Effect of water-aging on the antimicrobial activities of an ORMOSIL-containing orthodontic acrylic resin

Quaternary ammonium methacryloxy silicate (QAMS), an organically modified silicate (ORMOSIL) functionalized with polymerizable methacrylate groups and an antimicrobial agent with a long lipophilic alkyl chain quaternary ammonium group, was synthesized through a silane-based sol–gel route. By dissolving QAMS in methyl methacrylate monomer, this ORMOSIL molecule was incorporated into an auto-polymerizing, powder/liquid orthodontic acrylic resin system, yielding QAMS-containing poly(methyl methacrylate). The QAMS-containing acrylic resin showed a predominant contact-killing effect on Streptococcus mutans (ATCC 35668) and Actinomyces naeslundii (ATCC 12104) biofilms, while inhibiting adhesion of Candida albicans (ATCC 90028) on the acrylic surface. The antimicrobial activities of QAMS-containing acrylic resin were maintained after a 3 month water-aging period. Bromophenol blue assay showed minimal leaching of quaternary ammonium species when an appropriate amount of QAMS (<4 wt.%) was incorporated into the acrylic resin. The results suggest that QAMS is predominantly co-polymerized with the poly(methyl methacrylate) network, and only a minuscule amount of free QAMS molecules is present within the polymer network after water-aging. Acrylic resin with persistent antimicrobial activities represents a promising method for preventing bacteria- and fungus-induced stomatitis, an infectious disease commonly associated with the wearing of removable orthodontic appliances.     

Antimicrobial peptide incorporated poly(2-hydroxyethyl methacrylate) hydrogels for the prevention of Staphylococcus epidermidis-associated biomaterial infections

The effectiveness of the antimicrobial peptide maximin-4, the ultrashort peptide H-Orn-Orn-Trp-Trp-NH(2), and the lipopeptide C(12)-Orn-Orn-Trp-Trp-NH(2) in preventing adherence of pathogens to a candidate biomaterial were tested utilizing both matrix- and immersion-loaded poly(2-hydroxyethyl methacrylate) (poly(HEMA)) hydrogels. Antiadherent properties correlated to both the concentration released and the relative antimicrobial concentrations of each compound against Staphylococcus epidermidis ATCC 35984, at each time point. Immersion-loaded samples containing C(12)-Orn-Orn-Trp-Trp-NH(2) exhibited the lowest adherence profile for all peptides studied over 1, 4, and 24 h. The results outlined in this article show that antimicrobial peptides have the potential to serve as an important weapon against biomaterial associated infections.     

Combinatorial investigation of the structure-properties characterization of photopolymerized dimethacrylate networks

The effects of co-monomer composition and irradiation time in a model two-component dimethacrylate dental resin blend were evaluated using combinatorial methods to determine the degree of methacrylate conversion and resulting mechanical properties. 2-Dimensional gradient samples varying in monomer composition and light exposure time were fabricated. The conversion was measured using near infrared spectroscopy (NIR) and the mechanical properties (i.e., hardness and elastic modulus) were determined using nanoindentation via the continuous stiffness method. An excellent correlation was observed between the reaction conversion and mechanical properties for the cross-linked networks. The methacrylate conversion ranged from 40% to 85% and the mechanical properties increased over two orders of magnitude over this conversion range. The ultimate reaction conversion and mechanical properties depended on both the co-monomer composition and cure time.     

Effect of temperature and ageing on the mechanical properties of dental polymeric composite materials

Evaluation of the mechanical properties of some dental composite materials, Compact, Finesse and Prisma-Fil based on bisphenol glycidyl methacrylate resin was undertaken by applying compression, tension and hardness tests. The effects of temperature and ageing times on these properties were studied. There was a marked increase in the mechanical properties (compressive strength, diametral tensile strength, compressive elastic modulus and hardness) for all the investigated composites with increase of both temperature and time. This was explained in terms of the influence of temperature on the polymerization rate of the materials. The improvement in the mechanical properties of the samples, kept at 37 degrees C, was attributed to further and continued polymerization of the polymer content of their resin system. Such mechanical improvement was verified by the regression equation of linearity versus both temperature and time.     

