Polymerization Mode Research Articles

Two modes of asymmetric polymerization of phenylacetylenes having anL-amino alcohol residue and two hydroxy groups

Four novel chiral phenylacetylenes having an L-amino alcohol residue and two hydroxymethyl groups were synthesized and polymerized by an achiral catalyst ((nbd)Rh+[η6-(C6H5)B−(C6H5)3]) or a chiral catalytic system ([Rh(nbd)Cl]2/(S)- or (R)-phenylethylamine ((S)- or (R)-PEA)). The two resulting polymers having an L-valinol or L-phenylalaninol residue showed Cotton effects at wavelengths around 430 nm. This observation indicated that they had an excess of one-handed helical backbones. Positive and negative Cotton effects were observed only for the polymers having an L-valinol residue produced by using (R)- and (S)-PEA as a cocatalyst, respectively, although the monomer had the same chirality. Even when the achiral catalyst was used, the two resulting polymers having an L-valinol or L-phenylalaninol residue showed Cotton effects despite the long distance between the chiral groups and the main chain. We have found the first example of a new type of chiral monomer, that is, a chiral phenylacetylene monomer having an L-amino alcohol residue and two hydroxy groups that was suitable for both modes of asymmetric polymerization, that is, the helix-sense-selective polymerization (HSSP) with the chiral catalytic system and the asymmetric-induced polymerization (AIP) with the achiral catalyst. The other two monomers having L-alaninol and L-tyrosinol were found to be unsuitable to neither HSSP nor AIP because of their polymers' low solubility. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Shear bond strength of three dual-cured resin cements to dentin analyzed by finite element analysis

ObjectivesTo determine the shear bond strength to bovine dentin of dual-cured resin cements cured in different circumstances, the contraction stress and volumetric shrinkage in both polymerization modes, and to review the failure stress distribution at the cement–tooth interface with finite element analysis. MethodsThe volumetric shrinkage of RelyX Unicem, Panavia F 2.0 and DC Core Automix was determined by mercury dilatometry. Polymerization contraction stress was determined using a constraint tensilometer set-up. For the shear bond strength test, cement discs on bovine root dentin (self-cured and dual-cured), composite discs cemented to dentin (self-cured and dual-cured), and dentin cemented to dentin (self-cured) specimens were fabricated. Specimens were stored in water for 24h (37°C, 100% humidity) and tested (crosshead speed 1mmmin−1). FE modeling of the specimens was carried out in order to calculate the maximum shear stresses in the cement–dentin interface. Differences between groups were determined using two-way ANOVA with Tukey post hoc tests, and paired samples t-tests (α<0.05). ResultsPanavia F2.0 showed significantly lower volumetric shrinkage than the other cements. Dual-curing lead to higher contraction stresses for all tested cements compared to self-curing. RelyX Unicem showed higher volumetric shrinkage when dual-cured. Shear bond strength and maximum shear stress was positively influenced by dual-curing. DC Core Automix performed best and Panavia F2.0 worst in terms of shear bond strength and maximum shear stress. SignificanceCuring mode may play an important role in the final bond strength to dentin of indirect restorations, depending on the material used.

Influence of viscosity and polymerization mode on bond strength of dual-cure resin luting agent to dentin

