Stereoselective synthesis of biodegradable polymers by salen-type metal catalysts

Biodegradable polymers are a promising sustainable alternative to conventional petroleum-based polymers and have attracted recent extensive research interest due to their potential environmental friendliness and sustainability. Among them, aliphatic polyesters and polycarbonates are the most extensively studied ones. The metal-catalyzed ring-opening polymerization(ROP) of cyclic esters and ring-opening copolymerization(ROCOP) of epoxides with anhydrides or CO₂ are often considered to ...     

Enhancement of composite‐metal interfacial adhesion strength by dendrimer

The interface between carbon fiber reinforced polymer composites and metal plays a critical role in determining the strength of epoxy/metal laminated composites. We propose to introduce one dendrimer layer into the epoxy/metal interface, aiming to enhance the interfacial adhesion strength so that the interface could more effectively transfer the load from epoxy to metal. In this paper, the preparation and adsorption of dendrimer layer onto the alumina surface were systematically investigated. The results show that a highly stable and nanopatterned dendrimers layer was dip‐coated onto alumina substrates by adsorbing poly (amidoamine) dendrimers. It was confirmed that the dendrimers were adsorbed onto the alumina via acid‐base chemical interactions. The adsorption depends on the reaction time. The adhesion property between dendrimers and alumina was examined by sonication method. Copyright © 2010 John Wiley & Sons, Ltd.     

In vitro bioactivity of titanium implants coated with bicomponent hybrid biodegradable polymers

In order to improve the bioactivity and biocompatibility of titanium (Ti) implants, we designed a novel biodegradable hybrid (polycaprolactone/polylactic acid, PCL/PLA) membrane to coat Ti surfaces. The bicomponent PCL/PLA membrane was applied to a Ti substrate starting with the coating of Ti samples with a porous PLA film layer using a dip-coating technique. This was followed by deposition of electrospun PCL nanofibers onto the Ti substrate, resulting in a PCL/PLA bicomponent hybrid coating layer. The cytocompatibility, bioactivity and corrosion performance of PCL/PLA-coated Ti samples was compared to PLA-coated Ti samples and untreated Ti samples. When placed in Hanks’ solution, apatite formed on the treated Ti samples but not on untreated Ti samples. When assessing Ti cytocompatibility and MC3T3-E1 osteoblast adherence, proliferation, and survival, our results showed superior performance by polymer-treated Ti samples compared to untreated Ti samples, and maximal osteoblast cell viability was achieved with the bicomponent PCL/PLA hybrid coating layer. Furthermore, during the potentiodynamic polarization test in simulated body fluid, the polymer-coated Ti samples showed corrosion resistance. Therefore, the approach described herein may serve as a basis for the development of polymer-coated Ti surfaces that can be used in dental or orthopedic implants.     

Multi‐metal shell coated with surface modification of polystyrene bead cores to improve its adhesion metal shell

We investigated the delamination problem at the metal‐polymer interface and the mechanical buckling of the metal layer at a localized area of the metallic shell under compression between two parallel plates. First, polystyrene (PS) beads were synthesized by dispersion polymerization and then their sulfonation process. After sequential electroless deposition, the average size of multi‐metal coated sulfonated polystyrene (SPS) bead was ca 4.95 µm. Using the electromechanical indentation, the electrical resistance of a single metal‐coated SPS bead decreased with increasing compressive strain without delamination at the metal‐polymer interface, and its electrical resistance showed 5.65 Ω. Copyright © 2009 John Wiley & Sons, Ltd.     

提高PBO纤维/环氧树脂复合材料界面结合的研究

本文采用表面化学蚀刻与溶胀法结合、化学偶联法与氩气低温等离子体表面处理技术结合的方法对聚苯撑苯并二。唑（PBO）纤维进行表面改性。探讨了不同改性方法对纤维表面性能的影响。同时，采用FTIR和SEM等方法对处理前后纤维表面化学结构及形态进行了表征。     

Effects of an avidin-biotin binding system on chondrocyte adhesion and growth on biodegradable polymers

Cell adhesion to a scaffold is a prerequisite for tissue engineering. Many studies have been focused on enhancing cell adhesion to synthetic materials that are used for scaffold fabrication. In this study, we applied an avidin-biotin binding system to enhance chondrocyte adhesion to biodegradable polymers. Biotin molecules were conjugated to the cell membrane of chondrocytes, and mediated cell adhesion to avidin-coated surfaces. We demonstrated that immobilization of biotin molecules to chondrocyte surfaces enhanced cell adhesion to avidin-coated biodegradable polymers such as poly(L-lactic acid), poly(D,L-lactic acid), and polycaprolactone, compared to the adhesion of normal chondrocytes to the same type of biodegradable polymer. The biotinylated chondrocytes still maintained their proliferation ability. This study showed the promise of applying the avidin-biotin system in cartilage tissue engineering. [diagram in text].     

