Percentage Of Crosslinker Research Articles

Sonochemical synthesis and characterisation of thermoresponsive microgel particles

Thermoresponsive microgel particles of N-isopropylmethacrylamide and N, N′-methylenebisacrylamide were sonochemically synthesised in water containing sodium dodecylsulfate. Fluorescence spectroscopic measurements using the probes, pyrene and 1-pyrene-carboxaldehyde, showed that microgel systems with a higher crosslinker ( N, N′-methylenebisacrylamide) percentage had a more rigid structure. It was also found that a higher crosslinker percentage gave a more hydrophobic surface with a greater density of crosslinking whereas a lower crosslinker percentage gave microgel particles with polymer chains extending out from the surface. Electrophoretic mobility measurements indicated that the microgel particles were electrokinetically unstable since the surface layer of the particles only possessed a low charge (reflective of potentials <|25| mV). However, the majority of the systems were sterically stabilised.

Mechanical properties of cross‐linked collagen meshes after human adipose derived stromal cells seeding

The main goal of this study was to evaluate the potential of collagen meshes derived from porcine dermis as scaffolds for repairing pelvic organ prolapses. Mechanical properties of collagen meshes with different cross-linking percentages before and after Adipose Derived Stromal Cells (ADSC) seeding were studied as well as the cell-scaffold interaction. Uniaxial tensile tests of the collagen meshes with three different cross-linking percentages (full-, partial-, and noncross-linked) were carried out along orthogonal directions. Their mechanical properties were studied with the same tests before and after seeding with human derived adipose stem cells (ADSC) after 1 and 7 days. Histological analyses were performed to determine adhesion and proliferation of ADSC. Significant differences in mechanical properties of the unseeded meshes were observed between each orthogonal direction independently of the cross-linking percentage. A better cell adhesion rate was observed in the cross-linked meshes. An increase in the mechanical properties after cell seeding was observed with a direct relation with the degree of cross-linking. All meshes analyzed showed a marked anisotropy that should be taken into account during the surgical procedure. The cross-linking treatment increased cell adhesion and the mechanical properties of the collagen meshes after seeding. These results suggest that the mechanical properties of this type of collagen mesh could be useful as scaffolds for repair of pelvic organ prolapse.

Evaluation of Waterborne Coating for Controlled-Release Fertilizer Using Wurster Fluidized Bed

Coating through polymer film to control nutrient release can reduce the nutrient losses and minimize environmental contamination. In this research, the waterborne acrylate latex and additive (cross-linker aziridine) were used to develop coated controlled-release fertilizers by Wurster-type fluidized bed, and the influences of different cross-linker percentage on the coating properties and the nutrient-release profiles were investigated. The results indicated that the waterborne coating coupled with the 2 wt % of cross-linker could effectively decrease the swelling capacity of the membrane to 5.54 ± 0.32% while obtaining a suitable Tg (6.13 °C); the cumulative nutrient-release percentage was significantly improved to around 40% in 9 days at 40 °C. This organic solvent-free coating provided a promising option for the development of coated controlled-release fertilizer.

감마선 조사 방법에 따른 정형외과용 초고분자량 폴리에틸렌의 미세구조 변화

본 연구에서는 인공관절 베어링 부품으로 가장 널리 사용되는 초고분자량 폴리에틸렌(UHMWPE)을 대상으로 6가지 감마선 조사 방법에 따른 UHMWPE의 미세구조 변화를 비교 분석하였다. 감마선을 조사하지 않은 폴리에틸렌(UGI)과 비교하여, 기존의 멸균처리에 해당하는 공기 중 상온에서 감마선 조사한 폴리에틸렌(AR)의 결정화도와 가교정도는 유의한 차이를 보이며 증가하였다. 감마선 조사 환경 중. 상온에서의 산소(AR)와 진공상태(VR) 영향을 비교하면, AR과 VR의 결정화도는 유의한 차이가 없었으며, VR의 가교정도는 유의한 차이를 보이며 증가하였다. 감마선 조사 환경 중, 진공상태에서의 상온(VR)과 극저온(V77) 영향을 비교하면, 결정화도와 가교정도 모두 유의한 차이가 없었다. 그러나, VR과 V77에서의 가교정도는 AR에서의 가교정도보다 유의한 차이를 보이며 증가하였다. 3가지 감마선 조사 환경에 대하여 감마선 조사 이후 열처리(/S) 영향을 비교하면, 결정화도는 AR/S와 VR/S에서 유의한 차이가 없었으나, V77/S에서는 유의한 차이를 보이며 감소하였다. 또한, 가교정도는 AR/와 V77/S에서 유의한 차이를 보이며 증가하였으며, VR/S에서는 유의한 차이가 없었다.