Aim: To evaluate the influence of the viscosity and curing mode on the bond strength of two resin cements to dentin. Methods: Eight experimental groups were formed (n = 7) according to the dual-cure resin cements (Nexus 2 - Kerr Corp. and Variolink II - Ivoclar Vivadent), curing modes (dual-cure or self-cure) and viscosities (low and high). Resin cements were applied to pre-cured composite resin discs (2 mm thick, Sinfony -3M ESPE), which were fixed to bonded dentin surfaces. The restored teeth were either light-activated (XL3000 - 3M ESPE) or allowed to self curing only. After 24 h, the teeth were both mesiodistally and buccolingually sectioned to obtain bonded beam specimens (0.8 mm2 cross-sectional area). Each specimen was tested in microtensile strength at a crosshead speed of 0.5 mm/min until failure. Results: Data (in MPa) were analyzed statistically by three-way ANOVA and Tukey’s post-hoc test (pre-set a = 0.05). No significant difference was observed between resin cements (p=0.26) and viscosities (p=0.13), however, the curing mode affected the BS within the viscosities (p=0.01). Statistically significant difference was observed for low viscosity: Nexus 2: 23.8(10.6) (dual-cure) and 16.0(5.1) (self-cure); Variolink II: 28.7(8.7) (dual-cure) and 11.9(3.0) (self-cure). Conclusions: Light activation yielded higher bond strength for the low-viscosity versions of the resin cements.

In situ access to white light‐emitting fluorescent polymer nanocomposites via plasma‐ignited frontal polymerization

AbstractWe describe a facile fabrication of white light‐emitting cadmium sulfide (CdS)‐poly(HEA‐co‐NVK) nanocomposites [2‐hydroxyethyl acrylate (HEA) and N‐vinylcarbazole (NVK)] via plasma‐ignited frontal polymerization (PIFP), a novel and rapid reaction mode of converting monomers into polymers in minutes. Frontal polymerization was initiated by igniting the upper side of the reactant with plasma. Once initiated, no additional energy was required for the polymerization to occur. The chemical functional groups of the as‐prepared nanocomposites were thoroughly investigated using Fourier transform infrared spectra. The dependence of the front velocity and front temperature on the initiator concentration and weight ratios of HEA/NVK was also investigated in detail. Perhaps more interestingly, the white light‐emitting materials synthesized by ingeniously incorporating the compensating colors of yellow emitting from 3‐(trimethoxysilyl)‐1‐propanethiol‐capped CdS nanocrystals and blue emitting from carbazole‐containing polymer were conveniently applied onto a commercial UV light‐emitting diode (LED) to generate white LEDs. The subtle change in the weight ratios of CdS/NVK can significantly impact the color hue. The white light becomes gradually colder with the increase of NVK, but becomes gradually warmer with the increase concentration of CdS nanocrystals. In a broad perspective, these white light‐emitting materials designed by PIFP approach will open a new pathway to develop “QD‐polymer nanocomposite down‐conversion LED” in a fast and efficient way. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Influence of polymerization mode and C-factor on cohesive strength of dual-cured resin cements

ObjectivesThe aim of this study is to determine the influence of the C-factor and the mode of polymerization on the cohesive strength of various dual-cure resin cements. MethodsThree curing conditions were tested; chemical curing with free shrinkage conditions (C=0), and constraint shrinkage conditions (C=25), and dual-curing with free shrinkage conditions (C=0). Opaque polyethylene, brass (pretreated with Clearfil SE bond), and transparent polyethylene tubes respectively, were filled with the different cements. The tubes were 20mm long with an inner diameter of 1.6 or 1.8mm. Five cements, DC Core Automix, Panavia F 2.0, Maxcem, Multilink, and RelyX Unicem, were tested with ten specimens per group. The specimens were trimmed to an hour-glass shape with a neck diameter of 1mm, stored in water (37°C, 24h), and subjected to microtensile testing (1mmmin−1). SEM analysis was carried out on chemically cured samples of DC Core Automix C=0 and C=25. Data were statistically analyzed (Two-way ANOVA, Tukey's post hoc test, p<0.05). ResultsMost cements showed no significant differences between the curing modes. A high C-factor negatively influences the cohesive strength of some cements. SEM analysis shows that chemical curing of DC Core Automix in a high C-factor environment leads to more and larger microvoids in the cement. SignificanceConstraint shrinkage conditions, i.e. a high C-factor, can negatively influence the physical properties of a dual-cured resin cement, which would clinically be the case in the confined space of a root canal or post space preparation.

