Enhanced bone cell functions on poly(ε-caprolactone) triacrylate networks grafted with polyhedral oligomeric silsesquioxane nanocages

Poly(ε-caprolactone) triacrylate (PCLTA) developed in our laboratory is a photo-crosslinkable, injectable, and biodegradable polymeric biomaterial for diverse tissue engineering applications. To engineer its physical properties for bone regeneration, we incorporated PCLTA networks with a photo-reactive methacryl isobutyl polyhedral oligomeric silsesquioxane (POSS), which is a silicon-based monomer with a nano-sized cage. Homogeneous nanohybrid networks were prepared by photo-crosslinking POSS with two PCLTAs having molecular weights of ∼7000 and ∼20,000 g/mol at the POSS weight compositions (?_POSS) of 0–20%. The lower-molecular-weight PCLTA resulted in amorphous networks while the higher one resulted in semi-crystalline networks. POSS nanocages tethered in the PCLTA networks greatly enhanced the mechanical and rheological properties, but did not significantly alter the surface wettability and the capability of adsorbing serum proteins from cell culture media. Better mouse pre-osteoblastic MC3T3-E1 cell attachment, spreading, and proliferation were found on the stiffer PCLTA20k networks than on the PCLTA7k ones, and on the networks with ?_POSS of 10–20% than the networks containing no POSS. Mineralization of MC3T3-E1 cell cultured for two weeks showed a significantly higher alkaline phosphatase activity and more mineralized nodules on the PCLTA20k networks with ?_POSS of 10–20%, in correlation with their enhanced mechanical properties. The present results indicated that this series of nanohybrid PCLTA/POSS networks with improved mechanical properties and osteoconductivity has great potential as scaffolding materials for bone repair and regeneration.     

Effect of crosslinking method on collagen fiber-fibroblast interactions

Collagen, the major structural protein of the extracellular matrix in animals, is a versatile biomaterial used in various tissue engineering applications. Cross-linking influences the mechanical properties, resorption kinetics, and biocompatibility of collagen-based biomaterials. In this study, we evaluated the effects of crosslinking on collagen fiber-fibroblast interactions in vitro. Collagen fibers were left untreated or crosslinked by ultraviolet (UV) irradiation, dehydrothermal (DHT) treatment (3 or 5 days), or hexamethylenediisocyanate (HMDIC) exposure. The initial attachment, proliferation (through 8 days), and morphology of human dermal fibroblasts were evaluated on control and crosslinked bundles of 200 collagen fibers in vitro. Initial attachment (number of fibroblasts at day 0) was increased on UV and DHT5-treated collagen fiber bundles. Fibroblast proliferation was similar for control, UV crosslinked, and DHT crosslinked fibers. In contrast, fibroblast attachment was significantly decreased and proliferation was delayed on HMDIC crosslinked fibers. These results, coupled with our previous studies, suggest that UV crosslinking of collagen fibers provides a combination of biocompatibility, mechanical properties, and strength retention suitable for various tissue engineering applications. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1493–1498, 1997     

Methacryl-polyhedral oligomeric silsesquioxane as a crosslinker for expediting photo-crosslinking of Poly(propylene fumarate): Material properties and bone cell behavior