Preparation and mechanical properties of crosslinked 1,2,3‐triazole‐polymers as potential propellant binders

AbstractThirteen triazole polymers were prepared as potential rocket propellant binders by the reactions of various diacetylenes and diazides. The reaction of E300 dipropiolate (1) with diazide (2) obtained from tetraethylene glycol was selected to study the effects of concentration of the tetraacetylene functionalized crosslinker (3) on the mechanical properties of resulting triazole polymers. The modulus of the polymers increased, whereas the strain (% elongation at failure) decreased with increasing percentage of crosslinker. The resulting triazole polymers also showed that the desired mechanical properties could be obtained by adjusting the crosslinker concentration during the polymerization. Addition of 43 wt % aluminum filler did not significantly affect the strain. The modulus of these triazole polymers was comparable with typical polyurethane elastomeric matrices for rocket propellants. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Semi-interpenetrating polymer network hydrogels between polydimethylsiloxane/polyethylene glycol and chitosan

Abstract Synthesis and properties of semi-interpenetrating polymer networks (semi-IPNs) based on polydimethylsiloxane (PDMS)/poly(ethylene glycol) (PEG)-modified chitosan were studied. 1–20 wt% of PDMS or PEG was interpenetrated into chitosan hydrogels having 10 wt% of hexamethylene-1,6-di-(aminocarboxysulfonate) (HDA) as a water-soluble crosslinker. PDMS prepolymer was synthesized via acid-catalyzed ring-opening polymerization of octamethylcyclotetrasiloxane (D4), followed by hydrosilylation reaction with allyl alcohol to obtain hydroxyl-terminated PDMS. Effect of PDMS/PEG contents (1–20 wt%) and their molecular weights (2000 and 8000 g/mol) in chitosan semi-IPNs on percent crosslinking, water swelling properties, thermal stability, surface properties, water vapor permeability and tensile properties were investigated. Percent crosslinking of the PDMS/PEG-chitosan semi-IPNs ranged between 42% and 74% depending on molecular weight and percent of PDMS/PEG added. PDMS and PEG in the semi-IPNs enhanced water swellability and water vapor permeability of the films. Also, PDMS/PEG in chitosan semi-IPNs enhanced their thermal stability and surface hydrophobicity, while their tensile properties were sacrificed.

DSC studies on the curing kinetics of chitosan–alanine using glutaraldehyde as crosslinker

The curing of chitosan–alanine with glutaraldehyde as curing agent in the presence of Chlorpheniramine Maleate (CPM) is carried out with the help of differential scanning calorimeter (DSC). The effect of concentration of chitosan and percentage of crosslinker on the curing is studied at a rate of 5 °C/min. Cure kinetics are measured from 30 to 200 °C at four different heating rates (3, 5, 7 and 10 °C/min). It is observed that the crosslinking of chitosan–alanine is an exothermic process which results in a positive peak in the curves. An increase in activation energy (E α) is observed with extent of conversion.