Characterization of the physicochemical, antimicrobial, and drug release properties of thermoresponsive hydrogel copolymers designed for medical device applications

In this study, a series of hydrogels was synthesized by free radical polymerization, namely poly(2-(hydroxyethyl)methacrylate) (pHEMA), poly(4-(hydroxybutyl)methacrylate) (pHBMA), poly(6-(hydroxyhexyl)methacrylate) (pHHMA), and copolymers composed of N-isopropylacrylamide (NIPAA), methacrylic acid (MA), NIPAA, and the above monomers. The surface, mechanical, and swelling properties (at 20 and 37 degrees C, pH 6) of the polymers were determined using dynamic contact angle analysis, tensile analysis, and thermogravimetry, respectively. The T(g) and lower critical solution temperatures (LCST) were determined using modulated DSC and oscillatory rheometry, respectively. Drug loading of the hydrogels with chlorhexidine diacetate was performed by immersion in a drug solution at 20 degrees C (相似文献   

Hybrid natural-synthetic chitosan resin: thermal and mechanical behavior

Poly(methyl methacrylate) (PMMA) is one of the most commonly plastics used as dental-base material, due to its good biological compatibility and mechanical properties. Chitosan has wide application in chemical, biochemical and biomedical fields of research. In this work, chitosan (CTS) was functionalized with glycidyl methacrylate (GMA), to ease a further reaction with MMA. The resulting co-polymer was finally blended with PMMA and poly(butyl acrylate) PBA which works as a damper, the polymers were cured by UV to obtain the final resin. Characterization of UV-cured resins was carried out by thermal measurements, X-ray diffraction, atomic force microscopy (AFM), micro and nanoindentation, water absorption and elution in water. As a result a higher thermal stability of the final resin compared with the precursor co-polymer ((CTS-GMA)-g-PMMA) was obtained. The resin presented roughness in the nanometer scale and nanoparticles embedded in the acrylic matrix producing a tough material. However, XRD measurements show that all materials are in an amorphous state. Values of hardness and elastic modulus results were very near to those of the dentine. The results of elution in water of the tested resin samples show them as clinically acceptable as a dental base material.     

Heterocyclic methacrylates for clinical applications. I. Mechanical properties.

The mechanical properties of a number of heterocyclic and one cyclic methacrylate have been studied for their potential in low polymerization shrinkage systems. This study included both homopolymers and room temperature polymerizing systems using poly(ethyl methacrylate) powder with a heterocyclic methacrylate monomer. The one cyclic methacrylate studied, isobornyl methacrylate, gave an extremely brittle polymer; furthermore, it would not form a dough with poly(ethyl methacrylate). The homopolymers gave Young's moduli in the range 1.38-2.19 GN/m2, i.e. lower than poly(methyl methacrylate). The moduli of poly(ethyl methacrylate)/monomer systems are theoretically predictable from the moduli of the homopolymers involved. The above materials were generally ductile and the mechanical properties indicated a useful class of materials for clinical use.     

Hybrid natural-synthetic chitosan resin: thermal and mechanical behavior

Poly(methyl methacrylate) (PMMA) is one of the most commonly plastics used as dental-base material, due to its good biological compatibility and mechanical properties. Chitosan has wide application in chemical, biochemical and biomedical fields of research. In this work, chitosan (CTS) was functionalized with glycidyl methacrylate (GMA), to ease a further reaction with MMA. The resulting co-polymer was finally blended with PMMA and poly(butyl acrylate) PBA which works as a damper, the polymers were cured by UV to obtain the final resin. Characterization of UV-cured resins was carried out by thermal measurements, X-ray diffraction, atomic force microscopy (AFM), micro and nanoindentation, water absorption and elution in water. As a result a higher thermal stability of the final resin compared with the precursor co-polymer ((CTS-GMA)-g-PMMA) was obtained. The resin presented roughness in the nanometer scale and nanoparticles embedded in the acrylic matrix producing a tough material. However, XRD measurements show that all materials are in an amorphous state. Values of hardness and elastic modulus results were very near to those of the dentine. The results of elution in water of the tested resin samples show them as clinically acceptable as a dental base material.     