We present photo-crosslinkable hybrid organic-inorganic composites of poly(propylene fumarate) (PPF), an injectable and biodegradable polyester, and methacryl-polyhedral oligomeric silsesquioxane (mPOSS), which has eight methacryl groups tethered with a cage-like hybrid inorganic-organic nanostructure, for bone tissue engineering applications. Two PPF samples, one with a higher molecular weight (HPPF) and one with a lower molecular weight (LPPF), were blended with mPOSS at various mPOSS compositions. We emphasize on the role of mPOSS in modifying the photo-crosslinking kinetics of PPF and the physical properties of crosslinked products, and in regulating mouse pre-osteoblastic MC3T3-E1 cell behavior on the crosslinked substrates. The viscoelastic behavior of uncrosslinked PPF/mPOSS and the mechanical, degradation, and surface characteristics of photo-crosslinked PPF/mPOSS samples have been investigated. The crosslinking kinetics of PPF/mPOSS was characterized using the gel fraction and rheological properties such as storage modulus and viscosity of the samples crosslinked for 0.5-5 min. Blending mPOSS with PPF was found to decrease the viscosity of PPF and expedite the photo-crosslinking process, both of which are important in formation of PPF networks. In addition, tensile modulus was increased by crosslinking PPF with mPOSS up to the mPOSS composition of 15%, above which phase separation occurred. The degradation rate in 1 N NaOH solution could also be regulated by varying the mPOSS composition, while crosslinked PPF/mPOSS samples did not show detectable degradation in one week in phosphate buffered saline (PBS) and mPOSS did not significantly alter surface wettability and serum protein adsorption. MC3T3 cell adhesion, spreading, proliferation, differentiation, and gene expression were examined on crosslinked PPF/mPOSS disks. Addition of mPOSS did not introduce cytotoxicity or influence cell behavior evidently. It is interesting to note that crosslinked HPPF/mPOSS showed distinct physical properties and promoted MC3T3 cell functions compared with their LPPF counterparts possibly because of higher crosslinking densities.     

Effect of molecular weight on the surface morphology of crosslinked polymer particles in the RITP-dispersion polymerization

The RITP (reverse iodine transfer polymerization)-dispersion polymerization of methyl methacrylate (MMA) was conducted and the molecular weight and SEM images of them were investigated to propose the mechanism of the formation of surface morphology in crosslinked polymers. The morphology of the crosslinked particles varied depending on the sorts and contents of the crosslinking agents and iodine. As the iodine content increased under the same content of the crosslinking agent, the average molecular weight of the polymers [uncrosslinked portion of the polymers] decreased and the surface roughness simultaneously reduced. On the other hand, as the contents of the crosslinking agent increased, the molecular weight of polymers reduced and the surface morphology changed from smooth to rough in the absence of iodine. On the other hand, was the molecular weight was barely changed and the solubility increased upon iodine. Thus the mechanism of the formation of crosslinked polymers in the RITP-dispersion polymerization was proposed as the following; when crosslinking agent and iodine were simultaneously involved, the low molecular weight of polymers were first formed due to the effect of iodine and then the crosslinking was taking place, resulting in that iodine was a critical factor in controlling the molecular weight, particle size, solubility and the surface morphology in the crosslinked polymer particles.     

Synergistic effects of crosslinking and chitosan molecular weight on the microstructure,molecular mobility,thermal and sorption properties of porous chitosan/gelatin/hyaluronic acid scaffolds

In this study, synergistic effects of crosslinking and chitosan molecular weight on the microstructure, molecular mobility, thermal, and sorption properties of porous chitosan/gelatin/hyaluronic acid hybrid foams are reported. Fourier transform infrared spectroscopy has been utilized to confirm the covalent attachment of hyaluronic acid to gelatin and chitosan, and covalent chemical crosslinking between gelatin and chitosan. Detailed image analysis of scanning electron microscopy images of the porous scaffold hydrids reveal that the pore size of the materials formulated using either low‐ or high‐molecular‐weight chitosan increases significantly upon crosslinking using ethyl(dimethylaminopropyl) carbodiimide/N‐Hydroxysuccinimide. These microstructural changes are even more pronounced for the crosslinked hybrid scaffolds formulated using low‐molecular‐weight chitosan, highlighting a synergistic effect between crosslinking and the use of low‐molecular‐weight chitosan. Results obtained using differential scanning calorimetry demonstrate a significant reduction in molecular mobility reduction in molecular mobility for crosslinked scaffolds formed using high‐molecular‐weight chitosan compared to non‐crosslinked hybrids and crosslinked hybrids formulated using low‐molecular‐weight chitosan. Correspondingly, dynamic vapor sorption evidenced significantly lower water vapor sorption for crosslinked scaffolds formulated using high‐molecular‐weight chitosan. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44772.     