A semi-empirical model to simplify the synthesis of homogeneous and transparent cross-linked polymers and their application in the preparation of optical sensing films

We propose a simple, semi-empirical model based on Hansen's solubility parameters for simplifying the synthesis and the optimization of homogeneous and transparent cross-linked polymers in order to obtain optical sensing films. More than 740 experiments were undertaken to demonstrate the reliability of the model and several applications are proposed. We have demonstrated that our model can help in the synthesis and optimization (percentage of cross-linker, changes in hydrophilicity, selection of porogens, quantity of template etc.) of homogeneous and transparent MIPs and NIPs (molecularly imprinted polymers) with VOCs; after the synthesis of 440 polymers in the homogeneity zone only 4.32% of them (19 samples out of 440) were heterogeneous. We suggest a role for its use in the development of novel polymeric resins for detecting volatile organic compounds in water by measuring intrinsic fluorescence, in simplifying the synthesis of imprinted polymers and in decreasing the number of experiments required to optimize optical sensing membranes. In addition, it might also be used for synthesizing and optimizing MIPs with a non-volatile template.

Comparative Physical Properties of Hyaluronic Acid Dermal Fillers

Hyaluronic acid (HA) fillers are becoming the material of choice for use in cosmetic soft tissue and dermal correction. HA fillers appear to be similar, but their physical characteristics can be quite different. These differences have the potential to affect the ability of the physician to provide the patient with a natural and enduring result. The objective of this article is to discuss the key physical properties and methods used in characterizing dermal fillers. These methods were then used to analyze several well-known commercially available fillers. Analytical methods were employed to generate data on the properties of various fillers. The measured physical properties were concentration, gel-to-fluid ratio, HA gel concentration, degree of HA modification, percentage of cross-linking, swelling, modulus, and particle size. The results demonstrated that commercial fillers exhibit a wide variety of properties. Combining the objective factors that influence filler performance with clinical experience will provide the patient with the optimal product for achieving the best cosmetic result. A careful review of these gel characteristics is essential in determining filler selection, performance, and patient expectations.

Optimization of chlorpheniramine maleate (CPM) delivery by response surface methodology – four component modeling using various response times and concentrations of chitosan-alanine, glutaraldehyde and CPM

The aim of the current study was to investigate the effects of formulation variables on the release of drug and to optimize the formulation of chitosan-alanine beads loaded with chlorpheniramine maleate (CPM) for controlled release using response surface methodology (RSM). Drug loaded beads of chitosan-alanine were prepared and crosslinked by using glutaraldehyde as crosslinker. The release behavior of drug was affected by preparation variables. A central compos- ite design was used to evaluate and optimize the effect of preparation variables; chitosan concentration (X1), percentage of crosslinker (X2), concentration of drug (X3) and release time (X4) on the cumulative amount of drug release, Y in solutions of pH = 2.0 and pH = 7.4, respectively. The influence of each parameter was studied by factorial design analysis. Analysis of variance (ANOVA) was also used to evaluate the validity of the model. The statistical parameters reveal strong evidence that the constructed models for drug release in pH = 2 and pH = 7.4 are reliable.

The stabilisation of receptor structure in low cross-linked MIPs by an immobilised template

In molecularly imprinted polymers (MIPs) a high level of cross-linking is usually important for preserving the receptor structure. We propose here an alternative approach for stabilising binding sites, which involves the use of an immobilised template. The idea is based on the assumption that an immobilised template will “hold” polymeric chains and complementary functionalities together, preventing the collapsing of the binding sites. To test this postulate, a range of polymers was prepared using polymerisable (2,4-diamino-6-(methacryloyloxy)ethyl-1,3,5-triazine) and non-polymerisable (or extractable) (2,4-diamino-6-methyl-1,3,5-triazine) templates, methacrylic acid as functional monomer and ethylene glycol dimethacrylate as cross-linker. The level of cross-linking was varied from 12 to 80%. Polymerisations were performed in acetonitrile using UV initiation. Binding properties of the synthesised materials were characterised both by HPLC and equilibrium batch binding experiments followed by HPLC-MS or UV-visible detection. The adsorption isotherms of polymers were obtained and fitted to the Langmuir model to calculate dissociation constant, Kd, and concentration of binding sites for each material. The results strongly indicate that the presence of an immobilised template improves the affinity of MIPs containing low percentages of cross-linker. The low cross-linked MIPs synthesised with a polymerisable template also retain a reasonable degree of selectivity. Low cross-linked MIPs with such binding characteristics would be useful for the creation of new types of optical and electrochemical sensors, where induced fit or the “gate effect” could be used more effectively for generating and enhancing sensor signals.