Investigation of 3,4-methylenedioxybenzene methoxyl methacrylate as coinitiator and comonomer for dental application

In this study, 3,4-methylenedioxybenzene methoxyl methacrylate (MDBMM) was synthesized for the purpose of replacing both triethylene glycol dimethacrylate (TEGDMA) and tertiary amine, which was usually used as a comonomer and coinitiator for dental resin, respectively. Urethane dimethacrylate (UDMA) was chosen as a monomer. Real time near Fourier transform infrared (FTIR) with a horizontal sample holder and dynamic mechanical analyzer (DMA) were used to study the kinetics and mechanical properties, respectively. The results showed that the addition of MDBMM as a coinitiator in UDMA/TEGDMA/CQ (70/30/0.5 wt %) system led to the increase of the rate of polymerization. When compared with the commercial polymerizable amine, 2-(N,N-dimethyl amino)ethyl methacrylate (DMEM), MDBMM showed comparable initiating reactivity and led to higher modulus around human body temperature (37 degrees C). MDBMM as a comonomer resulted in slightly higher final double bond conversion than that of TEGDMA, which brought higher modulus around 37 degrees C. Therefore, MDBMM can be used as both potential coinitiator and comonomer for dental application.     

Antibacterial effects of home-made resin salve from Norway spruce (Picea abies)

Resin salve made from Norway spruce (Picea abies) is traditionally used in folk medicine to heal skin ulcers and infected wounds. Its antimicrobial properties were studied against certain human bacteria important in infected skin wounds. The sensitivity of the resin against Gram-positive and Gram-negative bacteria was studied in vitro by methods that are routinely used in microbiology laboratories. The resin salve exhibited a bacteriostatic effect against all tested Gram-positive bacteria but only against Proteus vulgaris of the Gram-negative bacteria. Interestingly, the resin inhibited the growth of bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococcus (VRE), both on agar plates and in culture media. The study demonstrated antimicrobial activity of the resin salve and provided objective evidence of its antimicrobial properties. It gives some explanations why the traditional use of home-made resin salve from Norway spruce is experienced as being effective in the treatment of infected skin ulcers.     

玻璃微珠改性双酚A甲基丙烯酸缩水甘油酯复合的树脂充填材料

背景：口腔复合树脂修复材料存在聚合收缩率大和机械强度低等缺点,不能很好地满足临床使用的要求。 目的：观察双酚A甲基丙烯酸缩水甘油酯和二甲基丙烯酸三甘醇酯的比例及改性实心玻璃微珠添加量对口腔复合树脂弯曲强度与聚合体积收缩率的影响。 方法：以硅烷偶联剂KH-550对实心玻璃微珠进行硅化处理。向双酚A甲基丙烯酸缩水甘油酯与二甲基丙烯酸三甘醇酯配比分别为7/3、6/4、5/5的口腔复合树脂中再分别添加质量分数10%,30%,50%,70%,90%的实心玻璃微珠,机械搅拌均匀后,快速填入模具中固化,设置不添加实心玻璃微珠的树脂作为对照参考,分析口腔复合树脂的机械性能和收缩率。 结果与结论：随着实心玻璃微珠添加量的增加,口腔复合树脂的弯曲强度呈先增加后减小的趋势,体积收缩率呈降低趋势：当双酚A甲基丙烯酸缩水甘油酯与二甲基丙烯酸三甘醇酯的比例为5/5、实心玻璃微珠的添加量为70%时,口腔复合树脂的弯曲强度最高,为(88.29±0.66) MPa(P < 0.05);当双酚A甲基丙烯酸缩水甘油酯与二甲基丙烯酸三甘醇酯的配比为7/3、玻璃微珠添加量为70%时,聚合体积收缩率最小,为0.898%。     