Effects of self-curing activator and curing protocol on the bond strength of composite core buildups.

To determine the effect of the polymerization mode of simplified bonding systems and the corresponding core buildup resin composite on the bond strength to dentin. Composite core buildups were bonded to flat prepared dentin surfaces of 320 human molars using a two-step etch-and-rinse (Excite, ER) and a two-step self-etching (AdheSE, SE) bonding system. Bonding systems were used both with and without their respective self-curing activators (Excite DSC, ER+SC; AdheSE DC, SE+SC). Six curing protocols for the dual-curing composite (MultiCore Flow) were examined: self-curing for 5 min (a); irradiation with light from each aspect for 10 s (b), 20 s (c), and 40 s (d); and irradiation with light from the occlusal aspect only for 60 s (e) and 120 s (f). Shear bond strengths were measured immediately after curing. Additional measurements were performed after water storage of the specimens for 24 h at 37°C. These specimens had been cured according the curing protocols given in the manufacturer's instructions (groups a and d). Failure modes were analyzed using scanning electron microscopy. Immediate bond strengths were significantly different among the bonding systems (p < 0.001): SE > ER > ER+SC > SE+SC. Immediate bond strengths of ER and SE were significantly lower when the composite was self-cured (p < 0.05). The use of SC activators reduced the bond strength and promoted adhesive failures to dentin. A severe incompatibility problem was observed between the composite and SE+SC. Dentin bonding of dual-curing composite core buildups in combination with simplified bonding systems is still unsatisfactory, even when SC activators are employed. For adequate bonding to dentin, polymerization of the dual-curing composite should always be light initiated.

Evaluation of Vickers hardness and depth of cure of six composite resins photo-activated with different polymerization modes

Aim:The current in vitro study evaluated Vickers hardness (VK) and depth of cure (hardness ratio) of six resin composites, polymerized with a light-emitting diode (LED) curing unit by different polymerization modes: Standard 20 s, Standard 40 s, Soft-start 40 s.Materials and Methods:Six resin composites were selected for the present study: three microhybrid (Esthet.X HD, Amaris, Filtek Silorane), two nanohybrid (Grandio, Ceram.X mono) and one nanofilled (Filtek Supreme XT). The VK of the surface was determined with a microhardness tester using a Vickers diamond indenter and a 200 g load applied for 15 seconds. The mean VK and hardness ratio of the specimens were calculated using the formula: hardness ratio = VK of bottom surface / VK of top surface.Results:For all the materials tested and with all the polymerization modes, hardness ratio was higher than the minimum value indicated in literature in order to consider the bottom surface as adequately cured (0.80). Curing time did not affect hardness ratio values for Filtek Silorane, Grandio and Filtek Supreme XT.Conclusion:The effectiveness of cure at the top and bottom surface was not affected by Soft-start polymerization mode.

Exploring the frontiers of synthetic eumelanin polymers by high‐resolution matrix‐assisted laser/desorption ionization mass spectrometry

New trends in material science and nanotechnologies have spurred growing interest in eumelanins black insoluble biopolymers derived by tyrosinase-catalysed oxidation of tyrosine via 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid (DHICA). Efficient antioxidant and photoprotective actions, associated with peculiar optoelectronic properties, are recognised as prominent functions of eumelanin macromolecules within the human and mammalian pigmentary system, making them unique candidates for the realisation of innovative bio-inspired functional soft materials, with structure-based physical-chemical properties. An unprecedented breakthrough into the mechanism of synthetic eumelanin buildup has derived from a detailed investigation of the oxidative polymerization of DHI and its N-methyl derivative (NMDHI) by linear and reflectron matrix-assisted laser/desorption ionization mass spectrometry. Regular collections of oligomers of increasing masses, spanning the entire m/z ranges up to 5000 Da (>30-mer) and 8000 Da (> 50-mer) for the two building blocks, respectively, were disclosed. It is the first time that the in vitro polymerisation of dihydroxyindoles to form synthetic eumelanins is explored up to its high mass limits, giving at the same time information on the polymerisation mode, whether it follows a stepwise pattern (being this the conclusion in our case) or a staking sequencing of small-sized entities. It also highlighted the influence of the N-methyl substituent on the polymerization process; this opens the way to the production of N-functionalized, synthetic eumelanin-inspired soft materials, for possible future technological applications.