Correlation between mechanical adhesion and interfacial properties of starch/biodegradable polyester blends

Biopolymers are preferred ingredients for the manufacture of materials because they are based on abundantly available and renewable raw materials that have benign environmental problems associated with their production, fabrication, use, and disposal; however, the wide use of biopolymers in engineering applications has not been achieved, mainly because of the inferior quality of many biopolymer‐based products. To overcome this limitation, studies have been initiated on blends of biopolymers and biodegradable synthetic polymers. We used the contact angle of probe liquids to measure the surface energy of polystyrene, the biodegradable polyesters polycaprolactone, poly(hydroxybutyrate‐co‐hydroxyvalerate), polylactic acid, polybutylene adipate terephthalate, and adipic poly(hydroxy ester ether), and normal starch. The surface energies were used to estimate the starch/polymer interfacial energy and work of adhesion. The calculated starch/polyester work of adhesion showed mixed correlation with published starch/polyester mechanical properties, indicating that factors other than interfacial properties might be dominant in determining the mechanical properties of some starch/polyester blends. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 920–930, 2001     

Effect of end‐tethered polymers on surface adhesion of glassy polymers

The adhesion between a glassy polymer melt and substrate is studied in the presence of end‐grafted chains chemically attached to the substrate surface. Extensive molecular dynamics simulations have been carried out to study the effect of the areal density ∑ of tethered chains and tensile pull velocity v on the adhesive failure mechanisms. The initial configurations are generated using a double‐bridging algorithm in which new bonds are formed across a pair of monomers equidistant from their respective free ends. This generates new chain configurations that are substantially different than the original two chains such that the systems can be equilibrated in a reasonable amount of cpu time. At the slowest tensile pull velocity studied, a crossover from chain scission to crazing is observed as the coverage increases, while for very large pull velocity, only chain scission is observed. As the coverage increases, the sections of the tethered chains pulled out from the interface form the fibrils of a craze that are strong enough to suppress chain scission, resulting in cohesive rather than adhesive failure. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 199–208, 2004     

Measurement of interfacial adhesion between glassy polymers using the JKR method

The surface and interfacial energies of polymers are measured using the JKR-type experiments. A novel method has been developed to prepare samples of glassy polymers for adhesion measurements. A thin layer of a polymer is coated on the surface of an O₂-plasma modified cross-linked poly(dimethylsiloxane) [PDMS] spherical cap resulting in the formation of a composite. Using the JKR theory, the surface energies of polystyrene [PS] and poly(methyl methacrylate) [PMMA] are determined from the measurements of the contact radius as a function of applied load. The results of the JKR-type experiments are compared to adhesion measurements done using the surface forces apparatus (SFA). Adhesion hysteresis was observed for PS-PS contact as well as PMMA-PMMA contact. However, no hysteresis was observed for PDMS-PDMS, PDMS-PS, and PDMS-PMMA contacts. The exact origin of the hysteresis is not clear at present. The current evidence suggests that hysteresis is due to rearrangement of the interface during contact.     

Improvement of adhesive bonding of thermoplastic polymers by different surface treatments

Injection moulded samples of six species of thermoplastic polymers were exposed to different surface treatments and successively glued together to form single lap shear joints. Lap shear strength and failure mode of these specimens were examined. The surfaces obtained after treatment were characterized by electron spectroscopy for chemical analysis, contact angle measurements and atomic force microscopy.     

Enhanced interfacial adhesion,mechanical, and thermal properties of natural flour-filled biodegradable polymer bio-composites

This study examined the interfacial adhesion, mechanical, and thermal properties of compatibilizing agent-treated and non-treated biocomposites as a function of the type of compatibilizing agent. The tensile strength, interfacial adhesion, and heat deflection temperature (HDT) of maleic anhydride-grafted poly(butylene succinate) (PBS-MA) and maleic anhydride-grafted poly(lactic acid) (PLA-MA)-treated biocomposites are greater than those of untreated maleic anhydride-grafted poly(styrene-b-ethylene-co-butylene-b-styrene) triblock copolymer (SEBS-MA) and maleic anhydride-grafted polypropylene (MAPP)-treated biocomposites. The storage modulus (E′) values and the tan δ_max temperatures (T _g) of PBS-MA and PLA-MA-treated biocomposites were slightly higher than that of the untreated biocomposites.     