Regulation of material properties in electrospun scaffolds: Role of cross-linking and fiber tertiary structure

We cross-linked scaffolds of electrospun collagen to varying degrees with glutaraldehyde using an ethanol-based solvent system and subsequently defined how the percentage of cross-linking impacts bulk and microscale material properties and fiber structure. At hydration, electrospun fibers underwent coiling; the extent of coiling was proportional to the percentage of cross-linking introduced into the samples and was largely suppressed as cross-linking approached saturation. These data suggest that electrospun collagen fibers are not deposited in a minimal energy state; fiber coiling may reflect a molecular reorganization. This result has functional/structural implications for protein-based electrospun scaffolds. Changes in fiber topology that develop during post-electrospinning processing may alter monomer organization, mask or unmask receptor binding sites, and/or change the biological properties of these nanomaterials. Hydrated scaffolds were mounted into a custom stretching device installed on a microscope stage and photographed after incremental changes in strain. Changes in fiber alignment were measured using the two-dimensional fast Fourier transform method. Fibers in all scaffolds underwent alignment in response to strain; however, the rate and extent of alignment that could be achieved varied as a function of cross-linking. We propose four distinct modes of scaffold response to strain: fiber uncoiling, fiber reorientation, fiber elongation and interfiber sliding. We conclude that bulk material properties and local microscale architecture must be simultaneously considered to optimize the performance of electrospun scaffolds.

Synthesis and properties of carboxymethylchitosan hydrogels modified with poly(ester-urethane)

Preparation and properties of carboxymethylchitosan (CMC) modified with polyurethane (PU) containing poly(ethylene adipate) (PEA) as a soft segment is described. Urethane prepolymer was first synthesized by the reaction of PEA with an excess of 1,6-hexamethylene diisocyanate (HDI) to terminate its ends with isocyanate functional groups, followed by chain extension reaction using ethylene glycol as a chain extender. Its chemical structure was characterized by 1H NMR and FTIR, molecular weight by GPC, and thermal behavior by DSC. To prepare PU-modified CMC (CMC-PU), 1–60 wt% of PU were introduced into the CMC solution of THF:H 2O mixture (50:50 v/v) in the presence of 10 wt% of hexamethylene-1,6-di-(aminocarboxysulfonate) (HDA) to increase network density. Formation of the network structure was confirmed by investigating percent crosslinking and water swelling properties of CMC-PU compared to CMC network without PU. When percent of PU increased from 1 to 60 wt%, percent crosslinking of CMC-PU gradually increased up to 82%, whereas equilibrium water content (EWC) dropped and retained at 1000%. SEM showed microphase separation of PU (10–50 μm) thoroughly dispersed in CMC surface and in the bulk. In addition, CMC-PU exhibited a slight enhancement in toughness properties. Cytotoxicity and biocompatibility tests indicated that CMC-PU was non-toxic.

Studies on the cure kinetics of chitosan-glutamic acid using glutaraldehyde as crosslinker through differential scanning calorimeter

The curing of chitosan-glutamic acid with glutaraldehyde as curing agent in the presence of chlorpheniramine maleate (CPM) is carried out with the help of differential scanning calorimeter (DSC). The effect of concentration of chitosan and percentage of crosslinker on the curing of chitosan-glutamic acid is studied at a heating rate of 5°C/min. Cure kinetics are measured by the DSC using scans from 25 to 220°C at four different heating rates (3, 5, 7, and 10°C/min) and it is observed that the crosslinking of chitosan-glutamic acid is an exothermic process which results in a positive peak in the DSC thermograms. The activation energy (Eα) is determined by Flynn, Wall, and Ozawa method for curing of the samples. An increase in activation energy (Eα) is observed with the extent of conversion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