Flexural strength of a composite resin light cured with different exposure modes and immersed in ethanol or distilled water media

Aim:The aim of this in vitro study was to evaluate the flexural strength of a composite resin polymerized with three different modes of light exposure.Materials and Methods:The three different modes of light exposure were conventional, 600 mW/cm2/40s; soft start, 300 mW/cm2/10s + 600 mW/cm2/30s; pulse delay, 600 mW/cm2/1s + 60 s of waiting time + 600 mW/cm2/39s). Twenty samples were prepared for each polymerization method. Flexural strength (FS) tests were carried out with a 2 kN load at a speed of 0.5 mm/ min. All tested groups were submitted to analysis of variance (one-way-ANOVA) and Tukey's test (P < 0.05).Results:When stored in water, conventional and pulse delay groups presented higher FS values which were statistically different from the soft start group. When stored in 100% ethanol, conventional and soft start groups presented higher FS values which were statistically different from the pulse delay group.Conclusion:Different polymerization modes and immersion media can affect the physical properties (flexural strength) of composite resin.

T-Cell Receptor Activation Initiates Multiple Modes of Actin Polymerization within the Immune Synapse

The immune synapse is a key point of communication between T cells and antigen presenting cells. The layout of this interface is driven in large part by a complex cytoskeletal structure. This report focuses on modulation of the cytoskeleton by T Cell Receptor (TCR) signaling using micropatterned surfaces presenting OKT3 (an antibody that activates the TCR signaling component CD3) and ICAM-1 to T cells. Previous studies by our group demonstrated that micro-scale features of OKT3 (red, top row) induce lamellipodial polymerization (white arrows) of actin (green) on surrounding regions of ICAM-1. We show here a second type of polymerization, the formation of linear, consolidated F-actin structures from sites of CD3 engagement (blue arrow), resembling actin comets observed in other systems. This mode of actin polymerization occurs concurrent to lamellipodium extension. Furthermore, polymerization is initiated by sharp, external corners of angular patterns of OKT3 (bottom row). This latter result suggests mechanical forces, which are concentrated at such corners under cellular tension, initiate this modality of actin polymerization. The different contributions of these behaviors on immune synapse function remain to be determined.

5,10,15,20-tetra(4-pyridyl)porphyrinato zinc coordination polymeric particles with different shapes and luminescent properties

Micro-scale three-dimensional coordination polymer particles (CPPs) have been synthesized from the surfactant-assisted reaction of Zn(OAc)2·2H2O and 5,10,15,20-tetra(4-pyridyl)porphyrin (H2TPyP) in DMF. The three-dimensional (3D) micro-prisms and micro-octahedra of the CPPs were obtained at different temperatures as found by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and a statistical analysis of the size distribution results. X-Ray diffraction (XRD) analysis revealed a circular hexametric cage structure cross-linked by a Zn–N axial coordination of the pyridyl ligands inside the micro-scale CPPs. Further support for this coordination polymerization mode of the micro-CPPs came from IR spectroscopy. The UV–vis spectra clearly show the formation of J-type aggregates in both the microstructures. The micro-CPPs show a stronger luminescence intensity over the individual porphyrin molecules, which is presumably due to the high surface area of the ZnTPyP-CPPs. Nevertheless, nitrogen adsorption/desorption isotherm measurements were performed to confirm the larger surface area and increased porosity of the micro-prisms and micro-octahedra relative to the self-assembled micro-rods of ZnTPyP, indicating the potential application of the two CPPs microstructures in the field of gas adsorption. The surfactant-assisted synthetic route appears to provide a promising method for the construction of highly organized three-dimensional organic micro-structures of 5,10,15,20-tetra(4-pyridyl)porphyrin derivatives.