Reactive blending of polymers by interfacial free-radical grafting

In blends of immiscible polymers, amphiphilic species are needed for both morphological stabilization and improvement of the mechanical properties throughout successive processing steps. In order to obtain the required concentration of amphiphilic copolymer at the interface, it seemed of interest to test the possibility of creating these species by in situ reactivity at the interface, for instance by condensation reactions occurring between functionalized polymers. There is another possibility based on the fact that most of the polymers are hydrocarbon compounds, so they are subjected to free-radical reactivity by hydrogen abstraction on the different hydrocarbon sites. The created free-radical polymeric species may react together leading to the well known reactions of crosslinking, grafting and/or chain degradation. Therefore, this work deals with reciprocal free-radical reactivity of two kinds of semi-crystalline polymers, namely one polyolefin (LDPE, HDPE, PP or EPR) associated with a polyamide (PA-11 or PA-6). The reaction has to occur mainly at the interface, where the resulting grafted copolymers have to be anchored for final stabilization of the biphasic system. The level of interfacial grafting and the resulting properties of the reacted blends were characterized carefully, confirming the efficiency of the interpolymeric grafting.     

Influence of surface properties on the interfacial adhesion in carbon fiber/epoxy composites

A polyacrylonitrile‐based carbon fiber was electrochemically oxidized in an aqueous ammonium bicarbonate solution with current density of up to 2.76 A/m² at room temperature. X‐ray photoelectron spectroscopy revealed that the oxygen content increased with increasing current density before approaching saturation. The increase can be divided into two regions, the rapid increase region (0–1.78 A/m²) and a plateau region (1.78–2.76 A/m²). The surface chemistry analysis showed that the interlaminar shear strength (ILSS) value of the carbon fiber/epoxy composite could be improved by 24.7%. The carbon structure was examined using Raman spectroscopy in terms of order/disorder in the graphite structure and the results indicated that the relative percentage of graphite carbon in the form of sp² hybridization increased above a current density of 1.39 A/m². The increasing non‐polar graphite carbon on the carbon fiber surface decreased the surface energy. As a result, both the surface free energy () and its polar component () decreased when current density increased above 1.78 A/m². The ILSS value had no direct relationship with the nature and surface density of the oxygen‐containing functional groups nor with the carbon structure. It is the surface free energy (), especially the polar component (), which played a critical role in affecting the interfacial adhesion of carbon fiber/epoxy composites. The ILSS value changed with increasing current density and could be divided into three distinct regions, as chemical interaction region (I), anchor force region (II) and matrix damage region (III). Copyright © 2013 John Wiley & Sons, Ltd.     

Biomedical applications of biodegradable polymers

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. To fit functional demand, materials with desired physical, chemical, biological, biomechanical, and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Special topic on bio-based and biodegradable polymers

正In the past decades,bio-based and biodegradable polymers have attracted wide and increasing interests because of the shortage of fossil resource,concerns on environmental pollution,demands for some medical fields as well as support of government policies.Depending on the sustainable source of organic carbon,biodegradability and biocompatibility,these polymers have shown promising applications in industry,agriculture,biomedicine and daily life.To impart excellent physical properties and functions to them,scientists and engineers have exploited versatile methods to tune     

Characterization of surface water on Au core Pt-group metal shell nanoparticles coated electrodes by surface-enhanced Raman spectroscopy

We utilized the strategy of 'borrowing SERS activity', by chemically coating several atomic layers of a Pt-group metal on highly SERS-active Au nanoparticles, to obtain the first SERS (also Raman) spectra of surface water on Pt and Pd metals, and propose conceptual models for water adsorbed on Pt and Pd metal surfaces.     

Layer-by-layer growth of oriented metal organic polymers on a functionalized organic surface

A metal-organic coordination polymer based on benzenetricarboxylic acid ligands and Zn(II) ions was grown on a COOH-terminated organic surface in a stepwise fashion. The deposited films were characterized using a number of surface analysis techniques, including X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. IR measurements show that the metal-organic coordination polymer grows in a layer-by-layer fashion and can be reversibly loaded with NH3. The deposition is very selective and occurs only on COOH-terminated regions of an organic surface, as demonstrated by AFM measurements.     

Synthesis of biodegradable polymers catalyzed by macromolecule - bimetal complexes

A series of biodegradablc modified aliphatic polycarbonates were synthesized from carbon dioxide and relevant comonomers using a macromolecule - bimetallic catalyst. The work was done to help the elimination of the pollution both from polymeric rubbish and from the greenhouse gas CO₂.