Effect Of Arm Number Research Articles

Effect of Arm Number and Length of Star-Shaped Glycopolymers on Binding to Dendritic and Langerhans Cell Lectins.

Many cell types in Nature are covered by glycans with a sugar shell on their surface. Synthetic glycopolymer-based materials can mimic these glycans in terms of their variety of biological processes, such as cell growth regulation, adhesion, inflammation by bacteria and viruses, and immune responses. However, the complexity of glycans is still very challenging to be mimicked completely to obtain specific and selective binding ability. Therefore, in this study we aimed to understand how the complexity in the sense of the effect of number of arms and lengths in star-shaped glycopolymers affect the binding activity with different lectins. The Cu-mediated reversible deactivation radical polymerization (Cu-RDRP) technique was employed for the synthesis of mannose containing star-shaped glycopolymers with varying arm number and length. Two sets of star-shaped glycopolymers with on average 1, 3, 7, 8, and 15 arms were successfully synthesized and characterized via 1H NMR, GPC, and DLS. The first set of glycopolymers (Set S1) encompasses 5 star-shaped glycopolymers with a different amount of arms per macromolecule but with equal arm length, whereas in the second set of 5 glycopolymers (Set S2), the amount of sugars per macromolecule was kept constant to obtain glycopolymers with similar glycovalency but in different configuration. Both glycopolymer sets were subsequently evaluated for their lectin-binding affinity toward a series of both newly and previously studied C-type mannose specific lectins present on dendritic and Langerhans cells. Briefly, while Set S1 glycopolymers with the same arm length and different molecular weight showed considerably different biological activities, Set S2 glycopolymers with different arm lengths and the same molecular weight displayed very similar binding abilities, which can indicate that multivalency can be more important than structure complexity to improve the binding behavior of glycopolymers.

Synthesis, characterization and effects of arm number on properties of amphiphilic polyurethanes as drug delivery carriers

ABSTRACTAmphiphilic polyurethanes based on methoxy poly(ethylene glycol) (mPEG) and poly(ϵ-caprolactone) diol (PCL) with different arm numbers such as two, three and four were successfully synthesized. Their structures were confirmed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR) and gel permeation chromatography (GPC). The effects of arm number on properties of amphiphilic polyurethanes were studied. Pyrene fluorescence probe technique and dynamic light scattering (DLS) analyses showed that the CMC value and the micellar size of the resultant amphiphilic polyurethanes decreased and the micellar stability against dilution enhanced with increasing the arm number of polyurethane. Using indometacin (IMC) as a model drug, the results indicated that the drug loading capacity and in vitro drug sustained release effect of polyurethane with four arms were better than those of polyurethanes with two and three arms.

The effect of arm number and solution concentration on phase separation of thermosensitive poly(2-isopropyl-2-oxazoline) stars in aqueous solutions

Four-arm star-shaped poly(2-isopropyl-2-oxazoline) (PiPrOx4) with calix[4]arene core was studied by methods of turbidimetry and light scattering in aqueous solutions at concentrations ranging from 0.0002 to 0.0364 g cm−3. The role of arm number in thermosensitive behavior was determined by comparing the experimental data with the results for eight-arm PiPrOx8 star. First of all, it is concerned with the growth of large aggregate fraction in PiPrOx4 solution and the formation of middle mode particles even at low temperature which causes the decrease phase separation temperatures. At relatively high concentrations (c >0.01 g cm−3), the dilution of PiPrOx4 solutions is accompanied by slow growth of phase transition temperatures, and the width ΔT = (1–2) °C of this interval does not depend on the concentration. In the dilute regime, ΔT rises and reaches 9 °C. It is shown that the changes of thermosensitive stars’ behavior with arm number reduction are caused by lower intramolecular density of PiPrOx4 in comparison with that of PiPrOx8.