Evaluation of Microleakage in Class V Composite Restoration using Different Techniques of Polymerization

ABSTRACT Aims The purpose of this study was to evaluate the effect of light intensity and curing cycle of quartz tungsten halogen (QTH) and plasma arc curing (PAC) lights on the microleakage of class V composite restorations. Materials and methods A total of 60 freshly extracted human maxillary premolars were used for this study. Standardized class V cavities were prepared and restored with microhybrid resin composite. According to the curing protocol, the teeth were then divided into three groups (n = 20): QTH curing (standard and soft start mode) and PAC high intensity irradiation. The microleakage was evaluated by immersion of the samples in 50% silver nitrate solution. The samples were then sectioned, evaluated under a stereomicroscope and scored for microleakage. Statistical analysis used Dye leakage scores were obtained, and analysis was done using Student's t-test. Results Light curing with QTH light in the soft start mode, showed the least leakage in the composite restoration, which was highly significant when compared with the other groups (p &lt; 0.01). Light curing with QTH light in the standard mode, showed moderate microleakage, which was statistically significant (p &lt; 0.05), when compared with the PAC high intensity curing. Curing with PAC light in high intensity mode resulted in severe microleakage along the cavity margins. Conclusion Within the limitations of the study, it may be concluded that: 1. The high intensity PAC light resulted in maximum leakage, when compared to the other groups in the study. 2. The soft start polymerization mode offers a distinctive advantage over the standard curing protocol, in terms of microleakage, for the QTH curing lights. Clinical significance In the clinical scenario, soft start curing regimen offers a distinctive advantage over the conventional mode of the QTH curing and the high intensity rapid curing offered by the PAC light. How to cite this article Chandurkar AM, Metgud SS, Yakub SS, Kalburge VJ. Evaluation of Microleakage in Class V Composite Restoration using Different Techniques of Polymerization. Int J Prosthodont Restor Dent 2012;2(1): 10-15.

Changes in chroma of two indirect composite materials polymerized with different polymerization systems

This study evaluated chroma change in two composite materials (Sinfony and Pearleste) polymerized with two different systems. Disk specimens were prepared using a metal halide unit (Hyper LII) and an exposure time of 60 to 180 s. The proprietary polymerization systems (Visio and Pearlcure systems) were used as the reference polymerization modes. After storage at 37°C for 24 h, CIE 1976 L*a*b* values were measured by using a dental chroma meter (ShadeEye NCC) with a gray background. The specimens were then immersed in water or tea. Color change from baseline to 4 weeks was evaluated by measuring ΔL*, Δa*, and Δb*, after which ΔE*(ab) values were calculated. The brightness of Sinfony specimens was reduced by tea immersion. The color of both materials shifted to yellow after tea immersion, although color change in Sinfony specimens was greater than that in Pearleste specimens. For both materials, color change was less after polymerization with the metal halide unit. In conclusion, Sinfony polymerized with the Hyper LII unit, and Pearleste polymerized with either system, were stable against discoloration due to tea immersion.

Microhardness of nanofilled composite resin light-cured by LED or QTH units with different times