In situ formation of silver nanoparticles in photocrosslinking polymers

Nanocomposites of cross-linked methacrylate polymers with silver nanoparticles have been synthesized by coupling photoinitiated free radical polymerization of dimethacrylates with in situ silver ion reduction. A polymerizable methacrylate bearing a secondary amino functional group was used to increase the solubility of the silver salt in the hydrophobic resin system. Fourier transform infrared spectroscopy (FTIR) revealed that the silver ion reduction had no significant effect on the degree of vinyl conversion of the methacrylate. X-ray photoelectron spectroscopy (XPS) measurements showed an increased silver concentration at the composite surface compared to the expected concentration based on the total amount of silver salt added. Furthermore, the surface silver concentration leveled off when the silver salt mass fractions were 0.08% or greater. Composites with low concentrations of silver salt (< 0.08% by mass) exhibited comparable mechanical properties to those containing no silver. Transmission electron microscopy (TEM) confirmed that the silver nanoparticles formed within the polymer matrix were nanocrystalline in nature and primarily ≈ 3 nm in diameter, with some large particle aggregates. Composites containing silver nanoparticles were shown to reduce bacterial colonization with as little as 0.03% (by mass) silver salt, while additional amounts of silver salt did not further decrease their surface colonization. With a substantial effect on bacterial growth and minimal effects on mechanical properties, the in situ formation of silver nanoparticles within methacrylate materials is a promising technique for synthesizing antibacterial nanocomposites for biomedical applications.     

Synthese von nitrogruppenhaltigen copolymeren durch radikalische copolymerisation

Radical copolymerization of a nitro group containing azo-dye monomer ( 1 ) and methyl methacrylate leads to significantly higher polymerization rates and higher molecular weights when dispersion technique is used instead of solution polymerization. The preparation of mechanically stable coatings and free films with good mechanical properties and transparency for electro-optical investigations is possible by a spin coating technique with the dispersion copolymers. The dye side chains of these copolymers can be poled in an electric field. The orientation of the side chains leads to a change of the light absorption in the dye absorption band. Results of m-line spectroscopy show that the copolymers possess wave guiding properties.     

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO2–CaO nanocomposite

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO₂–CaO nanocomposite were investigated using dimethyldiethoxysilane (DMDES) and tetraethoxysilane (TEOS), which could produce two and four siloxane linkages, respectively, after a sol–gel reaction. Methyl methacrylate was co-polymerized with 3-(trimethoxysilyl)propyl methacrylate and then co-condensed with DMDES (specimen D) and TEOS (specimen T), respectively, with calcium nitrate tetrahydrate under acidic conditions. The fracture toughness of specimen D was much improved compared to that of specimen T, whereas its fracture strength, hardness, and apatite-forming ability in simulated body fluid (SBF) were slightly decreased. The improved fracture toughness of specimen D without losing apatite-forming ability was explained by the decrease of siloxane linkage numbers and the introduction of alkyl groups in silica structure because covalently bonded siloxane linkages produce hard and brittle fracture behavior in the nanocomposite while the alkyl groups help to make the silica as linear chain structure. The practical implication of these results is that this new nanocomposite can be applied to the filler materials for bone cement and dental composite resin because of its good bioactivity and improved mechanical properties.     

Dental composites reinforced with hydroxyapatite: mechanical behavior and absorption/elution characteristics

The purpose of this study was to analyze the behavior in water as well as the mechanical and surface properties of experimental composites designed for dental restoration. Studied materials were composed of a visible-light-cured monomer mixture as a matrix (bisphenol-alpha-glycidyl methacrylate with triethyleneglycol dimethacrylate or hydroxyethyl methacrylate) and either micrometric or nanometric hydroxyapatite (HA) particles as a reinforcing filler. The surface of the filler particles was modified by using different coupling agents (citric, hydroxysuccinic, acrylic, or methacrylic acid). The hydrolytic stability of the evaluated materials was studied through elution-in-water and water-uptake tests. Mechanical and surface properties were examined through the results of flexural, hardness, and surface roughness tests. Means and standard deviations were calculated for each variable. Analysis of variance and multiple comparison tests were performed. Materials containing bisphenol-alpha-glycidyl methacrylate:triethyleneglycol dimethacrylate and micrometric-HA coated with citrate, acrylate, or methacrylate displayed the most favorable results. Improvements should be obtained by increasing the total filler amount, and by the introduction of nanometric-HA filler into a micrometric-HA reinforced composite resin system.     