X-ray photoelectron spectroscopy of rubber compounds: Temperature dependence and cross-link distribution

Rubber compounds are complex mixtures of ingredients, including many mobile and volatile species. Exposure to the ultrahigh vacuum environment common to surface analytical instruments can therefore cause significant changes in a rubber surface and produce misleading and even erroneous results. In this work it has been shown that stable, representative x-ray photoelectron spectra could be obtained if the specimen was precooled below a compound-dependent maximum temperature before exposure to the vacuum environment. Maximum temperatures were found to be −50 and −70°C for two typical tire rubber compounds, a wire adhesion formulation and passenger tire tread, respectively. Effects of specimen preparation were further investigated. High resolution x-ray photoelectron spectra of specimens precooled to −85°C and analyzed at −140°C indicated a correlation between the sulfur peak positions and the length of sulfur cross-links in the rubber. Specifically, a linear relationship was found between sulfur 2p binding energy and the percentage of monosulfidic and polysulfide cross-links as determined by standard bulk solvent swelling analysis for three different rubber compounds based on two different polymers.

Controlled release study of carbaryl insecticide from calcium alginate and nickel alginate hydrogel beads

AbstractIn this study, controlled release formulations for reducing environmental impact of pesticides have been produced by encapsulating as a model pesticide carbaryl (Carb) in the alginate beads. The various hydrogel bead formulations were prepared by the ionotropic crosslinking of sodium alginate (NaAlg) with calcium and nickel ions. The surface morphology of prepared beads was characterized with scanning electron microscopy (SEM). SEM confirmed the spherical nature and surface morphology of the particles. Bead characteristics, such as carbaryl entrapment efficiency, particle size, equilibrium swelling degree, and carbaryl release kinetics, were determined. The effects of the bead preparation conditions such as crosslinker concentration and type, carbaryl/sodium alginate (Carb/NaAlg) ratio and percentage of NaAlg on the carbaryl release from the calcium alginate (Ca‐Alg) and nickel alginate (Ni‐Alg) beads were investigated in distilled water at 25°C. It was observed that carbaryl release from the Ca‐Alg beads was slower than that of Ni‐Alg beads. The release results indicated that carbaryl release from both of the Ca‐Alg and Ni‐Alg beads decreases with the increasing crosslinker concentration, Carb/NaAlg ratio and percentage of NaAlg. The highest carbaryl release was found to be 100% for the Ni‐Alg beads at 3 days whereas the lowest carbaryl release was found to be 67% for the Ca‐Alg beads at 21 days. The swelling measurements of the beads were also in consistent with the carbaryl release results. The carbaryl release from most of the bead formulations followed Case II transport. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Nanoindentation of shape memory polymer networks

This work examines the small-scale deformation and thermally induced recovery behavior of shape memory polymer networks as a function of crosslinking structure. Copolymer shape memory materials based on diethylene glycol dimethacrylate and polyethylene glycol dimethacrylate with a molecular weight of 550 crosslinkers and a tert-butyl acrylate linear chain monomer were synthesized with varying weight percentages of crosslinker from 0 to 100%. Dynamic mechanical analysis is used to acquire the bulk thermomechanical properties of the polymers, including the glass transition temperature and the elastic modulus over a wide temperature range. Instrumented nanoindentation is used to examine ambient temperature deformation of the polymer networks below their glass transition temperature. The glassy modulus of the networks measured using nanoindentation is relatively constant as a function of crosslinking density, and consistent with values extracted from monotonic tensile tests. The ambient temperature hardness of the networks increases with increasing crosslinking density, while the dissipated energy during indentation decreases with increasing crosslinking density. The changes in hardness correlated with the changes in glass transition but not changes in the rubbery modulus, both of which can scale with a change in crosslink density. Temperature induced shape recovery of the indentations is studied using atomic force microscopy. For impressions placed at ambient temperature, the indent shape recovery profile shifts to higher temperatures as crosslink density and glass transition temperature increase.

