate the molecular and functional expression of TRPA1 and TRPM8 in dental pulp fibroblasts.
METHODS:
Human dental pulp fibroblasts were derived from healthy molar teeth. Gene and protein expression was determined by polymerase chain reaction and Western blotting. Cellular localization was investigated by immunohistochemistry, and TRP functionality was determined by Ca(2+) microfluorimetry.
RESULTS:
Polymerase chain reaction and Western blotting showed gene and protein expression of both TRPA1 and TRPM8 in fibroblast cells in culture. Immunohistochemistry studies showed that TRPA1 and TRPM8 immunoreactivity co-localized with the human fibroblast surface protein. In Ca(2+) microfluorimetry studies designed to determine the functionality of TRPA1 and TRPM8 in pulp fibroblasts, we showed increased intracellular calcium ([Ca(2+)](i)) in response to the TRPM8 agonist menthol, the TRPA1 agonist cinnamaldehyde, and to cool and noxious cold stimuli, respectively. The responses to agonists and thermal stimuli were blocked in the presence of specific TRPA1 and TRPM8 antagonists.
CONCLUSIONS:
Human dental pulp fibroblasts express TRPA1 and TRPM8 at the molecular, protein, and functional levels, indicating a possible role for fibroblasts in mediating cold responses in human teeth.

Evaluation of sources of uncertainties in microtensile bond strength of dental adhesive system for different specimen geometries

Objective: The aim of this research is to use finite element analysis (FEA) to quantify the effect of the sample shape and the imperfections induced during the manufacturing process of samples on the bond strength and modes of failure of dental adhesive systems through microtensile test. Using the FEA prediction for individual parameters effect, estimation of expected variation and spread of the microtensile bond strength results for different sample geometries is made. Methods: The estimated stress distributions for three different sample shapes, hourglass, stick and dumbbell predicted by FEA are used to predict the strength for different fracture modes. Parameters such as the adhesive thickness, uneven interface of the adhesive and composite and dentin, misalignment of axis of loading, the existence of flaws such as induced cracks during shaping the samples or bubbles created during application of the adhesive are considered. Microtensile experiments are performed simultaneously to measure bond strength and modes of failure. These are compared with the FEA results. Results: The relative bonding strength and its standard deviation for the specimens with different geometries measured through the microtensile tests confirm the findings of the FEA. The hourglass shape samples show lower tensile bond strength and standard deviation compared to the stick and dumbbell shape samples. ANOVA analysis confirms no significant difference between dumbbell and stick geometry results, and major differences of these two geometries compared to hourglass shape measured values. Induced flaws in the adhesive and misalignment of the angle of application of load have significant effect on the microtensile bond strength. Using adhesive with higher modulus the differences between the bond strength of the three sample geometries increase. Significance: The result of the research clarifies the importance of the sample geometry chosen in measuring the bond strength. It quantifies the effect of the imperfections on the bond strength for each of the sample geometries through a systematic and all embracing study. The results explain the reasons of the large spread of the microtensile test results reported by various researchers working in different labs and the need for standardization of the test method and sample shape used in evaluation of the dentin-adhesive bonding system. © 2007 Academy of Dental Materials.