Preparation and characterization of novel crosslinked poly[glycidyl methacrylate–poly(ethylene glycol) methyl ether methacrylate] as gel polymer electrolytes

In this study, glycidyl methacrylate was copolymerized with poly(ethylene glycol) methyl ether methacrylate to obtain a copolymer {poly[glycidyl methacrylate–poly(ethylene glycol) methyl ether methacrylate] [P(GMA–PEGMA)]}, which was crosslinked with α,ω‐diamino poly(propylene oxide) (Jeffamine) at various weight ratios and molecular weights to form novel gel polymer electrolytes (GPEs). The crosslinked copolymers were characterized by Fourier transform infrared spectroscopy and thermal analysis. The crosslinked polymers were amorphous in the pristine state and became crystallized after they were doped with lithium electrolyte. Furthermore, the crosslinking degree of the crosslinked polymers increased with increasing weight ratio of Jeffamine, and both the swelling properties and mechanical behaviors of the crosslinked polymers were heavily affected by the weight ratio and molecular weight of Jeffamine. The ionic conductivity (σ) of the GPEs from the crosslinked copolymers was determined by alternating‐current impedance spectroscopy. A higher molecular weight and increased weight ratio of Jeffamine resulted in a higher σ. The GPE based on P(GMA–PEGMA) crosslinked with an equal weight of Jeffamine D2000 exhibited the highest σ of 8.29 × 10⁻⁴ S/cm at 25°C and had a moderate mechanical strength. These crosslinked copolymers could be potential candidates for the construction of rechargeable lithium batteries. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology and mechanical properties of crosslinked PE/PE composite materials

Novel peroxide‐crosslinked composite materials based on ultra high molecular weight polyethylene fibers were studied in comparison with their non‐crosslinked homologues. Two material types were prepared, either by embedding the fibers in a low‐density polyethylene matrix, or by compacting neat fibers. The resulting composites were analyzed by differential scanning calorimetry, focusing on the typical double‐melting endotherm of the PE fibers, and by X‐ray diffraction, concentrating on the characteristic weak 010 reflection of the triclinic phase in the fiber. Mechanical testing of unidirectional composites showed crosslinking to be highly advantageous, yielding significant property enhancement, e.g., increasing the flexural modulus from 28 to 33 GPa in the compacted fiber composite. The advantage results from the crosslinking mechanism, entailing only partial melting that is confined to the fiber skin, while retaining a significant degree of crystallinity in the fiber.     

Intramolecular crosslinking of poly(vinyl alcohol)

Poly(vinyl alcohol) is crosslinked in dilute solution (c=0.1 wt%) with glutaraldehyde. The reaction product is characterized by viscometry and gel permeation chromatography (g.p.c.). The intrinsic viscosity decreases with increasing degree of crosslinking and does not depend on temperature. G.p.c. reveals that the reaction product is not homogeneous, but consists of a mixture of particles with different sizes, possibly both intra- and intermolecularly crosslinked molecules. The intramolecularly crosslinked molecules are smaller in size than the initial polymer molecules and their size depends on the degree of crosslinking. They possess a narrow particle size distribution even if the initial polymer sample had a broad molecular weight distribution.     