Effect of arm number of poly(acrylic acid) on cloud point temperature of poly(2-ethyl-2-oxazoline)

The phase transition behavior of poly(2-ethyl-2-oxazoline) (PEtOx) under complexation with star-shaped poly(acrylic acid) (PAA) having various arm numbers (two, three, four, and six) has been studied by turbidity and laser light scattering measurements. The change in cloud point temperature (T cp) of PEtOx was monitored as a function of pH, ionic strength, and arm number of the star polyelectrolyte. The shift in T cp to a lower value than that of pure PEtOx was more pronounced at pH 4.2 (pH pKa ), when the acid moieties are partially ionized. Dynamic light scattering showed that these complexes may have micellar core-shell type structure with a mean hydrodynamic radius (R h) ranging from 12 nm to ∼200 nm depending upon the temperature. Significant shift in T cp was observed for six-arm star poly(acrylic acid) complexes at both pH values. This change in the T cp is accredited to the differences in the driving forces of phase transition, including hydrogen bonding between carboxylic acid groups of PAA and the carbonyl moiety of PEtOx as well as the hydrophobic interactions.

A High-Strength Cement System for Improved Dental Restoratives

We have developed and studied a novel high-strength glass-ionomer cement system composed of poly(acrylic acid) with different molecular architectures. These poly(acrylic acid) polymers were synthesized via ATRP technique. The effects of arm number and branching on reaction kinetics, viscosity, and mechanical strengths of the formed polymers and cements were evaluated. The results showed that unlike the star-shaped polymer synthesis both hyperbranched and star-hyperbranched polymers syntheses proceed slowly at the early stage but accelerate at the later stage. The higher the arm number and initiator concentration are, the faster the ATRP reaction was. It was also found that the higher the arm number and branching that the polymer had, the lower the viscosity of the polymer aqueous solution is and the lower the mechanical strengths of the formed cement are. The mechanical strengths of three synthesized polymers-composed experimental cements were very similar to each other but much higher than those of Fuji II LC. The experimental cements were 31% - 53% in CS, 37% - 55% in compressive modulus, 80% - 126% in DTS, 76% - 94% in FS, 4% - 21% in FT and 53% - 96% in KHN higher than Fuji II LC. For wear test, the experimental cements were only 5.4% - 13% of abrasive and 6.4% - 12% of attritional wear depths of Fuji II LC in each wear cycle. The one-month aging study also showed that all the experimental cements increased their CS continuously during 30 days, unlike Fuji II LC.

Star‐shape poly(acrylic acid)‐composed glass‐ionomer cements: Effects of MW and arm number on mechanical properties

AbstractThis study reports the synthesis and characterization of the star‐shape poly(acrylic acid)s with different arm numbers and molecular weight (MW)s. The effects of arm number and initiator concentration on the atom‐transfer radical polymerization reaction kinetics and solution viscosity were studied. The effects of MW and arm number on mechanical properties were evaluated. The results showed that both arm number and MW had significant impacts on the polymerization kinetics, solution viscosity, mechanical strengths, and wear‐resistance. Decreasing arm number and increasing initiator concentration increased the reaction rate. Increasing arm number and initiator concentration decreased the solution viscosity. Decreasing arm number and increasing MW increased mechanical strengths and wear‐resistance. Within the limitations of this study, the experimental cement was 28% in compressive strength, 48% in compressive modulus, 39% in diametral tensile strength, 60% in flexural strength, and 62% in Knoop hardness higher but 19% in fracture toughness lower than commercial Fuji II LC cement. The abrasion and attrition of the experimental cement were only 1.3% and 9.5% of Fuji II LC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effects of Arm Number and Arm Length on Thermal Properties of Linear and Star-shaped Poly(D,L-lactide)s

Effects of Arm Number and Arm Length on Thermal Properties of Linear and Star-shaped Poly(D,L-lactide)s

Synthesis and application of a novel star-hyperbranched poly(acrylic acid) for improved dental restoratives

A new star-hyperbranched poly(acrylic acid) has been synthesized and incorporated into dental glassionomer cement for enhanced mechanical strengths. The effects of arm number and branching on viscosity of the polymer aqueous solution and mechanical strengths of the formed experimental cement were evaluated. It was found that the higher the arm number and the more the branching, the lower the viscosity of the polymer solution as well as the mechanical strengths of the formed cement. It was also found that the experimental cement exhibited significantly higher mechanical strengths than commercial Fuji II LC. The experimental cement was 51% in CS, 55% in compressive modulus, 118% in DTS, 82% in FS, 18% in FT and 85% in KHN higher than Fuji II LC. The experimental cement was only 6.7% of abrasive and 10% of attritional wear depths of Fuji II LC in each wear cycle. It appears that this novel experimental cement is a clinically attractive dental restorative and may potentially be used for high-wear and high-stress-bearing site restorations.