Factors influencing broth microdilution antimicrobial susceptibility test results for dalbavancin, a new glycopeptide agent

Performance of antimicrobial susceptibility tests with new agents requires careful consideration of the properties of the antimicrobial to ensure that the tests are standardized, reproducible, and reflect the true potency of the drug. Dalbavancin is a new glycopeptide with potent activity against gram-positive bacterial species. The investigations described here demonstrated that methodologic modifications of procedures are necessary to ensure consistent test results, both for quality control and for routine testing of clinical isolates. Dimethyl sulfoxide is the preferred primary solvent. The addition of 0.002% polysorbate-80 (a surfactant) to dalbavancin-containing wells in the reference broth microdilution assay resulted in consistent and reproducible MIC results for three quality control strains: Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, and Streptococcus pneumoniae ATCC 49619. The same degree of consistency was observed among clinical isolates of gram-positive bacterial species tested in several clinical laboratories. These results indicate that the addition of 0.002% (final concentration) of the surfactant in broth microdilution tests produces optimal dalbavancin MICs required for accurate and reproducible clinical laboratory tests, without untoward influences of substrate binding or media constituents.     

Synthesis of strongly basic anion exchange resins based on glycidyl methacrylate‐ethylene glycol dimethacrylate copolymer. Effect of amount and nature of diluent,and the degree of crosslinkage on the resins properties

A number of hydrophilic copolymers based on glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDM) were synthesized using the technique of suspension polymerization. A number of diluents such as dimethylpthalate (DMT), diethylpthalate (DET), dibutylpthalate (DBT) and bis‐2‐ethylhexylpthalate (diocylphthalate, DOT) were used. The resulting polymers were modified into strongly basic anion exchange resins using 50% aqueous trimethylamin hydrochloride solution. In this study, the effects of amount and nature of diluents on resin properties, i. e. porosity, density, mechanical properties and capacities, were investigated. The effect of amount of crosslinking agent, i.e. the amount of EGDM, was also studied. It was found that resin become porous as the number of methylene groups in diluents increases. The pore volume changes from 0.05 to 1.35 ml/g as the diluent change from DMT to DOT. The mechanical strength of the resin decreases on increasing the number of methylene groups in the diluent. However, the chloride capacity shows no significant change. By varying the amount of crosslinking agent (from 10 to 50%) the chloride capacity changes from 3.46 to 1.2 meq/g, respectively. The effect of crosslinking on porosity was also investigated. It was found that porosity of the resin increases on increasing the amount of EGDM. This is the first time that strongly basic anion exchange resin based on GMA‐co‐EGDM using different and varying amounts of diluents, as well as various degrees of crosslinkage, were synthesized and characterized. The important aspect of this study is that it provides a guideline for the synthesis of a resin with specific properties by selection of a diluent and varying its ratio with respect to the monomer.     

Biphenyl liquid crystalline epoxy resin as a low-shrinkage resin-based dental restorative nanocomposite