Composition and three-dimensional EM structure of double affinity-purified, human prespliceosomal A complexes

Little is known about the higher-order structure of prespliceosomal A complexes, in which pairing of the pre-mRNA's splice sites occurs. Here, human A complexes were isolated under physiological conditions by double-affinity selection. Purified complexes contained stoichiometric amounts of U1, U2 and pre-mRNA, and crosslinking studies indicated that these form concomitant base pairing interactions with one another. A complexes contained nearly all U1 and U2 proteins plus approximately 50 non-snRNP proteins. Unexpectedly, proteins of the hPrp19/CDC5 complex were also detected, even when A complexes were formed in the absence of U4/U6 snRNPs, demonstrating that they associate independent of the tri-snRNP. Double-affinity purification yielded structurally homogeneous A complexes as evidenced by electron microscopy, and allowed for the first time the generation of a three-dimensional structure. A complexes possess an asymmetric shape (approximately 260 x 200 x 195 angstroms) and contain a main body with various protruding elements, including a head-like domain and foot-like protrusions. Complexes isolated here are well suited for in vitro assembly studies to determine factor requirements for the A to B complex transition.

Tailored binding and transport parameters of molecularly imprinted films via macromolecular structure: The rational design of recognitive polymers

Testosterone recognitive networks were synthesized varying feed crosslinking percentage and length of bifunctional crosslinking agent to analyze the effect of manipulating structural parameters on template binding parameters such as affinity, capacity, selectivity, and transport. Crosslinking agent was varied from 50 to 90% and associated networks experienced a twofold increase in capacity and a fourfold increase in affinity, with equilibrium association constants ranging from 0.30 ± 0.02 × 104 M−1 to 1.3 ± 0.1 × 104 M−1, respectively. The higher concentration of crosslinking monomer increased crosslinking points available for interchain stabilization creating an increased number of stable cavities for template association. However, by increasing the length of crosslinking agent ≈ 4.5 times, the mesh size of the network increased resulting in 40% faster template diffusional transport. A 77% crosslinked poly(MAA-co-PEG200DMA) recognitive network had an association constant of (0.20 ± 0.05) × 104 M−1 and bound (0.72 ± 0.04) × 10−2 mmol testosterone/g dry polymer which was less by six and threefold, respectively, compared to a similarly crosslinked poly(MAA-co-EGDMA) recognitive network. Structural manipulation of the macromolecular architecture illustrates the programmability of recognitive networks for specific binding parameters and diffusional transport, which may lead to enhanced imprinted sensor materials and successful integration onto sensor platforms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Microfabrication of Intelligent Biomimetic Networks for Recognition of d-Glucose

Biomimetic, biocompatible polymer networks have been developed with tailored affinities, loading capacities, and transport properties for a given target molecule, and these networks promise to significantly impact a wide variety of biomedical fields, particularly diagnostic and therapeutic devices. Methods were developed to integrate these biomimetic networks with silicon substrates at the microscale, enabling the fabrication of microdevice platforms based on silicon technologies. Biomimetic polymer networks with recognition properties for d-glucose were micropatterned in fine dimensions onto silicon substrates and characterized by fluorescence and confocal microscopy studies. Novel copolymer networks containing poly(ethylene glycol)ndimethacrylate (where the number of EG repeat units n = 1, 4, and 14) at various cross-linking percentages (30, 67, and 80%) and acrylamide as a functional monomer were synthesized in polar, aprotic solvent with and without the target molecule present. Calculated diffusion constants for the target molecule decreased with decreasing cross-linker length, with the diffusion constant of PEG600DMA cross-linked networks being 5 times larger than that for the EGDMA-based networks. As the length of the cross-linking monomer increased, the target molecule affinity and capacity of the networks decreased. For networks demonstrating enhanced recognition, target molecule diffusion constants of control networks were approximately half of the recognitive network's value. Because diffusion was approximately Fickian, response times were extrapolated for thinner samples, which indicated the high potential for thin films of recognitive materials (i.e., 10 μm to 100 nm) to be used as robust micro- and nanosensor materials for various sensor platforms (e.g., micro- and nanocantilevers).