过氧化物交联聚乙烯热收缩管成型研究

简要介绍了聚乙烯高能辐射交联、硅烷化学交联和过氧化物化学交联,给出了交联前后分子结构变化的示意图,说明3种交联方法所得到的交联聚乙烯分子结构十分接近,在性能上基本没有差别。采用最新的过氧化物交联配方,并给出详细的生产工艺,使用最新研制的具有自主知识产权的活塞式挤出机加工成型交联聚乙烯热收缩管坯,并用自制的扩管装置扩张成型热收缩管。针对试验结果,对产品的凝胶率、力学物理性能和电性能进行了讨论,并比较了辐射交联、硅烷交联和过氧化物交联3种交联生产工艺在设备投资成本、产品质量控制、能耗、交联反应时间、产品的实际交联度和产品的表面质量等方面的优劣。     

Synthesis and crosslinking of partially disulfonated poly(arylene ether sulfone) random copolymers as candidates for chlorine resistant reverse osmosis membranes

Biphenol-based, partially disulfonated poly(arylene ether sulfone)s synthesized by direct copolymerization show promise as potential reverse osmosis membranes. They have excellent chlorine resistance over a wide range of pHs and good anti-protein and anti-oily water fouling behavior. Crosslinking of these copolymers that have high degrees of disulfonation may improve salt rejection of the membranes for reverse osmosis performance. A series of controlled molecular weight, phenoxide-endcapped, 50% disulfonated poly(arylene ether sulfone)s were synthesized. The copolymers were reacted with a multifunctional epoxy resin and crosslinked thermally. The effects on network properties of various factors such as crosslinking time, copolymer molecular weight and epoxy concentration were investigated. The crosslinked membranes were characterized in terms of gel fraction, water uptake, swelling and self-diffusion coefficients of water. The salt rejection of the cured membranes was significantly higher than that for the uncrosslinked copolymer precursors.     

Hydrophilization by coating of silylated polyoxazoline using sol–gel process

Hybrid films prepared from TEOS and polyoxazolines (Si–POx–Si) crosslinking agents were coated on different substrates in order to modify their surface properties. The film cohesion and adhesion on substrates were expected through the hydrogen bonding of the polyoxazoline crosslinked network. Low molecular-weight α,ω-unsaturated polyoxazolines (DA-PMOx)s were synthesized by a one step cationic ring-opening polymerization (CROP) of 2-methyl-2-oxazoline (MOx) with a good control over the molecular weight. Based on double thiol-ene coupling (d-TEC) a post-functionalization of DA-PMOx end chains gave in good yield polyoxazoline cross linker (Si–POx–Si). Glass and various polymer substrates (PP, PEI, POM, etc.) were spin coated by the organic–inorganic hybrid films through sol–gel process. AFM, SEM, visible reflectance spectroscopy and contact angle experiments allowed the full characterization of targeted surfaces and demonstrated the efficiency of the polyoxazoline coating.     

Radiation-induced crosslinking of UHMWPE in the presence of co-agents: chemical and mechanical characterisation

Radiation-induced crosslinking has been shown to have a beneficial effect on the wear resistance of ultra high molecular weight polyethylene (UHMWPE). Since we postulate that crosslinking takes place through reactions involving terminal double bonds, unsaturated additives were added to UHMWPE in this study to enhance crosslinking. UHMWPE specimens soaked in 1,7-octadiene, methylacetylene and ethylene, respectively, were irradiated with electron beam to different doses in single or multiple passages. FTIR spectroscopy was used for the chemical characterisation of the crosslinked polymer. Tensile tests were performed with all samples in order to monitor changes in the mechanical properties.Gel fraction measurements proved that crosslinking took place in all the irradiated samples, but 1,7-octadiene turned out to be the most effective additive for the present purpose, exhibiting a good efficiency in enhancing crosslinking. The FTIR analyses showed that consumption of vinyl double bonds is proportional to the irradiation dose, with an efficiency which increases with increasing their initial concentration, confirming the hypothesis of the involvement of these groups in the crosslinking process. In the case of UHMWPE with 1,7-octadiene irradiated to high doses in multiple passages, the results of the tensile tests indicated a significant decrease in both elongation at break (up to 65%) and ultimate stress (up to 25%). A possible explanation of the diminished strength of the crosslinked material has also been proposed.     