Low-shrinkage resin-based photocurable liquid crystalline epoxy nanocomposite has been investigated with regard to its application as a dental restoration material. The nanocomposite consists of an organic matrix and an inorganic reinforcing filler. The organic matrix is made of liquid crystalline biphenyl epoxy resin (BP), an epoxy resin consisting of cyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ECH), the photoinitiator 4-octylphenyl phenyliodonium hexafluoroantimonate and the photosensitizer champhorquinone. The inorganic filler is silica nanoparticles (～70–100 nm). The nanoparticles were modified by an epoxy silane of γ-glycidoxypropyltrimethoxysilane to be compatible with the organic matrix and to chemically bond with the organic matrix after photo curing. By incorporating the BP liquid crystalline (LC) epoxy resin into conventional ECH epoxy resin, the nanocomposite has improved hardness, flexural modulus, water absorption and coefficient of thermal expansion. Although the incorporation of silica filler may dilute the reinforcing effect of crystalline BP, a high silica filler content (～42 vol.%) was found to increase the physical and chemical properties of the nanocomposite due to the formation of unique microstructures. The microstructure of nanoparticle embedded layers was observed in the nanocomposite using scanning and transmission electron microscopy. This unique microstructure indicates that the crystalline BP and nanoparticles support each other and result in outstanding mechanical properties. The crystalline BP in the LC epoxy resin-based nanocomposite was partially melted during exothermic photopolymerization, and the resin expanded via an order-to-disorder transition. Thus, the post-gelation shrinkage of the LC epoxy resin-based nanocomposite is greatly reduced, ～50.6% less than in commercialized methacrylate resin-based composites. This LC epoxy nanocomposite demonstrates good physical and chemical properties and good biocompatibility, comparable to commercialized composites. The results indicate that this novel LC nanocomposite is worthy of development and has potential for further applications in clinical dentistry.     

Structure-property relationships of DEAEM-containing bone cements: effect of the substitution of a methylene group by an aromatic ring

New aromatic methacrylates were prepared by substitution of a methylene group from diethylaminoethyl methacrylate (DEAEM) by an aromatic ring at two different positions. Diethylamino benzyl methacrylate (DEABM) and N-methacryloyloxyethyl)-N-ethyl-m-toluidine (MEET) were polymerized and incorporated as co-monomers in bone cement formulations. Cements were evaluated in terms of curing and mechanical properties in addition to changes in their glass transition temperature by DSC and surface properties by contact angle measurements. The immediate effect of the presence of an aromatic ring within the amino methacrylate was that it modified the bone cements' physical appearance, as colored products were obtained. It was also observed that peak temperature increased and setting time decreased by the use of DEABM and MEET instead of DEAEM. Simultaneously, both tensile and compressive strength of bone cements were improved; this effect was related to a higher glass transition temperature. In addition, surface properties of cements were modified by the incorporation of the aromatic ring, being more hydrophilic at low molar fractions and more hydrophobic at high molar fractions. Based on these studies, it is concluded that the position of the aromatic ring within the amino methacrylate modified not only the cement's appearance, but also the setting and mechanical properties.     

Covalent attachment of a three-dimensionally printed thermoplast to a gelatin hydrogel for mechanically enhanced cartilage constructs

Hydrogels can provide a suitable environment for tissue formation by embedded cells, which makes them suitable for applications in regenerative medicine. However, hydrogels possess only limited mechanical strength, and must therefore be reinforced for applications in load-bearing conditions. In most approaches the reinforcing component and the hydrogel network have poor interactions and the synergetic effect of both materials on the mechanical properties is not effective. Therefore, in the present study, a thermoplastic polymer blend of poly(hydroxymethylglycolide-co-ε-caprolactone)/poly(ε-caprolactone) (pHMGCL/PCL) was functionalized with methacrylate groups (pMHMGCL/PCL) and covalently grafted to gelatin methacrylamide (gelMA) hydrogel through photopolymerization. The grafting resulted in an at least fivefold increase in interface-binding strength between the hydrogel and the thermoplastic polymer material. GelMA constructs were reinforced with three-dimensionally printed pHMGCL/PCL and pMHMGCL/PCL scaffolds and tested in a model for a focal articular cartilage defect. In this model, covalent bonds at the interface of the two materials resulted in constructs with an improved resistance to repeated axial and rotational forces. Moreover, chondrocytes embedded within the constructs were able to form cartilage-specific matrix both in vitro and in vivo. Thus, by grafting the interface of different materials, stronger hybrid cartilage constructs can be engineered.