Atypical micellization of star-block copolymer solutions

The self-assembly of star-block copolymer (B(y)A(x))(n) in a selective solvent for its outer block is studied by using dissipative particle dynamics, where (B(y)A(x))(n) denotes a n-armed star with each arm comprising of y solvophobic B-segments and x solvophilic A-segments. The effects of arm number, arm length, block length ratio y/x, solvent quality, and component compatibility on mean aggregation number (p) are examined. Unusual micellization behaviors are observed. The total number of arms in a multimolecular micelle n(*) is invariant with the arm number but grows with the segment concentration phi, which is different from typical micellization of short-chain surfactants. For a given phi, multimolecular micelles are formed for stars with n < n(*)(phi) and the mean aggregation number follows (p) = n(*)n. As n > or = n(*), only unimolecular micelles exist in the solution. According to the n(*)-phi relation, the critical multimolecular micelle concentration is found to grow linearly with arm number. As solvent quality deteriorates or component compatibility increases, the total arm number within a micelle rises.

Effects of arm number on the properties of transparent elastomers prepared from styrene–butadiene block copolymer

A series of the SBS transparent elastomers were prepared from star-shaped SBS having different arm number by solution-casting. Their structure and physical properties were characterized by scanning electron microscope, ultraviolet spectrometer, wide-angle X-ray diffractometer, differential scanning calorimetry, dynamic mechanical thermal analysis, tensile testing, and contact angle measurements. The results revealed that the miscibility, optical transparence (Tr), tensile strength (σb), elongation at break (eb), and elasticity at low temperature of the star SBS increased with an increase of arm number. The six-arm SBS having relatively high molecular weight exhibited a simultaneous enhancement of Tr (90% at 800 nm), σb (6.0 Mpa), and eb (1260%). This indicated that the SBS materials having six arms had higher transparence and elasticity than others. Moreover, the water contact angle on surface of the star-shaped SBS film increased with an increase of arm number that is enhancement of hydrophobicity. Therefore, the relatively high arm number and molecular weight played an important role in the improvement of the miscibility and properties of the SBS sheets as a result of the compacted architecture of the hyperbranched molecules. This work provides a convenient way to obtain materials with both high transparence and elasticity by increasing the arm number. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 729–736, 2006

Static and dynamic properties of computer simulated melts of multiarm polymer stars

Cooperative motion algorithm (CMA) is applied to simulate properties of polymer stars in dense systems which are considered as representations of polymer melts. Effects of arm number and arm length of stars on static and dynamic properties of model systems are analysed. Static properties are characterised by star sizes and their spatial correlations. Dynamic properties describing arm orientation relaxation and translational motion of stars are presented. Results indicate strong ordering effects for multiarm stars in the melt and suggest that the terminal relaxation of star melts can alternatively be controlled by arm orientation relaxation or by cooperative star translations depending in the two parameters of star structure i.e. arm length and arm number.

Order-disorder transition of star-block copolymers. 2. Effect of arm number

Order-disorder transition of star-block copolymers. 2. Effect of arm number

The effect of arm number on chromosome exchange distortion

A mathematical method is developed for the study of the theoretical effects of distortion on the yield of radiation induced dicentrics and centric rings. Expressions relating the magnitude of distortion to the number of arms in the karyotype are derived. The assumptions needed to arrive at these results appear to be flexible. The quantitative effect of low dose distortion is explicable in terms of a single parameter—the reduction in the target volume after the first exchange has taken place. Subsequent modification of the target volume can be ignored.