海水基耐温聚丙烯酰胺压裂液的性能优化

以丙烯酰胺、丙烯酸和2-丙烯酰胺-2-甲基丙磺酸（AMPS）三元共聚物（PSAM）为稠化剂,乳酸锆为交联剂开发出一种海水基耐高温压裂液,考察了PSAM的水解度、相对分子质量、AMPS含量、稠化剂和交联剂的浓度、配比等因素对冻胶形成及耐温耐剪切性能的影响,通过测试不同条件下冻胶的储能模量（G'）随时间的变化,研究了Ca²⁺浓度和AMPS含量对交联动力学的影响。交联动力学的研究表明,随AMPS含量加大,PSAM交联速度降低,达到交联平衡所需时间延长,随Ca²⁺浓度增高,交联反应速度越快,冻胶初始强度越高;耐温性能测试表明,当稠化剂中羧酸基含量与交联剂中锆离子含量之比n（-COOH）/n（Zr⁴⁺）≈1时,体系的耐温耐剪切性能最优,高含量AMPS提升压裂液的耐温耐剪切性能。在优化稠化剂结构条件下,稠化剂质量分数为0.6%、交联剂质量分数为0.3%配制的海水基压裂液,在150℃、170 s^-1下剪切120 min后,黏度保持在150 mPa·s以上,耐温耐剪切性能优秀。     

Crosslinking of ultra-high molecular weight polyethylene in the melt by means of 2,5-dimethyl-2,5-bis(tert-butyldioxy)-3-hexyne: 2. Crystallization behaviour and mechanical properties

Ultra-high molecular weight polyethylene, was crosslinked in the melt at 180°C by means of 2,5-dimethyl-2,5-bis(tert-butyldioxy)-3-hexyne. It is shown that crosslinks and entanglements, whether trapped or not, contribute to the same degree to the decrease in crystallinity of the polyethylene upon crosslinking. Crosslinking introduced a very stable type of radical into the polyethylene. It was concluded that an almost completely crosslinked material with high crystallinity and therefore good mechanical properties, could be obtained by using as little as 0.2–0.3 wt% of peroxide.     

Rheological behaviors of randomly crosslinked low density polyethylene and its gel network

Dicumy peroxide (DCP) modification of low density polyethylene (LDPE) below gel point (GP) produces modified LDPE (mLDPE) with wide molecular weight distributions while the random crosslinking beyond GP yields crosslinked LDPE (XLPE). Molecular weight distributions of mLDPE below GP and the sol-fractions of XLPE above GP were investigated. The sol-fractions in XLPE were extracted to prepare XLPE gels of different crosslinking densities. Both XLPE and the gels were subjected to shear action for studying dynamic rheology and relaxation modulus in the linearity region for revealing the role of entanglements and dangling chains to viscoelasticity of the randomly crosslinked network. The results revealed that the sol-fractions with molecular weight much higher than entanglement molecular weight contributed to equilibrium modulus in addition to the gel network, which lowered the DCP dosage for appearance of critical gel behavior of XLPE in comparison with the XLPE gel. However, rheological method yielded critical DCP dosages for appearance of apparent gel behaviors far beyond the chemical GP from the extraction experiment. The sol-fraction residing in the network gave rise to additional contribution to relaxation modulus of XLPE, shortening network relaxation time and improving equilibrium modulus.     

Changes in cultured arterial smooth muscle cells isolated from chicks upon cholesterol feeding

We have developed cultures of smooth muscle cells (SMC) isolated from arterial hypercholesterolemic chicks (cholesterol-SMC). These cultures are suitable for the study at the molecular level of the changes in arterial SMC induced by a cholesterol diet. By using a strong dose of cholesterol (5%) for 10 d, we obtained very proliferative SMC which became foam cells after 30 d in culture. On the other hand, SMC cultures isolated from control-fed chicks has a lower growth rate than the SMC ones under the same culture conditions. DNA synthesis was fourfold greater in cholesterol-SMC than in control-SMC cultures. Intracellular cholesterol concentrations were the same in both cholesterol and control SMC during the first 14 d of culture but afterward increased in differing ways: after 20 d of culture the cholesterol-SMC increased their cholesterol content to double the control. We give here the results obtained from transmission electron microscopy, lipid analysis, proliferation studies, DNA, RNA and protein synthesis, and then discuss their implications.     