Aim: To evaluate the influence of light-curing units and light-curing time on the microhardness of a nanofilled composite resin. Methods: Forty-five composite resin (Z350 - 3M) specimens were randomly prepared using Teflon ring molds (4.0 mm internal diameter and 2 mm depth) and divided into nine experimental groups (n=5): three polymerization units (conventional - 450 mW/ cm2 ; 2nd generation LED - 1100 mW/cm2 ; and 3rd generation LED - 700 mW/cm2 ) and three lightcuring times (20 s, 40 s, and 60 s). All specimens were polymerized with the light-curing tip positioned 8 mm far from the top surface of the specimen. After 24 h, Knoop microhardness measurements were made on the top and bottom surfaces of the specimen, with a load of 10 g for 10 s. Five indentations were made on each surface. All results were analyzed statistically by subdivided parcel ANOVA (Split-Plot) and Tukey’s tests (p<0.05). Results: There were no statistically significant differences for the polymerization unit and light-curing time factors in either top or bottom surface. For all experimental conditions, the top surfaces showed greater hardness than the bottom surfaces (p<0.0001). Conclusions: The mode of polymerization and the lightcuring time did not affect the hardness of the nanofilled composite resin, and increasing the lightcuring time did not improve the hardness of the bottom surface of the composite resin.

Design of a Microplasma Device for Spatially Localised Plasma Polymerisation

AbstractThere is considerable interest in the spatial control of plasma polymerisation such as to produce sub‐millimetre features with high fidelity, versatility and reproducibility, for example, for arrays or writable specific patterns. This study reports the design of a microcavity plasma device and a method for its fabrication, with the device comprising a single cavity of ≈400 µm diameter. The device can be fabricated within a short time and at low cost in a standard laboratory, with no need for a clean room facility. The device is capable of multiple operations in plasma polymerisation mode. XPS imaging combined with small‐spot ROI analysis showed localised thin film deposition of an acrylic acid plasma polymer with good retention of carboxylate groups from the monomer. The device can be configured with flexibility and addressed for plasma polymer writing of complex patterns. magnified image

Preparation and characterization of hyperbranched poly(ether ether ketone)s suitable as rheology control agents for linear poly(ether ether ketone)s

Hyperbranched poly(ether ether ketone)s (HPEEKs) that were suitable as rheology control agents for linear poly(ether ether ketone)s (LPEEKs) were first prepared via commercially available hydroquinone (A2 monomer, HQ) and synthesized 3,4′,5-trifluoro-benzophenone (BB′2 monomer, TF) effortlessly. The polymerization mode of A2 + BB′2 was demonstrated by MS. Moreover, FTIR, 1H NMR, 13C NMR, and 19F NMR spectroscopy revealed the structure and degree of branching (DB) of the resulting polymers. In comparison with A2 + B3 approach, HPEEK prepared using an A2 + BB′2 strategy possessed a higher molecular weight, and improved the melt processability of LPEEK. Remarkably, with the addition of HPEEK, the mechanical properties of LPEEK increased with a HPEEK content of 5%. The improved mechanical properties were attributed to the good miscibility. Moreover, the addition of HPEEK did not decrease the thermal stability of LPEEK. Open image in new window

Effect of Light-emitting Diode Photopolymerization Modes on the Push-out Bond Strength of a Methacrylate-based Sealer

Introduction The objective of this study was to investigate and compare the effect of different light-emitting diode (LED) polymerization modes on the bond strength of a methacrylate-based sealer used with Resilon or gutta-percha. Methods Forty extracted single-rooted teeth were sectioned off below the cementoenamel junction, and the root canals were instrumented by using rotary instruments to ISO #30/0.06 taper. The roots were randomly assigned into 1 of the following groups for root canal obturation: (1) RealSeal + Resilon and (2) RealSeal + gutta-percha. In each group, specimens were further subgrouped according to the LED polymerization mode used to cure RealSeal: (1) standard (20 seconds of maximum intensity) and (2) exponential (5 seconds of exponential power increase, followed by 15 seconds of maximum intensity). Specimens were stored in 100% humidity for 1 week at 37°C. Push-out test was performed at a crosshead speed of 1 mm/min on 2-mm-thick root slices obtained from coronal to apical direction. Multivariate analysis of variance and Tukey tests were used for statistical analysis of the data ( P = .05). Failure modes were examined under the scanning electron microscope. Results The tested polymerization modes had no significant effect on the bond strength values ( P > .05). RealSeal + gutta-percha yielded significantly greater bond strength than RealSeal + Resilon ( P < .05). In all groups, the bond strength values decreased significantly from coronal to apical direction ( P < .05). Adhesive failure at the sealer-dentin interface was the predominant fracture mode. Conclusions The exponential photopolymerization mode had no significant advantage over the standard regimen in terms of dentin bond strength.