Die Darstellung von Gelen als stationäre Phase für die Gelchromatographie

The influence of the mode of synthesis on the characteristics of crosslinked polymers is examined for crosslinked copolymers of ethylvinylbenzol/divinylbenzol and vinylacetate/divinyladipate. Homogeneously crosslinked gels are mostly suited for separation of oligomers; polymers are able to be separated by use of heterogeneously crosslinked gels. It is demonstrated that in case of a heterogeneously crosslinking polymerization the heterogenity of the copolymers with decreasing solvatizing ability of the inert component is increasing; this leads simultaneously to an increase of the excluded molecular weight.     

氟硅生胶的合成及交联特性

由1,3，5-三甲基三氟丙基环三硅氧烷的阴离子本体开环缩聚合成了氟硅生胶，并对生胶进行过氧化物交联。发现聚合过程存在氟硅聚合物和小分子环状物的平衡，控制聚合时间在40～60min,得到了高转化率和高分子量氟硅生胶，引入乙烯基共聚单体对分子量影响不显著，随着生胶中乙烯基含量增加，过氧化物交联氟硅胶的交联程度增加。     

Hydrophilic polystyrene/maleic anhydride ultrafine fibrous membranes

Polystyrene/maleic anhydride (PSMA) was synthesized to reach a viscosity‐average molecular weight of 700 kDa and fabricated into ultrafine fibrous membranes consisting of fibers with an average diameter of 300 nm. These ultrafine PSMA fibers were rendered insoluble in organic solvents by reactions with hydrazine and ethylenediamine (ED). The highly efficient incorporation of diamines into the fibrous membranes was easily achieved by brief immersions in either dilute (0.5 wt %) hydrazine for 1 min or ED ether solution for 2 min. Heating at 150°C for 5 min produced crosslinked PSMA with very little or no solubility in acetone with the retention of the fibrous membrane structure. The ED‐crosslinked membranes were particularly stable to both bases and acids as well as hydrophilic solvents, had a 46° water contact angle, and absorbed 22 times the amount of water as the as‐spun fibrous membrane. This post‐fiber‐formation crosslinking approach was robust, highly efficient, and fast and required very little crosslinking reagent. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ultrahigh molecular weight polyethylene with improved crosslink density,oxidation stability,and microbial inhibition by chemical crosslinking and tea polyphenols for total joint replacements

Highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) stabilized by vitamin E (VE) is widely applied in artificial joints as the bearings. Despite the approval, there is a discord that VE lowers the crosslinking efficiency, limiting its use at high concentration. In this work, we aim to obtain highly crosslinked and oxidation resistant UHMWPE through the conjunction of tea polyphenol and chemical crosslinking. We hypothesized that highly incorporated tea polyphenol with multiple reactive sites can ameliorate crosslinking efficiency of chemical crosslinked UHMWPE in comparison to VE. Epigallocatechin gallate (EGCG) as representative tea polyphenol was incorporated into UHMWPE at high concentration (2–8 wt%), followed by chemical crosslinking with 2 wt% organic peroxide. Unlike VE/UHMWPE blends as the control, chemical crosslinking achieved an increasing trend in crosslink density of EGCG/UHMWPE blends with increasing antioxidant concentration. High concentration of EGCG also enhanced the oxidation stability of UHMWPE. Intriguingly, EGCG endowed UHMWPE with an excellent antimicrobial property, which was inefficient in VE/UHMWPE. Cell viability was hardly affected by the high loaded antioxidant and peroxide. The chemically crosslinked UHMWPE blended with EGCG is proved to be a reasonable, cost effective and realistic alternative for use in artificial joints.