Effect of resin luting cement polymerisation mode and high powered polymerisation unit type on shear bond strength of leucite reinforced full ceramic system to dentine

This in vitro study evaluated the effects of light polymerised (LP) and dual polymerised (DP) modes of a resin luting cement polymerised with different high powered polymerisation units on the shear bond strength of a leucite reinforced full ceramic system to dentine. Ceramic specimens (n = 15) were bonded to dentine surfaces with a resin luting cement (Variolink II) in either LP or DP mode and polymerised according to one of four polymerisation profiles as follows: control group: 600 mW cm−2 conventional halogen light, 40 s; light emitting diode polymerisation unit group: 1500 mW cm−2 light emitting diode, 10 s; plasma arc curing (PAC) polymerisation unit 10 s group: 1370 mW cm−2 PAC, 10 s; and PAC 3 s group: 1370 mW cm−2 PAC, 3 s. Bond strength (MPa) data were analysed using two-way analysis of variance and Duncan’s test (α = 0·05). Polymerisation mode (p<0·01), type of light unit (p<0·01) and the interactions between the two were statistically significant (p<0·05). No significant differences were found between LP and DP modes except for the PAC 3 s group, in which the LP mode resulted in significantly lower shear bond strength values (10·43±1·02 MPa) compared with the DP mode (12·88±1·73 MPa).

Controlling cell growth on titanium by surface functionalization of heptylamine using a novel combined plasma polymerization mode

A novel bio-interface, produced by a combined plasma polymerization mode on a titanium (Ti) surface, was shown to enhance osteoblast growth and reduce fibroblast cell growth. This new method can securely attach a tailored interface to difficult materials such as Ti or ceramics. Here a more stable and higher density of NH₂ functional groups is able to withstand sterilization in ethanol. The biocompatibility, in terms of cell attachment and actin cytoskeleton development, was markedly improved in vitro, compared with untreated Ti surfaces and samples treated by other plasma modes. It gave a boosted (approximately six times higher) cellular response of osteoblasts in their initial adhesion stage. These factors should increase the formation of new bone around implants (reducing healing time), promoting osseointegration and thereby increasing implantation success rates.

Time Dependence of Switching Between Polymerization and Editing Mode DNA Binding by Klenow Polymerase

Klenow polymerase is the large fragment of DNA polymerase I from E. coli. Klenow possesses 5’-3’ polymerase and intrinsic 3’-5’ exonuclease activities with two distinct active sites that are located ∼30 angstroms apart. During DNA replication, proofreading activity enhances replication fidelity by excising misincorporated nucleotides from the 3’ end of primer strand. The first step of the proofreading process is sending the 3’-primer terminus to the proofreading site, which requires separation of the primer terminus from the template strand. Here we examined the binding of Klenow to matched and mismatched primed-template DNA (pt-DNA) by monitoring the steady state fluorescence intensity change of a single 2-aminopurine base site-specifically substituted in the template strand within the duplex part of pt-DNA. The changes in fluorescence intensity allow us to follow shuttling of the primer terminus between the polymerization and proofreading sites. We have found that partitioning of the primer between the two active sites depends on: 1) the number of mismatched bases at the primer-template junction, 2) the presence or absence of divalent ions, 3) the type of divalent ions, and 4) the time in the presence of the divalent ions. A significant time dependence of the partitioning between the two sites was observed with the matched and single mismatched pt-DNA in the presence of Mg2+. The slow kinetic dependence of the primer partitioning between the polymerization and proofreading sites in Klenow polymerase helps explain previous conflicting reports of the equilibrium partitioning between sites.